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Nigel_O

Original Poster:

397 posts

105 months

[news] 
Wednesday 25th April 2012 quote quote all
We have an ongoing discussion on our one-make forum (Fiat Coupe) about which end of the car should receive new tyres when only buying a pair. The advice appears to be that if you're replacing front tyres, we should move the part-worns from the rear to the front and put the new tyres on the rear and if you're replacing rears, we DON'T move the part-worn fronts to the rear.

Please bear in mind that (initially at least) we're talking FWD, and a fairly powerful one at that.

Established "wisdom" seems to suggest that the new tyres should always go on the rear, but I disagree.

In the dry, it will make no difference. In fact if anything, the old tyre will give marginally more grip due to less tread deflection under load. TBH, if you're driving hard enough to feel the difference, then you're going way too quickly for the public highway.

In the wet, surely you want the front tyres to have the deepest tread depth, so that they can clear the water. The rear tyres generally follow the fronts, so they have far less water clearing to do. Also, when braking in the wet, you need maximum water clearance on the axle that's doing the majority of the braking.

I accept that the probable reason for advocating new tyres on the rear is that for the majority of drivers, catching and understeer moment is a doddle compared with saving an oversteer event (especially for most FWD owners, who wouldn't know what oversteer was until they reverse through a hedge after lifting off halfway round a wet roundabout).

So - is "new tyres on the rear" simply a dumbing down to play to the lowest common denominator, or are there other genuine reasons for leaving part-worn tyres on the front? (or even moving them from the rear to put them on the front)

FWIW, I don't move my tyres round - I simply replace whichever ones are worn.

Discuss....

chris182

1,232 posts

39 months

[news] 
Wednesday 25th April 2012 quote quote all
Well your front wheels do the steering, most of the braking and also put the power down. This would indicate to me that having the best tyres on the front would be a good plan. I might reconsider on a powerful RWD car, but for a FWD car it is no contest IMO.

supersport

2,247 posts

113 months

[news] 
Wednesday 25th April 2012 quote quote all
There was a program some time ago, maybe Fifth gear, that looked at this and the effect of the worn tyres on the rear in the wet was unpleasant, the FWD car over steared into trees on bends.

I am sure this has been covered on here in the past but can't remember the explanation, but it certainly made sense. Something like, the rear is likely to be the lightest and therefore needs the grip from the tyres.


Nigel_O

Original Poster:

397 posts

105 months

[news] 
Wednesday 25th April 2012 quote quote all

ScoobyChris

268 posts

88 months

[news] 
Wednesday 25th April 2012 quote quote all
supersport said:
I am sure this has been covered on here in the past but can't remember the explanation, but it certainly made sense. Something like, the rear is likely to be the lightest and therefore needs the grip from the tyres.
I think the theory is that the rear of the car has a tendency to turn, pivoting around the front wheels and so the bigger the differential in grip, the more likely the car is to oversteer. I'm sure Stressed Dave put an explanation with some science...

Fifth gear did show some videos where VBH demonstrated it in a regular FWD hatch (Focus). However, in my FWD cars, I've always replaced worn out tyres, rather than putting them on a specific axle, and don't recall ever having an issue.

Chris

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SonicShadow

611 posts

40 months

[news] 
Wednesday 25th April 2012 quote quote all
I just replace whatever set need replacing. I really don't think it makes that much difference.

Besides, I cant rotate my tyres front to rear anyway - mine are staggered.

Bacon Is Proof

3,077 posts

117 months

[news] 
Wednesday 25th April 2012 quote quote all
If the difference in grip between the new and old tyres is that great, replace all four. idea

egomeister

4,252 posts

149 months

[news] 
Wednesday 25th April 2012 quote quote all
SonicShadow said:
mine are staggered.
Matched perfect and staggered special? hehe

I've also never worried about which end they are going on, I just make sure that they are matched across and axle, a good make and are the same age/evenly worn.

DJ_AS

299 posts

93 months

[news] 
Wednesday 25th April 2012 quote quote all
I understood the logic for putting the newest tyres on the rear to be as follows:

1. you're more likely to slide in the wet than the dry
2. a worn tyre is more likely to slide in the wet than newer tyre with deeper tread
3. if 1 and 2 are true, then you can condense that to you are more likely to suffer a slide on an older tyre (i.e. one with less tread)
4. if the tyres with least tread are on the rear axle, that is more likely to slide, if the tyres are on the front, that is more likely to slide
5. dealing with a slidy front (understeer) is easier / more intuitive to most drivers than dealing with a sliding rear (oversteer)

As a bonus, your rear tyres get rotated forwards and changed before the rubber perishes (this actually happened on my Ka - after 4 years there was plenty of tread on the rears but the rubber was cracking on the sidewall!)

What all this doesn't seem to take into account is the fact that the front wheels do almost all the work on a fwd car*. I've only had a few slidy moments in the wet / snow and they have ALWAYS been from the front of the car irrespective of where the 'best' tyres are. This year I fitted all season (not full winter) on the front axle only and it made a noticeable difference to performance in the bit of snow we had. I doubt I'd have noticed if they were on the rear.

