Front Mech Tire Clearance Issue

[kjarrett]

My Axis Pro build is coming along nicely, only shift & brake cables left, and then adjustments. Process has gone smoothly (my vintage skills are a good match for this vintage MTB) but I am concerned about the front mech tire clearance. See pic. It's even less now as I've had to lower the mech on the seat tube for chain clearance in the smallest cog (it was dragging on the pin at the bottom of the cage).

Not sure if it matters, but, the Axis has a 68mm shell and the Response Elite has a 73. I don't recall clearances being this tight before.

Also, the tires are 2.1" and I do want to keep them as I love how they perform and my substantial girth (just under 100 kg) requires them in my experience.

Thoughts welcome. Grateful for this forum. You are all so very helpful.

-kj-

 

[ishaw]

Re:

Nice looking build.

I think your clearance should be fine. The mech is still over the chain stay so the tyre would have yo go through that first.

The bb shell shouldn't really effect front mech position aside from perhaps the granny ring being further inboard. If you are worried, you could run a slightly wider bb axle as long as it doesn't mess with your chain line and shifting.

 

[kjarrett]

Re:

Thanks for the reply and yes, I realized I forgot to post a pic of how close the inner ring is to the chainstay. (Was to be part of this as well.) It’s very tight. Hadn’t thought about a wider axle, what would you recommend?

 

[ishaw]

Re:

Looks like an m560 lx crank. Designed to run with a bb axle length of 113-118 according to my research. What length do you have fitted?

https://www.sheldonbrown.com/bbsize.html#shimano

 

[kjarrett]

Good eye, they are in fact M560s - they were from my '93 Response Elite which has a 107 axle (73 shell). It was almost assuredly a factory fitment as the bike is/was nearly completely original (appears the only change from stock was the tires and saddle) when I bought it this pastr February (see below) from the original owner.

I'm keen to replace the BB anyway due to its age and am pretty sure I would like/prefer a larger Q factor. Suppose I will start shopping...hmmm

 

[My_Teenage_Self]

What's your chainline measurement? you should be aiming for 45-50mm.

 

[Janners BJJ Clunker Rider]

That is looking really nice. Interested to know how you get on with a longer bb axle length. I tried this on a Marin I was building for my wife. The DX mech then couldn't physically reach the outer ring. So worth checking the throw (or travel) available on the front mech. It might not be a problem as I swapped over to a STX mech and it was sorted. The LX mech might have the throw required, so just a heads up.

Janners

 

[kjarrett]

What's your chainline measurement? you should be aiming for 45-50mm.

Hard to read exactly but honestly it looks to be right between 47 or 48, so, 47.5 I'd say.

Thanks!

 

[kjarrett]

Re: Re:

Looks like an m560 lx crank. Designed to run with a bb axle length of 113-118 according to my research. What length do you have fitted?

https://www.sheldonbrown.com/bbsize.html#shimano

Have a 113mm on order, curious what the extra 3mm will feel like (vs. the 107mm) ... and I guess that will push my chainline right up to or slightly beyond the max of 50mm.

 

[kjarrett]

That is looking really nice. Interested to know how you get on with a longer bb axle length. I tried this on a Marin I was building for my wife. The DX mech then couldn't physically reach the outer ring. So worth checking the throw (or travel) available on the front mech. It might not be a problem as I swapped over to a STX mech and it was sorted. The LX mech might have the throw required, so just a heads up.

Janners

Thanks very much, I am fitting the cables this morning and expect to have a sense of the LX mech's range.

When I moved it over from the Response Elite yesterday, I saw that I had to adjust one of the limit screws to allow the cage to even reach the inner chainring, with no cable attached. So thinking a longer axle, and pushing things out a few MM, will be ideal.

-kj-