FastJake

I'm curious about the history of MTB geometry and why it changed the way it did. The first MTBs had slack angles and very long chainstays. Then things got shorter and steeper. A good example is the Bridgestone MB-1 listed below that basically has road bike geometry. Lately, head tube angles have slackened again but chainstays are still kept as short as possible. I realize there are other factors involved like suspension, wheel size, tire size, and others. So why did all these changes come about? Why did things get so steep in the early 1990s? Are the manufacturers making blind guesses and following trends, or is there a method to their madness?

(For the purposes of this thread I'm ignoring downhill, freeride, dirt jump, trials, etc. and focusing on the typical cross county bike that's more or less been around since the beginning.)

1977 Joe Breeze

• Head angle: 67.5 Seat angle: 70
• Chainstay length: 470mm
• Trail: 86mm

1993 Bridgestone MB-1

• Head angle: 72 Seat angle: 73.5
• Chainstay length: 425mm
• Trail: 66mm

2020 Giant XTC Advanced+

• Head angle: 69 Seat angle: 71.5
• Chainstay length: 432mm
• Trail: 89mm

2cam16

Paging Repack Rider

Chinghis

Here's a fun one for you. I bought a Small Pure Cycles gravel bike for my son, who's about my size. Testing it out, I felt it was very similar to my bike - a 1992 Specialized StumpJumper FS. So I measured all the tubes (but not the angles) - and the gravel bike was virtually identical to my old mountain bike. (So much so that I'm thinking of picking one up for myself and putting a flat bar on it.) The Stump's steel is much better, though.

qclabrat

interesting topic, I'm sure I've read a few articles on this throughout the years, will post up if I come across them again
the 2020 Giant is harder to compare, as I'm assuming it's a 29r with different geo needs

Here's my quick thoughts on the Breeze vs Grant's MB-1.
The Breeze probably pedaled terribly uphill but crushed the downs with the geo. All measures need to be pulled in with the slack HT, including the stays to keep the bike nimble and not ride like a tandem.
MB-1s made the bike a better all arounder especially upwards though sure it sacrificed some downward fun. With shorter stems and wider bars, the 29r are now able to go back to slacker HTs, remember the steep early 29rs which at times felt like a unicycle?

bikemig 

I thought the early MTBs were copies of Schwinn excelsiors that were turned into Klunkers back in the day.

https://mombatbicycles.com/MOMBAT/Bikes/Excelsior.html

That explains the slack angles and 26 inch wheels.

It's not surprising that as the manufacturers got feedback on their product, they tweaked the geometry so it would handle better. I have 1987 Stumpjumper Comp and the geometry is clearly different from my '92 Stumpjumper. The point is that there was a lot of experimentation going on.

base2 

Indeed a lot of experimenting and emperical data.
There was a geometry trend for a while that made mountain bikes behave with all the speed & precision of a shopping cart.

Lame.

Thankfully that trend is over.

A lot of orbiting around a central data cluster just to end up right back where we started.

bikemig 

There was nothing lame about coming up with a great idea (modding old Schwinns to ride offroad), copying that idea, and then improving on it over time.

base2 

Agreed.

I was actually referring to the steeper & steeper "racier" head tube angles (approaching 90 degrees [/snark]) making bikes that had a tendency to stand up & highside the rider at the most inopportune time..

Long & slack is a pleasent return. It gives a bit of freedom to weight placement & tracks better on the rough.

FastJake

Yep, this is what I was alluding to. Two decades of making bikes short and steep, only to make them longer and slacker again.

Happy Feet

I don't have any data for you but I remember the first mtb I converted for touring. It was an early generation model that had a horizontal top tube and slack geometry, more like a Surly long haul trucker. Heavy gaspipe tubing, Chrome rims, bull horn bars, stamped caliper brakes and 2x5 road gearing. Quite the beast.

Later, I had another early gen mtb, this time a Marushi MT5. Again, 2x5 gearing but a very well made frame with strong rims wonderful dropouts, bull horns, and cantis. Except for the bars the components moved to Al instead of steel. I think that was a 1985 model.

