Hi guys,

Looking for a bit of advice on tyres. Currently travelling South America and for one reason and another I've ended up with different tyres. Here's the question: can I mix a Coopers Discoverer S/T All-Terrain, M&S, Load Range D, on the same axle as a BFGoodrich All-Terrain, M&S, Load Range D. Obviously their tread patterns vary a bit, otherwise same spec. The tyres are new.

Any advice much appreciated.

Cheers,

James
cityofmythsriverofdreams.com

What vehicle are they on and are they all the same size?

Just to update this post, the tread pattern doesnt matter so much, the important factor is the physical tyre height if you are running in 4wd with a CDL engaged (or equivilant) then you will get even more transmission wind up on a firm surface with different height tyres on different axles.

If you are running rear wheel drive normally and 4wd occasionally on a loose surface it would be fine. Try and keep 2 of the same brand (height) tyres on the same axle, this will reduce the amount of heat build up in the differentials. I normally put the tyres with the best tread/grip on the front axle.

Hope that makes sense!

__________________
Cheers
Grif

'11 KTM 450 EXC
'09 Suzuki DR650
'00 Discovery Series 2 V8
'95 Defender 90 300 Tdi Overlander
http://gipperstravels.blogspot.ca

Hi Gipper,

Thanks for your response. The vehicle is a Land Cruiser model 78, so normally run in two wheel drive. The tyre size is 285x75x16 for both the Coopers and the BF Goodrich. I was thinking of running the Coopers and a BFG on the front axle and the two other BFG's on the rear. I had a notion it would be better this way re the transmission wind-up but wasn't sure. It seems you agree this would be an ok solution.
Thanks for your advice.

Cheers,

James
cityofmythsriverofdreams.com

Trans wind up is not a factor with the vehicle you have (ie part time 4wd)
You would be better with the two same tyres on front axle , and run the dissimilar tyres on the rear axle . There will be less likelihood of any effects to the steering that way . Even with a full time 4wd wind up is only a factor when running with centre diff in lock , which should only be done on low traction surfaces anyway , eg mud or snow , or bush tracks which are loose surface to aid stability . HTSH

I used to think it was best to have the good tyres on the front, but have now seen convincing evidence that this is not the case. Here is one example, there are others:

Vicki Butler Henderson explains why new tyres should go on the rear - YouTube

For those that don't know Vicky Butler Henderson is a rally driver, so knows how to handle a car.

transmission windup should never be a problem in either a part time 4wd or Full time 4wd because you shouldn't be running with the 4wd engaged (in P/T) or diff locked (F/T) on a grippy surface!!

The main problem is that the different tread patterns and tyre characteristics (sidewall strength etc) can give unpredictable handling, so generally it is frowned on to mix tyres on the same axle, but if you take it steady yuou should be fine, needs must and all that.

The VBH thing is for most drivers of modern passenger cars , with little car sympathy or ability to deal with loosing the rear end . What she didnt show you is what happens with worn front tyres when you encounter sufficient water and speed to aquaplane on a bend , the front end goes and you end up going straight on into the scenery . Having new tyres on front raises this speed a lot higher so its less likely that you will be at a speed that this will occur . I would much rather lose the rear end first than the front .

I would say from a handling point of view it would work better with same tyres on front and the disimilar on rear what ever the state of wear . Dont mix cross ply and radial on same axle tho !!

In a constant 4wd vehicle with the centre diff unlocked there won’t be any transmission wind up if you have different circumference tyres front and rear. I don’t, however, think it’s a good plan to run it like that for any period of time.

The centre diff, with different circumference tyres front and rear (even a small amount) will be constantly “working”. In normal use I expect that isn’t the case. I’m thinking this could lead to higher running temperatures, increased wear, oil degradation?

I’m pondering this myself at the moment as I’ve just fitted 2 new front tyres (due to sidewall damage) and I’m thinking I should change the rears even though they have maybe 5k miles left in them.

This is just my theory / thinking.

You neednt worry overmuch , its only a factor for vehicles with viscous centre diffs , ordinary open centre diffs that lock selectively will handle it quite easily . Its just one set of gears working slightly more than another set In a situation where you were heavily loaded and constantly climbing a steep hill then it might cause some excess wear on the side gears but slight. HTSH

Thanks for your continued input. I changed the tyres over the weekend, putting the mixed ones on the front - I note the comments re putting mixed tyres on the back being the preferred option. We drive very slowly and they don't get much rain up in northern Chile, Bolivia and Peru now it is their winter - wet/slippery roads might cause problems I guess, but we will be aware of this. Further north we will see. I will probably have changed them all around again by then.

