cooper's / bfg's

Submitted: Sunday, Feb 15, 2009 at 21:47
ThreadID: 66018 Views:3052 Replies:8 FollowUps:7
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before my next trip in july I need two new tyres, I currently run coopers but want to go back to bfg's, so, can I run a mix of cooper's and bfg's of the same size??
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Reply By: Best Off Road - Sunday, Feb 15, 2009 at 21:59

Sunday, Feb 15, 2009 at 21:59
I believe the deal is as long as the two on the front match, and the two on the back match all is OK legally.

But a call to the RTA may be in order.

Cheers,

Jim.

AnswerID: 349288

Reply By: shaneo86 - Sunday, Feb 15, 2009 at 22:15

Sunday, Feb 15, 2009 at 22:15
fully have a l at PIRELLI they are very good i got 4 and in the wet they have awsome grip like it says on the site http://www.4wdmonthly.com.au/tips_tyres.php

they step out abit but yea they kick in again guy at my work has the bfg's and in the wet they are .... yeah do your self a favour and give em ago i have and i wont go back to brigestone never ever slip and and slide all over the place with them
AnswerID: 349300

Reply By: Member - Paul C (WA) - Sunday, Feb 15, 2009 at 22:36

Sunday, Feb 15, 2009 at 22:36
Just make sure OD for both tyre brands is the same. Don't know how the two compare but two manufacturers with, say, 265/75/16 won't necesarily have the same OD.
You will place great stress on your drivetrain, when CD locked, if all four wheel are not turning at the same speed.
AnswerID: 349304

Follow Up By: Member - Jeff H (QLD) - Monday, Feb 16, 2009 at 02:03

Monday, Feb 16, 2009 at 02:03
Paul ,
Forgive me, 'cause I'm dumb as dog's hit, and really know nothing of tyre diameters.
Jeff H
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Follow Up By: Member - Tony B (Malanda FNQ) - Monday, Feb 16, 2009 at 11:50

Monday, Feb 16, 2009 at 11:50
Paul C - "265/75/16 won't necessarily have the same OD". You will have to explain that one too me as I was always led to believe that a tyre size is a tyre size? Should they not be all the same rolling circumference? Cheers Tony
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Follow Up By: Member - Paul C (WA) - Monday, Feb 16, 2009 at 18:33

Monday, Feb 16, 2009 at 18:33
I always thought the same until reseaching for new muddies last year. There are various differences between maufacturers.
See below.

Cheers
Paul
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Reply By: Member - Tony S (WA) - Monday, Feb 16, 2009 at 02:17

Monday, Feb 16, 2009 at 02:17
Sizes will be that close it will not matter.
If you are still uncertain check with the Mnf. or agents.
The rig

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AnswerID: 349320

Reply By: Member - Tour Boy ( Bundy QLD) - Monday, Feb 16, 2009 at 10:11

Monday, Feb 16, 2009 at 10:11
My transfer case is shot because the previous owner had put falkenis on the front and khumo's on the rear. In a constant 4wd vehicle even with the centre diff NOT locked it will cause bearing failure in the T/C according to the transmission specialist.
Both tyres are branded as the same size but the actual rolling height is 1 1/2 inches different.
He said to me never replace 2 always do all 4.

Cheers
Dave
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Reply By: Sea-Dog - Monday, Feb 16, 2009 at 12:05

Monday, Feb 16, 2009 at 12:05
If it was me I would not put two different brands on there unless I could physically hold them up side by side and check the rolling circumference to each other...

If you have part time 4x4 you can get away with a bit more than a constant 4x4 but when you are in 4x4 you really do want your tyres to be the same size.

There is OFTEN a huge difference between different makes with the same written size ie 285/75/16 etc may be a 33" in one brand and a 32 or thereabouts in another brand.
AnswerID: 349351

Reply By: That Troopy Bloke (SA) - Monday, Feb 16, 2009 at 12:39

Monday, Feb 16, 2009 at 12:39
BFG list a 265/75/16 as having a circumference of 2470mm, which equals 786mm dia.
Coopers list a ST 265/75/16 as having a diameter of 807mm, which equals a circumference of 2535mm.

