Thanks for flagging the article Josh - I hadn't seen that.

I've been struggling for some time with the decision whether to ride 25mm tubeless on my HED Jet+ wheels, or stick with 23mm tubed for the aero benefits. At least I assume there are aero benefits because the 23mm tyre meets your 'rule of 105' on these rims (21mm interior width) whereas the 25mm tyre does not.

With the GP5000 on the Jet+ and latex tubes, it looks like I lose 2.4W per pair in rolling resistance. That doesn't sound like much to gain back from aero-ness, especially in the blustery conditions I often experience here in the UK.

One further comment - there are no error bars on the measurements in the article, so we have no indication of what might be considered a statistically significant difference between two tyres. Are you able to comment from your own testing history?

marting,
I'd consider running something like the 23mm GPTT on the front and the 25mm GP5000 on the rear, or the Corsa 2.0 23front/25rear. We've run CorsaSpeed TLR 23 front/25rear with a number of our ProTour teams for the last year+ with excellent results.. and we've done it both tubeless and with latex tubes depending on wheels.

The aero importance of a rear wheels is reduced by ~25-30% or so, but mostly on the front half of the wheel which is where wider tires have the most negative effect. You are probably looking at less than 1 watt aero penalty for a wider rear tire, but could be looking at 2-4 watts aero penalty of running too large a tire on the front wheel.

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Would you really recommend running a GP TT on the front though? Even in the right size, that has some significant aero penalty as I understand. I'm eagerly awaiting the data on the Michelin power TT and the Corsa Speeds to see if it'll be the season I drop the gp5000. If the Power TT isn't an aero dog and has a tiny bit more puncture resistance than the Corsa Speeds I may be in. I've personally seen more races ruined on Corsa Speeds compared to any other tire so I'm hesitant there.

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Interesting article, it still shows that if speed is the final goal (for example, racing a triathlon on decent roads), tubeless is a solution searching for a problem, when alternatives are just faster and more reliable (sealant is hit or miss when operating at higher pressures).

But I find this statement from that aerocoach webpage, "generally speaking wider tyres have lower rolling resistance" as bizarrely out of context. Because, yes, that is technically true when the tires have the same tire pressure. But nearly no one rides (nor should ride) narrow tires and wide tires at exactly the same pressure.

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So it hasn't been widely discussed.. but the big secret to all of these really low Crr tires is very thin treads, no breaker strips, etc.. and that makes for a very round tire which means poor aero performance.

Back when we were trying to make super aero tires at Zipp, we realized pretty quickly that the more aero the tire, the worse the Crr and vice versa. So for years, the GP4000 occupied that sweet spot between aero and Crr, but as Crr has come down, aero has gotten worse for all of these tires. I look forward to seeing Xavier's aero data on all of these, but from what I've seen with the GP5000 testing, these super fast tires are sort of converging on the same aero as they are all essentially approaching a circular cross section.

From there any differences will mostly be in surface texture at the tread and whether or not there is a hard or soft tread lip/edge

J

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This is interesting. Is this a leading edge problem (e.g. separation in the transition from tyre to rim) or trailing edge (e.g. separation due to rapid gradient change off the round profile) Or both? Or something else entirely?

Yes, I think there's room for improvement in our language around this.. There has been a lot of media over the last 10 years about 'wider is lower Crr', but as you point out, this has generally assumed same pressure which makes it rather useless.

The data we are missing here is whether or not the wider tire has less hysteresis than the narrower one which would mean that it would have lower Crr for a given vertical spring rate. 10+ years ago, there was some evidence that this might be the case, but it was mostly all due to tire manufacturing. Many manufacturers use the same tread strip and breaker strip across multiple widths, so the wider version of the tire would have more sidewall relative to the narrower version and therefore less hysteresis overall.

This shows really clearly in the BicycleRollingResistance data for the 4 widths of GP5000.. the tested Crr's make it look like repeat runs of only 2 sizes as there are really only 2 layups for the 4 sizes of tire.

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Doesn't the length of the contact patch also come into play. As I recall from Bicycling Science, Crr is the product of the difference in energy absorbed and returned from deflection (hysteresis) and a geometric term proportional to the length of the contact patch. My understanding is that for equal hysteresis, a shorter contact patch (wider tire) would have a lower Crr than a longer one.

You might say "just as fast," but you'll have a hard time arguing "faster" at this point.