Cheers,

James

Don't really agree, she clearly tries to catch the slide and fails. I'm glad your so confident of your abilities. Ask 100 drivers if they are an above average driver and at least 99 will say yes, by definition half of those are wrong. I guess you must be in the other half

In your scenario above, all that will happen is you'll go backwards into the scenery instead of forwards! The reality is in most situations you have a better chance of saving the slide if it is understeer rather than oversteer simply by backing off the throttle.

There are a few demonstrations like this out there,and, despite being skidpan trained as part of advanced driver training it was persuasive enough to convince me to change from my policy of always having the less grippy tyres on the rear, but then, in order to improve any skill you have to be open to suggestion and change.



transmission windup on most full time 4x4s only really becomes an issue when there is massive disparity between axle speeds, for example if the vehicle is on a towing dolly. Then the prop should be disconnected.

Some of the AWD SUV type vehicles with electronically controlled AWD can have problems, even with something as minor as fitting new tyres on one axle and having old tyres on the other (Kia being one I know of)

[QUOTE=moggy 1968;424653]Don't really agree, she clearly tries to catch the slide and fails. I'm glad your so confident of your abilities. Ask 100 drivers if they are an above average driver and at least 99 will say yes, by definition half of those are wrong. I guess you must be in the other half

I suppose i am , being ex police traffic

It was just my opinion , as much advice given is just someone elses opinion

Most of us know you shouldnt run in part time 4wd on anything other than a loose surface, likewise with a permanant 4wd (ie Defender) not to run with CDL engaged unless again you are on a loose surface, unfortunately lots of people still drive with these systems engaged (even on asphalt - believe me Ive seen it!) and wonder why the steering wheel rips out of their hands when they try and turn a corner - they just dont get it - front to rear axle wind up wind up is an issue if the 4wd system is used on the WRONG terrain, likewise different height tyres front to rear will not help. As to how much damage it causes, depends on the vehicle, I know a Defender CDL isnt that strong and running extra heat through a diff at high ambient air temperatures will make oil seals leak. There again Defenders leak like a sieve anyway

Where to put the best tyres ?

Trying to get a nose heavy 4wd to NOT understeer is pretty difficult, I agree with Tacr2mans statement about aquaplaning, but also know that if you only have 1 pair of winter tyres they always go on the rear axle so you dont get oversteer whilst driving on ice - each to their own with this scenario really, but for me with a heavy 4wd barge if im having to drive slippery pistes in South America at modest speeds (normally with a huge drop on one side) id have my best tyres up front, as IMO a grippy front end will get you out of more trouble than a loose rear end will get you into, if however I was driving a rear wheel drive car or something a bit more 'tail happy' at speed id do it the other way round...

Like Moggy says its down to which end to crash with.... go figure....

Start riding motorbikes, front end grippy, rear end slippy =

__________________
Cheers
Grif

'11 KTM 450 EXC
'09 Suzuki DR650
'00 Discovery Series 2 V8
'95 Defender 90 300 Tdi Overlander
http://gipperstravels.blogspot.ca

got to agree with you there griff, I have had to post no end of times on a forum for Hilux's explaining to people why they shouldn't use 4wd on wet tarmac, or, in some cases, even dry tarmac. Some of these people have actually owned there vehicles for a long time (years) and still don't understand the basics of how they work! Usually they post complaining of vibration and banging through the steering!

If say I had a pair of mud terrains and a pair of all terrains, as I have run before, I would have previously run them with the mudders on the back and ATs on the front. Now though, I would consider running the MTs on the front. This would give you the road traction on the rears, where overwhelming evidence is now that's where you need it, whilst off road best traction would be on the front, which I think fits with your scenario of scrabbling for grip on a high and dodgy dirt track on the side of a mountain. Also, it would enable you to still utilise the rut climbing ability of the MTs.

of course, that's just my opinion and not based on any research or investigation, as against post 5!

[QUOTE=tacr2man;424745]well, yes, that would explain a lot.