Rim 'wear' measurements

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fastpedaller
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Rim 'wear' measurements

Post by fastpedaller »

Pottering around in the garage an hour ago with my vernier......
Mavic A119 and Open Sport rims (bought last year) have a wall thickness of 1.5mm (I recall someone else mentioned this a few days ago), so no news there :D .
I then thought it was worth seeing how deep the 'wear indicator groove' measured. Stated as the depth of groove on each side ie double-up for 'total wear'
Mavic A119 0.7mm
Mavic Open Sport 0.5mm
so all things being equal (metal-wise) the A119 has 40% more miles in it, or Open Sport has 29.6% less, depending how the maths is worked :(
It would be interesting to know what other manufacturer's rims measure as.
:idea: When I get a minute I'll measure a (not very worn) MA2 I have to get a comparison of wall thickness from 25-30 years ago.
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Gattonero
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Re: Rim 'wear' measurements

Post by Gattonero »

Since the failure in the sidewall of a road rim will mostly happen due to 90-100psi pushing from inside-out, the problem is not "how worn" are the sidewalls, but "how straight" they are.
When deformation starts to happen, then it's time to be worried, then replace.
Put a ruler on the sidewall, see if you can see daylight. If there is a small gap you're fine. If there is a big gap, then you will also notice the top (where the hook is) is coming out thus the sidewalls not been parallel anymore. In fact, when the rim is worn (assuming like most of the rims have flat and parallel sidewalls) it will become concave.
Modern rims are remarkably strong, and will only break when there is minimal amount of material left. Given that an accurate measurement of the thickness is not always doable (how many people do have a micrometer at home??), to check the integrity of the rim by its shape is a reliable, quick and convenient way to do.
It is by riding a bicycle that you learn the contours of a country best,
since you have to sweat up the hills and coast down them.
Thus you remember them as they actually are...
fastpedaller
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Re: Rim 'wear' measurements

Post by fastpedaller »

Gattonero, Your findings above appear to be spot on - A good indication of impending change (or doom!)

Interestingly, today I decided to clean up an old pair of Mavic MA2's I had hanging in the garage - I'd removed the hubs from them to sell the hubs a couple of years ago. They were pretty black from braking in the wet, but came up nice with a scrub-up :) On examining them closely I saw some corrosion around and to the eyelets, but nothing to prevent further use. More worryingly the braking surfaces looked (on one anyway) quite worn, so I set about measuring them, with the idea of binning them if necessary rather than selling them. I was a little surprised (though I shouldn't have been?) that the remaining metal (measured in several places) was more than a brand new Mavic rim hanging nearby!
MikeF
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Re: Rim 'wear' measurements

Post by MikeF »

Problem is that you can measure the rim thickness where the tyre sits, but you can't measure the thickness in the box section. If you have a brand new rim you might be able to compare the widths of the rim, and deduce wear from that. As Gattonero notes the wear surfaces become concave, but as the tyres I use never have pressures in them more than about 50psi, I'm not sure it's tyre pressure that makes them concave.
"It takes a genius to spot the obvious" - my old physics master.
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foxyrider
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Re: Rim 'wear' measurements

Post by foxyrider »

IME it's less the pressure pushing out causing concave braking surfaces but just as significantly the pressure of braking crushing the rim. This crushing action is caused by more efficient brakes/blocks.

For a rim to actually fail it will almost certainly involve wear, pressure and crushing. Looking at the failed rims they've had a reasonable thickness of material but this has been compromised by the crushing/pressure to cause a split. Only one rim failed specifically by wear, a wear groove adjacent to the bead causing a catastrophic failure at 90psi around 50% of the rim but only on one side. This last failure was in 2009, since then the only rim failures have been internal face cracking from spoke holes - over tensioning by shop builders the cause - those i've built with same rims/hubs never suffered the issue. My current crop of wheelsets despite many miles of abuse in all weather's have not suffered any noticeable rim degradation - I can only assume the design/materials are superior to the generic Alex/Mavic etc rims that failed as the use hasn't changed. (I know Campag rims of the 90's were often described as being made of cheese!)

