Vittoria Corsa Pro vs Corsa Speed

Triathlon Forum
201

well, i don’t stipulate to the optimal pressure being above 5bar for a 28mm tire for most riders on most roads. there is 1 certain violation of my rule, which is a 5mm difference between tire and internal bead width; then (as you say) the pressure question, then the insert question. the only other gentle disagreement i have with you is on the “we will never know.” i’m pretty sure we will know.

Our testing so far has shown over 70kg on smooth road, 5bar and below is not optimal. Those roads at UAE are silky smooth and DeGendt is 69kg.

This is my ONLY beef with hookless. To get optimal I need to push the limits of safety.

FYI the CPA seems to be unhappy. https://velo.outsideonline.com/...ill-be-a-mass-crash/

Maybe someone needs to look into this insert thing.

yeah, i’m not saying your testing is wrong. i’m just saying i’m not yet ready to stipulate to that. maybe it’s just that my roads aren’t smooth enough. i just can’t find an occasion where in my own testing for my own 77kg body that for a 28mm tire anything above 65psi isn’t slower. and even 65psi is high. if i lived in the UAE or even germany it would probably be different. but in the US or at least in the state everybody loves to hate (california) even freshly laid pavement is rougher than what you reference in the UAE. for me, cycling efficiency (acknowledging that efficiency is probably not the right word) - the translation of energy intended to speed - includes both a mechanical and biomechanical component. i say intended because i don’t know whether muscle vibration keeps the energy from translating to speed, or keeps me from using the energy at all. i just know that muscle vibration is a documented problem. that biomechanical cost approaches zero on a UAE road so i take your point there. i just can’t replicate anything like that where i ride and my roads are, by US standards, pretty good.

I showed a picture of the road we tested on. It’s not silky smooth. Cracks every 10-20m. It’s much rougher than UAE. As rough as most triathlons I have done.

Here are the two closest riders to your weight. Although they are 9 and 3kg less than you.

At 5 bar one is giving up 2 watts, the other 1 watt. Not much, but this grows as weight goes up. One guy is 68kg the other 74kg

At 65PSI (4.5 bar), they would be giving up 4 and 2 watts.

X axis is pressure in bar. Y is watts lost compared to “optimal”

28mm 5000TT tires.

FYI, we measured the vibration felt by the rider. In theory we could correlate this to fatigue

i respect the work you’ve done on this, and i salute you for doing the work. i just can’t, as of this moment, replicate this for my own riding and that road looks remarkably like home :wink: your precision and breadth of subjects far surpasses anything i’m doing, so i defer to your results. and i subscribe to your results. i just don’t yet stipulate to your results.

202

That doesn’t look like Zipp’s graph, I call fake news!
.

203

That doesn’t look like Zipp’s graph, I call fake news!

That is explainable. They weren’t zipps :slight_smile:

But all joking aside, one thing I was suspicious about the Zipp charts was we didn’t see any “smooth” road data.

And then we have to define what “smooth” is.

204

i think i owe you an explanation as to why i don’t yet stipulate to your conclusions on appropriate pressures for riders specific to particular tire pressures and road surfaces. let me do better than “it doesn’t jibe with my own results for me.” if i left it at that, i think that is a weak reply to your obviously much more rigorous work than anything i have done. i honor, but don’t stipulate, your results for these reasons:

  1. fatigue is not just cumulative, it is exponential. slope positive increasing. the 10th punch in the face in a boxing match is more debilitating than the 3rd. so, it depends how long the interval you’re testing your subjects. 1mi? 10mi? 40mi? 60mi? the one advantage i have in my testing is that i only have 1 subject and i can perform my tests over weeks and months over longer distances. the limit to my testing is that it’s just 1 subject and the atmospheric conditions, and changes in fitness, are not controllable or accounted for in any rigorous way.

  2. i’m a big pussy. when i’m riding in a group and we’re all of relative even strength and we hit (say) washboard i fare less well than others in my competitive set. muscle vibration might affect me more than it might affect the average bear. when my own testing reveals a pressure that works best for me, that’s a weakness of my testing as i consider its application to others: i might be more negatively affected by vibration-related fatigue than the typical person.

