TRIPLE CRANKSET

houston123

Hi,

Repairing a mates bike...a 27 speed TREK MOUNTAIN BIKE

The crankset is knackered and needs replacing.

I have a brand new TY-701 triple that is meant for 8 speed......would it work on 9 speed.

What issues would I get.

The bike is only used for commuting and does not get 'bashed' around.

Cheers.

cooldad

Yes, none.

Assuming it fits, and the BB spacing is the same. Unless you are changing that as well.

njee20

Technically 9 speed chainrings are narrower than 8, and using wider ones could exacerbate problems like chainsuck.

In reality Cooldad's post is spot on.

houston123

Great news.....

Just need to get the chainline correct.

I think I need a 73 x 122.5

The existing is a 73 x 113 but that is way out! :-(

The Rookie

njee20 wrote:

Technically 9 speed chainrings are narrower than 8, and using wider ones could exacerbate problems like chainsuck.

Are they? The chain roller width is the same between 8 and 9 speed (and 10 speed for that matter) so there would be no need for the chainring to be narrower.

Good to see you back on the forum by the way!

cooldad

HOUSTON123 wrote:

Great news.....

Just need to get the chainline correct.

I think I need a 73 x 122.5

The existing is a 73 x 113 but that is way out! :-(

The techdocs (should be online) will specify the BB specs.

njee20

The Rookie wrote:

njee20 wrote:

Technically 9 speed chainrings are narrower than 8, and using wider ones could exacerbate problems like chainsuck.

Are they? The chain roller width is the same between 8 and 9 speed (and 10 speed for that matter) so there would be no need for the chainring to be narrower.

Good to see you back on the forum by the way!

Thanks :-)

Whilst now rather out of date Sheldon Brown mentions their being 9-speed chainrings here but says it's to do with a slight offsetting of the teeth rather than actual width, my mistake. I remember Shimano offering 9 speed chainrings even on cranks they didn't otherwise change (M952 springs to mind), but like I say (as does Sheldon) in reality there was no reason to change perfectly functional 8 speed stuff.

The Rookie

That's my take, the chainrings are the same width but slightly closer together (much like the sprockets at the rear really).

mattyfez

I've been running an 8 speed tripple with a 9 speed chain and cassette for quite a while with no issues.

houston123

Hi,
Thanks for the info!

Can anyone confirm the bottom bracket length please?

Cheers

njee20

Looks like it's a 122.5mm axle, the shell width will depend on your frame and will either be 68 or 73mm - out with the tape measure.

houston123

Thanks for that....

Definitely 73.....I checked the chain line against the old one and it looks about 5mm out which makes sense

122.5 - 113 = 9.5

9.5/2 = 4.75 ....... close enough for me. :-)

njee20

Not sure what you're calculating there, but your calculation won't stack up unless he's already got a TY701 chainset, in which case yes, on a 113mm BB it'll be roughly 5mm too far inboard on both sides, but in that circumstance you've probably find cranks hitting the frame or similar.

If it's not a TY701 then you can't use the axle width to compare relative chain lines, axles are chainset specific not frame specific.

houston123

Hi,
The existing chainline was 50mm with a 9 speed triple.

The new triple is a brand new TY-701 that I had sitting around. When I put the new triple on the old bottom bracket (113) the chainline was approx 45mm... hence the new 122.5 bottom bracket should move it out to be 50mm......
Please tell me I’m making some sort of sense!

Cheers

The Rookie

Yes, but it’s easier than that, with few exceptions Shimano cranks use 122.5/123mm BB.

houston123

Obviously this was one of those exceptions.....
The old crank was Shimano, but with a 73 X 113 Bottom Bracket!

Put it all together last night with a 122.5mm..............

SORTED! 50mm chainline.

:-)

njee20

Ah ha, yes, in that case your logic was sound (as you've found) - was assuming you were talking about old chainset.