[Closed] We done the exploding plastic wheels?

Abuse anything enough and you can break it imo.

Wow! I do know fine well how dull and number obsessive roadies are these days but did you actually watch the entire 18minutes of a wheel spinning in a jig? If so do all us more normal folk a favour and post what time to FFWD to for the "explosion", eh?

😉

Ffwd, natch.

Pfft, this is a proper test

No. no it really isn't.

Unless of course you meant an IQ test.

Shows what you know

That second video, shame he didn't put as much effort in swinging the hammer as he did gurning.

Having read the piece about three times, I still don't understand the fundamentals of the test itself. What did they actually do?? Was it actually representative of anything the wheels might see in real world use?

Loading your resin system to maximise Tg onset and filament winding your brake track? (and then testing this feature?) - It's like making a tent out of steel and claiming yours is the 'most stable in the wind'

this forum would be a less populated place if everyone that dragged their brakes were punished by this happening ..... as it is they just get brake fade 🙁

I haven't bothered watching the video (obvs 🙄 ) so could someone please explain to me how the heat gets all the way from the rotor to the rim?

Its a rim brake roadie wheel

Do you need to view it in 4k to see the explosion?

From skimming the article it doesn't appear as if they tested an aluminium rim, just for a reference point it would have made sense.

So how are you really meant to tell if any of the results are actually [i]"better"[/i] if the type of rims that most road riders will actually have aren't even considered?

scotroutes - Member
I haven't bothered watching the video (obvs ) so could someone please explain to me how the heat gets all the way from the rotor to the rim?

Scotroutes and epicyclo- I applaud

If so do all us more normal folk a favour and post what time to FFWD to for the "explosion", eh?

7:30 for the Roval, which is the most drastic failure.

From skimming the article it doesn't appear as if they tested an aluminium rim, just for a reference point it would have made sense.

So how are you really meant to tell if any of the results are actually "better" if the type of rims that most road riders will actually have aren't even considered?

Not sure if you're serious or not? It's a test of carbon rims and how they handle heat, not a test of aluminium rims. Plenty of people have carbon rims, and their (in)ability to handle heat is a commonly leveled complaint. I'm not sure a 'reference point' of an alu rim would be any use whatsoever - have you melted many aluminium rims? They'll go to far higher temperatures, but everyone knows that.

I personally agree it's a test with little real world relevance sponsored by a brand, whose product miraculously vastly out performs every other on test. If you want to drag your brakes for 3 minutes at a time, whilst outputting 1200W, with zero airflow over your rims, then it's probably useful.

One thing I did find interesting is how long it took the rims to cool down (far longer than it took them to heat up). Now, again, zero airflow over the rims, but even so, I'd have expected a few seconds to cool down again, not >5 minutes.

I'd like to see something a bit more 'real world', and would like to see some Chinese rims chucked in for good measure. I'd also like to see multiple rims from each brand sampled, to see if there's much variation, I suspect there would be with some. I still think it's interesting in its most basic conclusion though - what temperature common carbon rims fail at, even if that doesn't really translate to real life.

Ha ha 😆

Thanks.

Is it really a representative test-
-Lever force
-Test pattern, do people really hang on the brakes constantly for 2+mins ?

I could go on, doesn't seem that scientific or well thought out, more of a willy waving contest.

Test pattern, do people really hang on the brakes constantly for 2+mins ?

Yes. I'm thinking Alpine Pass

In the old days people melted the glue holding on tubs in the same way

PS I think the real world gets more air flow than this test

PPS yes we need an Al rim for reference. An Al rim won't melt but enough heat will burst the tyre

My wife has the brakes on all the way down every hill. Doesn't ride bikes very much. 🙂

Oh 1200W. It's all BS then

Audit trail my worn answer

I would need to loose 12m of height a second to sustain that. On 1 in 4 that is 48 m/s think that is nearly 100mph. Oh and despite descending a 1 in 4 at 100mph and failing to slow down, I'm still only pulling on one brake lever!!!

Damn that is all wrong. I think it's only 1.2m a second. That sounds plausible

1200=mgh

m=100Kg
g=10
h=1.2m

That is under 10mph on a 1 in 4..

May be it is possible

I think weight becomes an issue though, due to inertia.

As above, I think it’s a test to pander to the strengths of the sponsor’s product, but probably some interesting conclusions that can still be drawn.

