Can you quantify a few mm difference in how geometry affects handling?

Discuss light weight issues concerning road bikes & parts.
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davidalone
Posts: 589
Joined: Fri Feb 10, 2012 4:27 pm

by davidalone

In the market for a new bike.

I've been looking lustfully at an Oltre XR4, but comments about the Pinarello F10/Gan's superb handling has piques my interest. So I set out to do a comparison:

__________ Size_____Front Center(mm)_____Chainstay (mm________BB drop (mm)
Oltre XR4 53 _________582____________________406____________________ 68
Oltre XR4 55_________588_____________________406____________________68 (I am between sizes on the Oltre, although the 55 is a touch better)
Pina F10 53__________583_____________________406 ___________________ 72
Pina Gan 53 _________583 ____________________408____________________ 72

Current Bikes:
Infinito 53___________586____________________ 409 ____________________ 68 ( I like the handling, would just appreciate just a little bit more low speed agility)
Cannondale 48______550 ____________________ 406 _____________________67 ( A little too jittery for my tastes, not the stablest of bikes at speed)

Discounting the cannondale, whose Front center is wayyy off from the others, how much does a few mm in front center and chainstay make in handling? the bianchi and the pina bikes are within a couple of mm of each other on front Center and BB drop and have virtually identical chainstay lengths.... Those who have ridden very man bikes, how does this translate out on the road?

Fiery
Posts: 412
Joined: Sat Mar 16, 2013 9:21 am

by Fiery

When wheel placement is so similar, you really have to take into account front end geometry (head angle, fork rake and the resultant trail) as well as details such as frame stiffness before you can make any definitive judgement - all of this assuming rider position, handlebar width, wheels, tyres and tyre pressure etc. are all identical between the bikes. Just looking at these numbers, any of the four frames could feel a little more agile than the Infinito, but those other mentioned variables could "override" this.

morganb
Posts: 533
Joined: Wed Mar 15, 2017 5:30 pm

by morganb

Why is your Cannondale so much smaller than the others? That's probably a big part of why you don't like the handling.

pdlpsher1
Posts: 1530
Joined: Thu Jul 19, 2012 6:09 pm
Location: CO

by pdlpsher1

I haven't ridden a lot of bikes either. I only own one road bike at a time. Recently I got a custom Ti frame built. I wanted comfort, stability, and neutral handling. My frame designer chose a low BB drop of 80mm (since I don't race) and long chainstays of 425mm (good for comfort, stability, and wide tire clearance). The fork rake is 48mm and HT angle is 72. I couldn't believe what a dramatic difference those few mm's made. The Ti bike rides like a completely different bike from my Fuji Transonic. The Ti bike becomes more stable the faster I go. I live on a big hill and going down the hill I hit 50mph. At 50mph I feel like I’m going slow. It's like driving a Porsche at 100mph but it feels like 60mph. The ride is smooth and handling is confidence inspiring. The BB of the Ti bike is about 1cm lower than the Fuji but I can definitely tell that I'm sitting closer to the ground.

So in a nutshell a few mm's make a huge difference in how the bike handles. But on a carbon bike I imagine two bikes with identical geometry could ride differently as carbon can be manipulated to provide different stiffness levels on each member.

darnellrm
Posts: 204
Joined: Thu Sep 10, 2009 1:06 pm
Location: NC, USA

by darnellrm

pdlpsher1 wrote:
Thu Feb 22, 2018 6:59 pm
I haven't ridden a lot of bikes either. I only own one road bike at a time. Recently I got a custom Ti frame built. I wanted comfort, stability, and neutral handling. My frame designer chose a low BB drop of 80mm (since I don't race) and long chainstays of 425mm (good for comfort, stability, and wide tire clearance). The fork rake is 48mm and HT angle is 72. I couldn't believe what a dramatic difference those few mm's made. The Ti bike rides like a completely different bike from my Fuji Transonic. The Ti bike becomes more stable the faster I go. I live on a big hill and going down the hill I hit 50mph. At 50mph I feel like I’m going slow. It's like driving a Porsche at 100mph but it feels like 60mph. The ride is smooth and handling is confidence inspiring. The BB of the Ti bike is about 1cm lower than the Fuji but I can definitely tell that I'm sitting closer to the ground.

So in a nutshell a few mm's make a huge difference in how the bike handles. But on a carbon bike I imagine two bikes with identical geometry could ride differently as carbon can be manipulated to provide different stiffness levels on each member.
Your frame geometry is a lot more than a feww mm's of change in reach. You basically have a frame with touring geometry. Stable and confident to you translates to sluggish to many of us. And smooth translates to flexy. To each his own!

RussellS
Posts: 720
Joined: Wed Feb 03, 2010 1:31 am

by RussellS

pdlpsher1 wrote:
Thu Feb 22, 2018 6:59 pm
My frame designer chose a low BB drop of 80mm (since I don't race) and long chainstays of 425mm (good for comfort, stability, and wide tire clearance). The fork rake is 48mm and HT angle is 72. I couldn't believe what a dramatic difference those few mm's made.

