Yep, that and tread pattern are the other obvious differences. To quote Chuck Zimmer, a former collegue of mine at GKN Aerospace, "As usual Damon, it's more than one thing!"

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

I just realized I have data that might shed some light on that...


The 24C and 26C of the SWT and TC tires measured within 0.2-0.4mm (24TC 0.2mm wider than 24SWT, 26SWT 0.4mm wider than 26TC) on the same rim width wise. The center tread area and "hatching" on the edges are the same basic pattern/shape (one "inconsistency" is that the TCs both appear to use the same tread mold, whereas the SWT molds appear to be "scaled" in the tread area).

The SWTs are thin enough tread that one would expect them to take a fairly round shape...but, it does appear that the TCs start stalling earlier somewhere between 5 and 10 degrees of yaw.

So...I guess it is mostly the "lip".

It would be interesting to see the results of the Flo-style rim shape optimization that used something like the TC as the tire baseline. I wonder how much different the resulting shape would be, and would it be faster than something designed around a GP4000S with the TC mounted?

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http://bikeblather.blogspot.com/

So I've not fully followed this thread, but are we saying the gpTT beats out the supersonic? Especially when new?
What size is this for? Currently I have 23 supersonics but ALL my races this year are hilly on rubbish roads, so considering the 25mm gps or this is an aero mistake?
In zipp 404 FC

I'm not sure it's clear. If you look at Tom's test spreadsheet, you can see that different generations (or individual tires) of the same make and model perform very differently when it comes to CRR. The 20C Supersonic, for example, goes from .0034 in 2012 to .0030 in 2016.

I have a 23C Supersonic on order. If the rubber and construction is the same as for its 20C brother, my guess is it will best the TT by a watt or two in CRR. As far as the aero goes, I doubt you can conclude much without testing specific tires on the specific rims you are using.

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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

Perfect! Nice comparison, and it does seem to suggest what you're saying could be true. Thanks for digging that up Tom!

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

Just a reminder, the latest entries for both the 20C and 23C SuperSonics shown in my spreadsheet are NOT of the very newest models from Conti, which apparently had an unannounced change to the model. My tests are from the just previous generation (perfectly smooth tire), whereas the newest tires (as identified by texturing alongside the tread area) haven't been tested yet (AFAIK).

Just thought I'd make that clear. Conti doesn't help with their "running changes" to their tire models...it reminds me of when Hed was making unannounced changes to their Jet wheels, which was frustrating since it affected aero performance :-/

edit: Oh...and the 23C SuperSonic IS already what I consider basically "tied" with the GP TT (i.e. within 1 watt for a pair at 40kph)...and it does so with nearly a full 2mm narrower width when mounted on the same rim.

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http://bikeblather.blogspot.com/

am i missing it or is the pressure data not there or maybe unimportant? do you have the "breakeven" point for where impedence takes over? or whatever it was in the silca data.

trying to figure out best pressures for me on conti 23 TT on hed jet + rims (i'm 165 lbs).

The test pressure for the vast majority of the tires in the list is 120psi, except for the entries noted that they were taken on a 21mm internal width rim, and thus the pressure was dropped to 100psi for the rankings to "match".

It's not possible to predict the "breakpoint" pressure from a smooth roller test. All that a roller test is doing is giving you a relative ranking of the energy losses in the particular tires. This is why I've done them at a consistent pressure...also, because I've mostly been testing tires falling within a fairly narrow width range (If I start testing wider tires more, I might have to consider a different test pressure, or protocol for them).

"Breakpoint pressure" is affected by not only the tires, but the load, the road roughness, the speed travelled, and the temperature...and possibly some other things in there as well. It's really something that can only be determined on a case by case basis. That said, if you look at those pressure vs. "Impedance" plots that Josh published, being quite a bit low on pressure is far less a detriment that being just a tiny bit too high. As I've said many times, "Tis far better to err on the side of too little pressure, than too much." ;-)

Personally, I weigh about the same as you, and run the same wheels, but 2mm narrower tires (SS 23) on my TT rig. Understanding that those Conti GP TT 23s measure quite wide (most likely close to 27mm on those rims), I would probably start in the range of 85-90 psi and experiment up and down from there.