Some of those first mtb's were made by manufacturers who wanted to get in the game by basically throwing their road components on heavier constructed but still road like frames with bulls or flats and fatter tires and calling them mtb's or more accurately ATB's. After that the design began to become a lot more trail specific but few would be what we call technical or downhill designs.

One thing about those early tires though. They were great all rounder's, if a bit heavy, and I would buy some more if they were still made. They had moderate tread on the sides but a continuous center bead that rolled very well when pumped up. The original gravel tire.

eshew

Simple, as stated above the Breezer and Ritchey bikes were built for repack dh. Pedaling performance was secondary, because it's fun to ride places. 28-30" handled bar width

Mid eighties the race scene went towards xc and the geometry changed to suit xc. Dh and trials were in the mix but most racers used their xc bikes. Handle bars are now ridiculously narrow, why? Oh that's right, long ass stems! Hite rite dropper is out but tapers off into nineties.

Late 90's dh & freeride came to help slacken angles but reach and wheelbase was still old school. Bars slowing begin to go wider, most stems still long 60mm is short.

2000-2012 some slackening on all-mountain bikes, reach still painfully short. Bars get wider, stems get shorter.

2013-now. Sometime figured longer reach slack head angles and short stems worked well. Everyone jumped on board and figured steep seat angles work well too. XC courses are now more technical and longer reach allows for slacker angles and still quick handling but with much needed stability. Short stems and wide bars are in! Oh, and droppers.

Much of the changes had to do with the trails available. Up though the 90's fire roads were the vast majority of what was available. Early 2000's North shore showed us built trails are fun. Whistler takes note and builds a park. Since then more handbuit trails started showing up, legality was questionable. Around a decade later many started to get govt approval and it was on. Now we buy bikes to ride on fun trails. If we still only had access to fire roads we wouldn't have the bikes we have today.
​​

Happy Feet

This is quite so. There is so much difference in design depending on what sort of trails one prefers. I really like flow trails and am a bit too old to be breaking myself on big drops or jumps, and I still pedal up the access roads, so a super aggressive technical bike doesn't appeal as much as a more slack and easier to pedal geometry. A lot of our local hills are gravity trails where pedaling can be minimal (except to get up) but in Utah I found a number of mixed bag horizontal routes that were 5-10 miles long. Really makes you think about choosing bikes.

Miele Man

I think a lot of the change in MTBs was done for similar reasons road bike geometry changed and that was because of racing. I had a BIANCHI MTB back in the mid-1980s and the chainstays on that bike (21" frame) were so long that I was able to mount a water bottle cage and 750ml water bottle BEHIND the seatube in front of the rear fender.



I think as more and more people started racing MTBs downhill that angles and chainstay lengths change to increase speed.

Cheers

Sertsa

I don't know if there's enough detail for your purposes in this video, but I watched it a couple days ago and found it interesting. Maybe you can contact the museum. Anyway, the video:

FastJake

What a coincidence, I'm in this video! I was in San Francisco for a work trip and took some time off to ride and visit the museum for the first time. They happened to be filming this when I was there. I tried to stay out of their way but you can see me in the corner at 27:40. It was really interesting but I didn't want to bother Will with my questions since he was busy.

Kapusta

The idea that we are returning back to the geo from days or yore is a bit far-fetched, IMO.

You can't just look at individual geo numbers, you need to look at the whole package.The numbers the OP is showing shows that we now have HAs and Trail #s similar to one bike and CS number closer to a different bike. These individual similarities do not mean a whole lot.

One critical number that is missing here is frame reach and seat tube angles. Frame reach is waaaay longer and STAs are much steeper.

Rajflyboy

Basically

Joe Breeze had his **** together way back then 👍

Repack Rider

Joe Breeze took my money and agreed to build the kind of frame I wanted, some time in mid-1977. He had taken the Albert Eisentraut course (alongside Bruce Gordon) and had built four or five road bikes for himself and a few other members of Velo-Club Tamalpais including Otis Guy and Marc Vendetti. He was one of the fastest downhill riders, second all time on Repack. He knew, more than anyone I could have asked, exactly how I planned to use the bike.