So in a nutshell a few mm's make a huge difference in how the bike handles.
Couple millimeters here, couple millimeters there, couple more millimeters over there, few millimeters right here. Add them all up and you are talking about 4-5 centimeters. A couple INCHES total. A few millimeters make squat difference. A few inches do make a huge, colossal difference.

Carcinogent
Posts: 35
Joined: Mon Sep 19, 2011 4:37 pm
Location: France

by Carcinogent

A little more information regarding STA/HTA and fork rake and (effective) TT length might give us more to go on for *better* advise.

However, about what you are asking those few mm make no perceivable difference.

The most important question is are you happy with your current fit/bike? If yes than going around your current bike numbers should be your guideline.

The Cannondale is definitely on the twitchy side (which imo is NOT what racing is about, no matter what the marketing tells you) and hence the instability at speed and most likley huge tendency to 'drop underneath you' and oversteer aka take a tigher arc through corners.

Couple of general things to note:
Longer chainstays = more stability
More trail = more stability
More BB drop = more stability

Mix, match, modify to suit your needs. :D

Stability = bike's ability to 'straighten itself up' and ride in a straight line no hands.

In the end it's a combination of the above as someobdy pointed earlier in their custom biek design.

Here is something which a lot of people would deny till the bitter end, though i stand firmly behind, is that most riders even PROs would be better suited by what is derogatorily called 'touring geometry' - longer chainstays and lower BBs.

morganb
Posts: 533
Joined: Wed Mar 15, 2017 5:30 pm

by morganb

Carcinogent wrote:
Fri Feb 23, 2018 3:17 pm
A little more information regarding STA/HTA and fork rake and (effective) TT length might give us more to go on for *better* advise.

However, about what you are asking those few mm make no perceivable difference.

The most important question is are you happy with your current fit/bike? If yes than going around your current bike numbers should be your guideline.

The Cannondale is definitely on the twitchy side (which imo is NOT what racing is about, no matter what the marketing tells you) and hence the instability at speed and most likley huge tendency to 'drop underneath you' and oversteer aka take a tigher arc through corners.

Couple of general things to note:
Longer chainstays = more stability
More trail = more stability
More BB drop = more stability

Mix, match, modify to suit your needs. :D

Stability = bike's ability to 'straighten itself up' and ride in a straight line no hands.

In the end it's a combination of the above as someobdy pointed earlier in their custom biek design.

Here is something which a lot of people would deny till the bitter end, though i stand firmly behind, is that most riders even PROs would be better suited by what is derogatorily called 'touring geometry' - longer chainstays and lower BBs.
I have a custom bike built like this, long chainstays, moderately slack HA (72.5), 75mm BB drop, but a race reach and stack. I enjoy it for riding but still prefer pure race geometry for racing. On tight and twisty descents and corners the more stable bike takes more effort, even if it is a pleasure to ride straight and in wide sweepers.

Carcinogent
Posts: 35
Joined: Mon Sep 19, 2011 4:37 pm
Location: France

by Carcinogent

morganb wrote:
Fri Feb 23, 2018 3:57 pm
Carcinogent wrote:
Fri Feb 23, 2018 3:17 pm
A little more information regarding STA/HTA and fork rake and (effective) TT length might give us more to go on for *better* advise.

However, about what you are asking those few mm make no perceivable difference.

The most important question is are you happy with your current fit/bike? If yes than going around your current bike numbers should be your guideline.

The Cannondale is definitely on the twitchy side (which imo is NOT what racing is about, no matter what the marketing tells you) and hence the instability at speed and most likley huge tendency to 'drop underneath you' and oversteer aka take a tigher arc through corners.

Couple of general things to note:
Longer chainstays = more stability
More trail = more stability
More BB drop = more stability

Mix, match, modify to suit your needs. :D

Stability = bike's ability to 'straighten itself up' and ride in a straight line no hands.

In the end it's a combination of the above as someobdy pointed earlier in their custom biek design.

Here is something which a lot of people would deny till the bitter end, though i stand firmly behind, is that most riders even PROs would be better suited by what is derogatorily called 'touring geometry' - longer chainstays and lower BBs.
I have a custom bike built like this, long chainstays, moderately slack HA (72.5), 75mm BB drop, but a race reach and stack. I enjoy it for riding but still prefer pure race geometry for racing. On tight and twisty descents and corners the more stable bike takes more effort, even if it is a pleasure to ride straight and in wide sweepers.
100% agree with this and mirrors to the T my experience. Though the difference between this geomety (long CS, etc.) and more racing oriented is not as extreme as what you can buy off the shelf. My next custom project will have 'tighter' wheelbase and I am curious how that would translate into ride feel especially in the twisty stuff.

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