Zipp NSW 858 hookless with Canyon Speedmax help/comfort me

Triathlon Forum
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same rider, same bike, same tire, same tire width. you take the tire off a wheel with a 19mm internal bead width and put that tire on a wheel with a 23mm internal bead width. is the ideal pressure the same for both wheels? that’s the question. i suspect the answer is no. but 1 test is worth 1000 opinions, assuming the test protocol is sound.

Isn’t the obvious answer no here? Not really sure where you are going with this though.

i don’t know that the answer is obvious. i think you and i suspect the same thing. but i’ve been surprised before. as to what i’m after i don’t know that i could’ve been more clear in my post to marcag, just above.

Why isn’t it obvious? If we kept the wheel width the same and put on a wider tire, it’s widely known pressure needs to be lowered. The contact patch changes and then you have to account for impedance. A wider wheel with the same tire, effectively does the same thing. The delta pressure may not be as much depending on the change in wheel width vs tire width.

I’m not sure this would explain your theory on the silca calculator. Their calculator is based on measured tire width. So whether it’s a change in wheel width or tire width, the calculator is accounting for it. Not saying the calculator is perfect and the end all be all. Josh has said that’s is a good starting point and recommends people do their own testing and try adjusting pressures from the calculator output.

if what you’re saying is true then this solves the issue. when josh’s calculator says 66psi is the right psi for a 30mm tire at my weight, my roads, etc., then what this really means is that it’s the right weight for a nominal 28mm tire. josh’s 30mm tire back in 2014 is today’s 28mm tire. that jibes exactly (or very close) to what i find when riding these wheel/tire combos. if this is the case then let’s not hear any more horsespit about hookless not giving you enough room to pressure up at the 28mm tire size and larger.

Yes, I think a good way to conceptualize is the reverse - two systems that both measure the same tire width, but one on a wide rim and one on a narrow rim. The biggest difference is the sharp tire flex angle at the pinch point on the rim. A narrower rim could conceivably increase RR if it causes a greater change in the rim-tire flex angle. The contact patch would need to remain the same (given same pressure, tire material, measured width) so this is the only remaining difference. It would be an interesting test.

Re: Horsespit - I don’t believe the final argument was that wide tires couldn’t be safely inflated to their optimal pressure, but that the fastest couldn’t be achieved with hookless due to the low absolute pressure constraint.

stevej’s post just triggered a way of looking at this that i hadn’t been considering. i have been making a lazy, fundamental and pretty consequential mistake if i now understand things right. i just shot a note off to josh about the silca calculator, to see if i now understand it correctly.

i just went out and measured the 28mm (nominal) tires on my wheels. i have a 22.4mm bead width cadex 50 ultra with a corsa pro with 28mm on the heatstamp and these measure 29mm and change. i have a goodyear supersport r with 28mm on the heatstamp and when pumped to pressure it measured 30mm dead on in width on a set of 404 firecrests, which measure 23mm at the inner bead width.

i remember at a vittoria launch a year and a half ago they had just updated the wheel they use when the attach a size to the tire mold. prior to then a 28mm tire measured 28mm on a rim with a 15mm bead width. they updated to a 19mm bead width. i suspect this is where a lot of tire companies are. 19mm or narrower bead width for sizing convention purposes, which so many of us are now riding wheels for road with beads that are 4mm to 6mm wider, maybe even 8mm wider, than what tire companies use for sizing purposes.

this means that when i look at the silca calculator for the right pressure for my 28mm tires, because of the wheels i’m riding these days i should be looking most often at the recommendations for a 30mm tire. if i do so the pressures i think are best based on my own riding, and the pressures silca’s calculator recommends, are almost exactly the same.

