Discussion
itsnotarace said:
1. Unless you have in-cabin adjustable brake bias, this is not true. The brake balance is fixed by the manufacturer.
2. 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.
3. 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.
4. 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.
1. 2. 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.
3. 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.
4. 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.
itsnotarace said:
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.If you get underneath your car you'll find it.
http://www.google.co.uk/search?q=brake+pressure+re...
2. That's not what i'm talking about at all.
3. I've had it happen twice. Where does that leave us?
4. Yes... and?
It seems almost everyone has given you the answer, but you think everyone is wrong. That's fine.
http://www.theaa.com/motoring_advice/safety/car-ty...
http://www.crewetyres.com/newrear.htm
http://www.autoexpress.co.uk/products/total_tyre_g...
http://audi-vw-clinic.co.uk/knowtyres.aspx
http://audi-vw-clinic.co.uk/Documents/2004prod.pdf
http://www.tyreplus.co.uk/tyre-tips.asp#rotate
http://www.great-central.co.uk/page_content/docs/p... (Pages 4 & 10)
http://www.etyres.co.uk/news/tyres-to-the-front-or...
http://www.twtyres.com/pdf_files/newtyres.pdf
http://www.tyresafe.org/news-and-events/detail/mot...
http://www.roadtyres.com/tyre-faqs.asp
http://www.performance-car-guide.co.uk/performance...
http://www.goodyeartires.com/faqs/Care.html#s9
http://www.popularmechanics.com/cars/how-to/424399...
http://www.tirerack.com/tires/tiretech/techpage.js...
And so on.
http://www.crewetyres.com/newrear.htm
http://www.autoexpress.co.uk/products/total_tyre_g...
http://audi-vw-clinic.co.uk/knowtyres.aspx
http://audi-vw-clinic.co.uk/Documents/2004prod.pdf
http://www.tyreplus.co.uk/tyre-tips.asp#rotate
http://www.great-central.co.uk/page_content/docs/p... (Pages 4 & 10)
http://www.etyres.co.uk/news/tyres-to-the-front-or...
http://www.twtyres.com/pdf_files/newtyres.pdf
http://www.tyresafe.org/news-and-events/detail/mot...
http://www.roadtyres.com/tyre-faqs.asp
http://www.performance-car-guide.co.uk/performance...
http://www.goodyeartires.com/faqs/Care.html#s9
http://www.popularmechanics.com/cars/how-to/424399...
http://www.tirerack.com/tires/tiretech/techpage.js...
And so on.
Thanks for the links. I'm still not entirely convinced though, the arguments seem empty and inconclusive. I'm not saying that I know the answers, because I don't, but I'm just undecided on this one. It just seems common sense to me to look at a FWD hatchback's normal tyre wear (almost all at the front) and infer which ends takes the majority of the load, and therefore put the tyres with the best wet weather grip there. In an ideal world I'd like to try a car with tyres each way round on a wet track
Thanks for that. I had a quick look at the Auto Express one and it makes the pointhat the 'theory' had changed because, it says, most people can cope with a front wheel skid better than a back wheel one. Possibly so.
But isn't it the case that in the wet, a front wheel skid is more likely to happen under heavy braking and end with you hitting someone?
I'm stuggling to see how the chance of a back wheel skid (which I've never experienced in a fwd car - been driving 30 years) outweighs lengthening my wet weather stopping distance (which I've had to call on before now) which directly increases my risk of hitting someone.
Interesting discussion, thanks for your input.
But isn't it the case that in the wet, a front wheel skid is more likely to happen under heavy braking and end with you hitting someone?
I'm stuggling to see how the chance of a back wheel skid (which I've never experienced in a fwd car - been driving 30 years) outweighs lengthening my wet weather stopping distance (which I've had to call on before now) which directly increases my risk of hitting someone.
Interesting discussion, thanks for your input.
RobM77 said:
Thanks for the links. I'm still not entirely convinced though, the arguments seem empty and inconclusive. I'm not saying that I know the answers, because I don't, but I'm just undecided on this one. It just seems common sense to me to look at a FWD hatchback's normal tyre wear (almost all at the front) and infer which ends takes the majority of the load, and therefore put the tyres with the best wet weather grip there. In an ideal world I'd like to try a car with tyres each way round on a wet track
Common sense, but wrong I'm afraid. If you consider that the front tyres are permanently trying to spin you off in to a ditch and are only prevented by the rear tyres resisting that urge, would you not want to improve your stability by having the 'grippiest' tyres at the rear? The effect might be relatively small, but when last I saw it tested (by Michelin on a low grip wetted surface) every 'normal' driver managed to spin the car fitted with new rubber at the front and worn rubber at the rear.Yes, in real terms it's probably a statistical outlier and every driver that posts on PH is possessed of l33t driving skilz and thus the normal rules of physics don't apply to them, but I'd always ask myself the question 'do I feel unlucky?'
heebeegeetee said:
itsnotarace said:
3. 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.
