Rim width

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schroeds
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Rim width

Postby schroeds » Wed Feb 25, 2015 9:54 pm

Looking at investing in some new hoops, and getting confused by all the hoopla (pun intended) around rim width.

I have identified a nice wheel at the right price but the rim is a conventional 21mm, however the new convention seems to be saying I should be at 23 front and more rear.

I gather the "ride quality" is the benefit...

So my question is this: is this a marketing driven issue or are there really benefits? If so what are they?

And how do wider tyres fit into all this? Do wider tyres on a narrow rim achieve the same, less or more than a wider rim?

Finally a request: can we base our answers as far as possible not on what the brochure says but what we have personally experienced or researched factual/proven data etc

Can of worms, I know!

Many thanks for input
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singlespeedscott
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Re: Rim width

Postby singlespeedscott » Wed Feb 25, 2015 10:16 pm

Wide tyres are definitely where it's at. As for rim width I personally thinks it's unimportant when dealing in road bike widths. A 25-32mm tyre is still going to have the same volume regardless of rim width. It's the volume that makes the tyre more comfortable not its width. Just run those fatter tyres at lower pressures to get the benefits of speed, comfort and grip.
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Nobody
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Re: Rim width

Postby Nobody » Thu Feb 26, 2015 8:58 am

schroeds wrote:So my question is this: is this a marketing driven issue or are there really benefits? If so what are they?

And how do wider tyres fit into all this? Do wider tyres on a narrow rim achieve the same, less or more than a wider rim?
It is marketing driven to a degree. Benefits are supposed to be straighter sidewalls so less stress on tyre sidewalls (Sheldon has mentioned this) and greater volume for same size tyre so the benefits of a bigger tyre. Also better rim to tyre match for aero benefits. I've been running 23 tyres on 17 & 19mm inner width rims (23 & 24.5mm outer) for years. They make your 23 tyres somewhere between 24 and 26mm in measurement depending on brand. Is it better than a skinny rim with a fatter tyre? I'd say only marginally. I doubt anyone would be able to tell in a blind test. Just get whatever.

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schroeds
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Re: Rim width

Postby schroeds » Thu Feb 26, 2015 9:25 am

Yeah it all seems subtle at best and witchcraft at worst!
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RonK
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Re: Rim width

Postby RonK » Thu Feb 26, 2015 12:30 pm

Wider tyres on wider and slightly shallower (than deep profile aero) rims have recently been shown to be more aerodynamic. The minor differences though are unlikely to matter to most of us.
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MattyK
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Re: Rim width

Postby MattyK » Thu Feb 26, 2015 12:35 pm

RonK wrote:Wider tyres on wider and slightly shallower (than deep profile aero) rims have recently been shown to be more aerodynamic. The minor differences though are unlikely to matter to most of us.

This conundrum has had me tossing up between some Fulcrum Quattros or a Kinlin XC279 build for about 6 months...

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Re: Rim width

Postby biker jk » Thu Feb 26, 2015 1:22 pm

I did a Kinlin XC-279 build a little while ago. Very solid rim at 23mm wide, 28mm deep. A 23mm Vittoria Rubino Pro tyre measures 25mm wide on this rim. You don't get the light bulb profile, so the wheel/tyre combination should be more aero. Cornering is slightly better with the wider contact patch and less deflection of the sidewall. I ran 10psi lower pressure and the ride is very good.

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schroeds
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Re: Rim width

Postby schroeds » Thu Feb 26, 2015 1:56 pm

I just pressed the button on some campy shamal mille with the yummy black brake track. 20.5mm rim so if my speed plummets I'm blaming you lot! !
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Re: Rim width

Postby warthog1 » Thu Feb 26, 2015 1:57 pm

biker jk wrote: A 23mm Vittoria Rubino Pro tyre measures 25mm wide on this rim. You don't get the light bulb profile, so the wheel/tyre combination should be more aero.


+1
The aero dynamic resistance is a larger factor in overall drag than rolling resistance;

Dear Lennard,
Before I go out and buy myself some fatter tires, what testing have you done with aerodynamics? Does the increased wind surface area with the larger tires cancel the positive effects of lower rolling resistance?
— Brad

Dear Brad,
Very good question. As you’re probably aware, the aerodynamic data put forth by Hed and Zipp in support of wider rims for improved aerodynamics shows that it definitely depends on the rim. In general, if you ride very fast, the aerodynamic drag of the fatter tires will cost you more in speed than the rolling resistance benefit will gain you.

In an email, Zipp lead engineer Josh Poertner said:

In general, a wider tire of (the) same construction will have lower rolling resistance for exactly the reasons (you stated). Ironically, the best description and data on this comes from studies done in Britain in the 1800’s looking to optimize the width and diameter of wheels for locomotives. There is also a lot of great info related to this in “Bicycling Science” from MIT press, as well as Paul Van Valkenberg’s writing on racecar tires.

Generally, though, the decrease in rolling resistance becomes smaller as the tires get bigger. So for example, going from a 19mm to a 20mm may save 1 watt, from a 20mm to a 21mm may save 0.8 watt and from a 23mm to a 25mm may save 0.3 watt. There is great data on this in “Bicycling Science,” using old Avocet Fasgrip tires, which were available from 18-32mm. The 28mm and 32mm were nearly identical, but moving from 18mm to 25mm saved a few watts.

