Rim flat-spot
 

I let my friend borrow my bike today so he could get a feel for disc brakes. when he gets back to my place he said i bashed the back tire going over a curb. i check it out and sure enough thers a flat spot on the rim. the spokes all aroudn it are super loose. how bad of a flat spot can you get away with before needing a new wheel altogether? if i retighten the spokes will i be fine or is it dangerous to be riding on? there are no cracks in the rim.
thanks for you help.

JJ

I guess it depends how bad it is, but i think you might need a new rim. A flat spot is hard to fix, since spokes work by pulling the rim inwards..

you could try various brute force methods like blocks of wood and hammers, but i don't think that is such a great idea...

Blocks and hammer only really works on cheapo chrome-plated steel rims. On lightweight alloy rims, you end up banging dents into the inner-edge of the rim rather than bending it outwards.

The wheel builder at my local shop has been able to get out some pretty bad flat spots on my DH rims.

I just know that i had a flat spot on what was otherwise a nice and not-much-used wheel, and i took it to at least 5 bike shops, all of whom said it was unfixable. It was only a couple mm, but enough to mess up braking.

The good thing is that incident induced me to learn how to build my own wheels.

Your rim is toast.
Go see your friend and tell him buy me a new rim you messed it up you buy me a new rim or i won't be your friend no more.

And of course new rim means rebuilt wheel... at least $40 labour at a bike shop (and that's just if they can re-use all the spokes and nipples), unless you do it yourself.

i like your plan. naw, my friends helpin me out with it.

its a cheap single walled rim, so i'm not surpised that it got messed up. ive got disc brakes so it shouldn't mess up braking too much i dont think.

i'll take a shot at the hammer method tonight, fully aware that it probably wont help. i guess this is a good excuse for me to get a better wheelset.

untill i can get the money for a new one, will it be ok if i still ride on it? i'm not doing any crazy drops or anything. its jsut light trail riding.

" i'll take a shot at the hammer method tonight,"
" will it be ok if i still ride on it?"

Maybe not after tonight!

I can't see you having any success with trying to beat it back into tue unless you take everything apart. Spoke tension would be fighting you.

Put the hammer away !!!

There are 3 ways to fix flatspots

1) In mild cases, you loosen the spokes at the flat spot, and tighten the spokes before and after the flatspot. Tightening them pulls in the rim on either side, and forces the flat spot back out to compensate. Then you can retighten the spokes at the flatspot, but they may have to stay a bit looser than the others.

2) For worse flatspots, you can use a rim puller. you loosen the spokes again, and the rim puller rests on the rim, with a hook on the inner side of the wheel and a huge screw to pull the rim out. This tool probably costs more than the rim, but a friendly shop might let you borrow theirs.

3) Put on a new rim. Sometimes easier than fixing the old one. Tape the new rim to the old rim, lining it up correctly. Undo each spoke & transfer it to the new rim. Tighten & true it up.

New rim, $12.99, free shipping: here

Free shipping code is FSP833


Check that the spoke length is appropriate though.

took it to a shop and they were able to get out the flat spot. thanks for all the replies.

So what did they do?