3. I've had it happen twice. Where does that leave us?
My car has more tread on the front than it does at the rear, it has summer tyres on all year round, I have increased the thickness of the rear anti roll bar so that it almost matches the front, I have adjusted the camber and toe geometry to give a much more neutral handling bias and I run rear tyre pressures close to what is in the front (34/33). By all your reasoning my car would be an absolute death trap and yet I can still push on (even in the wet) without ending up going backwards through a hedge on fire
heebeegeetee said:
It seems almost everyone has given you the answer, but you think everyone is wrong. That's fine.
I'd say it's pretty clearly divided with arguments both ways. I know people who have 12 year old cars still with the original manufacturer fitted rear tyres on - they don't even bother rotating them, just replace the fronts as they wear out. These people don't crash round every wet corner, maybe it's because they drive appropriately given the road conditions. In short:
Centre of mass behind front tyres. Cornering force from front tyres causes moment trying to create positive rotation of body about centre of mass. Cornering force from rear tyres (obviously acting in same direction as front tyres, else you wouldn't go around the corner) creates moment in opposite direction opposing this. Hence, front tyres make you spin, rear tyres stop it.
If you consider the humble handbrake turn - by locking the rear tyres, you prevent them from generating any cornering force, so any cornering force generated by the front tyres causes the rapid rotation.
Centre of mass behind front tyres. Cornering force from front tyres causes moment trying to create positive rotation of body about centre of mass. Cornering force from rear tyres (obviously acting in same direction as front tyres, else you wouldn't go around the corner) creates moment in opposite direction opposing this. Hence, front tyres make you spin, rear tyres stop it.
If you consider the humble handbrake turn - by locking the rear tyres, you prevent them from generating any cornering force, so any cornering force generated by the front tyres causes the rapid rotation.
itsnotarace said:
1. A bad workman always blames his tools?
2. My car has more tread on the front than it does at the rear, it has summer tyres on all year round, I have increased the thickness of the rear anti roll bar so that it almost matches the front, I have adjusted the camber and toe geometry to give a much more neutral handling bias and I run rear tyre pressures close to what is in the front (34/33). By all your reasoning my car would be an absolute death trap and yet I can still push on (even in the wet) without ending up going backwards through a hedge on fire
3. I'd say it's pretty clearly divided with arguments both ways.
4. I know people who have 12 year old cars still with the original manufacturer fitted rear tyres on - they don't even bother rotating them, just replace the fronts as they wear out. These people don't crash round every wet corner, maybe it's because they drive appropriately given the road conditions.
1. Hey - I'm blaming no-one but myself and never have done. I'm not 'blaming' my Golf with worn rears for spinning straight round on me when i was pulling 3g round my favourite roundabout, i'm just saying it happened. 2. My car has more tread on the front than it does at the rear, it has summer tyres on all year round, I have increased the thickness of the rear anti roll bar so that it almost matches the front, I have adjusted the camber and toe geometry to give a much more neutral handling bias and I run rear tyre pressures close to what is in the front (34/33). By all your reasoning my car would be an absolute death trap and yet I can still push on (even in the wet) without ending up going backwards through a hedge on fire
3. I'd say it's pretty clearly divided with arguments both ways.
4. I know people who have 12 year old cars still with the original manufacturer fitted rear tyres on - they don't even bother rotating them, just replace the fronts as they wear out. These people don't crash round every wet corner, maybe it's because they drive appropriately given the road conditions.
2. Well done you but that's still not the point. And who's to say you're not dog slow? Without competition experience you will be imvso. Btw, those tyre presures are bog standard. Most fwd's i've seen in our garage run same pressures all round.
3. Ah well i can challenge you on that one
. I provided 15 links saying that new tyres should go on the back. If the argument is clearly divided you'll be able to provide 15 links from 'authorities' (as opposed to unsubstantiated personal opinion) to say otherwise, but here's the challenge: Show us 5 before lunch time. I say you won't be able to because the argument is not clearly divided at all. As many of those links state, the average motorist thinks new tyres should go on the front; are you an average motorist? 4. Again, you're missing the point. What you're saying would be like me saying that because i've never made car to car contact it doesn't happen.
Look, classic cars manage just fine without any of the modern safety gear that we all take for granted, and what's more classic car drivers pay the cheapest insurance premiums too. The way you're using your argument is to say that classic cars prove that safety devices don't work, which wouldn't be true.
