# Replacing tyres on quattro cars.... Urban myth or truth??



## antcole (Apr 4, 2009)

Had to replace one tyre this morning following a blowout yesterday...

The only places open were the usual thieves at kwikfit etc...

The first one i went to said that due to it being a quattro, ALL the tyres needed to be renewed or "the gearbox would explode..."

The tyres were new recently and i figured 500+ quid is a bit rich for one tyre replacement.

Is it bull5hit?

I always thought the haldex sorted out any differences... were only talking 2mm of tread wear from new...

I settled for replacing two tyres at National and had to go for Pirelli P Rosso at 185 each!

Theres now part worn Pirelli P Zeros on the front and Rossos on the rear...

Whats the truth in this issue?


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## TTQ2K2 (Jun 25, 2009)

Yes. It's Bull. Haldex doesn't give a rat's patoot if tires are different age or make. It does care if the rolling radius is different...but if that difference is in the 1-2% range it's ok. Exceed that and you could get haldex failure, but no explosion.

cheers.


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## Mark Davies (Apr 10, 2007)

Yes, it's rubbish. I had a suspension problem which resulted in excessive tyre wear on my rear tyres which meant I had to replace just those. Even though my back tyres were considerably more worn than the front the Haldex was fine before I replaced them and once I replaced them with new ones it again miraculously survived.

Kwik Fit are not on their own in this. There are several large tyre fitters with exactly the same policy. I suppose we have to understand that these companies are not necessarily employing the highest calibre of staff whose technical knowledge may not be the best. They perhaps consider it safest to have a simple, cover-all policy to ensure their staff don't make expensive errors. Loses them a lot of business though.


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## stevebeechTA (May 16, 2009)

Hi Mark

how the devil are you. how is your car doing mate,have not seen you on for a bit.

steve


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## John-H (Jul 13, 2005)

antcole said:


> ... " due to it being a quattro, ALL the tyres needed to be renewed or "the gearbox would explode..."


 :lol: That is so funny - see here page 34 or so http://www.kisolutionz.com/ttforum/haldex.pdf I'm sure it says 5% difference somewhere (copes with bald and new tyres on the same axle or front to back) or if might have been on their website which has all changed so my links don't work.


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## m4rky (Jul 20, 2008)

This used to be true in the late 70's - early 80's before the advent of the viscous coupling when some (Not all) 4 wheel drives were literally permanent 4 wheel drive and the gears were permanently meshed.

If any of the wheels were a slightly different diameter it would wind up the gearbox's and sometimes cause damage.

The easy way to cure this though (as it would take a long time to actually wind the gears up) was to jack the car up and release any gear wind up that had occurred

Today though this concept would be a complete nonsense as has been said before.


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## jaqcom (Apr 20, 2009)

m4mky is absolutely correct, .........diddly squat, always best to replace in pairs if possible but blowouts are never planned lol


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## John-H (Jul 13, 2005)

m4rky said:


> This used to be true in the late 70's - early 80's before the advent of the viscous coupling when some (Not all) 4 wheel drives were literally permanent 4 wheel drive and the gears were permanently meshed.
> 
> If any of the wheels were a slightly different diameter it would wind up the gearbox's and sometimes cause damage.
> 
> ...


I've heard that said of some transmissions. They must be ones without a centre differential where differences in rolling diameters between front and rear would cause a tortional loading relieved only by wheel slip. Too much difference would cause too much load and extra wear. Jacking a wheel up could cause it to spin due to the multiplacation of the axle diff relieving any stored torque. Thankfully the Haldex system is a slip coupling where this could not happen.


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## m4rky (Jul 20, 2008)

John-H said:


> tortional loading relieved only by wheel slip


That's the phrase I was trying to remember  Having said all of the above though it took a lot of constant road driving to actually make this happen.


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## antcole (Apr 4, 2009)

Thanks for the replies chaps.

I thought it a little absurd that only one new tyre needed would mean all the rest were scrapped too...
The frisbee space saver is not actually the same size either so it kind of throws that theory out the window.

Like Mark Davies said, if there was one wearing more than the rest, who would know?

Also, over inflation and underinflation would result in different rolling radius size too, so in the words of Albert Einstein - "... Its all a load of 8ollocks..."

Not too sure if he said that but im sure he did once.

Thanks again.


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## JulienG (Nov 8, 2006)

Also here it mentions it is OK: 
http://www.vaglinks.com/Docs/Misc/HaldexTraction.com_Haldex_AWD_Traction_System.pdf


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## RobLawlor (Apr 14, 2013)

Yeah its rubbish, i was rolling around with 1 new tyre on the front after a blow out, that was october, and still no faults yet


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## Spandex (Feb 20, 2009)

John-H said:


> I've heard that said of some transmissions. They must be ones without a centre differential where differences in rolling diameters between front and rear would cause a tortional loading relieved only by wheel slip. Too much difference would cause too much load and extra wear. Jacking a wheel up could cause it to spin due to the multiplacation of the axle diff relieving any stored torque. Thankfully the Haldex system is a slip coupling where this could not happen.


Not quite. The TT has the Haldex unit *instead of* a centre diff, which is why it's not an issue (part of the Haldex's job is to act a bit like a diff, but it isn't one).

Cars with proper mechanical centre diffs are actually significantly less tolerant of differences in tyre diameter than cars with clutch-type couplings (like the TT) would be. This is because the planetary gears in a proper centre diff aren't designed to be spinning at high speeds on a constant basis (in normal use, with identical tyres, the ring gear/carrier will be the only thing rotating). They're designed to prevent wind-up at low speeds for short periods of time, like when you're manoeuvring.

