New tyres - which end?
Discussion
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....
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....
TBH, I would imagine that many IAM/Rospa drivers would not fare much better when presented with surprise oversteer. As with many things, the best way to learn about something is to do it, and you could imagine that a safe driver would do everything to avoid such an occurrence.
Perhaps it the even smaller group of people that are best placed to handle it - IAM drivers who also aren't totally averse to getting a bit sideways every now and then.
Personally, I like to play around with the limits of my car, but only when the consequences of getting it wrong are nothing more than the compulsion to turn around to get back into the desired direction.
I reckon wet trackdays or at least some skidpan training should be part of the IAM tuition - now THAT would get more youngsters interested.
After all, advanced driving shouldn't only be about driving within a vehicle's limits (although that should always be the aim) - it should also encompass what to do when those limits are exceeded.
Perhaps it the even smaller group of people that are best placed to handle it - IAM drivers who also aren't totally averse to getting a bit sideways every now and then.
Personally, I like to play around with the limits of my car, but only when the consequences of getting it wrong are nothing more than the compulsion to turn around to get back into the desired direction.
I reckon wet trackdays or at least some skidpan training should be part of the IAM tuition - now THAT would get more youngsters interested.
After all, advanced driving shouldn't only be about driving within a vehicle's limits (although that should always be the aim) - it should also encompass what to do when those limits are exceeded.
Most FWD cars (and for that matter, an awful lot of RWD and even 4WD) are tuned to understeer. Some mundane hatches and saloons are so bad that there's very little you can do about it once it sets in The steering is so numb and the suspension so full of rubber bushes that there's just no option to lift off or dab the brakes the bring the rear end into play.
I rather doubt that putting new tyres on the front would instantly reverse this and create an over-steery monster - I reckon the vast majority of cars that still have legal tread on the rear would still understeer with brand new rubber on the front.
Hell - even the handbrake isn't an option on many modern cars, with funny little switches in place of the good old lever.
Cars are getting dumbed down - admittedly this is a direct correlation with the requirements of the average, dumbed down driver, but it explains why there's still a huge following for 'pure' cars, such as Pug205s, Escort Mk1s and Mk2s, early beemers and the like.
I rather doubt that putting new tyres on the front would instantly reverse this and create an over-steery monster - I reckon the vast majority of cars that still have legal tread on the rear would still understeer with brand new rubber on the front.
Hell - even the handbrake isn't an option on many modern cars, with funny little switches in place of the good old lever.
Cars are getting dumbed down - admittedly this is a direct correlation with the requirements of the average, dumbed down driver, but it explains why there's still a huge following for 'pure' cars, such as Pug205s, Escort Mk1s and Mk2s, early beemers and the like.
joewilliams said:
I've always thought this.
However, my wife's Panda recently had two new tyres put on the front, with the original eco low-rolling-resistance tyres still on the back. Going round a damp roundabout, with no sudden change in inputs, the back end slid impressively sideways which woke up the kids
I swapped the tyres front to back, and it's back to predictable understeer.
IMHO, that was nothing to do with the "newness" of the tyres and everything to do with the fact that they were tragically mis-matched. If you had put two new eco low-rolling-resistance tyres on the front, I don't think you'd have had the kiddy-waking moment at all.However, my wife's Panda recently had two new tyres put on the front, with the original eco low-rolling-resistance tyres still on the back. Going round a damp roundabout, with no sudden change in inputs, the back end slid impressively sideways which woke up the kids
I swapped the tyres front to back, and it's back to predictable understeer.
Remember the old ad about mixing radials and crossplies? - similar effect in action here, I reckon
GravelBen said:
Obviously (as reiterated by the last twop posts) the blanket 'on the back' advice is fine for Joe Average Numpty-driver who doesn't want to think about driving, but a competent driver should be able to make their own decision without being subjected to a mass bleat of expectation to do the same. Personally I will continue to put tyres on the end that gives the best results.
YAY! - it would appear that after 6 pages of "deliberation", we have our answer (which is what I thought all along, but as the subject sparked a similar discussion elsewhere, I thought it would be entertaining and informative to repeat it on PH)So - I'll continue to do what I've done for years - when a pair of tyres wear out, I'll simply replace them on whatever axle they came from, in the (relatively) safe knowledge that I can handle a bit of lift-off oversteer and any amount of understeer (which with 400+bhp through the front wheels, I tend to get a fair bit of in the wet...)
Zero 1 said:
"OmG WhY ArE YoU TAlKinG abOut OvArStuRRR?" 
er.....I repeat a point I've made before - most 'ordinary' modern cars (even RWD and 4WD) are set up to understeer and simply cannot oversteer unless they are seriously provoked or are dangerously / intentionally defective.