I have GP4 rims from the late 70's that show no signs of wear at all despite many years and kilometres of use. OTOH I've had a lot of wear damage and failure since the advent of dual pivot calipers with a variety of rims.
Convention? what's that then?
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Gattonero
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Re: Rim 'wear' measurements

Post by Gattonero »

foxyrider wrote:.... OTOH I've had a lot of wear damage and failure since the advent of dual pivot calipers with a variety of rims.


+1
How many times have I said this? :wink:

BITD, in the early days of Mtb rims and brake pads would last several seasons.... but the brake power was so poor compared to today's braking compounds and rim materials/manufacturing.
"the candle that burns twice as bright, burns in half time"

MikeF wrote:... the wear surfaces become concave, but as the tyres I use never have pressures in them more than about 50psi, I'm not sure it's tyre pressure that makes them concave.


See above, today's braking compounds are a lot more agressive than what used to be, also the brakes like dual-pivots or v-brakes have more force.
Even 50psi on the tyre would give a reasonable force to deform a worn out rim
It is by riding a bicycle that you learn the contours of a country best,
since you have to sweat up the hills and coast down them.
Thus you remember them as they actually are...
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531colin
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Re: Rim 'wear' measurements

Post by 531colin »

Even the very earliest wear makes the brake track concave. Maybe the edges of the rubber pads compress more than the middle?
By the time the thickness gets down to around a millimetre there is a good chance of the tyre pressure opening the rim out.
My guess is that the (outward) load from tyre pressure is greater than the (varying, inward) load from the brakes, but somebody else will have to do the maths.
Depending on the shape of the rim, you also get wear to the sides of the box section....I have seen the odd one worn into holes, but i have never seen the rim actually fail here.....fail as in the box section separate.
MikeF
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Re: Rim 'wear' measurements

Post by MikeF »

531colin wrote:Depending on the shape of the rim, you also get wear to the sides of the box section....I have seen the odd one worn into holes, but i have never seen the rim actually fail here.....fail as in the box section separate.
Interesting to know that because there's no way of measuring the thickness here. A comparison can be made with an unused rim, but that won't tell you the thickness left.
"It takes a genius to spot the obvious" - my old physics master.
I don't peddle bikes.
Brucey
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Re: Rim 'wear' measurements

Post by Brucey »

single box rims usually fold out at the top before they wear through lower down; I think I've seen one or two only (from about a hundred or more worn-out rims that I've examined) that didn't do this.

However quite a few three-box rims are designed to wear through into the side boxes and this is meant to alert you (relatively safely) to the fact that your rims are worn out.

Just for fun (i.e. to see what would happen) I built a wheel with such a worn-out rim in it; (it uses a hub brake so if the rim goes a funny shape it isn't a big problem, just so long as the tyre stays on...). The rim is a fairly lightweight one, (about 520g) and it is obviously rather deformed where the worn area is, so a rim brake would be a no-no. In fact in the worn area (which is a hole right through, about six inches long), it flares outwards at a jaunty angle when the tyre is pumped up hard (~70psi in a 37mm tyre), with the deformation occurring in the upper wall of the side box, rather than in the rim brake surface. But the tyre stays on and thus far this wheel has seen much local load-carrying duty. I expected the rim to deform more or split more but so far (several hundred miles, much of it loaded) it hasn't.

From this experiment, I would conclude that if your three-box rim wears through (to a side box) whilst on tour, the wheel is unlikely to fail altogether in short order; the biggest inconvenience is likely to be the fact that you can't safely use the brake on that wheel any more.

It may be annoying that this failure mode can't so easily be seen coming, but on the whole I think it may be the lesser evil for those folk who can't or won't keep track of their rim wear using other methods.

cheers
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Gattonero
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Re: Rim 'wear' measurements

Post by Gattonero »

Do not forget the spoke tension, too.
Having 32 or 36 stainless 14g wires that pull with 80-100kgf on the rim, that is some pretty good force that would exacerbate the problem. A rim that is too worn can start to separate along the side.