Modern safety devices do work, but in a perfect world we wouldn't need them, and yes, if we all drive perfectly we'll never need the safety devices in our car. But how many of us don't use seat belts? In my 30 years of driving i've never had to call on a seat belt to save me, so do i need to continue using them? Yes, imo.
So you can be as big a driving god if you like, but what's right and what's wrong remains the same, and if you're putting your new tyres on the front axle then you're doing the wrong thing and that doesn't change no matter how much you want to argue it.
In short, it's entirely up to you: The advice is crystal clear (and is most certainly not divided) but if you want to consider that you know better than everyone, then that's absolutely fine. As we all know, the roads are full of people who think they know best and will ignore advice.
StressedDave said:
In short:
Centre of mass behind front tyres. Cornering force from front tyres causes moment trying to create positive rotation of body about centre of mass. Cornering force from rear tyres (obviously acting in same direction as front tyres, else you wouldn't go around the corner) creates moment in opposite direction opposing this. Hence, front tyres make you spin, rear tyres stop it.
If you consider the humble handbrake turn - by locking the rear tyres, you prevent them from generating any cornering force, so any cornering force generated by the front tyres causes the rapid rotation.
Thanks, that makes sense now Centre of mass behind front tyres. Cornering force from front tyres causes moment trying to create positive rotation of body about centre of mass. Cornering force from rear tyres (obviously acting in same direction as front tyres, else you wouldn't go around the corner) creates moment in opposite direction opposing this. Hence, front tyres make you spin, rear tyres stop it.
If you consider the humble handbrake turn - by locking the rear tyres, you prevent them from generating any cornering force, so any cornering force generated by the front tyres causes the rapid rotation.
StressedDave said:
Common sense, but wrong I'm afraid. If you consider that the front tyres are permanently trying to spin you off in to a ditch and are only prevented by the rear tyres resisting that urge, would you not want to improve your stability by having the 'grippiest' tyres at the rear? The effect might be relatively small, but when last I saw it tested (by Michelin on a low grip wetted surface) every 'normal' driver managed to spin the car fitted with new rubber at the front and worn rubber at the rear.
I accept your explanation of the physics but would ask if the general principle to fit the 'best' tyres on the rear can or should be qualified by "IF the rear tyres would otherwise be less than [adequate]".Take a FWD car that has 2mm tread on front tyres and 6mm on back and let's say that the front tyres wear at 3x the rate of the rear tyres. The owner decides to buy two new tyres. Applying the "best tyres at rear" principle would mean that the existing rears would be swapped to the front and new tyres with (say) 8mm tread put on the rear. Would 8mm tread on the rears offer any measurable advantage over the 6mm of the existing tyres in 'normal' driving?
Put another way, is the ability of the rear tyres to resist the oversteer force generated by the front tyres a function of the 'grippiness' of the rear tyres in absolute terms or of their 'grippiness' relative to the front tyres?
Edited by Observer2 on Friday 10th September 17:49
I take the view that if a FWD car has grippy tyres with say 6mm of tread on the rear, and if new tyres were needed on the front, then it would be fine to fit new (grippy) tyres to the front, and keep them there, rather than swap to the back. So grippy 8mm tread on the front, and 6mm grippy tread on the back would not concern me, as the rear grip demand is likely to be available from the 6mm tyres, and likewise for the front.
With brand new sticky tyres on the front, and barely legal ones on the back, there is the potential for the rear end to let go a lot sooner than the front, for example during wet conditions, with little warning to the driver before an incident.
With half decent tyres fitted on the front, even with less than 2mm tread, I have found it rare to lose grip on the front, but it does happen, and is easy to detect, and correct and plan to fit new tyres ASAP. The first warning that the rear tyres are unable to cope with the demands on them can be a whole lot more exciting to deal with, in my experience.
With driving experience of owning over a dozen FWD cars over 12 years of driving, I have lost front end grip a couple of hundred times I estimate, for one reason or another. I have lost rear end grip three times, and every time resulted in a spin. Luckily no serious damage was caused on two occasions, but once it did. On RWD cars then yes I admit a bit of tail out action has been deliberate on my part.
It might be the case that most drivers explore the limit less than I do, or are better drivers, so they might have less than three unexpected tail out moments in a FWD car in 10+ years, but it can happen, one day, and the surprise factor and difficulty in correcting make it essential to have grippy decent tyres with enough tread on the rear in my experience.
With brand new sticky tyres on the front, and barely legal ones on the back, there is the potential for the rear end to let go a lot sooner than the front, for example during wet conditions, with little warning to the driver before an incident.
