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Let's Discuss Frame Geometry

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Let's Discuss Frame Geometry

Old 10-05-20, 05:53 AM
  #26  
guy153
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Originally Posted by Moisture
how does the Chamois Hagar manage to get away with such an aggressive drop in chainstays without the pedals hitting the ground?
It is quite unusual to see such a low BB drop on a gravel bike. But 70mm is normal for a road bike and those fat tyres are at least 10mm taller. So ground clearance will actually be fine on most of the intended terrain.

Originally Posted by Moisture
Clearly, getting the geometry right has more to do with what is best suited to your personal needs. For me personally, I find that I lean forward slightly which puts enough weight over the front axle to cause a fair bit of understeer. I find that I have to be extremely gently during turn in, especially on gravel. My front wheel just plows. I'm planning to try using a wider and more aggressive front tire in the future.

I'm a taller and bigger rider, which may have something to do with the fact that I prefer a very upright riding position. But if I did manage to use some sort of swept back handlebars to achieve that stable rear biased handling im looking for, there just won't be enough weight over the front axle during steeper climbing.
I would go long and slack but also have a fairly long chainstay to balance it out. I don't know why people like such short chainstays but they're a great way to pop wheelies all the time when climbing and to actually fall over backwards when scrambling out of bomb holes.

I think some sort of stem which you can adjust on the fly would be a nifty idea.

Originally Posted by Moisture
Would you mind explaining the difference in stability/ versus precision trade off when comparing the head tube angle to fork rake? Can you achieve handling which is both stable and precise, especially at speed by contrasting these two measurements?
The main measurement that affects the steering is trail, which is a function of both HA and rake. Slacken the head and you increase trail, increase the fork rake and you reduce it again. Since there are therefore many ways to achieve the same trail-- you could go steep head and lots of rake or shallower head and less rake-- what are the differences there? They're more subtle but steep head and more rake will give you less wheel flop for the same trail which may be desirable if you plan on using front panniers etc.

Long trail is generally considered more stable and short trail more "agile".
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Old 10-05-20, 06:27 AM
  #27  
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Originally Posted by Ironfish653
The Zaskar was a good bike. In 1996. When 26x1.95 was the typical tire size and 80mm was a long-travel fork. Long-and-low was what worked on the NORBA style courses of the day, biased towards climbing and speed on the flats. When you look at rider position, it’s not that far off of a ‘sporting’ road bike of the same era.

Modern MTBs have bigger wheels, longer travel suspension (with much better dampers) and the geometry and rider position to take advantage of that. I’ve demoed a couple of new mid-range trail bikes in the last year, and their off-road capability just blows away my old F-1000.
Now, on a fast fire road, or on slicks in the city, the old XC bike probably has the speed advantage, but that’s what it was designed to do.
This ... all of it, and a good explanation why some of us, self included, still love old-school NORBA-geometry hardtails for non-technical off-road/in-city riding: they can be very light, quick, and agile.
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Old 10-05-20, 07:29 AM
  #28  
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Originally Posted by Ironfish653
The Zaskar was a good bike. In 1996. When 26x1.95 was the typical tire size and 80mm was a long-travel fork. Long-and-low was what worked on the NORBA style courses of the day, biased towards climbing and speed on the flats. When you look at rider position, it’s not that far off of a ‘sporting’ road bike of the same era.

Modern MTBs have bigger wheels, longer travel suspension (with much better dampers) and the geometry and rider position to take advantage of that. I’ve demoed a couple of new mid-range trail bikes in the last year, and their off-road capability just blows away my old F-1000.
Now, on a fast fire road, or on slicks in the city, the old XC bike probably has the speed advantage, but that’s what it was designed to do.
My understanding, is that the Zaskar was more of a singletrack bike in its day. As the competition began to catch up, it sort of became demoted to singletrack duty.

At any rate, mine is the XL size. I measured the seat tube at about 23". Its not a low riding bike, at least not with the seat raised up to my ideal riding position. It climbs hills like a beast though. Im not a crazy mountain biker, but the thing handles technical trails with effortless balance and inspires a lot of confidence to go very fast. Despite its age, I still think its a fantastic bike even today. Are there new bikes out there which perform better? I'm sure. But do they weigh 21lb fully equipped? This is the last of the American built GT frames and they've sort of developed a cult following versus the newer taiwanese made versions.

Mine has fairly modern compinents all around, such as a deore/alivio drivetrain and a Manitou Black Elite 100mm front fork. Can it hang with the newer mid range bikes? I'm sure, because its dependent on rider skill, and what the rider feels comfortable riding, not what someone else thinks is good, bad, modern or outdated.

