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The science behind wide rims?

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The science behind wide rims?

Old 10-26-11, 01:22 PM
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blaronn
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The science behind wide rims?

I know they've been around forever but new 23-24mm+ road rims seem to be making a surge lately (Velocity A23, HED Belgium C2, etc.) Alleged benefits include better aerodynamics with 23mm tires, less rolling resistance, more tubular-like feel, increased stability, and less chance for pinch flats. Is this science or just another marketing scheme to sell more stuff? (or just another cycling fad)

I've seen the Flo writeup on wide rims, but it seems to be largely opinion based.

Is there anything else out there that lends credibility to the wide-rim claims?
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Old 10-26-11, 01:39 PM
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Originally Posted by blaronn View Post
Is there anything else out there that lends credibility to the wide-rim claims?
Well, the wind tunnel data and rolling resistance tests all show that wider is better in nearly all conditions, it's not a matter of opinion.
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Old 10-26-11, 01:48 PM
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Aero is funny stuff; air frequently does things that you wouldn't expect, especially at low Reynolds numbers.

A big chunk of drag comes from the turbulence that comes from the airflow attempting to rejoin the free air stream after flowing over something structural. A way to reduce the turbulance is to fill in the void with something and minimize the amount of change in direction that the air has to make - this is the theory behind deep section rims and the tails on aero helmets. By making something wider, you might be able to fill in more of the turbulance zone, much the way making it longer does.

But cross sectional area increases drag too, so there is a tradeoff between potentially reducing drag from turbulance and definately increasing drag via an increase in cross sectional area. It may work, it may not, and there are undoubtably conditions where either scenario applies.

Big hand, small map - yes, under the right conditions it could very well work from an aero perspective. But the devil boy howdy lives in the details.

DG
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Old 10-26-11, 01:53 PM
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I've been wondering the same thing, especially because I liked the feel/ride quality of Madfibers so much. They're very thin, and today we've had a few threads on why this is bad. I felt like a set of Zipp 303s were a bit easier to spin up, although perceived effort can be kind of unreliable.



The rims are kind of narrow.
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Old 10-26-11, 03:42 PM
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Originally Posted by rpeterson View Post
Well, the wind tunnel data and rolling resistance tests all show that wider is better in nearly all conditions, it's not a matter of opinion.
Care to share links to these data & tests?
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Old 10-26-11, 03:45 PM
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Originally Posted by Seattle Forrest View Post
I've been wondering the same thing, especially because I liked the feel/ride quality of Madfibers so much. They're very thin, and today we've had a few threads on why this is bad. I felt like a set of Zipp 303s were a bit easier to spin up, although perceived effort can be kind of unreliable.




The rims are kind of narrow.
The wind tunnel data also supports that though Madfibers are quite deep, they are not more aero than a less deep wheel like a 404 or 303 (for sure the new 303 firecrest is "faster," but wind tunnel data isn't out yet that I've seen).
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Old 10-26-11, 03:53 PM
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Originally Posted by blaronn View Post
Care to share links to these data & tests?
Just google "Hed wind tunnel" or "Firecrest wind tunnel" and you'll find all sorts of stuff.

Same for "rolling resistance wide rim"
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Old 11-09-11, 06:49 PM
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Originally Posted by blaronn View Post
I know they've been around forever but new 23-24mm+ road rims seem to be making a surge lately (Velocity A23, HED Belgium C2, etc.) Alleged benefits include better aerodynamics with 23mm tires, less rolling resistance, more tubular-like feel, increased stability, and less chance for pinch flats. Is this science or just another marketing scheme to sell more stuff? (or just another cycling fad)

I've seen the Flo writeup on wide rims, but it seems to be largely opinion based.

Is there anything else out there that lends credibility to the wide-rim claims?
Here is some additional information about rolling resistance if that helps (
http://www.slowtwitch.com/...ling_events_226.html)
. If you have any additional questions for me, please feel free to ask.

All the best,
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Old 11-09-11, 07:06 PM
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Rolling resistance is not effected by rim width from what I've seen(only 2 data sets); i.e. the same tire on a 19mm rim and 22mm rim had the same rolling resistance. What I HAVE seen is that wider tires typically roll a little bit quicker than the same brand/model of a narrower tire.

What wider rims really do(and the only provable benefit I know of), is make the most aerodynamic system out of the tires customers have decided they are going to run either way. i.e. A Hed 3 with a 23mm tire is a friggin aerodynamic mess; however the new Zipp Firecrest wheels are lights out fast with 21 or 23mm tires.

The other things that I've seen is positive opinions on ride quality as you noted.

If anyone actually has data on RIM width actually affecting rolling resistance I'd love to see it.
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Old 11-10-11, 10:26 AM
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Originally Posted by Triguy View Post
Rolling resistance is not effected by rim width from what I've seen(only 2 data sets); i.e. the same tire on a 19mm rim and 22mm rim had the same rolling resistance. What I HAVE seen is that wider tires typically roll a little bit quicker than the same brand/model of a narrower tire.

