mikemartin

If I bought a tire rated at 120 psi, is it safe to fill it to that point from the rim's perspective? Basically what I'm asking are tires usually rated higher than the rims or the other way around? I currently use 700c x 35 tires and looking to downsize to 700c x 28. My current tires are maxed out at 85 psi. If I maxed out at 120 psi on my new tires, can I be confident then my rims could handle the pressure, or is it something to take into consideration? I'm newbie so sorry if this is a dumb question lol

Camilo

The tire and rim will be OK, but tire pressure should be based on your bike and body weight and the diameter of the tire. How much do you and your bike weigh?

Just as examples for me. On my road bike (total weight about 180 lbs bike+person), I ride 23mm tires at 100 PSI rear and 90-95 front.

On my cross/commuter bike (about 190 lbs bike+person+gear), I ride 32mm tires at about 55-60 PSI front and 60-65 rear.

Too much pressure can be harsh ride and actually slower because the tires aren't as compliant going over irregularities in the road surface. Slower also because the ride is less comfortable and more fatiguing. So, pumping to max is not necessarily the best thing, unless your body + bike weight indicates it's necessary.

ben4345

Some tires seem to like higher pressures too.

mikemartin

Im a big guy, 260lbs, my bike is a 2002 Trek 7500, probably 25lbs.

Doug5150

Tires and rims both have maximum-PSI ratings.
Tires only have one maximum-pressure rating, because they cannot account for any rim they might be put on.
With rims the maximum PSI rating depends on the overall width of the tire.

It is not often a problem that rims split, but it does happen. You'd need to check the rim manufacturer's website or email them for info on the max width/pressure of tires for the rims you have.

I would also agree that the tire sag under load is a better method of deciding useful pressure than simply inflating to the maximum.

oddjob2

As a big rider on an aluminum hybrid frame, I would recommend you stay on tires at least 32cm wide for comfort. I'm big too and I tend to avoid aluminum road bikes, preferring more compliant steel frames on 25-28cm tires.

dsbrantjr

Here's a chart of tire pressure vs bike + rider weight and tire size based on 15% tire height drop from an unloaded condition. The reasoning seems sound and avoiding rock-hard tires and filling-loosening impacts works well for me. I find the constant vibration from too-hard tires fatiguing and hard on my hands and arms. https://www.bikequarterly.com/images/TireDrop.pdf

FBinNY 

The rim stress is proportional to the tire pressure times the tire width, so a narrow tire at higher pressure exerts similar stress as a wide tire at lower pressure. Rim makers are aware of tire pressure ratings and build rims to handle them when. The only time you'd need to worry is when using a HP tire much wider than the rim, especially with narrow light rims where the maker would expect you to use narrow tires and build accordingly.

You might also be interested in this article about optimum pressure based on tire width and rider weight.

HillRider

I agree, rim failure at any reasonable pressure is not an issue unless the rim is bady abraded from brake wear. Also, tire width markings are often fiction. Typically, in my experience, 700cx23 tires run pretty close to their marked size. For nearly all others, that's not true. I have a "rain bike/beater" I use with wider tires because I sometimes ride it on Rail-Trails and other mild off road use. I've had "700-32" and "700-28" marked modestly treaded tires from name brands on it and both measured an actual 26 mm as installed.

In the past I used 700-25 tires on a couple of bikes and they routinely measured 22 to 23 mm wide. I've always thought that 700-23 was just truth-in-advertising applied to what used to be called 700-25.

rydabent

For safety I usually inflate my tires to about 90% of the max listed on the side wall. By safety, I mean that in the cool of the morning, if I inflate to 90% of max, in the afternoon on a hot hiway, the pressure could easily to the max.

LarDasse74

You will be perfectly fine inflating the 700X28c tires up their max. However, you will probably find that a 700X28c tire at 125 psi gives quite a harsh ride and you will want to go lower. I am approximately your size and I have used 28mm tires at high pressure and I did not like it... it rattled my water bottle bolts loose.

noglider 

It depends on the tire. Some tires feel fine at 125 psi, at least to me. Some feel like rocks at 90 psi.

jon c. 

