Tyre Pressure

[Silverfox]

Originally Posted by CJL

SBS Manual - http://www.sbstrailers.co.uk/pdf/Service_Manual.pdf

Tyre pressures on page 3.

Chris

Brilliant. Thanks.

[jwalker]

Originally Posted by hadd

Hi silverfox, It should say on the side of the tyre what pressure should go in there , my tyres take 60psi i always put 55psi in them

I have heard this said many times and it is not correct. The pressure on the side wall is a maximum pressure for the tyre inflation NOT the pressure the tyre is to be inflated to. (Though, in service it could be.) Your tyre wall will give you a maximum load which can be carried by the tyre at its maximum pressure at its rated speed. The actual pressure will depend on the load being carried by the tyre.
For info; if it's found that a tyre is running at its maximum load, it may be a good idea to check out its ply rating and possibly fit a higher ply-rated tyre since this will carry more load. The ply rating is just that, a rating, and it's quite possible to have a 6 or 8 ply rated tyre which only uses two actual plies in the side wall. It's a carry over system from when tyres did have extra plies as the rating increased.

[captnjack]

Originally Posted by Trailer Guy

I've often wondered myself Erin! I guess, theoretically, there could be a change in pressure, due to additional load, but it's likely compensated for by the deformation of the tire. Therefore the actual internal volume doesn't change (ergo pressure) as the tyre compensates for it.

Theoretically anyway! lol Doubtless there'll be someone along, far more astute than the pair of us, to correct us in a minute

The tire deforms slightly and the pressure goes up a little under load compared to if you inflated it while off the trailer.

Originally Posted by jwalker

I have heard this said many times and it is not correct. The pressure on the side wall is a maximum pressure for the tyre inflation NOT the pressure the tyre is to be inflated to. (Though, in service it could be.) Your tyre wall will give you a maximum load which can be carried by the tyre at its maximum pressure at its rated speed. The actual pressure will depend on the load being carried by the tyre.
For info; if it's found that a tyre is running at its maximum load, it may be a good idea to check out its ply rating and possibly fit a higher ply-rated tyre since this will carry more load. The ply rating is just that, a rating, and it's quite possible to have a 6 or 8 ply rated tyre which only uses two actual plies in the side wall. It's a carry over system from when tyres did have extra plies as the rating increased.

There's no load vs. inflation pressure table. Most people don't check their tires often enough and run them way underinflated. Trailer tires are small and need to be run at higher than car pressures to avoid excess deformation which will heat up the rubber like crazy and lead to blowouts. You're much better off filling the tire to the maximum rated pressure than trying to guess at the load you're actually using them at relative to their unknown allowable sidewall deformation.

A fully inflated to max rating tire just works your trailer suspension a bit harder instead of having tire sidewall flex bear some of the bumps and jostling. The springs can take it.

[jwalker]

Originally Posted by captnjack

You're much better off filling the tire to the maximum rated pressure than trying to guess at the load .....

So if I'm towing my empty trailer a 100miles I should have all six tyres inflated to 60psi... I suppose that's one way of doing it.

I guess it may well save me some fuel cos it'll likely be airbourne much of the time.

[captnjack]

Originally Posted by jwalker

So if I'm towing my empty trailer a 100miles I should have all six tyres inflated to 60psi... I suppose that's one way of doing it.

I guess it may well save me some fuel cos it'll likely be airbourne much of the time.

What do you suggest deflating them to and what's that based on?

[jwalker]

About 8psi.
Experience and intelligence.

[captnjack]

Originally Posted by jwalker

About 8psi.
Experience and intelligence.

You're wrong its 42psi.