Bottom bracket spacer
Bottom bracket spacer
Anyone know where can I buy a spacer to pack out the right hand cup of a bottom bracket, rather than buy a new longer one? I bought a double road chainset which came with a 110mm bottom bracket but have 135mm rear axle - so by how much do I need to "extend" the bottom bracket? Presumably the cassette is 2.5mm further to the right than a if it was a 130mm hub, so I need to adjust the bottom bracket by a similar amount to get the same chain-line. Or is it more complicated than that?
If you must, an old B/B lockring under the B/B cup would do it, but it probably isn't necessary. Take a look where the chainrings line up on the cassette, I doubt it'll be more than 1 sprocket out & modern chains bend a lot more easily than the old ones.
I have a 111mm axle on my Audax, with a Stronglight triple coupled to a 10 speed cassette on a 135mm axle. It lines up ok & runs perfectly
I have a 111mm axle on my Audax, with a Stronglight triple coupled to a 10 speed cassette on a 135mm axle. It lines up ok & runs perfectly
If at first you don't succeed - cheat!!
Re: Bottom bracket spacer
Steve wrote:Anyone know where can I buy a spacer to pack out the right hand cup of a bottom bracket, rather than buy a new longer one? I bought a double road chainset which came with a 110mm bottom bracket but have 135mm rear axle - so by how much do I need to "extend" the bottom bracket? Presumably the cassette is 2.5mm further to the right than a if it was a 130mm hub, so I need to adjust the bottom bracket by a similar amount to get the same chain-line. Or is it more complicated than that?
Hello,
A suitable spacer can be had by using a Sturmey Archer/Sachs ring which fits over the S/A Sachs sprocket before putting on the circlip. This type of modification is quite common and does not as mentioned cause any extra sress or problem with the bottom bracket.
You can buy the ring I mentioned, from any Sturmey or Brompton dealer for about 50p.
However, the bottom bracket of 110 that you have is the correct one and in my opinion should be used. The chainline 'you want' is probably not the one you should have and the bottom bracket supplied is the correct one.
After all that are you still with me?
John.
Well maybe I should check the chain-line with a piece of string & all that, but the problem I have is that when the chain is on the small ring I can only use half of the sprockets, as otherwise it rubs on the big ring. Surely the 110mm BB sold with the chainset would be for a 130mm axle, & as the cassette will be offset slightly on a 135mm axle, a slightly longer BB would be appropriate.
You're not supposed to use all the sprockets with each chainring. The chain can bend a bit but it will wear a lot more slowly if you try to keep it running roughly straight. Also you're not gaining any extra ratios by crossing the chain like that, they'll be duplicated by a straighter position on the other ring.
The sprocket spacings are of the order of 4-5mm so spacing the B/B will only get you 1/2 a gear difference.
The sprocket spacings are of the order of 4-5mm so spacing the B/B will only get you 1/2 a gear difference.
If at first you don't succeed - cheat!!
As bottom-brackets tend to be symmetrical these days, one that's 5mm longer (provided its tapers are exaclty the same length) ought to make the chainline just the same as if you had a 130mm rear end.
On a double I'd expect all but the smallest one or maybe two sprockets to be usable on the inner. The hub being 135mm moves the cassette only half a sprocket to the right, so that's two unusable sprockets and perhaps a bit of chain rub on the third. But you report chain rub across half the cassette, which sounds like another kind of problem. A likely cause of that much chain rub is if the chainset is designed with a thicker inside face on the outer ring, so that a super narrow 10-speed chain cannot drop into the gap between inner and outer, but you're using it with wider 9 or 8-speed chain.
If so, I'd suggest an experiment with slight increases in chainring spacing. Try inserting very thin shim washers, made by cutting bits out of a drinks can, between the outer ring and the spider (or inner, if the outer is not removable). As this is only a double, such a slight increase in ring spacing probably won't affect the front indexing, but will make a very significant difference to chain clearance that will likely make a lot more gears usable.
On a double I'd expect all but the smallest one or maybe two sprockets to be usable on the inner. The hub being 135mm moves the cassette only half a sprocket to the right, so that's two unusable sprockets and perhaps a bit of chain rub on the third. But you report chain rub across half the cassette, which sounds like another kind of problem. A likely cause of that much chain rub is if the chainset is designed with a thicker inside face on the outer ring, so that a super narrow 10-speed chain cannot drop into the gap between inner and outer, but you're using it with wider 9 or 8-speed chain.
If so, I'd suggest an experiment with slight increases in chainring spacing. Try inserting very thin shim washers, made by cutting bits out of a drinks can, between the outer ring and the spider (or inner, if the outer is not removable). As this is only a double, such a slight increase in ring spacing probably won't affect the front indexing, but will make a very significant difference to chain clearance that will likely make a lot more gears usable.
Chris Juden
One lady owner, never raced or jumped.
One lady owner, never raced or jumped.
Ah, CJ, you are most astute in your analysis of my problem, the full details of which I didn't go into originally. Yes it is a 10 speed chainset and yes I am using an 8 speed chain, and to make matters worse it is a 34/50. I have tried to eliminate the chain rub with 2mm spacers between the chain rings which means I can use 7 of the 8 sprockets with no rub, but of course the chain falls between the rings. So I will now try to get a 5mm longer BB of the same pattern, but was hoping to get a spacer to "extend" it rather than replace it.
Thanks for the advice everyone.
Thanks for the advice everyone.