With half decent tyres fitted on the front, even with less than 2mm tread, I have found it rare to lose grip on the front, but it does happen, and is easy to detect, and correct and plan to fit new tyres ASAP. The first warning that the rear tyres are unable to cope with the demands on them can be a whole lot more exciting to deal with, in my experience.
With driving experience of owning over a dozen FWD cars over 12 years of driving, I have lost front end grip a couple of hundred times I estimate, for one reason or another. I have lost rear end grip three times, and every time resulted in a spin. Luckily no serious damage was caused on two occasions, but once it did. On RWD cars then yes I admit a bit of tail out action has been deliberate on my part.
It might be the case that most drivers explore the limit less than I do, or are better drivers, so they might have less than three unexpected tail out moments in a FWD car in 10+ years, but it can happen, one day, and the surprise factor and difficulty in correcting make it essential to have grippy decent tyres with enough tread on the rear in my experience.
http://www.youtube.com/watch?v=gPCGnkApnDU
Some serious effort to regain control was needed after a small nudge.
Some serious effort to regain control was needed after a small nudge.
Just thinking about the 5th Gear VBH test again (the tread depth/aquaplaning point is the only real argument I can see in this discussion) - to me, the effective data I can actually see coming out of it is finding the specific speed at which (for a given surface/water depth/car) you can make the tyres with tread a aquaplane while the tyres with tread b don't.
Which doesn't seem very relevant to the real world, how often do you find yourself on a perfectly even surface with standing water, building up on a constant radius circle to find the most speed you can carry before aquaplaning?
Surely aquaplaning is generally caused by a finding a sudden change in road conditions or puddle of deeper water, and unless that depth & speed is within a certain specific range both ends will aquaplane and the 5th Gear test results will be irrelevant.
Exactly what that range is doesn't seem to have been tested, but off the cuff it would seem reasonable to think that if the difference in tread depth is only a few mm the different in water depth that can be cleared would be similar.
Any thoughts from more 'advanced' folk than me?
Which doesn't seem very relevant to the real world, how often do you find yourself on a perfectly even surface with standing water, building up on a constant radius circle to find the most speed you can carry before aquaplaning?
Surely aquaplaning is generally caused by a finding a sudden change in road conditions or puddle of deeper water, and unless that depth & speed is within a certain specific range both ends will aquaplane and the 5th Gear test results will be irrelevant.
Exactly what that range is doesn't seem to have been tested, but off the cuff it would seem reasonable to think that if the difference in tread depth is only a few mm the different in water depth that can be cleared would be similar.
Any thoughts from more 'advanced' folk than me?
Turkey said:
http://www.youtube.com/watch?v=gPCGnkApnDU
Some serious effort to regain control was needed after a small nudge.
Dunno about small nudge, you can see the back wheel come off the ground.Some serious effort to regain control was needed after a small nudge.
GravelBen said:
Surely aquaplaning is generally caused by a finding a sudden change in road conditions or puddle of deeper water, and unless that depth & speed is within a certain specific range both ends will aquaplane and the 5th Gear test results will be irrelevant.
I think in an fwd the rear end will aquaplane far more readily. As I've said, I see the logic of the 'rears' argument, though even having had a 205cti which was alledgedly famous for LOOS, probably driven at a time when my enthusiasm was greater than my skill or experience, I've still not encountered it.
I have had to brake very hard in the wet to avoid an accident a good number of times and been glad of maxium water displacement (= grip) where all the braking is going on, ie front.
Some intersting numbers here http://www.youtube.com/watch?v=zA6MUlVNkLM
I have had to brake very hard in the wet to avoid an accident a good number of times and been glad of maxium water displacement (= grip) where all the braking is going on, ie front.
Some intersting numbers here http://www.youtube.com/watch?v=zA6MUlVNkLM
Sticks. said:
As I've said, I see the logic of the 'rears' argument, though even having had a 205cti which was alledgedly famous for LOOS, probably driven at a time when my enthusiasm was greater than my skill or experience, I've still not encountered it.
I have had to brake very hard in the wet to avoid an accident a good number of times and been glad of maxium water displacement (= grip) where all the braking is going on, ie front.
Some intersting numbers here http://www.youtube.com/watch?v=zA6MUlVNkLM
As you say, all the braking is happening on the front, which makes controlling the rears that much more difficult. If turning is involved as well as braking then a set or rears not generating any grip at all can cause a big problem, as i found out.I have had to brake very hard in the wet to avoid an accident a good number of times and been glad of maxium water displacement (= grip) where all the braking is going on, ie front.
Some intersting numbers here http://www.youtube.com/watch?v=zA6MUlVNkLM
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