Just put a ruler on the sidewall, if the gap seems too big then replace. It's pointless to spoil a long planned tour that may have involved expensive travel tickets and accomodation, for the sake of saving £50 :?
It is by riding a bicycle that you learn the contours of a country best,
since you have to sweat up the hills and coast down them.
Thus you remember them as they actually are...
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531colin
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Re: Rim 'wear' measurements

Post by 531colin »

Gattonero wrote:..........Just put a ruler on the sidewall, if the gap seems too big then replace. ..........


But unless you have the experience, how do you know if the gap "seems too big"...?
You might just as well say "Replace the rim if it looks too worn".....how do you know?
If a rim looks worn, there are 2 things to do.....
1) measure the thickness using an Iwanson gauge, or modified vernier gauge, so you actually know how thick the wall is
2) start thinking about replacement wheels for your holiday.

Its not difficult to keep old, worn wheels for day rides and commuting, when you can keep them under observation, and have a reserve pair for touring.
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Gattonero
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Re: Rim 'wear' measurements

Post by Gattonero »

Any rim is different, there's no universal value for wear. I have observed many rims from different manufacturers, and most of them need to be very thin (<1mm) to get permanent damage.

A good rule of thumb is to observe the ruler, like said before: if the sidewalls (assuming they were not manufactured concave in the first place) are becoming concave, so that their top is flaring out over 2mm, then it's time to replace.

You may be lucky and still do another 2-3-5 thousand miles, but given how subjective is the rim wear for a given cyclist, I'd say it's not worth trying to milk out any possible mile out of a rim. The consequences are a ruined ride, trains are very expensive in this country :(
It is by riding a bicycle that you learn the contours of a country best,
since you have to sweat up the hills and coast down them.
Thus you remember them as they actually are...
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531colin
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Re: Rim 'wear' measurements

Post by 531colin »

Gattonero wrote:Any rim is different, there's no universal value for wear. I have observed many rims from different manufacturers, and most of them need to be very thin (<1mm) to get permanent damage.

A good rule of thumb is to observe the ruler, like said before: if the sidewalls (assuming they were not manufactured concave in the first place) are becoming concave, so that their top is flaring out over 2mm, then it's time to replace.

You may be lucky and still do another 2-3-5 thousand miles, but given how subjective is the rim wear for a given cyclist, I'd say it's not worth trying to milk out any possible mile out of a rim. The consequences are a ruined ride, trains are very expensive in this country :(


I think Open Pro are less than 1.5mm thick when new.
If the "top" of the rim flares out at all, it means the rim is too weak to withstand the pressure from the tyre.
How can rim wear be "subjective"? If its thicker than 1mm, its OK.....thinner than 1mm, replace.
Simples?

Do you mean put a straight edge on the brake track and look at the gap where the rim is concave?
If you get 1mm gap, its already dangerous.....because there isn't 1mm of metal that is safe to wear away on modern rims....if there is 1mm gap, the rim is already opening out due to tyre pressure.
If the rim was 2mm thick, you could safely wear away 1mm....but even then, you would need to be certain that the bits the ruler was on had no wear at all.
How do you measure the gap? I can measure the rim thickness directly.
Des49
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Re: Rim 'wear' measurements

Post by Des49 »

I have just measured some worn rims, the design can hide the measureable wear using an Ivanson gauge.

New Mavic MA40 2.0mm, well used MA40 1.7mm and loads of life left. The old Mavic rims were harder wearing for sure, modern ones are softer and wear quicker, plus thinner to start with!

Open 4CD, slightly worn as in the anodising on the braking surface is just gone, 1.6mm. An old design that lasts far better than the modern OpenPro.

Ryde Chrina new 2.0mm, worn out with holes visible on brake track as below pic, just less than 1mm on gauge on bead hook, but tricky to measure accurately.

Chrina
Chrina


Mavic Open Pro, new 1.6mm, worn out 1.0mm as measured, but when sectioned only 0.5mm in places. As picture below, I am currently riding one far more worn and concave than the example pictured below, only one year old! Using it locally only and will rebuild as soon as I have time.

OpenPro
OpenPro


Mavic X719, worn 1mm, when sectioned some areas 0.5mm. Another extremely soft rim which splays out with minimal wear, doesn't last long with any off-road use.

X719
X719
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