reminds me when i once owned a montego,the previous owner had fitted 14" alloys and guess what happened when i got a pucture?.... spare was a 13" steel rim
Many cars have different sized spare wheels. However, the tyre that's fitted has a bigger side wall profile to make up the difference so you still get the same overall diameter.
|
|
|
We are informed, for good reason, that new tyres, wherever they are fitted, need to be bedded in. This is to remove any moulding fluids etc. Tyres also tend to scrubb off any moulding "pips" quickly and "bed in" to the corner of the car to which they are fitted (suspension/steering movement etc).
Logic therefore says to me that when you drive out of the fitting depot with 2 new tyres on the back that you have
1 rear tyres which need bedding in to remove moulding fluids, and scrubbing in to suspension movement.
2 front tyres which need scrubbing in to their new movement regime.
How that can be safer than this,
1 rear tyres untouched, bedded and scrubbed in
2 front tyres which will need both
is, to be honest, beyond me.
In scenario 1 the rear wheels must surely have a more tenuous grip on the road.
In scenario 2 rear wheel braking stability must surely be better.
I agree that the rear wheels breaking grip is more unstable than the front doing so.
I must say that GWS has my vote.
|
|
I would rather listen to Michelin & the other big tyre companies & fit the new tyres to the back, They do have slightly more money spent on research, testing & experience over the years then anybody on here
|
I would rather listen to Michelin & the other big tyre companies & fit the new tyres to the back,
>>They do have slightly more money spent on research, testing & experience over the yearsthen anybody on here
Me too!
www.honestjohn.co.uk/forum/post/index.htm?v=e&t=36...3
Simon
>>"I also wear my tyres down to the legal limit, none of this changing them when they reach 3mm etc,
>>and I never have any problems.As long as you understand that the tyres are not as good as they were and you respect their performance accordingly, then I don't think that you can go too far wrong.""
All I read does not agree with your approach. In an emergency any less tread than 3mm will most likely see you sailing on in wet weather when you hit the brakes hard even if you " respect their performance accordingly".
I feel sure that will be well received if you are involved in an incident.
see for example
www.rospa.co.uk/roadsafety/advice/motorvehicles/tr...m
"it can be seen that the stopping distances in the wet start to increase dramatically at tread depths of below 3mm."
"RoSPA recommends that tyres are changed once the tread reaches 3mm in depth."
Rospa of course do not make or sell tyres
Independent research performed by the Motor Industry Research Association (MIRA)
www.conti-online.co.uk/generator/www/uk/en/contine...l
"The test results showed that significant increases in stopping distance began to appear when the tyre was worn down to 3mm"
|
|
|
|
Logic says to me that the moulding fluid is worn away very quickly indeed. The pips are neither here or there, again, they are gone in hours. If the suspension is so far out of adjustment that the tyre has to wear in, then you have big problems, and getting the suspension aligned properly is the priority before fitting new tyres.
Logic also tells me that anyone pushing brand new tyres straight after fitting them is probably heading towards the scene of the acident anyway.
The effects mentioned are overcome very quickly - hours of risk - the imbalance in tread can persist until the tyres are next changed - months of risk - , and as such the exposure to risk of an emergency which may cause loss of rear grip is higher.
Number_Cruncher
|
I tend to rotate the tyres round on my car so that they all wear at a uniform rate. Thus when one is ready for replacement then they all are and I end up with a matched set. I also wear my tyres down to the legal limit, none of this changing them when they reach 3mm etc, and I never have any problems. As long as you understand that the tyres are not as good as they were and you respect their performance accordingly, then I don't think that you can go too far wrong.
This also applies to the tyres on my Yamaha YZF-R6. I am lucky to get 3500 miles out of a rear tyre on that and at £125 or thereabouts a time I get every millimeter or wear I can out of it. That said I don't tend to use it much in the wet weather.
|
|
Surely tyre rotation is outdated now-I find my fronts wear quicker than rears,even with RWD,I'd sooner just replace them as needed.
|
Number Cruncher. My rear tyres wear flat. My front tyres wear out the edges as well partially due to turning on to full lock several times a day. The front and rear suspensions are different in purpose and geometry and are not necessarily worn out.
If I rotate the flat partially worn tread on to the front; the first time I go on to lock I do not have the full tread on the road . I agree with Sierraman and other posters as that it will take some time to bed the tread into the different manner in which a front wheel moves in comparison to a rear wheel.