One of those is not that an aluminium rim is needed. That’s like saying you need to include a family hatchback in super car group tests as a baseline. Totally irrelevant.

One thing strikes me about that test - if I recall correctly they used the same brake pads on every rim. Now I recently went on some tech/sales training at a major manufacturers UK HQ, and their top UK tech guy said you should always use the pads the manufacturer recommends as they’re matched to the resin in the rim. They won’t warranty any wheel that’s been used with anything other than their own brand pads as they know it compromises performance and longevity.

Sod em, they're only roadies and anyway they'll all be on discs soon enough.

One thing strikes me about that test - if I recall correctly they used the same brake pads on every rim. Now I recently went on some tech/sales training at a major manufacturers UK HQ, and their top UK tech guy said you should always use the pads the manufacturer recommends as they’re matched to the resin in the rim. They won’t warranty any wheel that’s been used with anything other than their own brand pads as they know it compromises performance and longevity.

Hang on a mo.... one of the supposed disadvantages of disk brakes for pro riding is the likely incompatibility of disk hub widths when using "neutral service" wheels. Now you're suggesting that caliper brake pads need to be matched to the rim?

Braking’s already compromised on neutral service wheels as they’re alu, the brake track is in the wrong place etc, but they fit, and they’re an emergency solution. With disc wheels they plain won’t fit if it’s QR and you’ve got through axles or whatever.

IMO they’re right to standardise pads, manufacturers say loads of stuff people ignore. It’s just another unnecessary variable.

I'm definitely not an engineer and am probably being very dense but on the bit I viewed the wheels where holding a pretty constant 19.5 MPH for 184 seconds with the brakes applied. Surely in a real world situation (ie coming down a hill) you'd come to a stop reasonably quickly or would be reducing the pressure on the brakes to maintain a constant speed as you scrub off speed. Isn't this test effectively showing someone pedalling and adding energy to the system whilst also braking? Surely the amount of force applied to the brakes is also relevant?

In a fairly litigious society with a fair few carbon rims out there I'm sure we would have heard is any carbon rims had actually exploded in the 'real world'.

-- Edit --

and am probably being very dense

Clearly this (again)! I've spotted the forces applied to the brakes in the bumpf at the beginning and probably talking tosh!

Not sure if you're serious or not? It's a test of carbon rims and how they handle heat, not a test of aluminium rims.

No I was quite serious, the test tells us that a carbon rim lasts between 120 and 1200+ seconds of simulated brake dragging depending on the model, but a fair few of the punters looking at this will likely be using aluminium rims and considering the upgrade to carbon, so putting a sample aluminium rim through the same test would provide a bits of useful context and would probably demonstrate a slightly different failure mode...

I don't see why it's such a terrible idea...

I'd also like to see how a carbon rim with an aluminium brake track got on under the same protocol, and if it failed in a different way...

The other thing that would have been useful would be seeing some sort of measurement of CoF, the Alto rim might last 1200+ seconds but is that 1200 seconds of effective braking, or terrifying, levers to the bar screaming towards armco and death?

The truth is it's half a job, and demonstrates what those funding the tests wanted, but it does not really provide enough information to make a truly informed decision... IMO of course.

No I was quite serious, the test tells us that a carbon rim lasts between 120 and 1200+ seconds of simulated brake dragging depending on the model, but a fair few of the punters looking at this will likely be using aluminium rims and considering the upgrade to carbon, so putting a sample aluminium rim through the same test would provide a bits of useful context and would probably demonstrate a slightly different failure mode...

Fair enough, I still maintain that as alu rims very rarely fail at all in this mechanism it's not at all useful. Indeed I think you'd have to get the rim hot enough to melt the bead of the tyre (as they're running it tubeless aren't they?), or to just melt the rim.

Which alu rim do you include too? An Open Pro? Can't imagine many people going from Open Pros to a carbon rim. A Ksyrium? Doesn't bear much relevance to many people's rims, etc etc.

The other thing that would have been useful would be seeing some sort of measurement of CoF, the Alto rim might last 1200+ seconds but is that 1200 seconds of effective braking, or terrifying, levers to the bar screaming towards armco and death?

As the force is constant the speed of the wheel offers exactly that, and it's pretty consistent at 19-20mph. Interestingly on the Altos it's more like 20-21mph, which does suggest a slightly lower CoF. Whether that's the difference between 'oh good, I'm slowing easily' and 'AAAAAAAAAAAAAGH, ARMCO FIRE DEATH' I don't know. Seems unlikely.

njee20 - Member

Fair enough, I still maintain that as alu rims very rarely fail at all in this mechanism it's not at all useful.