What wider rims really do(and the only provable benefit I know of), is make the most aerodynamic system out of the tires customers have decided they are going to run either way. i.e. A Hed 3 with a 23mm tire is a friggin aerodynamic mess; however the new Zipp Firecrest wheels are lights out fast with 21 or 23mm tires.

The other things that I've seen is positive opinions on ride quality as you noted.

If anyone actually has data on RIM width actually affecting rolling resistance I'd love to see it.
The wider tires roll faster because they make the contact patch shorter and wider. A wider rim (using the same tire) also makes the contact patch shorter and wider. If you are using an identical tire, a shorter wider contact patch has less rolling resistance. This is why a wider rim can effect the rolling resistance.
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Old 11-10-11, 12:32 PM
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You're using logic, I've seen data. The limited data I've seen, there was no difference. I know why wider tires roll faster. I know that wider rims make tires slightly wider. I however, have seen data which did not show any difference. I did not ask for logic, I understand the logic. I asked for data.

As far as I can tell my original assertion is correct. The only certain reason(proven at this time) wider rims are faster/better is that they create a faster system with the tires the end users have decided they will use, ~23mm. I'm of course not referring to shape, I think the new blunter trailing edge would be effective for whatever tire size one decided to design around.

I know my requests for data will go unheard. When people asked Hed for data, Hed went silent. However, Flo feel free to send a wide rim and a couple of tires to Al Morrison, I'm sure he'd be more than happy to try.
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Old 11-10-11, 12:48 PM
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Originally Posted by Triguy View Post
You're using logic, I've seen data. The limited data I've seen, there was no difference. I know why wider tires roll faster. I know that wider rims make tires slightly wider. I however, have seen data which did not show any difference. I did not ask for logic, I understand the logic. I asked for data.

As far as I can tell my original assertion is correct. The only certain reason(proven at this time) wider rims are faster/better is that they create a faster system with the tires the end users have decided they will use, ~23mm. I'm of course not referring to shape, I think the new blunter trailing edge would be effective for whatever tire size one decided to design around.

I know my requests for data will go unheard. When people asked Hed for data, Hed went silent. However, Flo feel free to send a wide rim and a couple of tires to Al Morrison, I'm sure he'd be more than happy to try.
Your request for data will not go unheard. Give me some time and I'll give you data.
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Old 11-13-11, 05:53 PM
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Originally Posted by Triguy View Post
You're using logic, I've seen data. The limited data I've seen, there was no difference. I know why wider tires roll faster. I know that wider rims make tires slightly wider. I however, have seen data which did not show any difference. I did not ask for logic, I understand the logic. I asked for data.

As far as I can tell my original assertion is correct. The only certain reason(proven at this time) wider rims are faster/better is that they create a faster system with the tires the end users have decided they will use, ~23mm. I'm of course not referring to shape, I think the new blunter trailing edge would be effective for whatever tire size one decided to design around.

I know my requests for data will go unheard. When people asked Hed for data, Hed went silent. However, Flo feel free to send a wide rim and a couple of tires to Al Morrison, I'm sure he'd be more than happy to try.
I was intrigued by your request for data so we ran a test over the weekend to gather some data. This data proves that our FLO WIDE RIDE rims create a shorter and wider contact patch. Here is a link to the blog article which highlights our experiment and results.

http://bit.ly/t8lmGk

All the best,
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Old 11-13-11, 05:59 PM
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Well, winter's coming. I suppose we have to talk about SOMETHING.
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Old 11-13-11, 06:15 PM
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Originally Posted by FLO Cycling View Post
I was intrigued by your request for data so we ran a test over the weekend to gather some data. This data proves that our FLO WIDE RIDE rims create a shorter and wider contact patch. Here is a link to the blog article which highlights our experiment and results.

http://bit.ly/t8lmGk

All the best,
OK. Nice job. Wider rims create a shorter and wider contact patch. Does this translate into lower rolling resistance? Theoretically, yes, but do you have actual rolling resistance data to prove it?
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Old 11-13-11, 06:33 PM
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I can see how changing the deformation with a wider rim could lead to lower resistance but it seems like this data focuses only on moment of inertia. More resistance from the moment of inertia, from a difference of 2mm specifically. Isn't that going to account for a very small portion of the tire's rolling resistance, and only applicable during acceleration? It looks to me like we need an actual measurement of resistance with the wide rim vs a narrower one.
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Old 11-14-11, 10:09 PM
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Originally Posted by wacomme View Post
OK. Nice job. Wider rims create a shorter and wider contact patch. Does this translate into lower rolling resistance? Theoretically, yes, but do you have actual rolling resistance data to prove it?
+1

I don't think anyone contests the claims that wider rims = wider contact patch. What I'm curious about is whether wider contact patch = decreased rolling resistance, *and* by how much. Chris, it sounds like you just know (through education or experience) that this would lead to lower Crr and you might be assuming that we know it too. Can you share any non-subjective sources that would enlighten those of us who don't know it?

Also, any idea how to quantify the significance of widening the contact patch by .32mm (80psi) or .16mm (120psi) on Crr? Those numbers *seem* very insignificant to me but without objective data/knowledge/experience to back that up it's just a guess. It sounds like you have the data/knowledge/experience to back it up but may take for granted that we do as well.

