FC-MT60 spindle length

[AshtanoJoe]

Want to use a shimano fc-mt60 triple crankset with STI for drop bars and road triple FD on a steel frame MTB. Nominal spindle length for this crank is 122mm. Would that be symmetrical spindle? Can I use a shorter spindle BB to bring the crankset in a few mm for better shifting while still keeping the crankset symmetrical in the frame?

Thanks,
AnJ

 

[hamster]

Shorter spindles may give clearance problmes both with the chainstays / rings and also the front mech (may not have space to engage inner ring). The 122.5 is symmetrical.
You will also end up with the chain running asymmetrically - so the chainline will be to gear 2 or 3 rather than 4.

I can't see why there will be better shifting with a closer chainset anyway.

 

[AshtanoJoe]

Re:

Better shifting because it brings the chainline in to be compatible with a road FD which you must use with STI road shifters. They like about 45mm, not so much 47.5mm and definitely not 50mm.

I think the idea is to find one that is not so short as to create chainring to chainstay interference, but short enough so that a road FD can shift smoothly across all three rings.

If the 122mm BB spindle is symmetric, then maybe a 118mm symmetric (if they exist) spindle BB could bring it inboard 2mm and still be centred in the frame.

 

[jimo746]

Re:

Trying to think of all the permutations I've had over the years... I'm sure I remember using a MTB triple front mech with drop-bar shifters (Sora), and a touring triple chainset.
you can get 117.5mm bottom bracket spindles, may be worth a try.

http://www.sheldonbrown.com/bbsize.html

 

[hamster]

Re: Re:

Better shifting because it brings the chainline in to be compatible with a road FD which you must use with STI road shifters. They like about 45mm, not so much 47.5mm and definitely not 50mm.

I think the idea is to find one that is not so short as to create chainring to chainstay interference, but short enough so that a road FD can shift smoothly across all three rings.

If the 122mm BB spindle is symmetric, then maybe a 118mm symmetric (if they exist) spindle BB could bring it inboard 2mm and still be centred in the frame.

The alternative is to use an MTB front mech, but clamp the cable on the opposite side of the bolt to normal. It helps if you file a small groove for the cable. Altering the cable position corrects for the different cable pulls between road and MTB front mechs. See the CTC Shimergo pages for more details.

 

[AshtanoJoe]

Re:

Can't seem to find anything about this on the CTC Shimergo site. Would you mind providing a link please?

Also, are you sure the 122.5mm BB used for many of that era cranksets is symmetrical? Reading elsewhere that spindle is longer on the drive side.

One way is to just test various different spindle length BBs to see how they fit. Or just use a 50-39-30 road triple and swap the inner ring for a 28 or 26, but a 46-36-24 would be preferable for touring.

 

[reindeer]

Re:

I am pretty sure that my xt 730 122.5 spindle is asymetrical and one side about 3mm longer, but might be wrong. If thats true, flipping sides might be an option.

Just saw this: http://www.ebay.com/itm/New-Old-Stock-S ... 0638051408

 

[FluffyChicken]

Re:

Do CX mechs give you a better chainlone option?

As the bottom bracket is a D-NL 122.5 one its symmetry is given in the coding. The last L means the left side is longer than the normal, so is must be asymmetric. Memory serves the D-N is 120 so its 2.5mm longer at the left.


You will probably get a 118 to work (vauge memory its an old original length for it with alpine?). LGF might know.

It's ~3mm less chain line so you'll have 44/44.5mm
If you're lucky and the rings are now not in the chain stay, then also try a 115 for a a mm less in the chainline.

All assuming a shimano bottom bracket, other manufacturers may very. Have fun playing with lemght to see what happens. Your chainstays might be the biggest problem.

 

[FluffyChicken]

Re:

Why do people suggest flipping it, that then puts the left foot in the wrong place?

 

[AshtanoJoe]

Re:

Not sure about CX. I thought they used mechs for compact road doubles, but could be wrong. I was planning to use a Tiagra 4503 triple fd which worked well on another conversion. It will work with a 47.5mm chainline if you use bar end shifters, but STI shifters don't seem to hold the same amount of cable tension and don't shift out quite as far.

Should have mentioned I'm only using Shimano cartridge bearings which I can pick up used cheap as chips. So I'll try for a 118 first.

Re having one foot in the wrong place, a lot of people don't seem to mind or notice the offset. Several times I've installed cranks and matching BBs only to find it off-centre. Fc-571 with its octa BB was way off and just the other day happened with a fc-5603, got not idea why, must have something to do with the frame design.