For me, i prefer 26" rims because the bigger ones tend to bend easier. Would bigger wheels and more suspension travel help? Maybe 1% of the time, for 1% of us who are skilled enough..

Originally Posted by badger1
This ... all of it, and a good explanation why some of us, self included, still love old-school NORBA-geometry hardtails for non-technical off-road/in-city riding: they can be very light, quick, and agile.
very true, but ive felt very confident on that bike navigating technical stuff too. In terms of a bike that can reasonably tackle the vast majority of what a intermediate rider can throw at it, hard to beat with such an overall light weight.

Considering that I started looking for a bike when lockdown came into effect, I had to make due with costco issue northrock until I this zaskar popped up on the used market. Next season I'll probably look into something more modern such as a scott scale to see what all the fuss is about.
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Old 10-05-20, 11:51 AM
  #29  
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Originally Posted by Moisture
Considering that I started looking for a bike when lockdown came into effect....
Yep, some pretty strong opinions from someone new to cycling. Nevertheless, kudos on so quickly joining the top 1% in MTB skills!
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Old 10-05-20, 06:42 PM
  #30  
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Originally Posted by Darth Lefty
Slanted top tubes were first commonplace on mountain bikes. They'd already dropped the top tube for more stand-over and raised the bottom bracket for more ground clearance. That made the head tubes very short, but when the suspension fork was added they needed more room underneath, so the whole head tube moved up. Several things were tried, like Cannondale's Killer V. The slant was just the simplest. The road bikers adopted it because it gave them a stiffer triangle for pedaling at the same time as a long seat post for more comfort. It also goes along with threadless stems, which also came from MTB because quill stems would slam down into the steerer, but don't provide much added stack.

The steeper seat tubes are a new development and they are a compromise of designing the bike with a long front center and long reach and slack steering, so a standing rider is in the middle of the bike and not OTB. This blog post by Peter Verdone describes the basic idea. This is pretty much a done deal on mountain bikes. Some people have tried it on gravel bikes (Evil Chamois Hagar is an example) but it seems for now that gravel bikes will remain pretty much just armored-up endurance road bikes.
bruce19 This guy actually did a great job explaining why TT's became slanted. Either way, I don't see how it would result in any cost saving at all.
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Old 10-06-20, 07:14 AM
  #31  
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Originally Posted by Moisture
My understanding, is that the Zaskar was more of a singletrack bike in its day. As the competition began to catch up, it sort of became demoted to singletrack duty.

Despite its age, I still think its a fantastic bike even today. Are there new bikes out there which perform better? I'm sure. But do they weigh 21lb fully equipped? This is the last of the American built GT frames and they've sort of developed a cult following versus the newer taiwanese made versions.
.
The Zaskar was GT’s tip of the line XC bike in the 90s. It was a good bike then, no doubt. A lot of the guys I rode and raced with rode them. I rode a Cannondale F-1000, which I still ride today. (You want to talk about cult following, look into vintage ‘Dales). I’d venture to say the Cannondale was the better climber, especially in tight technical sections, and more nimble in an all-out sprint, but the GTs were better coming down, especially if airtime was involved.

Mountain bikes have had 25 years of development since they built your GT, especially in wheel size and suspension design. While old school hardtails are quite capable, you have to have a pretty good arsenal of skill to get the most out of them.


The last two I demoed were a Giant Stance and a Cannondale Scalpel-Si. The Stance is a mid-range 27.5 FS Trail bike and the modern suspension, bigger wheels, and dropper seat post made it significantly easier to carry momentum through terrain like rock gardens and root ladders. I could clear those sections on my old bike as well, but it definitely took a lot more muscle and English to do it, and I for sure took more bumps.
The Scalpel is a carbon framed 29” XC race bike; a $7000, 21 lb full-suspension off-road weapon. It’s not as plush as the Stance, but it’s one of those bikes that works better the faster you ride it, and I don’t always want to ride that hard all the time.
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Old 10-06-20, 08:52 AM
  #32  
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Originally Posted by Ironfish653
The Zaskar was GT’s tip of the line XC bike in the 90s. It was a good bike then, no doubt. A lot of the guys I rode and raced with rode them. I rode a Cannondale F-1000, which I still ride today. (You want to talk about cult following, look into vintage ‘Dales). I’d venture to say the Cannondale was the better climber, especially in tight technical sections, and more nimble in an all-out sprint, but the GTs were better coming down, especially if airtime was involved.

