mk3's and rain

[gtimportfanatic]

does this answer ur question?

rolling on some of the shittiest tires can be.. i bought the car like that and i didnt think to change em til i got rims.. 205/55/16 in the front and 215/50/16 in he rear.. sucks

 

[SideWinderGX]

I only go out in the rain if I have too.
And if it is raining, even if it is light, 70 is pretty much my max, and almost 0 throttle, its just not worth having a tree in your passenger seat.

Why the hell are you going 70 in crappy weather?

rolling on some of the shittiest tires can be.. i bought the car like that and i didnt think to change em til i got rims.. 205/55/16 in the front and 215/50/16 in he rear.. sucks

:cry: That really sucks...not even raining that bad. Tires are important lol.

 

[jdub]

Although it is obvious why tire pressure is important in not hydroplaning, why is it the determining factor? Wouldn't....something else haha, maybe like water depth/temperature/tread thickness play a bigger role?

I'm not arguing with you, I'd just like to get more info on it

Like I said, standing water, road condition (grooved or not) and tread condition do play a role. Tire pressure is the primary thing the operator (you and me) can control, assuming the tires are good.

The basic formula was derived from NASA aircraft test data. On commerical aircraft, the tire pressures are in the 200 psi+ range for exactly this reason.

 

[IJ.]

I was out very early in the am doing some data logging runs and was doing 100 mph in a fairly heavy downpour, gave it a nudge and it came on boost and spun the rears

You could see the "OHHH SHIT I'M ABOUT TO DIE" moment on the log file.

That was on my old gt3540r which hit so hard the car was close to undrivable in the dry (see vids in my sig)

Since then I've changed ECU's and gone to DBW Traction Control to prevent this sort of thing ever happening again.

 

[Nick M]

It is all about the tires. And not driving an old Fox 3 5.0 Mustang.

 

[IJ.]

I had Falken 451's with 98% tread...

 

[SupraMario]

Why the hell are you going 70 in crappy weather?

70 is the speed limit on the highway....and I said 70 is my max, even in light rain. I've got new tires on my car. BTW did you not catch the part about only driving in the rain or bad weather when I have too?

 

[easternguy2005]

Good tires are like insurance I always think. Cause if something happens unexpected the better tire is most likely to save the car. I watch the supra's ass in the rain more than any other girl's.

I had to stop once for a light at high speed and my mind had immediately looked for a "out" like the grassy median valley to my left and hit the brakes. The brakes stopped me amazingly fast with any problem. I have confidence to stop, but not to accelerate in the rain.

 

[vas85]

When I first got my car on the 225's I'd light up first 4 gears if I leaned into boost but that i'd only ever try on a straight flat highway.

Currently even with 265's on the rear it still has a tendancy to break traction first 3 gears if I'm on it but common sense prevails... no point in doing stunts unless you're at a racetrack...

 

[LilMissMkIII]

I had brand new Falken 275s on the rear in some torrential rain on a freeway, and even going 60kph, she was sliding a bit

 

[honestabe]

The last time I gently touched my gas in the Supra in the rain I just spun my tires (and I have wide ass sticky SOB's that are superb in the rain). Just be careful Drew, the rain fucks up your handling abilities like ice.

Adam

 

[mattman]

Im running Cooper Zeon ZPT tires all new. Got about 9 inches of rubber on the road on the rears. I think there great in rain but im also not boosting. The only time I go sideways is when im trying

 

[suprageezer]

I only buy tires made for the rain since any cheap ass tire does half way decent when dry it's those few days a year when my Goodyear F1' s give me what I need to feel comfortable while driving in the rain. It's not my car I'm worried about in rain it's all the people driving 30K cars with 30.00 tires at 80mph that scares me. I increase my air pressure to 40psi when driving in the rain for better traction, something I've found from experience works wonders with my F1's, but they get better traction at 32 psi when it's dry.

 

[Wiisass]

Something you guys need to understand...vehicle weight has nothing to do with the speed hydroplaning occurs.

A tire hydroplanes at 9 times the square root of the tire pressure. At 35 psi = hydroplane speed of ~54 miles an hour (9 x 6 = 54).
With 65 psi = hydroplane speed of ~72 mph (9 x 8 = 72). This is for a smooth surface highway.

What does affect the hydroplane speed is tire tread and condition of the highway. With good tread and/or on a grooved road, water is channeled away...the speed is higher as a result. Standing water decreases the speed where hydroplaning occurs.

At first, I thought you were crazy. Then I started reading the NASA test report. It was long and kind of hard to read, but you are right, or close, kind of.

The actual equation for the speed in mph is 10.35 times the square root of the inflaction pressure. You use 9 if you want the speed in knots. But this is only for smooth or closed path tires that allow for no water escape and on a surface with standing water. So unless you're running slicks, it's pretty much worthless.

With tires with water escape channels it changes everything. It will depend on vehicle weight, tread design, tread width, amount of water, inflation pressure, etc.

Wider tires are less resistant to hydroplaning than skinnier tires. A lighter car might be easier than a heavier car. Different tread designs will greatly affect hydroplaning as well as the amount of grip available in the rain. There's a lot of variables.

But all I know, is you guys need to learn how to drive. It's not hard to drive in the rain. You just can't be a moron.

 

[jdub]

LOL...you're right, it is in knots
Actually, aircraft tires are not exactly "slicks"...they have grooves that also channel water. Standing water is not an accurate term...of course you have to have water on top of a hard (in this case) concrete surface. The tests were done with 0.10" water iirc. The big difference is car tires are better at it at low speeds (low as compared to airplanes) and it's due to the tread design. Which I acknowledged.