TBH though you can say the same of carbon rims

Which alu rim do you include too? An Open Pro? Can't imagine many people going from Open Pros to a carbon rim. A Ksyrium? Doesn't bear much relevance to many people's rims, etc etc.

Open Pro, CXP even something basic, I agree the failure would most likely be the pads or tyres beginning to melt, but without it actually being demonstrated that's just conjecture...

As the force is constant the speed of the wheel offers exactly that, and it's pretty consistent at 19-20mph. Interestingly on the Altos it's more like 20-21mph, which does suggest a slightly lower CoF. Whether that's the difference between 'oh good, I'm slowing easily' and 'AAAAAAAAAAAAAGH, ARMCO FIRE DEATH' I don't know. Seems unlikely.

Is the force constant? The pressure applied to the Pads is, and the wheel speed is, but that's down to what the motor controller is set at...

A simple way to do it might be to monitor the motor current (assuming torque isn't available) this would at least indicate the effects of friction betwixt pad and rim and how hard the motor is working to maintain 20mph...

Is the force constant? The pressure applied to the Pads is, and the wheel speed is, but that's down to what the motor controller is set at...

A simple way to do it might be to monitor the motor current (assuming torque isn't available) this would at least indicate the effects of friction betwixt pad and rim and how hard the motor is working to maintain 20mph...

Watch the video, that's almost exactly what the first slide says.

Motor controller is set for 1200W, pad force is constant, wheel speed is the variable.

The only improvement I can see is they could modulate the brake lever force with a servo and keep the speed constant, but judging by the speed's the CoF was fairly consistent. Anyone want to watch the whole thing and see if there's a correlation between wheels speed (assume that's proportional to 1/CoF) and time to failure? If there's not then it would be fair to assume the test is fair.

TBH though you can say the same of carbon rims

Can you? Pretty common failure mechanism among road rims I'd say. Certainly plenty of photos on Google and lots of stories on forums about it.

Anyone want to watch the whole thing and see if there's a correlation between wheels speed (assume that's proportional to 1/CoF) and time to failure?

There isn't - like I say, they're virtually all at 19-20mph at point of failure, and indeed from about 2 seconds into each test.

Can you? Pretty common failure mechanism among road rims I'd say. Certainly plenty of photos on Google and lots of stories on forums about it.

Another test would be to do it in a tank of typical british mountain biking/CX muddy slop. Wonder how long an aluminium rim would last before being worn out and exploding.

The biggest flaw TBH is that rim braking carbon is niche, and going to get nicher. Racers with money might use it, but MAMIL's with money will get disk brakes. Everyone with less money will be on aluminum rims. So the only people using carbon rims, are going to be lighter, and you'd assume know not to drag their brakes for 5 minutes constantly down a 1in4 slope.

I'm not that sure it is niche really. Niche among folk on here maybe, but carbon clinchers really aren't all that uncommon, all 3 of the guys I ride with most regularly own carbon clinchers (none race).

I accept that carbon rims will get more popular as discs proliferate though. I didn't take my nice, light, (carbon) rim braked bike to the Alps though for basically the reason in the test!

In a fairly litigious society with a fair few carbon rims out there I'm sure we would have heard is any carbon rims had actually exploded in the 'real world'.

There's a fair few descents where you can hold 40+mph for a good chunk of time - a nervous descender could easily be dragging brakes for 10+ mins over a long descent.

Is it really a representative test-
-Lever force
-Test pattern, do people really hang on the brakes constantly for 2+mins ?

I think it's representative so long as the lever force is representative of what you might actually achieve in the real world.
The time is also representative as it demonstrates the total capability of the rim to resist the braking temperatures - its a time at temperature mechanism. the key here are the temperatures achieved, so if you achieve those braking temps for 10 second on a real descent then you've used up 10 seconds of your 120sec 'life'. Hit the brakes hard for another 10 seconds, then that's 20 seconds of your wheel life gone. I'd have though that would be a handy thing to know or be aware of, especially if you hit the big Alpine descents a lot.

