Cyclone Posted July 9, 2012 Share Posted July 9, 2012 So the width of the tyre alters what depth of water is required to cause a car to aquaplane... So when comparing cars and talking about what speed they might aquaplane at it's also important to consider how wide the tyres are and what depth of water will be required as this could vary quite significantly between vehicles. Link to comment Share on other sites More sharing options...
Obelix Posted July 9, 2012 Share Posted July 9, 2012 So the width of the tyre alters what depth of water is required to cause a car to aquaplane... So when comparing cars and talking about what speed they might aquaplane at it's also important to consider how wide the tyres are and what depth of water will be required as this could vary quite significantly between vehicles. Yes. No. When comparing cars and their *propensity* to aquaplane then tyre geometry is very relevant. However, as soon as you have reached the depth of water necessary to actually start aquaplaning for then the only thing that matters is speed and tyre pressure. Basically it goes... Is the standing water such that I can expel it from the sipes in the tyres? If yes - then all well. Have I reached the limit for expeling water through the sipes? If so, I have to push the water round the sides of the tyre. If I have a thin long contact patch then it's easier to push it round so I can deal with more water Now once I'm accelerating water out of the way I have to consider aquaplaning. As long as the dynamic pressure is less than 9*sqrt(typre PSI) it's impossible for the water to force under the tyre and lift off the contact patch. I can alsways force water out of the way - if necessary by accelerating it forwards Once I reach the aquaplane speed however the excess water will deform and lift the contact patch and slip under it - and I've lost contact with the road surface. Link to comment Share on other sites More sharing options...
Cyclone Posted July 9, 2012 Share Posted July 9, 2012 Indeed, so any conversation about how likely a given vehicle is to aquaplane is meaningless unless you also know what amount of water is needed to cause the aquaplaning, otherwise you never know whether you're driving safely or not. Link to comment Share on other sites More sharing options...
Obelix Posted July 9, 2012 Share Posted July 9, 2012 Indeed, so any conversation about how likely a given vehicle is to aquaplane is meaningless unless you also know what amount of water is needed to cause the aquaplaning, otherwise you never know whether you're driving safely or not. Not really. If you are under the aquaplaning speed for the tyre pressure you can never aquaplane regardless of the water depth so hat's of quite considerable use. I could have grotty part worn tyres but as long as I have them at 30psi I know I wont aquaplane at 40mph. Link to comment Share on other sites More sharing options...
Cyclone Posted July 9, 2012 Share Posted July 9, 2012 Indeed. But I don't want to have to drive at 40mph just because it's a tiny bit damp, so I need to know whether my car will aquaplane in 1mm of water, or 10cm of water, I can then decide whether it's safe to drive > aquaplane limit for my PSI. Link to comment Share on other sites More sharing options...
Obelix Posted July 9, 2012 Share Posted July 9, 2012 Basically look at the volumetric area of the sipes in the contact patch. That will show you the amount you can push through the sipes and you can extrapolate that onto the road and see how much standing water you can expel through the sipes. Eg - sipe depth of 8mm, covering 33% of the contact patch - you can cope with 2.5mm of water. As the tyre wears down of course, you can cope with less. With more water you have to push it around the tyre. As soon as you start doing that you will be into the realms of fluid dynamics and thats quite complex to deal with. 10cm though will induce aquaplaning on any car know of if you are going fast enough. We once tried to test the theory to see if would hold up at the limit. We found a nice artifical ford - about 10 meters across and 1.5 meters deep that is used for offroad testing landrovers and trucks. Nice shallow entry and exit. It's perfectly possible to skim over that in a Focus at 60mph and exit the far side - if done right the front of the bonnet and bumper never even gets wet. Enter it too slow and as soon as you drop below the aquaplane speed the front digs in and vehicle flips. It's not recommended for casual experimentation.... Link to comment Share on other sites More sharing options...
DT Ralge Posted July 9, 2012 Share Posted July 9, 2012 This has got to be the best-informed thread I've ever read on SF. If only I could truthfully claim that I have followed and could repeat the information contained within it with confidence! I will save a recap for later when my head doesn't hurt so much. Link to comment Share on other sites More sharing options...
Cyclone Posted July 10, 2012 Share Posted July 10, 2012 Driving on the wet road could be dangerous because road becomes slippery That's not even a close approximation to a summary of the discussion, aquaplaning isn't to do with water acting as a lubricant (although it does). Link to comment Share on other sites More sharing options...
Mmrraww Posted July 10, 2012 Share Posted July 10, 2012 "Floor it"? Wow, sounds fun. What tread do you have on your tyres,though. What are you driving FWD, RWD, 4WD, tank? Have you tried it with cruise-control engaged? Do you accelerate all the way through or ease off (or is that "chicken"?) Are you choosing to do it on the straight, on a road with or without camber? How deep does the puddle need to be for real fun? At what point does it become less fun and more dangerous - have you tried it with muddy water in a ford, for instance - have you worked through all this or is it more fun when it is still a Russian Roulette moment. Why not make it real fun and take your hands off the wheel ... (don't try this at home, folks ...) Maybe you fancy water-skiing, then? (A recent delegate's daughter claimed it wasn't her fault that hitting a puddle sent her through a hedge - maybe she doesn't have your skills of controlling your chosen vehicle through a puddle/ford/lake?) Or maybe you are driving that tank and you just fancy being pulled for "driving without reasonable consideration for other road users"? (whether there are any pedestrians around or not, how does a PC know you wouldn't do it if there were some?) That's quite some interrogation there Well, for a start I've already mentioned I don't do that when others are around. How could i get pulled for doing it if nobody is around to witness it? Link to comment Share on other sites More sharing options...
Cyclone Posted July 10, 2012 Share Posted July 10, 2012 I dont think most of the posters have hit a flood on the road. It is dramatic. You need to be a good driver to copoe But a bad driver for it to happen. Link to comment Share on other sites More sharing options...
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