How do I figure the proper width of the bottom braket needed for a 9 spd/double.

I have a 68-109 in there now, but I'm getting chain rub on the larger chain ring while the chain is in the small ring and in the small gear in back. It just looks like the crank is pulled too far into the frame.
I have no problems with clearance from the chainring to the frame.

Should I have a 118 on there?
Or could there be other problems?

Thanks -

You have the Correct BB in there.You shouldn't be in the small small.You could even get that same rub in the small and second cog.Just don't do it.

Could be rear hub spacing and rear wheel dish as well. That may end up being easier repair if your front derailure does not have any more travel left in it. Otherwise you will have to replace it also.

Of course, he is right. Patient: "Hey doc it hurts when I do this" Doctor: "So don't do that"

With wider and wider rear-end spacing you will at some point be limited from cross-chaining. People used to do it but it was never a good idea. I would take his advise.

I get no rub once I put it into the 7 or 6 gear.
What threw me is that with my triple bike, I can ride the middle ring and the 11 cog without that problem... Probably shouldn't but I do...

The only other infomation I have is that this was originally a 7 or 8 speed bike - back in '98. So that might explain the rub past the 7 cog.

It also has nothing to do with the FD.Dish will have nothing to do with it. The rub is chain on big ring, so the FD has nothing to do with it.

Your triple probably also has a 42 ring rather than a typicaly 39 of a double.That makes a difference too.The other bike may have longer stays.That makes a difference Having been a 7 0r 8 speed has nothing to do with it. Solution is don't do it. If you insist,you could use a BB spacer,chainring spacers or maybe try a thinner chain.

Sydney,
If he were to replace the bottom bracket with one that had a longer spindle in order to move the crank set farther away from the frame, that would change the chain line so that (as wrong as it is) he could ride in the small chain-wheel up front and small cog in the rear. If you change the chain-line outward, the problem then becomes front derailure travel.
One could also change how the axle was spaced in the rear to put more space between the cluster side axle nut and the frame which would also move the chain-line but that would result in having to re-dish the wheel.

Does it now seem like I meant what I said in the first place?

I was trying to tell him how to do what he wanted, not to scold him for using all the gears his bicycle came with.

Bicycle companies are notorious for specifying bicycles with ill-matched components, also many people do after-market mods that require creative adjustments
FD has everything to do with chain-line.

FD is consequence of chain-line, not the cause.

In other words, if you change FD then it does not affect chain-line. But if you change chain-line then it affects the FD.

Your first reply grok85 is nicely put... confusing. Your second one beeing more clear.

What you said in the first place was nonsense as it was stated.It's alot easier and SMARTER to NOT do it.It's also alot easier and smarter to use a 1 or 2mm BB spacer or thin chainring spacer or a thinner chain if the n00b insist. You are not suppose to 'use all the gears' the bike comes with. Most bikes are equipped to manufacturers specs for proper chainline. Changing the chainline to bias toward the smaller cogs just creates problems the other way. Simpler to learn to use the gears as intended. AFWIW, I don't shove rainbows when things are being done wrong.

And I'm being unclear?

True, my original statement was unclear/poorly written,

Also a fact that doing nothing and working with what you currently have requires little effort.
BTW, I agree he should leave it alone.

In one post you have decided what somebody should do, what is smarter, what is easier and when things are being done wrong.

We all know what you're saying is correct, but why the ton of bricks routine?

People do things that they "shouldn't" all the time. He obviously is trying tou use that combo or he wouldn't have found out that the ring rubs in the first place. What are you afraid of, the chain wheel police? A 1 or 2 mm spacer is another possibility for adjusting chain line as long as he does not have a cartridge style bb and yes the chain ring spacers would work, but a thinner chain won't always work with an indexed set-up.


Raedeke, to answer your original question, "How do I figure the proper width of the bottom bracket needed for a 9 spd/double" I would say put the chain on the small chain-wheel up front and the middle sprocket in the rear and see if the chain is reasonably straight, if so it is probably right. If it isn't straight the chains bias (inboard or outboard) will tell you if BB/spindle length could be better served with a different size. But never forget you are free to do whatever you would like. For whatever reason using the small-small combo is very common even though it is not recommended, and it is best to avoid cross chaining, but after getting this question for the billionth time, I'll just tell you what you want to know.

