Carbon wheel testing

[John H.]

This could have some merit.

As a data point- Levi's Grand Fondo banned carbon rim brake clinchers for this very reason.
Brake draggers have a tendency to get blowouts, and/or delaminate rims.

[sandyrs]

Originally Posted by MesiJezi

Hmmm... I think they should probably test the alta rim to failure and publish the results of that test.

What they've done is set the arbitrary test parameters to a point where every wheel failed except theirs. The alta wheel could possibly have failed 1 second after the 40 minutes of testing were up, or with an additional .1 lbs of braking force, or with one additional watt of power applied... etc.

This testing certainly wouldn't have me running out to buy alta wheels over any of the other major brands.

Considering every other wheel failed within 5.5 minutes of "phase 1" I don't really see the merit of testing the Alto wheels until failure. Either you buy into the testing method here, in which case the Alto wheels have already proven themselves vastly superior to every other wheel ever, or you don't, in which case prolonging the flawed test is meaningless. But if you buy into it, do you really care if the Alto wheel lasts 10x, 12x, 100x longer than the others? By this testing procedure, they're already clearly "superior."

[OldCrank]

I found it interesting, and as someone who has had to feed his family by testing (semiconductors, power systems etc.) I consider myself more cynical than average.

The report passes several initial sniff tests.

But, yeah, a 1900W electric motor will crank the heat higher than I ever will while riding. Can somebody analyze some Strava power figures in the Alps and calculate a comparable braking "wattage" for descending (not braking minus braking force)?

The comments late in the article, from wrenches in the Alps sound propah: "Don't use carbohoops if you're an inexperienced brake-dragger on vacation".
BOOM

[zap]

When testing the Alto wheels (long video in the op link), rim temps start to decline after 300 or so seconds. To me, this indicates that the brake pads are no longer doing there job. So the rim may not explode, but you might miss a turn and fly over the guardrail.

[chiasticon]

Originally Posted by zap

When testing the Alto wheels (long video in the op link), rim temps start to decline after 300 or so seconds. To me, this indicates that the brake pads are no longer doing there job. So the rim may not explode, but you might miss a turn and fly over the guardrail.

yep. the speed shown is also higher than the other wheels. as Angry said: there's less friction, and so less heat, therefore they last longer. but there's also less actual stopping going on!

my biggest takeaway is that they didn't test any wheel "systems" other than their own. it's like Campy testing Sram and Shimano groups with Campy cassettes on the wheels and saying "see? it doesn't shift as well!" (a more valid comparison before 11 speed, I know. but still...)

the wheels were designed and tested to be used with specific brake pads, so test 'em with those. that said, both Boyd and Zipp (and maybe some of the others) have said that Swiss Stop Black Prince pads are OK to use with their wheels. which just takes me back to my first point: why aren't the Alto wheels slowing down as well?

[muz]

As an engineer, this strikes me as a bogus test. The way you test a brake system is this: You use a heavy flywheel to drive the carbon wheel under test. Bring it up to test speed, then apply brakes with no additional power added. If a brake system is effective, it will bring the wheel to stop quickly. Repeat until failure, increasing flywheel weight if necessary.

The obvious fallacy in the cited test is that efficient wheels which can apply a lot of braking force will be stressed more than wheels with slippery brake tracks. Which wheels would you choose going down an Alpine pass in the rain?

[ergott]

Max temps are interesting and Boyd did real well there at over 300deg.

That seems like a more realistic measure of stopping power before failure.

[DRZRM]

This makes sense if you are testing braking effectiveness, but their intent was not to see which rim stopped best, either initially or over time, It was rather a test of which rim would not fail violently under ham fisted and unsafe braking.

The safest riders will brake hard before corners and accelerate again, they may brake hardest, but they are unlikely to put their rims at risk because they get back off the brakes and accelerate after the turn (I suppose a very long straight decent or a huge group ride like a fondo in which high speed until the corners is unsafe or impossible could/would make that less true). My understanding is that carbon failure is more likely among folks more uncomfortable descending who continually drag their brakes over long periods until their rims delaminate and can fail catastrophically. This test may not be a perfect representation of that type of abuse (there are totally fair critiques of the test above, especially the critique about using a common brake pad) but to suggest it does not fairly "test braking" ignores the point of the test and article, of course it doesn't.

I did read the whole linked article, but didn't watch the longer video. If, as stated above, temperature drops after 300 seconds (5 minutes right?) by that point hadn't the Altos already outlasted all but one of the other wheels. Overheating clearly negatively impacts brake function, and it delaminated the Altos too, but they didn't fail catastrophically. It won't make me rush out and buy any, I'm 6'3" and 220, I would never own carbon rim brakes, but it seems like a valid thing to test for, even if the test could and should be improved.