Re. Michelin et al doing the research.....
Why does replacing the rear tyres only suddenly improve the grip and braking performance of the partly worn front tyres?
I definitely agree that having poor grip on the rear is a bad thing.
--
I wasna fu but just had plenty.
|
The part worn fronts will have more grip due to less tread block movement. Try to move the tread of a new tyre with your fingers and you can move the tread blocks 2-3MM easily, now try the same with the part worn tyres.
Saloon car racers that race on road tyres grind off the tread to reduce tread block movement and gain grip.
New tyres get fitted to the rear of my cars.
Its pointless for say Michelin to work to tollerences of 1MM on width and lay of the various rubber compounds and fabrics for the end user to fit a tyre of a different make to the other side of the same axle.
Its also a very good indication of how a car has been maintained, if I saw a car I was interested in buying with 4 different makes of tyre fitted (ie changed as single units) I'd not buy it, has the rest of the car been treated in the same way?
|
if I saw a car I was interested in buying with 4 different makes of tyre fitted (ie changed as single units) I'd not buy it, has the rest of the car been treated in the same way?
Or has he just been unlucky and had some unrepairable punctures?
I've quite often had a puncture, only to find that the local kwik-fit doesn't stock the same make/type/tread of tyre as the old one, or the manufacturer no longer makes it.
|
I've quite often had a puncture, only to find that the local kwik-fit doesn't stock the same make/type/tread of tyre as the old one, or the manufacturer no longer makes it.
I've only had one puncture in the last 13 years and that was repairable.
|
|
|
|
My friend has a Merc E 430 parked on his drive at the moment with rear tyres wider than the front tyres. There are other makes/models with this characteristic, indeed all performance bikes are like it. To be safe, if the front tyre(s) need replacing, should they all be done?
I would suggest that a loss of grip on one tyre on a bike is more "interesting" than on a car.
Michelin can recommend whatever they like, some manufacturers recommend no fuel/oil additives but Millers etc seems to be widely used.
|
>>To be safe, if the front tyre(s) need replacing, should they all be done?
In the case of differing tyre sizes, then it isn't practicable to swap tyres around, and not economic to change otherwise good rear tyres just because you have fitted front tyres.
The point of the advice is to maximise available reserves against dangerous slipping while being practical.
I agree about your point about the motorcycle - although on a bike, it is the front tyre which must be in the best condition, because loss of front grip will take you off a bike quicker than loss of rear grip, which is more benign.
>>Michelin can recommend whatever they like...
Indeed, it is only advice, it isn't law. Thankfully we all have the freedom to choose. In a practical sense, most!! posters on this forum will take a responsible attitude to their tyres, and this really isn't a big issue. I can't imagine that many on here will wait until their tyres are right on the verge of being illegal beofre changing them out. Although I am advocating the engineering good sense of the advice, I am extremely happy that we can all choose our own response to the advice.
Number_Cruncher
|
N C, I was posting from the "devil's advocate" point of view, really. Your engineering sense is correct.
I read somewhere, can't remember where, that in general the average motorist uses a small proportion of the grip available from the tyre anyway.
I must confess that in 40+ years of driving I have never experienced any difficulty with having new tyres fitted at whichever "end" needed them. I have had 2 sets of fronts fitted to the Xantia whilst the back soldiers on with the Michelins it arrived with, 4 years ago. (How long they have been on there I don't know but this time it looks like all 4 will be replaced at the same time. I suppose both ends will slide the same, then) (LOL)
PS all 4 will be the same (Probably Kleber Dynaxters) but the space saver Michelin will still be there, unused, I hope.
|
>>I read somewhere, can't remember where, that in general the average motorist uses a small proportion of the grip available from the tyre anyway.
That is extremely believable.
I think that if you are getting to the limits of your tyres performance on a dry road in summer, then you are probably driving quite dangerously.
On the other hand, I don't think the average motorist is very good at assessing how little grip he has available when conditions are less than ideal. It only takes a cold/wet snap to begin to see tyre tracks leading off into fields via "unauthorised" routes!
Number_Cruncher
|
|
|
>>Why does replacing the rear tyres only suddenly improve the grip and braking performance of the partly worn front tyres?
Where does anyone say that this happens?
Number_Cruncher
|
As I said in the above scenario, if I am losing grip on the front end my preferred solution is to replace those tyres.
I am now being told to have the best tyres on the rear.
So how will that will get rid of my problem of poor front end grip?
