Geometry & Suspension design - what creates bike characteristics

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Geometry & Suspension design - what creates bike characteristics
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Posted: Aug 15, 2022 at 5:29 Quote
This post is purely just for my own curiosity. It would be really cool if some kinematics experts, bike designers, or geometry experts could weigh in.

My question is, what geometry figures create certain bike characteristics like playfulness vs. composure?

I've recently switched bikes from a Kona Process 153 CR, to Rocky Mountain Element Carbon 50. The differences in how these bikes ride is so interesting. The Element is an amazing bike, as backed up by every review of it. My assumptions were that it would be a lightweight, fun, playful, short-travel trail bike. But that's not really how it feels. In contrast, the Process 153, albeit a much bigger and heavier bike, was oodles more jibby, jumpy, and playful than the Rocky. So what gives?

The Element feels super composed, stable, planted. You get loads of traction in all scenarios. But it doesn't really like going airborne. The Process 153 would take flight if you looked at it the wrong way. The Process also felt like a more spritely climber, although it's weight would hold it back. Both bikes are great, but exhibit almost opposite ride qualities.

Thoughts?

Posted: Aug 15, 2022 at 9:47 Quote
The new element is slacker, and longer than the previous generation process 153 so it makes sense that it feels more stable. Just set your suspension up a little stiffer and it should feel more playful.

Posted: Aug 15, 2022 at 10:56 Quote
TheSlayer99 wrote:
The new element is slacker, and longer than the previous generation process 153 so it makes sense that it feels more stable. Just set your suspension up a little stiffer and it should feel more playful.

Yes definitely need to fiddle with the suspension. Still, questions about the how it's geometry can change the ride so much. It takes a lot more effort to lift the front end, specifically for steep drops.

Posted: Aug 15, 2022 at 11:01 Quote
Kinda crazy how close all the numbers are; but the Kona was quite a bit shorter wheelbase and rear center.

Posted: Aug 15, 2022 at 12:18 Quote
Isn't that difference in BB drop pretty significant?
More so than the relatively minute changes to wheelbase and head tube angle.

Posted: Aug 15, 2022 at 17:36 Quote
16rally wrote:
Isn't that difference in BB drop pretty significant?

Looks it, though the difference when sagged will be a bit less (assuming the same sag %) as the Process has more travel to sink into.

If I'm working it out right and we assume 25% sag for both:

Element: 43 + (120*0.25) = 73mm sagged BB drop
Process: 29 + (153*0.25) = 67.25mm sagged BB drop

So there is still a fair difference, just not as much as the unsagged numbers appear.


I'm no expert but would expect the shorter rear centre and wheelbase of the Process to make it feel more agile.

Also, correct me if I'm wrong but isn't the Element 29" and the Process 27.5" wheel? Smaller wheels tend to be more agile and flickable.

Suspension tune and linkage behaviour can make a big difference to poppy vs planted feeling too.

I think its a combination of a whole bunch of factors and how they interact with each other.

Posted: Aug 15, 2022 at 20:51 Quote
Gravelben wrote:
16rally wrote:
Isn't that difference in BB drop pretty significant?

Looks it, though the difference when sagged will be a bit less (assuming the same sag %) as the Process has more travel to sink into.

If I'm working it out right and we assume 25% sag for both:

Element: 43 + (120*0.25) = 73mm sagged BB drop
Process: 29 + (153*0.25) = 67.25mm sagged BB drop

So there is still a fair difference, just not as much as the unsagged numbers appear.


I'm no expert but would expect the shorter rear centre and wheelbase of the Process to make it feel more agile.

Also, correct me if I'm wrong but isn't the Element 29" and the Process 27.5" wheel? Smaller wheels tend to be more agile and flickable.

Suspension tune and linkage behaviour can make a big difference to poppy vs planted feeling too.

I think its a combination of a whole bunch of factors and how they interact with each other.

For starters there’s more to dynamic measurements than just calculating percentages, mainly axle path. So unless you do a full computer simulation of the kinematics or physically measure them at sag you won’t know truly the dynamic measurements. The process has been made in both wheel sizes since 2017, so there’s no difference there.

Also the change in wheelbase comes mostly from chainstay length and head angle, so it will make a huge difference to handling. While suspension design plays a role, modern suspension can be set up pretty much however you want it to feel with some effort.

Posted: Aug 15, 2022 at 21:03 Quote
TheSlayer99 wrote:
Gravelben wrote:
Also, correct me if I'm wrong but isn't the Element 29" and the Process 27.5" wheel?

The process has been made in both wheel sizes since 2017, so there’s no difference there.

As of the 2021 model year, the *carbon* Process (CR and CR/DL) have been available only with 29" wheels. A 27.5" carbon Process was last offered for model year 2020.

That said, a 29 mm BB drop was on the 29" version; the 27.5 had a 10 mm BB drop.

Posted: Aug 15, 2022 at 22:52 Quote
tup I stand corrected, good to know. The only Process I've ridden was a mates older 27.5" 153 so I had assumed the 153 was a 27.5" version.

Posted: Aug 16, 2022 at 7:19 Quote
I have found 10mm of chainstay length makes a huge difference in how light the front end is. I have a ht with sliding dropouts (425-445mm cs range) so I'm able to play with cs length while keeping everything else the same, and 10mm one way or the other creates significant changes in riding characteristics.

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