When Joe had taken the Eisentraut course, he was joining a tradition four or five generations old, with techniques and designs that reflected the success and failure of millions of individual units. He could read any of dozens of books on building a road bike. But he wasn't building a road bike. Joe had to completely re-0design the bicycle. For starters, the chainline has to move away from the centerline to accommodate the wider tires. Then of course, what geometry, chainstay length, etc.? With no other point of reference, he chose the Schwinn geometry of the bike he was riding at the time.

When Gary Fisher asked Tom Ritchey to build his frame and one for a friend in 1979, Tom had seen and discussed Joe's frames. Gary also went with the geometry he was most familiar with, so Tom built them that way. Whatever their limitations, the Ritchey frames out performed everything else on the market. When the major companies needed to get up to speed without the five years of experimentation that had led Marin County builders to the new design, they bought a Ritchey MountainBike. Example: the "Bullmoose" handlebar was not a particularly good design, It was originally a one-off for Tom's personal bike, but people copied it anyway.

Charlie Cunningham, for what it is worth, rode what would now be called a "gravel bike" until alloy 26" rims became available in 1979. When he switched to 26" balloon tires, he stayed with drop bars and steep geometry. But no Cunningham bike has ever won a DH event, they are strictly XC.

Joe Breeze once built a bike with an 80-degree head angle, just to see what would happen. He says that after he learned to ride it, it felt normal. then when he got back on his regular bike, it felt like steering through mud. You can learn to ride just about anything. The top three times on Repack are held by guys riding frames they paid less than $20 for.

FastJake

I included STA in the original post. But you're right, most modern bikes use much steeper seat tubes than the example I picked. For what it's worth, here are the reach figures for those same three bikes:

1977 Joe Breeze frame reach: 393mm
1993 Bridgestone MB-1 frame reach: 431mm
2020 Giant XTC Advanced+ frame reach: 403mm

Kapusta

Oops, I missed the STAs you listed.

71.5 is incredibly slack STA for a 2020 bike. If that is the correct STA for that XTC, it is an outlier.

I am a little puzzled about those frame reach numbers. Are these all for the same sized frame? Where did you even get those frame reach numbers from for the older bikes? That was typically not even listed until recently.

FastJake

It's correct, but yes, unusual. I didn't mean to cherry pick, but just looked for something that looked like a "typical" new XC bike.

I tried to use a "medium" size frame for an average rider like myself. The Giant is a 17.3" frame, the Bridgestone is an 18.1" frame. The Breezer is more difficult because it has a 22" seat tube but a downward sloping top tube. It would be helpful if I knew how tall Joe Breeze is. Saddle height is not listed on his drawing. In any case, frame reach doesn't change dramatically with small changes in frame size.

For reach on the older bikes I drew the front triangles in SolidWorks to calculate reach.

https://www.sheldonbrown.com/bridges...3/pages/63.htm
https://www.giant-bicycles.com/us/xt...nced-plus-2020

Sertsa

Very cool! Looks like a fascinating place, and he evidently has a wealth of knowledge. If I ever make it to the area I need to visit it.

Rajflyboy

thanks for posting this 👍

FastJake

I agree, thanks for the post!

TheMountBike

Bike geometry has changed all over the days. The bikes started small, but now you can see different frames, sizes, suspensions, and weights actually change almost everything. In addition, it allows the riders to add or leave off unnecessary Parts according to their needs. Here are the things that changed bike geometry forever. They are now boasting longer top tubes, slackers, head angles, and shorter chainstays. In addition, bikes have got a higher stack. So, your position on the bike is well and truly optimized. Then people may consider a range of 325-350 millimeters in bottom bracket height.350+ millimeters bottom bracket height may fit you well. I think bikes should be shorter now. I am happy for the tall people. Because they comfortably ride the ride. But MTB wants the small and mediums to be a little smaller.