Hello all,

It's advisable to get tyres changed in pairs isn't it, i.e. on the same axle?

I seem to recall it's also advisable to keep the same type of tyre on each wheel (i.e. all 4 wheels)?

Regards,

Richard.

Hello all,

It's advisable to get tyres changed in pairs isn't it, i.e. on the same axle?

Yes ideally, although if i was replacing a punctured tyre that was only say half worn, i would only do the one.

I seem to recall it's also advisable to keep the same type of tyre on each wheel (i.e. all 4 wheels)?

Regards,

Richard.

Yes again, if you have different brands or even tread patterns / different rubber compounds then the performance of each tyre will be different, so one will grip better than the other, this will potentially make the car quite nervous in the handling department.

There is nothing wrong (legally) in having 4 different tyres on a car - providing they are the same size and correct speed rating, but it's something i wouldn't do.

You can always tell a used car that has been used just to get from A-B, rather than maintained when needed as this is a big give away IMO.

I would agree with the above, except that I notice that the OP has a 4x4, in which case it is highly advisable to replace tyres in car sets, unless you've had a puncture.

I would agree with the above, except that I notice that the OP has a 4x4, in which case it is highly advisable to replace tyres in car sets, unless you've had a puncture.

When you say "car sets", you mean all tyres at once? What's the reason?

I'll certainly try to stick to one tyre type, my experiences of the standard tyres yesterday were quite favourable actually. Although they don't seem to be rated for Winter use in any way, I guess Skoda had their reasons for choosing them!

When you say "car sets", you mean all tyres at once? What's the reason?

So that all the tyres have the same rolling circumference, to avoid undue strain on the haldex clutch.

If I had a 4x4 I'd swap the tyres front-rear when the fronts were half worn, then replace all 4.

So that all the tyres have the same rolling circumference, to avoid undue strain on the haldex clutch.

If I had a 4x4 I'd swap the tyres front-rear when the fronts were half worn, then replace all 4.

That is sound advice and I may follow that scheme...

That said though, I think the wear (I think when you say strain, you mean wear? The clutch is designed to take that level of strain, see later) on the Haldex clutch from such conditions (i.e. excessive slip/engagement) is very minor, that's what a Haldex "engineer" told me anyway. He said that even after a simulated lifetime of use, the clutch plates show almost no wear at all. In everyday use, there is almost always some degree of slip due to toe-in.

In fact, he said that in design terms, the hardest issue they have to overcome is not wear over a lifetime of use, but the torque spikes when the clutch is suddenly engaged with full torque.

I've seen the "even out tyre wear" advice from a number of sources in relation to 4wd systems that don't have central differentials. The issue isn't so much the clutch in a p/t system as torque windup breaking driveshafts.

I was always under the impression the 4wd cars need all 4 doing at same time to do with rolling resistances however 4wd systems have changed a lot and i would imagine something with the Haldex style 4wd system wouldn't notice too much. whereas old calibra 4wd systems etc it was a major issue.

i swap my fronts and rears every 5k anyway. and i drive a fwd car.

I've seen the "even out tyre wear" advice from a number of sources in relation to 4wd systems that don't have central differentials. The issue isn't so much the clutch in a p/t system as torque windup breaking driveshafts.

Driveshafts, that's a different matter I guess!

The Haldex system does have a torque transfer limiting feature, also they reckon that using different sized (e.g. worn) tyres isn't an issue with their system.

I suspect (having thought a little about it) that the amount of slip from having worn tyres at front and new tyres at rear (for example) might not be enough to activate the clutch?

I was always under the impression the 4wd cars need all 4 doing at same time to do with rolling resistances however 4wd systems have changed a lot and i would imagine something with the Haldex style 4wd system wouldn't notice too much. whereas old calibra 4wd systems etc it was a major issue.

i swap my fronts and rears every 5k anyway. and i drive a fwd car.

Yup, as I said earlier, even though I question whether different wear tyres really matters with Haldex, I still think it's a good idea. I think this used to be recommended back in my MX-5 days...

Hmm. A shoal of red herrings here.

First, rolling circumference is not an issue. There is no car transmission system in existence that can't cope with the small differences in rolling circumference that occur because of slightly different tyre pressures or different levels of wear.

Quite significant differences in rolling circumference between front and rear occur normally as the car is loaded and unloaded. These changes do not affect the transmission.

The size specified on the sidewall of a new tyre is the size of the tyre — the brand is irrelevant. A Dunlop 185/65x14 is the same size as a Goodyear 185/65x14.

The most important thing to remember about replacement of tyres is that, where possible, they should be in matched pairs at each end. The rears should match each other; the fronts should match each other.

If the front pair aren't the same as the rear pair, the effect will be to change the handling balance of the car. It won't be 'dangerous', but it will be different from what you would experience with four identical tyres.

For example, if the rears grip better than the fronts, you will get more understeer than with a 'four square' arrangement. If the fronts grip better than the rears, you will find it easier to induce oversteer.

If you've got an unused full-size spare when you come to replace a pair of tyres, aim to buy the same type as the spare. Deploy the spare plus one new one, and stick the other new one in the boot. A spare that sits in the boot unused for years will end up unusable, because rubber degrades slowly over time.

Wind-up of any part of the transmission does not happen on road vehicles, because they are built either with diffs or devices that perform the same role — viscouses or clutch-packs. If they were not, the transmisions on our cars would not last more than a few hundred miles.

And finally: spacesavers.

Don't use them. The idea that they are safe at up to 80km/h is horse****. If you are forced by circumstances to deploy a spacesaver, crawl to the nearest service area, and — even if you have ABS — leave generous stopping distances. If you do not have ABS, the effect of braking will be exactly as you expect: the car will be destabilised, and it will swerve sharply, 'steered' by either the front wheels if the bike tyre is at the front, or by the rears if it's at the back.

A long time ago I carried out a careful (!) experiment with a Tipo Tds on a hot, dry road. The Fiat had a spacesaver fitted to the nearside front. I ran the car up to 30 and gave the brakes a moderate stomp — not emergency braking, just a sharp check to the car's speed. What happened was exactly what you would expect: the car turned right. With a fat Pirelli on one side and a bike tyre on the other, it would be foolish to expect anything else.

Fitting a spacesaver to a car with ABS has the result of making the car's stability totally dependent on the ABS.

Interesting advice on the wind-up and tyres, thanks!

As for space savers, I've used one in the past, I think they are ok as long as you understand they are just for emergencies and are only to get you to the nearest garage (slowly)!

Quite significant differences in rolling circumference between front and rear occur normally as the car is loaded and unloaded. These changes do not affect the transmission.

No they don't; changes in rolling radius do, but the length of the tread does not magically shrink when you put 4 bags of cement in the boot and 2 big mates on the back seat!

The size specified on the sidewall of a new tyre is the size of the tyre — the brand is irrelevant. A Dunlop 185/65x14 is the same size as a Goodyear 185/65x14.

Make that the "nominal size" and I'll agree. It's commonly accepted that different makes have different actual sizes, and weigh different amounts (sometimes quite significantly) for a nominal size.

Wind-up of any part of the transmission does not happen on road vehicles, because they are built either with diffs or devices that perform the same role — viscouses or clutch-packs. If they were not, the transmisions on our cars would not last more than a few hundred miles.

Well I got the stuff about torque wind up from people who're qualified "automotive engineers" and/or have years of experience of AWD on anything from Subaru Justys to Alvis 6x6s.