cmyers_uk
Member Since: 10 Apr 2005
Location: Near Bristol, UK
Posts: 433
 
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Interesting comments thanks, I will replace all four as I want to change brands to michelin.
I know Audi and Volvo insist upon it.
My thoughts were if you kept the same circumference on each side of each axle it should be ok.
My next question is does the circumference change with psi, if so isnt 42psi in rear and 32 in front in effect the same as having 5mm on front 3mm on rear?
Cheers
Chris
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 3rd Jun 2008 4:01 pm |
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cmyers_uk
Member Since: 10 Apr 2005
Location: Near Bristol, UK
Posts: 433
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Appreciate that they have a vested interest but this is straight from michelin. Not sure if they mean identical circumference or not,
Michelin strongly recommends that tyres on 4x4 vehicles are used in identical sets of 4 (same size, make, pattern, load index/speed symbol). The vehicle manufacturers' recommendations should also be followed.
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| 3rd Jun 2008 4:15 pm |
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Davro
Member Since: 30 Jun 2007
Location: London
Posts: 352
 
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CostCo insist that if you are just buying 2 new tyres for a front-wheel drive car, the new ones must go on the back, maybe they just couldn't decide a policy for 4wd , so opted for the easy option !
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| 3rd Jun 2008 4:15 pm |
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scoobystiv8
Member Since: 01 Nov 2007
Location: Barnard Castle
Posts: 205
 
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Interesting read.
When changing tyres on a 4x4 vehicle there are a number of important things to consider. Two of the most important (and costly if ignored) are matching tread depths between new and used tyres if not replacing a full set and maintaining the correct rolling circumference if changing tyre sizes.
Matched tread depths are important as too large a difference can, on certain vehicles result in "wind-up" of the 4WD system differential causing serious damage. This will be dependent to some extent on the type of differential and 4wd system used on a particular vehicle.
For instance consider the following:
A vehicle fitted with 265/70R16 (Nissan Patrol size)
A new tyre will, according to the industry standard dimensions (ETRTO) have an overall diameter (O/D) of 792mm.
Average tread depth when new will be around 10mm.
A tyre with 5mm remaining tread depth will have an overall diameter of 782mm (original O/D - [2x5mm]).
To obtain the theoretical rolling circumference of the tyre you multiply the O/D by 3.05.
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Calculation:
New tyre rolling circumference
792 (original O/D) x 3.05 = 2416mm
Tyre with 5mm remaining tread depth
782 (O/D worn tyre) x 3.05 = 2385mm
Difference of 31mm
This means that the new tyre will have 31mm further to travel for every revolution of the wheel.
A tyre of this size will rotate approximately 413 times per km, therefore for every km driven the new tyre will travel an extra 12830mm or approx 13 metres!!!!
Tyre manufacturers and retailers have differing views about the maximum allowable difference in tread depths between new and worn tyres fitted to a vehicle but in general most recommend a difference of no more than 3 - 4 mm. All manufacturers will recommend fitting at least matched axle sets. D3 V8 SE AUTO
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| 3rd Jun 2008 5:11 pm |
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Gareth
Site Moderator
Member Since: 07 Dec 2004
Location: Bramhall
Posts: 26774
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I think the change all four tyres rule only applies to cars which have a viscous coupling instead of a center diff.
Older Discos had a mechanical lockable differential gear, which would tolerate a good deal of difference between front and rear axle speeds. Of course it could wind up if you locked the diff on tarmac, but that was never recommended anyway.
I am pretty sure the D3 has a mechanical centre diff, which only locks when required. So on that basis I think its would be fine to change individual tyres as required.
A Viscous Coupling will try to resist difference in speed between axles no matter what surface its driven on, and in so doing would either rapidly wear itself out or overheat, or wear the tyres prematurely.
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| 3rd Jun 2008 5:58 pm |
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Pelyma
Member Since: 06 Jan 2005
Location: Patching, Sussex
Posts: 15496
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I had new tyres on the front and bald on the back, never noticed any issues with the car and it certainly didn't go into safe mode. Like Gareth says I believe it makes a difference on what type of 4x4 system you have. Follow what the handbook says, the XC90 says replace all 4 the LR one does not. Who knows more about your car, LR or Costco? I think it would have more credibility if a specialist such as our sponsor says you should replace all 4, but I'd still want to know why it didn't say so in the handbook. DS3 TDV6 HSE - Silver with Alpaca (old one) Gone
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| 3rd Jun 2008 6:04 pm |
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countrywide
Member Since: 16 Sep 2007
Location: UK
Posts: 6019
 