If he wants to accelerate the wear on his drivetrain that's his business. He came here looking for a solution to a problem that (as it turns out) HE was the root cause of. The simple solution is to stop ****************** crosschaining the ******************** bike.

This is real simple.If he has a shimano 9 speed double octalink crank the 68x109.5 IS correct.You are also INCORRECT about the small chainring middle sprocket business....Using the small/small may be common for n00bs,but why encourage it??

Why encourage things that cause abuse of equipment?. ...A BB spacer will absolutely work with a cartridge BB. There are different chain widths availabe among manufactruers in 9 speed and they all work with a shimano double.

Because what you said was all so wrong. The answer was DON'T do it.

This is truely lame.

You are truely subjective in your assesment.
He can do what ever he wishes. You may not like it but never forget he is free to do whatever he would like.

What I said was not wrong, just not what you would do. I wouldn't do it either but if he wants to, how can anybody stop him?

I haven't encouraged anything, I answered his question.
And if you use a spacer on the bb then you will have to re-adjust the front der. and then the available trave comes into play.

What you don't see is that you have no problem with your modification, (the bb spacer), but anybody else's is encouraging the abuse of their equippment.

"This is real simple.If he has a shimano 9 speed double octalink crank the 68x109.5 IS correct."
They may be the correct parts but it does not mean he has a good chain line.
How is it that you check chain line? or do you just take what the manufacturer gives you and pray that it works?

All chain widths will not work on a indexed rear cluster. But it I guess that is ok because it was your suggestion.

Well the way to check chainline is outlined at the park tool site. with a double it's from the center of the two rings. Not relative to the small one. I did not say all chain widths.

I guess this is what one calls PC rainbow shoving.But as far as good advice, it's bankrupt and barnyard waste.

Just remember, I said up front DON'T do it!! But, a BB spacer,if he insists is a cheap,simple and acceptable way way to do it.It's the answer when short stays cause chainring rub when in the small ring and small cogs other than the smallest. So you have to make a minor FD adjustment.Big deal. I have yet to see a FD that didn't have enough travel to handle the additional throw required by a 1 or possibly 2mm spacer. But as already stated:Best answer is DON'T do it.There is absolutely no need.

I have seen it.
A long time ago, but still, I can't erase my memory. Just because you haven't yet experienced something that I have experienced doesn't mean that it will not happen again or that it shouldn't be cautioned against as a possibility. I believe that it should be left alone also. It's not bankrupt advise, it's what he wanted to know. I have faith that with all the reccomendations against it that he would have opted out, but if he wants to try, he is free to do so. In your opinion, the only good advise is the advise you give. The rainbow shoving is your deal, not mine. It is his bike. If you think you are going to stop cross chaining in your lifetime you're the only one dealing in barnyard waste.

Whatever....

Sorry to have created such a controversy. Perhaps I can add a couple bits of information that might assist in making this thread go away...

First - My intention for the thread wasn't to find a way to ride a 39/11 combo. It was to try and find out if I had bought the correct width BB.
Second - The reason I know it rubs isn't because I'm out riding it and had problems, but by putting the parts together. Once I had the chain on, it just happened to be in the 39/11 location and I wasn't sure if the rub was normal or if I had screwed up and bought a BB that wasn't the correct width.
Third - 9 times out of 10 I ride how I should and am avoiding cross chaining. My comment about my triple is true - It happens when I'm not thinking and distracted by the lovely scenery here in Colorado... whether on the horizon or on the bike path in front of me...

I appreciate all the advice and even some of the interesting assumptions made on my behalf. Perhaps next time instead of jumping to conclusions, some clarifying questions would have been more appropriate. I'll also strive to pose my questions more concisely next time. But as a n00b... I'm still learning the ropes.

Thanks again.

It's correct. The problem is not uncommon even when using the small ring and second smallest cog,especailly with short chainstays....but dang,I already said that.