BB spindle length.

[mac-highlander]

Hi,
I was wanting to fit a SR Sakae SX triple chainset to my 130 rear dropout spaced Dawes galaxy. Now the spec for cranks says it needs a 127.5mm bb spindle length.

Would I be right in assuming I’d need to loose some length off that to fit on a 130 spaced dropout rear end. My first guess would be 5mm off length to loose 2.5mm per side.

Can anyone confirm this or help point me in right direction for bb spindle length. Also assume other length I need would just be width of the bottom bracket she’ll on frame and assume English threaded.

Cheers

 

[Vapin' Joe]

The reason the spindle length is 127.5mm is to prevent the inner ring fouling on the chainstay, any shorter and it is likely to. It should not effect the chainline.

 

[mac-highlander]

Yes but chainline on an 8 speed 130mm dropout road bike will be nearer centre line than 8 speed 135mm drop out mtb. And assume chain stay will be a similar amount inboard so won’t fowl if I adjust by correct number (assuming 2.5mm per side so 5mm total)

 

[FrankCrank]

I would say the dropout spacing is a red herring here, the BB spindle recommendation is what I'd use. Even then it's not guaranteed, frame dimensions can differ between manufacturers, and especially the chainstay profile. Nothing wrong with mixing different components on a project, but expect a degree of trial and error to avoid disappointment.

 

[mac-highlander]

According to other people and shimano etc etc the chainline is further towards centre (though can’t find a consensus on how much). My brain tells me this as well as the dropout is 2.5mm per side nearer centreline as is mating surface on hub so cassette is gonna be closer to centreline but seems to be conflicting info on how far.

So using same spindle length will mean front chainrings are further out than they need to be.

 

[Ming the Merciless]

Main thing is that inner chain ring doesn’t foul frame and that derailleur is able to shift across all the rings. If that’s achieved then differences in chain line aren’t a big deal.

 

[88robb]

Hi,
I was wanting to fit a SR Sakae SX triple chainset to my 130 rear dropout spaced Dawes galaxy. Now the spec for cranks says it needs a 127.5mm bb spindle length.

Would I be right in assuming I’d need to loose some length off that to fit on a 130 spaced dropout rear end. My first guess would be 5mm off length to loose 2.5mm per side.

Can anyone confirm this or help point me in right direction for bb spindle length. Also assume other length I need would just be width of the bottom bracket she’ll on frame and assume English threaded.

Cheers

Yes, you need a shorter spindle. For your 130mm spaced frame, use a 122.5mm spindle (assuming a standard 68mm wide bottom bracket shell). This will give you the correct chainline.

 

[mac-highlander]

Yes, you need a shorter spindle. For your 130mm spaced frame, use a 122.5mm spindle (assuming a standard 68mm wide bottom bracket shell). This will give you the correct chainline.

Great I was thinking 122, 122.5 or 123 would be grand in place of 127.5 on a mtb setup. Many thanks.

Now to find me a nice value bb of correct size

 

[Ajax Bay]

Yes, you need a shorter spindle. For your 130mm spaced frame, use a 122.5mm spindle (assuming a standard 68mm wide bottom bracket shell). This will give you the correct chainline.

Respectfully, I would treat this assertion with considerable caution. As said up thread (by nearly all others), it's the clearance to the chainstay which is critical and a 122.5mm spindle may make that real close or even a foul: not worth the risk for minimal benefit.
The chain line matters little: after all you'd only be shifting it 2.5mm inwards and the width of the cassette is what, 35mm?
Why does the OP @mac-highlander think this chainset (?1980s - I have the double version on a bike built in 1981) is designed for a 135mm dropout? Surely it predates the move from 130mm to 135mm by a decade.

a SR Sakae SX triple chainset to my 130 rear dropout spaced Dawes galaxy. Now the spec for cranks says it needs a 127.5mm bb spindle length.
. . . other length I need would just be width of the bottom bracket she’ll on frame and assume English threaded.

The Galaxy BB shell will have BSA threads and be 68mm.
Edit: This chainset will have been first used with a 126mm OLD drop outs and a 6speed block /freewheel. Don't know where you get the 'MTB' angle - 'being sold as . . . '. So if anything for chainline (which I've said is unimportant) you'd want a longer spindle, not shorter.

 

[88robb]

Respectfully, I would treat this assertion with considerable caution. As said up thread (by nearly all others), it's the clearance to the chainstay which is critical and a 122.5mm spindle may make that real close or even a foul: not worth the risk for minimal benefit.
The chain line matters little: after all you'd only be shifting it 2.5mm inwards and the width of the cassette is what, 35mm?

You're right. That spindle is way too short and will probably make the chainring hit the chainstay. It's not worth the risk for almost no benefit. That chainset is from the 126mm era anyway.

 

[mac-highlander]

You're right. That spindle is way too short and will probably make the chainring hit the chainstay. It's not worth the risk for almost no benefit. That chainset is from the 126mm era anyway.

Seen a few being sold as mtb chain sets but with what you guys said and thinking if released in 86 they were probs touring though often came with 48,38,28 which would be about right for v early mtb and as I can’t verify the 127.5 spindle length anywhere but velobase I am doubting that figure too. Reckon I’ll use a cheap 2nd hand shimano bb of 122.5 and fit it and see how far out it is before I get a new BB then I’ll know for sure rather than guessing.

 

[88robb]

Yep, good plan. A 122.5 is a safe bet to test with. You'll know right away if the chainline is off.

 

[mac-highlander]

Yep, good plan. A 122.5 is a safe bet to test with. You'll know right away if the chainline is off.

Even if I mark middle of shell and middle of bb pop drive side crank on and line it up to current chainrings, with a bit of care, I should be able to see close enough how far out I am and which way.

Many thanks guys