How to correct a 'flat spot' radial alignment?

[Black_Blade]

In an attempt to get my bike back in service while I attempt to repair the problems with cassette on the original wheel, I have used another wheel. This one only had five sprockets instead of seven on it, but I adjusted the deraileur and it seems to change gears ok.

The problem I now ran into is that when I spin the wheel...I see it moving a bit laterally and rubbing one of the brake calipers (does this in two spots actually) and also noticed that one of these bad spots also has a radial 'flat spot' that looks to be about 4 spokes along the rim in length.

After watching the tutorial on truing a wheel, I gathered to loosen spokes to allow the flat spot to move away from the hub. But the spokes in this area are already loose...what do you do to correct this kind of problem?

I do not have a truing stand, been attempting to do this on the bike.

[Alex Ramon]

Hi Black,

If adjusting the spokes' radial alignment doesn't work, the flat spot may not be repairable. Some people have had success with removing the spokes and carefully (but forcefully) hammering down on the flat spot with a rubber or soft hammer.

[Black_Blade]

Hmmm, wonder if just call it and look for a new wheel. Bike is gonna be side lined I guess, original wheel has missing spacers in the cassette and my 'replacement' wheel has been abused in the past and has this flat spot.

[Joe_W]

Well, sometimes the brute force method Alex mentioned works. You can also try to tighten all spokes excluding those at the flat spot and the immediate vicinity (two spokes in each direction?). What is the condition of the rim (and the wheel in general)? If the rim is shot but the rest is ok, replace the rim (they are consumables), rims start at 15€, heck most of my tyres are more expensive! If the rest of the wheel is also in a bad condition you would have to get a new wheel.

Oh, how bad is the flat spot? 1mm-2mm is not much of a problem with wide soft tyres.

[Black_Blade]

(03-24-2010, 02:49 AM)Joe_W Wrote:  Well, sometimes the brute force method Alex mentioned works. You can also try to tighten all spokes excluding those at the flat spot and the immediate vicinity (two spokes in each direction?). What is the condition of the rim (and the wheel in general)? If the rim is shot but the rest is ok, replace the rim (they are consumables), rims start at 15€, heck most of my tyres are more expensive! If the rest of the wheel is also in a bad condition you would have to get a new wheel.

Oh, how bad is the flat spot? 1mm-2mm is not much of a problem with wide soft tyres.

Other than the flat spot, the rim looks pretty good, I don't imagine its any kind of a quality rim tho...just run of the mill. The wheel came off an old 15 speed Triumph (if that means anything).

So maybe just tightening up everywhere but where the spokes are loose (flat spot), it may force the rim back into shape? It is tough to say how many mm the flat spot is... but its enough that the brake pad will rub about 1/4" up onto the side wall of the tire (when inflated). When I first spun the wheel, I thought it was a lateral run out that caused the wheel to snub against the brakes at that point, but it turned out to be the pad rubbing up against the tire above the rim.

[Joe_W]

Ouch, brake rubbing against the tyre is bad, and the flat spot sounds quite bad, from the description. I'd probably give the rubber mallet method a shot, in my opinion (well, judging from the description, I cannot see the wheel, my crystal ball is for for polishing) the rim is done for anyway, so you'll probably not break too much there anyway. When it seems a bit more roundish (sort of) I'd try to correct the radial truing via spoke tension.

A rear wheel for thread on freewheels can sometimes be found at the LBS for a bargain price, mine was 15€ with two (used but still ok) tubulars and a 6 speed freewheel. I'd try that first, replacing the rim will be more expensive (rim 15€, spokes another 16€ + work) but can be worthwhile if the hub is still good (check tutorial on hub overhaul before replacing the rim).