Tire width and rolling resistance.

Jan 26, 21 9:41

Post #1 of 29 (3080 views)

New take on things.

"We now feel picking the right size tire is more a matter of looking at what level of comfort (and grip) is required. At some point, a smaller tire isn't able to provide the same comfort level (and grip) as its bigger counterpart because it will start bottoming out.
If you want to go as fast as possible, choose your required comfort level and pick the smallest tire that can provide that comfort for you."

https://www.bicyclerollingresistance.com/...KOG_Opmz8#conclusion

Rather timely find, as I was shopping for wider tubulars to use instead of my old, but unused, 21.5mm Vittoria Corsa CXIII's. I'll just stick with those pumped up to 130psi ;-)

Swimming Workout of the Day:

Favourite Swim Sets:

2020 National Masters Champion - M50-54 - 50m Butterfly

Last edited by: JasoninHalifax: Jan 26, 21 9:57

Re: Tire width and rolling resistance. [JasoninHalifax] [ In reply to ]

Jan 26, 21 9:55

Post #2 of 29 (3062 views)

JasoninHalifax wrote:

New take on things.

"We now feel picking the right size tire is more a matter of looking at what level of comfort (and grip) is required. At some point, a smaller tire isn't able to provide the same comfort level (and grip) as its bigger counterpart because it will start bottoming out.
If you want to go as fast as possible, choose your required comfort level and pick the smallest tire that can provide that comfort for you."

https://www.bicyclerollingresistance.com/...KOG_Opmz8#conclusion

Not so new of a take, exactly...I was saying basically the same thing almost 4 years ago: https://forum.slowtwitch.com/...ost=6348919#p6348919

"To me, the driving factor for choosing tire width for a given application is the tire pressure I want to run for a given course. In other words, if the course conditions require lower pressures for comfort reasons, then I'm going to choose a tire width that allows for that pressure without causing other concerns, such as bottoming rims and/or "snakebite" flats. Of course, expected speeds/wind angles also comes into that calculus. This is how I ended up selecting 42mm wide tires for BWR this year...knowing the amount of off-road conditions, I basically wanted to be able to run close to MTB pressures ;-)

That type of thinking is somewhat opposite of how most folks approach the subject (i.e. pick a tire width and then ask "what pressure should I run?"...I like to think that it's not that wider tires allow lower pressures, but lower pressures require wider tires ;-)"

http://bikeblather.blogspot.com/

Re: Tire width and rolling resistance. [JasoninHalifax] [ In reply to ]

Jan 26, 21 9:56

Post #3 of 29 (3060 views)

Stop it! I still ride 23’s, and ever since everyone went gaga over 25’s, the 23’s have been on sellouts, and sales, and way cheaper. Please don’t make them popular again, and make the prices go back up.

Athlinks / Strava

Re: Tire width and rolling resistance. [Tom A.] [ In reply to ]

Jan 26, 21 9:59

Post #4 of 29 (3055 views)

Tom A. wrote:

JasoninHalifax wrote:

New take on things.

"We now feel picking the right size tire is more a matter of looking at what level of comfort (and grip) is required. At some point, a smaller tire isn't able to provide the same comfort level (and grip) as its bigger counterpart because it will start bottoming out.
If you want to go as fast as possible, choose your required comfort level and pick the smallest tire that can provide that comfort for you."

https://www.bicyclerollingresistance.com/...KOG_Opmz8#conclusion

Not so new of a take, exactly...I was saying basically the same thing almost 4 years ago: https://forum.slowtwitch.com/...ost=6348919#p6348919

"To me, the driving factor for choosing tire width for a given application is the tire pressure I want to run for a given course. In other words, if the course conditions require lower pressures for comfort reasons, then I'm going to choose a tire width that allows for that pressure without causing other concerns, such as bottoming rims and/or "snakebite" flats. Of course, expected speeds/wind angles also comes into that calculus. This is how I ended up selecting 42mm wide tires for BWR this year...knowing the amount of off-road conditions, I basically wanted to be able to run close to MTB pressures ;-)

That type of thinking is somewhat opposite of how most folks approach the subject (i.e. pick a tire width and then ask "what pressure should I run?"...I like to think that it's not that wider tires allow lower pressures, but lower pressures require wider tires ;-)"

I remember! I've never switched from 23's for the road. If only I could still find 20mm tires for my specialized trispokes....

