Discussion
My old Cavalier was a very run of the mill car, in very good mechanical nick. It was the 1.7 turbo Diesel. I lost the back end driving around a smallish roundabout at around 10-15mph, very suddenly, and nearly wrote the car off. I was not pressing on, and was very surprised by what had happend. The pressures were all okay as I check them religiously every week or so.
The weak link in that case was the poor rear tyres (Pirellis). The car had equally poor Pirellis up front, all had around 3mm of tread, and the road was fairly wet but not waterlogged. I soon switched the tyres for Toyos all round, and in over a year if driving the car around that roundabout most days at similar speeds, never had a problem again.
Since then it has always been my choice to have the best tyres on the rear. If the front ones go bad it is obvious from the wheelspin when accelerating, and skidding when braking hard, like the Nankangs on my ZS when I bought it. I can drive around this and plan to get new tyres ASAP, i.e. new on the front wheels, the swap them to the back.
I believe the problem with front engined, FWD cars having the worst tyres on the back is that the rear end has far less weight pressing down on the tyres, so if the back end becomes unsettled with poor tyres on the rear, it can lose traction and swing round fairly easily.
It only takes one moment to learn a lesson, and I'm glad I had no damage caused in my Cavalier when I learnt the one about not having poor rear tyres on a FWD car. I go along with the official advice from the AA etc. on this one.
The weak link in that case was the poor rear tyres (Pirellis). The car had equally poor Pirellis up front, all had around 3mm of tread, and the road was fairly wet but not waterlogged. I soon switched the tyres for Toyos all round, and in over a year if driving the car around that roundabout most days at similar speeds, never had a problem again.
Since then it has always been my choice to have the best tyres on the rear. If the front ones go bad it is obvious from the wheelspin when accelerating, and skidding when braking hard, like the Nankangs on my ZS when I bought it. I can drive around this and plan to get new tyres ASAP, i.e. new on the front wheels, the swap them to the back.
I believe the problem with front engined, FWD cars having the worst tyres on the back is that the rear end has far less weight pressing down on the tyres, so if the back end becomes unsettled with poor tyres on the rear, it can lose traction and swing round fairly easily.
It only takes one moment to learn a lesson, and I'm glad I had no damage caused in my Cavalier when I learnt the one about not having poor rear tyres on a FWD car. I go along with the official advice from the AA etc. on this one.
Edited by Turkey on Sunday 29th August 20:12
Turkey said:
The weak link in that case was the poor rear tyres (Pirellis). The car had equally poor Pirellis up front, all had around 3mm of tread, and the road was fairly wet but not waterlogged.
How can you blame it on having worse rear tyres if the fronts were just as bad?
You say you never had a problem with that roundabout after changing to different tyres all round, but presumably you never had a problem with the Pirellis before that occasion either?
Edited by GravelBen on Monday 30th August 13:32
On my FWD shopping cart the new RE040's always go on the front, and the fronts rotated to the rear. My reasoning is that the front wheels have to transmit the power to the road surface, steer and also provide 85% of the braking power.
I guess having more traction at the rear of the car might be beneficial to inexperienced drivers.
I guess having more traction at the rear of the car might be beneficial to inexperienced drivers.
itsnotarace said:
On my FWD shopping cart the new RE040's always go on the front, and the fronts rotated to the rear. My reasoning is that the front wheels have to transmit the power to the road surface, steer and also provide 85% of the braking power.
I guess having more traction at the rear of the car might be beneficial to inexperienced drivers.
Your reasoning may seem logical but is quite wrong! See the vid link elsewhere on this thread.I guess having more traction at the rear of the car might be beneficial to inexperienced drivers.
Do experienced drivers need less tread/grip then? I feel a new law coming on. Learner drivers must have at least 7mm tread, old farts like me are ok with slicks.
Wow two bites already. I'm telling you my thoughts on the matter, not dictating what you should or shouldn't do 
I would also suggest experienced drivers are much less likely to be caught out by LOOS, and if they were, they would know what to do in that situation to correct it
If you are suggesting that an extra 3 or 4 mm of tread will prevent you spinning on black ice or diesel then I would call BS
Deva Link said:
That's right. The laws of physics don't apply to driving Gods.
blueg33 said:
Do experienced drivers need less tread/grip then?
