Frame Geometry vs. Handling Characteristics
10-22-18, 09:42 AM
#1
Virgo
Thread Starter
Frame Geometry vs. Handling Characteristics
I have a couple vintage road bikes now, I've owned several over the last 5-6 years. I'm beginning to become mindful of the differences in handling characteristics between my frames, but I can't really articulate the differences between them. The one I'm riding most now has 73/73, and my other one is 72ST/71HT. I prefer the handling of the 73/73 frame better. It just feels better - balanced? I have the saddle and bars adjusted the same on both bikes, the fit is identical to within 1/8". I had a bike that was 74ST/73HT and I couldn't get the saddle back far enough but otherwise it had a nice ride.
Most of my riding is commuting, around 100-150 miles a week, mostly flat. I don't know if that's relevant, just putting it out there.
Can anybody describe their experience with different geometries? What might I be experiencing that I don't like about the more slack geometry?
Most of my riding is commuting, around 100-150 miles a week, mostly flat. I don't know if that's relevant, just putting it out there.
Can anybody describe their experience with different geometries? What might I be experiencing that I don't like about the more slack geometry?
10-22-18, 11:44 AM
#2
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Trail, is a distance on the ground , between a line thru the steering axis
[Head tube angle just part of it. ]
and a plumb line straight down from the axle center..
[fork rake and bottom radius, r=1/2 of wheel/tire outside diameter.]
it is a significant part of "handling"...
...
[Head tube angle just part of it. ]
and a plumb line straight down from the axle center..
[fork rake and bottom radius, r=1/2 of wheel/tire outside diameter.]
it is a significant part of "handling"...
...
Last edited by fietsbob; 10-22-18 at 11:49 AM.
10-22-18, 12:11 PM
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I'm entirely agnostic, no, check that, entirely enthusiastic about different geometries and how they feel. I just see them as different, none better or worse. And I wonder why people like riding the same thing day in, day out. (Yes, you can take that any way you want.)
10-22-18, 12:15 PM
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Fork rake/fork geometry has an effect on how far forward the front wheel sticks out. You could make a bike with 72 degree angles handle nearly the same as a bike with 73 degree angles (and vice-versa), by changing out forks. (this presumes similar distance between wheels. weight distribution, etc). Gugie is really good at explaining this.
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10-22-18, 12:39 PM
#5
Virgo
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I will say that the bike with the slack angles is a little harder to get to turn. I thought it may have been the headset and overhauled it a couple months ago. I will measure the trail for each bike and post after I get home today.
10-22-18, 12:52 PM
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And the rider's fit to the bike has a big impact on handling as well. If you take pair of bikes with the same geometry but slightly different frame sizes, and set them up to fit the same rider, the rider will find that they handle differently.
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10-22-18, 01:52 PM
#7
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Find a pair of walls that meet to create a "point" that you can place your bike's crank dust cover against, and measure the forward distance from this protruding corner (vertical line) to your handlebar. Then measure the saddle-to-bars reach (which it sounds like you've already done).
Is the forward reach from (bb to handlebar) the same on both bikes?
As USAZorro mentioned, the "front center" distance (from bb to front axle) is also a crucial part of how weight is distributed between the front and rear wheels (more weight on the front wheel makes the steering heavier and more stable).
A longer front-center distance also inhibits a rider's ability to draft closely and safely behind a leading rider, which matters more in competition (and matters none while riding alone).
A shorter stem length will tend to quicken/lighten the steering response and feel, so how a frame fits the rider thus affects how the fitted bike will perform.
A 71-degree headtube angle is off-road geometry, as found on cyclocross/gravel bikes and on traditional mtb's and hybrids.
Depending on the stem length needed on a particular frame/rider combo, even a 75-degree headtube angle can be quite stable in spirited riding.
Lots of bikes in between these two extremes!
69-degrees square versus 76 degrees square.
I've done lots of riding on both, at speeds up to 50mph, and their handling quirks become less noticeable and less significant after riding the same bike for a few days:
Last edited by dddd; 10-22-18 at 02:01 PM.
10-22-18, 02:18 PM
#8
Virgo
Thread Starter
Also, this wasn't asked but the angles I stated are measured, not nominal.
