How critical are tyre diameters ?

Hi to all,

Could anyone out there give me the benefit of their experience with Freelander 1 tyres ?

I've got to change my 2 front tyres on the Freebie as both have developed flat spots on the tread and so 'thump' at speed and are driving me mad on long journeys. I just went to have them rebalanced and the tyre bay man said short of changing them I'm stuck with the problem.

The front's have 5mm tread and the rears 6mm - there's only 8mm on new ones !

All 4 are Pirelli Scorpion STRs originally fitted at the same time.

My question is, do I really need to change all 4 and chuck 2 perfectly good rear tyres or could I get away with fitting only 2 new Pirellis and putting them on the back and swapping the current rear ones to the front ? Will a 2mm tread difference cock up my IRD ?

Just for a bit of extra info, car has 65k on the clock, IRD sound with no fall out in the oil, VCU changed at 58k.

Thanks for any advice..................

if u do a quick search on here this subject has been covered extensively and a huge amount of info telling the dos and dont's


hope that helps u

If I had to change two tyres I'd always put the new ones on the back, it's important for the vcu to have the larger rolling radius on the back but be carful though as different make tyres of the 'same size' aren't necessarily the same size!!

As mentioned above, do a search as there's lots of info on here about

in a word
"VERY"

even same make but different names like Michelin latitudes and syncrones do not mix AT ALL

Hi All,

Thanks for the replies. I know tyres are critical and have read lots of the threads, but my question was really if I fitted two new Pirelli Scorpion STRs on the rear and put the older Pirelli STRs on the front, would a tread difference of 2mm be critical ?

In essence the ones I'm having to ditch have 1.5mm less tread than the rears at the moment and they were fitted at the same time. As front and rear tyres wear at different rates there will always be a small difference. I wouldn't dream of fitting a different make or even different model tyre of the same make and front and back axles. But if I fitted like for like ??

Cheers,

think it is 5mm max difference for the f1 vcu

newest on the rear

go drive it around for a bit then go feel the vcu temp. that'll tell you if it's too much

trax said:

think it is 5mm max difference for the f1 vcu

newest on the rear

go drive it around for a bit then go feel the vcu temp. that'll tell you if it's too much

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+1 on this.

IRD ratios were changed around 2001, so more tolerant now to tyre difference.

Goes against the grain not to put the new tyres on the main drive wheels...but best play safe.

Longbolt said:

+1 on this.

IRD ratios were changed around 2001, so more tolerant now to tyre difference.

Goes against the grain not to put the new tyres on the main drive wheels...but best play safe.

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you aren't meant to put new on the front as they need to be scrubbed in else you can go all over the shop when cornering.

i've stuck new on the front before though and never had an issue. it's like new brakes.. just take it easy until they are bed in.

Hi Trax,

Thanks for the reply. When you say 5mm is the max allowed do you mean 5mm difference in rolling diameter or circumference ?

Forgot to mention that my car is a 2005 model.

Cheers.........

perkins said:

Hi Trax,

Thanks for the reply. When you say 5mm is the max allowed do you mean 5mm difference in rolling diameter or circumference ?

Forgot to mention that my car is a 2005 model.

Cheers.........

Click to expand...

rolling.

but tbh, 2mm difference.. pfft. you'd get that with not watching your tyre pressures.

you just need to be careful that you use the same size, manufacturer and model of tyre as these vary wildly - even if they are marked as the same size.

as above it was more tolerant with later models, and you can always feel (or get an ir gun for £10) the vcu temp after a good run.

I don't think the newer IRDs are more tollerant of larger rear tyres. The older ones had a slight ratio difference so the rears were turning a tad slower - putting slightly larger tyres on the back then would mean this equalled out the difference. So with the older ratio and driving in a straight line, slightly larger tyres would be a benefit. However, when cornering, it would be advantageous to have the rear axel turning slower, so slightly larger on the rear is better on the later 1:1 ratio IRDs (as well as older ones).

I'd +1 that it would be OK to replace just 2 tyres and put the new ones on the back - so long as they are exactly the same. Make sure all the markings are identical on ols and new tyres. 1.5mm to 2mm of tread difference I would not think will harm the transmission.

I acknowledge you've got a replacement VCU, but worth using this as a time to do a 1 wheel up test just to make sure its still OK.

OK - so if I've got this right - if I put just two new ones on the back exactly the same as the slightly worn old ones on the front I can happily go round corners all day long. If I put a whole set of new ones on I can drive up and down the M6 until I meet myself coming back the other way but not come off for fear of the IRD going bang !!!

You know that old adage about too much advice .... I'm thinking I might just flip a coin.

Sorry to be sarky, but it seems if you look at a Freelander sideways something expensive falls off or breaks.

I might just get the wife to decide and then I can blame her - does that sound like a good plan ?

perkins said:

OK - so if I've got this right - if I put just two new ones on the back exactly the same as the slightly worn old ones on the front I can happily go round corners all day long. If I put a whole set of new ones on I can drive up and down the M6 until I meet myself coming back the other way but not come off for fear of the IRD going bang !!!

You know that old adage about too much advice .... I'm thinking I might just flip a coin.

Sorry to be sarky, but it seems if you look at a Freelander sideways something expensive falls off or breaks.

I might just get the wife to decide and then I can blame her - does that sound like a good plan ?

Click to expand...

Qualiity plan

perkins said:

OK - so if I've got this right - if I put just two new ones on the back exactly the same as the slightly worn old ones on the front I can happily go round corners all day long. If I put a whole set of new ones on I can drive up and down the M6 until I meet myself coming back the other way but not come off for fear of the IRD going bang !!!

You know that old adage about too much advice .... I'm thinking I might just flip a coin.

Sorry to be sarky, but it seems if you look at a Freelander sideways something expensive falls off or breaks.

I might just get the wife to decide and then I can blame her - does that sound like a good plan ?

Click to expand...

just stick 2 new uns on the back. blame the forum is it goes wrong if you want

Always gets me a bit. You're best off with larger tyres on the rear. Within a set of parameters cos it reduces gearing difference and wind up. But the recommendation is four new tyres which instantly gives more wind up.
Personally I'd make sure my Vcu is ok. If the diameter difference is only a few mms I'd put same make and model on the rear.

Hi Diesel Do,

I agree with your logic, but it does seem daft that you have to trick the car into behaving like a front wheel drive vehicle to preserve the drive train !

All the best,

Perkins

perkins said:

Hi Diesel Do,

I agree with your logic, but it does seem daft that you have to trick the car into behaving like a front wheel drive vehicle to preserve the drive train !

All the best,

Perkins

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New tyres should always go on the back, regardless of the vehicle. This is to ensure that the rear has better grip than the fronts in the wet. The Freelander's drive train just makes sure you do

Diesel Do said:

Always gets me a bit. You're best off with larger tyres on the rear. Within a set of parameters cos it reduces gearing difference and wind up. But the recommendation is four new tyres which instantly gives more wind up.
Personally I'd make sure my Vcu is ok. If the diameter difference is only a few mms I'd put same make and model on the rear.

Click to expand...

I'm with you on this one. I have never been OCD about this. I have always fittted new pairs to the back. I have always checked the VCU is o.k. when I have serviced the car. I have occasionally mixed brands (in pairs) when the old ones aren't available any more (Synchrome to Scorpion / Scorpion To Latitude cross) checking that the circumference difference wasn't excessive. I've just changed my first VCU in 11 years of Freelander ownership (2 cars). It had just done 105K which I don't think is bad.

Undulations in normal tarmac will make more difference in rotational speeds of the front and rear axels than 1.5 - 2mm of tread depth.