I don't think so. It's much like sliding *on* ice which may be more familiar to everyone! Whichever the direction the wheels-on-water are pointing does not lengthen or shorten the aquaplaning. What is lethal in aquaplaning is that during the 'hoovercrafting' the car unresponsive to any form of human input is more than likely to be traveling at speed, or at least more than 48 mph (80 kph).
I'd place a lot of money on the tyre fitters adding about 30psi to each tyre regardless of the recommended pressures.
Correct, theres a standard formula used to determine aquaplaning speed and it is almost irrestpective of tyre design - the major contributing factors are tyre pressure and speed, and to be aquaplaning you have to be driving dangerously fast for the conditions. The main area of fault in most drivers is to try to steer or brake out of the "hover" - when the car touches down again the tyres are at the wrong speeds and/or pointing in the wrong directions which causes further slip or a spin.
So whether you have massive tread or slicks makes no difference to the speed you start aquaplaning at?? Hmm.
Z
Assuming you're within the legal tyre lower limits and normal max tread depth - apparently it makes less difference than you think although obviously i makes some difference. The pressure and speed make the largest difference in the overall equation which would include tread pattern effectiveness. Increasing pressure and reducing speed both reduce AP likelyhood. Same equations are used for aircraft landing speeds/tyre pressures irrespective of tyre choice so as i say - its a general equation but the main factors are speed/pressure.
Whether the tyre of a moving vehicle loses contact with firm ground or not hinges on how fast the water in the foot print of the tyre can be drained away. That heavily depends on tyre tread design. A bald tyre (a slick) relies on the sheer weight to display the water but when it's moving faster than 80 kph this fails and it rises on top of the water film, irrespective of the weight as in landing aircraft* or the dambuster (bomb). When speed falls, the vehicle or bomb sinks. To drain the water as quickly as possible in the foot print, the dimensions of the grooves (and sipes) are of critical importance. For instance, a tread depth of 1.6 mm (min. legal requirement) the tyre will rise on top of the water film (aquaplaning, hydroplaning) at over 90 kph (54 mph). With a tread depth of 3 mm, at which point most Germans will change their tyres (this is from what I read), a correspondingly higher speed is required to lift the tyre off ground. An asymmetrical tyre (or tread) is better (the other half of the channels draining the wrong way are turned around to face the correct direction), at least in theory.
An overinflated tyre is better because the foot print is smaller (less water to displace, and the water columns inside the channels have a shorter distance to traverse before being expunged), but there are other considerations against this strategy (less traction on dry land,..etc.). Tread pattern designs help but there has not been any great breakthrough in recent years (in the manner of the doping of rubber to produce better wear resistance in Michelin's).
So, tread depth and speed of the vehicle are the make-or-break determining factors in the making of the extremely dangerous aquaplane.
*Aquaplaning in an aircraft is not that alarming as it is already flying, gliding or hovering (OK, I've got that now!). Once the speed has come down sufficiently, a proper (safer) touch down ensues.
I'd rather not oversteer in a front wheel drive machine. New tyres on the rear.
Cue a big grin or a wail of fear? :)
It can be fun if you're expecting / aggravating / larking about. But when you're not it can result in a trip to Sketchleys.
Hmm, maybe, maybe not. It reads that you were over-correcting, is all.
Yes, absolutely - the reason why the ass end swung out of line is just because of the new tyre coating. It'll take a few hundred miles for this to wear off in the wet. During this time the car will not be fun at all in the wet. Absolutely no fun at all.
Something very similar happened to me many years ago in that I had new tyres put on the back, it rained on my way home and the car was a handful. I also had many experiences and discussion points, detailed on
Possibly, but it would have been easier to buy the same again.
It'll be down to the new tyre coating, give it a week (actually that'll depend on your mileage and use) and it'll be back to normal...
Perhaps. That depends very much on the driver and the road of course. I had to try reasonably hard to understeer our Ka but it would certainly do it in the dry.
Agreed but there's a flaw here. Once you do start to steer, the rear wheels need their tread otherwise they'll break away. If you have lots more tread at the front, say, 7mm and much less at the back, say 3mm, you may find the rear tyres unable to hang onto the road surface and they'll break away.
This causes a Sketchleys moment.
And the quality of the tyre plus how effective it is in wet conditions.
This effect is _reduced_ if you have less grip at the front end.
It used to be.
I disagree. Under normal circumstances what you've written is absolutely one hundred percent sensible. Put the grippy tyres where their grip is used most often, so on a front wheel drive Fiesta, the front wheels do all of the steering, all of the going and around 80% of the braking effort too. But under normal circumstances the driver wouldn't expect to get anywhere near the grip limits of the car, so, the tyre tread depth is academic.
That's a huge oversimplification of course.
Under extraordinary circumstances, things can get messy if the rear wheels have less grip than the front. Many drivers find it harder to correct a little dose of oversteer in a front wheel drive machine compared to understeer, myself certainly, so it becomes a greater dose of oversteer, then it becomes a proper slide and may finally result in a spin. If the front wheels of a front wheel drive machine are just starting to skid on a wet road at moderate speed, with less weight on the back and less tread depth, the rear wheels are also going to be skidding. Lift off, the the front end bites, the rear end gets light and the tail swings out. If the front runs out of grip before the rear, lifting off may stop the car from skidding and the rear wheels, well they were never skidding in the first place.
Naturally enough, trying the above in a low gear at high speed can encourage the rear to break away...
