HOT: Active* forum members generally gain 5% discount at starbike.com store!
Weight Weenies
* FAQ    * Search    * Trending Topics
* Login   * Register
HOME Listings Blog NEW Articles FAQ Contact About




Post new topic Reply to topic  [ 7 posts ] 
Author Message
PostPosted: Sun Dec 08, 2013 5:47 pm 
Offline

Joined: Sun Jan 11, 2009 2:43 am
Posts: 1
Hey Guys, thanks to all the posters, so much good info out here on WW. I wanted to ask a question about frame geometry characteristics. More specifically what could cause one bike to have a rear wheel that jumps around/slips a lot more than another during out of the saddle efforts? Below is a Bike Comparator with both measurements entered.

The first bike a 2008 56 Cervelo SLC-SL (red) jumps around like crazy. The second (green), a 2008 56 Cannondale six13, is much more stable.

The first thing I notice in the Comparator is the top tube and seat stay angles, much much different.

Maybe it’s not the geometry (stiffness?, weight?) or frame at all (bars?).
Any thoughts would be appreciated.

https://dl.dropboxusercontent.com/u/535 ... 3%2056.xls" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;


Top
 Profile  
 
PostPosted: Sun Dec 08, 2013 6:06 pm 
Offline

Joined: Sun May 16, 2010 7:28 pm
Posts: 652
Is guess it has to do with technique more than anything. A stiffer frame of course will do that more.


Top
 Profile  
 
Posted: Sun Dec 08, 2013 6:06 pm 


Top
  
 
PostPosted: Sun Dec 08, 2013 6:11 pm 
Offline

Joined: Sat Jan 26, 2008 10:25 am
Posts: 219
Location: Cantabria
Same wheels? Most probably stiffness but it's hard to tell. A bicycle is an hyperstatic system, thus any variation of the characteristics of any component varies the forces other componets are submitted to.

A house with solid foundations, for instance is an isostatic system, hence is easier to trace what does what.

That's why bicycle manufacturers can fill thosand of catalogues with marketing bullshit and still (almost) everything is possible. :)

Can you elaborate on yur description?


Top
 Profile  
 
PostPosted: Sun Dec 08, 2013 6:27 pm 
Offline

Joined: Tue Sep 14, 2010 3:28 pm
Posts: 1405
The longer chainstays on the Cannondale are giving you more traction. High cadence(low torque) out of saddle sprints will help your technique, so you can keep the rear wheel down on the Cervelo.


Top
 Profile  
 
PostPosted: Mon Dec 09, 2013 1:17 am 
Offline

Joined: Mon Oct 15, 2007 9:28 pm
Posts: 953
Chainstay length, bb height, and amount of weight on front end.


Top
 Profile  
 
PostPosted: Mon Dec 09, 2013 1:24 am 
Offline

Joined: Wed Oct 23, 2013 9:55 pm
Posts: 39
I`ve noticed the same thing on my old R900 Cannondale. Uphill out-of-saddle sprinting causes the rear wheel to skip off the ground. On my SuperSix HM it doesn`t skip. It isn`t wheel related since I`ve run the same wheels on both.
I`m thinking it is related to weight distribution while sprinting, which would be due to frame geometry as well as bar positioning. It`s a combination of putting your weight on the handlebars while pulling up on one of the pedals.

While writing this I just noticed that boots2000 has just said essentially the same thing.


Top
 Profile  
 
Posted: Mon Dec 09, 2013 1:24 am 


Top
  
 
PostPosted: Tue Dec 10, 2013 8:59 am 
Offline
User avatar

Joined: Tue Jan 23, 2007 11:22 am
Posts: 3657
Location: Leg hurty
I used to be big on the old CAAD 4 and 5 Dales. I raced on them for quite a few years.
It was a characteristic of that frame to have lots and lots of 'tail wag'. My team mates used to laugh and joke about it and we all noticed the same effect even with different sizes and fits etc.
They would step out and bounce around all over the place, but always came back and never caused anything more than a few raised eyebrows in the sprints.
We always put it down to the huge amount of lateral stiffness in the rear triangle (them chainstays were by far the meatiest around at the time)
Interestingly, I ride a BB30 CAAD 9 now, and don't notice it to the same extent, It seems much more stable. This would indicate it isn't probably material related, or indeed the chainstays as the CAAD 9 has enormous tubes and bags of stiffness. Probably just a quirk of the geometry.
Could be worth you pulling up a geometry chart and overlaying them to look for similarities if it really bothers you.
Alternatively, just keep riding it and get used to it, alter your technique a little bit to compensate.
What I'm trying to say is......some frames just do that, not much you can do but learn to live with it. :thumbup:

_________________
Pedalling Law Student.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 7 posts ] 


Who is online

Users browsing this forum: eigner, jb, KLabs and 33 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  

   Similar Topics   Author   Replies   Views   Last post 
There are no new unread posts for this topic. Geometry advice needed on a prototype Merckx frame

in Road

SWijland

14

1059

Wed Jan 22, 2014 9:44 pm

legs 11 View the latest post

There are no new unread posts for this topic. Frame Geometry "Comparator"

in Road

itsacarr

7

867

Sun Apr 20, 2014 2:27 am

BikeCAD View the latest post

There are no new unread posts for this topic. Felt F1 Pr Geometry?

in Road

boots2000

7

634

Sun Oct 26, 2014 6:10 pm

LionelB View the latest post

There are no new unread posts for this topic. Emonda SL geometry

in Road

BigPoser

3

254

Wed Nov 05, 2014 6:03 pm

BigPoser View the latest post

There are no new unread posts for this topic. Colnago C59 geometry compared to EP?

in Road

wilwil

0

184

Sun Aug 31, 2014 11:53 am

wilwil View the latest post


It is currently Fri Dec 19, 2014 9:18 am

All times are UTC + 1 hour




Advertising   –  FAQ   –  Contact   –  Convert   –  About

© Weight Weenies 2000-2013
hosted by starbike.com


How to get rid of these ads? Just register!


Powered by phpBB