Mountain bikes have had 25 years of development since they built your GT, especially in wheel size and suspension design. While old school hardtails are quite capable, you have to have a pretty good arsenal of skill to get the most out of them.


The last two I demoed were a Giant Stance and a Cannondale Scalpel-Si. The Stance is a mid-range 27.5 FS Trail bike and the modern suspension, bigger wheels, and dropper seat post made it significantly easier to carry momentum through terrain like rock gardens and root ladders. I could clear those sections on my old bike as well, but it definitely took a lot more muscle and English to do it, and I for sure took more bumps.
The Scalpel is a carbon framed 29” XC race bike; a $7000, 21 lb full-suspension off-road weapon. It’s not as plush as the Stance, but it’s one of those bikes that works better the faster you ride it, and I don’t always want to ride that hard all the time.
So you're saying that the Zaskar was meant to be an overall fair balance between up and down hill?
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Old 10-06-20, 09:32 AM
  #33  
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This thread highlights the importance of the rider's experience--not the years of experience, but the on-the-bike riding experience.
@Mooisture really likes his bike. He feels good on the bike, he feels like he can trust it and make it work.

Long ago (back when tMoisture's Zaskar was young) I had an entry-level Univega MTB. I rode the snot out of that bike and I knew it intimately. I knew then and still know that I didn't have high-level skills or anything, but I knew how to make that bike work as well as it possibly could.

One day a Gary Fisher sales rep brought a bunch of dealers to the trail head, to let them test-ride the (then) new Sugar 1. It was Gary Fisher's (and MTB's generally) first foray into lightweight, long front-end FS XC MTBs .... it was sort of a next-gen, forward-thinking development of MTB design. The bike did everything better than everythng else, with the possible exception of big-drop, North Shore-type obstacles (back in the day when anything with 100 mm of travel was an "extreme free-ride" bike.)

Even though I was not a dealer or affiliated with a shop, after I chatted with the guy for a while, he let me ride it for half an hour.

I brought it back well before my time had elapsed. Yes, it was light-years ahead of my low-end Univega---but to me, it was Not a "better" bike. I didn't know how to make it work. The front end kept washing out, because I didn't know how to ride a bike with all the weight in the back---which made it a great descender and a good climber--tons of traction, suited to seated rather than standing climbing, and balanced on the downhills---but I didn't know how to make it work for me. All I knew was that pig of a Univega, which did nothing as well as the Sugar .... in the hands of a rider who knew how to make it work. I didn't know how to make the Sugar work.

Moisture loves his bike. Yes, he is way over the top and maybe a little confused about some stuff .... but there is no faking his enthusiasm.

For me, I didn't get another MTB for two decades---life changed, and off-road riding (in fact, riding in general) just wasn't happening for a while. When I finally got a new (used) MTB, it was a 2007(?) Cannondale Rize---FS, gigantic travel Fox suspension, Industry 9 wheels (26" wheels which i also like --- I don't ride a lot of high-speed stuff, and I like the tighter, more technical stuff (even though I can't clear most of it any more.)) .... Amazing.

When I say "Amazing," I mean it. I was amazed that even with twice the travel, the bike didn't feel mushy or sluggish. What it did was make up for losing two decades of MTB skills---I cannot explain how much technique I have lost. Road riding is great for fitness, but MTB builds bike-handling skills at ten times the speed--and I lost all those skills in my time off the trails.

And it hardly mattered. Modern suspension really is so good , and modern design also, that I could ride the bike up and down stuff I completely lacked the skill to clear--because the bike made up for it. I was able to ride sections which would have taken 100 percent of my ability before ... and now, with only ten percent of the ability, the bike made up for the rest.

But ... do I Enjoy riding more? Actually, no. To me, clearing difficult sections (relatively) is part of it, but knowing that I am really riding at my and the bike's limit is much bigger ... and I will probably Never reach that with the Rize. I will have different experiences---still fulfilling and exciting and enjoyable, but different.

Mr. Moisture, enjoy your Zaskar. Enjoy thrashing it to its very limits, and finding new limits in yourself. That is really what matters .... not parts spec, or suspension travel, or cutting-edge design. What matters (IMO) is the actual riding experience---the joy of riding the bike. You have that, and it is not something you can buy. You could buy a $7000 bike and not like it as much.

if you are young enough and have the time to ride, you could probably buy a modern bike and learn to use it to its limits (I am too old and my riding time is too limited.) But you could possibly eventually get a modern MTB and see how far the sport/art/tech has advanced since the '90s.

