Tyre sizes

Submitted: Wednesday, Mar 31, 2004 at 09:49
ThreadID: 11692 Views:3476 Replies:17 FollowUps:21
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Hi all

I know this subject has been covered many times and I have looked at all the threads that I could but I have a specific question.

Our LC 100 TD came with Dunlop Grand Treks. Tyre placard says 275/70R16 which is what they are. We want to do a trip to the centre later this year and plan to do a suspension upgrade and get new tyres before we go.

After a lot of research (including here) and talking to people the choice for tyres came down to BFG A/T or Coopers ST. We inclined slightly to the Coopers. From the Coopers web site it appears as though they do not supply our size - the closest is 285/75R16. BFG have both. I know there are arguments for and against going up a tyre size and we have not finally come to a view about that - BUT the real question is - could we put the Coopers on and be legal in NSW.

Thanks for any input.

Bob & Joëlle
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Reply By: Member - Rohan K - Wednesday, Mar 31, 2004 at 10:26

Wednesday, Mar 31, 2004 at 10:26
Bob (or is this Joëlle?), the short, blunt and technical answer is "no". If 275/70/16 is the largest wheel/tyre combination on the tyre placard, then the (absolute) largest "legal" size you can go is 818 mm. That means the 285/75/16 Copper STs are too big by almost 15 mm (i.e. almost twice the allowable diameter increase).

Sorry.
AnswerID: 52620

Reply By: Baz (NSW) - Wednesday, Mar 31, 2004 at 10:32

Wednesday, Mar 31, 2004 at 10:32
Hey Bob i would go the BFG's, stay with the same size you have, save's getting the speedo adjusted, not much difference but maybe enough to get booked for speeding, and they are both very good tyres, IMHO.

Baz.

ps, I have BFG A/Ts 55,000ks 25,000 off road not a prob not even a flat, touch wood.
AnswerID: 52621

Follow Up By: Bob et Joëlle - Wednesday, Mar 31, 2004 at 10:37

Wednesday, Mar 31, 2004 at 10:37
Rohan,

Its Bob at the moment

Rohan and Baz - thanks very much for the prompt reply - at least it makes the decision easy !

Bob
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Follow Up By: Member - Rohan K - Wednesday, Mar 31, 2004 at 11:04

Wednesday, Mar 31, 2004 at 11:04
Bob, if you can find a suitable (common/popular) larger size that is still legal, I'd go with it. While the speedo reading will change (by about 3%) most vehicles understate the actual speed by a few % anyway and if uncertain, you just drive at 107 kph intstead of 110.

The little bit of extra lift and the larger footprint you get are worth going up in size if you can.
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Reply By: flappan - Wednesday, Mar 31, 2004 at 10:58

Wednesday, Mar 31, 2004 at 10:58
You could go up one size , to 265/75/R16 and get a slight increase.

If my maths is correct (but may not be), the BFG AT 265/75/R16 comes in at 31.8 inches (807mm) and the 275/70/R16 is 31.3 inches (795mm)
AnswerID: 52623

Follow Up By: Bob et Joëlle - Wednesday, Mar 31, 2004 at 12:22

Wednesday, Mar 31, 2004 at 12:22
Flappan,

Thanks - Coopers also have this size - they say 806 mm. This gives me back the decision to make just when I was feeling comfortable and lazy.

I don't really understand the measurements - what does the 265 and 275 refer to, I assume the 70 and 75 are 7" and 7.5" rims sizes - i.e. width - is this right ? Where do I get the extra size from ?
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Follow Up By: charlie - Wednesday, Mar 31, 2004 at 12:34

Wednesday, Mar 31, 2004 at 12:34
Bob the 265 and 275 refer to the width of the tyre 265mm or 26.5cm etc. The 70 and 75 refer to the aspect ratio, or the percentage of the width that the tyre wall is high. For example 265/70 are 26.5 cm wide and the sidewall is 70% of this all the way around. When you add the wheel size (16 inches) you add this to the 70% of 26.5 x 2 (top and bottom sidewall) and you will get the height/diameter of the tyre. Just remember that the aspect ratio is only between the wheel and the outside edge of the tyre so you have to add it twice.

Hope I didn't cofuse you more with my wording.