As I've written, it's under exceptional circumstances where you may need more grip at the back.
For a useful comparison, fit nearly new tyres to the front and on-the-verge-of-replacements on the back. 7mm front, 2mm rear. Then find a quiet roundabout in the rain and just tackle it at ordinary speeds, then gradually (*gradually*) wind the speed up a little, or try some gentle braking mid-way around. You'll either see the ESP / SCS / whatever it's called light come on and you'll lose speed, or you'll encounter a skid.
Absolutely, yes. I get all excited at the prospects of replacing the tyres once the tread depth gets to 3.5mm... :p
Yup. It's all a bunch of marketing hype really...
Cue the cheer from the cheapskates on the back and applause at the better (third) landing... :)
Stupid? You may or may not be in a position to try a car set up with 7mm of tread on the front tyres, 2mm of tread on the back and have a large, quiet wet roundabout to play with... but try it. Then swap it over and try it.
You may be quicker with better rubber at the front right until you exceed the grip levels available from the front. Then you'll be sideways.
But the new tyres were new, thus had that wretched coating on them... they can be lethal in the wet.
Nah it's just because they're new. And possible over-pressure too, possible, although in my experience this doesn't make _too_ much difference.
In a few hundred miles their relative and absolute grip levels will be
*significantly* better.
Big grin, but only because the circumstances were ideal for that sort of antics - no other cars, wide road, no oncoming traffic (until I'd spun of course), sloped kerbs with 20 yards of flat grass behind them on both sides without much in the way of obstacles.
Yes. It was unexpected but managed to avoid needing a dry cleaners :)
I probably was.
Hasn't been too bad since then and I haven't backed off much... still I haven't hit another large puddle yet.
Economics, am now a Costco member and they do the Michelin's for =C2=A350+V= AT and sell Michelins only. The Continentals cost =C2=A385 usually and wear quite a bit quicker (allegedly). I only really consider fuel saving tyres (and these are the two main contenders as far as I know) as am a bit of an eco-warrior.
Going to keep them in place I reckon.
I hope so :)
Peter.
Understeer, yes, but I said oversteer.
Of course. I was assuming the rear tyres still had a reasonable amount of tread, but the more tread you have on the front the faster you can go before you start aquaplaning.
Maybe once you are aquaplaning, but more grip at the front means you are less likely to aquaplane in the first place.
Erm, thats whats I said. :-)
OK, I was assuming that the rear tyres are still in good working order, otherwise get 4 new ones!
Indeed. I've learned a _lot_ about oversteer with a 255 bhp RWD coupe with no traction control! Really makes you appreciate why most cars on the road are front wheel drive. The only time I've ever come close to oversteer in a front wheel drive car (in normal conditions) was with a loaded Focus estate, but then I've never really driven one with worn out tyres only on the back.
Z
Incorrect. Whether or not an aquaplane will occur depends solely on the tread depth and the speed. Grip or no grip at the front doesn't come into the equation.
As the wheel rolls on, more and more footprint-sized quantity of water is slipped under the wheel. This is squeezed out just as fast. The wheel stays in contact with the ground as long as the (water) outgoing rate keeps up with the incoming rate. The problem is that there is an upper limit to the outgoing rate (which is a function of the tread design). The moment the incoming rate (directly proportional to the speed of the car) exceeds the outgoing rate, there is water in the footprint....bang! aquaplane. Grip is nowhere in sight.
Thanks for the valuable contribution. It was really worrying as the mystery deepened and no clear answer was in sight. The OP being not gracious enough to answer my questions for more details to clarify the circumstances under which the accident occurred did not help.
Dang, I must have missed that post (goes back to search...)
Probably about 40-45 mph.
Pretty much full depth. They have three deep grooves running around the circumference of the tyre in the middle, all are about 8-9mm deep. They also have a tread pattern on the shoulders, not much less than that.
Weight distribution was normal.
They're probably about 10% the recommended pressure, having been on the back of the car. Fair bet that the tyre place didn't pump them up.
Thanks,
Peter.
By 'grip' I meant grip due to tread depth. Apologies if I got the terminology wrong.
Z
That's the thing about Usenet. One slip can make you out to be a complete idiot. *cough* :-p
Although for what it's worth and yeah I'm going off topic, it's sadly all too easy to get the older generation mark three Fiestas to oversteer. Their set up isn't great when you start doing something just slightly iffy. This is carried into the mark four Fiesta (and the Puma, and the Ka) but Ford worked hard to tame the chassis. It's harder to get them to oversteer, but not impossible...
It's not uncommon for people to change tyres at 3mm, yes, but it's also not uncommon for people to replace at the limit and keep pairs at 3mm.
Oh yes. It's what happens when you start to aquaplane and the speed at which you're going. I'd rather aquaplane at 40 than at 55, say.
Heh I was implying that it used to be, but not any more...
The above can happen when all four tyres are brand new, but if you rotate your tyres, it's not impossible to have say 5mm on the front and 4mm on the back.
Oversteer in something rear wheel drive is (usually) a lot more predictable than something with front wheel drive. I played about with the Ka's handling on various tracks and airfield days and changed the suspension, wheels and tyres to reduce the snappy tail out moments when you were just a tiny bit careless, but he still caught me out on the circuit. It was hugely satisfying when you were alert enough to feel it start to go and were able to apply enough power / steering input (more or less, usually less) to correct things... also many opportunities to hang your head in shame because you overcooked it *again* heh. :p
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