|Right crank is closer to the downtube||Woof the dog|
Jan 5, 2002 10:34 PM
|by about 4-6mm, when measured from the end of the crank.
Someone said that it is normal because of the way the bottom bracket is installed into the frame. True or not?
Thanx a bunch
|4 to 6mm is a lot of difference||nee Spoke Wrench|
Jan 6, 2002 6:18 AM
|It's also the amount of difference between a 68 and 73mm bottom bracket. Do you suppose you could have a 73mm bottom bracket in a 68mm BB shell?|
|4 to 6mm is a lot of difference||Woof the dog|
Jan 6, 2002 12:54 PM
|good question, just how likely is this scenario? I will check it out. thanx
|Most road BB's are one size||spookyload|
Jan 6, 2002 10:33 PM
|I would think that size difference true if it was a mountain bike. Most road bikes use a 69mm BB shell as a standard. Unless you are using Italian threads, then it is different, but that wouldn't even fit into an English BB. Oh yeah, and some freak will post after me about Mavic BB's too, but god only knows what the french are using these days. I would look more into an asymetric frame design, like my Litespeed has. It would explain why it is closer on one side to your downtube. Is it causing problems? If so you can look into shimming it on the drive side to move the crank outboard more. Keep in mind also that the right crank has chainrings that are compensated for, so you might not get your crankarms symetrical in width to the downtube because of that.|
|Most road BB's are one size||Woof the dog|
Jan 7, 2002 1:48 AM
|frame is m4 festina, the one with aerodynamic tubes and the tiny space that seems to be made to fit only 20c and barely 23c tires. I am starting to wonder if those idiots at the bike shop/specialized sold me the frame that was not sold before due to misalignment - the left seatstay is welded lower than the right one (or the other way around). It was a replacement for a cracked frame. I always get the feeling that I get cheated over everything because they probably think a misaligned frame is good enough for a lightweight dog like myself. If I had a fat wallet and grey hair maybe they'd treat me better. Bastards!
But seriously, the old frame was specialized allez comp 99 model. The bottom bracket is ultegra and now I use it in this m4, which seems to be a tt frame really.
thanx for listening
woof the tao-dog.
|More things to check||nee Spoke Wrench|
Jan 7, 2002 6:06 PM
|1. Are your cranks perfectly in line? A bike that new would probably have a splined crankset. If you're not real careful when you install one of those, you can misalign the splines. That buggers the crank arm splines and, I assume, wouldn't let the arm go on all the way.
2. Are the bottom bracket shells for both bikes the same? I'd assume they were, but one measurement is sometimes worth a thousand assumptions.
3. Does the bottom bracket spindle stick out from the bb shell the same amount on both sides?
4. How does the back wheel sit in the frame? Does it seem to fit about the same between both the chainstays and the seatstays?
Let me know what the results are and we'll get you back on the road.
|Close, but not exactly right.||nee Spoke Wrench|
Jan 7, 2002 5:42 PM
|English threaded bottom brackets commonly come in 68 and 73mm shell sizes. Most English threaded road bikes have 68mm bb shells and most mountain bikes have 73mm. The other common bracket width is 70mm, which is Italian threading and a larger diameter as well. Just for fun, I checked Sutherland's, and Spookyload's 69mm is about the only BB shell width that wasn't listed for anything.
Prior to the splined spindle bottom brackets, Shimano actually used the same bottom brackets for both road and mountain use. For example UN52 was offered in both 68 and 73mm shell widths, and was the Shimano part number for both 105 and LX.
You didn't say what kind of bike and crankset you're working with. Assuming you have a Shimano square taper cartridge bottom bracket, it's easy to tell which size it is. Take the whole cartridge completely out of the frame. The shell width "68" or "73" is printed in the middle of the cartridge. I'm hoping a $30.00 bottom bracket will solve your problem.
|You are right about 68mm||spookyload|
Jan 7, 2002 7:21 PM
|I measured mine and it was 69. Could be my micormeter off though too. I don't think the bottom bracket could cause a crank arm to be closer to the down tube though. Another solution to get them even is to buy a BB with an adjustable chainline like the Race Face(assuming it is square taper), but being it is a newer Specialized M4 I doubt it. You might be able to shim the Dura Ace over 2mm and still get the lock ring tight on the non-drive side.|
|re: Right crank is closer to the downtube||mackgoo|
Jan 7, 2002 12:02 PM
|Just out of curiosity is the diference the same when measuring to down tube seat tube and chain stay?|
|re: Right crank is closer to the downtube||Woof the dog|
Jan 7, 2002 8:17 PM
|Thanx to everyone for the suggestions.
