"it has less tread than the GP4000 SII and weaker sidewalls."

i think you're right about the weaker sidewalls. i don't think you're right about the less tread. unless you know something i don't know. everything i read says that the power competition is beefier in the tread, slightly less so in the sidewalls.

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Dan Empfield
aka Slowman

2.9mm GP4000 SII vs 2.6mm Power Competition according to BRR

Old 26 rims, 2.5 fast fred tires, latex tubes. No suspension.

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My latest book: "Out of the Melting Pot, Into the Fire" is on sale on Amazon and at other online and local booksellers

Actually the tests do basically confirm previous work. There's currently a relatively large group of tires very closely matched near the top of the heap now...so, other factors start coming into play when it comes time to select a tire.

One of the things I want to point out from that testing is that even on the somewhat large diameter roller that Wheel Energy uses, the curved contact patch is going to act like an "amplifier" to Crr, just not to the same extent as the smaller diameter rollers that myself and others use in our home tests. Even with that amplification, the spread between the tires tested isn't very large...within a handful of watts, so it's really not surprising that he was having a tough time determining differences in roll-down tests and the hill climb tests outside. The differences on a flat surface are going to be a fraction of the ones on the drum...which were small to start with. Combine that with all of the other uncontrollable variables, and you can see why roller testing is the preferred method for fine discrimination as opposed to rolldowns or hill climbs.

His personal roller tests were really just a repeat of the Wheel Energy smooth roller test...just with higher "amplification" due to the smaller drums. I wonder how he compensated for wheel rollout in those tests? It's pretty difficult to get an accurate roll out for various tires and pressures on rollers...which is why I resorted to measuring the drum speed instead of wheel speed in my tests (I put a magnet on one of the rear drums and mounted an ANT+ speed sensor to the roller frame.

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http://bikeblather.blogspot.com/

Okay. Thx. Didn't brr show the power comp as slightly puncture resistance tho? Vs 4000s2?

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Dan Empfield
aka Slowman

be careful people, someone has obviously hacked Dan's account

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TEAM F3 Undurance

Not one of the newer accel based ones. I put a magnet on the end cap and used a Garmin Speed/Cadence sensor. You can see it here: http://bikeblather.blogspot.com/...rs-chartand.html?m=1

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http://bikeblather.blogspot.com/

LOL

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http://bikeblather.blogspot.com/

Identical on the tread, worse on the sidewall iirc. Considering the uncertainty around the aerodynamics of the Power Competition, the logical choices are either the GP4000 SII where the aero likely washes the crr hit and you get better sidewall protection or the GP TT which probably has equivalent aerodynamics but better crr (TT has better sidewall, worse tread puncture resistance... sort of a wash).

For myself, personally, I'm sticking with GP4000 SIIs. The only tire that sways me is Vittoria's new tubeless Corsa Speed. According to Xavier (AeroCoach) they are "incredibly aerodynamic" when paired with the Jet+ rims. If that's true, coupled with their very low crr, it could be... very very fast.

...however, the idea of putting those tires on and taking them off makes me shudder.

I didn't find the Vittoria CS to be that hard to mount on Zipp FC rims, although in general that's a very easy rim to mount tires.

I've taken a Corsa Speed on and off a Hed Jet+ Black wheel a couple of times now...it requires a lever for the last bit going on (with most clincher tires/wheels I can do totally by hand), and metal levers are a good thing to have to get it started off, but it's not nearly the death struggle some other tubeless tires can be <cough...Hutchinson...cough>.

My issue with it is getting it to seal and hold air when set up tubeless...it leaks down worse than a latex tube inside. I've noticed some sealant "weeping" from under the sidewall coating (i.e. through the casing), so maybe it's just going to take a few days for the sealant to help things out.

For now I'd take those statements from Xavier with a grain of salt...he mentioned 2 other things at the same time that had me scratching my head. First, he said that a certain tire INCREASED Crr with wear (something I've never seen)...and secondly, he said the Corsa Speed rolled faster with a latex tube than when set up tubeless. I found no difference between the 2 conditions on my roller tests (makes me wonder if his tubeless setup was leaking air fast during the test!) So, that doesn't really give me much confidence in the veracity of the aerodynamic claim on the CS/Hed+ setup.

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http://bikeblather.blogspot.com/

Oh good... my only experience thus far has been with Hutchinson. Never. Again.

Yeah, I thought his statement about crr going down with a latex tube was a bit strange as well. With regards to his aero claims, I have the itch to try something different so...

*cue X-Files music*

Still hysteresis, but from torque rather than coasting.

Torque losses are a component that is generally ignored. I've noticed that a GP4000 makes more noise on a steep climb than a Corsa CX, which has nothing to do with pressure, but might have something to do with tire design and torque losses (or not). I haven't gotten ambitious enough to spend a day doing a controlled test that would satisfy me.

I'm still surprised that you got better results with such high pressure. IMO this would indicate a pretty huge hysteresis loss from torque. Schwalbe's testing on MTB tires indicates that Crr on rough surfaces is best with low pressures. http://www.mtbonline.co.za/..._Eng_illustrated.pdf Maybe 20psi on the front and 80psi on the rear would be ideal for a steep MTB climb?

Lots of things about the Bikeradar test are disappointing. Using butyl tubes in racing tires, no concept of how to do a controlled field test, no mention of vibration losses, etc. A better test is here: http://www.velonews.com/...s-cycling-tires-fast They tested a lot of the same tires (at Wheel Energy as well) and got different results.

Did your testing involve parts of the climb being ridden stood up?
If so I can see how that may explain the results you found.

It's possible to get reasonable results for estimating rolling resistance from rolldowns but differences are small so you have to be pretty obsessive about details. Most people aren't obsessive enough to get good data from rolldowns. Bottom line, the issue isn't that rolldowns can't work, it's that in a practical sense most people don't make them work.

On closer review, I'd like to add the caveat that something seems amiss with some of the rank order as compared to my and the BRR testing. The Turbo Cotton appears way too far down the list, comparatively...and the S-Works Turbo Tubeless I have didn't roll anywhere near that fast (relatively) on a smooth drum test.

Also, Wheel Energy appears to highly underestimate the effects of latex vs butyl tubes.

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http://bikeblather.blogspot.com/

Which sealant? Has it gotten any better? I used Bontrager TLR and a teaspoon of craft glitter on the Corsa Speeds and didn't get any weeping. It held air really well too. It's been pretty normal to need a few days of sidewall sealing on some soft cx and mt tires though.

Orange Seal. I started with 20ml and it leaked down fast. I tried another 15ml and still no change...although I may have goofed on the amount and not put in the full 15. I even tried laying it on alternating sides.

I then put in another 20ml, and now it seems to be holding air well.

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http://bikeblather.blogspot.com/

Got it. I usually go with the full 60ml/2oz per tire. It seems a good ounce or so is needed to seal sidewalls on supple tires and then the rest is left for 'sealing' stuff. I used to use a syringe and apply a bead of latex (mold builder from Hobby Lobby) against the rim's sidewalls all the way around before inflating the tires, but I don't think it really ever did anything other than waste time.