Bicycle Mechanics - Re-dishing the rear wheel to center it with frame - the long term effects
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I have an older Peugeot road bike (i suppose it is technically a touring bike, because it has loops for attaching racks and stuff, and wider forks), with a broken spoke on the rear wheel. The hub was a Maillard Helicomatic Hub, which was mentioned here:
Apparently its pretty bad, and in fact I did not have the tool to remove it, so I could not repair the spoke. I chose to get a new rear wheel (the entry level one), with a freewheel hub. Everything seemed ok, but I am noticing that the rear wheel is off-centre with respect to the frame. Now the nuts on the axle are symmetric, and fit withing the frame, but the rim seems to be offset (which i think is because the frame was designed for a helicomatic hub). Now I have two solutions for this: use a combination of washers to shift the hub slightly over on the axle, or re-dish the wheel in the right direction to shift the rim over. I have not measured it, but I think Im off centre by 3-5 mm or so.
My questions are:
Has anyone tried to centre a wheel using one of the mentioned methods?
Is there a better solution to my problem?
If I chose to re-dish the wheel, will it be a weaker wheel?
Is shifting 3-5 mm too far for a dishing techniques?
Please let me know of any advice! (Note: I do not know much about either method I mentioned, so any info will be appreciated)
in my reading on wheel dishing, you end up having to do both. respacing the axel to be centered on the hub, and then dishing the wheel to be centered on the frame.
So if I am understanding you correctly, the hub is centered, but the wheel is not? So is the wheel not centered over the hub?
If that is the case, you may only need to re-dish the wheel.
It require's measurement of the hub resting on the axel in relation to the frame, and then measuring the amount of dishing required.
It's easiest done with a dishing tool, which is basically just a device to measure precisely how much dishing needs to be done.
Then it's a lot of tinsy moves with a spoke wrench, and re-truing the wheel
05-13-10, 08:01 AM
The type of freewheel or cassette is totally irrelevent to whether the wheel sits properly in the frame. If the rim is properly dished and the frame/dropouts properly aligned the rim will be centered. It is true that the rim may need to be dished further in respect to the hub flanges with some freewheels/cassettes, but it is always centered over the locknuts. Either the wheel is not properly dished or the frame/dropouts are not properly aligned. If you bought the wheel from a shop ask them to check the dish. If not just reverse the wheel in the frame. If off in the opposite direction respective to the frame) the dish is wrong, if in the same direction the frame has a problem. Also note that it is very common to have to jockey the wheel a bit to center it on less expensive bikes.
Dishing is not just moving the rim over but also keeping the tension appropriate, and moving washers is dependent on what clearance you have on the right side for the chain as well as your derailleur adjustment limitations. In the old days we used to move spacers when we could get away with it to minimize the amount of dish or to accommodate a change in freewheel or rims when things were not very standardized. Do not do so without understanding the ramifications.
Can't answer your questions fully until you determine if the wheel is the problem and in which direction it is off center.
"Respacing the axel (sic) to be centered on the frame" is not appropriate - not sure what that means.
Now regarding the hub, it is centered, by which I mean the following: it has one tightening nut on top of the nut which holds the bearings in (one nut on both sides), and then fits snugly to the frame. Thats what I meant by centered hub. So if the hub rests snugly in the frame, the wheel rim is off centred relative to the frame. Now I hope this is due to the fact that the wheel is not centered over the hub (which is strange, because this is a new wheel. But its a cheap wheel, and manufacturers are not always perfect), in which case I will have to retighten the spokes to shift the wheel like you mentioned.
Now the reason I am a bit concerned about this operation, is because it seems like 3 or so mm is a long way to dish the rim using spoke tension. Or maybe its not, I just dont have a lot of experience with wheel truing. Maybe I bough the wrong wheel for my frame? I would not mind doing the dishing approach, but I wanted to make sure that after going 3mm I wont have one side over tightened or something, and then have a spoke snap as im riding far from home.
Regardless of wheel or cassette width all frames are built symmetrical (for spacing) right and left and likewise so are all wheels. Assuming it has the same axle width the new wheels should center properly. If you have horizontal dropouts you control the chainstay centering, but the seatstay centering should be automatic.
If it doesn't center you need to find out if the problem is with the wheel or the frame. The easiest way is to install the wheel reversed (cassette on the left). If the wheel is dished properly the rim will be off center to the same side, and if it's not dished properly it will mirror and be off center to the opposite side.
If you've added spacers to the left side of the axle to make up added axle width, you will need to re-dish the wheel. There are no long term ill effects from this if you do it by degrees, but be aware that right side nipples will already be pretty tight and need a bit of torque to turn, possibly causing the spoke to twist a bit as you work. One thing that helps is to have the wheel braced in a stand, or the bike frame, and gently push the rim towards the spoke you're turning to relieve some load while you work.
Thanks for the quick replies everyone! I will try flipping the wheel later today, and figure out what is causing the problem. If its anything noteworthy, I will post it in a couple of days.
05-13-10, 08:25 AM
The center line of the freewheel needs to align with the centerline of the set of chainwheels. This is setting the chainline. The bike achieves this by correct frame alignment and correct chainset installation, with the hub spacers installed as new. Chainline needs to be checked. If the chainline is correct, then your rim positioning can only be adjusted by dishing. Done correctly, there are no unusual long term consequences. Nearly every rear wheel sold or built for a geared bicycle is dished. It's normal.
Internal hubs are possible exceptions.
05-13-10, 08:39 AM
Road Frank brings up a good point, which I forgot to mention. As you have changed to a freewheel hub you first need to check the chainline, which requires several measurements and first of all requires a properly tracked and aligned rear triangle. Easy to check whether rear triangle is centered - just run a string from outside of one dropout around head tube to the outside of the other dropout and measure the distance between string and seat tube on both sides. If not equal you have a problem. See Sheldon and other sites if you really want to try to address that yourself. If OK hopefully the dropouts are aligned properly as well - harder to check without gauges.
Chainline is just the distance from center of the frame to the centerline of the chainwheels and the centerline of the freewheel/cassette. Front measurement is distance from chainwheel centerline to edge of bottom bracket shell plus one-half width of shell, rear requires subtracting distance from right dropout to centerline of freewheel from one-half of the distance between dropouts. Chainline would need to be corrected by changing the spacers on the axle or possibly with a bottom bracket spacer. Once correct you can then address dish.
05-13-10, 12:56 PM
If frame is okay, then increase the tension of the freewheel side spokes by 1 turn and decrease the tension of the non-freewheel side spokes by 1/2 turn. Start at the valve stem and work your way around the wheel. This will bring the rim ~3mm toward the freewheel side. Reverse these steps if you want to dish in the opposite direction.
Final fine-tuning of rim is needed to ensure acceptable run-out of +/- 0.5mm.
05-13-10, 02:15 PM
Previous post assumes of course that overall tension is correct - may not be.
05-13-10, 04:17 PM
I assume the frame is off, and that the old wheel was redished to be centered. Personally, I would use the spokewrench to center the rim, if the off center is towards the drive side-thereby relieving some of the dish and creating a stronger wheel. If the off center is on the non-drive, I would seriously consider moving some spacers around (if feasible) in order to avoid furthering the dish.
05-13-10, 05:29 PM
You may have bought yourself more trouble than you bargained for. Redishing the wheel will not help if your drivetrain does not work properly. If you can find some local help do so now, and again the spacers are to be moved only if you can still have a good chainline. You are welcome to check my profile for my background if you have any concerns about whose advice to follow.
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