If I have wet feet I do not buy a pair of new gloves.
--
I wasna fu but just had plenty.
|
|
I suspect that older tyres tend to harden, if left on in the belief that the fronts are more important. I've changed my mind for two reasons: 1. Michelin advice is likely to be better founded than loose talk:) Ignoring their advice might be damaging in an investigation. 2. A few years ago I nearly lost the rear end of my Golf in the wet, in circumstances where the new front tyres were much fresher than the rears. Probably above 3mm, certainly not near 1.6mm, which is lunacy. Glad I'd had (and remembered1) skid pan training. Advanced driving tells you that you can still make errors, despite efforts not to, and I am no exception.
|
I'm talking first hand experience in my own car which has had around 6 front tyre changes and 4 rear changes in 92,000 miles over 5 years- so not just loose talk. ;)
Very interesting to hear about the experiences of others.
Thanks for all the inputs.
I agree that aging tyres cause a problem and replaced those on SWMBO Mazda with Dynaxers for that reason- the rears ,Yokohama ,were still original at 5 y.o..
--
I wasna fu but just had plenty.
|
I strongly suspect that poor road surfaces and unbalanced brakes (probably 75% of all cars) are far more likely to cause sudden loss of control under heavy braking than having the tyres on the front better/worse than the ones on the rear.
But a simple experiment if it snows.
Find a quiet road and brake hard/steer etc (experiment) with tyres in current set up and then swap them and compare the results?
Then lets see experience versus loose talk versus tyre company statements?
|
|
I was talking about grip in cornering. As was Michelin. Add other factors, in cornering, and it just gets worse.
|
|
And i ought to add, I'd only experiment on a wide open space like a track.
|
If you lose the rear (oversteer) you still you still have steering input and power to pull the car around the bend to correct the slide.
If you lose the front (understeer) how do you regain control? Brake, accelerate or wind on more lock and you still head straight on.
|
Dox, lifting off the accelerator should stop the understeer. Works for me. Unless you are in a Porsche when it can allegedly snap you into oversteer!
--
I wasna fu but just had plenty.
|
How long between lifting off and the tyres gripping? Its not just a case of lifting off, but slowing down to the point that the tyres grip again, by which time you're through a hedge and well into a field.
Watch a FWD rally car on gravel enter a corner on opposite lock ( after de-stabilising the rear into oversteer) and exit on the power. See one understeering or front brakes locked and watch it go straight on into the ditch
|
Fast enough to regain control. But I am talking moderate speeds on public roads on tarmac.Not terminal understeer at extremely high speeds.
Unable to really comment on rallying. But competition cars are surely set up to produce the understeer/oversteer for the purpose to which they are used?
--
I wasna fu but just had plenty.
|
|
Rally drivers are paid to drive on the edge, and practice, practice, practice. Most of us have never even tried geting out of a slide, but front end drift is easier to withstand, as instinctive, untrained repsonse is to lift off, usually restoring grip as GWS says. Rear end loss though requires thought, rapid action and some skill to overcome. What surprised me on the skid pan was how quickly and energetically you needed to twirl the wheel, to keep control. Can't see the mundane standard of driving coping with the thought of keeping the power on, avoiding braking, and steering into the turn without some training. Hence Michelin are being realistic, rather than optimistic about most drivers capabilities.
|
GWS, speed was'nt mentioned, just loss of grip. Lose the front grip at 5MPH on snow / ice / frost /diesel and your a passenger, lose the rear grip and you still have steering, brakes and power application to get you out of the slide.
Nortones2, if a tyre has lost its grip you are on the edge too are you not, whether its 5 or 50MPH.
The new tyres fitted to the rear will have less grip than the part worn now fitted to the fronts because;
The new rears have a coating of mould release agent (usually silicone) that takes a 100 - 200 miles to wear off.
The new rear tyres have a deeper tread and the tread blocks can be easily moved / distorted by the road surface causing lack of grip.
|
|
Have to agree to disagree Dox, but why don't you write to Michelin and point out the error of their ways?
|
Dox,
Funny you should mention ice. My car started to understeer on a right hander on the ice we had before Xmas, I lifted off and car came back on line. I knew the road was icy so admit I was driving pretty gently anyway.
New tyres always grip better in my experience, and am always cautious bedding the tyres in for the first 100 miles.
--
I wasna fu but just had plenty.
|
Have to agree to disagree Dox, but why don't you write to Michelin and point out the error of their ways?
