sanmi

Trying to salvage some of the parts that came on my old Bianchi for other projects (flipping).

I spent a few hours on the wheels - the hubs are in decent shape and I was able to get the spoke tension nice and even. The front wheel spins well and runs pretty true. The rear wheel is laterally true and does not hop up and down when I spin it in my hands, but there is a noticeable flat spot of about 3-4mm deep for about 10cm along one section of the rim. The spoke tension on the drive side is even and appropriate. If I work the spoke tension to address the flat spot, the rim starts to hop out of my hands when I spin it. And I still can't get the flat spot all the way out. So I'm guessing this is a damaged rim. My question is whether this is safe to ride (e.g., if the air in the tire will provide enough deflection to "smooth out" the flat spot) or if I need to trash these rims and salvage the hubs and maybe spokes.

Any experiences with old flat spotted rims? Thanks.

jj1091

I'm sure it would be safe to ride, but maybe annoying with a noticeable hump in it. I had an old steel wheel with a permanent flat spot like you're describing on my '75 Peugeot, which had 38c tires on it, so the fatter tire softened a lot of the hump. Sometimes you get a tire that doesn't seat well on a rim or is a bit deformed, and even though the rim is perfectly true, you still end up with a hump in the spin. I'd say to just install the tire, air it up and ride it, and see if the flat spot is less noticeable.

dabac

I’d detension or partially unlace the wheel, then have a go at pulling the flat spot out. A 4 mm dip will be felt while riding.
It’s strange that you didn’t run out of thread on those nipples.

Retro Grouch 

Depending on the rim it might not be possible to get the flat spot out.

When they make rims, they roll the extrusion into a coil. Then they cut the coil and flatten the individual loops. If the manufacturer didn't somehow adjust for the saw kerf, you will always have a flat spot opposite the valve stem hole where that material was removed. You can't adjust that out but I haven't found it to affect the ride-ability of the wheel. If it bothers you (and it definitely grates on me) I think the best solution is to buy a more expensive rim.

prathmann

Some bike shops may have a tool for pulling out flat spots on rims.
https://www.brx.gr/en/product/rim-repair-tool-pull

cny-bikeman

Riding on a bike where the spokes have been loosened to reduce a flat spot is a bad idea, as you have seriously weakened the wheel. Unless the flat spot is physically pulled or pushed out you will not be able to have a stable wheel that is also reasonably round.

Aubergine 

AnoHer problem is that you will not be able to adjust the brake properly with a dent that deep. (Assuming rim brakes.) If the brake pads are adjusted for the main part of the rim, they will rub won the tire at the dip, which will wear it rapidly and eventually blow it out.

I have never been able to successfully pull out a 4mm dent in a wheel just by fiddling with the spokes, for what it is worth.

fietsbob

Working Blind, I cannot say "Is it Safe?" No Opnion there..


In the shop on cheap kids bikes with steel rims an application of Newtonian Physics was used..

flat spot from impact to the outside, was reversed by a slightly greater force applied to the inside out of the rim,

Slamming the wheel down over a protruding wooden beam end.. after loosening the spokes in that sector..




....

cny-bikeman

In the case of a very minor flatter area it's possible to redistribute tension enough to increase roundness, but of course one can't pull out a flat spot with spokes.

Aubergine 

Yes. I’ve been able to get a wheel true by retensioning when it’s a couple mm out of true, but 4 mm needs something else to push the flat spot out.

maddog34

"If I work the spoke tension to address the flat spot, the rim starts to hop out of my hands when I spin it."

Bull Crap.

and not one of the responders asked the OP what type of rim the OP is working on....
As in: aluminum or steel? single wall or double wall? Worn or fairly decent condition?

jj1091

Having a bad day? Probably would have been more beneficial to just ask the OP this question yourself.

sanmi

The rims are 1989 Araya 20A aluminum double walled box sections.

As I mentioned in my original post, I am hoping to salvage these wells for a future flip project. They came to me pretty beat up. I'm hoping to make them safely rideable, but if that is not possible I will just salvage the hubs for some other project. It's not really a big deal if the rims are dead. I'm just wondering what folks' experience has been with this kind of rim damage.

Right now, the wheels are evenly tensioned and spin well, but there is a noticeable flat spot across from the valve hole. I guess I'll start by mounting some tires and see if I notice it on a cautious ride around the block. Unfortunately these are pretty narrow rims so the widest tire I'll be able to run is likely 25c.

prathmann

I'd still suggest checking your local bike shops for one that has the type of rim tool mentioned in post #5 and let them have a try at removing the flat spot. And you shouldn't have any trouble using tires wider than 25mm (not 'c') on Araya 20A rims as long as you have enough clearance on the frame and brakes.

ThermionicScott 

Those are great rims, and well worth trying to keep in service! The inner width is 14mm, and I've had no trouble with tires up to ~30mm. Currently using 700x28C Paselas that measure their full 28mm.

fietsbob

Nobody measures anything here! how many MM out of round is the flat spot?






....

prathmann

About 3 to 4 mm according to the initial post.

fietsbob

its not that much.

curbowman

You might find this useful: how to fix a damaged rim yourself:

dabac

I regularly rig up cradles and c-clamps and pull out flat spots. It will usually work out fine.
That might put a stop to any shaping attempts.
Straight across from the valve hole is where you’ll usually find the seam in the rim.
If that one isn’t round(enough) from the start, it’s really difficult to fix later.
And if it’s a pinned seam, it’s likely to come apart if you try to get creative with the shaping.

3alarmer 

...this, and I also have one of these:



But to start with a box section alloy rim is a lot more difficult to reshape (the advantage being it's harder to deform in the first place.) And the seam on the rim is, indeed, gonna be about where you're doing your reshaping.

Were I you, I'd probably first try loosening the spokes along the arc you want to move outward (the flat spot) in a manner that is even on both sides (same number of turns). Start with maybe a turn and a half or two turns.


^^^the flat spot is centered at 6 on the clock^^^

Then tension the spokes tighter at 4 and 8 (again, evenly on both sides, so the rim stays centered.) that will move it outward some, usually in a nice curve. But if you want to detension the whole section and rig some sort of puller or cradle, it needs to work like the commercial tool pictured for success.

ThermionicScott 

That was cool. Thanks for sharing it.

norcalmike

Gravedigging here.
I have a similar issues with a Saturae HC20 with a flat spot in it. I have 2 bike shops in my town. One said they dont have that tool anymore and the other told me they can't bend back aluminum.
looking for more DIY ideas.
I was thinking a wood jig on a vice or maybe even making that rim stick thing in the video. I dunno. Just want matching orig wheels.
Unless someone has another HC20, repair is my only option

ThermionicScott 

I don't have pictures, but one thing I've done is to clamp two shallow wood blocks to my bench, undo the 4 spokes around a flat spot, then place the rim on those two blocks and use a larger clamp between a thin block on top of the flat spot and the underside of the bench to press out the flat spot. It's not the most precise method, but it can reverse a lot of the bend. Just check your work often so you don't overdo it.

norcalmike

sounds similar to this method I found. I don't need much. A little flex should do it.