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 Post subject: Frame Geometry
PostPosted: Thu May 02, 2013 8:48 pm 
Retro Guru

Joined: Sat May 07, 2011 9:28 am
Posts: 758
Location: Nottingham
Right!!

I have two frames, each with a similar seat tube length, but one has a97cm wheel base, theother 102. Top tubes only 1cm different. I am assuming the shorter wheel base, and therefore steeper angled frame will be more responsive, better cornering etc, the longer wheel base more stable, prob better down hill at speed.

What is the truth!!

Cheers
Matt


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 Post subject: Re: Frame Geometry
PostPosted: Thu May 02, 2013 9:18 pm 
Retro Guru
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Joined: Sat Apr 02, 2011 11:16 am
Posts: 799
Location: Camden, London
wheel base also impacted by length of chain stays, clearance as well as fork rake


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 Post subject: Re: Frame Geometry
PostPosted: Thu May 02, 2013 11:00 pm 
Old School Grand Master
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Joined: Fri Oct 14, 2011 8:41 pm
Posts: 8246
Location: Cumbria
That's the theory :D

Shaun


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 Post subject: Re: Frame Geometry
PostPosted: Fri May 03, 2013 12:06 am 
Feature Bike
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Joined: Fri Aug 11, 2006 8:13 pm
Posts: 1143
Location: York-ish UK
daugs wrote:
wheel base also impacted by length of chain stays, clearance as well as fork rake


Yep.

I buy this expanation:

http://www.rivbike.com/kb_results.asp?ID=34

Other factors being equal (or at least quite similar) I'm beginning to suspect that bottom bracket height accounts for a lot of how a bike rides. Not sure why though: C of G perhaps.


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 Post subject: Re: Frame Geometry
PostPosted: Fri May 03, 2013 7:46 am 
Retro Guru

Joined: Sat May 07, 2011 9:28 am
Posts: 758
Location: Nottingham
doctor-bond wrote:
daugs wrote:
wheel base also impacted by length of chain stays, clearance as well as fork rake


Yep.

I buy this expanation:

http://www.rivbike.com/kb_results.asp?ID=34

Other factors being equal (or at least quite similar) I'm beginning to suspect that bottom bracket height accounts for a lot of how a bike rides. Not sure why though: C of G perhaps.



Excellent link, thanks for sharing that.
Matt


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 Post subject: Re: Frame Geometry
PostPosted: Fri May 03, 2013 9:05 am 
Old School Grand Master
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Joined: Fri Oct 14, 2011 8:41 pm
Posts: 8246
Location: Cumbria
Not sure about the logic of the link in respect of the OP. if the main triangle is the same then the effect of reducing the size of the rear triangle and reducing the fork rake will automatically reduce the wheelbase......... don't see how it can have any other outcome.

Having ridden a good number of bikes the main thing that makes then feel more responsive is a good set of light wheels. That's why BITD we swapped our 27X1 1/4 wheels for sprints and tubs........

Next thing is probably fork rake as that effects the trail and hence the castor action that actually keeps bikes upright :D

All IMHO :)

Shaun


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 Post subject: Re: Frame Geometry
PostPosted: Fri May 03, 2013 4:06 pm 
Old School Grand Master

Joined: Tue Oct 09, 2007 1:55 pm
Posts: 8221
Location: New Forest, UK
I don't think that there is a specific link between better cornering and wheelbase (apart from popular mythology that short wheelbases were fast). Extremes of trail / head angle certainly cause twitchiness, shimmy and roll-steer.

A lot will also depend on the frame materials: too flexy or too heavy? In short you probably have to build them up to find the truth as to which suits you best.


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