Experienced drivers are more likely to be driving appropriately given the available surface traction and weather conditions so yes, statistically speaking I bet I'm not far off.I would also suggest experienced drivers are much less likely to be caught out by LOOS, and if they were, they would know what to do in that situation to correct it
If you are suggesting that an extra 3 or 4 mm of tread will prevent you spinning on black ice or diesel then I would call BS
itsnotarace said:
Wow two bites already. I'm telling you my thoughts on the matter, not dictating what you should or shouldn't do
I would also suggest experienced drivers are much less likely to be caught out by LOOS, and if they were, they would know what to do in that situation to correct it
If you are suggesting that an extra 3 or 4 mm of tread will prevent you spinning on black ice or diesel then I would call BS
FWD cars are unbalanced, in that the front wheels always have far more grip than the back because they are driven. This is why new tyres must go on the back, because when conditions of grip are reduced, the rear wheels will need all the help they can get.Deva Link said:
That's right. The laws of physics don't apply to driving Gods.
blueg33 said:
Do experienced drivers need less tread/grip then?
Experienced drivers are more likely to be driving appropriately given the available surface traction and weather conditions so yes, statistically speaking I bet I'm not far off.I would also suggest experienced drivers are much less likely to be caught out by LOOS, and if they were, they would know what to do in that situation to correct it
If you are suggesting that an extra 3 or 4 mm of tread will prevent you spinning on black ice or diesel then I would call BS
If, in wet or slippery conditions, you have the best tyres on the front you will be exacerbating the imbalance further.
There simply is no need to put the new tyres on the front.
heebeegeetee said:
FWD cars are unbalanced, in that the front wheels always have far more grip than the back because they are driven.
Please explain that sentence because it makes no sense to me. Unless you meant having the weight of the engine over the front wheels increases grip, in which case that makes slightly more sense.Please can someone also explain how having additional grip at the rear helps stop the car when 85% of the braking is done at the front?
heebeegeetee said:
If, in wet or slippery conditions, you have the best tyres on the front you will be exacerbating the imbalance further.
There simply is no need to put the new tyres on the front.
Except that most of the braking is done through the fronts, so in wet conditions, less tread depth = less water dispersal = longer stopping distance. For all the other arguments about balance etc, is there one to show I'm incorrect about that? If so, I just want to know. Thanks.There simply is no need to put the new tyres on the front.
itsnotarace said:
Please can someone also explain how having additional grip at the rear helps stop the car when 85% of the braking is done at the front?
I am not qualified to explain, but the reasons are clear on the video link and tyre manufacturers say the same.My take on it is that particularly under braking or hard cornering if the back has less grip than the front then the back tries to overtake the front (as it has less retardation) thus inducing a spin
Sticks. said:
heebeegeetee said:
If, in wet or slippery conditions, you have the best tyres on the front you will be exacerbating the imbalance further.
There simply is no need to put the new tyres on the front.
Except that most of the braking is done through the fronts, so in wet conditions, less tread depth = less water dispersal = longer stopping distance. For all the other arguments about balance etc, is there one to show I'm incorrect about that? If so, I just want to know. Thanks.There simply is no need to put the new tyres on the front.
I'm not qualified to give detailed answers either, but let's have a go:
Under braking the front of the car dips and conversely the rear of the car rises, thus creating such an imbalance of grip that the hydraulic pressure to the rear brakes needs to be reduced via a mechanism, otherwise the rear brakes will lock readily. ABS helps but will not necessarily reduce stopping distance if the rears are struggling for grip.
When cornering the front wheels have torque transmitted through them and thus will have more traction than the rear wheels, even when there's quite an imbalance of tread depth between front and rear.
It's not too far from the truth to say that on a fwd car the only job the rear wheels really have is to keep the car off the ground.
I agree that all logic says that the best tyres should be on the front of an fwd which is why i used to put them there myself, and had to find out twice that it was completely the wrong thing to do.
I tell you, when the back comes round it does so ever so quick.
. Can i just also add in response to other comments made, the only cars i have ever had 'prodigiously understeer' have all been rwd, including, i'm sad to say, my Boxster at Anglesey.
blueg33 said:
My take on it is that particularly under braking or hard cornering if the back has less grip than the front then the back tries to overtake the front (as it has less retardation) thus inducing a spin
The back of the car is already very much unweighted during heavy braking anyway - example:Whilst on track I frequently get the inside rear wheel off the ground entirely due to the weight transfer and body roll, having an extra few mm of tread is not going to help me turn the corner as all the weight is on the opposite corner at the front of the car, with a small proportion being on the outside rear.