Swimming Workout of the Day:

Favourite Swim Sets:

2020 National Masters Champion - M50-54 - 50m Butterfly

Re: Tire width and rolling resistance. [JasoninHalifax] [ In reply to ]

Jan 26, 21 9:59

Post #5 of 29 (3055 views)

JasoninHalifax wrote:

Rather timely find, as I was shopping for wider tubulars to use instead of my old, but unused, 21.5mm Vittoria Corsa CXIII's. I'll just stick with those pumped up to 130psi ;-)

...also, it's not just about "comfort", but about not being above the pressure breakpoint for the conditions. You may be able to handle the 130psi discomfort, but you'll be considerably slower.

http://bikeblather.blogspot.com/

Re: Tire width and rolling resistance. [Tom A.] [ In reply to ]

Jan 26, 21 10:07

Post #6 of 29 (3045 views)

Tom A. wrote:

JasoninHalifax wrote:

Rather timely find, as I was shopping for wider tubulars to use instead of my old, but unused, 21.5mm Vittoria Corsa CXIII's. I'll just stick with those pumped up to 130psi ;-)

...also, it's not just about "comfort", but about not being above the pressure breakpoint for the conditions. You may be able to handle the 130psi discomfort, but you'll be considerably slower.

I'm 91kg, so I think (IIRC) that my "breakpoint" is a bit higher than someone who weighs, say, 70kg. By the time racing starts, I hope to be closer to the 81kg mark. I typically ride 95-105'ish PSI on 23mm clinchers. 130psi is just thrown out there as a number, and a bit to get a rise out of you. Probably should have said 200psi! In reality, it will probably be closer to the 100-110 psi mark, depending on course and conditions. I'll play around with the pressures to see what gives me the nicest feel on corners and sprinting.

Swimming Workout of the Day:

Favourite Swim Sets:

2020 National Masters Champion - M50-54 - 50m Butterfly

Re: Tire width and rolling resistance. [JasoninHalifax] [ In reply to ]

Jan 26, 21 10:11

Post #7 of 29 (3037 views)

JasoninHalifax wrote:

Tom A. wrote:

JasoninHalifax wrote:

Rather timely find, as I was shopping for wider tubulars to use instead of my old, but unused, 21.5mm Vittoria Corsa CXIII's. I'll just stick with those pumped up to 130psi ;-)

...also, it's not just about "comfort", but about not being above the pressure breakpoint for the conditions. You may be able to handle the 130psi discomfort, but you'll be considerably slower.

I'm 91kg, so I think (IIRC) that my "breakpoint" is a bit higher than someone who weighs, say, 70kg. By the time racing starts, I hope to be closer to the 81kg mark. I typically ride 95-105'ish PSI on 23mm clinchers. 130psi is just thrown out there as a number, and a bit to get a rise out of you. Probably should have said 200psi! In reality, it will probably be closer to the 100-110 psi mark, depending on course and conditions. I'll play around with the pressures to see what gives me the nicest feel on corners and sprinting.

<thumbs up emoji>

http://bikeblather.blogspot.com/

Re: Tire width and rolling resistance. [Tom A.] [ In reply to ]

Jan 26, 21 10:20

Post #8 of 29 (3025 views)

Tom A. wrote:

JasoninHalifax wrote:

Tom A. wrote:

JasoninHalifax wrote:

Rather timely find, as I was shopping for wider tubulars to use instead of my old, but unused, 21.5mm Vittoria Corsa CXIII's. I'll just stick with those pumped up to 130psi ;-)

...also, it's not just about "comfort", but about not being above the pressure breakpoint for the conditions. You may be able to handle the 130psi discomfort, but you'll be considerably slower.