  3. i might be wrong.

so, i don’t mean to dishonor or short-sell your own results and i would happily point people to your conclusions. i just thought the discussion would be better served if i put more flesh on the bones of the delta between your results and mine.

205

i think i owe you an explanation as to why i don’t yet stipulate to your conclusions on appropriate pressures for riders specific to particular tire pressures and road surfaces. let me do better than “it doesn’t jibe with my own results for me.” if i left it at that, i think that is a weak reply to your obviously much more rigorous work than anything i have done. i honor, but don’t stipulate, your results for these reasons:

  1. fatigue is not just cumulative, it is exponential. slope positive increasing. the 10th punch in the face in a boxing match is more debilitating than the 3rd. so, it depends how long the interval you’re testing your subjects. 1mi? 10mi? 40mi? 60mi? the one advantage i have in my testing is that i only have 1 subject and i can perform my tests over weeks and months over longer distances. the limit to my testing is that it’s just 1 subject and the atmospheric conditions, and changes in fitness, are not controllable or accounted for in any rigorous way.

  2. i’m a big pussy. when i’m riding in a group and we’re all of relative even strength and we hit (say) washboard i fare less well than others in my competitive set. muscle vibration might affect me more than it might affect the average bear. when my own testing reveals a pressure that works best for me, that’s a weakness of my testing as i consider its application to others: i might be more negatively affected by vibration-related fatigue than the typical person.

  3. i might be wrong.

so, i don’t mean to dishonor or short-sell your own results and i would happily point people to your conclusions. i just thought the discussion would be better served if i put more flesh on the bones of the delta between your results and mine.

I don’t feel in any way you dishonor or short sell the results. I appreciate the debate, there is not enough of it these days to help cut through a lot of the BS presented by manufacturers. There is sooooo much. Let’s not get into base layers …LOL.

I did not layer in the fatigue. That is a useful component, and like other areas, the riders should be able to decide, “yes I’ll give up 3 watts to not need 6 weeks to recover from Roubaix”. Part of the experiment was to see if we could quantify road and ideal pressure pre-race and quantify fatigue post race. The answer to both was yes.

FWIW, the riders were doing 100km per day of this testing, at a pretty good clip and yes, they were wiped. This is where my comment “they now hate me” comes from. Imagine the “rough roads” I showed at 90 PSI :-). Poor 60kg guy. Funny part he had a first date with a girl planned that night. The guys were teasing him on his ability to perform. But they all TOFTT

I do plan to do more tests and get a larger pool of data. I can overlay the 80 something kg guy on the plot :slight_smile: I actually did it myself. I will share what I can. I can’t share it all.

206

well, i don’t stipulate to the optimal pressure being above 5bar for a 28mm tire for most riders on most roads. there is 1 certain violation of my rule, which is a 5mm difference between tire and internal bead width; then (as you say) the pressure question, then the insert question. the only other gentle disagreement i have with you is on the “we will never know.” i’m pretty sure we will know.

Our testing so far has shown over 70kg on smooth road, 5bar and below is not optimal. Those roads at UAE are silky smooth and DeGendt is 69kg.

This is my ONLY beef with hookless. To get optimal I need to push the limits of safety.

FYI the CPA seems to be unhappy. https://velo.outsideonline.com/...ill-be-a-mass-crash/

Maybe someone needs to look into this insert thing.

yeah, i’m not saying your testing is wrong. i’m just saying i’m not yet ready to stipulate to that. maybe it’s just that my roads aren’t smooth enough. i just can’t find an occasion where in my own testing for my own 77kg body that for a 28mm tire anything above 65psi isn’t slower. and even 65psi is high. if i lived in the UAE or even germany it would probably be different. but in the US or at least in the state everybody loves to hate (california) even freshly laid pavement is rougher than what you reference in the UAE. for me, cycling efficiency (acknowledging that efficiency is probably not the right word) - the translation of energy intended to speed - includes both a mechanical and biomechanical component. i say intended because i don’t know whether muscle vibration keeps the energy from translating to speed, or keeps me from using the energy at all. i just know that muscle vibration is a documented problem. that biomechanical cost approaches zero on a UAE road so i take your point there. i just can’t replicate anything like that where i ride and my roads are, by US standards, pretty good.

