Determining Tyre Upsizing

[rainsey]

G'day all,

Current rim steel 15 x 7J
Current Tyre 31 x 10.5

(Here is where I show my ignorance) On the above mentioned rim, and ignoring the vehicle that it is going on, how does one calculate what tyre you can upsize to. By this will a, for example, 32 x 11.5 go on a 15 x 7J rim safely??

Obviously the diameter is irrelavant (I think, as 15" is 15 ") I take it the size is dependant on what the 7J rim can take width wise?? Am I correct and saying this, what can you squeeze onto a 7" rim without becoming a hazard to your gene pool??

Cheers

Rainsey

[Slunnie]

legally about 10.5" or 265's

[Slunnie]

Mind you this will vary a little between tyres and the manufacturer will state for each tyre.

[ozy1]

i have run 32x11.5's on a 7 inch rim, and did so quite saftly, never had a drama, at the moment, i also have a 33x12.5 mounted on a 7 inch rim, thou its only a spare and works, butim not a fan of that, side walls are to exposed for my liking, and bulging out a bit.

[Utemad]

Best way is to check a manufacturer's website. This is the BF Goodrich mud terrain spec sheet.
Minimum rim size for a 10.5in tyre is 7in.
Minimum rim size for a 11.5in tyre is 8in.

There is a 33x10.5in That would look good on your Rodeo

BF Goodrich KM mud tyre spec sheet

[Gwagensteve]

Go the 33 10.5 and keep your 7's. These are a much better size than the 32 11.5, and will suit a rodeo well.

I used to run 33 9.5's but they were a touch narrow to give good tread wear on a heavy car.

[MereMale]

With doing these changes, I'm wondering if anyone knows how much it throughs your speedo out by plz.
As went up to 35's.

Mere

[Utemad]

With doing these changes, I'm wondering if anyone knows how much it throughs your speedo out by plz.
As went up to 35's.

Mere

The only accurate way to know is to check your new speed with a GPS. There are too many variables other wise. Such as:
Accuracy of your speedo before the new tyres.
Real size of your new tyres? (unlikely to be exactly 35in with a tape measure)
Is you speedo accurate thoughout its entire range?

Doesn't take long.

When I did mine I kept my GPS in the vehicle for about 500km. I zeroed both trip meters before I started (GPS and car). When I did my calculations I came out at 5% under read on the speedo. However when I set my electronic box to 5% and went for a drive I discovered that it was still under reading by 1%. Reason being is that most of the test driving was at 100km/h and my speedo was spot on at 100km/h but at 60km/h it was under reading by 1%. Just goes to show that speedos are not accurate throughout their entire range.

For the record I went from worn 225/75 16 to new 31in tyres. The 31s measured as 30in but don't know about the 225s.

[GUJohnno]

A great size for the rodao is the 235/85/16s.
It's basically a 32 x 9.5" Tyre. It's not as wide as you were looking for but it will fit in easy.
The great thing about this size is that it is one of the most common size tyres available out in the bush. It is the size that the troopys and standard Landcuisers come with.
Most of these are 10-12ply tyres and are very strong. I had these on my Bravo (Cooper St's) and did numerous out back and high country trip and never got a puncture.
If you intend doing outback trips, try to stick to a readily available size.

Johnno.