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Difference in geometry, size, or frame material?

by dottigirl
Sat, Aug 13, 2016 19:29
8

Apart from the reach - that's a given - what's the difference in riding a bike that fits you v one too big or small.

I know it's a weird question, but I have 48cm Kinesis Racelight T2 (alu frame), and a 51cm Spesh Ruby (carbon). The Ruby is undoubtedly the lighter bike, especially as it doesn't carry the heavier kit of the Racelight (mudguards, heavier saddle bag)

In ride comparison however, the Ruby feels wallowy around the BB. Not as direct or responsive when cornering. I appreciate the Racelight is the more aggressive setup, and the Ruby is higher, certainly around the front.

But, what's that wallowy feeling? Size, geometry, or difference between carbon and alu? Or are there too many variables?

 

If I've lost you, what's the difference in feel between alu and carbon?

Thanks.

If you're new please join in and if you have questions pop them below and the forum regulars will answer as best we can.

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8 comments

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jollygoodvelo | 8 years ago
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I have a hybrid bike I used to describe as 'wallowy'.  Not slow as such, not flexy under power (I don't have that much power), just that every time you did something it seemed to react slowly compared to my other bike.  One day I had a hunch and checked the spoke tension in the rear wheel.  Quite a few of the spokes were very slack indeed: 15 minutes of twirling a spoke key later and it was much improved.

 

You also get some 'slack' in the system from certain tyre designs: when you apply power through the chain, it pulls the hub around, which pulls the spokes, which pulls the rim, which pulls on the tyre.  Very soft sidewalls will allow the bead of the tyre to flex before the tread catches up: you can reduce this with better quality tyres (higher TPI numbers) or higher pressures.

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Hxs | 8 years ago
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size and Geometry are the same topic (IE: different size change geometry), watch this
Geometry Explained:
https://www.youtube.com/watch?v=wfx3LqsCFSA

and then about carbon fiber, make a note that carbon fiber are directional material unlike metals, so same geometry and shape can ride vastly different depend on how it lay up. It can ride like anything, ultra stiff or ultra cushion or mix of both in different area, it's really up to the designer.
https://www.youtube.com/watch?v=_4ALUyrTe90

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turnerjohn | 8 years ago
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I had a Roubeux years ago as my winter bike, flexing wasn't in the BB (wasn't to bad under power) but the Zert rear stays...felt like I constantly had a puncture and whilst comfortable it did my head in ! Went back to Trek, a  Madone 5.2 which is imoa a perfect (for me) winter bike ...could be worth a look for you ?

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drjohn | 8 years ago
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The feel of a carbon bike depends on the grade (stiffness) and placement of carbon fibre in the plastic. This means an engineer can optimise the bike for different things. Cynics would say that a carbon frame can be optimised for cost by using less carbon fibre and more plastic. So, some carbon frames are stiff and some are not. 

The selling pitch for the Ruby (or Roubaix)  is that the flex in the frame and forks lets the wheels ride over bumps without bouncing you up and down. This has been proven to improve speed over rougher surfaces (in an independent timed test involving bikes with a simulated rider load, rolling down a hill).

This is quite an effect, usually the frame should not make much difference in this regard so it must flex a lot. I'm sure it will feel softer because of it.

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dottigirl | 8 years ago
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Thobson - thanks, sounds like the same as me.

Wheels, tyres and pressures are similar or the same between bikes, that's why I'm looking at the frame sets.

Long term, I'll be selling the Ruby frameset, but I haven't decided what to replace it with - another Kinesis or something different.

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CXR94Di2 | 8 years ago
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Those frames are small so you're are probably a light weight? Aluminum has a harsher ride but not significantly. Tyres will play a big role in feel. Ensure they have the correct pressures. If the difference is still apparent then it must be just different setups and that's life.

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Jimnm | 8 years ago
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Try altering tyre pressures or even changing tyres. Trial and error to get the best results possible. Good luck.

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thobson | 8 years ago
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I have  a M aluminum bike (Planet X London Road) and a M/L carbon bike (Giant Defy). I find the medium bike is more responsive, especially when cornering. I'm not sure how much is down to geometry etc but I have a shorter stem on the M/L bike which should in theory make the steering sharper than the other bike, but this is not the case. I think the size of the frame makes a big difference

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