Hollowtech 2 axle lengths???

munster

Guys
Can anyone shed some light on axle lengths of hollowtech 2 MTB cranks.
The reason I'm asking as I have a cross bike with really wide stays and the road chainset axles aren't wide enough. I read somewhere that MTB chainsets have different length axles, is that true?
Cheers
Munster

Chunkers1980

No.

The Rookie

I think it's yes, as i understand it road ones are narrower as they don't use spacers and are sized for a 68mm BB shell while MTB are sized for a 73mm and you use 2 2.5mm spacers to make up a 68 to a 73 and another spacer is in their so you can accomodate BB mounted devices.

Which is why you can't use a road BB on an MTB as they don't have enough thread as they don't need it to accomodate the spacer(s)

nicklouse

The Beginner wrote:

I think it's yes, as i understand it road ones are narrower as they don't use spacers and are sized for a 68mm BB shell while MTB are sized for a 73mm and you use 2 2.5mm spacers to make up a 68 to a 73 and another spacer is in their so you can accomodate BB mounted devices.

Which is why you can't use a road BB on an MTB as they don't have enough thread as they don't need it to accomodate the spacer(s)

not quite true.

The Rookie

OK....the truth is?

nicklouse

munster wrote:

Guys
Can anyone shed some light on axle lengths of hollowtech 2 MTB cranks.
The reason I'm asking as I have a cross bike with really wide stays and the road chainset axles aren't wide enough. I read somewhere that MTB chainsets have different length axles, is that true?
Cheers
Munster

the axle lengths are the same for both the 68 and 73mm


i guess you are having issues with the rings catching on the chain stays?

MTB cups are thinner than the road versions but have more thread on the drive side.

But the chain line is 43mm for road double and 45mm for a road triple and 50mm for typical MTB triple (but again there are doubles with 46mm and triples with 48mm)

what is your frame? what size rings are you wanting to use?

nicklouse

The Beginner wrote:

OK....the truth is?

road cups are wider. but do not use spacers.

you can use road cups if you have to but if you are using spacers then yes there may be insufficient threads in the BB which may cause issues. like too much thread on a MTB might bottom out in a road frame but the distance between the bearing faces will be too narrow.



Hope BBs are a great example. they do the same bearings for both road and MTB.
MTB come with 3 x 2.5mm spacers. the road come with 2 x 1mm spacers.

The Rookie

Thanks for that Nick.....

(Note I did say think.......)

munster

The frame is a bit of a custom one. My step father lived in the US for some time and went on a frame building course in California. He has made a few frames, a titanium mixte? frame for my mum, a roadster frame for himself and I asked him to make me a steel frame with carbon seat stays based on a kinesis crosslight 3 frame. I eventually got it when they came back to the UK but he had forgotten to flatten the stays during the build. He has flattened them a bit but is reluctant to go any more incase he goes too far!
I was hoping to run a 36 - 44 chainset but the inner ring catches, I have tried a mountain BB cups with spacers but I seem to run out of axle. I have managed to set it up as a single chainring and it clears the frame but ideally I want to sort it out properly, any help is appreciated.
I would like to stick to Shimano if I can but would try other makes if need be.

Chunkers1980

I'd say its a case of shifting the chain line. When you say catches - by how much?

nicklouse

so what cranks have you tried?

using road cranks with MTB cups will do as you said run out of axle.

and MTB cranks with 36 middle and 44 outer could work.

BB width? 68mm 5mm of spacer on the drive side and 2.5mm on the non drive.

munster

I tried my original shimano 600 cranks and bb (Sq taper) not a chance.
Have tried FSA cranks and BB from my Raleigh cross bike, not a chance.Have tried Suntour NCX compact ( I think) with shimano HT2 BB, both road and MTB. Can only get that to work as single chainring with 1 spacer on drive side. Anymore and I will hit the chainstays with the crank on non drive side. Suntour cranks are arse about face though. L/H has axle and nut screws on r'h side prior to crank to load bearings.
Hence my question on Shimano MTB axle lengths.
I don't want to bend anymore of the stay but unless someone comes up with a winner I may have to.
On earlies tomorrow so I shall catch up with this tomorrow pm if thats ok.
Thanks for the replies so far.
Munster
PS BB is 68. Rear end is 135oln if that makes a difference.

nicklouse

i would be trying an MTB HT2 set up.

as you dont seem to have tried that. and the effective BB width is greater than the difference due to the thinner cups.

The Rookie

What width square taper axle? They go to 128mm, 5mm more per side than a relatively conventional 118mm, they also go down to 103mm!

munster

I shall try a 128mm sq taper as I have the cranks.
But what HT2 cranks should I be looking at if I go that way?

nicklouse

munster wrote:

I shall try a 128mm sq taper as I have the cranks.
But what HT2 cranks should I be looking at if I go that way?

Have a look on the makers webby as he will list the Chainline as a minimum. Some even give C/L distances for the rings.

Some even do cranksets for fat bikes.

Without any measurements I will not advise.


What width rear hub does it run?

munster

135 rear end