42

Re: Horsespit - I don’t believe the final argument was that wide tires couldn’t be safely inflated to their optimal pressure, but that the fastest couldn’t be achieved with hookless due to the low absolute pressure constraint.

because i didn’t answer this clearly with my last post: the reason why i think this becomes for many or most* people a non-issue is this: the absolute highest pressure i (on the wheels i ride) would ride for the fastest outcome according to the silca calculator on a 28mm tire (nominal size) is 5 bar on the nose. in a triathlon. (weight 50/50). this assumes new (smooth) pavement, highest performance tires, fastest speeds, and a proficiency level i don’t possess.

the “many or most*” people we’re talking about (among are those who’re riding hookless for road) are riding wheels with an inner bead width of around 23mm. almost nothing less than 22.4mm. there is one CADEX, not really a tri wheel, that’s narrower than 22.4mm. there’s the ENVE foundation wheels at 21mm of bead width. everything else i see so far is between 22.4 and 25mm. there are very few wheels out there in hookless that folks will ride narrower than 22.4mm, and nothing narrower than 23mm for zipp.

because tires measure wider than their nominal sizes on these wheels - in my case 2mm wider on average - i’m looking for a 30mm tire on the silca chart even though the tire says 28mm. this is because silca’s chart asks for the measured width.

the folks who might find 5 bar not enough are those who weigh more than my 170lb. but again, this assumes these folks are Pro 1/2 riders with the fastest tires on the smoothest roads at the highest speeds. the only place you really run into any issues are if you’re trying to run, say, a 26mm tire, which will measure 28mm on these wheels. then, yes, you can bump up against 5 bar. which is the main reason why i’ve always felt (and written) this is a tech best used for 28mm (nominal) tires and wider. but if you’re like me and you don’t run anything narrower than 28mm tires 5 bar is just not an issue and it seems now that cadex, zipp, enve, me, silca, all appear to agree on this via the calculators and charts i’ve seen and used.

43

this means that when i look at the silca calculator for the right pressure for my 28mm tires, because of the wheels i’m riding these days i should be looking most often at the recommendations for a 30mm tire. if i do so the pressures i think are best based on my own riding, and the pressures silca’s calculator recommends, are almost exactly the same.

Wait… so you have always been using the stamped tire width to input into the silca calculator? And not the actual measured width w/ calipers?

44

Forget calculators

Real world results :

A 59kg woman on. 22mm internal Cadex hookless wheel with 25mm tires had over 5 bar optimal pressure. Maybe moving her to 28 would help, maybe it would take an aero penalty since by your logic a 28 will now measure 30.

A 85kg main on a 22mm interval Cadex hookless wheel with 28mm tire had over 5 bar optimal pressure. Maybe moving to a 30mm tire would help, maybe it would take an aero penalty by your logic measuring 32.

Same for 3 of the pro riders (average 165lbs) on hooked wheels, 23mm internal, with 28mm tires. We tried 30mm tires they were still over. So the hope for the rider above is low.

Your theory that “few riders” would be impacted may require some real world testing.

Queue up the “but is your data accurate” :slight_smile:

45

stevej’s post just triggered a way of looking at this that i hadn’t been considering. i have been making a lazy, fundamental and pretty consequential mistake if i now understand things right. i just shot a note off to josh about the silca calculator, to see if i now understand it correctly.

Yes, you’re correct.
The Silca calculator very clearly mandates measured tire width. Calculating based on measured width rather than nominal width will implicitly correct for rim width variance in the pressure recommendation; it’s an included variable for the purposes of the statistical modeling.

What is interesting, though, is that absent a measure of tire height or circumference it still seems possible to predict optimal tire pressure to a fairly high degree of accuracy. Contact patch is obviously very important here, but maybe there is something going on with the increase in internal space that occurs with a wider rim that helps this measure function as a reliable constant?

46

this means that when i look at the silca calculator for the right pressure for my 28mm tires, because of the wheels i’m riding these days i should be looking most often at the recommendations for a 30mm tire. if i do so the pressures i think are best based on my own riding, and the pressures silca’s calculator recommends, are almost exactly the same.

