Mixing tyre sizes

Submitted: Friday, Apr 09, 2004 at 15:26

ThreadID: 11948 Views:1876 Replies:7 FollowUps:3

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tessa_51

Hi folks. Am about to replace the 5 tyres on my 2000 Prado with 265/75/16 BFG A/T's. That still leaves me with 1 265/70/16 Grandtrek in reasonable condition. I know I'm not supposed to mix tyre sizes for safety reasons, but is there any mechanical reason why I cant cary the G'Trek as a second spare.

Tessa

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Reply By: GaryInOz (Vic) - Friday, Apr 09, 2004 at 16:43

Friday, Apr 09, 2004 at 16:43

If you have a LSD in the rear, you will not be able to use it on the rear (will chew out the clutch pack).

Unsafe to use it on the front (car wil pull and brake unevenly)

Illegal to use diferent sized tyres on same axle (= NO INSURANCE COVER, "unroadworthy")

=>Carrying a different sized spare spare = carrying a boat anchor.

No one can stop you from carrying a boat anchor......................

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If the tyre is new (or close to it), put it up on the trader section here or see if the tyre store will take a "trade-in" and use the procedes towards a correct sized tyre.

AnswerID: 53783

Reply By: GO_OFFROAD - Friday, Apr 09, 2004 at 17:27

Friday, Apr 09, 2004 at 17:27

An incorrect 6th "emergency" spare, is better than no spare, and if you had to borrow a tyre/rim from someone, what chance is it it will be the same size as yours anyway......

The difference between the standard 265/70/16 and a 265/75/16 is only the difference between a bald tyre on one side, and a new tyre on the other anyway.

AnswerID: 53785

Follow Up By: GaryInOz (Vic) - Friday, Apr 09, 2004 at 18:55

Friday, Apr 09, 2004 at 18:55

1.3" actually.....enough to burn out a clutch pack over a resonable time

FollowupID: 315454

Follow Up By: GO_OFFROAD - Friday, Apr 09, 2004 at 19:40

Friday, Apr 09, 2004 at 19:40

well a new AT or MT has 17mm of tread, so that is very close to 1.3 when you take in the total tyre height ;-)

And if its a 6th spare, it can be run for just a short distance, as the difference = less than 15 revolutions of the spider gear per km.

HArdly enough pressure to even engage the lsd....

FollowupID: 315457

Reply By: AK - Friday, Apr 09, 2004 at 18:56

Friday, Apr 09, 2004 at 18:56

Tessa
Are you going to give the Prado a lift when you increase the tyre size or just use the same susspension?
Apparently your car will now be unroadworthy with the new tyres without an engineers certificate.
Just my thoughts
AK

AnswerID: 53797

Follow Up By: tessa_51 - Friday, Apr 09, 2004 at 20:00

Friday, Apr 09, 2004 at 20:00

Thanx AK
Have already done the lift - OME and Polyairs have given me what I am told is 40mm lift. As I understand the situation the 75's will give me another 15mm of lift which amounts to a total of 55mm. I believe that is almost legal without a certificate!!!!
Tessa

FollowupID: 315461

Reply By: Member - Rohan K - Friday, Apr 09, 2004 at 19:33

Friday, Apr 09, 2004 at 19:33

tessa, the reply above from GaryInOz is correct. The difference between the two (theoretically) is almost 7% - too much to be running in 4x4.

The 265/75/16 may be legal (in NSW), as long as the overall diameter as specified by the manufacturer is less than 803 mm. However, a standard (read HT) 265/75/16 is 803.5 mm so it is unlikely your ATs will be only 803 mm. Therefore, as stated by AK, they would not be legal (technically speakin).

AnswerID: 53802

Reply By: Wil - Friday, Apr 09, 2004 at 20:25

Friday, Apr 09, 2004 at 20:25

Tessa
Your Playdo is full time 4x4 machine. A different size tyre will create major problem with drive line. Sell it on the traders & pay for a sixth. Small amount for peace of mind and keep up with the tyre rotation to share the wear. Will be better for the truck in the long run.
Cheers

AnswerID: 53811