minimum inner rim width for a 3" tire ?

I researched this quite a bit before I bought my bike. What I found seemed to suggest you can use a variety of tire rim widths, however the tire will have a different profile for each width and it and will be more prone to issues on too narrow of a rim. I believe to have a nice "normal" rounded profile you would need about a 40-50mm rim width for 3" tire. We are currently running 2.8" tires on our 50mm rims and they have a nice stable wide profile. If I were to put my tires on narrow rims they would be taller, narrower, and more oval shaped. I guess with less air pressure they would flatten out, but I think they will start having issues with a narrower rim under that situation, especially when cornering, etc.

Perhaps some of the people with more experience can help you, but we are very happy with the 50mm wide rims running mid-fat tires.
 
Dirt biker said:
So 3" on 26mm would be a recipe for disaster?

Try looking at this forum link, they discuss this subject at length:

http://forums.mtbr.com/26-27-5-29-plus-bikes/minimum-rim-width-2-8-3-0-3-25-3-8-a-1059258.html

The weight you are pushing and the type of riding you do as well as preferred air pressure is all going to be a factor. The consensus seems to be about 40mm minimum for a 3" wide tire from what I recall. If you don't mind the tires being sloppy and you aren't turning hard, etc perhaps it can be a bit narrower. I think you will have better control with a 2.2" tire on 26mm rims. I cannot begin to explain the frustration I had when buying a bike, 99 out of 100 failed due to rim width. There are very few bikes with 35mm or wider rims. The industry seems to love narrow rims.
 
It also depends on the fit between the tire mounting lip and the rim sidewall inside. The less overlap there is, the more likely you may be to have potential de-mounting issues under sideloading of the tire, and that problem could be exacerbated by the taller profile it'll have on a narrower rim, especially at lower tire pressures.
 
Also, if you decide to try a wider tire on a narrow rim you may want to stay clear of the lighter weight tires. Some people have reported that the sidewalls can be weak due to trying to make a large tire lighter. The narrower the rim, the stronger the sidewalls need to be to compensate - and especially at low tire pressures. Just remember the tire profile is altered by the rim width. When you mount a wide tire on a narrow rim you are pinching in the sidewalls and making the tire profile more teardrop shaped. In contrast, if you mount a narrower tire on a wider rim the tire profile will flatten out. Perhaps if you explain why you want to run wider tires you may get some better advice.

I went with wide tires because I migrated to an e bike from a motorcycle and I carry my dog with me when I ride. I need the extra width for extra stability. Cecil likes to look and lean from side to side while we ride and he can shift his weight a bit. Plus we are carrying a lot of weight (280 lbs including the bike). Narrow tires won't work well for me, and we have a lot of hills and sometimes we get up to 40-45mph going downhill. So after careful consideration I decided to go with fat tires. Then the problem became drag, and fat tires have a lot of drag and they are more difficult to pedal. I revised my search for mid-fat tires and settled on the 2.8-3.2" width range. Next I decided that by going full suspension I would be able to pump them up harder and reduce the drag considerably. With a tire in this width range a rim width of about 50mm gives me a tire profile that is similar to that of a motorcycle. It is profile that is more stable at higher speeds and less reactive with shifting weight. This is why I wanted to run 3" tires.

Now someone only wanting increased traction in dirt might want something different and a little less width on their rims might be desirable. Perhaps a 40mm wide rim might be better for them. Tire choice also has a lot to do with it, the knobbies will be in different positions on different rim widths and a narrower rim will allow some knobbies to remain on the side of the tire. This did not concern me, I prefer a motorcycle type profile as I would prefer to run a supermoto type street tire (Super Moto X, Hookworm, Beach Bum, etc).

Hopefully this was helpful. I researched this subject quite a bit.
 
Thank you. Can you recommend a 24 inch rim that has 40mm inner width? The widest rim from Halo is 35mm i think.
 
Dirt biker said:
So 3" on 26mm would be a recipe for disaster?

No. It would be typical of what was available when 3" tires first showed up.

The main problem with a wide tire on a narrow rim is that it flexes easily to the side. To counter this tendency, you have to use more pressure than would otherwise be necessary. So it negates some of the benefit of the wider tire-- the option to lower the tire pressure for more cushioning.

