How far are your bars behind your front wheel axle?

Discuss light weight issues concerning road bikes & parts.
uraqt
Posts: 814
Joined: Mon Apr 03, 2006 8:53 am

by uraqt

that is a big change and it's going to take miles to get use to it... I had a change/fit that was just about the same ... too drastic for me I tried to keep the fit as best I could for about 500 miles, but I couldn't get use to the change on steep climbs out of the saddle. While I feel that I had a good fit, and I know there are "issue" with my current fit..I had to move back to original set up.

I don't think you can do a fit on a trainer... they have to be on roads and done over time.. and that means you and your riding buddies have to learn how to fit and/or buy the software. And to make it worse as your flexibility, riding skills and strength change so does your fit.

Sorry there is no easy way to get a bike fit! Just like steep climbs you have to do the work!

C

by Weenie


saba
Posts: 21
Joined: Wed Sep 06, 2017 1:40 am

by saba

I've been working on a little side project called bikegeo for fitting issues like this.

Image

On my BMC Roadmachine 61cm with 25mm of spacers, 120mm -6 deg stem, I'm:

Code: Select all

>>> import bmc
>>> axle_x = bmc.roadmachine[2017][61]['points']['front axle'][0]
>>> bars_x = cockpit(bmc.roadmachine[2017][61], (120, -6, 25))['bars'][0]
>>> axle_x - bars_x
122.18659451049905


Or 122mm behind the front axle, approximately.

Ettore
Posts: 16
Joined: Fri Nov 03, 2017 8:44 am

by Ettore

TobinHatesYou wrote:
evan326 wrote:Unless I'm completely misunderstanding what to measure, I'm going from the center of my bars at the stem with a plumb, and measuring from the front axle to that. If I had a third hand or friends I'd take a photo.


I'd have to see how you're setting everything up. How are you leveling out your bike? I use two Feedback Sports bike stands for example.

Anyway, I did the math on my H1 Emonda with a shorter front-center and a longer 110mm stem...and the distance behind the stem was 105mm based on advertised geometry.

Ettore also did the math, with proof, on his bike geometry and his bar is 126mm behind the front axle (thanks to a slack head tube angle and bigger rake than normal)

So do you trust the math or do you trust your eyeballs?


He can also place the bike on a level surface and hang a string with a weight on it from the center of his bars, and measure the horizontal distance from the string to his front axle. If he wants eyeball-proof.

basilic
Posts: 653
Joined: Wed Jan 05, 2011 8:05 am
Location: Geneva, Switzerland

by basilic

for those who think that obtuse means stupid, a sinus is a snot-producing cavity, and a tangent something you go off on to avoid answering a straight question:

- place bike on level surface, front wheel against a wall
- measure horizontal distance from front hub to wall
- measure horizontal distance from center of bars to wall
- subtract

Do the same with center of BB and tip of saddle for saddle setback (pro-tip: turn the bike around)

niklasp
Posts: 65
Joined: Thu Jul 14, 2016 5:36 pm

by niklasp

basilic wrote:for those who think that obtuse means stupid, a sinus is a snot-producing cavity, and a tangent something you go off on to avoid answering a straight question:

- place bike on level surface, front wheel against a wall
- measure horizontal distance from front hub to wall
- measure horizontal distance from center of bars to wall
- subtract

Do the same with center of BB and tip of saddle for saddle setback (pro-tip: turn the bike around)


Now you made me feel stupid. Measured difference saddle tip / BB recently, this method would have helped me alot...

mattr
Posts: 3477
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

BdaGhisallo wrote:Indeed. Coming up with an optimum fit for a rider does not automatically lead to a well handling bicycle based on that fit. It takes a different skill set to design a well riding bike and, in my experience at least, very few "fitters" have that skill set.
:D A guy i used to ride with spent a *lot* of money on his fit for his MTB. Allegedly gained significant power and was more comfortable.

Unfortunately the bike was all but unrideable, resulting in a season of multiple falls and injuries and eventually a fused wrist.

Refused to even entertain the idea that the fitter might not have known what he was doing........

Now only rides to the shops/green trails with his kids.

mattr
Posts: 3477
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

basilic wrote:for those who think that obtuse means stupid, a sinus is a snot-producing cavity, and a tangent something you go off on to avoid answering a straight question:

- place bike on level surface, front wheel against a wall
- measure horizontal distance from front hub to wall
- measure horizontal distance from center of bars to wall
- subtract

Do the same with center of BB and tip of saddle for saddle setback (pro-tip: turn the bike around)
This was in a cycling magazine in the 80's (before fitting was the massive industry it is now)

Think it was an article about how to copy set up from one bike to the next.

