Time to replace rim?

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bgnukem
Posts: 569
Joined: 20 Dec 2010, 5:21pm

Re: Time to replace rim?

Postby bgnukem » 7 Jan 2021, 1:31pm

I've found my rims to start deforming at around 0.8mm thickness, and also some Mavic rims measuring 1.0mm thick when new!

Typical initial thickness of the rims I've bought and used over the last 10y or so has been 1.4mm maximum, so there's not much wear allowance and this problem can creep up on you during winter riding with the abrasive mud, salt and grit all over the roads....

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Mick F
Spambuster
Posts: 50688
Joined: 7 Jan 2007, 11:24am
Location: Tamar Valley, Cornwall

Re: Time to replace rim?

Postby Mick F » 7 Jan 2021, 3:17pm

Sweep wrote:
Mick F wrote:
Sweep wrote:Do you have a link?
This is mine.
https://www.rolsontools.com/product/diamond-gauge/
There's no way on God's Earth that I paid that! :lol:

£3ish from Toolzone in Plymouth. They don't list it now though.

thanks for looking Mick - explains why I couldn't find it.
eBay?
£3.99 with free postage.
Item location: Maidenhead.
https://www.ebay.co.uk/itm/Jeweller-Sto ... %3A2334524
Mick F. Cornwall

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Sweep
Posts: 6876
Joined: 20 Oct 2011, 4:57pm
Location: London

Re: Time to replace rim?

Postby Sweep » 7 Jan 2021, 3:20pm

Mick F wrote:
Sweep wrote:
Mick F wrote:This is mine.
https://www.rolsontools.com/product/diamond-gauge/
There's no way on God's Earth that I paid that! :lol:

£3ish from Toolzone in Plymouth. They don't list it now though.

thanks for looking Mick - explains why I couldn't find it.
eBay?
£3.99 with free postage.
Item location: Maidenhead.
https://www.ebay.co.uk/itm/Jeweller-Sto ... %3A2334524

thanks mick
Sweep

mig
Posts: 2322
Joined: 19 Oct 2011, 9:39pm

Re: Time to replace rim?

Postby mig » 9 Jan 2021, 11:34am

do people tend to find that rims, generally, wear evenly? both side to side and around the rim?

what sort of pressure would a road type brake block apply to a rim?

i'm lucky in that fact that my rear wheels last longer in the winter as most of my miles are on fixed so i rarely use the back brake. i'd assume though that the drive side of the rear wheel wears more quickly as it's dirtier.

Brucey
Posts: 42272
Joined: 4 Jan 2012, 6:25pm

Re: Time to replace rim?

Postby Brucey » 9 Jan 2021, 11:59am

brake blocks have a coefficient of friction that is (very) approximately unity. So if you stop hard (about 0.5G) and you plus the bike weigh a certain amount then the pressure on the rim is going to be about half your bodyweight. The net load on the rim arising from tyre pressure is a lot more than that from rim brakes, but the latter is not so well distributed, and generates a fatigue component.

The fatigue stresses increase substantially (even when you are not braking hard) as soon as the rim is sufficiently worn (unevenly worn that is) that the braking action becomes uneven. If it gets to this stage then the remaining rim life (during braking) may be minutes or even seconds.

Rear rims tend to wear more on one side than the other, but it isn't always the same side, possibly varying depending on what kind of chain lube you use and how much of it ends up on the rim. I think it is most often the case that the drive side of the rim wears faster than the other side though.

Also if you use DP calipers the brake blocks don't behave identically on both sides; the brake block on the centre-pivoting arm tends to wear the same bit of the rim through the life of the brake block, whereas the one on the other side tends not to (the contact position of the brake block tends to move up the rim as the brake block wears). I have always assumed that this ought to make it more likely for the rim to wear out first on the RHS of the front wheel and the LHS of the rear wheel, but I don't know if that really happens or not.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

pwa
Posts: 13683
Joined: 2 Oct 2011, 8:55pm

Re: Time to replace rim?

