Help with Tyre Jargon Please!

Submitted: Monday, Apr 04, 2005 at 17:02
ThreadID: 21777 Views:6503 Replies:9 FollowUps:5
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Hi There

We are about to take off on a round Oz trip in a couple of months and the time has come to fit some new tyres. We have a 2003 Hilux SR5 and currently have the standard H/T tyres.

On the plate that has all of the specifications for tyres/loads says we need to fit 255/70R15, now I get what that means, but what I don't get is when a tyre is explained such as 30X9.50R15LT. We are having a very hard time trying to find AT's or Muddies in the 255/70R15 size...but there are plenty of options in the 30X9.50R15LT size and want to check if that is suitable/legal for the Hilux. What I want to know is how to convert 30X9.50R15LT to read xxx/xxR15, if that is all possible?

Hope that makes sense, I am feeling rather confused!

Thanks in advance for your help.
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Reply By: Lone Wolf - Monday, Apr 04, 2005 at 18:26

Monday, Apr 04, 2005 at 18:26
I think a lot of this confusion stems back from the 1970's. You see, what happened was, is that all of the tyre fitters back then had about the same status as say, a chimney sweep.

They all got together, and decreed that they would elevate themselves in the workforce hierarchy, and they adopted a cunning plan. What they did was basically invent their own secret code, which is like tyre changing 101 meets the Free Mason's secret handshake.

So, almost overnight, you average Joe Blow blue shorts & singlet tyre changing dude, was suddenly.......... well............ just full of new fandangled tyre speak. This was a good thing at first. Hubby would send his wife down to the Tyre Mart, and she would be bamboozled by the Gobbledygook tyre speak, and a lot of women fell for this, like these dudes were almost like men in uniform!

Wife would then go home, and tell hubby that she had some 250R/75/15/Magnums put on, and the husband, not to be outdone by a tyre monkey, would then invent his own code........."Well, Darling, if I was him, I would have put 260/2567FT/16/5's on the front, at 36 psi, & 765/XXX/17 on the rear at 200 kpa!" This little rebuttal would have made him look all good again.............

So, as time went on, the numbers became blurred, and it simply became a p1ssing competition. As time evolved, some of the mud stuck, and we still know the numbers today. Just pretend you understand the secret code, or bow to the Tyre God, and humbly say..........."I want those black round ones please...."

Sorry, just can't help myself somedays...........

AnswerID: 105128

Follow Up By: Member - iMusty (VIC) - Monday, Apr 04, 2005 at 18:53

Monday, Apr 04, 2005 at 18:53
Do they come in Green?
FollowupID: 362281

Reply By: howesy - Monday, Apr 04, 2005 at 18:38

Monday, Apr 04, 2005 at 18:38
255 is the width
70 refers to aspect ratio ( profile is 70% of width)
R refers to the tyre rating
15 is the rim diam.

30 refers to the standing height of the tyre in inches.
9.5 is the width in inches instead of cm
R refers to the tyre rating
15 is the rim diam.
LT refers to the tyre type (light truck for instance)

You will pay twice the price buying the 255. Which incidently is a 10 inch tyre. 30X10X15 's are as common as mud and cheap as chips go for this size and save dollars and enjoy the choices available.
AnswerID: 105132

Reply By: Exploder - Monday, Apr 04, 2005 at 19:07

Monday, Apr 04, 2005 at 19:07
How ya going

255 section width in mm or width of tred
70= Aspect ratio or hight of tyre
R= tyre constructon in this case radial
15= Rim diameter in inches

30*9.5r15LT is a bit smaller then your current 255/70R/15 the closest is 31/10.5R15 which r just a bit bigger say 265/75R15 i think. That will put your speedo out by about 3km no biggy. The LT in all this stands for Light Truck construction which is a must for bush driving make sure you get a 6to10 ply construction

hear r some aprox cost's for u
BFG AT 31/10.5R15LT $258
cooper AT 31/10.5R15LT $229
ST " " " $243
cooper at 30/9.5R15LT $218
Bridgestone AT 3110.5R15LT $220
Goodyear At 31/10.5R15LT $186

AnswerID: 105142

Follow Up By: Shaker - Tuesday, Apr 05, 2005 at 09:26

Tuesday, Apr 05, 2005 at 09:26
30/9.5 x 15 is actually 3.14% bigger diameter!