It's how i still do it today.

basilic
Posts: 653
Joined: Wed Jan 05, 2011 8:05 am
Location: Geneva, Switzerland

by basilic

niklasp wrote:
basilic wrote:snip


Now you made me feel stupid. Measured difference saddle tip / BB recently, this method would have helped me alot...


That's also how I felt when I read about this method (in a post by the framebuilder Dave Kirk iirc). As mattr says, probably ancient wisdom.
Works well for reach and stack, too.

rothwem
Posts: 41
Joined: Wed Jul 09, 2014 4:45 pm

by rothwem

All you guys with fancy cad software.

I did it with an excel spreadsheet. I basically just subtracted the reach + stem horizontal extension from the horizontal front-center measurement.

One thing I thought was interesting was that when I calculated the front center for a few different bikes, it didn't always match the F-C on the geometry charts, and I think its because certain companies measure the chainstay length as a horizontal, while others measure it as BB-rear drop.

AJS914
Posts: 1947
Joined: Tue Jan 28, 2014 6:52 pm

by AJS914

rothwem wrote:I just got a bike fit, and the new position is a solid 10mm back at the seat and 30mm back at the bars.



Why did you get a fit in the first place? Was there an issue?

rothwem
Posts: 41
Joined: Wed Jul 09, 2014 4:45 pm

by rothwem

AJS914 wrote:Why did you get a fit in the first place? Was there an issue?


Yea, I've been having nagging on/off knee problems over the past couple years. I mainly was interested in seeing what the fitter said about my cleat positioning, but I got on the trainer and the first thing he said was that I was way too forward and low.

AJS914
Posts: 1947
Joined: Tue Jan 28, 2014 6:52 pm

by AJS914

If you trust the guy's experience, give it some time and try it out. There's no real right or wrong answer but you want to be comfortable on rides and get power to the pedals.

I've shorted up my reach in the last 5 years. I didn't really even fit my old Litespeed anymore for a number of reasons. I'm also 51 now and don't want to be as stretched out and low as I was when I was 25.

youngs_modulus
Posts: 512
Joined: Wed Sep 20, 2006 1:03 am
Location: Madison, WI USA

by youngs_modulus

saba wrote:I've been working on a little side project called bikegeo for fitting issues like this.

Image


This is awesome. I can't wait to play with bikegeo when I get home tonight. Well done!

To everyone else:

If you know how to code even a little bit (even just basic HTML) you'll be able to use this program. You can follow Saba's example to feed in the geometry of your bikes and compare them like this:

Image

You can do this in a spreadsheet, but it's awkward and error-prone. You can also do this in CAD, but many CAD programs are expensive, and using bikegeo would be way faster than learning CAD.

It's written in python, which is easy to follow even if you're just learning how to program. If you have any interest, check it out.

saba
Posts: 21
Joined: Wed Sep 06, 2017 1:40 am

by saba

Well, I guess now I have to do a little documentation.

Another use is to compare frame sizes for a particular model:

Code: Select all

with canvas():
    draw_bike(bmc.teammachine[2018][47])
    draw_bike(bmc.teammachine[2018][51])
    draw_bike(bmc.teammachine[2018][54])
    draw_bike(bmc.teammachine[2018][56])
    draw_bike(bmc.teammachine[2018][58])
    draw_bike(bmc.teammachine[2018][61])


Image

The project was born out of need to work out what size Salsa Fargo I would need, since it's geometry is so weird.

evan326
Posts: 480
Joined: Wed Sep 14, 2016 8:51 pm
Location: RVA,USA

by evan326

TobinHatesYou wrote:
evan326 wrote:Unless I'm completely misunderstanding what to measure, I'm going from the center of my bars at the stem with a plumb, and measuring from the front axle to that. If I had a third hand or friends I'd take a photo.


I'd have to see how you're setting everything up. How are you leveling out your bike? I use two Feedback Sports bike stands for example.

Anyway, I did the math on my H1 Emonda with a shorter front-center and a longer 110mm stem...and the distance behind the stem was 105mm based on advertised geometry.

Ettore also did the math, with proof, on his bike geometry and his bar is 126mm behind the front axle (thanks to a slack head tube angle and bigger rake than normal)

So do you trust the math or do you trust your eyeballs?

I hope you don't think I was trying to argue with you, especially because you're right :lol:
I didn't have the bike level like a fool. It's 120mm :beerchug:

by Weenie


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