Going back to cornering, there are so many other variables to take into account rather than just tread depth. There is a good article (actually about anti roll bars) that discusses this further
http://grassrootsmotorsports.com/articles/lean-les...
article said:
Put simply, the larger the contact patch of the tire, the more traction exists against the road surface, holding all else constant. But when the vehicle begins to lean or roll to one side, the tires are also forced to lean or roll to one side.
This can be described as a camber change in which the outside tire experiences increased positive camber (rolls to the outside edge of the tire) and the inside tire experiences increased negative camber (rolls to the inside edge of the tire.) So a tire that originally enjoyed a complete and flat contact patch prior to body roll must operate on only the tire edge during body roll.
The resulting loss of traction can allow the tires to more easily give way to the forces of weight transfer to the outside edge of the vehicle. When this happens, the vehicle slides sideways-which is generally a bad thing.
This can be described as a camber change in which the outside tire experiences increased positive camber (rolls to the outside edge of the tire) and the inside tire experiences increased negative camber (rolls to the inside edge of the tire.) So a tire that originally enjoyed a complete and flat contact patch prior to body roll must operate on only the tire edge during body roll.
The resulting loss of traction can allow the tires to more easily give way to the forces of weight transfer to the outside edge of the vehicle. When this happens, the vehicle slides sideways-which is generally a bad thing.
Edited by itsnotarace on Tuesday 31st August 20:10
heebeegeetee said:
Under braking the front of the car dips and conversely the rear of the car rises, thus creating such an imbalance of grip that the hydraulic pressure to the rear brakes needs to be reduced via a mechanism, otherwise the rear brakes will lock readily. ABS helps but will not necessarily reduce stopping distance if the rears are struggling for grip.
Unless you have in-cabin adjustable brake bias, this is not true. The brake balance is fixed by the manufacturer.heebeegeetee said:
When cornering the front wheels have torque transmitted through them and thus will have more traction than the rear wheels, even when there's quite an imbalance of tread depth between front and rear.
Weight is transferred to the outside, assuming all other factors are equal such as a constant radius curve there will be an equal amount of weight being distributed along the entire length of the vehicle. Physics does not know which wheels are being driven.heebeegeetee said:
It's not too far from the truth to say that on a fwd car the only job the rear wheels really have is to keep the car off the ground.
I think you are confusing a car with a Sedgeway. heebeegeetee said:
I agree that all logic says that the best tyres should be on the front of an fwd which is why i used to put them there myself, and had to find out twice that it was completely the wrong thing to do.
I have been driving FWD hot hatches for 17 years and I have never experienced loss of traction at the rear of the car due to having a few less mm of tread.heebeegeetee said:
I tell you, when the back comes round it does so ever so quick. .
As does any car that snaps into oversteer when you are not expecting it. Power induced oversteer is the exception because it occurs relatively progressively as you apply throttle.. Funnily enough (as they're RWD) Mercedes reckon new tyres are best on the front of their more recent cars.
They reckon the electronics takes such good care of the back it's pretty well impossible for the driver to screw it up unless he's a complete imbecile (and trust me, I've tried!) so they say you might as well put the new tyres on the front of their cars where there's a chance they might be useful.
There was a lot of controversy when they printed this in the W204 (latest C Class) manual and I think it's been removed now.
They reckon the electronics takes such good care of the back it's pretty well impossible for the driver to screw it up unless he's a complete imbecile (and trust me, I've tried!) so they say you might as well put the new tyres on the front of their cars where there's a chance they might be useful.
There was a lot of controversy when they printed this in the W204 (latest C Class) manual and I think it's been removed now.
