Hi All, I know there are several threads on here about tyre pressures for non standard tyre sizes...
But but it seems not many are running the same as me (255/50 R18 106 XL) so I've been doing some research.
Firstly I found this web site very informative...
The Ultimate Tire Pressure Resource - TirePressure.com
and I used if to get the pressure vs Load graph presented below.
I'm not claiming this is a way to fix a good pressure for another tyre size, but it should set some minimums to make sure our tyres can carry our vans safely.
I'm just aiming to add to the debate (hopefully).
Things that jumped up at me...
1) The load rating vs pressure is only based on the rating not the tyre size at all; but that made sense when I stopped to think about it..
2) The actual load it will carry varies with pressure but only up to 42psi for XL tyres, and only up to 36psi on regular (=SL, but usually not marked), above that the tyre is not rated to carry any additional weight.
3) A tyre rated 99 SL will cary the same load at 36psi as the 99 XL will at 42psi, initially this seemed counter intuitive; but the rating is all about the MAX loads it will carry...
3.1) this means a 95SL will carry 691kg at 36psi which roughly the same load as 99XL (685kg) at the same pressure, but the 99XL carries on to 42psi and 777kg
3.2 or to put it another way a 103 rated tyre will cary a max of 874kg; if it's an SL it will do this at 36psi, but if it's an XL it will need 42psi....
(seems too me XL tyres are heavier duty versions of lighter tyres, not the same tyre with extra load capacity)
4) The familiar ratings we use for our vans; eg T32 needs a 103 rated tyre need some care when it comes to full loaded vans and using pressure lower that these two limits.
5) If you want pressures lower than the two limits you really need to know how heavy your van is... and maybe are better off with tyre rated above the usual values.
I'm planning on getting mine on a weighbrige both empty and with typical work and camping load ups.
At the plated weight (its a T32) and the above tyre rating of 106XL; 36.2 psi is enough to carry the van.
If I'm down at 720kg on the front of an unloaded van I'll only need 29psi for the load rating!
I've started at 45F and 40R even empty, but will now drop it to 40F & 36R and see how it feels and heats up the tyres.
Speaking of which; I read about assessing the pressures based on temperature rise after a drive; big rise pressure is too low, little or no rise pressure is too high..
Does anyone have any more experience/ knowledge of this?
Way way back, in my car racing days, we used to compare the centre and edges of the tread and lower the pressures till the centre was at or below the edges (depending on the camber).... but that was a long time ago!
Last one..
Anyone with a T32 SPORTLINE prepared to send me a pic of their tyre sticker from the door frame?
Cheers
Ian
But but it seems not many are running the same as me (255/50 R18 106 XL) so I've been doing some research.
Firstly I found this web site very informative...
The Ultimate Tire Pressure Resource - TirePressure.com
and I used if to get the pressure vs Load graph presented below.
I'm not claiming this is a way to fix a good pressure for another tyre size, but it should set some minimums to make sure our tyres can carry our vans safely.
I'm just aiming to add to the debate (hopefully).
Things that jumped up at me...
1) The load rating vs pressure is only based on the rating not the tyre size at all; but that made sense when I stopped to think about it..
2) The actual load it will carry varies with pressure but only up to 42psi for XL tyres, and only up to 36psi on regular (=SL, but usually not marked), above that the tyre is not rated to carry any additional weight.
3) A tyre rated 99 SL will cary the same load at 36psi as the 99 XL will at 42psi, initially this seemed counter intuitive; but the rating is all about the MAX loads it will carry...
3.1) this means a 95SL will carry 691kg at 36psi which roughly the same load as 99XL (685kg) at the same pressure, but the 99XL carries on to 42psi and 777kg
3.2 or to put it another way a 103 rated tyre will cary a max of 874kg; if it's an SL it will do this at 36psi, but if it's an XL it will need 42psi....
(seems too me XL tyres are heavier duty versions of lighter tyres, not the same tyre with extra load capacity)
4) The familiar ratings we use for our vans; eg T32 needs a 103 rated tyre need some care when it comes to full loaded vans and using pressure lower that these two limits.
5) If you want pressures lower than the two limits you really need to know how heavy your van is... and maybe are better off with tyre rated above the usual values.
I'm planning on getting mine on a weighbrige both empty and with typical work and camping load ups.
At the plated weight (its a T32) and the above tyre rating of 106XL; 36.2 psi is enough to carry the van.
If I'm down at 720kg on the front of an unloaded van I'll only need 29psi for the load rating!
I've started at 45F and 40R even empty, but will now drop it to 40F & 36R and see how it feels and heats up the tyres.
Speaking of which; I read about assessing the pressures based on temperature rise after a drive; big rise pressure is too low, little or no rise pressure is too high..
Does anyone have any more experience/ knowledge of this?
Way way back, in my car racing days, we used to compare the centre and edges of the tread and lower the pressures till the centre was at or below the edges (depending on the camber).... but that was a long time ago!
Last one..
Anyone with a T32 SPORTLINE prepared to send me a pic of their tyre sticker from the door frame?
Cheers
Ian