Until that day, you have something which is worth way more than money---you have good time on the bike.

Thrash that Zaskar and love every second of it.

Last edited by Maelochs; 10-06-20 at 09:38 AM.
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Old 10-06-20, 09:45 AM
  #34  
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Originally Posted by Moisture
So you're saying that the Zaskar was meant to be an overall fair balance between up and down hill?
Yes it was; XC is shorthand for Cross-Country, which means up, and down, and was the predominant form of MTB racing in the 1990s, often referred to as the NORBA era, after the US sanctioning body.

The XC hartdtail bikes of that era were probably the zenith of 26” MTBs, before long-travel suspensions and the birth of 29ers.

They are are still very capable bikes, and in many ways more versatile than modern MTBs.
I‘m still riding my 1996 Cannondale F-1000, and I have a hard time justifying it’s replacement.
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Old 10-06-20, 10:12 AM
  #35  
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Moisture

Since you’re new to the world of mountain bikeing, and riding a suitably vintage steed, get a copy of Mountain Bike! by William “don’t call me Bill” Nealy (1st ed. 1992) it’s a great guide to bike handling skills, and a really fun read.

It’s been my bike-handling bible since back in the day, and good skills are one of those things you can carry from bike to bike regardless of where and what you’re riding.
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Old 10-06-20, 10:13 AM
  #36  
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Originally Posted by Moisture
So you're saying that the Zaskar was meant to be an overall fair balance between up and down hill?

I don't know about the Zaskar not one thing but the concept of balance, which is actually compromise, is a main driver in the manufacturing of production items including bicycles. For example a company may have to buy a huge amount of a special material to make just one small part of a bike as designed in a perfect world to get an optimal performance but the cost of that material might price the product right out of the market. Or an operation that is labor intensive might be replaced with a less labor intensive operation to reduce either cost or build time, all to the detriment of performance. This is one of the reasons why mass production reduces costs. In a handmade custom shop where the customer is happy to open the old wallet and lead time is not essential all of this is part of the "attention to detail" and other quality/workmanship considerations that we love to brag about but this costs money. Factories are always looking to produce things faster, less expensive and with less hand labor. If they can save $5.00 in materials they can reduce the finished product cost by $50.00 All that hand labor has not just wages but perks and bennies and this is added to the cost at the retail level.


Throw enough money at a problem, in this case weight, rigidity and size which is really all that matters, not degrees of angle because we don't care what degrees of angle we have if the product performs as we want, throw enough money at it the problem, it goes away. But of course there are not enough buyers of bicycles out there willing to spend freely to keep the industry afloat.
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Old 10-06-20, 12:54 PM
  #37  
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Originally Posted by Maelochs
This thread highlights the importance of the rider's experience--not the years of experience, but the on-the-bike riding experience.
@Mooisture really likes his bike. He feels good on the bike, he feels like he can trust it and make it work.

Long ago (back when tMoisture's Zaskar was young) I had an entry-level Univega MTB. I rode the snot out of that bike and I knew it intimately. I knew then and still know that I didn't have high-level skills or anything, but I knew how to make that bike work as well as it possibly could.

One day a Gary Fisher sales rep brought a bunch of dealers to the trail head, to let them test-ride the (then) new Sugar 1. It was Gary Fisher's (and MTB's generally) first foray into lightweight, long front-end FS XC MTBs .... it was sort of a next-gen, forward-thinking development of MTB design. The bike did everything better than everythng else, with the possible exception of big-drop, North Shore-type obstacles (back in the day when anything with 100 mm of travel was an "extreme free-ride" bike.)

Even though I was not a dealer or affiliated with a shop, after I chatted with the guy for a while, he let me ride it for half an hour.

I brought it back well before my time had elapsed. Yes, it was light-years ahead of my low-end Univega---but to me, it was Not a "better" bike. I didn't know how to make it work. The front end kept washing out, because I didn't know how to ride a bike with all the weight in the back---which made it a great descender and a good climber--tons of traction, suited to seated rather than standing climbing, and balanced on the downhills---but I didn't know how to make it work for me. All I knew was that pig of a Univega, which did nothing as well as the Sugar .... in the hands of a rider who knew how to make it work. I didn't know how to make the Sugar work.

Moisture loves his bike. Yes, he is way over the top and maybe a little confused about some stuff .... but there is no faking his enthusiasm.

For me, I didn't get another MTB for two decades---life changed, and off-road riding (in fact, riding in general) just wasn't happening for a while. When I finally got a new (used) MTB, it was a 2007(?) Cannondale Rize---FS, gigantic travel Fox suspension, Industry 9 wheels (26" wheels which i also like --- I don't ride a lot of high-speed stuff, and I like the tighter, more technical stuff (even though I can't clear most of it any more.)) .... Amazing.