I showed a picture of the road we tested on. It’s not silky smooth. Cracks every 10-20m. It’s much rougher than UAE. As rough as most triathlons I have done.

Here are the two closest riders to your weight. Although they are 9 and 3kg less than you.

At 5 bar one is giving up 2 watts, the other 1 watt. Not much, but this grows as weight goes up. One guy is 68kg the other 74kg

At 65PSI (4.5 bar), they would be giving up 4 and 2 watts.

X axis is pressure in bar. Y is watts lost compared to “optimal”

28mm 5000TT tires.

FYI, we measured the vibration felt by the rider. In theory we could correlate this to fatigue

That’s probably at 35kph? Crr watts scale linearly, but a couple watts at 35kph can easily mean the difference in winning or losing a sprint at 65kph. Definitely not a use case to most on this forum, but one anyone racing bikes should take into consideration.

207

That’s probably at 35kph? Crr watts scale linearly, but a couple watts at 35kph can easily mean the difference in winning or losing a sprint at 65kph. Definitely not a use case to most on this forum, but one anyone racing bikes should take into consideration.

Good question. I was lazy and did it at 11 m/s so 39.6km/h. let’s call it 40km/h

The whole thread kind of went in a direction when you asked about the tests. But let’s remember, way up there, we were debating if the 2watts of RR was worth the puncture resistance delta.

We are probably collectively giving up more than that with the wrong tire pressure.

We probably need to revisit where we get our pressure recommendations from. I did ask about it on the EC discord server. I am curious where people get their recommendations.

BTW, you called out the expected results. I was actually surprised by the results. You don’t seem to be.

208

i think i owe you an explanation as to why i don’t yet stipulate to your conclusions on appropriate pressures for riders specific to particular tire pressures and road surfaces. let me do better than “it doesn’t jibe with my own results for me.” if i left it at that, i think that is a weak reply to your obviously much more rigorous work than anything i have done. i honor, but don’t stipulate, your results for these reasons:

  1. fatigue is not just cumulative, it is exponential. slope positive increasing. the 10th punch in the face in a boxing match is more debilitating than the 3rd. so, it depends how long the interval you’re testing your subjects. 1mi? 10mi? 40mi? 60mi? the one advantage i have in my testing is that i only have 1 subject and i can perform my tests over weeks and months over longer distances. the limit to my testing is that it’s just 1 subject and the atmospheric conditions, and changes in fitness, are not controllable or accounted for in any rigorous way.

  2. i’m a big pussy. when i’m riding in a group and we’re all of relative even strength and we hit (say) washboard i fare less well than others in my competitive set. muscle vibration might affect me more than it might affect the average bear. when my own testing reveals a pressure that works best for me, that’s a weakness of my testing as i consider its application to others: i might be more negatively affected by vibration-related fatigue than the typical person.

  3. i might be wrong.

so, i don’t mean to dishonor or short-sell your own results and i would happily point people to your conclusions. i just thought the discussion would be better served if i put more flesh on the bones of the delta between your results and mine.

I don’t feel in any way you dishonor or short sell the results. I appreciate the debate, there is not enough of it these days to help cut through a lot of the BS presented by manufacturers. There is sooooo much. Let’s not get into base layers …LOL.

I did not layer in the fatigue. That is a useful component, and like other areas, the riders should be able to decide, “yes I’ll give up 3 watts to not need 6 weeks to recover from Roubaix”. Part of the experiment was to see if we could quantify road and ideal pressure pre-race and quantify fatigue post race. The answer to both was yes.

