bike-izle

Hi,

I'm currently installing a new SRAM Apex 2X10 drivetrain. All was well until I realized that the rear spacing/hub is 135 mm (Shimano XT hub) and that the chainline is different. The chain rubs and wants to climb up onto the big ring when cross chaining (small-small).

I guess I need a different crankset, right? Are there "road" double cranks (50-53 chainring, maybe a little smaller) out there with a wider chainline?

Thanks

ThermionicScott 

bike-izle

Yeah I know, but it still seems unsafe, and it'd be nice to have the "legit" chainline anyway....

Troul 

A wider bb might help enough?

Eggman84

Using modern 2 piece cranks pretty much dictates the front chainline. You could use a crankset and square taper BB to reduce the chainline, assuming the there was space between the chain stay and chain . Other alternative is to use a larger small in ring, or smaller large ring, so that the chain does not "catch" the large chainring when you are in the small small combination.

70sSanO

cpach

This is how pretty much all disc brake road bikes are, particularly if they have short chainstays. Some crank manufacturers have made some steps to try to improve performance when used with the chainline 2.5mm out on disc frames by altering the shaping and spacing of charings among other things. I would recommend running it.

dsaul

SRAM has started making some of the Rival and S-series cranksets in a wide axle version for 135 rear axle use. The problem of the chain climbing the shift pins on the large chainring has been going on ever since chainstays got really short. I can't use the two smallest cogs(in the small chainring) on my road bike with a 130 axle, due to the 407mm chainstay length.

JohnDThompson 

This is not unusual, and as @ThermionicScott notes, a reason to avoid that particular gear combination. The problem is exacerbated by short chainstays and a large difference between inner and outer rings on the crank.

While you can do various things with spacers to make that gear combination usable, doing so will often make other gear combinations unusable, so it's best to just avoid that gear combination.

Iride01 

I think the sum of all posts here is the answer. Chain line is not something that can be adjusted on many new cranks. Some have a little you can do with spacers, like the Race Face Cadence crank I bought five or six years ago. I've also seen DIYer's post adding spacers between the chainwheels and spider. Other ways to alter chainline are on the back wheel. Spacers on the axle if you have the clearance. Some don't, some do. Might have to change wheel dish wheel if it takes a lot to get back into where you need to be.

It's an experiment though. Once you leave the realm of what the mfr put on your bike, then it's up to you to see what fits and doesn't.

Kapusta

Since I spend a lot more time in my big ring and 3 biggest cogs (common in rolling terrain) than my small ring and 3 smallest cogs (never), I actually prefer the chain-line I get with a road crank-set and 135mm rear hub.

I would just avoid the bad combos, but that's just me. Seems like a better solution than buying a new crankset, changing ring-size (unless you already wanted to do that), or moving the existing crank-set over just to accommodate a combo you don't even need.

Interested to know what you decide to do and how it works.

leob1

A new crank, maybe. Better technique, definitely. I have a bike with Sram Apex, the front derailer is really bottom of the barrel, you should upgrade that. The front shifter are tuneable, you can move it a half shift so you can use that to reduce the chain rub, practice doing that. And don't cross chain, there is no reason to do that. Practice double shifting, shifting both the front and back at the same time so you can get to the gear you want. There is no reason to cross chain.

fietsbob

Have you measured what the rear component of the chain line is..

to compare it with the front.. ?

Kapusta

I think what he means is that the chain is rubbing the big ring (and therefore wanting to climb on to it), not the derailleur.

bike-izle

Shimano XT rear hub, which I believe has ~47.5 mm chainline.
SRAM Apex crank, which is around 46 mm chainline. It's got a 53 big ring, so that definitely plays a role.

Not a big difference in chainline if the numbers are correct, but it still rubs.

mcours2006

I experience the same problem putting a modern groupset on a 126mm dropout and shorter chainstay. While most of the gears work okay, I can't dial it in perfect. The same groupset on a modern frame with 130 mm spacing works flawless and crisp.

I think mine has more to do with the shorter chainstay than the shorter dropout.

I think this is something you'll just have to learn to live with.

Kontact

126 and 130 are the same chainline. 130 adds cogs on both inside and outside keeping the same cassette centerline.