mrblue

Hello,

I have a very small amount of clearance between my front tire and the brake caliper. Is there a formula I can use to figure out how much less clearance I'll have if I switch to a slightly wider rim (19mm)? My current wheel/tire combo is:

• 25c tire
• Pressure: 80psi
• Rim internal width: 16.25mm
• Rim external width: 24.6mm
• tire width inflated: 24.9mm

Thanks.

Iride01 

Rim internal width probably isn't going to make much difference for the amount you are changing. But if you pushing less than a mm or two of clearance already, then already from one tire model to the next of the same size you are gambling even with out the rim change.

mrblue

Hi! Thanks for your input. I plan to use the same tire (with the same pressure). Do you know of a way to calculate how much clearance might be lost moving to a 19mm from a 16.25mm internal rim width? At the moment I have ~3mm clearance between my tire and brake caliper.

Bill Kapaun

Different brands/tires may behave differently depending on tire construction.
You probably wouldn't lose very much,but 3mm is 1/8".
I would consider that inadequate my self. How big of a pebble could get stuck in the tire before problems arise?

Iride01 

This is what I have based my thoughts on rim width verses tire width. Though I've never actually measured myself or worried much about it.

https://www.velonews.com/gear/techni...-vs-rim-width/


The graphic sort of shows it all. There were some similar articles about it too that I've read at the time nixing the often stated idea that it's a big deal. But it was long ago and I don't remember where I'd find them.

mrblue

Yes, I agree. I find the small amount of clearance I do have to be really annoying. However, I don't really want to go to a 23c tire (as I like the 25c). My only other option is to use a different brake caliper. Campagnolo reduced the amount of clearance under the brake calipers with 12 speed Record. No idea why. Campy does weird stuff like making wheels with 6.5mm valve holes so your presta valve rattles around.

mrblue

Thanks. I'll read through this.

mrblue

Ok. I read the article or at least most of it. My head hurts now. Too much engineer talk. Sorry, I'm a finance guy.

So what I was able to take away from that is as the rim widens the height of the tire (same size, same pressure) won't necessarily increase. Or if it does, not very much. Is that an accurate take-away?

Again, I apologize, all the engineer-speak really made my head swirl.

Iride01 

That's what I took away from the article too. If you think about it, circumference of a tire is pretty much built into it from the start. So rim width isn't going to matter much.

If you are using 25 mm tires the generally conservative chart from Sheldon Brown's site shows that a 19mm internal rim width is not recommended for a 25 mm tire. Does your tire maker say what size rims it recommends for that tire?


https://www.sheldonbrown.com/tire-sizing.html


I'm sure many get away with it, but it's something you should consider if you aren't as experienced a rider and know how to interpret issues of tire, rims, inflation and road that you might feel while riding. Particularly at speed on curves.

Are you needing to change rims and that is all you can find? Or is there some issue you are trying to solve?

stevel610 

If I read your your measurements for internal and external correctly, each side of your rim wall is 4 mm wide?

Elvo

Hard to tell since manufacturer stated tire size and elasticity are all over the place. But the tires will definitely balloon bigger with 19mm internal.

squirtdad

Don't think a calculation will work.....as tires can have variance and in some cases just are bigger than stated. I had pair of Michelin pro 4 service course in 25mm in real life they were 27mm+

My conti gp 5000 at 28m measured true on the bike, same with vittoria Corsa control tubular in 30mm

Iride01 

Remember that the OP.... as far as I know..... is planning on using the same tires on the other rims. So things like elasticity and differences from one tire to the next are pretty much not in play.

DiabloScott

The calculation goes like this:
1. What do you have on there now?
2. Is there a little more room?
3. If yes, you could try wider rims or tires, but it might not work.

ClydeClydeson

I am curious as to why OP wants to make this change.

Generally speaking, you should avoid using a rim that is wider than your tire, and your current rim is almost the same width as your tire. A wider rim will result in the tire being minimally wider, but the rim will probably be wider than the tire.

gsa103

The bead to bead distance of the tire is essentially constant, so when you widen the rim by 3mm, I expect you're going to lose about 1.5mm all the way around (both sides and the top). If you currently have 3mm that's going to be very tight, because you should have around a millimeter left.