Rim width clearance, (dis)advantages of 25mm width
 

I have searched for hours and can't find much on 25mm rims. If I am running 25c tires, what would the implications be on running 23 vs 25 wide rims? Pro's/cons of each? Also How do I check if my frame will accept a 25 wide rim?

It'll typically be more difficult to change tyres

Measure how much clearance you have with your current tires.

https://janheine.wordpress.com/2013/...ire-can-i-run/

23 mm tire on 25 mm is oretty extreme. I wouldn't do it.

When I switched from my old carbon clinchers which were around 20mm to my Enve 3.4's which are 24/26, about the only difference I noticed was the tire being wider on the rim since it wasn't being pinched as much. Well, the ride was nicer too.

I'm running 23c Continental GP4000 tires on a 25mm rim. They measure about 26.5 wide on that rim. I use the same air pressure that I was using for my older rims with 25c tires. I've had no problems, and wouldn't buy a narrower rim.

The rim is tubeless compatible, so the beads lock in pretty well. Perhaps a different rim might be a little less secure? Some other threads have mentioned difficulty when replacing tires, with a tight bead fit. But my rims are very easy when changing tires.

My only concern was that the tire sidewalls are a little more exposed to sharp objects on the road, being more spread out instead of curved back toward the rim.

On a different gravel bike with mini-V brakes, the brakes just weren't designed for rims that wide. The brake arms are supposed to be more or less vertical, not angled outward. But the rims are too wide for that to work--the adjustment spacers between the pads and the arms are too thick.

My solution was to grind down the pads on my bench grinder.

Sheesh, I have 23s on 24.5mm rims (Pacenti SL23). It's fine. Y'all really need to not be so worried about this stuff. The tire sits wider. That's all.

I think he was being sarcastic.

Nope. I was being serious.

Well then. I'll just leave it at that then.

This chart is pretty definitive and quite conservative relative to what you guys are advocating:
http://s120.photobucket.com/user/old_fool/media/bikeparts/tire-to-rim.png.html
I'm assuming a 4 mm differential between inside and outside width. That's pretty standard. Sheldon Brown admits the chart is a bit conservative, but even if you're willing to fudge one tire size larger, there is no way you should run 25 mm tires on a 25 mm outside (21 mm inside) rim. That is three sizes beyond the recommendation. Do what you want, but a little discretion might be in order.

That chart is dumb.

I think 6mm is closer to normal width differential. I've got Zipps and the difference is close to 8. In fact the newest wheel in 26 width comes with 23 tires in a package deal.

I was talking about and assuming the OP was talking about inside rim width, not outside. Putting a 23mm tire on a rim with a 25mm inner width...essentially stretching the tire 1mm on each side.

Edit, scratch that. I was talking about exterior.

Yes, here's the Enve chart, that's a much bigger differential than 4mm, also they recommend a 23mm...I run 23 in the front, 25 in the back (until I've used up my 23's anyway.:
QUICK SPECS

FRONT / REAR
Material:Carbon Fiber
Rim Depth:35 / 45
Internal Rim Width:18.5 / 16.5
External Rim Width:26 / 24
ERD:584 / 566
Built Weight:1412.4
Rim Weight:367 / 392
Recommended Tire Size:23mm

Larger differential possibly because it is carbon. I dunno. But for many Al rims, the 4 mm differential is petty standard.

Right, but as you say those are only 18 mm inside. That isn't out of line for a 23 mm tire, at least not much. But in common Al rims with a 4 mm differential, you have to be more careful.

The Pacenti 23 has a 4 mm differential inside to outside. The Velocity A23 has a 5 mm differential. Clearly we need a chart based on interior width to always be safe.

That would make sense.

All I know, the wider rims feel a lot nicer than my old ones...of course, they're a much better wheel overall as well, so it's hard to judge.

I have 32mm tires on my beater which replaced 25s, but I'm not sure the size of the rim. The tire is too wide, but my usual top speed on that bike is around 12mph - I'm not sure I'd want to take any fast turns with them and the one flat I've gotten with them was a front flat and it was very noticeable once the air started coming out. Very, very squirrelly.

I'm still confused.

25 tire on a 25mm outer width rim is bad? If I'm running 25c GP4000's do I want a rim with an outer width of 23 or 25?

I'm not sure the correct word is "want." Until very recently, standard road rims ran from 15mm-19mm outside. Tires are still designed for that geometry because that's what most folks still run. Of course you can run a 25mm tire on a 25mm outside measure rim. The question is what's optimum. For sure on a deep aero rim designed for TT, 25-25 would be good. As above, some rims are designed for 23-25. However as also noted above, going with a wider rim exposes portions of the tire to the road surface which were never designed for that except when cornering.

Although many on here advocate lower pressures for use with wider rims, I've found that I get more flats and sidewall cuts if I do that. I've started inflating my tires on wide rims to greater pressures than I used on narrower rims, which fixes the sidewall=on-the-road issue. I still get the benefits of greater rim strength and more aero cross section of the wider rims.

As usual with engineering, there's not one best answer.

Outside to outside width measurement is pretty useless, it's the inner width that counts. A 700x23c is fine on a 25mm rim, it's not like we are talking about putting a 700x23c tire on a 35mm wide rim.

Thanks.

So are you saying that a 25 tire will be more aero on a 25 wide rim versus on a 23 rim? Which rim width would give better grip through high speed corners shod in 25c tires?

OP, you need to know the inner width of the rims in question, pure and simple. Let us know.

I assume those tire-rim safety charts are to keep the tire bead from popping off the rim? But this seems to be more of a concern if the tire is extremely wide compared to the rim.

I googled the title from the chart link above, and found this from Schwalbe:

http://bikeforums.net/attachment.php...hmentid=485308

That Schwalbe link also says:
~~~~

HED's recommendations are way different. (Those rim widths are outside dimensions. The "25mm" Ardennes Plus rims are 25.6mm outside at the top of the rim, 25.2 at the bottom of the brake track. The inside dimension is 20.6 mm)~~~

And the wider rims have less of an effect on the tire shape than I would have expected. The tires get both taller and wider, not just wider. I don't quite get it--but the wider rim is filling up more of the circle, so maybe it makes sense. This drawing is supposed to be from actual tire measurements.

From HED, via a slowtwitch blog post:

http://bikeforums.net/attachment.php...hmentid=485310