Michelin recommend new tyres to the rear dont they? I'm saying the same are'nt I?
Has no one ever noticed that new tyres have less grip than the old ones they replace, do you all drive like grannys?
|
Costco will only put new tyres on the rear, whatever you say to them, even if the other tyres have only been on for a couple of weeks.
This makes Costco's offer of 20% off 4 tyres a bit odd, because if you always put the new tyres on the rear, you will never need 4 tyres on a front wheel drive car. I beat them though, I swapped the tyres round when half worn, so I needed 4 and got the discount.
|
I know im one of the minority by saying that i always want the best tread on the front of a fwd car, and am not trying to persuade anyone else to, but......
Unless you have tried tyres both ways round I think the comments being made are a little patronising ? Surely it is not sensible to just quote theories etc?
I have tried both ways in the same car over the same surfaces and I know where I want my best tread.
Stick to manufacturers advice is good advice. I just cant personally make sense of it !
But as someone said before we do have our own choice !
And i also agree that you do not have to be driving fast to lose control. An accident where you cant stop at 5 mph (or 55mph) is down to loss of control/bad driving ! If thats because of where your tyres are placed then just think about it ?
|
I think there are some who are mixing up the likeliehood of a tyre skidding, and the consequences of a tyre skidding.
In most cases, a front tyre slipping isn't dangerous. Simple remedies will keep you on the road.
Rear wheels slipping will, in more cases, result in an accident.
So, even if your front wheel drive car does understeer, does loose grip if you over accelerate, can lock its front wheels as the braking force isn't limited, this doesn't make it unsafe. It may be undesirable, but not unsafe.
Losing grip on the rear axle does tend to be unsafe.
Number_Cruncher
|
Whilst I agree with your summary and the difference of tyre slippage versus consequences of.
I have to disagree strongly with understeer not being dangerous.
My reason. A car travels at say 10 mph on snow/ice and steers to avoid a child/object. The steering doesnt happen the child/object gets knocked down. That is dangerous.
The same car, at the same speed on the same surface, mangaes to turn and avoid the child, because the better tread allowed more purchase and allowed steering.
The above is only relevant on substantial tread differences ( I would always recommend replacing tyres rather than risking safety anyway) but if it applies on a substantial difference of tread it stands to reason that it will apply on lesser differences too. This scenario is easily tried in safety by anyone willing to change their tyres when bad weather is around with enough time and room to experiment.
Multiply it by speed, in rain etc at roundabouts, bends etc and understeer is positviely dangerous (imo anyway). I am not saying oversteer isnt either but keeping the steering is far more likely to get you out of danger than get you into it.
But i am not trying to persuade anyone to change the position of their tyres; just to consider it and possibly try it, before telling me that it is better, without any experience to back it up?
|
>>without any experience to back it up?
I don't think it's possible for any of us to really judge the knowledge and experience of any others of us. All we can see and judge is the text we post.
Number_Cruncher
|
I am not trying to "have a go" at anybody but the scenario i tried to describe is way more important than the part you highlighted. Sorry!
I disagree strongly with tyre company advice and I put the tread where I want it. Each and every one of us has that choice; or to follow advice given if without personal experience.
Nobody can refute my illustration, unless they have the experience though. It is easy (relatively) to try it..
I would be very interested in any genuine comment/reason from any tyre expert against it though who could suggest it is safer the other way round with a reason/demonstration to prove it !
|
Yes, understeer is undesirable, and can cause accidents.
The ideal is neutral steering. But, that isn't easy to achieve all the time.
Oversteer is really dangerous, because you have to be skilled and ready to be able to deal with it. If you are skilled, and you are expecting it, yes, you can correct it. But, if you are unskilled, or, if it catches you unawares, oversteer will put you off the road quickly.
So, thee is the desire to acheive neutral steering, but the serious danger of oversteer if you set the vehicle up too close to the threshold. Therefore, most cars are designed with a margin of understeer, and this tyre advice is just a part of the maintenance regime to ensure that this understeer margin is not erroded. The advice we are discussing is a bit like the modern equivalent of the MOT requirement that cross-plys go on the front axle, and radials on the rear if you have a mixed set-up.
As I mentioned in a post above - fitting the best tyres to the rear is only advice, not law. It is your (and my) freedom to put the tread where you (or I) want it, as long as we remain within the fairly lax requirements of the law.
