Yes. What front wheel are you using?

A 23 or smaller on the front is a good idea for crosswind stability IMO, even if it's a hair slower. And usually it isn't slower.

Like trail said, gotta know the rim and what races you are doing.

I'm using some locally made rims. Wide rims though. 26.2mm wide at the brake track, 17.1mm internal width.

23

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What rims are you using?

See post #4 above.

23mm. The 23mm TT already isn't exactly a great aero performer. The 25mm would be a disaster and, contrary to popular belief, the 25mm tire will not have a lower crr.

Post #4 doesn't answer the question.

best for aero is 23mm
not gp TT but GP4ks2
you need the air to flow and TT is flat, without any thread. TT on rear is perfect, 25mm

I switched to 25 front and back on my 404s a couple weeks ago after riding 23 for a couple years. I don’t have any objective data on the change, but I enjoy the ride so much more that I don’t really care if I fall from 52nd to 55th in my age group.

Really? Did they screw up the GPTT25 they way they appear to have scewed up the SS23?

OP, the best option for the front if you want some puncture resistance and and low Crr is probably the Attack23. It has "aero grooves" oriented the right way now.

Pressure? The spring rate of the tire is dominated by pressure. The lower limit is set by pinch flat worries... and if you use latex tubes, you can run low pressure. If you hit something hard enough to pinch flat you are probably wrecking the rims (or about to). I once hit a pothole hard enough to dent both rims, but the tubes were fine.

Still experimenting with pressure.

Happy to get any recommendations.

I weigh 175.

85psi felt a little low.

90 felt pretty good.

Ran 105 on my 23s.

I ride in Florida in midday heat so I am a little skittish on putting too much air in the tires, whether justified or not.

I was just going to make a point along these lines. The roads in my area have deteriorated so badly that I can't be confident running 23 mm tires much anymore. Running larger tires and lowering the pressure makes a lot of difference in how much I get beat up. The OP might want to take that aspect into account if they know their courses. Aero and RR might not necessarily be the top considerations if the pavement is less than optimal.

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Stay aero my friends.

Nope, crr is primarily driven by compound and tire construction. The whole "wider is faster" myth is because CRR tests are normalized around tire pressure instead of casing tension. As a result, wider tires have a higher "spring rate" by default. You wouldn't run a 29x2.0 MTB tire at 90psi (it would be rock hard) so why would you run a 25mm tire at the same pressure as a 23mm tire? You wouldn't (or shouldn't). Once you adjust for pressure, the size of the contact patch and the amount the tire deforms does not change meaningfully. As a result, crr is driven primarily by compound and casing ("spring material" if you will).

Wide tires ≠ more comfort either. Wide tires allow you to obtain a more comfortable ride by running a lower pressure with less risk of a rim strike on account of having more volume.

A narrow tire and a wide tire of the some construction will have the same spring rate at the same pressure. I think Josh Poertner and Damon Rinard have both measured this. If you run them both at 100 psi, they'll ride about the same and the wide tire will have lower Crr. If you run the wide tire with less pressure, the Crr may be the same, but then you gain more comfort with the larger tire.

90 psi should be plenty for 23s. You could probably get by with 80 or even less if you use latex tubes.

The casing tension of the wider tire will be higher and thus its “spring rate” (not a 100% accurate term here but close enough) will be higher. Damon chimed in on this last year when Flo released their preliminary casing tension study saying that normalizing for casing tension was indeed the correct approach. TomA has mentioned this as well. Hopefully he joins this thread. I’ll find and link Damon’s comment when I’m back in front of my laptop.

Casing tension has been missed by most in the industry because 1.) its difficult to measure and 2.) humans are wonderfully prone to placebo effect. BikeRadar has a story last year where they compared the GP4000S II in three different widths. Even though they ran all three tires at the same pressure (95psi if memory serves) they stated that the 28mm tire was “smoother” and all the other usual marketing gibberish.

GreenPlease wrote:

23mm. The 23mm TT already isn't exactly a great aero performer. The 25mm would be a disaster and, contrary to popular belief, the 25mm tire will not have a lower crr.

Huh? I though the GP TT was gernally accepted as the fastest choice in tyres? Is that not the case?

I've been using 2 x 23mm GP TT with latex tubes on my cervelo for ages. Have I been disadvantaging myself? My new bike comes with a 23mm GP Attack III on the front and a 25mm GP Force III on the back. Is that a better choice than 23/25mm GP TTs?

It's one of the fastest tires from a CRR standpoint. It is not that great of a tire from an aero standpoint. However, to quote Tom A "a low crr can make up for a lot of aero sins". See TomA's testing of the Turbo Cotton (which is an aero brick). The 23mm GP Attack III should be a very fast tire. If it follows in the same footprint as the Attack II it's likely just a touch thicker than the GP TT and thus rolls a touch slower *but* it's likely more aero than the GP TT given its tread pattern.

Thanks. Very informative. I didn't realise tread pattern was such a factor. I guess I just assumed that the smoother a surface, the lower the air resistance.

Not all tread patterns are created equally. The GP4000 SII was an accident as far as we know. Schwalbe did some active development for the tread pattern of their "Ironman" tire. I'm not sure if they used the same pattern on the Pro One.

