Bicycle Mechanics - bottom bracket size help?

i recently had my LBS install a bunch of stuff including a sugino xd2 500 triple crankset and new ird bottom bracket on my surly crosscheck.

now according to VO's site, sugino recommends a 113mm bb for a road bike to a 115mm for a bike designed for larger tires. riv says a 107 to 110 for a road bike, and 113 for a bike with bowed chainstays such as most mtn bikes. sheldon's chart shows 113 to 118 with as small as 107 fitting certain road bikes.

when i got the bike back i noticed that there is quite a bit of space between the crankarms and the chainstays. maybe an inch give or take, i haven't measured it yet. there is also quite a bit of space between the small chainring up front and the chainstay. i asked what size they installed and was told a 118mm. i mentioned that i had heard 113 to 115 and was told that 118 is the minimum for a decent chainline, and to not have the chain rubbing adjacent cogs on the cassette when in cross-up gears.

i measured from the middle chainring the to the center of the down tube, and i get definitely more than 45 which is what shimano specs for a road triple according to sheldon's chart on bb size. as accurate as i can measure it looks like 48-49. i shifted to the middle chainring in the back (12-25 9spd) and the chainline definitely flares out slightly at the crank.

am i correct in assuming that i need the 113 considering that 48-49 is 3-4 more per side, and 6-8 overall. 118 minus that 6-8 would leave me at 112 -110. as i mentioned the mechanic (who has been very helpful and seems very knowledgeable) said that a 113 wouldn't fit.

anyone who has installed a triple on a crosscheck, what size bb did you use and how is the chainline?

should i take it somewhere else? can the spindle alone be swapped ($15) or do i have to buy a new bottom bracket ($50).

THANKS

You need to match your front to your rear chain line. You've measured your front, now measure your rear. However, based on the data you've presented, I'd say that you should have a shorter axle.

Is the BB a cartridge unit?

The mechanic lied. Take it back to the shop and tell the owner/manager that you want a proper-sized 113 installed at no extra cost. Try to get some free stuff too for them having wasted your time and lying to you.

i've gone back and talked to the mechanic. they offered to swap out the bottom bracket for a narrower size at no charge, but if it rubs too much and needs replaced i'm on my own.

right now i have full range of gearing with the slightly flared chainline. the chain has a VERY slight rub when on the small cog in the rear and the small ring in front. it seems to shift ok, but i'm of the understanding that chainline is important.

should i swap to a 113 and get the straighter chainline, even though i might rub more when on the 12 and 13 cogs in the rear (which i understand i should be using those gears when on the small ring up front anyway)?

thanks for the help

Rub WHERE?

camelride, what is the width of your hubs? 135 or 130mm? 8,9 speed? What gears do you ride the most?

In the small ring, I assume it's 26t, you never want to have the chain in the 12 or 13 cogs, which I assume are the smallest on your cassette? You only need to use maybe 5 cogs in the 26t.

You can run through your gears while at the shop to see what works, but frankly, I'd go somewhere more knowledgeable and friendly. (on your own?:rolleyes: ... sounds like someone woke up on the wrong side of the rock!)

garthr-
i have shimano deore hubs (135) and a 9spd 12 -25 cassette. the small ring is a 24 and is generally only used with the top 4 or 5 cogs. just to be clear they are very friendly at the shop and offered to swap it at no cost to whatever i want, but if it rubs the middle chainring too much for my liking when in the small front and smaller rears i would have to pay for labor and such to have it swapped again. they were certainly accommodating and not stand-offish.

i just measured my front and rear chainlines. as accurately as i can tell the front is 49.3mm and the rear is 45.35mm. that's a 4mm difference, so swapping to the 113mm spindle would bring in it 2.5mm and close the difference to the front being 1.55mm larger.

if i understand everything i've been reading, that's pretty spot on.

Sounds like you have it solved. 113 it is. I'm surprised the shop didn't mention the use of shims if needed with the 113 BB. The come in 1,1.5 and 2mm sizes, they go between the lip of the BB on the drive side and the frame. This allows a bit of customizing the drivetrain beyond just changing the BB length. While you have your solution solved, I offer this so you know if you ever need a minor adjustment in the future on this or any other bike, shims are an a very low cost solution. 30 cents.

:cheers:

thanks for the info garthr:thumb: i'll probably swap out to a 113 and keep the shims in mind.