The only way to get a FWD car to oversteer for ANY reason other than lift-off is to have rear tyres that are almost slick or geometry that's seriously skewed (such as weird toe-out angles, barmy spring rates or over-high tyre pressures)
Yes, I know that FWD race cars such as BTCC are set up to have a 'flighty' rear end, but this is by design as the drivers are generally highly skilled and able to handle a bit of oversteer. Even so, I'm struggling to recall an instance of a FWD BTCC car oversterring without reason (usually because of a nudge or drifting off-line).
My own FWD car is set up to be fairly pointy (uprated rear ARB, increased spring & damper rates, increased negative camber on the front, 2.2 turns lock-to-lock rack) and it was already regarded as a fairly good FWD chassis. However, I cannot get it to oversteer without provocation and never when on the power. In the wet, I reckon the only way that new tyres on the front and worn tyres on the rear would cause oversteer is in standing water and with the rears well below the legal limit (which can hardly be the fault of putting the new tyres on the front)
AnotherGareth said:
More likely is that you are a cautious driver. Possibly you have enough experience of powerful rwd cars to have learned delicacy of inputs so as to not be taking liberties in powerful fwd cars?
I'm cautious when in the presence of other road users - I take the view that everyone else on the road is a potential idiot and out to get me - that way I'm rarely surprised by another driver's actions.However, when the opportunity arises, I'm far from cautious. I enjoy finding the limits of traction - I find it edicational as well as fun. As well as trophies for safe driving (from road safety trials) I also have trophies from hillclimbing and I've won the FWD handling discipline at Ten of the Best twice in the last six years (came second twice too).
I certainly have no fear of driving at (or just beyond) the limits of a car when the conditions allow (which clearly is extremely rare on the public highway). However, for whatever reason, I struggle to make my car oversteer for any other reason than lifting off or braking halfway round a slippery bend. In the dry, it'll get a bit squirmy when provoked, but I've only ever lost the rear end once in the dry (made the mistake of trying to change gear while flat in second gear around a long left-hander - the tank-slapper than ensued was fairly spectacular - I hit the lock stops in both directions trying to save it - which I ultimately failed to do...)
As for RWD, I'm crap. I've never liked power oversteer. This is partly down to the fact that the only RDW cars I've ever owned were a Chrysler 180 (yes, I was the one..) a Sierra 1.8 and a Ferrari F355. The later was spectacularly quick round the bends and hugely enjoyable to drive at anything up to 9/10, but I never really got near its limits for fear of interfacing with the scenery. I already know at this point that when a mid-engined car starts to spin, its generally difficult to get it back - I once managed to spin it in a straight line on the brakes (changed down too early on a slippery wet track and locked the rears)
Back on topic, are there really any FWD cars around that are so prone to oversteer that you're best advised to put new tyres on the back, or are the "gurus" just working to the lowest common denominator and advising everyone to do it, just in case?....
S. Gonzales Esq. said:
I thought the point (as shown in the video I linked to earlier) is that having deeper tread on the front makes the rear tyres more likely to aquaplane on wet corners.
Am I the only one thinking that the posters talking about dry grip have missed the point of this advice entirely?
This is the point (or at least part of it). Let's create a pair of scenarios, based on a FWD car that has worn-out front tyres and half-worn rear tyres (surely an incredibly common occurence in the FWD community)Am I the only one thinking that the posters talking about dry grip have missed the point of this advice entirely?
Scenario 1
Owner listens to perceived wisdom and fits the new tyres on the rear and transfers the half-worn rears to the front.
IMHO, aquaplaning will onset much earlier, becuase the tyres that are doing the majority of the water clearance will be the half-worn jobbies now on the front. The tyres with the greatest tread depth are not having to do very much at all.
Scenario 2
Owner fits the new tyres on the front and leaves the part-worns on the rear. The new front tyres will therefore clear the vast majority of the water, leaving the rears with only a little water clearance to do.
If the part-worn rears are THAT worn that they will still aquaplance after the fronts have cleared a path, then they shouldn't be on the car anyway.
And as for dry grip - you're right - it's irrelevant, as a worn tyre probably has more grip than a new one (which I think I mentioned in the original post, or soon after)
Speedy11 said:
Thats all very well but when going around a corner the rear tyres take a slightly different path to the front.
Yes, but the difference at road speeds is tiny and irrelevant - certainly at speeds where aquaplaning is a danger, the rear tyres will essentially follow in the tracks of the fronts. Check it out next time you're driving in the rain - when you're following a car round a bend at anything over 30mph, there will be a single pair of tracks in the water. This is because the steering angle required to navigate bends in the road (as opposed to corners or junctions) is actually pretty small - probably less than a quarter of a turn of the steering wheel
@ crocodile tears - to be fair, a 306 has a propensity to turn around even with good tyres on it - one of the pointiest FWD cars I've ever driven. It must be scary in the wet with iffy rubber on the rear.