I spent some time comparing these angles against modern bikes a while ago and I agree with your statement that 72/71-ish seems to be used on CX bikes and 73/73 seems to be used more on road/racing bikes. The stack and reach of the slack angle bike are also shared with CX bikes. I never ride off road, so any advantages to the slack HT angle in that respect are never realized. I also never do any group rides.
10-22-18, 02:22 PM
#9
Virgo
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It would take some convincing, though, for me to be sold on frame size being a bigger factor than geometry in this case.
10-22-18, 02:33 PM
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Fork rake/fork geometry has an effect on how far forward the front wheel sticks out. You could make a bike with 72 degree angles handle nearly the same as a bike with 73 degree angles (and vice-versa), by changing out forks. (this presumes similar distance between wheels. weight distribution, etc). Gugie is really good at explaining this.
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10-22-18, 02:37 PM
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10-22-18, 02:41 PM
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Wouldn’t more weight be over the front wheel on the smaller frame? Weight distribution would have an effect. Especially concidering a rider outways the bike by a factor of what, 8?
10-22-18, 02:43 PM
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10-22-18, 04:16 PM
#14
Virgo
Thread Starter
front center - 24 3/8” (620mm)
31 3/4” B.B. to HB center (806mm)
73 squared frame - 2” trail (50mm)
front center - 25 5/8” (650mm)
31 7/8” B.B. to HB center (809mm)
I dropped my phone on my ride home and cracked my screen :-/
I basically want a 23” or 24” frame that rides like the 73 squared bike. I don’t mind the 25” frame but I think it looks goofy with 3” of seatpost. Very small fistful.
So what’s the deal with front center? Those two dimensions are very different between the two frames.
Last edited by Phamilton; 10-22-18 at 04:40 PM. Reason: Added another dimension
10-22-18, 04:59 PM
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I have no idea about numbers. I know frame and tire sizes, stems, etc, but not much else.
To me, one bike rides one way, another bike rides another way. Too many variables, including me.
To me, one bike rides one way, another bike rides another way. Too many variables, including me.
10-22-18, 05:11 PM
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For what it's worth... :
My 1976(?) Holdsworth "531 Special" 650b conversion ("Gugificazione") and my 2016 Square Built custom have the same geometry and dimensions: both have 60 cm (c-c) seat tube and 57 cm top tube, very similar fork offset (hard to measure, around 6 cm). Both have 73° parallel head and seat tube with horizontal top tube. They have different wheels, but a similar wheel diameter.
That is, the Holdsworth takes 584x38c tires (so nominal diameter 660 mm) while the Square Built has 559x53 tires (so, nominally, 664 mm). I emphasize the word "nominal" because at present the Holdsworth has a 42 mm tire in front. Which would make up the difference. But as I measure them the difference between the 38 and the 42 is really negligible, definitely less than 4 mm, so let's continue to emphasize the word "nominal."
Obviously there is a significant difference in the width of the tire, but that is really the only significant difference that shows up in the numbers.
The Holdsworth is butted 531, the Square Built is Columbus SL; the frames weigh in around 74-76 oz, I don't have the numbers on front of of me. If I recall correctly, the SquareBuilt has an appreciably heavier fork.
Anyway. You're wondering: what's the point? Well, the bikes handle differently. The Holdsworth has a tendency to shimmy, the Square Built does not. The Holdsworth feels more responsive, more agile. Both are comfortable, but the Square Built moreso. Neither is appreciably faster (they have the same engine). But they really feel like different bikes. They [iI]are[/I] different bikes.
My 1976(?) Holdsworth "531 Special" 650b conversion ("Gugificazione") and my 2016 Square Built custom have the same geometry and dimensions: both have 60 cm (c-c) seat tube and 57 cm top tube, very similar fork offset (hard to measure, around 6 cm). Both have 73° parallel head and seat tube with horizontal top tube. They have different wheels, but a similar wheel diameter.
That is, the Holdsworth takes 584x38c tires (so nominal diameter 660 mm) while the Square Built has 559x53 tires (so, nominally, 664 mm). I emphasize the word "nominal" because at present the Holdsworth has a 42 mm tire in front. Which would make up the difference. But as I measure them the difference between the 38 and the 42 is really negligible, definitely less than 4 mm, so let's continue to emphasize the word "nominal."
Obviously there is a significant difference in the width of the tire, but that is really the only significant difference that shows up in the numbers.