Charlie
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Follow Up By: Bob et Joëlle - Wednesday, Mar 31, 2004 at 12:38

Wednesday, Mar 31, 2004 at 12:38
Thanks Charlie - so slightly narrower and slightly taller at 265/75R16 - so is this a good idea or not ?
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Follow Up By: charlie - Wednesday, Mar 31, 2004 at 12:46

Wednesday, Mar 31, 2004 at 12:46
Bob I went to 305/70 on my 80 series and noticed a slight drop in power from take off. Mine is a td so a petro; might not notice it as much. My tyres are apparently illegal now but at the time in Qld it was allowable to go 50mm taller than standard. Mine are the same height as 285/75's just to give you an idea of what changing the percentages does. On sand these tyres are noticable better infact they grip better in all situations including on road wet/dry. I got the Cooper ST's because of the waranty and had BFG's in the past and was happy with them too but had the pre KO type and heard too many stories of the All terrain KO's falling apart.

Going higher helped my 4wding and have a 3inch lift. The choice is still up to you. I don't think I would ever go narrower but......

Charlie
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Follow Up By: Member - Rohan K - Wednesday, Mar 31, 2004 at 16:27

Wednesday, Mar 31, 2004 at 16:27
Bob, slightly narrower gives a slightly smaller contact area. Slightly taller gives a slightly larger contact area. Slightly narrower but slightly taller probably gives you about the same contact area only a longer, narrower one.

I'm a firm believer that off-road, a longer foot-print is better that a short, wide one. Unfortunately for you, there are others that take the oposing view.

Check out this site. It's the best I've seen on explaining (almost) all things to do with tyres.

car bibles
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Reply By: The Banjo - Wednesday, Mar 31, 2004 at 11:51

Wednesday, Mar 31, 2004 at 11:51
Yep re the BFG's - why muck around ? They have 3 poly plies on the side plus 3 poly and two steels on the tread..... tough as....I too have just closed a good run on my first set - 80k with nairy a flat.....sure you do get some tread chipping off on the stones (but chipping only - not chunking) - show me the perfect tyre - I'm staying with BFG's - $255 fitted and balanced in Adelaide for the 245/70 R16 AT/KO.
AnswerID: 52635

Reply By: 10 Para (Qld) - Wednesday, Mar 31, 2004 at 12:01

Wednesday, Mar 31, 2004 at 12:01
Bob have a look at this site for the tire size http://www.miata.net/garage/tirecalc.html
AnswerID: 52638

Follow Up By: Bob et Joëlle - Wednesday, Mar 31, 2004 at 12:30

Wednesday, Mar 31, 2004 at 12:30
Hey great site - so 275 etc is the width, 75 etc is the diameter - so is there an advantage in a slightly narrower, larger tyre or do I just stay with the stock tyre size ?
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Follow Up By: Bob et Joëlle - Wednesday, Mar 31, 2004 at 12:33

Wednesday, Mar 31, 2004 at 12:33
Nope - just looked again and it is not that simple - now I really am confused - HELP !!
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Follow Up By: charlie - Wednesday, Mar 31, 2004 at 12:35

Wednesday, Mar 31, 2004 at 12:35
Look at my follow up above
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Reply By: Bob et Joëlle - Wednesday, Mar 31, 2004 at 12:41

Wednesday, Mar 31, 2004 at 12:41
Thanks everybody - so now the question comes down to this (according to our slight inclination to get the Coopers) - do we get BGF 275/70R16 A/T or Coopers 265/75R16 ST ??
AnswerID: 52644

Reply By: Bob et Joëlle - Wednesday, Mar 31, 2004 at 12:45

Wednesday, Mar 31, 2004 at 12:45
Or maybe BFG 265/75R16 I suppose if we are wrong about the choice of Coopers as seems to be suggested !!!!
AnswerID: 52645

Follow Up By: 10 Para (Qld) - Wednesday, Mar 31, 2004 at 12:58

Wednesday, Mar 31, 2004 at 12:58
Bob have been down that track myself and the upshot of it is that you can go to a 265/75 that will be 11mm taller you are alowwed 15mm or you can just put on the 285/75 and take the chance if you go the 285/75 then you will not be legal,your speedo will be out,your low range will not be as low but you will get some good stuff as well which is why i supose you are looking at the bigger tires, me i am still with the the 275/70 at the moment but as soon as the patrol gets back for NZ on go the 285/75 for the Aussi trip because the cooper st c is a 10 ply tire and is rate abour 1500kg per tire.
Regards
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Follow Up By: 10 Para (Qld) - Wednesday, Mar 31, 2004 at 13:14

Wednesday, Mar 31, 2004 at 13:14
Bob check out the coopers st c its a new tire the st and stt are prone to chipping the st c have fixed that
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Follow Up By: Member - Rohan K - Wednesday, Mar 31, 2004 at 19:38

Wednesday, Mar 31, 2004 at 19:38
10 Para, the ST-C has attempted to fix that issue but it does so via a softer compound that will wear somewhat faster. The ST-C is principally designed for users that spend 80% of their life on dirt roads. For those that spend that 80% on tar, it would not be a good choice.