I'm not going to get into a thread whereby we try to out-do each other with our "experience" [please do not incorrectly infer that this means I have none!]. The main point I will make is that experience isn't *always the best guide. In this case, I would argue that the main flaw in relying on experience is that the really dangerous phenomenon is loss of rear grip during an emergency, i.e., an extreme event, not in a controlled, provoked, slide.
* Note: I am not saying experience is *never* the best guide - but it is *sometimes* not valuable above all other forms of information.
Number_Cruncher
|
|
I agree with NC here, but just a couple of points. On snow and ice, tread has little bearing on the matter, I'd suggest, as here the compound is more important. Understeer doesn't mean there is no steering available. Short of complete loss of adhesion, understeer can be corrected readily by instinctive reaction: wind on more lock. To reduce the scope of the issue under discussion, I'd suggest that the advice by Michelin ("for extra safety in unforeseen or difficult situations (emergency braking, tight bends etc) particularly on wet surfaces") is relevant. This is where the natural, untrained response to the need to reduce speed approaching a bend can cause a shift from neutral or understeer to oversteer simply by braking, intensified by lifting the throttle. Given that this sort of event is unusual to most, tyre manaufacturers are sensible to try to encourage good tread depth at the rear, to avoid the unplanned-oversteer outcome.
|
This is not ar argument I want to "win".
I dont mind where other people put their best tread; all I ask is that they have decent tread.
However, poorly maintained cars generally, especially brakes, where probably 75% (or even more?) have unbalanced brakes, are far more likely to cause ends of the vehicle to swap at critical moments. This combined with road imperfections etc makes this a rather futile argument anyway.
But It is virtually impossible to induce oversteer in an ordinary fwd car at any time other than complete lunacy in the middle of a bend at high speed etc. It is highly likely the brakes will cause the car to swap ends, not the tyres. ask any mot station how many cars have balanced brakes? Its not a legal requirement (or mot fail; as long as brakes are within pretty poor limits).
With several years (too many really) of drving all sorts of vehicles I have never (repeat never) experienced sudden, unplanned oversteer ina fwd car. Have driven thousands with brakes that will put you in a ditch way before poor tyres will though. And experienced severe understeer often! And nearly always new tyres on the front makes a big ddifference!
You will not convince me to change where I put my best tyres nor will I change yours. But don't assume that it is because I am ignorant of the differences of tyres.
And a final note regarding driving on snow/ice. try driving on half worn tyre and then put new on and see what difference they make! I think you will be surprised how much difference just tread depth makes; before you even begin to think about compounds, tread patterns, types of tread, etc etc.
|
>>complete lunacy in the middle of a bend at high speed etc.
Indeed, although I would replace the words "complete lunacy", with "emergency scenario".
I agree about your point about imbalanced brakes - I find it amazing that people drive with cars like this!
Number_Cruncher
|
|
I have rather more than several years experience on most types of vehicle, including goods. Be that as it may, whilst driving said goods vehicle years ago, I saw under our noses, a mini swap ends repeatedly as it oversteered. On a bend, in the wet. Pirouetting is the best description. Luckily he missed everything and stayed on the road, so you obviously must try harder. BTW, read the motoring jounos boy racer accounts re lift-off oversteer on recent, well treaded fwd vehicles, e.g Peugeot 205. And here: www.telegraph.co.uk/motoring/main.jhtml?xml=/motor...l
|
Ok, i must try harder! I have actually experienced a spin in an old mini but it was lift off in mid bend at a crazy speed, with a lsd fitted. Not a road example where I have never managed it (and not for the want of trying); Totally different to a normal road set up. used to grass race a mini, and used to use totally bald tyres on the back and that just would not oversteer. Not sure how your example ever did! And as for P205, I didnt think you could get them to step out of line even in mid bend under heavy braking !
The moral of the story from my perspective anyway, is please make sure you have decent tread on all your tyres and put them where you think is best!
|
|
Can't argue with that last comment, about decent tread, all round:) I'm about to replace all four of mine, as the garage swapped them round, so they are all down to 4mm.
|
The Pug 205 & series one 405 will swop ends mid corner if you dont know how to drive a proper handling Peugeot correctly.
Many a 205 has ended up backwards through a hedge on twisty country lanes or worse on its roof.
Dont get me wrong they both have superb handling but there is limits to what the chassis can actually do, ignore the warning signs & go past the limits of the chassis & your then just a passenger.
|
|
|
|
|
|
