Something went seriously wrong with your testing. Not trying to be a jerk, just being objective.

jeffp wrote:

doesn't make sense compared with Tom's testing. he had GP TT at 13w per tire at 40kph. if you take 12w off that puts your corsa at 1w

It doesn't work that way. The rollers cause much greater deflection in the tires than flat road, so they exaggerate the power requirements. My CRR calculation takes into account the weight, the roller diameter and distance, etc. So ignore the roller watts. It's the CRR that matters. If you really want, you can convert it into road watts, based on your weight &etc. Then it would come out to the 25-30 watt range for a pair of tires.....


For kicks, try this:

http://www.analyticcycling.com/ForcesTires_Page.html




Use the defaults but change the slope to 0. It would take about 289.5 watts (total, including CRR, wind resistance, &etc) to go 12mps (about 26.8 mph) with the Contis. With the Vittorias, it would take about 285.3 watts.

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which is what tom had for the GP TT

Uh huh.

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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

Yeah...that's odd. What "vintage" Open Corsa is that?

Also, I forget, but what diameter and material are your rollers?

And what are you using for your wheel speed indicator? If it's possible, if you trigger wheel speed off of the roller instead of the wheel, then rollout doesn't matter :-)

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http://bikeblather.blogspot.com/

This is a very new "Corsa Speed." Rollers are aluminum, ~3.4 inch.

I see that you measure the roller speed. Great idea. I'm working with a very old powertap however.

I don't think this result is that extraordinary. The BRR guy has this tire at 7.7 watts vs. 9.9 for the Conti GP TT. After adjusting for rollout, my test probably shows a somewhat larger difference. I'll run it again, a little more rigorously. But this difference is much bigger than any variation in test conditions could explain.

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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

Are you considering that he tested the GP TT with a butyl tube and the Corsa Speed tubeless (should be same as with latex tube)? Also the GP TT he tested was a 25C, while I (and you) tested a 23C?

For some reason, I couldn't get as consistent results from my PT wheel data as from the crank PM...I think it might have to follow with the relatively low power levels of the testing and the resolution of the PT readings. I still use the PT wheel for most testing, but not its power output.

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http://bikeblather.blogspot.com/

Some observations for discussion mainly from my own field testing. I'm only interested in tyres at the faster end of the spectrum and these observations are for clinchers from Vittoria (including specialised), Veloflex and continental. It would be fairly easy to prove or disprove some of these ideas but it would take time that I don't have right now.

The crr of different models of tyre respond differently to changes in temperature. In other words to account for changes in tyre temp the correction factor for each tyre, if wanting to be precise, would be unique.

The crr of Continental tyres is effected more by temperature than Vittoria. I don't have enough experience with the VF record to form a judgement. In particular continental tyres seem to get proportionally slower when tyre temp gets below about 10'C.

Initial 'break in' of Continental tyres leads to a greater reduction of crr than with cotton cased tyres.

My gut feel is that long term break in of Vittorias can make them really fast. It would seem that it's not just road miles that count here like with continental but actual age to.

Tyres with 'negative relief' tread pattern, like continental, have a slight advantage when tested on rollers (or turbo in my case) if the tread pattern comes into contact with the roller. I expect this is more pronounced on the small diameter roller of a turbo.

I had a 'magic' Conti Attack (this was before Tom A's testing of different Attack tyres). From new it was split/cracked ever so slightly where the tread ended and the sidewall begun. It was amazing so I bought another one, unfortunately that was normal.

I first bought a Conti TT 3 years ago. It was fast but the tread delaminated. Not too badly but in small, symetrical diagonal waves along the grain of the carcass. I thought it might have been due to using it to warm up on the turbo, it only had a few couple of hundred miles on it. Last year I thought I'd test one again but exactly the same happened within 100 road miles. I have't tested to see if crr is effected.

Interesting observations.

For now I'll just add that I have seen the split/cracking/delamination on Continental's Attack, Force, and GP TT tires several times. I know one of my friends have sent some back that did it after a fairly short while and gotten them to send new ones.

this is the crux of it all- are these findings enough for the TT tyre to show up at all your tri's OR does the aero of the 4000s overcome the rr deficit?
its a doozy!