When I say "Amazing," I mean it. I was amazed that even with twice the travel, the bike didn't feel mushy or sluggish. What it did was make up for losing two decades of MTB skills---I cannot explain how much technique I have lost. Road riding is great for fitness, but MTB builds bike-handling skills at ten times the speed--and I lost all those skills in my time off the trails.

And it hardly mattered. Modern suspension really is so good , and modern design also, that I could ride the bike up and down stuff I completely lacked the skill to clear--because the bike made up for it. I was able to ride sections which would have taken 100 percent of my ability before ... and now, with only ten percent of the ability, the bike made up for the rest.

But ... do I Enjoy riding more? Actually, no. To me, clearing difficult sections (relatively) is part of it, but knowing that I am really riding at my and the bike's limit is much bigger ... and I will probably Never reach that with the Rize. I will have different experiences---still fulfilling and exciting and enjoyable, but different.

Mr. Moisture, enjoy your Zaskar. Enjoy thrashing it to its very limits, and finding new limits in yourself. That is really what matters .... not parts spec, or suspension travel, or cutting-edge design. What matters (IMO) is the actual riding experience---the joy of riding the bike. You have that, and it is not something you can buy. You could buy a $7000 bike and not like it as much.

if you are young enough and have the time to ride, you could probably buy a modern bike and learn to use it to its limits (I am too old and my riding time is too limited.) But you could possibly eventually get a modern MTB and see how far the sport/art/tech has advanced since the '90s.

Until that day, you have something which is worth way more than money---you have good time on the bike.

Thrash that Zaskar and love every second of it.
This was such a thoroughly refreshing read, that i simply have to take a moment to commend you. Clearly, you have an extremely capable thought process and I could not have possibly agreed more with you.

With mountain biking being so important with balance, you've brought up a good point. Many of us will always be the limiting factor of how fast we can tackle a complex trail - not the bike itself. Even if it's not a good one. So when a bike offers the right blend of capability without simply doing the brunt of the technical work for you, its easy to see why one might be so enthusiastic about it. You actually feel a sense of accomplishment when you are able to match your level of experience with both your bike of choice and the trail you are riding.

Considering that I'm still young and have limited experience with good quality bikes, going from a cheap Northrock XC27 to my Zaskar made me feel like I was riding something capable. Whether I was riding through the city or going through trails, I immediately felt very comfortable and balanced on that bike. Every single trail I went through that day, I kept getting better and faster. I was having a great time, even though obviously, I can do better on a well selected modern bike. You can't enjoy the qualities of life by taking things for granted. Given that the Zaskar may not be as special to some of you as it is to me, when I do upgrade to a better bike in the future, it simply gives me more room to expand on the way I'm able to enjoy biking.
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Old 10-06-20, 12:57 PM
  #38  
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Originally Posted by Ironfish653
They are are still very capable bikes, and in many ways more versatile than modern MTBs.
I dont contest this statement for a second. But what is it about these quality vintage bikes which really set the standard for what we expect in a modern bike, that makes them so capable?
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Old 10-06-20, 01:09 PM
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Originally Posted by guy153
It is quite unusual to see such a low BB drop on a gravel bike. But 70mm is normal for a road bike and those fat tyres are at least 10mm taller. So ground clearance will actually be fine on most of the intended terrain.



I would go long and slack but also have a fairly long chainstay to balance it out. I don't know why people like such short chainstays but they're a great way to pop wheelies all the time when climbing and to actually fall over backwards when scrambling out of bomb holes.

I think some sort of stem which you can adjust on the fly would be a nifty idea.



The main measurement that affects the steering is trail, which is a function of both HA and rake. Slacken the head and you increase trail, increase the fork rake and you reduce it again. Since there are therefore many ways to achieve the same trail-- you could go steep head and lots of rake or shallower head and less rake-- what are the differences there? They're more subtle but steep head and more rake will give you less wheel flop for the same trail which may be desirable if you plan on using front panniers etc.

Long trail is generally considered more stable and short trail more "agile".
So mountain bikes tend to have a slacker HT angle in order to increase stability at lower speeds, especially for the technical stuff, and vice versa for something designed for the road? But how would steering which require more effort to turn decrewse stability at higher speeds? Wouldn't it be the other way around?