Also have a hard time arguing "more reliable" I'm not sure what your argument is there. Tubeless virtually eliminates an entire class of flats (pinch) and changes the probability of most other types of flats from 100% chance of going completely flat to <100% chance.

You're right that sealant is hit or miss at high pressure. But tubes are miss or miss. And even if high pressure tubeless doesn't seal at high pressure, it still almost always seals by around 50-60PSI.

I think the only remaining argument is that it's just not worth the hassle. Which I understand. Particularly for wheels that aren't used very often, like race wheels.

In terms of the aero differences I'll publish all the stuff on the site, but as a summary we tested a few of the tyres in the tunnel to get the CdA change as well as at the velodrome to tie everything together. We made it simpler by taking to the velodrome two different classes of racing tyre - the best superlight weight race day only tyres (Corsa Speed and Michelin Power TT) and then slightly thicker race/training tyres (GP 5000 and Spec Turbo Cotton). The Michelin was more aero than the Corsa Speed in the tunnel by a small amount, but round the track came out pretty much identical to the Corsa Speed overall as the Corsa Speed had better Crr. It was similar with the Turbo Cotton/GP 5000 as the Turbo Cotton won on Crr but lost on aero making them both the same.

We still saw the same differences between the classes as we had done previously (so there was about a 3w penalty per tyre for the GP5000/Turbo Cotton vs the Corsa Speed/Power TT), giving you around 6-7w for a pair of wheels. Not loads but not insignificant if you want to go as fast as possible, but it's clear (to me at least) that something like a GP5000 tubeless is an absolute winner for long course tri, but for shorter TTs Corsa Speed tubeless is a great option. I've trained on GP5000 tubeless for ages and really don't have a problem with them in terms of punctures - but also find the clincher version excellent too.

We are going to be adding to the test list (we were meant to get the new Goodyear TT tyre last week but they didn't end up sending us one), if anyone has any suggestions on what they'd like to see do let me know, it is more of a TT focused test though. We do internal testing for third parties as well so the actual list is bigger than it looks with prototype/proprietary tyres and things. There's a real big push in the pro peloton for tyre optimisation this year.

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Yup. :)

So far, happy with my GP5000 + latex tubes as an allrounder that is quite fast, isn't fragile, and doesn't require filling with goo on a periodic basis (I'll take regular pumping up over that thanks)

and yet...

what you're saying is if you take the BEST tubed tires, and you put in the BEST possible tubes, the very BEST you can hope to do is equal any of several available tubeless tires, which were the choice of 70 percent of the pro field in kona who were competitive. these athletes can race anything made by their tire sponsors and tubeless is what they choose.

among those top athletes who didn't choose tubeless were those who chose basically the same tubeless tire wrapped into a tubular.

unless something drastic happens to tubed tires(or their tubes), i think it's pretty clear that the trend is going in one direction. one must ask oneself why that is. i don't produce the trends. i just report them.

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Dan Empfield
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Cue paralysis by overanalysis.
Spoiler alert: fast tires are fast. There really isn't a wrong choice among the top 5-10 race tires on the market, and the molding difference from tire to tire can account for more than the difference between different brands (MY Conti 5000s test faster on my rollers back to back against MY Specialized Turbo Cottons for example)

Choose the one you got a local shop deal on, or a brand that you've had good luck with not getting flats in the past, or the one you won a race with that one time.

As for the tubeless vs tube debate, everyone will have their own pros and cons.
I'd wager tubeless is best for someone who either never works on their bike (ie. takes it to the shop for flat tubes) or someone who is very confident in their technical ability to set up and deal with any tire issues down the road (and perhaps is looking for a wider tire & lower pressures)
regular tubes (& latex for racing) are still going to be the go-to for the majority of ppl that just want to ride their bike a lot.

For triathlon racing purposes, i do think that a circumstance where i'd veer towards tubeless would be one in which a flat tire virtually ends your race. If losing 5min changing a tube means the podium is gone and you might as well DNF, then tubeless + sealant gives a chance that a flat seals itself to keep you rolling to T2.
On the other hand, a tubeless tire that doesn't seal itself enough to be ridable could present a problem if the rider isn't absolutely confident they can dismount and get a spare tube installed (or get a plug to work), which tends to be more difficult & MESSY, than if you were running tubes to start with.

I think that's the expected outcome. Though the difference is pretty darn small.