FWIW, the riders were doing 100km per day of this testing, at a pretty good clip and yes, they were wiped. This is where my comment “they now hate me” comes from. Imagine the “rough roads” I showed at 90 PSI :-). Poor 60kg guy. Funny part he had a first date with a girl planned that night. The guys were teasing him on his ability to perform. But they all TOFTT

I do plan to do more tests and get a larger pool of data. I can overlay the 80 something kg guy on the plot :slight_smile: I actually did it myself. I will share what I can. I can’t share it all.

there were 2 more factors i intended to mention but, in my old age, i just forget. (i remembered them on my morning run i just took, as i contemplated our conversation.)

  1. i find (i’d be interested to know if you find the same) that the pressure necessary to achieve the appropriate sag rate (or whatever) that delivers best performance has to be normalized down as the internal rim width increases. when i ride 28mm tires my wheels are, variously, 22.4mm and 23.0mm in internal width. i suspect when you’re testing you’re using wheels the riders of the team with whom you’re working are obligated to ride. this can be as narrow as 19mm internal width, based on the wheels i see top teams riding.

  2. i discovered, in my own riding, that i can put about 3psi less pressure in an otherwise identical wheel if that rim is hookless. independently, and unknown to me until after i’d voiced my own finding, zipp told me their testing said lower the pressure 5 to 6psi for hookless. so, in there somewhere.

these are factors that would apply to anyone. i could imagine, then, if you were using (say) a current dt swiss arc dicut 50, 20mm internal width, hooked beads, and you found that the ideal pressure for a rider my size might be 80psi, i could see that pressure diminished by 8psi, maybe 10psi, if you put me on a CADEX 50 Ultra (which is i think the fastest road wheel i own, and has a 22.4mm internal bead width). i still think i’m better off closer 5 to 10psi below even that (60psi to 65psi), if you’re talking the roads that i ride and on which you tested. but i think those points 4 and 5 might help close the gap between your findings and my own experience, depending on the wheel you used for your testing. if you did your testing on a CADEX 50 Ultra then what i just wrote doesn’t help ;-/

i could see this being a problem if you just took a standard pressure calculator, no matter how rigorously developed, and how accurate on the wheel used, and applied this to a hookless wheel on a wider rim. i think a good pressure calculator should probably have internal rim width and bead type as data inputs.

209

there were 2 more factors i intended to mention but, in my old age, i just forget. (i remembered them on my morning run i just took, as i contemplated our conversation.)

  1. i find (i’d be interested to know if you find the same) that the pressure necessary to achieve the appropriate sag rate (or whatever) that delivers best performance has to be normalized down as the internal rim width increases. when i ride 28mm tires my wheels are, variously, 22.4mm and 23.0mm in internal width. i suspect when you’re testing you’re using wheels the riders of the team with whom you’re working are obligated to ride. this can be as narrow as 19mm internal width, based on the wheels i see top teams riding.

  2. i discovered, in my own riding, that i can put about 3psi less pressure in an otherwise identical wheel if that rim is hookless. independently, and unknown to me until after i’d voiced my own finding, zipp told me their testing said lower the pressure 5 to 6psi for hookless. so, in there somewhere.

these are factors that would apply to anyone. i could imagine, then, if you were using (say) a current dt swiss arc dicut 50, 20mm internal width, hooked beads, and you found that the ideal pressure for a rider my size might be 80psi, i could see that pressure diminished by 8psi, maybe 10psi, if you put me on a CADEX 50 Ultra (which is i think the fastest road wheel i own, and has a 22.4mm internal bead width). i still think i’m better off closer 5 to 10psi below even that (60psi to 65psi), if you’re talking the roads that i ride and on which you tested. but i think those points 4 and 5 might help close the gap between your findings and my own experience, depending on the wheel you used for your testing. if you did your testing on a CADEX 50 Ultra then what i just wrote doesn’t help ;-/

i could see this being a problem if you just took a standard pressure calculator, no matter how rigorously developed, and how accurate on the wheel used, and applied this to a hookless wheel on a wider rim. i think a good pressure calculator should probably have internal rim width and bead type as data inputs.