If I read that chart correctly, I'd have exceedingly soft tires at their recommended pressure.

mprelaw

Even at 260, I don't think you should need to go to 120 psi on 28 mm tires.

Al1943

I think 28 mm tires at 120 psi will be a reasonable choice for paved roads. If I were you I'd try Michelin tires for their sidewall strength and soft rubber.
One of my riding friends is about you size and rides 25 mm tires at 110 psi but has lots of tire problems, especially in the sidewalls.
I weigh 162 and ride 23 mm Michelins at 118 in the rear and 110 in the front. The pressure has never been a problem and my wheels roll very well.

davidad

The pressure on the sidewall of a tire is 1/2 the pressure necessary to blow the tire off of the rim.

FBinNY 

I keep seeing this, but I've never heard it confirmed within the industry. In any case, that offers little indication that a rim can take the combined stress of a wider than expected tire at high pressure.

With correctly mounted tires, and hook edge rims blow off is rare, but not unheard of. But rim fracture is increasingly common.

Bill Kapaun

I'm into skinny tires at higher pressures myself-
However, I started having issues with SV tubes @ 120 PSI. It was probably a bad batch?, but I'd get "blisters" on the side of the valve stem.
I dropped down to 110 PSI and haven't had that issue since.

ben4345

My gatorskin 700x23, feels good at 115 PSI (front wheel). My re-fuse 700x25 did so much better at 105-110PSI and Tserv 700-25 does really well at 100-110 PSI.
So, it still depends a little on the tire and riders preference.

JanMM

The chart's set up to result in 15% tire drop. If you are habituated to riding at high/max pressures, then 15% could feel exceedingly soft. Or compliant, or forgiving, or comfortable.

Doug5150

No offense, but who told you that? I have spent a lot of time online looking for all kinds of bicycle-tire-making info, and have not run across it.

Figuring a number based on the thread-per-inch construction and typical nylon thread used, bicycle tires maximum pressure should be somewhere around 450 PSI,,,, if they are constructed with the threads spaced one-thread-width apart (-oddly enough it doesn't matter what thickness the threads used are, just proportionately how far they are spaced apart. If you have a few thick threads or lots of little threads, the total strength ends up about the same as long as the spacing is proportionately the same). Cheaper tires with more space left in-between the threads might top out at around 250-300 PSI or so; this would correspond with thread spacing of 1.5-2X between threads.

In this video at the 4:55 time they show one Continental MTB tire being hydro-tested to failure.
https://www.youtube.com/watch?v=JM_x0qPM8Ok (the UK "How Its Made" video about bicycle tires)
The narrator says "all tires have to withstand 8 PSI, but this one manages almost 20".... which is wrong, of course. Most tires can handle way more than 20 PSI. ...If we assume that he meant to say "bars" instead of "PSI", then the numbers would be 120 psi (all tires would have to withstand) and 300 PSI (that the Continental knobby tire failed at).

I can't see which tire is being tested in the video--but on the Continental site, nearly all of the non-tubeless MTB tires have max inflation pressures of either 60 or 65 PSI. And we might guess that they are bursting at around 300 PSI. The tire in the video also does not come off the rim. It appears to burst in the sidewall, near the bead.

Also note that the TPI of the current Continental MTB tires varies from 84 TPI (total) to 240 TPI, and yet the pressure ratings of them (and likely the bursting pressures also) is all nearly the same. More threads != higher pressures, the thread spacing is the main factor in that.

I'd agree.
Often it is ultra-lightweight road rims. Often rims with spoke holes badly drilled (nicks in the holes' edges). Often both of these, at the same time.


Sidewalls cracking from brake wear is something else entirely. That doesn't indicate anything wrong with the rim or tire. Maybe the owner, tho'.

Doug5150

I have found a reference related to the above info, which appears to be a misquote.

On this PDF by Frank Berto-
https://www.bccclub.org/documents/Tireinflation.pdf

on page four, it is claimed that tires are tested to withstand at least twice the maximum pressure indicated on the sidewall.

This would also agree with the Continental tire video that (ignoring the narrator's error) the MTB tire with a maximum inflation pressure of 60-65 PSI has to withstand at least ~120 PSI without failing in any way.