Tyre/rim matching.

[quixoticgeek]

I have a set of wheels with Pacenti TL28 rims, they have an inner bead width of 23mm. Is there any reason that putting a pair of 28 Continental GP 4 seasons on them would cause me problems?

Cheers

J

[quixoticgeek]

Any particular width of Conti tyre?

oops, missed that out. I meant to say 28mm conti gp 4 season.  Will edit OP.

J

[LittleWheelsandBig]

http://engineerstalk.mavic.com/en/the-right-tyre-width-on-the-right-rim-width/ gives a ETRTO table of rim versus tyre width but it is overly conservative in my opinion.

[quixoticgeek]

http://engineerstalk.mavic.com/en/the-right-tyre-width-on-the-right-rim-width/ gives a ETRTO table of rim versus tyre width but it is overly conservative in my opinion.

Yeah, I found that, and it seemed to suggest that a 19mm rim is the max for a 28mm tyre. Which seemed wrong in my head. Hence asking here for wiser minds.

J

[Aushiker]

Sheldon Brown RIP also suggests a maximum of 19mm.

[LittleWheelsandBig]

The major problem with rim/ tyre combinations outside of that chart is that the differences between minimum and maximum tyre pressures narrow. In the worst cases, to zero.

I've had a tyre/ rim combo where I could get it mounted but the tyre would blow off the rim as soon as noticeable side load was applied i.e. in every corner. Back in the day, we mounted 2.2" MTB tyres on cut-down MA40 rims, it just meant the tyre pressure couldn't be too low.

If you are going tubeless (probably not with Conti), there are additional complications, where it can be a little easier to blow the tyre off the rim.

If you have the tyres already, mount them and see how they look, try to roll them off with your hands and so on.

[dim]

https://www.youtube.com/watch?v=Py9Loc8xjoo

problem that you have with conti GP is that they never measure true .... on a wider rim, such as HED Belgium Plus, a 28 Conti GP 4000 measures well over 30mm when pumped up ...

I'm using 25mm IRC Formula Pro RBCC tubeless tyres on my HED Belgiup Plus rims and they measure true (25mm wide when pumped up, and that matched my rim width .... I prefer to match tyre width to rim width

I used Specilized Turbo Cottons previously and the 24mm wide measured close to 28mm on these rims

I don't like Conti GP 4000, but if I were to use them again, I'd get the 23mm for my rims

[Brucey]

ETRTO charts are a bit conservative, judging by the recommendations of many rim manufacturers, these days. Many suggest that a tyre only a little bit wider than the external width of the rim will be OK.

However it is all very well them saying 'such and such will be OK' but in nearly every case this is specifically not recommended by the tyre manufacturer.  So if you stray outside the tyre manufacturer's recommendations, you are basically on your own.

I harbour a lurking suspicion that the bias angle of the plies varies slightly with rim width once the tyre is fitted, and with it the Crr of the tyre changes, because balance of the stresses in the carcass is changed, and the way the carcass deforms is different.  This is most likely to be the case when fitting a narrow tyre onto a wide rim.

 This may mean that (for example) a 23mm tyre that is 25mm (actual width)  when fitted on a wide rim, may roll differently from a 25mm tyre (actual width) that is mounted on a narrower rim.

It may also mean that various Crr test data may be flawed, (or may at least only apply to one rim width) in that the width of the test rim may skew the results.

cheers

[rogerzilla]

I used to run Conti GP 18mm tyres on average road rims, so I doubt they'll blow off - although this depends how close you go to the max pressure on the sidewall, and I would be wary of more than 90psi.  If the max pressure is low, like it is on Schwalbe Duranos, be very wary indeed.

They won't give as good a ride as they would on a narrower rim.

[mzjo]

FWIW I have had more problems with fitting narrow tyres to wide rims than the other way round. The only problem I found with wide tyres is rapid wearing at the bead (with 30mm Michelin tyres on a 17mm rim; enough to not persist with the idea)