I will look at #4. I do have data for the same riders, same road, 2 different internal rim differences. The wider is 23. I need to double check the narrower spec. I suspect 21.

I suspect it will be very difficult for a calculator to be uber precise. As I mentioned we do believe we have a protocol for road testing ideal pressure for a given wheel/rider/road. Now, can we approximate it while minimizing the test effort ?..I’d say 50/50 chance. That is the goal.

When aero testing I would always ask the person what pressure he used. If it was off the Silca calc, I would do a run at Silca recommended pressure and it was very often better. This is one of the drivers of this test. The other were the zipp charts you showed that didn’t have data for smooth surfaces nor aero data for wide. That and about 4 other factors drove this.

210

there were 2 more factors i intended to mention but, in my old age, i just forget. (i remembered them on my morning run i just took, as i contemplated our conversation.)

  1. i find (i’d be interested to know if you find the same) that the pressure necessary to achieve the appropriate sag rate (or whatever) that delivers best performance has to be normalized down as the internal rim width increases. when i ride 28mm tires my wheels are, variously, 22.4mm and 23.0mm in internal width. i suspect when you’re testing you’re using wheels the riders of the team with whom you’re working are obligated to ride. this can be as narrow as 19mm internal width, based on the wheels i see top teams riding.

  2. i discovered, in my own riding, that i can put about 3psi less pressure in an otherwise identical wheel if that rim is hookless. independently, and unknown to me until after i’d voiced my own finding, zipp told me their testing said lower the pressure 5 to 6psi for hookless. so, in there somewhere.

these are factors that would apply to anyone. i could imagine, then, if you were using (say) a current dt swiss arc dicut 50, 20mm internal width, hooked beads, and you found that the ideal pressure for a rider my size might be 80psi, i could see that pressure diminished by 8psi, maybe 10psi, if you put me on a CADEX 50 Ultra (which is i think the fastest road wheel i own, and has a 22.4mm internal bead width). i still think i’m better off closer 5 to 10psi below even that (60psi to 65psi), if you’re talking the roads that i ride and on which you tested. but i think those points 4 and 5 might help close the gap between your findings and my own experience, depending on the wheel you used for your testing. if you did your testing on a CADEX 50 Ultra then what i just wrote doesn’t help ;-/

i could see this being a problem if you just took a standard pressure calculator, no matter how rigorously developed, and how accurate on the wheel used, and applied this to a hookless wheel on a wider rim. i think a good pressure calculator should probably have internal rim width and bead type as data inputs.

I will look at #4. I do have data for the same riders, same road, 2 different internal rim differences. The wider is 23. I need to double check the narrower spec. I suspect 21.

I suspect it will be very difficult for a calculator to be uber precise. As I mentioned we do believe we have a protocol for road testing ideal pressure for a given wheel/rider/road. Now, can we approximate it while minimizing the test effort ?..I’d say 50/50 chance. That is the goal.

When aero testing I would always ask the person what pressure he used. If it was off the Silca calc, I would do a run at Silca recommended pressure and it was very often better. This is one of the drivers of this test. The other were the zipp charts you showed that didn’t have data for smooth surfaces nor aero data for wide. That and about 4 other factors drove this.

well shoot, i’m honored. obviously my pressures on our compatibility chart are noticeably lower than josh’s. i think we discussed this in an earlier thread and i mentioned the hooked/hookless thing, and wider rims, as reasons why josh and i don’t jibe. zipp’s data from the rolling road is kind of suspicious low. i’m probably closer to zipp than to josh, but i think rim width and bead style closes much or most of the gap between josh and i.

211

That’s probably at 35kph? Crr watts scale linearly, but a couple watts at 35kph can easily mean the difference in winning or losing a sprint at 65kph. Definitely not a use case to most on this forum, but one anyone racing bikes should take into consideration.

Good question. I was lazy and did it at 11 m/s so 39.6km/h. let’s call it 40km/h

The whole thread kind of went in a direction when you asked about the tests. But let’s remember, way up there, we were debating if the 2watts of RR was worth the puncture resistance delta.

