MidTNBrad

I'll be in the market for a new set of alloy rim brake wheels later this year and I've started looking around at some rim spec's and I have a question about width.

My current wheels have a width of 17mm inner, 22mm outer and I'm running GP 5000 in 25mm. At 90 psi, my normal riding pressure, they measure at a hair over 26mm wide. My bike is from 2016 and came OEM with 23mm, so it was never designed to take say 28s and the 25s I have are tight but do fit.

My question is that most modern rims I'm checking out have wider IW than the 17mm I have now. I’m seeing anywhere from 18mm - 21mm. Will these wider internal widths have any noticeable effect on the actual width of the tire? My intuition says that a wider IW will take up more volume at the base of the tire, thus leaving less volume for it to balloon out and may actually cause the tire to become more narrow. Or I could be completely wrong and the wider IW will cause the tire to be wider across the board. Also, are wider rims exclusively designed to take above 25mm tires? Will I see any issues with staying on 25s if I get a wider rim?



Any thoughts?

WhyFi

Yes, your tires will be wider on 18-21mm rims.

A lot of rims are being optimized for 28mm tires, now, but many are still compatible with 25mm tires. Check the manufacturer's compatibility page before you buy, but I can't imagine that any in the 18-21mm range wouldn't be compatible (though some of the older compatibility specs are notoriously conservative).

Iride01 

Rim manufacturers are following the trend that more people are using wider tires. So wider internal width usually allows wider external dimensions with reasonable weight and other design considerations. And some people are looking for a particular profile for performance and aesthetics. If you are one of those, then you should already know what you want in those numbers.

For the few millimeters a internal width changes I don't expect it to make a big concern for the external width of the tire unless perhaps the tire clearance to the bike is already very marginal.

Silver Steve

I also have a rim brake bike from 2016. A Giant TCR. I upgraded my wheels to Light Bicycle AR46s which have an internal width of 21mm (external 28mm).
Light Bicycle's website says a 700x25 GP5000 (tubed) tire will measure 26.54mm on a rim with the internal width or 21mm

Make sure to measure your frame an rim brake calipers to find out what will fit. I am able to fit a 30mm actual width tire in my TCR. I did have to use thinner brake pads due to my new rims 28mm external width.

biker128pedal

The wider rim increases the circumference so the height and width will increase. The amount of height and width depends on the tire. So in addition to width take a look and height clearance.

Whatever you get you may have to go with a smaller tire. I’ve bought one tires just for fitting purposes. Oh with age the tire will expand about a little so don’t cut it too close when new.

chaadster

The graphic is from HED, as I recall; it has been a few years, but that’s what I recall.

I’ve run 23mm Schwalbe One/Pro One on 19.4mm IW rims for 10 years and find that perfect, though I’m sure 20mm IW would be essentially the same. I also ran, for many years, 25mm tires on 24mm internal Velocity Blunt rims, and they had a cool, stretched look but rode a little harshly. I tried 28s and settled on 30s as my favorites for that bike as my utility/commuter.

Point being, I think 23s would be nice on rims up to 21 internal, but I’d size up a notch on rims wider than that…or just not get rims wider than that.

rm -rf

My HED Ardennes+ rims are 25.5mm outside, 20.5mm inside width.

23mm
I originally used my existing 23mm GP4000 tires. Back in 2017, they measured 27.0 mm. These were about 26 to 26.5 mm when the tires were newer.
Just 1mm wider on each side than the rim! They rode fine, no problems. These rims are "tubeless ready", so the beads lock into the seat when I first inflate them. It's more secure than older rims, I suppose. I'm guessing that most wider rims are also tubeless ready.

I switched to 25mm for a while, and they were fine.

It appears that the newer GP5000 are more true to size, where some sizes of the older tires measured larger than their stated size on most rims.

28mm
I used 25mm for a while, then went to 28mm, since I have room for them in the frame.
The newer front tire: 29.5mm
The older rear tire that was moved from the front: 28.8mm

At 170 pounds, I use 70-72 psi front, 78-80 psi rear. Fast and smooth!

rm -rf

Clearance
My old bike had very little room for larger tires. I used 25mm, and the front had just a few mm clearance under the fork. I rode on a repaved road that had fine, damp sand on the surface. My tires picked up the grit and I could hear it hitting the fork -- the paint had long superficial scratches at the tire location. No real damage, but no fun to ride that way.

On my current bike, I considered going to 32mm tires for the local rough roads. But I'd have less than my current 4-5mm clearance, so I stayed with my 28mm tires. I suppose 3mm might be okay.

I use a hex "L" wrench to measure the gaps -- a 4mm wrench is 4mm across the flats.