Wheels/Tyres: what pressure?

[tompip]

hello, i have 20 inch wheels on my XC60, the info inside my door does not cover this size rim only 17 and 18 inch rims,does anyone know if there is another PSI for this size rim. thanks in anticipation.

[Ninja59]

Have you not already posted this once?

[tompip]

hi, not the bit about the info inside my door does not cover this size rim only 17 and 18 inch rims,

[Daim]

The pressure doesn't vary between the rim sizes (or at least shouldn't) as the pressure doesn't say anything about the volume.

2.5 bar is a standard safe number. Use the standard pressure for the nearest size you can get... If that is an 18", use that. Keep an eye on it yourself (drive a while, get out and instantly feel the tyre - if hot, then increase the pressure by 0.1 bar until you find it to be cooler - not straight away!).

[Paddler Ed]

I've got a slightly more hi-tech approach to Daim's recommendation, based on a tyre manufacturer's recommendation (Cooper Tyres):

Originally Posted by Daim

2.5 bar is a standard safe number. Use the standard pressure for the nearest size you can get... If that is an 18", use that. Keep an eye on it yourself (drive a while, get out and instantly feel the tyre - if hot, then increase the pressure by 0.1 bar until you find it to be cooler - not straight away!).

Here's an explanation of the 4 psi rule that I've posted in the past.

Originally Posted by Paddler Ed

Try the 4psi rule for tyre pressures; it'll go some way to addressing Clan's comment re the manufacturers pressures being too low, and also works when non-standard tyres are fitted.

Here's the 4psi rule info from a couple of different sources, and in my own words based on those sources.

Start at y psi, drive for an hour (100km or so) a then check the pressure; it should be y+4 psi. If it's over that, ie +5 then the tyre was too soft (ie it got too warm) and under then tis too high (ie it didn't get warm enough). Amend the pressure by a 1/2 the difference and try again; it should cool or warm up accordingly and then you should be towards y+4. Check when you get home what y is now once it has cooled down (ie the next day) before you unload if you set it loaded, and again when you unload. You now know what to set the pressure at for the next trip. Do the same for unloaded/everyday driving and then record that and you'll be sorted hopefully!

Here's probably one of the better explanations of it; it's long, but read through it.


And here's the Cooper tyres info:

I know in Aus we ran about 42psi in our Toyota Landcruiser when we were touring or everyday; touring it was a benefit because we were loaded, everyday because we had a freeway run to get anywhere, when on gravel/dirt roads for more than 3km, it was about 30psi, and when on the trails properly it was down to 20psi, so quite a big drop. That gave the tyres a reasonable footprint, without being excessively hard work. Main reason I went for those pressures was it increased traction and reduces the likelihood of punctures as the tyre is allowed to follow the terrain... it does increase the chance of the bead rolling however on road and harder surfaces at speed, so we'd only run at 50-60kmh on low pressures.

Hope that helps,

Ed

Ed