Effect of rim width on inflated tire diameter?

[zmalwo]

So I have a bike that might or might not fit a 28mm tire. just wondering if rim width have any effect on final tire width like would a wider rim make tires wider under same psi and vice versa?

[zmudshark]

Narrow rim for narrow fit.

[sitzmark]

Depends on the tire. Not all 28's measure 28 when installed on the same rim (all other parameters remaining the same). Rim with narrower internal width will *probably* narrow external sidewall width but will likely be accompanied by a rise in tire height which may complicate caliper and other clearances.

[fa63]

Actually, a wider rim results in both a wider AND taller tire.

https://forums.roadbikereview.com/attachments/wheels-tires/322119d1464957570t-23mm-25mm-rims-wheel-width.jpg

Rim with narrower internal width will *probably* narrow external sidewall width but will likely be accompanied by a rise in tire height which may complicate caliper and other clearances.

[zmalwo]

Actually, a wider rim results in both a wider AND taller tire.

https://forums.roadbikereview.com/attachments/wheels-tires/322119d1464957570t-23mm-25mm-rims-wheel-width.jpg

Thank you all for the info, it make sense because the tire will try to keep it's round by increasing it's height to compensate for the wider width. So I guess my 2014 zonda wheels are perfect for narrow frames.

[spoonrobot]

That graphic does not reflect reality. Neither do any of the several mathematical models one can find online. The few people who have quantitative data are not sharing.

There are innumerable tire/rim combinations where a wider rim leads to a wider and shorter tire. I've measured most of the dozens of tire/rim combos I've installed at the shop and it's extremely rare to see a tire get taller going to a wider rim. Something like 17iw to 19iw? Maybe. 17iw to 23iw? No way, tire is definitely getting shorter and it'll keep getting shorter the wider you go.

[weisan]

So I have a bike that might or might not fit a 28mm tire.

All I can say is...don't go with Continentals. They tend to go wide(r). But for that reason, I LOVE em'.

[yinzerniner]

So I have a bike that might or might not fit a 28mm tire. just wondering if rim width have any effect on final tire width like would a wider rim make tires wider under same psi and vice versa?

Some tires fit larger than others, but generally Contis and Schwalbe fit larger and Spec and Vitorria fit close to spec on 17c rims. But it's very trial and error, and you really have to ask the question about specific rims and tires and the height and width when used in combination. Also keep in mind that all tires stretch a bit after use, but the amount of stretch is impossible to predict as it involves usage variables.

That graphic does not reflect reality. Neither do any of the several mathematical models one can find online. The few people who have quantitative data are not sharing.

There are innumerable tire/rim combinations where a wider rim leads to a wider and shorter tire. I've measured most of the dozens of tire/rim combos I've installed at the shop and it's extremely rare to see a tire get taller going to a wider rim. Something like 17iw to 19iw? Maybe. 17iw to 23iw? No way, tire is definitely getting shorter and it'll keep getting shorter the wider you go.

This statement is hogwash. The graphic EXACTLY represents reality, as it was performed with a specific tire and a specific rim, and the measurements were based on molds taken from the specific combinations. Do some research before you post:
https://www.slowtwitch.com/Products/Things_that_Roll/Training_Wheels/Ardennes_long_term_review_4056.html

And I can say without a doubt that that going from a 17c ID (2016 Reynols Assault Tubeless) to a 23c ID (Reynolds ATR2 700) made my Schwalbe Pro Ones wider AND taller.

Two other variables that people tend to forget is the actual rim sidewall height and bead hook design, as both with effect the final shape of the inflated tire. If either are larger then the inflated tire will be smaller, and vice versa.

To the OP, you'd be better off asking the question with more specifics, like the exact frame, tire, rim model and the PSI's you're looking to use. Also, when you say "fit"are you looking for standard road clearance of 4mm on each side, or are you comfortable with less clearance? All questions that are pertinent to getting you the best answer.

[spoonrobot]

I know where the graphic came from, and I thought it was ridiculous the first time I read it. Plaster casts? That sounds like nonsense someone would make up to attempt to increase credibility. And a sample size of two tires and three rims does not reflect the hundreds of different rims and tires in the market place. One can't generalize from extremely small sample sizes, HED is in the business to sell product - not push forward the knowledge base of the industry.

What were the measurements of the tire for each rim? At what pressure and sag% did you measure the tire?