^^^^
I hear what you are saying and I know the rear of the car is lighter etc thats why brake balance is set up with a bias to the front. You don't address the reason for putting tyres with more wear on the rear though. Surely if the rear is going light you need to maximise grip, hence newer tyres on the rear. The clearly applies more in the wet, as tread depth has less relevance in the dry
I hear what you are saying and I know the rear of the car is lighter etc thats why brake balance is set up with a bias to the front. You don't address the reason for putting tyres with more wear on the rear though. Surely if the rear is going light you need to maximise grip, hence newer tyres on the rear. The clearly applies more in the wet, as tread depth has less relevance in the dry
blueg33 said:
I hear what you are saying and I know the rear of the car is lighter etc thats why brake balance is set up with a bias to the front.
http://www.stoptech.com/tech_info/wp_brakebiasandperformance.shtmlSome good diagrams on there explaining it - stationary car
Moving car
blueg33 said:
You don't address the reason for putting tyres with more wear on the rear though. Surely if the rear is going light you need to maximise grip, hence newer tyres on the rear. The clearly applies more in the wet, as tread depth has less relevance in the dry
If the rear is unweighted during braking, it will have less grip anyway. Just about all of the grip and therefore stopping power will come from the front of the car. Think back to the days when we didn't use to have ABS. If you locked up the brakes when travelling in a straight line and then got out the car to look at the road, you would only ever see that the front wheels had locked up, not the rearsFor arguments sake, lets flip this around and I conform to manufacturers recommendations and fit my new tyres to the rear of the car. Let's say my front tyres have 2mm of tread and the rear tyres have 7mm tread. Lets then say I drive down the motorway at 70mph, it's dark and it starts raining hard. Suddenly I hit a massive patch of standing water. What happens?
What happens is the front tyres are unable to clear the standing water and the car begins to aquaplane. I lose all steering and 85% of my braking ability. Great. I crash.
Let's reverse the situation and we fit the good tyres to the front. What happens? The front tyres clear the water better than the rears, and I can safely steer and brake to a halt. I would not immediately spin off the road because the rears will always follow the fronts through, just the same as accelerating in a front wheel drive car will correct a slide from the rear.
itsnotarace said:
Let's reverse the situation and we fit the good tyres to the front. What happens? The front tyres clear the water better than the rears, and I can safely steer and brake to a halt. I would not immediately spin off the road because the rears will always follow the fronts through, just the same as accelerating in a front wheel drive car will correct a slide from the rear.
It's not about braking. It's about those accidents where people say "I was just driving along at 30 and the car went from underneath me." There was one on here just the other day.http://www.youtube.com/watch?v=l5YsQ_a_ijA
itsnotarace said:
blueg33 said:
I hear what you are saying and I know the rear of the car is lighter etc thats why brake balance is set up with a bias to the front.
For arguments sake, lets flip this around and I conform to manufacturers recommendations and fit my new tyres to the rear of the car. Let's say my front tyres have 2mm of tread and the rear tyres have 7mm tread. Lets then say I drive down the motorway at 70mph, it's dark and it starts raining hard. Suddenly I hit a massive patch of standing water. What happens?What happens is the front tyres are unable to clear the standing water and the car begins to aquaplane. I lose all steering and 85% of my braking ability. Great. I crash.
Let's reverse the situation and we fit the good tyres to the front. What happens? The front tyres clear the water better than the rears, and I can safely steer and brake to a halt. I would not immediately spin off the road because the rears will always follow the fronts through, just the same as accelerating in a front wheel drive car will correct a slide from the rear.
My only "off" in a FWD car was a deer avoidance manouvere in the wet not long after I had fitted new tyres to the front but left the part worn rears. The car (volvo V70) spun onto the verge. I was surprised as I became a passenger very suddenly. Maybe it was the tyres, maybe inept driving, I will never know, but I now go with the guidance from the manufacturers, ie most tread on the rear
itsnotarace said:
She could have just yanked on the handbrake or lifted sharply, I guess that wouldn't make good viewing though
It is what happens though. This is not the "ragged edge" driving, where you've got hold of the car by the scruff of the neck and you know what you're doing - this is ordinary drivers bimbling along and the car suddenly lets go. Very difficult even for an ace driver to catch these things on a public road as you don't usually have much space to play with.There was a good video on one of the motoring programmes a few years ago where they did this with small superminis in various tyre combinations - the bizzare thing when new tyres were on the front and worn on the rear the car spins out at lower speeds that if all 4 tyres were worn.
Apparently it's all about the difference in grip - centrifugal force means the car is always trying to go sideways, so if the fronts grip and rears don't then the back-end lets go earlier than if all 4 tyres are evenly worn.
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