Shame they don’t run the test for different dia of tyres, which was the issue? How much difference does a 6-7mm increase in diameter of the new tyre Vs the old tyre make?
The Energy E-V is only available in two sizes - 185/65 R15 and 195/55 R16 - so that’s 622mm diameter for the 15" rim and 610mm for the 16" rim.
Thus 3mm tread difference (6mm on the diameter) makes a 1% smaller tyre
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Over distance that’s significant.
I think they were just comparing the power transfer characteristics of the two systems under poor traction conditions. The point for me is that the impact of different diameter tyres (even by a small amount) isn’t as irrelevant as I thought with Torsen diffs on 4X4.
Please explain some more John, I am not following your thought train. What I see in the video is how the torque split is set up differently and yes some different reactions to the setup comparing the two?
The discussion was, on having a wheel/tyre combination with a maximum difference of 6mm diameter on the same axle, therefore necessity to fit two new tyres each time and as the OP posted the tyres were not that old and therefore not that worn down. As most of us know fitting different sized wheels and tyres messes up the speedo reading more than anything else but that’s a whole inch larger.
Well, if there is that much difference (1%) 100 revolutions of the smaller tyre will be 99 of the larger (100 revolutions of a 610mm diameter tyre is 191.64m)
Would you expect that much difference between tyres fitted at the same time - no idea but 3mm seems a lot. I think the garage told me I had 2mm one side and 3mm the other on my front tyres at recent MOT test so 1nm (2mm on the diameter) seems very plausible.
That’s still one revolution every 300 or about 600m so any limited slip diff really is going to have to be able to cope with this without friction material pointing its toes skyward.
What I think the video is about John is how the VW (Haldex) and the Audi (Torsen) react differently to having two or three wheels with no grip. The point for me is they are different. So our rubbishing Our advice to Maxime might have been a bit premature. I found this to potted history excellent. ,
Limited slip differentials allow some slip, no problem. The main job that a differential allows is going around corners, a couple of mm difference in tread depth is irrelevant. Limited slip differentials were only really used when wheelspin was expected. Modern electronics do the same job and viscous couplings are a great way to avoid unnecessary stress.
John, I have a car which has summer and winter tyres. The summer tyres fit on 17 inch wheels, the winter tyres on 16 inch. The tyres have, in theory, the same diameter as the winter tyres used are of a different profile. I could have two 17 inch wheels on one axle and 16 inch on the other without any noticeable difference. The speedometer reads the same with either set of tyres, the diameter of the wheels themselves is irrelevant.
Discoveries had a diff lock. It was made very clear that the diff lock should only be used in slippery conditions and never on a rolling road.
A bit.
If Maxine has a 4x4, with a specific type of diff then the advice to change all 4 tyres at the end of their lifespan, even if one or two have a bit of tread left, is sensible.
Otherwise…?
A thought on the tyres rated for electric cars; most electric cars use tyres that have low rolling resistance to maximise the range. A manufacturer would be unlikely to get those tyres accepted for an ICE car.
That wasn’t the discussion, of course tyres should be changed when worn. I’m addressing this aspect of Maxim’s post “This is particularly relevant for modern Volkswagen Group cars (VW, Audi, Skoda, SEAT) with 4motion and Torsen all wheel drive transmission” which was not addressed in subsequent posts poo pooing the idea that there could be an issue. Which I agreed with at the time.
Yes, but if you have a 4WD system which splits power unevenly (as Audi like to do) one axle will be worn a bit before the other - in which case it might well be a bad idea to put new tyres on that axle but leave the nearly worn tyres on the other even if they are legal.
Also both Maxine and Al have been advised to put two new tyres on the same axle of a 2WD car when one tyre has suffered irreparable damage but the other is almost new which seems overkill - though admittedly the fact that the French regulations insist on the same make of tyre on one axle make it significantly harder to replace just one tyre out of two.
The logical reductio ad absurdum to this is that, should one tyre out of 4 on a 4x4 not be repairable after, say, 2000km you should replace all 4.
I’ll bet that’s a cost most 4x4 owners didn’t budget for when they bought their cars 
I’d always replace the two tyres on an axle, which has been expensive in the past, regardless of FWD, RWD or AWD. I’d never replace all four unless worn. So really the discussion is academic for me but it did make me explore Torsen vs Halda AWD. Now I think the Halda in my Tiguan is a bit Micky Mouse.
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What’s the issue?
most SUV and 4x4 owners dont budget for a lot of things when buying them, Image is the thing to have on the school run. I run 2, 4 wheel drive Volvos and have never had the problems mentioned here, both have the haldex system fitted. If one tyre should, and has in the past, become irreparable, then both tyres on that axle are changed depending on the mileage without any adverse effects.
Isn’t that what the garages say? If one tyre is irreparable, change both tyres on that axle.
What people have been discussing is the need to change both, when only one has a problem.
I don’t know what “depending on the mileage without adverse effects” means here, unless you meant to say only one tyre is changed.
I’m very glad this topic has been raised as I clipped a kerb yesterday, resulting in a small but irreparable cut in the tyre wall.
At least I knew (thanks to the forum) I would have to buy two new tyres today at the garage, and got a fair price for them as I’m a regular. Instead of a nasty surprise!
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No, if only one tyre is damaged and they have only covered a minimum mileage on that axle then i will only change same for same ie 1 tyre of the same make and model as the previous. If they have both covered considerable mileage then i change both on the same axle.
I understand, but that wasn’t exactly what you said, which is why I queried it. 
Aston Martin don’t provide a spare tyre. In the boot is an elegant mahogany box with a can of puncture juice. You inject this via the valve, rotate the wheel, the juice coats the interior and finds it way into the hole, encouraged by escaping air and on you go. But not at eyeball-print-on-retina speeds.
This stuff works, but only when there’s a puncture in the tread. I had some - minus the mahogany box - for my TVR. My problem was that a demented neighbour had drilled a hole in all 4 tyres, into the sidewall.