By the way, thanks for running those tests and compiling it in the blog. Very informative.
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Old 11-14-11, 10:20 PM
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Originally Posted by rpeterson View Post
Just google "Hed wind tunnel" or "Firecrest wind tunnel" and you'll find all sorts of stuff.

Same for "rolling resistance wide rim"
I admittedly didn't follow and read all links but the only thing I found close to a study on the effect of wide rims on rolling resistance showed no improvement.
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Old 11-14-11, 10:30 PM
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Originally Posted by FLO Cycling View Post
I was intrigued by your request for data so we ran a test over the weekend to gather some data. This data proves that our FLO WIDE RIDE rims create a shorter and wider contact patch. Here is a link to the blog article which highlights our experiment and results.

http://bit.ly/t8lmGk

All the best,
I applaud your taking the time to actually measure the difference in contact patch, and having the guts to post the results. It's unfortunate that a 27% increase in rim width only shortens the contact patch by 2.9% (@120psi), but that's the nature of dealing with round things. What did you use to measure those ink stains to the hundredth of a mm, btw?

If we assume that each of the resultant forces in Tom Anhalt's figure 2 move towards each other by half that amount, then the net resultant torque due to tire sidewall flex only decreases by 1.45%. Considering the magnitude of typical rolling resistance, it's no wonder that difference doesn't show up in any real-world Crr testing.
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Old 12-30-11, 04:29 PM
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Originally Posted by wacomme View Post
OK. Nice job. Wider rims create a shorter and wider contact patch. Does this translate into lower rolling resistance? Theoretically, yes, but do you have actual rolling resistance data to prove it?
First of all I owe everyone here an apology. For some reason I was not notified when this thread was updated. I am sorry that it has taken me so long to reply.

To answer your question, we do not have actual rolling resistance data to prove it. Our discussions to date have been based on theory using different contact patch lengths while keeping all other variables the same. That said, we would not be opposed to performing such a test. We have spent a lot of dollars on R&D to date and do not have the budget to purchase this equipment. If however, anyone knows of a lab where we could test our wheels vs. a standard wheel, we would certainly look into the opportunity assuming the price it right.

Do you know someone who could test the wheels for us?

Again... I'm really sorry about responding so late to your question.
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Old 12-30-11, 04:32 PM
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Originally Posted by wphamilton View Post
I can see how changing the deformation with a wider rim could lead to lower resistance but it seems like this data focuses only on moment of inertia. More resistance from the moment of inertia, from a difference of 2mm specifically. Isn't that going to account for a very small portion of the tire's rolling resistance, and only applicable during acceleration? It looks to me like we need an actual measurement of resistance with the wide rim vs a narrower one.
I'm guessing you are correct. The difference would more than likely be small. However, rolling resistance exists even without acceleration. As long as an object is rolling (acceleration or no acceleration) rolling resistance exists.
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Old 12-30-11, 04:34 PM
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Originally Posted by blaronn View Post
+1

I don't think anyone contests the claims that wider rims = wider contact patch. What I'm curious about is whether wider contact patch = decreased rolling resistance, *and* by how much. Chris, it sounds like you just know (through education or experience) that this would lead to lower Crr and you might be assuming that we know it too. Can you share any non-subjective sources that would enlighten those of us who don't know it?

Also, any idea how to quantify the significance of widening the contact patch by .32mm (80psi) or .16mm (120psi) on Crr? Those numbers *seem* very insignificant to me but without objective data/knowledge/experience to back that up it's just a guess. It sounds like you have the data/knowledge/experience to back it up but may take for granted that we do as well.

By the way, thanks for running those tests and compiling it in the blog. Very informative.
The numbers are certainly small. See my post above. Perhaps we can find a place to do an actual rolling resistance test.
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Old 12-30-11, 04:37 PM
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Originally Posted by frenchyge View Post
I applaud your taking the time to actually measure the difference in contact patch, and having the guts to post the results. It's unfortunate that a 27% increase in rim width only shortens the contact patch by 2.9% (@120psi), but that's the nature of dealing with round things. What did you use to measure those ink stains to the hundredth of a mm, btw?

Thanks for the compliments. To answer your question, we used a set of digital calipers to measure the contact patch lengths.

If we assume that each of the resultant forces in Tom Anhalt's figure 2 move towards each other by half that amount, then the net resultant torque due to tire sidewall flex only decreases by 1.45%. Considering the magnitude of typical rolling resistance, it's no wonder that difference doesn't show up in any real-world Crr testing.

You make a good point. The theory is more than likely correct but the differences may be very small and tough to detect.
Take care,
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Old 12-30-11, 04:55 PM
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I'm sure its true but its all about tradeoff. rolling resistance, aero, weight,

I'm also going to throw out there the theory that the ride is better on wider rims due to them being able to absorb bumps better since the tire is spread wider and the bump will push into the tire more so than it would on a rounder narrow tire in which the bump will force the tire to spread outwards. And I base this on absolutely nothing.
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Old 12-30-11, 05:08 PM
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tape a flashlight on the back of ur bike. turn the flashlight on. you are now travelling at the speed of light.
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