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This doesn't make sense, if your turning left for instance, the passenger side wheel will turn less than the drivers side and this will be the same on the rear, so how does this affect the centre diff. If your doing tight turns, the rear wheels turn less than the front wheels which have a wider arc to take.
It makes no sense that a few mm difference is that critical or you would suffer transmission wind up all the time. Also if the road is uneven the distance travelled will change to far more of an extent than the tyre wear.
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| 3rd Jun 2008 6:14 pm |
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dukes
Member Since: 15 Oct 2007
Location: suburbia
Posts: 102
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I totally agree...it makes no sense, sounds like an easy way of scaring you into a set of 4 (expensive) tyres.
My perelli's were shot on the inside after 17,000 mls, by the way, they do seem to tear them up a bit!
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| 3rd Jun 2008 6:46 pm |
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sideview
Member Since: 02 Dec 2006
Location: in the valley
Posts: 1663
 
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Sounds to me like Costco sees an opportunity to make more money  The LR manual recommends ideally replace sets of 4, but if necessary replace as axle sets and put the new ones on the back.
Common sense 4 tires of the same wear offer the best drive, but if the other two aren't worn it wouldn't make a difference in how they handle. Drive train issues sounds far reaching to me. I'm not so good at giving advice...may I offer you a sarcastic comment instead?
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| 3rd Jun 2008 6:53 pm |
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simon
Member Since: 11 Jan 2005
Location: Shropshire
Posts: 18296
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Gareth wrote:I think the change all four tyres rule only applies to cars which have a viscous coupling instead of a center diff.
Must be why Audi insist on all four.
Mind you, on D3 v2 I've had two new ones on the passenger side over the last few months... so I guess thats OK as far as things go.
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| 3rd Jun 2008 7:17 pm |
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discocuzzy
Member Since: 02 Feb 2008
Location: surrey
Posts: 2752
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When i had a couple of older Subaru Turbos they always recomended changing all tyres at the same time as it would affect wear on the tranfer box.
Had great pleasure in getting through a set of P Zeros in under 10k  "you cannot teach stupid people to do clever things"
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| 3rd Jun 2008 7:33 pm |
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Davro
Member Since: 30 Jun 2007
Location: London
Posts: 352
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Looking at swapping my front/back over to gain a little more miles and also make sure I need 4 new ones together !, should I get the tracking done or just make sure they are balalnced ?. Is this someting the dealer should offer to do when in for a service ?
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| 3rd Jun 2008 7:51 pm |
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Neil Pettersen
Member Since: 23 Nov 2007
Location: Cutting the grass
Posts: 1254
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simon wrote:.. it was a Quattro and apparently according to Audi, could cause premature wear to the drive train ....
Now, that's got to be a question for JMC 
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| 3rd Jun 2008 8:52 pm |
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BLFarrar
Member Since: 02 Aug 2006
Location: Deepest, Dankest, Darkest, Dingiest......Le Halifax, West Yorkshire...with strong links to Ireland
Posts: 6222
 
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| ......I can see the point |
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...if the "system" goes into some contingency mode when it detects a mismatch in rolling wheel rotation & presumably it does this from the brake discs sensors...???
..what puzzles me is how this is calculated as it assumes the vehicle is traveling on a perfectly flat road & the vehicle going dead straight...
As the whole point of having a differential is to allow the wheels to rotate at different rates (as they would going around a bend) - standard on any two wheel drive car.....FWD or RWD
On a LR 4x4 the diffs on each axle & the centre diff allow all the wheels to rotate at differing rates.......i.e. the front offside wheel would rotate at a different to that on rear offside......also this has take into account road "camber" (do they still camber roads ?)
If the "system"recognises different wheel diameters & circumferences (as suggested if worn tyres & unworn tyres mixed on same axle / vehicle) how does it differentiate "normal" mismatch accommodated by diffs - caused by differing track each wheel takes ? & accommodate vehicle steering.
I realise by raising this as a query I will no doubt get machine gunned from all & sundry.......I'd just like an explanation....it has been a bit quiet here recently BREXIT - done properly.
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| 3rd Jun 2008 9:25 pm |
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DG
Site Moderator
Member Since: 12 Dec 2005
Location: The Gaff
Posts: 50978
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Rubber is rubber FFS  21 year LR veteran > D2 GS 2003 > D3 S 2006 > D3 HSE 2009 > D4 HSE 2013 > D4 HSE 2015 > D5 HSE 2018 > DS HSE R-Dynamic P300e 2021
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| 3rd Jun 2008 9:27 pm |
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