I'm using this link here to try and understand- https://www.bikeexchange.com/blog/bike-geometry-charts

So I understand that for very technical stuff, youd probably want a longer front end and relatively short chainstays along with smaller 26" wheels. For higher speed stuff with less tight turns, im sure a long chainstay will be useful. Especially on uphills. For road use, youd probably need to balance the two fairly evenly, no?

What do you think of GT's triple triangle tech? Do you think it helps improve frame geometry and increases stiffness reasonably? Or is it more gimmick?
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Old 10-06-20, 02:16 PM
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here's a pic of my Zaskar - widely regarded (by me) as the best bike in the world -


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Old 10-06-20, 03:01 PM
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Originally Posted by Moisture
I dont contest this statement for a second. But what is it about these quality vintage bikes which really set the standard for what we expect in a modern bike, that makes them so capable?
The 90s represented the first generation of high performance mountain bikes, as opposed to the more relaxed, cruiser-like ATBs of the 80s. Suspension was still in it’s early phases, so being fast meant climbing and speed on the flats, not bombing downhills; so you ended up with steep, almost road bike geometry, and the signature long-and-low cockpit layout. Good XC bikes are light and agile, and good at getting your power to the ground.
Sure, modern big-wheel long-travel bikes do better in technical off-road situations, but those Classic XC bikes have more all-around bike capabilities.

Originally Posted by Moisture
What do you think of GT's triple triangle tech? Do you think it helps improve frame geometry and increases stiffness reasonably? Or is it more gimmick?
GT’s Triple Triangle was a carryover from it’s BMX day’s, and used as it’s visual signature on its MTB lineup.
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Old 10-06-20, 03:13 PM
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Originally Posted by Moisture
here's a pic of my Zaskar - widely regarded (by me) as the best bike in the world -
wow, you must be really tall!

Here’s a Zaskar in it’s original trim, to illustrate what the period XC setup looked like



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Old 10-06-20, 03:45 PM
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If you think this bike is great, just wait til you get one that fits you.
This is absurd:

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Old 10-06-20, 04:22 PM
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OK, clearly a joke thread. Someone went to a lot of effort to come up with BF's 2nd most absurd bike fit pic. Cube still holds 1st
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Old 10-06-20, 05:10 PM
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Originally Posted by HD3andMe


This has to be a joke, right?
The best you know is the best you’ve tried, eh?
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Old 10-06-20, 05:54 PM
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Originally Posted by HD3andMe
Modern long travel bikes do better in non-technical off-road riding as well. As do modern short travel bikes.

There's really no comparing an ancient HT to even a modern HT. Times have changed, for the better.
Both bikes pictured in this thread might be blue, but they are definitely not the same.

A bike like this is still pretty capable off-road, though definitely harder to ride, than a modern bike, but put it on slicks, or 26” BMX tires, and they’re damn effective city bikes as well.

[img]blob:https://www.bikeforums.net/fdd871ed-fcd9-4375-aac8-eeaea4877bc3[/img]


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Old 10-07-20, 01:41 AM
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Originally Posted by Moisture
So mountain bikes tend to have a slacker HT angle in order to increase stability at lower speeds, especially for the technical stuff, and vice versa for something designed for the road? But how would steering which require more effort to turn decrewse stability at higher speeds? Wouldn't it be the other way around?

I'm using this link here to try and understand- https://www.bikeexchange.com/blog/bike-geometry-charts

So I understand that for very technical stuff, youd probably want a longer front end and relatively short chainstays along with smaller 26" wheels. For higher speed stuff with less tight turns, im sure a long chainstay will be useful. Especially on uphills. For road use, youd probably need to balance the two fairly evenly, no?

What do you think of GT's triple triangle tech? Do you think it helps improve frame geometry and increases stiffness reasonably? Or is it more gimmick?
The way trail works is a little bit like a gear ratio. Longer trail is like putting a higher gear on the steering-- you need to turn it less to get the same result but it takes a bit more force. The wider the handlebar however, the more you're gearing it back down, which is how MTBs end up feeling fairly normal again. They have really wide handlebars and lots of trail. But it's not exactly the same because you don't only steer with the handlebar.

You're right that the stability always increases with speed. If a bike tips a bit to one side, the wheel flop causes it to steer to that side, which rights it-- if you fall left, you steer left, which throws your weight right (and therefore back up) because of centrifugal force. The centrifugal force depends on speed. If you try to ride a bike in a straight line at low speed it always takes bigger steering corrections to keep upright than it does at higher speeds.