The only thing that is missing is for people to calibrate themselves as to how hard to pull on the lever to manage the braking temperatures so they can manage rim life. I suspect its one of those things where there is a temperature threshold - so one degree below it's not an issue, 1 degree above then you're eating into your rim life. Your better long descent strategy might actually be to drag your brakes gently to control speed thereby generating lower rim temperatures, rather than to roll to a higher speed then hit the brakes harder generating much higher braking temperatures.

Constant lever force is ok I think, it's a lab test. In the same way that headtubes are tested by sticking a big bar through the tube and applying force there'll always be a degree of simulation which won't bear much relevance to the real world.

I don't have any actual problem with the test itself, I'm just cynical becuase there are enough oddities (1200w power output, zero mass, no air flow etc), and the fact the sponsor's wheels perform so much better makes me dubious. Maybe that's unfair, and Alto rims really are the ones for people who live in the mountains.

In a fairly litigious society with a fair few carbon rims out there I'm sure we would have heard is any carbon rims had actually exploded in the 'real world'.

As said, it really is a common failure mechanism. I've read about members on here experiencing it. Someone stopping to avoid a bin lorry on a steep descent on Chinese rims IIRC.

Your better long descent strategy might actually be to drag your brakes gently to control speed thereby generating lower rim temperatures, rather than to roll to a higher speed then hit the brakes harder generating much higher braking temperatures.

That's where I found the time to cool interesting, being roughly twice as long as the time to heat up, which does suggest that even 'proper' technique will likely result in a rim which gets progressively warmer on a technical descent.

+1 fifeandy

Brake dragging is really not a good idea

The usual advice is the opposite to that - higher speeds mean more air cooling and more 'free' braking due to wind resistance.
Dragging results in more heat build up in the wheel and less ability to cool it.

But how much cooling do you want and need? It's all about managing peak temperatures with carbon. Above a certain temperature the glue is affected and therefore rim life is. Below that threshold the glue is fine, so as long as you manage your rim temps then you can drag your brake as long as you like. Mechanical wearing of the rim then becomes the issue that determines rim life just as with alloy rims.

At any given applied brake force a certain amount of energy is imparted into the rim. The temperature that 'builds up' depends on how well you can cool the rim. At relatively light braking forces the temperature is quite cool and constant i.e. it doesn't build up and continue to increase. At very heavy braking forces you might not be able to cool quickly enough so rim temps might very well continue to rise and build up.

The aerodynamic braking effect is marginal. In the same way as you need more and more power to get to higher speeds because drag increases to the square of speed, when it comes to braking the same effect applies - the drag reduces to the square of speed, so aerodynamic drag as an aid to braking is not very effective other than at very high speeds. As soon as you slow down the drag effect drops off very very quickly.

Old rules may not apply. You might need to choose between descending more slowly and carefully to manage rim temps and preserve rim life, or descending quickly and brake harder, but eat up rim life more quickly.

But it's all academic. For the majority of us who are not hitting the Alpine descents week in week out, I suspect it's not an issue unless you're routinely a really heavy braker. And for those of us who do hit the Alpine descents how many of us are really hitting them like a Pro? I don't, I'm like an old woman.

And for those of us who do hit the Alpine descents how many of us are really hitting them like a Pro?

purely anecdotal, but a bloke who works for a locally-based team told me they delammed 6 front Campag Boras during the Pyreneen stages of the TdF two or three years back. Obviously being tubulars they didn't result in any spectacular failures but it's interesting that the riders *probably* aren't your average brake dragger unused to 80+km/h descending.

And for those of us who do hit the Alpine descents how many of us are really hitting them like a Pro? I don't, I'm like an old woman.

But that means you're braking far more, and you have clinchers, and you don't have the full width of the road to use, and you have to worry about what's around corners etc etc.

The "pros are fine" point is a really daft one IMO!

so aerodynamic drag as an aid to braking is not very effective other than at very high speeds

I don't, I'm like an old woman.

And for those of us who do hit the Alpine descents how many of us are really hitting them like a Pro?

Someone stopping to avoid a bin lorry on a steep descent on Chinese rims IIRC.

[url= https://www.bikerumor.com/2017/12/14/enve-mavic-boyd-respond-alto-cyclings-carbon-rim-brake-test/ ]Mavic, Enve and Boyd respond to test[/url], they agree with points made here - Alto do so well because it appears their rims generate lower friction, so yes, they don't heat up as much, but they also don't stop as well. They also say their rims would have stopped you so much earlier they're effectively penalising better braking performance. Mavic just say they're lying (paraphrasing).