I have been looking at the big fat tires on my old one-speed clunker that I use for close to home errands. I am thinking that with narrower tires it might even be a viable backup to my regular commuter bike in an emergency. Now with my good bike, I can go the the Mavic website to see what tire width ranges the rims will take. Is there some rule of thumb for minimum tire width on unknown rims? I am not trying to replace a 2.125" tire with a 23 mm tire, but maybe replacing a 2.125" 40 psi max tire with 1.6" 75 psi max street slicks. Is there a formula like 1.x times the inside width of the rim or width of rim plus x mm?
Thanks,
Raymond

Sheldon Brown's web site has an article with just about every tire size made and what range of tire widths you can run. His site is a wealth of information on anything bicycle. This link should take you to the tire area

https://www.sheldonbrown.com/tire_sizing.html

Raymond, it might work as long as your rims don't bottom out or as long as the tube doesn't squit out from between the tire and the rim and bust a gut.

I tried to put a new "fits all rims" Kenda mountain bike tire on a 26 X 1 3/8" rim. That did not work. the new mountain bike wire bead diameter was too small.

It should be easy enough to try.

One thing I am sure of is that you CAN put a 1.75" tire on an old fat-tire 2.125" rim. I see this all the time on old fat-tired bikes. The narrow tire fits so well on the 2.125" rim that it confuses some collectors who think the old ballooner is a younger middleweight rather than the old ballooner it actually is.

If you really want to go light, keep your eyes open for an old 26 X 1 3/8 roadster-type three-speed. You probably won't find any single speeds because they were mostly three-speeds. Look for one with a coaster-brake style hub. You should be able to find one at a yard sale, flea market, or thrift shop for less than $25.00

Sturmey Archer made this kind of hub for some time. Don't get the more common 3-speed hub without the kick-back coaster brake or you will need to mount hand brakes on your ballooner which is complicated and takes away from the look of the ballooner.

Doh! Thanks riderx. I am always referring others to Sheldon Brown's website, then when I have a question, I never thing to look there!

Mike, thanks. My first "serious" bike as a kid was a Huffy Sportsman with a 3-speed Sturmey Archer hub. But my favorite bike, which I will have to restore, was a Schwinn Wasp Newsboy Special. It was a heavyweight version of the regular Wasp with a Bendix two-speed rear end and using something like 2 5/8 inch tires. It was a TANK, but you could load it with a ton of newspapers and go to work thanks to the 2 speeds.

That's exactly what I was looking for. I have 700x35 Matrix tires on my Trek 700. I still need to measure the inside of my rims, but I'd like to put 32 or 28 mm tires on, so Sheldon's site is very helpful.

Jonathan

My commuter bike has rims as wide as any hybrid, but I have no problem running 28mm. The Vredensteins are cheap , tough, fast and have a groovy reflective hoop. I use them on trails and mud as well as roads.
Some 28mm, like Panaracer, are a bit narrow and fragile for hard urban use, more like a 25mm.

That is a good point MichaelW. On my commuter bike I had some inexpensive 700x28 Continental Sports that I recently replaced with Specialized Armadillo 700x28, strictly for the Kevlar belt. I could not believe the difference in cross section. The Specialized lays down a big wide, flat footprint probably as big as a 35 mm tire, or larger. The Continentals were more rounded and gave the impression of riding on a footprint just a few mm wide. I am thinking seriously of putting them back on or at least getting a similar Continental tire with Kevlar belting. In several spots on my commute I am not able to avoid all the usual urban street debris, especially little shards of broken glass so doing all I can to prevent flats is a high priority.

I was getting pinch flats a lot running 27 x 7/8 tires on my Weinmann rims. Just off of Sheldon's chart, and boy did I pay. Usually in inconvenient locations. 27 x 1 does the job.

my friend is a real idiot, he got 2.3" tires on some regular xc wheels. He has got 3 flats in like a week and he just dosent understand that the tire size is too big right? isnt he getting flats because of the tires being too big for the rim or something?

Probably so, but flats are usually a symptom of too-thin tires on wider rims. Your friend risks damaging the sidewalls of the tires because they are flexing on turns. That could be a spectacular crash. Problem is, if you ride with him, you get to pick up the pieces.

As a rule of thumb always get a tire, that when inflated will have a cross section of a larger diameter than the width of the rim. When you look down on the top of the rim you should see some side walls "sticking out". If you are going to go over rough ground or have a heavy load etc. go for more and more tire width.

Pat,
Thanks! That is kind of what I was wondering. If all that really matters, on a "low intensity" bike at least, is that the tire be wider than the rim as you describe. In this case, the bike in question is my fat-tired cruiser that is primarily for running errands around the neighborhood. No 30 mph cornering or off road. Though with less resistant tires it might be an alternative for commuting if for some reason I can't use my regular bike. Of course, a new road bike would be an even better alternative.
Regards,
Raymond

Rainman,
Having a wider tire than rim always matters! If the tire is not wider than the rim it will not get "round", a tire that is not round will not corner right because it messes up the geomtry of the turn. A tire that is circular will contact the road in a fixed relation to the lean of the bike, a tire that is oval will have a continually changing relation to the lean of the bike, ( man this is hard to explain without drawing pictures). In other words a round tire gives a predictable turn, an oval tire gives an unpredictable turn, it will make the bike feel like it's diving one second, sluggish the next.

Round tires tend to roll better too!

A tire that is wider than the rim is much easier to mount and dismount than a thinner one.

A wider tire gets far less pinch flats and less rim damage from impacts and conering improves because of the larger "contact patch" as well