I'm finding it harder to argue against the "new on the rear" assertion. Maybe I've been lucky with my cars, or my chosen setup, or maybe I never let my rear tyres get so worn that there's a chance they'll aquaplane (although I still maintain that the rear tyres MUST have less water to clear, straight line OR corner, simply because they're following in the tracks of the fronts).
Perhaps this is the issue - it's not the fact that the rear tyres will aquaplane, it's the fact that the fronts won't - there's a big imbalance in wet grip so that the rear end will always let go before the rear, even if they're following in the wheeltracks of the fronts.
I'm finding it harder to argue against the "new on the rear" assertion. Maybe I've been lucky with my cars, or my chosen setup, or maybe I never let my rear tyres get so worn that there's a chance they'll aquaplane (although I still maintain that the rear tyres MUST have less water to clear, straight line OR corner, simply because they're following in the tracks of the fronts).
Perhaps this is the issue - it's not the fact that the rear tyres will aquaplane, it's the fact that the fronts won't - there's a big imbalance in wet grip so that the rear end will always let go before the rear, even if they're following in the wheeltracks of the fronts.
As the OP, I have a little more information to add, in the form of actual experience, rather than theory.
I have two Fiat Coupes - one is a highly modded 450-bhp example, the other is one of the very earliest dealer 16v non turbos, that quite honestly struggles to keep up with modern diesel rep-mobiles.
Recently, the 450bhp car decided that the diff would like a sniff of the open air, so it punched a hole in the gearbox and then ate its own planet gears. The resultant rebuild caused me to put the 16v into daily use.
However, when I bought the 16v, the front wishbones were shot to bits, which had munched the outer edges of the front tyres, causing some VERY weird handling traits. I replaced the wishbones, but the handling was still iffy, with terminal understeer and a vicious self-centering effect. In an attempt to pinpoint the cause, I did a front-rear wheel swap.
All of a sudden, the neat handling was back - I could tip it into a corner with confidence, knowing it wasn't going to do something silly halfway round.
Then it rained....
Firstly, I'd forgotten what it was like to drive a car with an open diff (the 20vt Coupe has Viscodrive - a cheap stab at providing LSD-like handling benefits).
Secondly, I'd forgotten what lift-off oversteer was, but I was very quickly reminded, with a gorgeous slo-mo drift around a greasy roundabout.
All of this was down to a pair of rear tyres with shoulders at the legal limit (tread depth across the rest of the tyre is well within the limit)
So - which is best?
Well, personally, the handling was SO bad with the iffy tyres on the front that I still reckon they're better off on the rear, although I don't much like the slightly loose feeling when cornering modestly hard in the wet.
Ultimately though, even though the handling felt truly awful when the dodgy tyres were up front, it was inherently safer, as rampant understeer could be controlled by slowing down a bit. With the half-slicks on the rear, slowing down just made matters worse.
I got the 450bhp car back a couple of weeks ago, following a new gearbox, with a Quaife ATB. Just started to enjoy matters, when it ate its own cambelt and took two thirds of the valves with it, so the 16v is back into daily use again.
Time for some new tyres though, as the weather is turning.
Now - which end should I put them on?.....
I have two Fiat Coupes - one is a highly modded 450-bhp example, the other is one of the very earliest dealer 16v non turbos, that quite honestly struggles to keep up with modern diesel rep-mobiles.
Recently, the 450bhp car decided that the diff would like a sniff of the open air, so it punched a hole in the gearbox and then ate its own planet gears. The resultant rebuild caused me to put the 16v into daily use.
However, when I bought the 16v, the front wishbones were shot to bits, which had munched the outer edges of the front tyres, causing some VERY weird handling traits. I replaced the wishbones, but the handling was still iffy, with terminal understeer and a vicious self-centering effect. In an attempt to pinpoint the cause, I did a front-rear wheel swap.
All of a sudden, the neat handling was back - I could tip it into a corner with confidence, knowing it wasn't going to do something silly halfway round.
Then it rained....
Firstly, I'd forgotten what it was like to drive a car with an open diff (the 20vt Coupe has Viscodrive - a cheap stab at providing LSD-like handling benefits).
Secondly, I'd forgotten what lift-off oversteer was, but I was very quickly reminded, with a gorgeous slo-mo drift around a greasy roundabout.
All of this was down to a pair of rear tyres with shoulders at the legal limit (tread depth across the rest of the tyre is well within the limit)
So - which is best?