I'm 91kg, so I think (IIRC) that my "breakpoint" is a bit higher than someone who weighs, say, 70kg. By the time racing starts, I hope to be closer to the 81kg mark. I typically ride 95-105'ish PSI on 23mm clinchers. 130psi is just thrown out there as a number, and a bit to get a rise out of you. Probably should have said 200psi! In reality, it will probably be closer to the 100-110 psi mark, depending on course and conditions. I'll play around with the pressures to see what gives me the nicest feel on corners and sprinting.

<thumbs up emoji>

Actually, you can help me a bit.

back of the envelope psi "equivalent". (assume tubulars with a round cross section for ease of calculation)

a 23mm tire has a cross sectional area of 415mm^2 a 21.5mm tire has an area of 363mm^2, making the wider tire 14.4% larger in area. Am I correct in thinking that the equivalent PSI for a the smaller tire would be 14% higher than the larger one? Or am I way off?

Swimming Workout of the Day:

Favourite Swim Sets:

2020 National Masters Champion - M50-54 - 50m Butterfly

Re: Tire width and rolling resistance. [JasoninHalifax] [ In reply to ]

Jan 26, 21 10:35

Post #9 of 29 (2994 views)

JasoninHalifax wrote:

Tom A. wrote:

JasoninHalifax wrote:

Tom A. wrote:

JasoninHalifax wrote:

Rather timely find, as I was shopping for wider tubulars to use instead of my old, but unused, 21.5mm Vittoria Corsa CXIII's. I'll just stick with those pumped up to 130psi ;-)

...also, it's not just about "comfort", but about not being above the pressure breakpoint for the conditions. You may be able to handle the 130psi discomfort, but you'll be considerably slower.

I'm 91kg, so I think (IIRC) that my "breakpoint" is a bit higher than someone who weighs, say, 70kg. By the time racing starts, I hope to be closer to the 81kg mark. I typically ride 95-105'ish PSI on 23mm clinchers. 130psi is just thrown out there as a number, and a bit to get a rise out of you. Probably should have said 200psi! In reality, it will probably be closer to the 100-110 psi mark, depending on course and conditions. I'll play around with the pressures to see what gives me the nicest feel on corners and sprinting.

<thumbs up emoji>

Actually, you can help me a bit.

back of the envelope psi "equivalent". (assume tubulars with a round cross section for ease of calculation)

a 23mm tire has a cross sectional area of 415mm^2 a 21.5mm tire has an area of 363mm^2, making the wider tire 14.4% larger in area. Am I correct in thinking that the equivalent PSI for a the smaller tire would be 14% higher than the larger one? Or am I way off?

Well...based on your mass mentioned above, I plugged the 23mm measured width and the 21.5mm measured width into the "Berto Drop" pressure calculator I made for roller testing, and got (for a 50kg wheel load) pressures of 115 and 127psi respectively. So, that's looking more like an ~10% increase.

It's not all about the x-section area...casing tension comes into play as well (above is all assuming SAME tire construction).

http://bikeblather.blogspot.com/

Re: Tire width and rolling resistance. [Tom A.] [ In reply to ]

Jan 26, 21 10:38

Post #10 of 29 (2985 views)

Tom A. wrote:

JasoninHalifax wrote:

Tom A. wrote:

JasoninHalifax wrote:

Tom A. wrote:

JasoninHalifax wrote:

Rather timely find, as I was shopping for wider tubulars to use instead of my old, but unused, 21.5mm Vittoria Corsa CXIII's. I'll just stick with those pumped up to 130psi ;-)

...also, it's not just about "comfort", but about not being above the pressure breakpoint for the conditions. You may be able to handle the 130psi discomfort, but you'll be considerably slower.