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http://bikeblather.blogspot.com/

Gotcha, thanks. I haven't measured their width, but at 90psi they were just slightly wider than the 25mm external of the jet +. (where I ran them at my first race on this setup over the weekend - on smooth concrete)

So for rougher surfaces I'll go more toward 85. How low would you think would be too low?

When you start getting snakebite flats...and when that happens, it just means you're running too narrow of a tire for the pressures you need to run for the conditions ;-)

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http://bikeblather.blogspot.com/

still contemplating switching out the gp4000s for the gpTT but just wanted to know how, if anyone, is getting along with them. Are they puncture magnets? The 4000s have been kind to me re: punctures, it makes me nervous going for something else now!

I have had the same success as the 4k's. I put them on for a race last year and then just left them on. No flats all season even as my daily driver. I ran the 25 in the back.

There are many of us on here who have used Supersonics without a problem. Add a Vectran layer and you hare going to have even fewer problems.

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I hope to do some more testing on rough surfaces. But the testing I did a few years ago never supported the ultra-low pressures that seem to be in vogue today. In fact, I determined that I was best off running 70+ psi for my Mtb hill-climb races on rocky fire-roads! Take my word for it, I tested that a lot.

Likewise, Alan Morrison's tests showed that higher pressures decreased Crr all the way to 140 PSI, even when he simulated a rough surface on the rollers. If you look at the photos for the BRR site, you'll see his roller surface isn't exactly smooth either. And every single one of his tests show steadily decreasing Crr with higher pressures (up to 120 psi, at least).

We can go all the way back to Jobst Brandt, who found the same thing. Here's a blast from the past from a guy who's an asshole, but who tested more tires than any of us and definitely knows his stuff. He nicely refutes the absurd Zipp contention about your whole bicycle lifting up as it goes over roughness:

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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 ride GPtt 23 mm now for some years a couple of thousand km a year and I do remember a single puncture (there might have been another one) .
I had at least three sets of GPtt in that time, so most of the tires lived their life without a single puncture.
The other two punctures I had were actually no punctures but snakebites as I tried to ride with 7 bar. Therefore I'm back to 8,5 bar again.

i have placed my tire comments on the front page. i expect and, i guess, in a twisted way hope, to catch a lot of grief here. (what's wrong with me?)

there's obviously a lot more to write that i didn't write i the spirit of brevity, and because i just don't yet have the secret tire prescriber algorithm:

inputs:

- wheel of choice
- front or rear
- road texture

outputs:

- tire model
- tire width
- tire pressure

it's all fascinating! i'm eager to see how this ends up.

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Dan Empfield
aka Slowman

Excellent compilation of the facts and summary of the current situation Dan. Thanks for posting this.

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

So, run higher tyre pressures and buy a softer saddle?

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'It never gets easier, you just get crazier.'

You've convinced me that there are better options for race day tyres, so thank you.

Still going to use GP4000s2's for everything else though.

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'It never gets easier, you just get crazier.'

Jens, there's no surprise to me (nor to Al any longer after we discussed this) that Al's testing didn't "see" the breakpoint pressure. After all, he had only applied the wires to one if the 2 rear rollers (i.e. only half the wheel load had "roughness) PLUS the other thing not realized at the time was that with small diameter rollers (where the contact patch is more distorted for a given load) in order for the roughness effect to scale, the "roughness" would need to ~3X greater than an equivalent flat surface roughness.

If you recall, Al sent me the exact same tires he tested on the rollers for me to do my pressure vs. Crr testing using my VE course, the results of which where published here on ST in 2009 in an article I wrote on tubes.

Also, the BRR setup, although it uses diamond plate on the drum, omits a key factor in the additional losses at higher pressures, in that there is no damping mechanism between the wheel and the load. It's not that additional roughness causes "lift off", as many mistakenly assume, but it's that additional energy is dissipated in the butt, hands, and feet of the rider.