I use ultegra bb and ultegra cranks. I don't have the old frame, and I checked the alignment of a new frame and it seems to be within 2 mm everywhere (of course it was not too precise with all the strings all over). Plus the seatstay being welded lower than the otherone on the seattube seems to have no affect upon the rear triangle(s) as a whole - the back wheel is centered between the chainstays. Interestingly the bike does steer a tiny bit left when riding no hands, but it is almost unnoticeable. I notice my right knee hits the top tube more often than the left one, probably due to that difference.
I will have a bikeshop tighten the left crank, but to tell you the truth, I refuse to believe it is the wrong bottom bracket or something is loose. It seems unlikely knowing that it was like this since last april, and it doesn't seem to affect me one bit. My knee pain started before I got this frame for some other reasons I figured out.
I will just keep riding it for now as the bike is just a tool, not a perfection. I will try and figure it out thanx to you.
Woof the dog.
|regarding back wheel and chainstay/seatstay||Woof the dog|
Jan 7, 2002 8:21 PM
|the wheel is centered 'tween chanstays, but it is closer to the left seatstay due to it being welded a bit lower by the seattube there. I don't see how this would affect the alighnment. Hell, you could weld one seatstay 3 inches lower than the other one. the only possible problem would the the placement of the bridge. no?
|How about this?||nee Spoke Wrench|
Jan 8, 2002 6:59 AM
|You have a pretty "cutting edge" frame that will only fit skinny little tires. I wonder if your bottom bracket shell might be a little narrower than standard. Have you ever measured it? I'm thinking that if it was my bike, I'd put a 2mm spacer behind the right side of the bottom bracket.|
|how safe is it to add spacers?||naf geezer|
Jan 8, 2002 9:54 AM
|is it a done thing or common?
what if any stresses does it add to the b/bracket and is it a simple way in acheiving a better chainline as well?
sorry for digressing but was interested.
Jan 8, 2002 10:55 AM
|Adding a spacer or two to a bb is perfectly o.k. and is usually done to improve chainline. It's not a rare operation at all.|
|perfectly,||Woof the dog|
Jan 9, 2002 1:53 AM
|An old mechanic i talked to said its not perfectly safe, plus I'd have to adjust front dr.
He said that 4mm isn't a lot and that I could just move my cleat that distance. I think cleat moving is the best solution, what do you think?
Thanx a bunch
Woof, the fast dog.
|I think the spacer is the best solution,||TJeanloz|
Jan 10, 2002 10:51 AM
|There are plenty of threads on a bottom bracket- I have no idea why somebody would think it wasn't safe (I could see the safety issue if we were talking about moving it 1.5cm, but not 4mm).
Moving the cleat is NOT a good idea. That will put your foot contact area with the pedal in a different place and affect your pedaling. Will you be able to notice 4mm, or will you only be left wondering why your knee starts to hurt? I don't know- but anybody riding with clipless pedals should have a RAD fitting done and leave the cleat where the RAD says it should be. That is my opinion on moving cleats.
|I think the spacer is the best solution,||Woof the dog|
Jan 11, 2002 2:48 AM
|ok, where do I get such a spacer? My lbs is too far away for this wet weather. Thanx a bunch
|How about this?||Woof the dog|
Jan 8, 2002 10:40 AM
|I took a closer look at it yesterday and the difference is no more than 4 mm. Right crank arm is definitely closer to the d.tube and also the chainstay. I will talk to my LBS about installing such a spacer. The guy should know what to do. Thanx a great deal!
Woof the dog.