Mine is more like 25.5mm or 26mm outside width IIRC - but those are Jet Blacks, so maybe they are a bit different? Or maybe your sample is just quite small?

IME, it's not so much that one type of tire heats up differently than another, than it is that higher Crr tires heat up more (in an absolute sense) than lower Crr tires...which makes sense from a physics standpoint.

That's also why my temperature compensation is in terms of %change per degree. I also found that when riding on the road, the tires DO end up hotter than ambient (with the delta larger for higher Crr tires), with the absolute number controlled by the ambient air temp. That's why I "correct" my results to 20C ambient.

All tires take quite a bit of time to heat up and stabilize, which is why I've settled on the protocol of running the tires for 5 minutes at 95 rpm, followed by a quick power meter zeroing, and then 4 minutes at 90 rpm. The data reported is then the average of the final 2 minutes of the 90 rpm stretch. With that initial higher power "charge" the steady state temp at 90 rpm seems to occur earlier. It also seems to result in a fairly steady power requirement in the final 2 minutes, but I can usually still detect some power drop during the first 2 minutes of the 90 rpm run if I look at the power trace carefully (i.e. power axis magnified).

Btw, in your Crr numbers you're stating, are you missing a zero?

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True, but as we've seen, if the Crr is low enough, then despite that early stall condition, the tire/wheel combo can be faster overall, especially within the narrow (relatively speaking) yaw angle range in which I'd expect a fast guy like Jens to be operating ;-)

That said though, if one can find a smooth tire (like the SS) that has nearly the same low Crr, then yeah...it's probably better to go that route, from an overall speed standpoint.

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http://bikeblather.blogspot.com/

I just put fresh 4000s tyres (23) on a flo 90 front and super 9 rear. Sans a puncture I'm leaving watts in the Table it seems. After all these years of the King being recommended on this forum why has it taken this long for info to come out? Or wS it always out there if you dug deep enough ...

Always been out there. The GP4ks is still a very good tire crr+aero, and for the average triathlete it is a good option. Anything beyond that is mostly a matter of risk tolerance. I've always felt most comfortable with the GP4ks but this year I think I'm going with a pair of Conti TTs to save a few watts.

It's always been out there. GP4ks have great aero and puncture resistance, so they are the best choice for most people. They don't have the best Crr and they aren't the flat out fastest though (usually).

Thanks for your work on testing the TT and the Corsa speed. I was looking at those 2 for my enve 7.8. I decided on the GP TT because of the added protection from vectran layer.But since enve does not recommend latex tubes, I'd be using light butyl tubes. My other option is to run the corsa speed tubeless. It doesn't have an anti puncture barrier, but sealant should take care of punctures, right?

I might have to bite the bullet and try both out.

 

Yep, that's me. Hope you have a good comeback year! What races are you planning?

World Masters Games, US Nationals, UCI Master Worlds (Austria), Oregon & CA state TTs, Mt. Ashland Hill Climb. Some of these may just turn out to be vacations if I'm still in poor shape....

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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

Say what?

That's what I said. I had my shop call enve and check

I talked to someone at Enve a couple of months ago and they said that latex tubes were ok to use on the new rims with the new textured brake track.

What's their rationale? What do the wheels have to do with the tubes you run?

Taken from their website

https://enve.zendesk.com/...ENVE-Clincher-Wheels

Their "inflate the tube outside the tire" example is laughable...and I bet they were using plastic rim strips with the latex tubes. Don't do that. Use tape intended for tubeless applications.

Of course,braking on carbon surfaces is silly in the first place, so....

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Never specifically had a problem with my 404 or 808/Super-9. Although I tend to minimize braking as much as possible.

Agreed: We know +/-10 degrees yaw is more common than we used to think, so that range is most important. Wider yaw is less important. But not unimportant. An objective weighting scheme is attractive, to include high yaw performance at the right level of importance.

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Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)

This sounds unlikely.
A trip would normally be expected to cause early transition from laminar to turbulent flow but rather than cause flow separation and an early stall it would normally cause the exact opposite. Turbulation would energise the boundary layer, delaying flow separation (stall).
Earlier transition to turbulent boundary layer would increase drag a little. So at low angles of attack the drag would likely be higher for a "tripped" design. However at greater angles of attack (i.e. bigger "wind yaw" angles) the tripped boundary layer should be more robust to separation and delay a sharp increase in drag due to stall.
Of course if some other part of the tyre/wheel trips the flow further aft anyway, then drag may always be higher for the tripped tyre, but I don't think your comments about flow separation are correct. This is just based on the underlying aerodynamics. I don't have any direct experience with tyres/wheels.

Tom, what are your thoughts on tire choice for a rear wheel in a frame that fares the majority of the leading edge, for example my P3C? Should we be biasing our decision-making even further towards crr and not worrying so much about aero? On my Renn 555 in the back of my P3C I've been running the Force 24C because a) low crr, and; b) it is fairly wide which might help a bit with arse comfort (Renn disc is very stiff, obviously).

That tire probably isn't the very best match to the Renn but I'm thinking with probably the upper 80% of the leading edge being hidden from the wind anyway, maybe it doesn't matter. But then I wonder if what happens at the trailing edge is important. Overthinking, no doubt.

But in general, in a fared back wheel is crr the boss?

Cheers,
Rich.

No, you're right to worry about what happens at the trailing edge as well. Too much of a discontinuity isn't a good thing there either drag-wise.

Yes, for rear tire selection, Crr tends to weigh in more than aerodynamics than it does on the front. That said, there are a LOT of tires with low Crr that aren't uber-wide, so it's not necessarily an "either/or" situation. But, as you point out, other factors (such as the ability to run a lower pressure with a slightly wider tire, and hence "comfort") might come into your personal calculus as well.

In other words, "it depends" ;-)

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Sorry, you're right and I've sloppily misused the word "trip." The edge of the tread doesn't trip the flow in terms of boundary layer transition, but it may disrupt the flow. And in the adverse pressure gradient on the leeward side of the tire, this may lead to the earlier separation seen on some tires than on otherwise similar tires with a smother tread edge. We can often see earlier stall and the characteristic increase in drag.

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Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)

I'm curious how much of that observation about "open tubular" style constructed tires is due to the "lip" ("Don't you give me no lip!" ;-), and how much is due to the naturally rounder leading edge shape that a very flexible casing with a thin glued-on tread will take...especially as compared to some of the "tunnel queen"-type tires like the GP4000S that have a decidedly parabolic profile molded into the tread area?

This sounds like something that could be studied with CFD...

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