BTW, I've had my STs for 10,000 kms, half of which has been off-road, and not a chip or crack yet. (fingers are crossed).
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Reply By: flappan - Wednesday, Mar 31, 2004 at 12:56

Wednesday, Mar 31, 2004 at 12:56
I would recommend 265/75/R16 regardless.

Coopers or BFG , its a matter of opinion.

I have BFG's on all mine , but admit , I would have like a set of Coopers. I found Coopers to be $50 a tyre dearer , but I couldn't see them being a better tyre as such (not the ST's anyway).

As for the size, slightly larger is always handy , but being only 10mm narrower really means stuff all.
AnswerID: 52646

Follow Up By: Baz (NSW) - Wednesday, Mar 31, 2004 at 13:18

Wednesday, Mar 31, 2004 at 13:18
Bob, go with the same size you have now 275/70/16 in the BFG/ATs then there will be no hassle's old one's off, new one's on, and your off on your trip, easy !!!

Baz.
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Reply By: Bob et Joëlle - Wednesday, Mar 31, 2004 at 13:46

Wednesday, Mar 31, 2004 at 13:46
he he he - now I have 3 different answers - which I suppose goes to show there is hardly ever a single solution - thanks everybody - this is a great forum - I have really learned a lot since starting to look at it - and even more when I ask questions - thanks again !!!!!!!!!!!
AnswerID: 52650

Reply By: Member - Andrew K (WA) - Wednesday, Mar 31, 2004 at 15:06

Wednesday, Mar 31, 2004 at 15:06
Bob,
The Jury is still out on Coopers having fixed the chipping issue with the new STC tyre. They're only just been released and If you decide to go with them you'll be the guinea pig that we will all be asking 6-12 months down the track 'how are they'

Regards
Andrew
AnswerID: 52658

Follow Up By: Joe - Wednesday, Mar 31, 2004 at 15:20

Wednesday, Mar 31, 2004 at 15:20
Hi Bob,
A friend of a friend is running them at moment, the feed back is the chipping issue seems fixed, but they are not now wearing well from mileage point of view, so they may have fixed the chipping by making them softer?
Regards
Joe
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Follow Up By: Bob et Joëlle - Wednesday, Mar 31, 2004 at 15:53

Wednesday, Mar 31, 2004 at 15:53
I don't think I have enough experience in this area to be a very good guinea pig so it looks like the BFG's for us - thanks fellas
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Follow Up By: Member - Rohan K - Wednesday, Mar 31, 2004 at 16:30

Wednesday, Mar 31, 2004 at 16:30
Bob, get the 75 profile BFG - 275/75/16.
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Follow Up By: Bob et Joëlle - Wednesday, Mar 31, 2004 at 17:00

Wednesday, Mar 31, 2004 at 17:00
Rohan,
Thanks - that car bibles site is another good one - unfortunately BFG does not appear to make a 275/75/16 and according to my calculations (which I can now sort of do) it would be just above the legal limit - I am starting to feel really conservative about this issue as Baz suggested and will probably just put the same size back on - maybe I will get more adventurous with a bit more experience. We have another couple of months before we have to make a final decision so I will keep an eye on the posts - thanks for the help - I appreciate it.
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Follow Up By: Member - Rohan K - Wednesday, Mar 31, 2004 at 19:56

Wednesday, Mar 31, 2004 at 19:56
Bob, a 275/75/16 is only 1 mm larger than allowed and you'd be bound to find one that is less than your 818 mm limit.

Any 265/75/16 will be well within the allowable limits.

I'd still be inclined to go with a 265/75/16, in any of the brands/models mentioned above. One of the reason the Cooper ST is so popular (and the reason I chose them) is that they fit somewhere between an AT and an MT.

You can read a lot more about these and other tyres over on the OL forum too.
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Reply By: WarrenM - Wednesday, Mar 31, 2004 at 17:17

Wednesday, Mar 31, 2004 at 17:17
Hi I agree with Rohan regarding wider footprints. I had a Rangie that we used in North of WA and fitted wider tyres. We put up with having to use low range for about 3 months and then went back to standard size and back to high range.
Our current Rangie has 235.75/15 BFG T/A Long Trails on Cheviot alloys but we will be going to 2i5 or similar on standard rims.
Warren
AnswerID: 52673

Reply By: Member - Bill (WA) - Wednesday, Mar 31, 2004 at 18:44

Wednesday, Mar 31, 2004 at 18:44
I have a 100 ser V8 2003 and have Cooper ST 305/70R16

