Chain rub w/ short chainstays

Discuss light weight issues concerning road bikes & parts.
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ricerocket
Posts: 506
Joined: Mon Sep 27, 2010 8:38 am

by ricerocket

I have pretty aggressive geometry on my bike, with some of the shortest chainstays (395mm) I've found on any non-TT bike.

I've been running SRAM Red w/ 11-28T and 52/36 combo up front, with the promise of no-rubbing in all gears.


I'm not the best front derailleur tuner, but no amount of tinkering would get rid of rubbing at the front derailleur in the lowest gear. I brought it to my bike shop, and they made it even worse!

Is this something I should jsut give up on given my short chainstays? Or do you guys think it's possible to tune out the rub?

AZR3
Posts: 846
Joined: Wed Sep 12, 2012 9:00 pm
Location: Az USA

by AZR3

I had a 2011 Cervelo S3 with short chain stays, I think they were the same length of memory serves, and I couldn't get it to work quietly with that exact same setup and figured it was the chain stay length. I thought SRAM said minimum chain stay length was like 405, but I could be wrong

alcatraz
Posts: 2572
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Are you rubbing the fd or big chainring?

What crank/spindle are you using?

Do you have horisontal dropouts? What happens if the wheel is mounted in the back? Are you sure the wheel is parallel to the hanger?

MaxPower
Posts: 114
Joined: Fri Sep 20, 2019 9:30 pm

by MaxPower

Well... The latest shimano mechanical road stuff is like that if you follow the instructions for the fd (witch you kind of have to do, as the mechanical fd's are sssooooo fine tuned and the complete functionality of correct shifting and trim positions is out the window if you don't follow the instructions to the letter... I used a ton of time figuring that one out... Instead of just reading and following the instruction in detail)

They spec 0-1mm space between fd cage and outer cassette limits (if i remember correctly) and that spacing will rub under load.

ricerocket
Posts: 506
Joined: Mon Sep 27, 2010 8:38 am

by ricerocket

alcatraz wrote:
Mon Oct 21, 2019 6:26 am
Are you rubbing the fd or big chainring?

What crank/spindle are you using?

Do you have horisontal dropouts? What happens if the wheel is mounted in the back? Are you sure the wheel is parallel to the hanger?
I'm rubbing the FD in the lowest gear combo (36-28), where I end up spending a lot of time mostly due to the terrain here.

They're a set of Praxis rings on a S-Works crank.

They're not horizontal, just standard road dropouts.

Valbrona
Posts: 1538
Joined: Fri Oct 28, 2011 3:25 am
Location: United Kingdom of Great Britain and Northern Ireland

by Valbrona

Band-on FDs allow users to change the angle of the FD slightly, like in a toe-out fashion. Not so with fixed hanger.

It might sound counter-intuitive, but try raising the FD a little.

alcatraz
Posts: 2572
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

What about a combination of toe out and cable tension to eliminate the rub? Give it half a turn on the barrel adjuster then whatever rub is left should be small enough to be eliminated with toe-out. It's just a suggestion, I know the manual doesn'r suggest it. :)

Does that create problems elsewhere? Like dropped chains upshifting? With good chainrings it can handle it I think.

On bikes where I don't have rub I enjoy it but where I do I take as a reminder that I'm crosschained. Only the last gear rubs a bit.

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