Wait… so you have always been using the stamped tire width to input into the silca calculator? And not the actual measured width w/ calipers?

yeah. dumb, huh? this is why i spent so long fretting over the difference between all of us on one side and silca on the other. thanks to you and your post it got me to take another look at what silca was calculating and, in fact, now there’s a pretty small difference between silca and cadex, zipp, and so on. either explicitly or contextually i think all the other calculators and charts (enve, zipp, cadex) use nominal tire size. rene herse, i don’t know what they’re using. but if you don’t have rim width as an input i think you can only rely on measured tire size.

silca still recommends pressures that are a little higher than these wheel brands, but now the difference is in the single digits of psi.

47

stevej’s post just triggered a way of looking at this that i hadn’t been considering. i have been making a lazy, fundamental and pretty consequential mistake if i now understand things right. i just shot a note off to josh about the silca calculator, to see if i now understand it correctly.

Yes, you’re correct.
The Silca calculator very clearly mandates measured tire width. Calculating based on measured width rather than nominal width will implicitly correct for rim width variance in the pressure recommendation; it’s an included variable for the purposes of the statistical modeling.

What is interesting, though, is that absent a measure of tire height or circumference it still seems possible to predict optimal tire pressure to a fairly high degree of accuracy. Contact patch is obviously very important here, but maybe there is something going on with the increase in internal space that occurs with a wider rim that helps this measure function as a reliable constant?

you might intuit that putting a tire on a wider rim would make the tire height lower, but in practice when i’ve measured the tire is slightly taller. maybe it’s because you get less of the light bulb thing going on. its remarkable how much difference a fairly small amount of rollout makes in the way a bike handles. tire height/circumference makes much more difference than changing, say, fork rake. you would think it’s rake. but really it’s tire height, once you get into gravel, because the difference in usable tires is so huge. that’s why i’m always talking about tire radius as a design input when you construct a plan for a gravel bike.

48

this means that when i look at the silca calculator for the right pressure for my 28mm tires, because of the wheels i’m riding these days i should be looking most often at the recommendations for a 30mm tire. if i do so the pressures i think are best based on my own riding, and the pressures silca’s calculator recommends, are almost exactly the same.

Wait… so you have always been using the stamped tire width to input into the silca calculator? And not the actual measured width w/ calipers?

yeah. dumb, huh? this is why i spent so long fretting over the difference between all of us on one side and silca on the other. thanks to you and your post it got me to take another look at what silca was calculating and, in fact, now there’s a pretty small difference between silca and cadex, zipp, and so on. either explicitly or contextually i think all the other calculators and charts (enve, zipp, cadex) use nominal tire size. rene herse, i don’t know what they’re using. but if you don’t have rim width as an input i think you can only rely on measured tire size.

silca still recommends pressures that are a little higher than these wheel brands, but now the difference is in the single digits of psi.

lol. I’ve done dumber things. Earlier today, I was actually going to ask you to give me your inputs to the silca calculator cause I was pretty sure you were doing something wrong. But I figured it had to do with choosing the right the surface. Glad we are able to close this door a little.

Anyway, back to what we were discussing which I’m not sure what that was at this point.

49

Re: Horsespit - I don’t believe the final argument was that wide tires couldn’t be safely inflated to their optimal pressure, but that the fastest couldn’t be achieved with hookless due to the low absolute pressure constraint.

because i didn’t answer this clearly with my last post: the reason why i think this becomes for many or most* people a non-issue is this: the absolute highest pressure i (on the wheels i ride) would ride for the fastest outcome according to the silca calculator on a 28mm tire (nominal size) is 5 bar on the nose. in a triathlon. (weight 50/50). this assumes new (smooth) pavement, highest performance tires, fastest speeds, and a proficiency level i don’t possess.

the “many or most*” people we’re talking about (among are those who’re riding hookless for road) are riding wheels with an inner bead width of around 23mm. almost nothing less than 22.4mm. there is one CADEX, not really a tri wheel, that’s narrower than 22.4mm. there’s the ENVE foundation wheels at 21mm of bead width. everything else i see so far is between 22.4 and 25mm. there are very few wheels out there in hookless that folks will ride narrower than 22.4mm, and nothing narrower than 23mm for zipp.