I'm 91kg, so I think (IIRC) that my "breakpoint" is a bit higher than someone who weighs, say, 70kg. By the time racing starts, I hope to be closer to the 81kg mark. I typically ride 95-105'ish PSI on 23mm clinchers. 130psi is just thrown out there as a number, and a bit to get a rise out of you. Probably should have said 200psi! In reality, it will probably be closer to the 100-110 psi mark, depending on course and conditions. I'll play around with the pressures to see what gives me the nicest feel on corners and sprinting.

<thumbs up emoji>

Actually, you can help me a bit.

back of the envelope psi "equivalent". (assume tubulars with a round cross section for ease of calculation)

a 23mm tire has a cross sectional area of 415mm^2 a 21.5mm tire has an area of 363mm^2, making the wider tire 14.4% larger in area. Am I correct in thinking that the equivalent PSI for a the smaller tire would be 14% higher than the larger one? Or am I way off?

Well...based on your mass mentioned above, I plugged the 23mm measured width and the 21.5mm measured width into the "Berto Drop" pressure calculator I made for roller testing, and got (for a 50kg wheel load) pressures of 115 and 127psi respectively. So, that's looking more like an ~10% increase.

It's not all about the x-section area...casing tension comes into play as well (above is all assuming SAME tire construction).

So you're saying I SHOULD run (nearly) 130 psi?? ;-)

Swimming Workout of the Day:

Favourite Swim Sets:

2020 National Masters Champion - M50-54 - 50m Butterfly

Re: Tire width and rolling resistance. [JasoninHalifax] [ In reply to ]

Jan 26, 21 11:27

Post #11 of 29 (2945 views)

JasoninHalifax wrote:

Tom A. wrote:

JasoninHalifax wrote:

Tom A. wrote:

JasoninHalifax wrote:

Tom A. wrote:

JasoninHalifax wrote:

Rather timely find, as I was shopping for wider tubulars to use instead of my old, but unused, 21.5mm Vittoria Corsa CXIII's. I'll just stick with those pumped up to 130psi ;-)

...also, it's not just about "comfort", but about not being above the pressure breakpoint for the conditions. You may be able to handle the 130psi discomfort, but you'll be considerably slower.

I'm 91kg, so I think (IIRC) that my "breakpoint" is a bit higher than someone who weighs, say, 70kg. By the time racing starts, I hope to be closer to the 81kg mark. I typically ride 95-105'ish PSI on 23mm clinchers. 130psi is just thrown out there as a number, and a bit to get a rise out of you. Probably should have said 200psi! In reality, it will probably be closer to the 100-110 psi mark, depending on course and conditions. I'll play around with the pressures to see what gives me the nicest feel on corners and sprinting.

<thumbs up emoji>

Actually, you can help me a bit.

back of the envelope psi "equivalent". (assume tubulars with a round cross section for ease of calculation)

a 23mm tire has a cross sectional area of 415mm^2 a 21.5mm tire has an area of 363mm^2, making the wider tire 14.4% larger in area. Am I correct in thinking that the equivalent PSI for a the smaller tire would be 14% higher than the larger one? Or am I way off?

Well...based on your mass mentioned above, I plugged the 23mm measured width and the 21.5mm measured width into the "Berto Drop" pressure calculator I made for roller testing, and got (for a 50kg wheel load) pressures of 115 and 127psi respectively. So, that's looking more like an ~10% increase.

It's not all about the x-section area...casing tension comes into play as well (above is all assuming SAME tire construction).

So you're saying I SHOULD run (nearly) 130 psi?? ;-)

Turns out that at your mass, yeah...probably (that's a starting point).

http://bikeblather.blogspot.com/

Re: Tire width and rolling resistance. [Tom A.] [ In reply to ]

Jan 26, 21 11:33

Post #12 of 29 (2934 views)

Thanks Tom! That's a lot higher than I was expecting.