What they are missing is the aerodynamic piece. We have data from the Zipp 303 launch showing the 303 with different width tires (see graph). The figure tells the story of how you can really optimize for tires below a certain (width) number, but eventually the tire really dominates the airflow and ruins everything. In general, our wheels are optimized around 23mm tires, which means that 21mm tires usually run about equal, maybe a fraction of a watt faster, but don’t change the behavior of the wheel. Moving to a 25mm adds drag, but can also change the stall behavior of the wheel. And by the time you are at 27mm, you have something that behaves quite differently.

The question really needs to be in regards to the balance of lower Crr (coefficient of rolling resistance) from the wider tire against the aero penalty. The 303 was designed to be as good as possible with 23mm tires, and as a result, its rim is 28.5mm wide. To behave similarly with the 25mm, it would likely have to be at least 2mm wider. In the graph you see how the 25mm tire has the same curve shape as the 23mm tire on the X45 (code for 303FC clincher). The 27mm tire is on the 285FC (code for 303FC tubular), and you notice that not only is the drag higher, but the curve shape is completely different. In fact, the curve shape looks more like the Easton or Mavic. This is indicative of the rim not being able to clean up the dirty air behind the tire. Ultimately, the offset should be Crr watts vs. Aero watts. In this case you have grams of drag on the left; every nine grams is one watt, so from 23mm to 25mm, you have nearly no penalty up to 10 degrees, and then three-to-six watts at the higher yaw. With the 27mm, you have something like no penalty to five degrees, and then a five-to-eight watt penalty after that.

Ultimately for the Specialized I would say that the 0.2 watt (0.3 to 0.8 watt) of rolling resistance does not overcome the zero-to-six-watt aero penalty.

Last interesting note: we have been working with Jordan Rapp on this since he noticed that his ‘training Firecrest’ wheels with 25’s were ‘twitchy’ compared to his race wheels with 23’s… we thought this might be largely aerodynamic, but the shorter contact patch (you) discuss is actually the culprit; the longer contact patch serves to resist steering input and adds a slight damping effect to steering inputs. By lowering tire pressure to increase contact patch, the effect could be eliminated, even though the aero properties of the wheel remain the same.

― Lennard



Read more at http://velonews.competitor.com/2012/03/ ... Acy8J3b.99

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schroeds
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Re: Rim width

Postby schroeds » Thu Feb 26, 2015 2:54 pm

to summarise:

If you ride "very fast" and are lucky enough to hit a somewhat elusive sweet spot in the relationship between rim and tyre width - a sweet spot that's variable depending on your angle of lean at any given time - then you could save potentially somewhere between 0.3 and 2 watts. Since you're riding very fast lets say you're pushing out 250 watts, the best you'd hope for is well under 1% faster/less effort.

Have I got that right?
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MattyK
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Re: Rim width

Postby MattyK » Thu Feb 26, 2015 5:26 pm

biker jk wrote:I did a Kinlin XC-279 build a little while ago. Very solid rim at 23mm wide, 28mm deep. A 23mm Vittoria Rubino Pro tyre measures 25mm wide on this rim. You don't get the light bulb profile, so the wheel/tyre combination should be more aero. Cornering is slightly better with the wider contact patch and less deflection of the sidewall. I ran 10psi lower pressure and the ride is very good.


Assuming that was in response to my post, I'm guessing it's pretty much impossible to quantify a 23 x 28mm rim vs a 21 x 35mm rim... Plus the arguments of weight, looks, spare parts, stiffness, cost, reliability and so on...

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biker jk
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Re: Rim width

Postby biker jk » Thu Feb 26, 2015 5:44 pm

MattyK wrote:
biker jk wrote:I did a Kinlin XC-279 build a little while ago. Very solid rim at 23mm wide, 28mm deep. A 23mm Vittoria Rubino Pro tyre measures 25mm wide on this rim. You don't get the light bulb profile, so the wheel/tyre combination should be more aero. Cornering is slightly better with the wider contact patch and less deflection of the sidewall. I ran 10psi lower pressure and the ride is very good.


Assuming that was in response to my post...


You assume wrongly.

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schroeds
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Re: Rim width

Postby schroeds » Thu Feb 26, 2015 5:45 pm

Plus the fact that in my case I would have to buy new brakes to accommodate a wider rim.

Plus if you change wheels (ie to race etc) having different rim widths is a PITA
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singlespeedscott
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Rim width

Postby singlespeedscott » Thu Feb 26, 2015 7:27 pm

Think about it this way. Do you want to be comfortable on the majority of your rides. If the answer is yes go the fat tires and don't worry about the width. If you spend the majority of your time riding over 40kmhr on smooth hot mix go the smaller tyre with the fat aero rim.
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schroeds
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Re: Rim width

Postby schroeds » Thu Feb 26, 2015 7:35 pm

Now THAT makes sense (or maybe it's just what I wanted to hear! )
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Re: Rim width

Postby RonK » Thu Feb 26, 2015 8:14 pm

schroeds wrote:I just pressed the button on some campy shamal mille with the yummy black brake track. 20.5mm rim so if my speed plummets I'm blaming you lot! !

You won't regret getting Shamals.
Cycle touring blog and tour journals: whispering wheels...

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Re: Rim width

Postby dnalwon » Wed Mar 25, 2015 10:33 am

Switched to HED Ardennes with wider rims 2 years ago and the improved handling was very noticeable especially cornering. Also, ride is a little smoother.
Only advice is to go with the stallion build (28 spokes on rear) if in doubt.

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