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PostPosted: Wed Jun 08, 2016 12:27 am 
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Hello,

After ordering a pair of custom built wheels with a 19mm internal width (24mm outer -- Kinlin x22), I did some research on what tires are recommended for wide rims. It seems there is a disparity between what is recommended. According to the ETRTO chart for recommended tire/width combos, mounting a 23mm tire on a 19mm internal width rim is not considered safe. However, most manufactures recommend 23mm tires for aerodynamics. I race, but value my safety over aerodynamics. I do a lot of 70+ km/h descending, and want to make sure that my tire will be secure. What am I risking (or not risking) by running a narrow tire on a wide rim?

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I ask because 25mm tires on a 24mm rim will not fit on my frame, so I am limited to 23mm tires.

Thanks for the help.


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PostPosted: Wed Jun 08, 2016 12:56 am 
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Location: Loveland, CO
For ETRTO I think rim width comparison should be done on internal width and not external width. On my Hed wheels the external width is 25mm but the internal width is pretty wide at 21mm. I'm using 25mm Conti 4000SII on these rims and they seem too narrow for the wide internal width of the Hed rims.


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PostPosted: Wed Jun 08, 2016 1:01 am 
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pdlpsher1 wrote:
For ETRTO I think rim width comparison should be done on internal width and not external width. On my Hed wheels the external width is 25mm but the internal width is pretty wide at 21mm. I'm using 25mm Conti 4000SII on these rims and they seem too narrow for the wide internal width of the Hed rims.

Thanks for the input. Not sure what you mean, I believe the chart does refer to internal width, as was I in my post.


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PostPosted: Wed Jun 08, 2016 1:40 am 
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Posts: 235
I have a pair of carbon rims that are 19mm internal width with a pair of 23mm GP4000SII tyres mounted. I corner with great confidence and control in both crits and descents.
The rims are tubeless ready which means the beads stay put almost too well. Of course I use tubes too.

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PostPosted: Mon Jun 13, 2016 1:11 pm 
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Posts: 73
My Easton's are 19mm wide inside/28mm outside and run 23mm Pro One's tubeless that measure 27mm inflated to 90psi. Simply awesome! Get the volume and ride of a larger tire without the weight penalty plus better aerodynamics if that matters to you.


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PostPosted: Fri Jun 17, 2016 8:32 am 
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On the topic of aero - don't believe everything you hear. 25mm hold the candle - better rolling resistance, comfort, cornering (due to larger contact patch), aero.

http://flocycling.blogspot.com/2016/06/ ... study.html

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PostPosted: Fri Jun 17, 2016 8:49 am 
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petereps wrote:
However, most manufactures recommend 23mm tires for aerodynamics.

Weird at a time where a good deal of the world tour peloton seems to be on 25mm. Maybe they just haven't updated their blurbs yet?

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PostPosted: Fri Jun 17, 2016 11:40 am 
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I tried 25mm GP4K's on my Bora wheels (17mm internal 24mm external) and found them unpleasantly large. Came up and over 27mm and looked quite bulbous. Went back to 23mm GP4K's which came up at a 25mm and was much happier. Handling better and comfort comparable to my winter wheels which run 25mm's on 15C rims (nice lightbulb effect though). I've tried different tyre pressures and they seem best at 95/100 for me at 57kg. My thoughts are that it depends on the tyre/wheel combo but you want the tyre to be a fraction wider than the rim but not much, maybe 1mm. I'm also sure Zipp were recommending 23mm tyres with all their rims for speed?

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PostPosted: Fri Jun 17, 2016 1:52 pm 
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i like the shape of 23c tires on 25mm rims.. i like going fast down hills and leaning over a lot. i find 25c tires have too much of a balloon profile for my liking. you can still run lower pressures too as you have a lot more air under the tire.
also with the effect that wider rims have on the real width of tires when mounted pretty much makes the terms 23mm tire and 25mm tire redundant..

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PostPosted: Fri Jun 17, 2016 7:27 pm 
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Your tires look like balloon because wheels are not wide enough. Look at wheels with 27-28 mm outer width. Inner width plays a role of increasing the volume and outer width to sit flush with a tire.


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PostPosted: Fri Jun 17, 2016 9:53 pm 
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I'm with sugarkane. Most "23mm" tires are actually 25mm+ on 18 or 20mm inner width rims. 75 to 82psi is more than enough, and much wider with the tires and steering seems to slow down. I did 105 miles with 11k feet of climbing (so 170km and 3300m of climbing) on mixed surfaces 2 weekends ago. Perfect on tires that called themselves 23s but actually are about 26.25mm wide on Pacenti SL25s (20mm inside width).

Also worth noting is that tubulars generally run true to size, so the "25mm tubulars" that most pros are on are actually narrower than a lot of 23mm clinchers that people run on wide rims.

To talk about the sizes that are printed or embossed onto the tires is something of a tail-chasing exercise these days. Has been for a while.

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PostPosted: Fri Jun 17, 2016 10:10 pm 
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^Agreed. When I use r clinchers on wider rims (HED C2) they are "23"mm. Any bigger and the volume gets so large they start feeling like balloons and mushy feeling. And yes, tubulars don't change with rim width as clinchers do. I run tubulars primarily and can see no reason to go bigger than 25mm. In a clincher world with a wider rim, that would translate to a 23mm tire for all round good road feel and handling. Save the larger tires for commuters and gravel.

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PostPosted: Sat Jun 18, 2016 8:10 pm 
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I wonder why the OP would think they are not safe though. I am racing on 25mm IRC tubeless tyres at the moment. On my Pacenti SL23 V1 rims they are 27mm and I am not slower. So wide works quite well.

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PostPosted: Sat Jun 18, 2016 8:33 pm 
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I could see the case where a clincher could actually be too narrow for a wide rim, and instead of the air pressure exerting most of its force sideways, forcing the bead firmly in its seat, the tire is so narrow that the force is more upwards and the bead never really gets seated properly and can "pop off" the rim. I would think the discrepancy would have to be fairly large however, like using a 21mm clincher on a fairly wide rim.

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PostPosted: Sat Jun 18, 2016 10:25 pm 
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This might be the case with some modern tyres and modern rims, especially if tubeless, but there are no guarantees that will work for any and all tyre-rim combination of a particular width. That's exactly where ETRTO standards come from, determining width combinations that have enough of a safety margin to be expected to work most conditions and with most tyres and rims. Here's Mavic's take on the subject: http://engineerstalk.mavic.com/the-righ ... rim-width/


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