The Holdsworth is butted 531, the Square Built is Columbus SL; the frames weigh in around 74-76 oz, I don't have the numbers on front of of me. If I recall correctly, the SquareBuilt has an appreciably heavier fork.
Anyway. You're wondering: what's the point? Well, the bikes handle differently. The Holdsworth has a tendency to shimmy, the Square Built does not. The Holdsworth feels more responsive, more agile. Both are comfortable, but the Square Built moreso. Neither is appreciably faster (they have the same engine). But they really feel like different bikes. They [iI]are[/I] different bikes.
Last edited by rhm; 10-22-18 at 05:15 PM.
10-22-18, 05:14 PM
#17
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10-22-18, 05:20 PM
#18
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10-22-18, 05:20 PM
#19
Virgo
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For what it's worth... :
My 1976(?) Holdsworth "531 Special" 650b conversion ("Gugificazione") and my 2016 Square Built custom have the same geometry and dimensions: both have 60 cm (c-c) seat tube and 57 cm top tube, very similar fork offset (hard to measure, around 6 cm). Both have 73° parallel head and seat tube with horizontal top tube. They have different wheels, but a similar wheel diameter.
That is, the Holdsworth takes 584x38c tires (so nominal diameter 660 mm) while the Square Built has 559x53 tires (so, nominally, 664 mm). I emphasize the word "nominal" because at present the Holdsworth has a 42 mm tire in front. Which would make up the difference. But as I measure them the difference between the 38 and the 42 is really negligible, definitely less than 4 mm, so let's continue to emphasize the word "nominal."
Obviously there is a significant difference in the width of the tire, but that is really the only significant difference that shows up in the numbers.
The Holdsworth is butted 531, the Square Built is Columbus SL; the frames weigh in around 74-76 oz, I don't have the numbers on front of of me. If I recall correctly, the SquareBuilt has an appreciably heavier fork.
Anyway. You're wondering: what's the point? Well, the bikes handle differently. The Holdsworth has a tendency to shimmy, the Square Built does not. The Holdsworth feels more responsive, more agile. Both are comfortable, but the Square Built moreso. Neither is appreciably faster (they have the same engine). But they really feel like different bikes. They [iI]are different bikes.
My 1976(?) Holdsworth "531 Special" 650b conversion ("Gugificazione") and my 2016 Square Built custom have the same geometry and dimensions: both have 60 cm (c-c) seat tube and 57 cm top tube, very similar fork offset (hard to measure, around 6 cm). Both have 73° parallel head and seat tube with horizontal top tube. They have different wheels, but a similar wheel diameter.
That is, the Holdsworth takes 584x38c tires (so nominal diameter 660 mm) while the Square Built has 559x53 tires (so, nominally, 664 mm). I emphasize the word "nominal" because at present the Holdsworth has a 42 mm tire in front. Which would make up the difference. But as I measure them the difference between the 38 and the 42 is really negligible, definitely less than 4 mm, so let's continue to emphasize the word "nominal."
Obviously there is a significant difference in the width of the tire, but that is really the only significant difference that shows up in the numbers.
The Holdsworth is butted 531, the Square Built is Columbus SL; the frames weigh in around 74-76 oz, I don't have the numbers on front of of me. If I recall correctly, the SquareBuilt has an appreciably heavier fork.
Anyway. You're wondering: what's the point? Well, the bikes handle differently. The Holdsworth has a tendency to shimmy, the Square Built does not. The Holdsworth feels more responsive, more agile. Both are comfortable, but the Square Built moreso. Neither is appreciably faster (they have the same engine). But they really feel like different bikes. They [iI]are different bikes.
I wonder how much more differently they would handle if they had different frame angles and trail, etc. Just how I think.
10-22-18, 05:23 PM
#20
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10-22-18, 05:24 PM
#21
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10-22-18, 05:29 PM
#22
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Uh huh. Yeah. Sure.
Hey, I believe you!
Yeah. Sure I do.
Hey, I believe you!
Yeah. Sure I do.