Postby pwa » 9 Jan 2021, 12:18pm

While we are on the topic, can anyone suggest a decent gizmo for measuring rim thickness. Keeping on top of this is easier if you have the right tool. I suspect many of us don't.

backnotes
Posts: 418
Joined: 16 Jan 2011, 8:36am

Re: Time to replace rim?

Postby backnotes » 9 Jan 2021, 12:44pm

This for £3.99

https://www.ebay.co.uk/itm/Jeweller-Sto ... 3969747681

was suggested a couple of posts up. Is that what you are after, or something altogether fancier?

Jdsk
Posts: 5343
Joined: 5 Mar 2019, 5:42pm

Re: Time to replace rim?

Postby Jdsk » 9 Jan 2021, 12:53pm

backnotes wrote:This for £3.99

https://www.ebay.co.uk/itm/Jeweller-Sto ... 3969747681

was suggested a couple of posts up. Is that what you are after, or something altogether fancier?

That, or ordinary digital callipers with a shim to get past the overhang, and then subtract.

Jonathan

Mike Sales
Posts: 5383
Joined: 7 Mar 2009, 3:31pm

Re: Time to replace rim?

Postby Mike Sales » 9 Jan 2021, 12:55pm

Jdsk wrote:

That, or ordinary digital callipers with a shim to get past the overhang, and then subtract.

Jonathan


There may be an overhang on both sides.

pwa
Posts: 13683
Joined: 2 Oct 2011, 8:55pm

Re: Time to replace rim?

Postby pwa » 9 Jan 2021, 1:04pm

Jdsk wrote:
backnotes wrote:This for £3.99

https://www.ebay.co.uk/itm/Jeweller-Sto ... 3969747681

was suggested a couple of posts up. Is that what you are after, or something altogether fancier?

That, or ordinary digital callipers with a shim to get past the overhang, and then subtract.

Jonathan

I just wondered if there were vernier calipers with ends shaped to cope with the overhang. I will have a trawl to see if I can find something like that.

Brucey
Posts: 42272
Joined: 4 Jan 2012, 6:25pm

Re: Time to replace rim?

Postby Brucey » 9 Jan 2021, 1:11pm

Mike Sales wrote:
Jdsk wrote:

That, or ordinary digital callipers with a shim to get past the overhang, and then subtract.

Jonathan


There may be an overhang on both sides.


if you have to articulate the caliper by five degrees or so for the jaws to clear the rim concavity on the outside it

a) means the rim is almost certainly badly worn and
b) introduces a small measurement error only.

So a shim on the inside of the rim only is usually adequate. If you think this isn't the case you can (as suggested by CJ, years ago) make a gizmo from an old spoke which sits both sides of the rim.

If you use digital calipers then no subtraction is required; the calipers are set to zero over the spacers and then the thickness measurement is read directly from the display.

Whichever method is used, the end radius on the tool jaws/spacers may affect how accurate the measurement is, because the inside of the rim may not allow good access beneath the overhang if the tool/spacer isn't small enough.

FWIW Colin has shown how you can grind caliper jaws to measure rims easily, upthread.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

pwa
Posts: 13683
Joined: 2 Oct 2011, 8:55pm

Re: Time to replace rim?

Postby pwa » 9 Jan 2021, 1:33pm

If you look for calipers to measure the thickness of vehicle brake discs you see tools that will probably do the job, but at a price. I must investigate the size of these tools to be sure they will fit in the space.

https://www.amazon.co.uk/BGS-9177-Digit ... B075DL5SJS

Andy Short
Posts: 52
Joined: 9 Dec 2007, 3:45pm
Location: Bristol

Re: Time to replace rim?

Postby Andy Short » 13 Jan 2021, 8:15pm

I found an old vernier caliper in my toolbox and ground away part of the measuring surface so it has almost 'ball' measuring faces that get in behind any lip.
I have checked all my rims and set 1mm as my limit. One set of MTB rims are down to 1.1mm and weinmann concaves down to 1.2mm.

I found a dumped wheel which had split. It measured 0.8mm and was a cheap 'road' rim.
Road wheels run at higher pressure than MTBs, but MTBs tyres have larger tyres so larger area. As force equals pressure times area, I would treat all rims the same and suggest 1mm limit in all cases where there are no wear indicators.