So, proper 4x4s can have problems with different tyre diameters, but it will wear out the centre diff, not the gearbox and it's related to excessive wear on the diff components, not to stress from transmission wind-up.


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## Pugwash69 (Jun 12, 2012)

Nearly three years since the OP, I suspect all bets are off now. :?


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## Spandex (Feb 20, 2009)

Doh...


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## Skeee (Jun 9, 2009)




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## Spandex (Feb 20, 2009)

Well come on then Antcole. We're here now, so you might as well tell us. Did your gearbox explode??

Actually, he drives a DSG so there's a good chance it exploded on its own anyway. :wink:


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## Skeee (Jun 9, 2009)

Did Antcole go to the same place as Kal:- viewtopic.php?f=2&t=327957


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## John-H (Jul 13, 2005)

Spandex said:


> John-H said:
> 
> 
> > I've heard that said of some transmissions. They must be ones without a centre differential where differences in rolling diameters between front and rear would cause a tortional loading relieved only by wheel slip. Too much difference would cause too much load and extra wear. Jacking a wheel up could cause it to spin due to the multiplacation of the axle diff relieving any stored torque. Thankfully the Haldex system is a slip coupling where this could not happen.
> ...


I didn't say it was one  I don't know picking holes across the ages :lol: :wink:


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## RobLE (Mar 20, 2005)

I changed two tyres (same axel) last year - same brand, both directional and to say the 15 mile drive home was not "fun" is an understatement - never seen the traction control light come on before but it was on at virtually every corner - shocking!

Gararge kindly did me a great deal on two additional tyres so they all matched and it was all back to normal.

I was amazed at the difference it made - they said they'd only ever seen that happen once before - on a new Transit van!


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## darylbenfield (Jun 29, 2011)

antcole said:


> Had to replace one tyre this morning following a blowout yesterday...
> 
> The first one i went to said that due to it being a quattro, ALL the tyres needed to be renewed or "the gearbox would explode..."


 [smiley=bigcry.gif] [smiley=bigcry.gif] :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol:


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## Spandex (Feb 20, 2009)

John-H said:


> Spandex said:
> 
> 
> > John-H said:
> ...


There's no statute of limitations on hole picking...


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## John-H (Jul 13, 2005)

:lol: Just be careful who owns the hole - actually, can you own a hole or just that which surrounds it? I remember my uncle offering me a Polo mint and telling me to take the hole - cruel man!


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## forker (Jul 20, 2012)

dear all

key in this is to remember that when we drive on a road that isn't arrow-straight each wheel describes a different path; look at a wet road or the drive-away patch from a carwash on a dry day.

When we go round a bend the inside wheel doesn't go as far as the outside wheel and the rears don't go quite as far as the fronts. Mopping up that distance difference is what the diff is for in general for 2wd and what diffs+haldex does on our cars. Therefore subtly-different tyre sizes due to - for example - different wear levels is no issue, is normal, is what the OEM validated when signing the car off, &c. Another story from a tyre vendor is just that; a story. Chuckle, and move on.

F


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## Spandex (Feb 20, 2009)

forker said:


> dear all
> 
> key in this is to remember that when we drive on a road that isn't arrow-straight each wheel describes a different path; look at a wet road or the drive-away patch from a carwash on a dry day.
> 
> ...


Actually, this isn't true of most proper 4wd cars (I don't include the TT in this category). A centre diff is often not designed to have the planetary gears running at speed or for any length of time - it's just there for rare (temporary) occasions when traction is lost at either the front or rear. So, true 4wd vehicles _can be_ very fussy about differences in tyre diameter, even to the point where two pairs of theoretically identical sized tyres from different manufacturers are enough to cause long term damage to the diff.

As said though, Haldex isn't a diff and is less fussy about tyre size differences.


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## kasandrich (Sep 5, 2011)

I know this is an old thread, but I was just browsing.

If you have no centre diff, transmission wind up is in fact very quick. when you turn a corner all 4 wheels are going round different speeds. I also have a Kia Sorento 4x4 with part time 4x4 and no centre diff. If I put that into 4wd and turn the steering you can feel the tyres slipping every few metres to sort itself out. I have once done it on tarmac and it made a big clonk as the wind up tension was relieved. But thankfully no damage


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## John-H (Jul 13, 2005)

I think that just tells you that if the Haldex clutch seized up on your TT then you might get the same symptoms but because you don't, it's obviously free to slip and differences in tyres are therefore irrelevant. If you have a problem with tyres - skipping ESP lights etc then there's something else wrong :wink:


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## brian1978 (Jul 10, 2013)

Thickfit? I wouldn't take a pushbike to them for a puncture repair.

I took them up on the offer of a free battery check, when my mothers car wouldn't start unless it was pushed. Started with a jump though. Told them the symptoms and they "tested" the battery and tried to sell me some tyres and this engine treatment garbage, bit like a flush for the fuel. Which is fine they are a business and the tyres where legal were getting on a bit.

What did bother me was after they hooked the battery up to a machine to "test" it they told me it had an internal problem with the second cell or some other garbage, I took them at their word and purchased a battery.... across the road......at ECP :twisted: well it was £57 cheaper :roll:

Next morning same symptoms, dead battery. Turned out it was a faulty starter motor that was open circuit draining the battery. Diagnosed my my mechanically minded mate in 10 seconds. Just told him the issue and he went. "Hmm Peugeot 207, try the starter I've seen them go open circuit causing it to drain the battery"

Other problem, my aunt took a car to them for a tyre, they without her permission took one of her brake calipers to bits and then refused to put it back together unless she paid for a pad and disk as "it was illegal and they can't put the old parts back on"

Crooks!


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