Check this tyre calculator:
FollowupID: 362338

Follow Up By: Exploder - Tuesday, Apr 05, 2005 at 18:38

Tuesday, Apr 05, 2005 at 18:38
yep thats right my bad.
FollowupID: 362416

Reply By: muzzimbidgie - Monday, Apr 04, 2005 at 19:48

Monday, Apr 04, 2005 at 19:48
All tyre retailers have a chart that converts from one to the other. Check it out.
AnswerID: 105160

Reply By: BenSpoon - Tuesday, Apr 05, 2005 at 00:30

Tuesday, Apr 05, 2005 at 00:30
google gold

tyre calculator
AnswerID: 105219

Reply By: SAoffroader - Tuesday, Apr 05, 2005 at 15:24

Tuesday, Apr 05, 2005 at 15:24
Most SR5's need to have a load carring index of 112 and most 31x10.50r15 have only got an index of 109 so therefor not legal fitment.You can fit a 265/70r15 some have 112 index which l think is much better size and a few more available.
AnswerID: 105279

Follow Up By: Melly - Tuesday, Apr 05, 2005 at 16:29

Tuesday, Apr 05, 2005 at 16:29
Hi SAoffroader

I was aware that we need to have a load index of 112, which is partly the reason why we are finding it so hard to find the right "legal" tyres, call us girly wusses but we want to be legal. Unfortunately nearly every "tyre expert" centre we have contacted has really been no help to us as they try to talk us into fitting illegal tyres.

I'll have a look into the 265/70r15 size. I wonder why the make the Hilux such a bugger to fit tyres...maybe they are in cahoots with Bridgestone as the Desert Duellers seem to be the only tyres that legally fit and have the correct load rating.

Thanks for everyones help!
FollowupID: 362394

Reply By: Melly - Tuesday, Apr 05, 2005 at 17:56

Tuesday, Apr 05, 2005 at 17:56 now after my crash course in tyres we have a few options...not really the options we were after but still its not all bad. All these have the correct load rating of 112 or over.

Cooper AT's or ATR's 265/70R15
Goodyear Wrangler ATR's 265/70R15
Bridgestone Dueler AT D691 255/70R15 *The only tyre with the EXACT specs
Michelin LTX AT's LT265/70R15

None of the 30x10.5R15's nor the 30x9.5R15's had a load rating over 112....mostly were 104 or 109. No muddies :(

I bet there are a hell of a lot of SR5 owners out there driving with illegal tyres, we don't want to risk the insurance company telling us they aren't covered in the case of an accident or some other misfortune.

Now im gonna go and apply for a job at Beuarepairs or Bob Jane.

Thanks again for all the responses.

AnswerID: 105291

Reply By: Onayr - Monday, Apr 11, 2005 at 13:44

Monday, Apr 11, 2005 at 13:44
Just so that those out there are aware....

The rear axle load rating on the SR5 Hilux is 1570kg (front 1180kg).
According to the vehicles placard:-

"The sum of the load carrying capacities of tyres fitted to any axle or axle group of this vehicle shall not be less than the relevant load shown above."

This basically means that a load rating of 100 (785kg per tyre) is completely legal and insurance shouldn't have a problem with this. For this reason the 30x9.50R15 with 104 load rating is fine... the 31x10.50R15 109 load rating is fine aswell, just the overall diameter is too big...legally.
I work in a company that supplies after market tyres to Toyota for their Hilux SR5 and fit 30x9.50R15 104Q with no dramas at all.
If you would like some more info :
AnswerID: 106144

Follow Up By: Onayr - Monday, Apr 11, 2005 at 14:02

Monday, Apr 11, 2005 at 14:02
Should also point out that the 30x9.50R15 are a Light Truck construction whick is generally a heavier case construction than the standard 255/70R15 and also carry a deeper tread depth.
FollowupID: 363192

Reply By: Truckster (Vic) - Monday, Apr 11, 2005 at 14:05

Monday, Apr 11, 2005 at 14:05
google is your friend, theres a trillion websites explaining these differences. also tire calculators to convert sizes.
AnswerID: 106148

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