Love them.. Im reading about 6% less on my speedo OD 833mm

authorities dont seem to have a problem here in WA with this size

AnswerID: 52691

Reply By: dogart - Wednesday, Mar 31, 2004 at 19:09

Wednesday, Mar 31, 2004 at 19:09
Bob,

I've just put the new Bridgestone A/T's the 694's (not the 693'S)
on the Jackaroo size 265/70R16.
Fantastic. Did Kalbarri for 10 days, soft sand, mud and rock, excellent.
Cost $228 each fitted.

look at www.tirerack.com for some good reviews on tyres

my 2c worth anyway!

cheers
wolf
AnswerID: 52695

Reply By: Truckster (Vic) - Wednesday, Mar 31, 2004 at 20:40

Wednesday, Mar 31, 2004 at 20:40
Think more about what you can get when your in a remote area if you need a replacement... IF you blow 2 tires, and they are destroyed, then you need to be able to get tires without having to wait a week for them to come in....
AnswerID: 52712

Reply By: rolande- Wednesday, Mar 31, 2004 at 21:09

Wednesday, Mar 31, 2004 at 21:09
The most popular sizes will usually be cheaper as well, I was quoted $40 per tyre less for 265/70/16 than for 275/70/16, wider tyre, about the same height (1.8% difference).
Rolande
AnswerID: 52721

Reply By: Member - JohnR (Vic) - Wednesday, Mar 31, 2004 at 21:54

Wednesday, Mar 31, 2004 at 21:54
Folks,

Everyone is talking about tyre size limits, sorry I have a number of questions.

Are they limited in each state and what are they in each state where there is a known limit?
Is it an arbitary limit and how long has the limit applied for?
What basis is the limit applied on?
What are the legal and financial penalties applying?
At what stage of wear are the tyres measured to be non compliant?

I would have thought there were other things that would have been more offensive like some lightng possibilities and the lift that some use.
Cheers,
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John

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AnswerID: 52731

Follow Up By: Member - StevenL - Thursday, Apr 01, 2004 at 00:42

Thursday, Apr 01, 2004 at 00:42
John,

My research indicates that most states (certainly my state - SA) have referenced their motor vehicle standards Acts to adopt the National Australian Design Rules. These indicate that the outer diameter of any replacement wheel/tyre combo must not exceed the outer diameter of the largest listed wheel/tyre combo on the wheel/tyre placard affixed to the vehicle, by 15mm. I have heard that it used to be 3% but that now it is just a flat 15mm.

The example is my Prado where it is difficult because of the limited availability of 17" tyres for off-road use. The tyre placard says 265/65R17. Mathematically the outer diameter (OD) of this size tyre is ((256mm x 0.65) x2)+(17" x 25.4) = 776.3mm. The recommeded Cooper replacement is A/T's in 265/70R17. Using the maths the OD for these is 802.8mm but Coopers brochure lists them as actually being 31.4" (797.6mm). This is still an increase of 21.3mm which would be technically illegal.

In the face of this I asked my tyre dealer what the story was and he said he would have to check as he was not sure but he had fitted quite a few of these and had no problems. Maybe he actually knew but did not want to lose the potential sale????

My Toyota dealer also showed me another Prado ready to be delivered to a customer where the dealer had done the fitting of the Cooper A/Ts as a pre delivery option. Again I asked "is this legal" and the response was "as far as we know, yes".

Go figure!

As to your last question, tyres are considered to be at the end of their working life at a tread depth of 1.6mm.

Steven
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Follow Up By: Member - JohnR (Vic) - Thursday, Apr 01, 2004 at 05:21

Thursday, Apr 01, 2004 at 05:21
Steven, thanks for your comprehensive reply. The 15mm is often quoted but as to the height or axle height or diameter there is usually a missunderstanding I think.

The tread depth is always of course for water evacuation and in some circumstances like in some muds and clays the Coopers would be too shallow at that tread depth of 1.6mm one would imagine.
Cheers,
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John

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Reply By: Member Colin - NSW Bungendore - Wednesday, Mar 31, 2004 at 22:56

Wednesday, Mar 31, 2004 at 22:56
As far as I am aware, the regulations regarding tyres sizes, suspension lifting, lights etc. are, or will be Aust wide. Of course the rego systems vary from state to state - I dont think WA has any checks, NSW is annual.
The other issue is insurance - if you have a prang we know what the Ins Co will do - if the car isn't standard - or the modifications haven't been checked, you will undoubtably 'do your dough'.

So the moral here is - be careful !
AnswerID: 52735

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