The Attack 3 is bigger than the old Attack by quite a lot. It's wider than a 23mm Michelin Comp. But it only weighs 165-175g IRL and the grooves are oriented properly for some potential boundary layer tripping, so I'd guess it's as good as the GPTT 23 for Crr and better for aero.

If it's the tread that's special I wonder why they didn't replicate it on other tires? The GP4000 has another advantage which might be the primary one, and that is a thick tread with a shape that gives it a more "pointy" profile. Tires with thin tread and supple casings (and low Crr) tend to be very rounded. Particularly the "open tubulars".

That too (re thick tread). At least a two companies actually have copied the GP4000 tread pattern. One of them was... Wolf Pack?... some tire company started by a former Conti engineer. I forget the other company/tire but it was someone like Maxis. We just happen to know that the GP4000 S tread works but that doesn't mean others don't work. If you look at the tread on the Attack II it's nearly identical to the Schwalbe Ironman tire.

If you can still find one, the 24c Conti GP Force (gen 2) makes a fine front tire even though it was designed for the rear.

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"They're made of latex, not nitroglycerin"

Hmm, I didn´t do any research on that but I use 23 front because it matches the rim. With 19mm internal width the 23mm tire effectively becomes 25+mm anyway. And this matches perfectly the 26mm outer rim-width. Then again I am only 70kg so weight is no real issue. Rear is 25mm, and both are GP TT.

I rode GP 4KIIs before and couldn´t tell which one is faster. The TT however rolls and feels smoother, and I just hope that equals faster ;-)

I did exactly this recently.. Nashbar was selling the 22/24mm Force/Attacks cheap so I picked up another Force and put it on the front.

That was a sweet deal. I picked up a pair of Force tires. Went back to order a couple more to stash away for later, but they were sold out. Thinking of getting a 25c TT for the rear and saving the Force that's currently there for later use on the front.

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"They're made of latex, not nitroglycerin"

So are you saying the 23mm GP 4000sii is the fastest tire to have on a front wheel assuming a 25mm rim when considering both aero and rr? I cant imagine the aero difference would make up for 2-3 watts of rolling resistance difference. I'm looking for the absolute fastest setup which i guess is a TT on the back and still trying to figure out the front.

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Depends.

p3c w/ omega x. 25mm wide generic u shaped chinese clinchers. presumably good roads for the race (indian wells 70.3). averaging ~25-26mph.

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Would be a 25mm Corsa Speed on the back, and probably either a 23mm CS or a 20mm SS on the front.

If you are more risk averse, the 23mm Attack on the front and 25mm GPTT.

rruf's suggestions above are perfect. Personally, I have not had good look with the CS. PITA to mount and, once mounted, very flat prone.

You think the CS are worth it over other options even without tubeless wheels? bicycle rolling resistance says add 1.5-2 watts for latex which puts them just a tad under the GP TT? I suppose that means the aero pattern is that much better?

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I've got a new 23mm Conti Supersonic if anyone wants to buy it. It's the new version.

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The CS won't have an aero advantage over a GP TT in my opinion. You could get an oddball rim/tire combination where it is faster due to some unforeseen interaction but you're just as likely to get that with the GP TT as well. If you're running latex tubes my bet would be on the new Attack for a front tire.

Okay. Sounds like a 23mm Attack and 23/25 TT on the back will be my move then. My p3c struggles with clearance for a 25mm 4000sii so I'd lean towards a 23mm but maybe the TT doesnt blow up nearly as much?

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23mm TT often ends up being much larger than that. 26mm on my Jet+ rims.

I don't think BRR's setup and protocol are that great. I've tested really thick latex tubes (~120g) vs really thin ones (~50g) on rollers and couldn't measure a difference. I think Tom has measured tubeless vs latex and also didn't measure a difference.

An advantage of using the CS on a non-tubeless rim is that they are easier to mount! If you want to use a fast tire on a too-tight tubeless rim you can try a Pista with the latex tube. It's just as fast as the CS, and maybe faster.

I don't think the Vittoria tires are very aero, but if your rim is wider than the tire at the brake track, and yaw is low, they are probably the fastest even on the front. My 23mm CS is only 24.2mmm wide on a Kinlin XC279 which is 17.0mm internal.

My understanding is the BRR doesn't test with latex so it sounds like to me they are just guessing.

Look at TomA's testing. He tested the vittoria corsaspeed tubeless and with a latex tube. There is zero measurable difference.

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Kind of hoping Wolf Pack bring out a Super Sonic clone with the old 23 tyre width (the version before the current model).

Pirelli Have a very similar tyre to the gp4000ii.

I have to assume Hutchinson is their contract manufacturer. Personally I’d like to see Wolf Pack make a GP4000 Sii clone in 23mm, tubeless, and with no puncture protective layer. IMO that would be a very popular tire. In terms of aero + crr it would be better than a GP TT (by my my estimation) but with better flat protection.

so i have the aeolus 6 xxx which is 28 wide at the brake. They say they are designed for 25 mm tires. That being said, would a 23mm still have an aero advantage?