Swimming Workout of the Day:

Favourite Swim Sets:

2020 National Masters Champion - M50-54 - 50m Butterfly

Re: Tire width and rolling resistance. [JasoninHalifax] [ In reply to ]

Jan 26, 21 11:35

Post #13 of 29 (2929 views)

JasoninHalifax wrote:

Thanks Tom! That's a lot higher than I was expecting.

I'd still play with it and try running lower...until you start feeling like it's bottoming on harsh edges. The latex tubes inside will help fend off "snakebite" flats, but not completely ;-)

http://bikeblather.blogspot.com/

Re: Tire width and rolling resistance. [Tom A.] [ In reply to ]

Jan 26, 21 11:43

Post #14 of 29 (2918 views)

Tom A. wrote:

JasoninHalifax wrote:

Thanks Tom! That's a lot higher than I was expecting.

I'd still play with it and try running lower...until you start feeling like it's bottoming on harsh edges. The latex tubes inside will help fend off "snakebite" flats, but not completely ;-)

Back in the days when I raced (and was a bit lighter than I am now, getting back into it), I typically ran vittoria 21mm tubs anywhere between 90 psi in the wet up to 120. Never pinch flatted. That's the nice thing about tubs, there's a nice wide "envelope" of pressures that can be safely run. So that "was" going to be my starting point, but if you're saying that I can actually go a bit higher than that, then that gives me a bit more room to work with.

Swimming Workout of the Day:

Favourite Swim Sets:

2020 National Masters Champion - M50-54 - 50m Butterfly

Re: Tire width and rolling resistance. [JasoninHalifax] [ In reply to ]

Jan 26, 21 21:13

Post #15 of 29 (2812 views)

JasoninHalifax wrote:

New take on things.

"We now feel picking the right size tire is more a matter of looking at what level of comfort (and grip) is required. At some point, a smaller tire isn't able to provide the same comfort level (and grip) as its bigger counterpart because it will start bottoming out.

If you want to go as fast as possible, choose your required comfort level and pick the smallest tire that can provide that comfort for you."

The assumptions are wrong. Tire sink is a good proxy for comfort on very large bumps, but on small bumps and irregularities tire pressure is the dominant factor. The psi they chose based on tire sink, which happens to level out the Crr, will result in increased comfort as you increase tire size. You will also be less likely to bottom out.

If you want to maximize speed though, aero drag is the other thing to consider. Plus the last time I checked, the lowest Crr tires you can buy only come in a small size... make it simple...;)

Re: Tire width and rolling resistance. [JasoninHalifax] [ In reply to ]

Jan 27, 21 0:07

Post #16 of 29 (2778 views)

JasoninHalifax wrote:

I remember! I've never switched from 23's for the road. If only I could still find 20mm tires for my specialized trispokes....

One never knows, therefore I have stocked 20mm GP4k and 20mm SS (also the old one) for the next decade.

Re: Tire width and rolling resistance. [Tom A.] [ In reply to ]

Jan 27, 21 0:49

Post #17 of 29 (2761 views)

Thanks for this Jason and Tom! Perfect reasons for me to stick with what I was already doing - a bit like Jason at 95+ kg and Tri spoke on the front.

130 psi (but Veloflexes)

Re: Tire width and rolling resistance. [JasoninHalifax] [ In reply to ]

Jan 27, 21 6:27

Post #18 of 29 (2662 views)

JasoninHalifax wrote:

Tom A. wrote:

JasoninHalifax wrote:

New take on things.

