Tyre legalities

Submitted: Saturday, Nov 10, 2001 at 01:00
ThreadID: 542 Views:1448 Replies:2 FollowUps:2
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We are wanting to change over to Cooper S/T's on our Jack but they only come as a 245/75R16 and we are running at present 245/70R16 Cooper H/T's. What are the legalities on running say 75's on the front and 70's on the rear until the 70's are worn out? My gut feeling is it would be illegal but someone may know otherwise. Look forward to any replies.
Grant.............happy trails.
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Reply By: Mark - Sunday, Nov 11, 2001 at 01:00

Sunday, Nov 11, 2001 at 01:00
Grant,

Not sure about the legalities but it would probably not do your transmission much good as the front wheels would be turning at a different rate than the rears. As an example BFG 245/70 16 complete 705 revolutions per mile whereas the 245/75 16 completes 680 revolutions per mile. With the center diff locked this would give problems such as transmission wind-up.

Mark
AnswerID: 1395

Reply By: Col - Monday, Nov 12, 2001 at 01:00

Monday, Nov 12, 2001 at 01:00
Grant,

Dont mix your tyre sizes! I am looking seriously at the Cooper S/T's. A couple of other members of the Jackaroo Club have put them on. The size they went with was 255/70. I believe that also kept them legal in regard to the load rating, with a very minor reduction in speedo accuracy.

Regards,

Col
AnswerID: 1411

Follow Up By: Grant - Tuesday, Nov 13, 2001 at 01:00

Tuesday, Nov 13, 2001 at 01:00
Thanks guys, I hadn't considered the trans wind-up but we never run locked on firm surfaces so never thought about it. It's a good point though, coz one day we just might. Theres a light truck type and a P-metric type S/T tyre in the Coopers catalogue and it may be a difference in the number of ply's. Anyone know what P-metric is? The P-metric's are the only ones with a 70 type. Don't really want to go wider as more punctures may eventuate, would rather go thinner, but higher would be better for more underbody clearance. The speedo problem I would have to put up with. I will have to go to the nearest Coopers man and trust what he tells me. Thanks again.
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Follow Up By: Mark - Wednesday, Nov 14, 2001 at 01:00

Wednesday, Nov 14, 2001 at 01:00
Grant,
P-metric: This is the United States version of a metric sizing system established in 1976. P-Metric passenger car tire sizes begin with "P", which simply means "Passenger"
Also I priced a set of Cooper ST's recently for my Disco and the size was 235/70 R16 maybe an option.

Mark
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