Originally Posted by muz

As an engineer, this strikes me as a bogus test. The way you test a brake system is this: You use a heavy flywheel to drive the carbon wheel under test. Bring it up to test speed, then apply brakes with no additional power added. If a brake system is effective, it will bring the wheel to stop quickly. Repeat until failure, increasing flywheel weight if necessary.

The obvious fallacy in the cited test is that efficient wheels which can apply a lot of braking force will be stressed more than wheels with slippery brake tracks. Which wheels would you choose going down an Alpine pass in the rain?

[ergott]

I'd rather have rims that brake better and are no likely to fail under most conditions than one that won't fail but the braking performance isn't as good. If I'm going on terrain that will have high traffic and steep, twisty descents I'll leave those wheels behind. 95% of the riding out there is just fine for all those wheels.

[muz]

Yes, I follow your argument. The problem is that when you brake, you are supposed to slow down, which in turn reduces the load on the brake track. When it's driven by a motor, not so much.

Imagine this thought experiment. Let's say Enve engineers were allowed to spray their rim with a lubricant when they felt like it. Do you think their rim would have failed? You can't apply constant pressure on the brake lever and assume that all rims are behaving the same. In real life, if you don't slow down, you pull harder on the lever. This is why you need a flywheel that you stop rather than work against a motor.

BTW, you can make the flywheel very large if you want to simulate dragging your brakes.

Originally Posted by DRZRM

This makes sense if you are testing braking effectiveness, but their intent was not to see which rim stopped best, either initially or over time, It was rather a test of which rim would not fail violently under ham fisted and unsafe braking.

The safest riders will brake hard before corners and accelerate again, they may brake hardest, but they are unlikely to put their rims at risk because they get back off the brakes and accelerate after the turn (I suppose a very long straight decent or a huge group ride like a fondo in which high speed until the corners is unsafe or impossible could/would make that less true). My understanding is that carbon failure is more likely among folks more uncomfortable descending who continually drag their brakes over long periods until their rims delaminate and can fail catastrophically. This test may not be a perfect representation of that type of abuse (there are totally fair critiques of the test above, especially the critique about using a common brake pad) but to suggest it does not fairly "test braking" ignores the point of the test and article, of course it doesn't.

I did read the whole linked article, but didn't watch the longer video. If, as stated above, temperature drops after 300 seconds (5 minutes right?) by that point hadn't the Altos already outlasted all but one of the other wheels. Overheating clearly negatively impacts brake function, and it delaminated the Altos too, but they didn't fail catastrophically. It won't make me rush out and buy any, I'm 6'3" and 220, I would never own carbon rim brakes, but it seems like a valid thing to test for, even if the test could and should be improved.

[chiasticon]

Originally Posted by muz

This is why you need a flywheel that you stop rather than work against a motor.

this is what Zipp does, since at least 2010. I'm sure they have something more advanced now: https://youtu.be/hlvuQi5S-NQ?t=5m35s

Enve does something similar to the test in question: https://www.youtube.com/watch?v=t2ix_WbfqGs

[Heisenberg]

fwiw the Alto hoops stop well with Black Princes. They're not at Zipp Showstopper level, but they're about as good as a Bora.

They're also freakishly stiff, but ride quite well. They'll reveal any noodles your frame has.

[m4rk540]

Originally Posted by DRZRM

This makes sense if you are testing braking effectiveness, but their intent was not to see which rim stopped best, either initially or over time, It was rather a test of which rim would not fail violently under ham fisted and unsafe braking.

The safest riders will brake hard before corners and accelerate again, they may brake hardest, but they are unlikely to put their rims at risk because they get back off the brakes and accelerate after the turn (I suppose a very long straight decent or a huge group ride like a fondo in which high speed until the corners is unsafe or impossible could/would make that less true). My understanding is that carbon failure is more likely among folks more uncomfortable descending who continually drag their brakes over long periods until their rims delaminate and can fail catastrophically. This test may not be a perfect representation of that type of abuse (there are totally fair critiques of the test above, especially the critique about using a common brake pad) but to suggest it does not fairly "test braking" ignores the point of the test and article, of course it doesn't.

Braking technique can be a scapegoat. Out here, from first hand accounts, almost all carbon rim failures have occurred on short, super steep descents, 2 to 3 miles at 8% plus. The riders were not "brake draggers" but the majority did weigh over 200 pounds.

[glepore]

Originally Posted by Heisenberg

fwiw the Alto hoops stop well with Black Princes. They're not at Zipp Showstopper level, but they're about as good as a Bora.

They're also freakishly stiff, but ride quite well. They'll reveal any noodles your frame has.

Lightweight/Carbone Ultimate stiff?

[Heisenberg]

Originally Posted by glepore

Lightweight/Carbone Ultimate stiff?

Stiffer. I've never ridden a stiffer wheel.