because tires measure wider than their nominal sizes on these wheels - in my case 2mm wider on average - i’m looking for a 30mm tire on the silca chart even though the tire says 28mm. this is because silca’s chart asks for the measured width.

the folks who might find 5 bar not enough are those who weigh more than my 170lb. but again, this assumes these folks are Pro 1/2 riders with the fastest tires on the smoothest roads at the highest speeds. the only place you really run into any issues are if you’re trying to run, say, a 26mm tire, which will measure 28mm on these wheels. then, yes, you can bump up against 5 bar. which is the main reason why i’ve always felt (and written) this is a tech best used for 28mm (nominal) tires and wider. but if you’re like me and you don’t run anything narrower than 28mm tires 5 bar is just not an issue and it seems now that cadex, zipp, enve, me, silca, all appear to agree on this via the calculators and charts i’ve seen and used.

Mostly agreed. Most riders in most situations will not have any performance issues with tubeless and the pressure/size requirements. But the only time we worry about performance issues is when we’re trying to maximize speed/efficiency.

Personally I weight 145lbs, my bike weighs 22, 24ish with bottles, and has rim brakes. At 70.3’s I’ll average ~27mph. When doing preseason testing last year 23’s and 25’s were inseparable. Didn’t test 28’s and above because with 19mm internal rims at that speed it was pretty obvious they would be slower. With different rims the equation may change. These numbers are probably similar for most front pack AG or pro Triathletes.

All of this to say there are so many variables on this equation that we could go on forever. Weight, rim width, tire width, tire construction, rim profile, frame interaction, psi, altitude, road surface, wind direction, spoke count, disc/rim brake, sealant ozs, tire wear. Trying to find the perfect setup for a specific situation is fun but ultimately impossible.

50

you might intuit that putting a tire on a wider rim would make the tire height lower, but in practice when i’ve measured the tire is slightly taller.

I haven’t seen this, but I’m also only on hooked rims. Might be something going on there that’s worth looking at.

…regardless, though… can’t get something from nothing, and even if height doesn’t change the shape of the tire does, as the casing volume remains more or less (it is slightly elastic) the same. There is some mechanism in play that allows it to function for purposes of inflation pressure calculation as though it were a “nominally” larger tire.
Some rim manufacturers have been saying for a while that wider rims decrease rolling resistance, and this at least suggests that maybe they aren’t wrong.

Totally agreed, re: tire height, and tire shape is also important. This is fairly obvious in re: offroad tires, where shape determines how the tread pattern interfaces with the ground, but this also occurs with road tires. I think it’s part of why there has always been such a strong divide between camps as to which brands of road tire handle the best. A Conti isn’t shaped the same as a Vittoria, and it does make a difference at some level. Wider rims/tires likely help to minimize these differences in road tires.

51

you might intuit that putting a tire on a wider rim would make the tire height lower, but in practice when i’ve measured the tire is slightly taller.

I haven’t seen this, but I’m also only on hooked rims. Might be something going on there that’s worth looking at.

You can make an ideal model of a tire with math but it’s not straightforward math.

You can set the chord length of the circle drawn by the tire equal to the inside rim width and the circumference of the tire as a fixed number. From there you can calculate the chord angle, radius, saggital, and by extension height of the circle from the chord (aka tire height). A smarter person than me could combine these into one neat equation, but I just use excel instead of algebra.

What you find is pretty intuitive. The tire height increases quickly for (theoretical) rim sizes from 0mm to ~15mm. Makes sense as the flat-ish part of the tire near the rim is becoming vertical. Then it levels off until falling again when the tire sidewalls are stretched beyond vertical. It appears to peak at a 19mm rim for max tire height on a 25, although I’d say the difference between 15-23mm rims is imperceptible (0.2mm)