Well, personally, the handling was SO bad with the iffy tyres on the front that I still reckon they're better off on the rear, although I don't much like the slightly loose feeling when cornering modestly hard in the wet.
Ultimately though, even though the handling felt truly awful when the dodgy tyres were up front, it was inherently safer, as rampant understeer could be controlled by slowing down a bit. With the half-slicks on the rear, slowing down just made matters worse.
I got the 450bhp car back a couple of weeks ago, following a new gearbox, with a Quaife ATB. Just started to enjoy matters, when it ate its own cambelt and took two thirds of the valves with it, so the 16v is back into daily use again.
Time for some new tyres though, as the weather is turning.
Now - which end should I put them on?.....
If the issue was only about aquaplaning, my opinion would be that the new tyres should always go on the front, as the rears will follow in the front tyres' path, and thus have far less water clearing to do
However, this is inly one aspect, and it's looking more like the "new on the rear" argument is coming from Joe Public's ability to handle understeer more easily than oversteer. Quite understandable.
I would class myself as a fairly decent driver (trophies for safe driving, trophies for fast driving), but I still feel uneasy when the back end isn't doing as I want (apart from a recent quick blat in a Caterham round Curborough Sprint Course, which felt utterly natural going sideways).
For "ordinary" drivers who don't deliberately provoke a car at the limits of traction or grip, the normal reaction when one end starts to slide is to lift off or even brake. We all know what will happen if this is done while oversteering, so my opinion is that the tyre manufacturers' guidance is for the masses and is simply safety-related.
However, this is inly one aspect, and it's looking more like the "new on the rear" argument is coming from Joe Public's ability to handle understeer more easily than oversteer. Quite understandable.
I would class myself as a fairly decent driver (trophies for safe driving, trophies for fast driving), but I still feel uneasy when the back end isn't doing as I want (apart from a recent quick blat in a Caterham round Curborough Sprint Course, which felt utterly natural going sideways).
For "ordinary" drivers who don't deliberately provoke a car at the limits of traction or grip, the normal reaction when one end starts to slide is to lift off or even brake. We all know what will happen if this is done while oversteering, so my opinion is that the tyre manufacturers' guidance is for the masses and is simply safety-related.
7db said:
Should we look at this from a vehicle dynamics point of view?
Your car manufacturer has spent ages ensuring that your car is an understeer-characteristic car (by which I mean the steering angle required is greater than the d'Alembertian angle, rather than that it ploughs on into the hedge when you drive a corner too fast). Isn't the risk that by increasing the grip at the front you create an oversteer-characteristic car?
Oversteer characteristic cars have a critical speed at which the required steering angle for any turn reduces to zero -- or put another way - they spin out of control and you die* if you go fast enough.
I don't know how low that critical speed can be, but this is the reason I don't monkey with my suspension or put new tyres on the front.
... and this is the reason why I HAVE arsed about with my geometry. I have a "safe" FWD car - a Fiat Coupe. It was already an OK handling thing, but with a 2/3 front weight bias, it was always going to understeer when pushed, especially when on the throttle.Your car manufacturer has spent ages ensuring that your car is an understeer-characteristic car (by which I mean the steering angle required is greater than the d'Alembertian angle, rather than that it ploughs on into the hedge when you drive a corner too fast). Isn't the risk that by increasing the grip at the front you create an oversteer-characteristic car?
Oversteer characteristic cars have a critical speed at which the required steering angle for any turn reduces to zero -- or put another way - they spin out of control and you die* if you go fast enough.
I don't know how low that critical speed can be, but this is the reason I don't monkey with my suspension or put new tyres on the front.
I've more than doubled the bhp, so I wanted to make it corner properly as well. Quaife diff, 25mm lower springs, adjustable dampers, uprated rear ARB, bit of extra camber at the front, polybushes everywhere. The end result is a car that turns in really well, but never feels like it wants to oversteer. It'll still understeer when hard on the throttle (although the Quaife has made an immense difference), but it is really planted. By comparison, I also have a completely unmolested Fiat Coupe non-turbo (about 1/3 of the bhp of my modded one), which now feels truly awful to drive - vague steering, roly-poly suspension, understeer everywhere, wet or dry
So - why do manufacturers build in such a huge safety margin to mainstream cars? I've spent many hundreds dialing out understeer on my quick Coupe and (IMHO) I've made the car much better, with no handling downsides (other than a slightly firm / jiggly ride at town speeds). It certainly won't bite back, but the precision is vastly improved.
Perhaps we're back to the conclusion about which end to put new tyres on - the reason that most people drive cars - it's simply a method of getting to somewhere else - the car is nothing more than white goods, with no involvement (or desire to be involved) from the driver's perspective. Damn - are PH'ers a dying breed?
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