"We now feel picking the right size tire is more a matter of looking at what level of comfort (and grip) is required. At some point, a smaller tire isn't able to provide the same comfort level (and grip) as its bigger counterpart because it will start bottoming out.
If you want to go as fast as possible, choose your required comfort level and pick the smallest tire that can provide that comfort for you."

https://www.bicyclerollingresistance.com/...KOG_Opmz8#conclusion

Not so new of a take, exactly...I was saying basically the same thing almost 4 years ago: https://forum.slowtwitch.com/...ost=6348919#p6348919

"To me, the driving factor for choosing tire width for a given application is the tire pressure I want to run for a given course. In other words, if the course conditions require lower pressures for comfort reasons, then I'm going to choose a tire width that allows for that pressure without causing other concerns, such as bottoming rims and/or "snakebite" flats. Of course, expected speeds/wind angles also comes into that calculus. This is how I ended up selecting 42mm wide tires for BWR this year...knowing the amount of off-road conditions, I basically wanted to be able to run close to MTB pressures ;-)

That type of thinking is somewhat opposite of how most folks approach the subject (i.e. pick a tire width and then ask "what pressure should I run?"...I like to think that it's not that wider tires allow lower pressures, but lower pressures require wider tires ;-)"

I remember! I've never switched from 23's for the road. If only I could still find 20mm tires for my specialized trispokes....

I have a few 20c old stock supersonics in a bag if you're interested. I got rid of my trispoke long ago and still have the tires.

Re: Tire width and rolling resistance. [JasoninHalifax] [ In reply to ]

Jan 28, 21 6:53

Post #19 of 29 (2532 views)

The calculation isn't about area, or even about drop, it's more about tire spring rate and in particular, dynamic spring rate.

When we built the SILCA pressure calculator, we used a few thousand field optimization points, essentially hundreds of actual break-point pressure calculations that are then curve fit with equations that allow us to interpolate the areas between known break points tested on known surfaces with known tires, etc... The calculator also has a pinch flat calculation built into it which looks at the amount of energy required to bottom the tire out at your weight for a given speed, so it will give you an idea of whether or not a given tire is appropriate for a given surface, at least on the smaller end of the spectrum

https://info.silca.cc/...-pressure-calculator

http://www.SILCA.cc
Check out my podcast, inside stories from more than 20 years of product and tech innovation from inside the Pro Peloton and Pro Triathlon worlds!
http://www.marginalgainspodcast.cc

Re: Tire width and rolling resistance. [joshatsilca] [ In reply to ]

Jan 28, 21 6:58

Post #20 of 29 (2529 views)

joshatsilca wrote:

The calculation isn't about area, or even about drop, it's more about tire spring rate and in particular, dynamic spring rate.

When we built the SILCA pressure calculator, we used a few thousand field optimization points, essentially hundreds of actual break-point pressure calculations that are then curve fit with equations that allow us to interpolate the areas between known break points tested on known surfaces with known tires, etc... The calculator also has a pinch flat calculation built into it which looks at the amount of energy required to bottom the tire out at your weight for a given speed, so it will give you an idea of whether or not a given tire is appropriate for a given surface, at least on the smaller end of the spectrum

https://info.silca.cc/...-pressure-calculator

I have a link to your calculator on my favourites bar (forgot I had it because I haven't ridden outside in months!), and it's on my Zwift laptop which I really just use for Zwift and Golden Cheetah. when I went to it, It tells me I have a risk of bottoming out a 21mm tire at an optimal 124/127 psi. So bang on Tom A's recommendation. I'm assuming that means clinchers though, I should be fine running tubulars at those pressures.

Swimming Workout of the Day:

Favourite Swim Sets:

2020 National Masters Champion - M50-54 - 50m Butterfly

Last edited by: JasoninHalifax: Jan 28, 21 7:00

Re: Tire width and rolling resistance. [joshatsilca] [ In reply to ]

Jan 28, 21 7:22

Post #21 of 29 (2499 views)

joshatsilca wrote:

The calculation isn't about area, or even about drop, it's more about tire spring rate and in particular, dynamic spring rate.