If your goal is to use low pressure to increase traction and soften the ride, then you should look for a wide rim. If you'll always use high pressure to minimize rolling resistance or prevent rim damage, then you need not be so concerned about how wide the rim is.

What tire do you have in mind, for what kind of riding?
 


DT Swiss source

for 3.0" wide tires, they allow rims inner width ranging 25 - 50mm.

I've personally been using 2.4" tires on 19mm inner width rims for > 10k km at minimal recommended pressure.

No issues whatsoever even with high-speed hard cornering. Tire profile looks kinda funny with such big tires on small rims but it perfectly works :D
 
That chart is so inconsistent as to be more of a fashion guide than a technical reference.

There are rims now in production with as little as 13mm inside width (narrower than any on the chart). These are often used with tires as wide as 38mm or even wider. It's not ideal, but it's common practice even among some OEMs. It looks like the authors of the chart have a pragmatic outlook about rims with inside width between 18 and 19.9mm, but less so about other sizes.

Did you notice that they seem to believe tires become insensitive to maximum pressure once they exceed 2.9 inches in width? And that they know about 5 inch wide tires, but not 4 inch wide rims (which are the usual counterpart)?

If you use tires between 1.5 and 3 times as wide as the rim's inside width, you're in well charted territory. It's sometimes appropriate to exceed these general limits, but it's a good idea to know why you're doing that.
 
Chalo said:
That chart is so inconsistent as to be more of a fashion guide than a technical reference.

this chart is only for DT Swiss rims & wheels and it surely accounts for liability / safety margins.

That's why it doesn't include 5" rims as they don't produce any.

For the max tire pressure, as annotated in the bottom right corner, they say it's the max the rim can safely handle.

I would say this doc is a good safe margin ref.
 
Ivanovitch_k said:
For the max tire pressure, as annotated in the bottom right corner, they say it's the max the rim can safely handle.

That doesn't make sense. The hoop stress in a tire is a function of the tire's pressure and the internal surface area of the tire. So a 5 inch tire has more than 1.67 times as much stress on the casing and the rim bead as a 3 inch tire at the same pressure. The maximum safe pressure in one of those sizes is not the same as for the other. (Which is more or less irrelevant, because you don't get a 5 inch tire to run it at maximum pressure.)

I would say this doc is a good safe margin ref.

It is safe. It's not equally so for all the sizes listed.
 
I think there may be situations where you would want to run a 5" wide tire at high pressure. I have been riding motorcycles a long time. Here in California we are permitted to split lanes. I have split lanes on a variety of bikes and tires. I have to say that narrower tires with more rounded profiles are outright dangerous when riding at a decent speed over the nearly parallel grooves in the center of the lanes. A tire run on a wide rim has a flatter profile that is more stable and less *squirrely* at speed, at least this has been my experience with motorcycle tires and 250,000 + miles. I can recall 140/70 tires (on appropriate width rim) and they were horrible compared with 180/55's (on appropriate wider rim) on a similar bike which would track without a hiccup.

Furthermore, mounting a wider tire on the 140/70 rim would make the bike even more unstable in the same situation due to the excessively rounded tire profile. Wide tires on wide rims are more stable at speed, a wide tire mounted on a narrower rim is going to have a more rounded profile and it is going to be less stable at speed but easier to throw the bike over to the side to maneuver. Perhaps this effect is less pronounced on bikes compared to motorcycles considering the sidewall height of the tires and lower tire pressures desired by many riders, but I would be willing to bet that it still applies at least to some degree. And with motors being added to bikes the bikes are now running on the streets at higher speeds with higher tire pressures.
 
Chalo said:
Dirt biker said:
So 3" on 26mm would be a recipe for disaster?

No. It would be typical of what was available when 3" tires first showed up.

The main problem with a wide tire on a narrow rim is that it flexes easily to the side. To counter this tendency, you have to use more pressure than would otherwise be necessary. So it negates some of the benefit of the wider tire-- the option to lower the tire pressure for more cushioning.

If your goal is to use low pressure to increase traction and soften the ride, then you should look for a wide rim. If you'll always use high pressure to minimize rolling resistance or prevent rim damage, then you need not be so concerned about how wide the rim is.

What tire do you have in mind, for what kind of riding?

Thank you, then I'll probably stick with what I have. It's Halo Contra and I don't have any practical reason for using a 3 inch tire, I just wanted to :)
 
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