We are probably collectively giving up more than that with the wrong tire pressure.

We probably need to revisit where we get our pressure recommendations from. I did ask about it on the EC discord server. I am curious where people get their recommendations.

BTW, you called out the expected results. I was actually surprised by the results. You don’t seem to be.

I’m really not, as I’ve seen it in the data I’ve collected doing my own aero testing. I was running lower pressures on the track (concrete) because the track is a bit bumpy and grainy (Rock Hill, SC). But, I found that my fastest times in the IP were done with higher pressures than I would have thought optimal, but was trying because of the Silca Calculator. Then additional testing on a smoother track here at home confirmed my suspicions with actual data. After that I just use the Calculator for about everything and tend maybe go a couple of PSI lower just to be safe if I know there’s maybe a particularly rough section in the course.

TBF I’m not running 21c tubulars at 125 PSI like we all used to, but with the wider high performance tubleess tires the pressures are still well over 5 bar unless I know I’m going to be on some dirt. I tend to optimize things based on what 80-90% of the course will be. I’ve also found that my 32c Road tires on 25 hooked internal/32 external rims (tires meaure 34) are significantly faster on dirt/gravel, silca calls it Cat 1 Gravel, than any actual gravel tire I’ve run. That said, I’m either running a 28/28 combo on the 23 internal/30 external rim, or a 25/28 on 21internal/27.5 external rim.

212

well, i don’t stipulate to the optimal pressure being above 5bar for a 28mm tire for most riders on most roads. there is 1 certain violation of my rule, which is a 5mm difference between tire and internal bead width; then (as you say) the pressure question, then the insert question. the only other gentle disagreement i have with you is on the “we will never know.” i’m pretty sure we will know.

Our testing so far has shown over 70kg on smooth road, 5bar and below is not optimal. Those roads at UAE are silky smooth and DeGendt is 69kg.

This is my ONLY beef with hookless. To get optimal I need to push the limits of safety.

FYI the CPA seems to be unhappy. https://velo.outsideonline.com/...ill-be-a-mass-crash/

Maybe someone needs to look into this insert thing.

yeah, i’m not saying your testing is wrong. i’m just saying i’m not yet ready to stipulate to that. maybe it’s just that my roads aren’t smooth enough. i just can’t find an occasion where in my own testing for my own 77kg body that for a 28mm tire anything above 65psi isn’t slower. and even 65psi is high. if i lived in the UAE or even germany it would probably be different. but in the US or at least in the state everybody loves to hate (california) even freshly laid pavement is rougher than what you reference in the UAE. for me, cycling efficiency (acknowledging that efficiency is probably not the right word) - the translation of energy intended to speed - includes both a mechanical and biomechanical component. i say intended because i don’t know whether muscle vibration keeps the energy from translating to speed, or keeps me from using the energy at all. i just know that muscle vibration is a documented problem. that biomechanical cost approaches zero on a UAE road so i take your point there. i just can’t replicate anything like that where i ride and my roads are, by US standards, pretty good.

I showed a picture of the road we tested on. It’s not silky smooth. Cracks every 10-20m. It’s much rougher than UAE. As rough as most triathlons I have done.

Here are the two closest riders to your weight. Although they are 9 and 3kg less than you.

At 5 bar one is giving up 2 watts, the other 1 watt. Not much, but this grows as weight goes up. One guy is 68kg the other 74kg

At 65PSI (4.5 bar), they would be giving up 4 and 2 watts.

X axis is pressure in bar. Y is watts lost compared to “optimal”

28mm 5000TT tires.

FYI, we measured the vibration felt by the rider. In theory we could correlate this to fatigue

With premier wheels and 26mm 5000 STR tires. Vitorria latex tubes

40k/hour

Road very similar to the photo above

93 kg rider

What inflation would you recommend please?

213

With premier wheels and 26mm 5000 STR tires. Vitorria latex tubes

40k/hour

Road very similar to the photo above

93 kg rider

What inflation would you recommend please?