Probably not what you were asking....and maybe you have already assessed...but there is considerable work showing better crr with lower than traditional tyre pressure (definitely <100psi and even less).

....it seems that this thinking has not filtered to the velodrome where the traditional tyre pressures of 200+ psi are still routinely used.

Even wooden tracks are not entirely smooth and, particularly as a light rider, I feel those little bumps a whole lot more with 200psi compared with ~100psi.

Should trackies use lower psi??


Randolph

Neutral Support, and priorities.

If you're going to get a wheel from a motorcycle in the event that you can't get your darn sealant spewing nightmare fixed, the advantage of being able to ride through small punctures that will seal with tubeless - but would probably necessitate a stop & repair with a tubed wheel - wins out. Or at least that's the theory (see below).
Likewise, if you are in it to win it - or top ten it, or whatever - you prioritize that over being able to self-support your way to a "finish no matter what happens" type result.

FWIW, the pro I was wrenching for at Kona last year switched *off* tubeless after being one of the first to adopt it after they experienced an "impossible to self-repair" flat in a race early last season. It will be interesting to see if other pros do as well after they get more time in on tubeless, and experience some system failures.

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[i][/i]
Yup, very well-said. Because materials properties and the laws of physics are harsh mistresses ... they catch up with you every time ...

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Exactly. Which is why tubes are slowly on their way out. :)

Just out of curiosity, have you actually made an honest attempt at road tubeless yourself? Did you have difficulty with setup? Have a bad experience out on the road?

For triathlon racing, i have not used tubeless as there is zero speed advantage, and l have a few sets of race wheels that l love which are not tubeless compatible. So the $ investment to go in that direction would be considerable.

I also do all of the work on our household's bikes and the last thing in the world that l need would be to have to constantly mess with wheels and sealant and cleaning out tires on a regular basis.

But if the tubeless systems were truly faster, or allowed one to save maintenance time, or allowed one to get back on the road without having a big psi loss, then l could be convinced. It just seems that for high pressure road applications for those that actually have to do all of their own repairs, trends or no trends, tubeless road is just not yet ready for prime time.

That is my opinion today, but if/when the tech changes for the better, then my opinion will definitely be subject to change.

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Alright, for those of us with a basic understanding of CdA and Crr but nothing much more when it comes to physics, if you had to pick one clincher and one tubeless tyre from your testing to race on, which are they and are there any specific reasons why?

As always, everyone here appreciates your tireless testing, data simplification, and regular input. Thank you!

At what speed and in what conditions?

Kind of agree for racing, tubes still seem to be the best way, the TT bike might sit for months at a time wheels not turning, so drying out the sealant and requiring the tyres to be removed cleans and re sealed evey now and then. PITA

On the road bike tho it makes more sense, better puncture resistance and better feel, bike is used more so just have to top up sealant via the valve every few months.

I presume these rough numbers are based on weighted averages. How much difference do you see at high yaw angles? If not watts but at least what sort of angle do the tyres stall? (I know this will differ with different wheels but hopefuly an indication)

I recall from the swissside work on steering torque produced a couple of years back was that the GP4000 held on for much longer at higher yaw before stalling although I think this was only comparing conti tyres at the time.

Thanks for the kind words!

I suppose explaining my personal choices would help to flesh things out as I do race bikes. I ride TTs quite a lot and use Vittoria Corsa Speeds exclusively - but change out the tyres as often as possible as we find that Corsa Speeds wear out in terms of Crr as well as puncture resistance. I set them up tubeless with around 40ml of sealant and occasionally ride a tubular disc in the rear if it's a hilly TT (with a tubular Corsa Speed), as our tubular discs are really light. I was putting sealant in the tubulars but it kills the latex tube that's sewn inside and you get random blowouts so stopped doing that.

I train on Continental GP5000s on the road (tubeless), and did a 6hr crit (round a motor circuit, it was quite solid!) at the end of last year on Continental GPTTs with latex tubes. That was a slightly faster setup than GP5000 tubeless and the surface was okay so I wasn't worried too much about punctures.

I love a good tan sidewall so would be up for using Turbo Cottons for training, the Wolfpack tyres we're going to be testing arrived today so will give them a shout as well as a tan sidewall option (along with Veloflex but I've had a fair few flats in the past with Veloflex when I raced on them ~10yrs ago).

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