The most recent I did was a GP4kIIS from a Sun Assault 13.2/18.4 to a Flo 30 19.4/24.0 - at 90psi the tire width went from 23.2 to 25.0 and height went from 23.4 to 21.8. The pressure required for the tire to hit 15% sag changed by 3% but I'm not confident that measurement is robust as it doesn't seem to match the expected change in internal area of the tire - which itself is hard to calculate as the tire/rim combination is not round. Using a nominal value reduces the low-order affects as to be worthless.

Regardless, as I said:

I've measured most of the dozens of tire/rim combos I've installed at the shop and it's extremely rare to see a tire get taller going to a wider rim.

You have one tire moving between two rims. I've seen dozens of tires moving between dozens of rims. Tires becoming taller on wider rims is not 100% true 100% of the time. As I said I've only seen it rarely, in my experience with a fair amount of combinations. If someone wants to believe the results of an observation of 1 or even 3 then that's their business.

I've also seen several tires that have not stretched during use - most recent was a turbo cotton that has stayed within a tenth of a mm for width and height over 2500 miles.

Research on the internet is fun and all but getting out into the real world, handling product and gathering your own data allows for a strong position from which to discuss the nuances of the sport. I highly recommend it if you can find the time.

[fa63]

Going from a HPS TB14 rim (17c inner) to HED Belgium+ (20.7c inner), both my 25mm Conti GP4KSII and 25mm Michelin Pro4 Endurance were wider AND taller. I know this because the tires wouldn't clear the brakes vertically with the HED+ rims, but were OK with the TB14.

[yinzerniner]

Read your initial post, in which you categorically stated:
"It's extremely rare to see a tire get taller going to a wider rim. Something like 17iw to 19iw? Maybe. 17iw to 23iw? No way, tire is definitely getting shorter and it'll keep getting shorter the wider you go."

Your full denial is incorrect and should be noted as such. You're providing an absolute statement when you later argue that there are NO absolutes when it comes to wider rims and tire shape. Your statement is generalizing while you decry generalization.

And the plaster cast might have been for show but it also provides valuable data as it creates an exact profile for which the graphic comparison and exact measurement can be done. Plaster casts are incredibly important for all types of precision manufacturing, measuring, comparison and prototyping, and your outright dismissiveness of the method shows your imbalance on the topic.

I think we're arguing the same point but coming to completely different conclusions which ironically also proves the point - that the OP needs to do their own research and/or ask for more specific examples to get an answer as to whether 28mm tires will fit with their frame.

You've cited one example of a tire getting shorter as the ID increased, and referred to numerous other examples of a similar behavior. In my case, the dozens of times I've switched between larger and smaller ID rims and the same tires I've really only seen the height lessen at the extreme ranges of tire to rim size, like 23mm GP4k on the 23mm ID ATR rim. But almost no one would ever use that combo anyways as the tire shape is severely compromised.

As for sag %, I have no idea how to calculate that but for PSI I'm always pretty consistent, with a baseline of 80psi on 17c rims 28mm tubeless tires, then going +/- 5psi per tire size change and +/-2.5 psi per rim ID change. When running tubes would increase the baseline 10psi. So for the Assaults was running 80 psi on the 28mm Schwalbe Pro Ones and 95psi on 25mm GP4K, and 65psi with 28mm Pro Ones and 80psi with the GP4K on the ATR. Since it's not an exact science will always adjust up/down a bit after a few rides just to get the right balance.

I do wish I had more time to get a bigger knowledge base but based on the exact tire combinations stated your generalization doesn't hold up. Then again, this might be due to the fact that I've only started checking out the measurements on "larger" ID rims, not the 13c and 15c which which commonplace just 5 or so years ago.

[saab2000]

My anecdotal experience is that wider rims create a more round tire shape, at least if we don't go extreme with the tire, when it will still have a "light bulb" shape.

But 23s or even 25s are rounder on wide internal width rims.

I use this picture of a 23mm Vittoria on a 20mm internal Pacenti rim to make the point. This was the wheel set that made me question and vastly reduce my tubular tire usage. The ride was virtually indistinguishable from a quality tubular.

This is purely anecdotal and I have zero evidence to support this conclusion other than a lifetime of riding and paying attention to this stuff. Running these at about 80 PSI rear and 75 in the front gives about the best ride/handling feel I've ever had on a clincher on paved roads.

https://c1.staticflickr.com/9/8578/28681140142_6efd0e51c8_c.jpg


I have also done this with 25s and the results are similar but I can run about 5 PSI lower pressure. I haven't tried 28s, nor am I inclined to do so on a paved road bike. At some point there is a place where other compromises come into play, like aero losses and heavier weights.