Josh Poertner did a great test confirming and illustrating this effect recently with Silca. You can find that here: https://silca.cc/...y-and-previous-works
https://silca.cc/...stance-and-impedance

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http://bikeblather.blogspot.com/

Tom, I realize challenging you on this subject is a little like you challenging me on the 9th century writings of al-Jahiz. But that's not going to stop me! ;-)

I note first that Josh's write-up begins with precisely the lift-off scenario that is so absurd. The pebbles in chipseal are 1/4 or 3/8 inch, with the protruding edge typically being a fraction of that. So we're talking PSI in the thousands for one of these. Rubber ain't that hard. Do you remember polyurethane skateboard wheels? They're completely solid and higher on the durometer scale than bike tire rubber. Yet even those can ride over pebbles and what not and absorb the roughness.

In your article you write:



Now, just a few days ago, you and others asserted that the minuscule lip on open tubular tires made a significant aerodynamic difference. I just just measured a tire at 22.5mm with 100psi, then inflated it to 130 psi and measured it at 23.35mm. So let me ask: are you sure you held CdA "fixed"?

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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

Ha!...that's not going to happen...ever ;-)


Aaah...I think you might be misunderstanding that. He starts out with a "rigid" wheel example, but when he begins discussing pneumatic tires, he's not describing any sort of "lift off", but instead that a large portion of that bump encountered is absorbed by the tire and a portion is used to raise the bike a much smaller amount. The tire never loses contact with the surface and the bike doesn't go airborne. It's just a way of describing how a portion of the energy is absorbed by the tire (and mostly returned to the surface in the trailing half of the contact patch) and a portion gets transmitted through the tire and into the frame, where it is eventually dissipated as heat in the rider's body. The stiffer you make that air spring, the less energy is absorbed by the tire and the more is transmitted.

Urethane skate wheels also deflect some...that's why they're faster than the clay and steel wheels they replaced. Pneumatic tires just take that same concept to a whole new level.



In my testing, the CdA of just the tires may have changed with differing pressure (and the resulting width growth of the tire), but you need to remember a couple things:

• First, the VE testing was done at basically zero yaw. If you look at the wheel-only testing that Cam Piper did for me with the full range of S-Works Turbo tires on the same wheel (CLX64), you can see that at zero yaw, the CdA differences between tires that are nominally 2mm different than each other only vary in CdA by ~.0005-.001m^2. You measured a difference of ~1mm going from 100-130psi on your tire, so logically one could assume a difference of half that amount (.00025-.0005m^2) for that case. Those values are within the "noise" of the measurement technique (VE), and are also well below the large step in "power required" seen at the higher pressures. For example, in my testing, I saw a difference in power required between 8 and 9 bar of ~20-30X that amount. http://bikeblather.blogspot.com/...t-3-after-party.html
  
• Secondly, Josh's testing was performed using the classic "regression" approach, in which separate estimates of CdA and Crr are calculated. He would've "seen" the large jumps in CdA required for that to be the source of the increased power requirement if changing CdA was the case.

Based on that, I find it highly doubtful that changes in tire width and the effects on wheel CdA are what is being observed with the "breakpoint" results.

To be fair, I haven't seen the data that Chris and Jon at Flo are referring to for such dramatic difference in wheel/tire CdA with pressure changes...and I wonder if they are referring to the values at zero yaw, or at larger yaw angles?

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http://bikeblather.blogspot.com/

Dan, how much do you think the apparent market dominance of the GP4kS2 can be attributed to the concurrent availability of independent Crr data, along with corroborating aero data on the tire's performance?

Prior to the availability of that data, everyone pretty much had only "feel" to go by...

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http://bikeblather.blogspot.com/

"concurrent availability of independent Crr data, along with corroborating aero data on the tire's performance?"

you are in no small part responsible for that tire's dominance. somebody needs to buy you a new car.

it was the right tire, right price, right durability, right time in history, right distributor selling it, right people noticing the value of it and describing the value in factual terms that made compelling sense in all places that mattered.

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Dan Empfield
aka Slowman

Yup...and that makes a higher bar for anyone wanting to knock it off the pedastal. They've got to come with data now...which is something I'm more than happy to have played a small part :-)

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http://bikeblather.blogspot.com/