Suzuki Grand Vitara

[TAKTAK]

Hey guys,

my sister bought a Grand Vitara 8 months ago from one of the biggest used car places around here (Eddie Wrights)

When she bought the car she was handed an MOT passed paperwork, with no advisories.

It's just been through it's first MOT (under her ownership) and they have brought up a few interesting points (advisory), one of which being that the front and rear tyre sizes differ.

The fronts being 235/60 16's and the rears being 235/70 16's.

As well as a few other faults such as lamp operation (affecting adjacent lamps), as well as breakpads pitted.

Sure, wear and tear is accepted and expected, but different size tyres?

Where do we stand?

As the tyre issue was obviously inherent at time of sale...

Cheers in advance

[Russ]

Tyres can be different sizes aslong as they are the same size on the same axel, at least thats what i thought.

[GoNz0]

whjat russ says, plenty of cars have 2 sizes, mine for example comes as stock with 245x40x17 rear and 225x45x17 fronts so the MOT place is full of s*** and should be avoided in the future.

i would also ask how they know if the brake pads are pitted as they would need removing to see this and i don't know of any mot place that would do that as its not required.

[TAKTAK]

Cheers guys

It's just an over-zealous MOT test station then

We presumed that it was because it was a 4x4 that they had given an advisory for the tyres

[Guy]

Yep, both of my cars run different sizes front + rear.

The BM is 235/45/17 Front + 255/40/17 Rear, likewise the Nissan is 225/40/18 + 255/35/18 at the rear.

As long as each axle contains the same size then theres no problem at all.

Following on from Gonzo, MOT testers are NOT allowed to touch, or remove anything that isnt on the test. Iirc nothing gets removed from the car on the test anyway. (bar checking the spare in the boot *If one is present*).

[kalniel]

Yep, both of my cars run different sizes front + rear.

The BM is 235/45/17 Front + 255/40/17 Rear, likewise the Nissan is 225/40/18 + 255/35/18 at the rear.

As long as each axle contains the same size then theres no problem at all.

Those are 2WD cars no? If you're sending the same gearing to both axles on a 4WD and the wheel radius is different (as in the OP's case) then you're going to cause the central diff to be working overtime, and totally mash up any diff locking (don't know if the vitara does that though).

[Flibb]

Those are 2WD cars no? If you're sending the same gearing to both axles on a 4WD and the wheel radius is different (as in the OP's case) then you're going to cause the central diff to be working overtime, and totally mash up any diff locking (don't know if the vitara does that though).

Most 4x4s dont lock the centre diff unless you tell it to, either put it in diff lock mode or engage 4 wheel drive. In normal drive if you spin one wheel out you dont get any purchase on the other axle

[Guy]

Those are 2WD cars no? If you're sending the same gearing to both axles on a 4WD and the wheel radius is different (as in the OP's case) then you're going to cause the central diff to be working overtime, and totally mash up any diff locking (don't know if the vitara does that though).

They are

I wouldnt have thought a vitara has the ability to lock any of the diffs.

I had forgotten about that though. Although I would say its more of a rule for actual off-roaders. As a fair few people I know run different fitments front + rear, on there Skylines, GT-4's etc.

[kalniel]

They are

I wouldnt have thought a vitara has the ability to lock any of the diffs.

I had forgotten about that though. Although I would say its more of a rule for actual off-roaders. As a fair few people I know run different fitments front + rear, on there Skylines, GT-4's etc.

Apparently it has two different modes of locking the central diff. Either of which is going to spell nasty mechanical trouble if you do them with these tyres fitted. So whether or not it's an actual MOT test item, I think the garage has a really good point in flagging these and I would get them changed ASAP (and ask for a refund or at least a contribution from the seller).

But being sold a car with an existing MOT doesn't mean that the car is still in the same condition as when the MOT was tested.

[Guy]

Apparently it has two different modes of locking the central diff.

Well you learn something new everyday!

[Tumble]

a Vitara is an exceptionally good off-road vehicle actually.. it'll have 3 gearbox setups - 2H (normal driving, rwd), 4H, where the centre diff locks up, the front axle becomes live and the auto locking hubs (if you got em) engage and the front wheels are driven as well & 4L, for the really tricky stuff. If you use the car in 2H all the time, then it should be fine, but if you do use the 4H/L modes, then the different tyre sizes are going to be a big factor in increased wear rates on the transmission AND the tyres.

[Konan555]

4x4 minefield! Anyone tried to drive a Calibra with tyres that are 0.000003% out?

If you're running in 2WD, you're fine. If you're running a locked 4x4 on the road, it doesn't matter what tyre sizes you have, you'll break things when (or if ) you do anything but travel in a straight line. I don't actually know about the Vitara, but from the operation Tumble describes, it may not have a center diff at all.

If you have a permanent 4x4 system/mode, rule of thumb is you want to avoid mismatched tyre sizes. Only time it may not be so crucial is on an off roader with a permanently open diff.

My pajero, for example...

2H: Regular RWD car. Not going to be stressed by different tyre sizes front/rear

4H: 4x4 with open center diff. Center diff allows for different speeds so should run on with mismatched tyres front/rear

4HLc: 4x4 with locked center. Should only be engaged where the terrain allows the wheels to slip - since the wheels can slip anyway, the tyre size isn't paramount

4LLc: Same as above

And the Sierra....

Permant 4x4 with viscous coupling: Front wheels are driven via a viscous coupling, allowing the front/rear axels to turn at different speeds with increasing resistance as the difference in speeds goes up. It's able to cope with a slight difference in tyre size but, at continuous high speed, will be working the viscous slightly harder than it would if they where matched, leading to a premature faliure. The same would apply for a permanent 4x4 with center LSD.

And then there's electronic cluth rear... torsen...etc etc

If you want to work out if you can run odd tyre sizes, you really have to go back to the mechanics of the individual system.

[GoNz0]

i used to love ragging my mates sierra 4x4 round bends !

[Konan555]

i used to love ragging my mates sierra 4x4 round bends !

I just can't help but plant my foot a moment or two before it's really sensible. I find a lot of people are surprised at what a 4x4 does once they're in one

[Tumble]

I don't actually know about the Vitara, but from the operation Tumble describes, it may not have a center diff at all.

If you have a permanent 4x4 system/mode, rule of thumb is you want to avoid mismatched tyre sizes. Only time it may not be so crucial is on an off roader with a permanently open diff.

My pajero, for example...

2H: Regular RWD car. Not going to be stressed by different tyre sizes front/rear

4H: 4x4 with open center diff. Center diff allows for different speeds so should run on with mismatched tyres front/rear

4HLc: 4x4 with locked center. Should only be engaged where the terrain allows the wheels to slip - since the wheels can slip anyway, the tyre size isn't paramount

4LLc: Same as above

Most Japanese 4x4s are pretty similar in 'box setups - your Pajero is going to be a lot more sophisticated/modern than than a Vitara - I'm going on what I've seen in the cars that the 4x4 club lads run - my little '78 Daihatsu had the system I described (pretty sure all the small Jap cars had it until quite recently). When in 4H/L mode, the vehicle behaved like my Landy with the centre diff locked up - guess the theory was that you wouldn't need to run the 4x4 fully unless you really needed to, so there was no need for an open centre system when the front axle was driven....

[Konan555]

Yup, sounds about right with what I was thinking. In these cases, it's just a straight gear drive to the front without a planetary in sight. Very simple, very robust and not for tarmac use... matching tyres or not.

Nobody's ever called my Pajero sophisticated before