This means that for each rotation, the Cooper ST would travel 65mm further.

I would be sticking with the same tyres front and rear.

Cheers
Glenn
AnswerID: 349352

Follow Up By: Member - Tony B (Malanda FNQ) - Monday, Feb 16, 2009 at 17:13

Monday, Feb 16, 2009 at 17:13
Glenn - So in Queensland you can have the same size tyre but drive on illegal tires? Because by what you have posted above puts one of the same size tires 21mm larger and outside the allowed 15mm.

Hope someone can explain this logically as I always thought the Maths for a 265/75/16 should always be the same! Otherwise how do you keep it leagal?

Cheers Tony
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Follow Up By: jpfe8851 - Monday, Feb 16, 2009 at 18:17

Monday, Feb 16, 2009 at 18:17
Glenn,

The Tyre and Rim Manual specifies a 265/75R16 to have a nominal diameter of 804mm. I agree that various brands and patterns will vary up to say 10mm, but I am sure your BFG was a 265/70R16 which has a nominal 778mm, and may well be larger in the BFG case due to fairly deep tread.

Tony B, you are correct that at present and until Qld adopts the ew National Code of Practice (NCOP) the largest tyre will be 15mm larger OD than the largest optionalfitting for a make or series. In the case of most Landcruiser and Patrols which had an 7.50R16 on the base models (covers the make or series part), you can go up to 825mm as the 7.50R16 is 810mm in diameter. In the case of LC200, the standard tyre is 803 plus 15 = 818mm.

When the NCOP is adopted in Qld, scheduled for July 1 according to QT, then upsizes by up to 50mm will be allowed without certification.

Bear in mind that you can get an upsize certified by an engineer along with a lift provided it meets the bumps stop provisions... but that's another thread...

Cheers,
John
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Follow Up By: That Troopy Bloke (SA) - Monday, Feb 16, 2009 at 20:18

Monday, Feb 16, 2009 at 20:18
Guys, don't shoot the messenger, I'm just quoting the info these companies put out themselves.
I don't know the ins and outs of all this stuff either.

Here's the links I quoted from:

BFG

Coopers

If BFG have made a mistake, take it up with them.


Cheers
Glenn
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FollowupID: 617667

Follow Up By: jpfe8851 - Monday, Feb 16, 2009 at 23:50

Monday, Feb 16, 2009 at 23:50
Not having a go at you Glenn... thanks for putting in the links as this gives an opportunity to clear the misunderstanding up.

Rolling circumference is different than unloaded circumference. Rolling circumference measures the distance travelled by one rotation of the tyre when inflated to a nominal pressure which will be lower than the unloaded circumference by a significant percentage. There is no standard for measuring rolling circumference as this will vary substantially according to load and pressure so is best ignored. Overall diameter (OD) is commonly quoted by tyre manufacturers and best used for comparative purposes such as the OP was looking at.

In my view (I am involved in the tyre industry), the variations between different brands and patterns are not significant at normal pressures however, excepting in full time 4WD systems. The variation is not so important off road or on gravel for any 4WD due to the loose surface offsetting the marginally different OD's and on road, part time systems can be disengaged. But and in any case, 4 like tyres is the safest and best solution.

For the record, the BFG site you linked to, also showed loaded radius (in mm not inches as indicated). Loaded radius is the distance measured from the wheel centre to the ground for a properly inflated tyre at any load. In other words, if under any load, you should inflate the tyres so that the radius measured from the wheel centre to the ground equals the tyre's published loaded radius for normal running. This is one of the best methods of determining the correct pressure under any given load.

Hope this helps clear up the confusion.

John
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FollowupID: 617711

Reply By: Member - one way ticket (VIC) - Tuesday, Feb 17, 2009 at 21:32

Tuesday, Feb 17, 2009 at 21:32
thanks to all, I will do all four
AnswerID: 349557

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