Rim thickness - worn out?

[Brucey]

its worth bearing mind that the stresses are not uniform in the rim, and nor is the wear likely to be either.

A thickness of 1.1mm immediately beneath the rim hook is nothing to worry much about, but the same thickness lower down is much more of a concern.

BTW the image I posted is distorted; it has (accidentally or deliberately) been stretched vertically. This won't alter the rim wall thickness per se but you can't scale vertical and horizontal dimensions in the same way.

cheers

[reohn2]

Seriously, it's a good question - and a serious matter.
Many years ago - probably 40 or more - my rear wheel collapsed in the centre of Brighouse, on my way home from work.
I'd had to make a severe brake application, and it caused the heavily worn rim to disintegrate.
If it'd been on my front wheel, or at any significant speed, I could have been seriously injured.
The thought of it happening downhill makes me cringe.
Could be fatal.
I'm over cautious now.

There was a funny side to it. The acoustics were impressive.
First there was a springy "twang", and then a bang like a pistol shot, as the tube burst.
Then there was a cacophony, like the sound of a load of empty dustbins falling off the back of a lorry.
I was right by a 'bus stop, with waiting passengers.
One lady ran for cover into a shop doorway!

A friend with whom I often rode part way on the way home was riding behind me, and he said that it took him a second or two to realise what had happened.
He said that the pistol shot was accompanied by a puff of what appeared to be gunpowder.............I always apply plenty of French chalk, or cheap talc, inside the tyre when fitting it.
He'd stopped right by the 'bus queue, and it appeared that I'd really caused quite a stir.
No encores though.

Can't be careful enough.

We had a rear rim begin to fail on the tandem whilst coming back to Rotterdam for the ferry,I managed to ride about 80miles with tyre and rim held together with zip ties.

Has anyone mentioned disc brakes.... ....better not eh?

[Mick F]

You can't measure lower than the rim bed.
The internal bit inside the box section is - well - inside the box section.

Mine seems concave from the outside. I did think about putting a straight edge across it and measuring the concavity but it was problematical to get a meaningful measurement. Got the tyre back on now, so it's not so easy to do it.

Imaginary straight edge vertically. Centre of concavity would be at the web.
Just under top of tyre hook is 1.1mm

[Brucey]

if the rim wears through into the box section the brakes don't work very well but the failure doesn't usually cause the tyre to come off the rim.

As mentioned upthread most rims flare out under pressure before they fail, so keeping track of the rim width (which is very easy using Vernier calipers) is as good as anything really.

cheers

[Mick F]

Thanks.
Good to know.

Just been looking at it, and I reckon there's plenty-ish time left for the rim.

Also, been on the Sun Ringle website.
Seems there's some variation in spec here.
Sun Ringle on the left, SJS Cycles on the right.

Maybe there's a difference between 700c etc and 406?

[geocycle]

if the rim wears through into the box section the brakes don't work very well but the failure doesn't usually cause the tyre to come off the rim.


cheers

So would you advise setting the blocks closer to the square section of the braking surface? I've never been sure whether a high or a low position is best.

[Mick F]

With my rims - on both bikes - the brake blocks are basically the same width as the sides of the rim.
Very little leeway at all.
Can't set them high or low, they have to be spot on.

[rjb]

At one time it was suggested that you overinflate your tyres periodically to check if the rim is still ok. I thought the pressure was 50% overpressure. I havent seen this mentioned recently, does anyone still do this.?

[Mick F]

100psi in the rear Moulton, and 120psi in the rear Mercian.

50% over would mean 150psi and 180psi.
Grief.

Good job I've got a good track pump.



Tell you what, I'll see if I can get 150psi into the rear Moulton. The wheel is still off the bike and the pump is available .........................

.................... if you hear nothing else from me today, I'll be in hospital with shrapnel injuries.

[Mick F]

I'll leave it at 150psi for a day or three.
28mm Continental Sports Contact tyre. I don't think they're rated that high!

[bgnukem]

Tyre max. pressure will be the limiting factor in overpressure testing rims. Having said that, a wider tyre at lower pressures can exert an equivalent force on the rim to a narrower tyre at higher pressures (though of course the maximum design pressure of the wider tyre will tend to be lower).

The rim sidewall thicknesses of new rims I've measured (using an Iwanson gauge) have been between 1.0mm (Mavic XM317 - lasted 2k miles then sidewall blew out) and 1.4mm (Rigida/Ryde Chrina). Recently bough some H-Plus SON Archetypes which also measured 1.4mm new. Rose bike's own brand 'Xtreme' rim didn't seem to be any thicker, nor a DRC ST19.

Still looking for the elusive rim with 2mm thick sidewalls which might last more than 5 minutes of winter riding!

[rjb]

I'll leave it at 150psi for a day or three.
28mm Continental Sports Contact tyre. I don't think they're rated that high!

Good grief i dont think you are meant to leave it like that..If the rim is going to fail it would have done so by now, give your tyre a break and deflate it. ps i see you have been on the porridge giving it that welly.

[Mick F]

Over two hours.
Still in one piece and no shrapnel.

I'll let it down now.


...................... and relax.

[JohnW]

I'll leave it at 150psi for a day or three.
28mm Continental Sports Contact tyre. I don't think they're rated that high!

IMG_0415.jpg

It's a flippin' good inner tube that retains 150psi for three days Mick.
I put 100psi onto my bike when I prepare to set off, but it's always down to between 80 and 70 next day.
I use mainly Continental tyres and tubes.

Actually though, this is an aside to the main subject and I inspect my rims pretty regularly. As soon as they start to show any signs of wearing concave I inspect every time I ride. I inspect all round, because they don't wear evenly.

[simonhill]

I had a CR 18 rim split on me. 26", me light, moderately loaded bike.

I was touring in Thailand and inflated my rear using garage air, fairly high for me - maybe 60 or 70 psi. I didn't hear anything, but when I started to ride I noticed brakes were catching.

On inspection I found 2 splits in rim, running longitudinally, maybe 1 and 2 CMS in a line. I lowered tyre pressure, eased off brakes and carried on riding carefully.

Rode like this for a day and a half on good surfaces flattish roads till I found a replacement CR rim, albeit un-eyleted.

Not recommending, but these must be tough old rims.

My current Sputnik/Andra are double walled and from enquiries on here when I was worried about wear I was told I could exceed wear line through the outer as the rim is still supported by the inner. Maybe MickF should look for a double walled rim.