  • I read somewhere that Audi believe best tyres go on the front as they do the most work. Don't know if thats true.

SonicShadow

611 posts

40 months

[news] 
Wednesday 25th April 2012 quote quote all
egomeister said:
SonicShadow said:
mine are staggered.
Matched perfect and staggered special? hehe
Not sure what you mean?

Getragdogleg

4,591 posts

69 months

[news] 
Wednesday 25th April 2012 quote quote all
When buying tyres for the Golf I put the new ones on the rear and the ones from the rear on the front because the rear just follows and has no power going through so the tyres do not wear, the life of a tyre is not just the tread but also the age of it and I often see cars in the workshop with the original tyres on the rear with bad side wall cracking but lots of tread, these tyres are condemned and replaced, a waste of money and potential use.

To me it makes sense to keep all the tyres a similar age rather than just keep changing the fronts all the time and letting the back perish but not wear out.

Since the most work is done by the front, power, braking and steeling then having tyres that have scrubbed the newness off by being used on the rear means the handling does not change for the driver, there is no release agent to get off, no new feel that is often present when you drive on new tyres for the first few miles.


itsnotarace

4,149 posts

95 months

[news] 
Wednesday 25th April 2012 quote quote all
Nigel_O said:
I accept that the probable reason for advocating new tyres on the rear is that for the majority of drivers, catching and understeer moment is a doddle compared with saving an oversteer event (especially for most FWD owners, who wouldn't know what oversteer was until they reverse through a hedge after lifting off halfway round a wet roundabout).

So - is "new tyres on the rear" simply a dumbing down to play to the lowest common denominator, or are there other genuine reasons for leaving part-worn tyres on the front? (or even moving them from the rear to put them on the front)
I provoked nerdrage from a cockster owner on this forum last time I suggested exactly that!

Anyway, my thoughts are that the front wheels handle 85% of the all braking, all of the steering and all of the acceleration so that's where I would want the new tyres.

You will also notice that the fifth gear test only looked at cornering in the wet and aquaplaning and completely ignored stopping distance in a straight line.

http://www.youtube.com/watch?v=l5YsQ_a_ijA





HustleRussell

6,435 posts

46 months

[news] 
Wednesday 25th April 2012 quote quote all
DJ_AS said:
5. dealing with a slidy front (understeer) is easier / more intuitive to most drivers than dealing with a sliding rear (oversteer)

As a bonus, your rear tyres get rotated forwards and changed before the rubber perishes.
This is pretty much my thinking.

Control- when a driver who isn't used to sliding gets into a slide, the natural reaction is to lift off the throttle and possibly apply the brakes. Lifting off is exactly the right course of action to take if the car is understeering. The forwards weight transfer of the deceleration and the reduction in power that the tyre is attempting to deliver to the road will usually be enough to restore traction and bring the car under control. No other driver input is required- the steering wheel can be held in the same position it was in when the understeer was initiated.
Very few drivers as a proportion are able to deal with oversteer. If a FWD car begins to oversteer, and the driver takes the course of action described as above (lift off throttle and maintain steering angle) it could well result in further loss of control.

Tyres last too long on the rear axle of a FWD car and they are usually ineffective long before they are low on tread.

kaf

323 posts

33 months

[news] 
Wednesday 25th April 2012 quote quote all
Tyre manufacturers recommend best on the rear for the reasons previously explained, a rear breakaway is rapid, with little warning and very difficult to capture.

A front end loss of grip tends to give you more warning, you can feel the steering getting lighter, it tends to be less violent and us easier to recover.

In addition a blow out on a rear tyre will cause you more problems than a blow out on the front where you at least have some steering control and a worn tyre is more likely to blow out than a new one.


james_gt3rs

3,308 posts

77 months

[news] 
Wednesday 25th April 2012 quote quote all
I'd put them on the rear, cos understeer is much easier to recover from than oversteer when you're not expecting it.

Also have a search for this topic, stressed dave had a concrete explanation of the physics involved, I think it was called 'terminal oversteer', worth a read.

jontymo

610 posts

36 months

[news] 
Wednesday 25th April 2012 quote quote all
On the back for new tyres, laws of physics and being able to control the back when losing it than the front.

jontymo

610 posts

36 months

[news] 
Wednesday 25th April 2012 quote quote all
On the back for new tyres, laws of physics and being able to control the back when losing it than the front.

Bacon Is Proof

3,077 posts

117 months

[news] 
Wednesday 25th April 2012 quote quote all
Is everyone neglecting the theory that tyres bed in to their situation?

Getragdogleg

4,591 posts

69 months

[news] 
Wednesday 25th April 2012 quote quote all
Bacon Is Proof said:
Is everyone neglecting the theory that tyres bed in to their situation?
No, I'm not, I am helping the tyres out by letting them into life gently, they only have to play follow the leader for the first part of life, then once happy they can go round and round nicely they get upgraded to the front to play, that is where the real forces and bedding in occurs.

davepoth

23,321 posts

85 months

[news] 
Wednesday 25th April 2012 quote quote all
Exactly the above - snap oversteer when you lift mid corner is not a characteristic most of us would like in a daily driver.
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