Silca says 91. Sounds about right

214

Do you mind sharing your test protocol that you have used for your own testing?

215

Excellent

Thank you

I’ve been doing 90 so good to go

Really good to have you here in the board.

😃

216

Do you mind sharing your test protocol that you have used for your own testing?

sure. i keep riding the same routes over and over again with different equipment, pressures, etc. doesn’t take into consideration weather, temperature, wind, changes in fitness. very scientific.

217

Here are the two closest riders to your weight. Although they are 9 and 3kg less than you.

At 5 bar one is giving up 2 watts, the other 1 watt. Not much, but this grows as weight goes up. One guy is 68kg the other 74kg

At 65PSI (4.5 bar), they would be giving up 4 and 2 watts.

X axis is pressure in bar. Y is watts lost compared to “optimal”

28mm 5000TT tires.

FYI, we measured the vibration felt by the rider. In theory we could correlate this to fatigue

Thank you for posting this data. This has been my thought for several years and it’s nice to confirm with hard data.

Are you using any other sensors besides an aero sensor to get the chart you posted? I guess what I am asking, if I were to aero test, would I be able to run a similar test keeping everything else the same but just change tire pressure and/or tire size to be able to see the delta between runs?

My understanding of an aero sensor that you give it an Crr estimate/constant and it ultimately gives you CdA. Obviously, if you change tire pressure and width, Crr is going to change. But you would leave your Crr constant during all runs inside the aero sensor and then work out the math afterwards to see gains or losses.

I’m trying to figure the math behind the scenes when your delta between runs is more Crr than CdA necessarily.

218

Thank you for posting this data. This has been my thought for several years and it’s nice to confirm with hard data.

Are you using any other sensors besides an aero sensor to get the chart you posted? I guess what I am asking, if I were to aero test, would I be able to run a similar test keeping everything else the same but just change tire pressure and/or tire size to be able to see the delta between runs?

My understanding of an aero sensor that you give it an Crr estimate/constant and it ultimately gives you CdA. Obviously, if you change tire pressure and width, Crr is going to change. But you would leave your Crr constant during all runs inside the aero sensor and then work out the math afterwards to see gains or losses.

I’m trying to figure the math behind the scenes when your delta between runs is more Crr than CdA necessarily.

Short answer, you could do this with an aero sensor and GC. A ST member did this in 2022
Sorry for the slow voice…probably sounds better at 1.5x speed

https://youtu.be/rT9J4ywWo9g?si=_Y_gF6nPCAXqDt0w

In practice, we did a whole different level of sophistication. Yes, more sensors were used. This allowed to measure error and correct/ignore bad data and get much more reliable results. But yes you could do a crude version as above.

219

Thanks for sharing these test results, this is good stuff.

220

Wonderful full tire geekery one this thread.

Question that I have that I haven’t been able to find data on is what effect does tire width to rim width have in aero drag.

For example, on a 26.5mm external 19mm internal rim with a depth of 60mm, how much aerodynamic drag is added by using a 28mm tire vs 25mm tire.

I know there is a lot of variables with rim shape and fork/bike interaction, but with all of the testing aerocoach has done, is it possible to compile an average amongst different wheels with similar specs to get a general guide?

We talk about optimal sizing often, but not a lot of specifics on what the actual numerical penalty/advantage there is. I think it would in determining the question people have when trying decide between sizes for tradeoff on comfort vs speed.

That’s a super deep rabbit hole. I would suggest digging around and finding any wheel manufacturers who have pretty robust white papers. Then you have to kind of use that to SWAG other wheelsets. A pretty current one with different depth and width wheels is done by Parcours wheels. There’s just way too much variability in rim shapes and philosophies to really put together any kind of definitive list.

So I got a response back from them. Very good explanations.

To summarize they tested various wheel depths on rim brake variants with 25c and 28c tires. Internal width of 19 and external 26. The difference in drag was 3-5w on the front wheel depending on wheel depth with deeper wheels have less. Not insignificant and actually a bit higher than I would’ve thought.