At the back the aero doesn't seem to matter and on the front the TT would need to be some 3.5W worse aerodynamically. Considering the TT's tall profile that seems unlikely. Much will depend on individual rim measurements.

It may be more a case of will those using the 4000 be willing to give up some of the puncture resistance that they feel they need?

What would be great is if a tyre company followed specialised's lead, but with a low crr tyre, and gave the options of tyre sizes in small increments. I suspect though it wouldn't be financially viable.

On that topic a new way to measure tyre size would also be useful. Something like a top of tyre bead to tyre bead measurement which could be used alongside the current system. All manufacturers would already have this measurement as they'd need it for the tyres construction.

I'm still waiting on my Garmin speed sensor. In the meantime, I ran both tires again at 120 PSI and 25.2 mph.

Here's what I got:

Vittoria Corsa: 57 watts (crank); 55 watts (hub)
GP TT: 66 watts (crank); 65 watts (hub)

This is on the TT bike instead of the road bike, so the weight distr. and wattage are a little different for both.

Based on the crank power, that gives me CRRs of .030 for the GP TT and .0259


Since I ran the GP TT second this time, I figured I'd run it a bit more. I did observe that the by the 5th minute, the power had dropped from 66 watts to 63 watts at the crank and 65 to 63 at the hub. As has been suggested above, it could be that Conti tires improve disproportionately with temperature. That would certainly explain why historically they have done relatively poorly on my tests. I use the first stable reading, rather than allowing the tires to warm up.

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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

AAAHHHHHHHH!!!

This hurts my brain. Ok so now we also have to take temperature into account. Run the Corsa Speed for cool races and the Conti GP/SS for hot ones?

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/kj

http://kjmcawesome.tumblr.com/

No, it's more like: run the Contis on the rollers, where they get to temperatures that will rarely reach in real world conditions on the road; run the Corsa Speed the rest of the time.

It's worth noting that the Contis still took more power after warming up. I'll do a roll-out later today to adjust the speeds. But I doubt that will make up the difference.

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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

And is this one of the ones with the tan walls or grey walls? Also you said it measured ~22.7mm. This was a 23mm version. What is the internal width of the wheel you are running it on?

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Grey walls. I'll check the internal rim width when I take it off. For comparison, I have the same Corsa Speed tire on a Jet 9+ front wheel and it measures 24.60. It's a very nice match for that rim.

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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

There is scaling invloved due to the roller's small diameter compared to the infinite diameter of the road.

When and where are they from? My two samples from early summer last year (also grey sidewall) measure more like 27mm on my HED Jet Black, which should have same internal bead width.

The Earth is flat?! ;p

Hi jens... racing again?

You may want to look at the new Conti SS tires as well. And the "open tubular" tires universally suck for aero. May not want to use one on the front.

The more relevant question is where is my Hed Jet from. It is supposed to measure 25mm on the outside. It's closer to 24mm.

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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

Sorry... rounding error. It's about 143 million times bigger diameter than his rollers.

I'm giving it a go. I'm hoping that some people in my have aged more quickly than I have! ;-)

I've certainly heard the claim about open tubulars, but I'm skeptical. The discontinuity is minuscule -- certainly much smaller than the tire/rim gap for most tires.

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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

I have to agree with rruff.
Over many years of wind tunnel testing I've been hoping for a handmade tire to do well in the tunnel.
Even though the tread edge is miniscule, nevertheless it seems to trip the flow and separate it from the tire -- and almost always from the rim as well. Leads to early stall and the accompanying increase in drag, unfortunately.

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

I think the problem is that it occurs in a bad spot. Lot's of tests confirm this.

Regarding the tire-rim interface, I think it is generally best for the brake track to be slightly wider than the tire. This minimizes separation from both leading and trailing edges at high yaw.

Good luck with your racing! My ability to exercise and recover took a sudden downturn a couple years ago and I haven't found a reason. Oddly on short efforts (~1 min or less) I'm as strong as ever, but aerobically I'm down 10% or more on power, and can't recover worth a damn. And I'm only 56!