Bicycle Mechanics - Wheel Alignment
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12-04-05, 02:26 AM
After fitting 5 gears on by old bike it felt as if the bike was pulling to one side. On viewing the bike held in a straight ahead position from rear, it looks like the rear wheel does not follow the front wheel, ie they lie on two different longitudinal planes. Is this because the distance of the hub from the frame at the side of the gears is different from the side without the gears? In that case, do I have to insert some spacers on the opposite side of the geared side of the rear axle? OR is there any other method commonly followed for fitting gears on a non geared bike?
I'm no expert but this sounds like a problem with the dish in your rear wheel.
Dishing a wheel means that the rim and tire will be moved off center relative to the hub but centered withing the dropouts. This is necessary for getting the freewheel to fit and the rim to be centered. Did you put a 5 speed freewheel on a single speed hub? Others who know more about this will be able to tell you if it will be possible to dish that wheel.
12-04-05, 04:14 AM
Thank you very much for your reply. I did visit the site you recommended before I wrote this thread. I failed to mention earlier that I feel the rear wheel feels as if it is pointing away form the straight ahead condition. The planes of the two wheels are not even parallel.
I need to find out whether I have the same hub fit on the bike though.
12-04-05, 04:48 AM
I found the solution in 'Bicycle Frame/Hub Spacing' on the Sheldon Brown website. Thanks a ton
The planes of the two wheels are not even parallel.
This condition could only be explained by the way the wheel axles are mounted in the frame and/or fork, or by a frame that is out of alignment. In other words one or both of the axles are not perpendicular to the plane through the center of the frame.
12-05-05, 12:45 AM
Thanks. you pinpointed it. The rear axle was adjusted such that the portion of the wheel at the front is centered wrt the fork and brakes. Does that mean I need a longer axle and some spacers on the side opp to the geared one? Or is 'dishing' the wheel a better option?
Not sure I understand the problem.
The rear wheel rim should be centered between the chain stays and seat stays. The brake calipers should be centered so that the brake pads are equal distance from the rim.
If the bike has vertical dropouts the wheel should be fastened to the dropouts with the full weight of the bike on the wheel. In other words, do not mount the wheel to the bike when it is upside down.
If the rim is off-center on the wheel (out of dish) you can confirm this by reversing the wheel on the bike to see if the rim is then closer to the other side of the bike.
Dish may be changed by adjusting the spoke tension.
You may find helpful information at http://www.sheldonbrown.com.
12-06-05, 04:05 AM
Thank you for the tips and sorry for not being able to explain the problem effectively. What I have observed is that axis of the rear axle is not perpendicular to the forward direction of the bike, but the rim is equidistant from the rear fork. I feel I should loosen the axle nuts, deflect the fork such that the rim is at the centre of the fork AND the axis of the axle is perpendicular to the forward direction of the bike and then add spacers on the axle to the opposite side of the gears (ie left side of the rim) before retightening. Please let me know if there are reasons against trying this.
I don't know of a bicycle with a rear "fork". Check the definitions of chainstays and seatstays and then tell us if the rim is centered between the two chainstays and also the two seatstays. I don't know if you need a spacer washer on the axle but I do know that adding a spacer will not change the angle between the axle and the center plane of the frame.
Does the frame have vertical dropouts or horizontal dropouts?
My question is: what did you change on your bike to make the rear rim go out of alignment? since I assume the situation had not occured before. Did you by chance have an accident on the bike? Even a minor accident that you thought wasn't a big deal? Or jumped a curb etc? An accident may have knocked the rear stay out of alignment or bent one or both of the dropouts. Even if you haven't had an accident have you checked the welds on the frame where the rear stays go into the seat tube and the bottom bracket? If all of that is good then you either need a spacer or you need the rim redished as JONSAM replied, more then likely the redish will cure it since this does happen to rims.
12-07-05, 02:52 AM
There was no problem when the bike was with a single freewheel (as I had bought it).This problem came when the bike was converted to a 5 speed derailer. It has horizontal dropouts. The situation is such that the rim is centered between the chain stays and the seat stays but sits skewed in the dropout slots, such that, when viewed from behind, the rear wheel appears to have turned to the right with respect to the forward direction of the bike. I hope I have been able to define my problem.
Frames with horizontal dropouts usually have a way of adjusting the position of the axle within the dropouts. Is it possible to loosen the axle and straighten the wheel in the frame so that the axle is perpendicular to the frame?
12-08-05, 07:56 PM
Thank you all for all your help. The 'dish out' on the rear wheel after the job wasn't sufficient and the bike mechanic had taken a shortcut to align the rim with the chain stays by fitting the axle skewed. Now I have a properly aligned rear axle with the rim exactly equidistant in the chain stays. However, the largest gear out of 5 (22 teeth) causes the chain to slip off the singel chainwheel (the chain falls on the inner side - between the frame and chainwheel).
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