When we built the SILCA pressure calculator, we used a few thousand field optimization points, essentially hundreds of actual break-point pressure calculations that are then curve fit with equations that allow us to interpolate the areas between known break points tested on known surfaces with known tires, etc... The calculator also has a pinch flat calculation built into it which looks at the amount of energy required to bottom the tire out at your weight for a given speed, so it will give you an idea of whether or not a given tire is appropriate for a given surface, at least on the smaller end of the spectrum

https://info.silca.cc/...-pressure-calculator

re: spring rate. I think I get that, just that there's no easy way to measure spring rate in a tire, especially if you don't have the tire in question. In essence, using the cross sectional area (I think, although my assumptions could be way off) might be a good proxy for spring rate if you have a starting point. My thought process goes along the lines that area is proportional to tire volume (I know there's a small difference because the outer radius of the tire torus changes), and volume at a given pressure is proportional to the number of air molecules, and the number of air molecules at a given volume is proportional to the spring rate. I know it's not quite right, but puts me in the right ballpark at least.

Using that calculus, I know that if I were to run 20mm tires, at my current weight, I'd need to run pressures that exceed the max pressure rating of most clinchers, somewhere around 140-145psi by my calculation. (assuming 105 to 110 is ideal on a 23mm tire). Your calculator gives me 136 psi (optimal) with a warning to run 155psi because of pinch flat risks.

Swimming Workout of the Day:

Favourite Swim Sets:

2020 National Masters Champion - M50-54 - 50m Butterfly

Re: Tire width and rolling resistance. [joshatsilca] [ In reply to ]

Feb 11, 21 13:33

Post #22 of 29 (2100 views)

joshatsilca wrote:

The calculation isn't about area, or even about drop, it's more about tire spring rate and in particular, dynamic spring rate.

When we built the SILCA pressure calculator, we used a few thousand field optimization points, essentially hundreds of actual break-point pressure calculations that are then curve fit with equations that allow us to interpolate the areas between known break points tested on known surfaces with known tires, etc... The calculator also has a pinch flat calculation built into it which looks at the amount of energy required to bottom the tire out at your weight for a given speed, so it will give you an idea of whether or not a given tire is appropriate for a given surface, at least on the smaller end of the spectrum

https://info.silca.cc/...-pressure-calculator

I am nut sure i understand the above.
Is it possible to have the same spring rate between a 23 mm tire and a 25 mm tire with appropriate pressure?
And would that result in the same perceived 'comfort'?

Re: Tire width and rolling resistance. [Jo O.] [ In reply to ]

Mar 6, 21 12:14

Post #23 of 29 (1717 views)

Sorry to be over a month coming back to answer this!

Yes, you can use air pressure to get to equivalent static spring rates between tires of different sizes when testing using he same impingement anvil.. which is to say that if you use a test rig you can find the point at which a 23 and 25 are equal for flat surface, or equal for 5mm half round, or equal for 5cm cobble shape.. etc. the challenge comes in that when the impinging object shape changes, the pressure required for equal spring rate changes non-linearly between the tires.. and this non-linearity favors the larger tire as the reduced angle of the casing just outside the contact patch of the tire allows the larger tire to more easily adapt contact patch geometry over rough surfaces.

So if we tune a 23 and a 25 to have identical flat surface spring rates.. the 25 will then give us decreasing spring rates as we impact it with ever smaller bumps..

http://www.SILCA.cc
Check out my podcast, inside stories from more than 20 years of product and tech innovation from inside the Pro Peloton and Pro Triathlon worlds!
http://www.marginalgainspodcast.cc

Re: Tire width and rolling resistance. [joshatsilca] [ In reply to ]

Mar 6, 21 12:57

Post #24 of 29 (1681 views)

joshatsilca wrote:

https://info.silca.cc/...-pressure-calculator

LOVE the calculator.

Is aerodynamics taken into account in this calculator in any way?

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Re: Tire width and rolling resistance. [joshatsilca] [ In reply to ]

Mar 6, 21 14:46

Post #25 of 29 (1636 views)

joshatsilca wrote:

.
.. the pressure required for equal spring rate changes non-linearly between the tires...

Can you quantify this non-linearity?

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