But sometimes you can have too much stability. If you put a really long trail on a bike then at high speeds it can feel like it's hard to make a turn if you want to like you're a passenger on a runaway train. So the amount of trail you want is sort of tuned to the kinds of speeds you expect to be doing. MTBs do actually go pretty fast downhill but I guess it's all so gnarly and bumpy and anyway you don't get that train feeling. I think shorter trail actually gives you more agility at lower speeds, but on MTBs it's confused by the wide handlebar.

Long chainstays and big tyres also give you more stability but at the expense of agility. A really long-low slack 29er is basically a monster truck that will just sail over everything. But is it as much fun? The other hugely confounding factor in all this is the human brain. If you ride a particular bike for a bit it soon starts to feel really intuitive and "just right". Get on another bike and it's weird and you don't like it. But ride it for a bit and you start to like that one more and you don't want to go back to the first one. I think this is why MTBs got gradually longer and slacker over the years. If you'd come out with a 2020 MTB in 1986 everyone would have hated it. The jump from what they were used to would have been too big. At the actual cutting edge of racing you want to make the bike that an elite rider is actually fastest on, and she will get used to and get the most out of any design you put her on very rapidly. So it is objective because you can measure it with a stopwatch. For the rest of us, well we end up with some bike or other and for some reason we either love it or we don't, but it's based on all kinds of subjective factors. People who ride a lot of bikes are maybe more tuned into being objective about the differences. For me it's just some feel weird at first, others don't, and they all feel great after a bit.

I do think the triple triangle "tech" is a gimmick. The top of the ST is reinforced because it has to hold the seat so it makes sense to attach the SS there. On a butted steel frame the TT becomes thin, like 0.5mm, about 80mm away from the ST, but the top of the ST is 1.2mm. A much better place to be attaching the stays. A lot of GT frames are aluminium and perhaps they're not butted so it doesn't make as much difference. But also why do you want the rear triangle so stiff? The seatpost is going to flex anyway, and perhaps a more "compliant" rear triangle gives you a smoother ride. But the look of those GT frames is certainly distinctive and I like diversity on an aesthetic level. There's no reason why we all need to ride the most technically optimized frames possible.
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Old 10-07-20, 04:15 AM
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Originally Posted by guy153
The way trail works is a little bit like a gear ratio. Longer trail is like putting a higher gear on the steering-- you need to turn it less to get the same result but it takes a bit more force. The wider the handlebar however, the more you're gearing it back down, which is how MTBs end up feeling fairly normal again. They have really wide handlebars and lots of trail. But it's not exactly the same because you don't only steer with the handlebar.

You're right that the stability always increases with speed. If a bike tips a bit to one side, the wheel flop causes it to steer to that side, which rights it-- if you fall left, you steer left, which throws your weight right (and therefore back up) because of centrifugal force. The centrifugal force depends on speed. If you try to ride a bike in a straight line at low speed it always takes bigger steering corrections to keep upright than it does at higher speeds.

But sometimes you can have too much stability. If you put a really long trail on a bike then at high speeds it can feel like it's hard to make a turn if you want to like you're a passenger on a runaway train. So the amount of trail you want is sort of tuned to the kinds of speeds you expect to be doing. MTBs do actually go pretty fast downhill but I guess it's all so gnarly and bumpy and anyway you don't get that train feeling. I think shorter trail actually gives you more agility at lower speeds, but on MTBs it's confused by the wide handlebar.

Long chainstays and big tyres also give you more stability but at the expense of agility. A really long-low slack 29er is basically a monster truck that will just sail over everything. But is it as much fun? The other hugely confounding factor in all this is the human brain. If you ride a particular bike for a bit it soon starts to feel really intuitive and "just right". Get on another bike and it's weird and you don't like it. But ride it for a bit and you start to like that one more and you don't want to go back to the first one. I think this is why MTBs got gradually longer and slacker over the years. If you'd come out with a 2020 MTB in 1986 everyone would have hated it. The jump from what they were used to would have been too big. At the actual cutting edge of racing you want to make the bike that an elite rider is actually fastest on, and she will get used to and get the most out of any design you put her on very rapidly. So it is objective because you can measure it with a stopwatch. For the rest of us, well we end up with some bike or other and for some reason we either love it or we don't, but it's based on all kinds of subjective factors. People who ride a lot of bikes are maybe more tuned into being objective about the differences. For me it's just some feel weird at first, others don't, and they all feel great after a bit.

