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[geoffr70]

Hi peeps. I'm after gettig a spare wheel for my caravan. It's got 4 studs.

How do I find out what the offset is etc (don't even know what that means tbh).
Also, stuff like et39 or something, what does that mean? Basically I just need to know these figures so I can get a wheel that will fit the the bolt holes. Could i measure the centres? Thanks

[aaronjb]

"ET<something>" is the offset: http://en.wikipedia.org/wiki/Offset_(wheel)

Measuring the centres of the bolt holes will get you the PCD (Pitch Circle Diameter)

Offset isn't easy to measure accurately, but might well be stamped on the wheel somewhere. Though there are instructions on the link for measuring & calculating it (accuracy just depends on how good you are with a ruler then)

[geoffr70]

One of those 'ahhhhh!' moments!

Thanks for that! 

[Kevin Wood]

You will need to know a couple of parameters.

PCD - The diameter of the circle described by the wheel mounting studs. Easy to measure on a 4 stud wheel. Just measure the dimension between two opposite studs centre-to-centre. Normally combined with the number of studs - i.e. an Omega has a PCD of 5x110 (5 studs, 110mm PCD).

Centre diameter - the diameter of the central section of the hub which fits into the bore in the centre of the wheel.

Offset - this is your ET35 or whatever. Offset laterally between the centre of the tyre tread and the mounting face of the wheel hub. A positive offset moves the wheel further away from the hub.

Kevin

[geoffr70]

I understand now! Thanks

[RobG]

http://www.nice-wheels.co.uk/pcdandoffset.html

[Andy B]

....
Centre diameter - the diameter of the central section of the hub which fits into the bore in the centre of the wheel. .....

Caravan wheels often don't centre on the hub, it's the taper seat nuts that centralise them. 

[o-meg-a]

and it may be easier to buy two matching steelies and replace both on the caravan

rather than trying to find one that matches the other on on there in terms of offset etc, as there are soo many variations.

[Andy B]

..... as there are soo many variations.

I agree that there are many many different wheels around, but recent caravans use a limited number of them.
My caravan had no spare when I bought it, mine came from a local caravan breakers yard for £20 including an as new tyre.