40m tyre on 17m rims , possible or not?

[Bing Bong]

I currently have steel rims with an internal measurement of 17m on my tourer but want to put 40m tyres on. I know the accepted way of calculating maximum tyre size is to multiply the internal measurement by 2, giving 34 in this case, but a bike mechanic has said that I should be able to run 40m tyres OK. Anybody got any experience of 40m tyres on 17m rims or thoughts ?

 

[si_c]

You can always give it a try, but I think you'd probably find that it balloons too much and cornering will feel a bit squirly.

 

[Hacienda71]

I've been running 35mm on 15 mm rims with no issues on my cx bike. I have a pair of 17mm rims and am going to run 40's on those. My 15 year old Stumpjumper has narrow rims but has had tyres 2 to 2.5 inches and it is fine, I have hammered black trails on that and raced xc on it so I don't think you will have a major problem. I suspect there is a bit of a fashion thing going on with wider rims. All that said I would use a reasonably robust carcass tyre if you are going to hammer any off road stuff.

 

[raleighnut]

steel rims

Throw them away and get decent wheels

 

[Ming the Merciless]

40 metre tyres 😲

 

[Big John]

Just found this

https://www.lightbicycle.com/newsletter/tire-size-chart-for-bicycle-rim.html

 

[Yellow Saddle]

40 metre tyres 😲

Try and keep up with trends, will ya?

 

[bobzmyunkle]

You can always give it a try, but I think you'd probably find that it balloons too much and cornering will feel a bit squirly.

My experience suggests you might find cornering on fast descents a little disconcerting.

 

[fossyant]

Narrow road rims with 38c tyres on my CX bike, absolutely no issues.

 

[iandg]

I use the "Sheldon" guide. If you scroll down there is a table that lists rim/tyre width compatibility.

It suggests:

If you use a very wide tyre on a narrow rim, you risk sidewall or rim failure. This combination causes very sloppy handling at low speeds. Unfortunately, current mountain-bike fashion pushes the edge of this. In the interest of weight saving, most current mountain bikes have excessively narrow rims. Such narrow rims work very poorly with wide tyres, unless the tyres are overinflated...but that defeats the purpose of wide tyres, and puts undue stress on the rim sidewalls.

 

[Bing Bong]

Throw them away and get decent wheels

Why?

 

[Yellow Saddle]

Why?

Throwing them away wasn't my suggestion, although I did think it. It is a good suggestion and you'll be doing yourself a favour. Aluminium-rim wheels are cheap and their braking performance is miles and miles better than that of steel rims.

 

[Alex321]

Throwing them away wasn't my suggestion, although I did think it. It is a good suggestion and you'll be doing yourself a favour. Aluminium-rim wheels are cheap and their braking performance is miles and miles better than that of steel rims.

And in the process, they can get some with 19 or even 21mm internal width, which will be much happier with the 40mm tyres they want to use.

 

[FishFright]

Back in the day 2.1" tyres on a Mavic 517 (17mm internal) rims was perfectly normal .

 

[Dogtrousers]

I use the "Sheldon" guide. If you scroll down there is a table that lists rim/tyre width compatibility.

It suggests:

Sheldon's table goes up to 37mm tyres on 17mm rim but it also says "this chart may err on the side of caution".

So it's pushing the limits. You probably won't die instantly as a result. It'll probably be OK, if not optimal. I wouldn't do it unless there was some sort of problem that forced me to. Why not stick with 34mm or whatever. Are they causing a problem?

Or, as others suggest, use it as an excuse to get some better wheels.