I do think the triple triangle "tech" is a gimmick. The top of the ST is reinforced because it has to hold the seat so it makes sense to attach the SS there. On a butted steel frame the TT becomes thin, like 0.5mm, about 80mm away from the ST, but the top of the ST is 1.2mm. A much better place to be attaching the stays. A lot of GT frames are aluminium and perhaps they're not butted so it doesn't make as much difference. But also why do you want the rear triangle so stiff? The seatpost is going to flex anyway, and perhaps a more "compliant" rear triangle gives you a smoother ride. But the look of those GT frames is certainly distinctive and I like diversity on an aesthetic level. There's no reason why we all need to ride the most technically optimized frames possible.
I really can't thank you enough for all of this fantastic information. If you look around at what some other people are posting on here; its funny, but totally useless from an informative perspective.

You may have noticed that with the newer GT frames, they actually did away with the welds at the seat tube in order to allow for some flex which makes sense. You brought up a good point - why would you want the rear triangle to be doubly reinforced into the top tube, when this is generally an area which should allow for some compliance?

However - I believe that the engineers were able to use lighter and slightly thinner tubing to their advantage to make a frame thats obviously still stiff, yet light. Like i mentioned somewhere earlier, I weighed my entire bike in at 21LB. I think that;s pretty darn impressive for a fully equipped XL hardtail. But the ride is stiff. Punishingly stiff. After I mounted my shock absorbing seatpost, I have to admit that the stiffness of the frame feels alot better now.

From the perspective of a bike which can comfortably do everything, I am picturing a relatively slack head tube angle to make up for the wider handlebars (About 71 degrees) and a fairly aggressive fork rake. I think this way, we can comfortably balance handling on both ends of the spectrum from a speed/terrain perspective, so long as the fork rake isn't anything too extreme.I understand that gravel and road bikes are suited to smoother terrain and tend to maintain a higher average speed. Considering that most of them are fitted with dropbars which sort of numb overall response, I guess this is why manufacturers dial up the head tube angle pretty aggressively.on these sort of bikes.

Obviously, the stem shape, and even the way it is forged also plays a rather big role in terms of steering response. I assume that a longer stem would be more ideal for higher speed riding, and probably for climbing hills, since it allows you to lean forward over the handlebars a bit more for better power transfer? I do like the feel of a short stem though. I don't have to lean forward so much and it really helps emphasize on the accuracy of a longer handlebar without making it feel too slow and sluggish.

So if you were able to build your own frames (For road, gravel and singletrack respectively) what would be the distinctive characteristics in design between the three? And what sort of material would you prefer to use? Me personally, I love the ride quality of steel, cromoly, hi tensile etc. Its wonderfully smooth and really seems to make up for the added weight. I know that Titanium is difficult to work on, but I think that is what i'd want to focus on. My understanding is that the Down Tube and Chainstays, particularly at the weld points take the most stress from riding and consequently need to be the strongest area, while the area where the seat tube and top tube intersect is usually a different shape to offer a little bit of compliance for the rider. I'm sure you can make a comfortable aluminum frame though.
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Old 10-07-20, 04:20 AM
  #49  
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Originally Posted by Rolla
If you think this bike is great, just wait til you get one that fits you.
This is absurd...
lmao

So what sort of insane bike frame size/shape would I need which fits me comfortably? This frame measures at 23inches from the top of the seat tube to the center of the bottom bracket. I understand that stack/reach are far more important measurements when determining the fit of a bike, but my point is, hard to come across something which will fit me comfortably without looking into sometihng custom.. I have a 34" inseam, which i'm sure is not the longest in the bike world.
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Old 10-07-20, 04:26 AM
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Originally Posted by shelbyfv
Someone went to a lot of effort to come up with BF's 2nd most absurd bike fit pic. Cube still holds 1st
Where can I have the honour of viewing the contender for first place?

You should have seen my setup before this. I didn't realize how gargantuan I feel on these bikes. I was using a 30mm stem mounted backwards, on top of my stem riser. It sort of worked OK.. well, better than having it on forwards at least. Except it was totally inept going up any hills. Not enough weight over the handlebars.

Originally Posted by Ironfish653

A bike like this is still pretty capable off-road, though definitely harder to ride, than a modern bike, but put it on slicks, or 26” BMX tires, and they’re damn effective city bikes as well.

[img]blob:https://www.bikeforums.net/fdd871ed-fcd9-4375-aac8-eeaea4877bc3[/img]
Have to admit, it looks all around purposeful. Let me guess, is this Cannondale Volvo your bike? It looks like it can't decide between XC and gravel trail duty, but in a good way. I like how it has some sort of shock absorption below the head tube. How capable do you reckon a good fixed front fork would be on more technical stuff?
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