10-22-18, 06:20 PM
#23
Virgo
Thread Starter
The context for the question I suppose is that I’m sort of perpetually thinking about my next frame. For practical reasons I keep two bikes. I’m feeling like I’m about ready for another one, and want to go with a 23” or 24” frame, and vintage. So I know that I really enjoy how the 73 squared bike rides and handles, and don’t really care so far for the way the 72/71 bike rides/handles. I’ve had it for 6 or 7 years, longer than anything else that’s come and gone during that time, but didn’t start measuring anything until the last 3 frames. So when I replace it, ideally I can avoid a geometry that provides similar handling characteristics by understanding a little about what makes a frame with a given geometry handle in a very general sense. I don’t have enough experience as a rider to say “this one planes” or “stiff yet compliant”. I don’t know why I suspect the differences I’m experiencing are geometry related. In my mind that seemed like the logical place to look, but I admit I didn’t explore the logic much. I suppose if the differences in handling come from too many variables to ever produce any consistent result then I might be wasting my time, but I find bike stuff to be a very satisfying way to waste time.
Last edited by Phamilton; 10-22-18 at 06:22 PM. Reason: I just left something out.
10-22-18, 06:38 PM
#24
Virgo
Thread Starter
Another thing I remember is that the 73 squared bike is WAY easier to ride out of the saddle. Like, it’s almost fun to do so, and I’m pretty lazy. I will do it sometimes just for fun. That’s actually probably the biggest difference, or at least the most noticeable.
Overall, the 73 squared bike goes where I want it to, when I want it to, and how. But I don’t want to be disappointed when I get my next frame in a 73 squared and find it handles weird. The 72/71 bike is a little sluggish, but that’s the best I can articulate it. It generally goes where I want it to, but it takes its time doing so and requires some effort, comparatively speaking, and isn’t always within an inch of where I point it. I hit a lot more potholes and stuff like that with the 72/71.
Overall, the 73 squared bike goes where I want it to, when I want it to, and how. But I don’t want to be disappointed when I get my next frame in a 73 squared and find it handles weird. The 72/71 bike is a little sluggish, but that’s the best I can articulate it. It generally goes where I want it to, but it takes its time doing so and requires some effort, comparatively speaking, and isn’t always within an inch of where I point it. I hit a lot more potholes and stuff like that with the 72/71.
Last edited by Phamilton; 10-22-18 at 06:44 PM. Reason: I don’t want to give a reason every time. I edit a lot.
10-22-18, 06:45 PM
#25
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Well, you really can't go wrong with 73°parallel geometry.
But as for "this one planes" and all the similar praise for this frame or the other one, (in my opinion) the speaker is not talking about geometry, but rather "fit," broadly defined. I mean, obviously, the seat tube and the top tube should be of a length that fits the rider's proportions; but they should also be of the suitable tube gauge.
Imagine two riders who fit the same frame size, but one weighs 150 lbs, the other 225 lbs. If the lighter rider finds a frame to "plane," the other will find it noodly; if the heavier rider finds it "planes," the other rider will find it too stiff.
Similarly, imagine two riders of the same bodily dimensions, and the same weight. They really do fit the same frame size, but one pedals at 60 rpm, the other prefers 105 rpm. These two will have different expectations of their frames; a bike that planes for one will be poorly suited to the other.
Those are extreme examples. The bike industry has found that they don't matter. Almost anyone can ride almost any bike, and this is true for you and for me. And one of us may ride a bike and have truly magical experience. Cool! But it won't be just the geometry that gives us that experience; but several factors aligning in our favor.
Good luck with that!
But as for "this one planes" and all the similar praise for this frame or the other one, (in my opinion) the speaker is not talking about geometry, but rather "fit," broadly defined. I mean, obviously, the seat tube and the top tube should be of a length that fits the rider's proportions; but they should also be of the suitable tube gauge.
Imagine two riders who fit the same frame size, but one weighs 150 lbs, the other 225 lbs. If the lighter rider finds a frame to "plane," the other will find it noodly; if the heavier rider finds it "planes," the other rider will find it too stiff.
Similarly, imagine two riders of the same bodily dimensions, and the same weight. They really do fit the same frame size, but one pedals at 60 rpm, the other prefers 105 rpm. These two will have different expectations of their frames; a bike that planes for one will be poorly suited to the other.
Those are extreme examples. The bike industry has found that they don't matter. Almost anyone can ride almost any bike, and this is true for you and for me. And one of us may ride a bike and have truly magical experience. Cool! But it won't be just the geometry that gives us that experience; but several factors aligning in our favor.
Good luck with that!