The weight of the car has little (if any) impact as to when the tires will hydroplane. Since this came from aircraft, I'll give you an example:

An A320 has a normal landing weight in the 90,000# range...it's tire pressure is 200 psi. It hydroplanes at 127 knots.
A B747 has a normal landing weight in the 450,000# range...it's tire pressure is 205 psi. It hydroplanes at 129 knots.

In any case, it gives you an idea of what to expect...it's not hard and fast. I mentioned the conditions that have the biggest effect. What you can do is inflate your tires close to max pressure if you have to do a road trip in the rain...the point? It will increase the speed where hydroplaning occurs.

 

[arizzle]

i loved running my stock 5spokes w/ some 98% BF's , loved them in the rain and when i installed my 18s my rear tires are just useless in the rain as they are dry. im running Kumho's Mx's 275/35/18 and Kumho supra712's up front which are nice a sticky up front.

now me saying that the tires are slippery, its all about how you drive and your habits. dont take your bad habits when its dry out to the wet and raining days. when it starts to rain some people decide to drive like they would when its a nice sunny day. SLOW DOWN!:aigo:

 

[Poodles]

Last I knew wider tires where easier to hydroplane...

I run Kumho SPT's and never have an issue in the wet. Get some good tires or stop driving like a tool...

Good example of how good my tires are is going down the highway and hitting a large puddle that would usually suck you in, I go straight through it like it's not even there...

 

[Wiisass]

LOL...you're right, it is in knots
Actually, aircraft tires are not exactly "slicks"...they have grooves that also channel water. Standing water is not an accurate term...of course you have to have water on top of a hard (in this case) concrete surface. The tests were done with 0.10" water iirc. The big difference is car tires are better at it at low speeds (low as compared to airplanes) and it's due to the tread design. Which I acknowledged.

The weight of the car has little (if any) impact as to when the tires will hydroplane. Since this came from aircraft, I'll give you an example:

An A320 has a normal landing weight in the 90,000# range...it's tire pressure is 200 psi. It hydroplanes at 127 knots.
A B747 has a normal landing weight in the 450,000# range...it's tire pressure is 205 psi. It hydroplanes at 129 knots.

In any case, it gives you an idea of what to expect...it's not hard and fast. I mentioned the conditions that have the biggest effect. What you can do is inflate your tires close to max pressure if you have to do a road trip in the rain...the point? It will increase the speed where hydroplaning occurs.

Right, but the ribs are closed path, like I mentioned. It's what the test report says as the application for a rule like that. There are also a couple assumptions, but it's not too important to get into them as long as we aren't trying to use this rule and apply it to cars.

Weight of the car have everything to do with it. What do you think inflation pressure means in the very simplified equation. They're using inflation pressure as an approximation for the cars weight at that corner divided by the contact patch area of the tire.

All I'm trying to say is that, even though these cars weigh more than a lot of planes, that equation doesn't apply.

Increasing inflation pressure to a lot higher than it should be because you think it will increase your tires resistance to hydroplaning is not a good idea. There are a other reasons that you shouldn't do that if you want grip in other directions. And you should know better than saying something like that on here.


Arizzle, do you have your tires confused? MX's are awesome tires in the dry and decent in the wet. And I thought 712s were crap.

 

[jdub]

Right, but the ribs are closed path, like I mentioned. It's what the test report says as the application for a rule like that. There are also a couple assumptions, but it's not too important to get into them as long as we aren't trying to use this rule and apply it to cars.

Weight of the car have everything to do with it. What do you think inflation pressure means in the very simplified equation. They're using inflation pressure as an approximation for the cars weight at that corner divided by the contact patch area of the tire.

All I'm trying to say is that, even though these cars weigh more than a lot of planes, that equation doesn't apply.

Increasing inflation pressure to a lot higher than it should be because you think it will increase your tires resistance to hydroplaning is not a good idea. There are a other reasons that you shouldn't do that if you want grip in other directions. And you should know better than saying something like that on here.

Arizzle, do you have your tires confused? MX's are awesome tires in the dry and decent in the wet. And I thought 712s were crap.

First of all, I was talking in the context of when a tire hydroplanes...not the overall suspension dynamic that will make a car lose traction on a wet road.

Second, you are wrong...tire pressure has everything to do do when a tire hydroplanes and weight doesn't mean squat. Care to explain why a 450,000# plane hydroplanes at the same speed as a 90,000# airplane? The physics applies to cars as well...lower inflated tires provide a larger patch area (as you said). This larger area is the same as having a larger water ski...it will "pop" to the water surface at a lower speed. Once that happens, there is no friction with the road...you become a water ski.

Third, I did not say to over inflate tires...I said you can take them up close to max pressure. If you are doing a long road trip in the rain, you will increase the speed the car hydroplanes and you'll save gas too. From a performance standpoint, it's not a good idea to leave them that way. But guess what, we can actually change tire pressure to match road conditions for a trip.

BTW - where do you get "these cars weigh more than a lot of planes"...I think I was talking about an Airbus 320 and a Boeing 747? You know, the plane you could put a couple Supra's each in the cargo holds (with room left over) and still carry 300 passengers.
The plane I happen to fly

Get your facts straight before you talk down to me.

 

[Wiisass]

Right, but the equation your quoting, only applies to smooth or closed pattern tread tires. Meaning NOT tires that are on cars not including slicks, but since this is about tires on the street, those would not be included anyway.

Oh and almost forgot, it also only applies when the standing water depth is greater than the tread depth. At the time of the study, there wasn't much data on hydroplaning when the water depth was less than the tread depth.

Tire pressure is only in that equation because of the assumption that weight on the tire divided by area of the contact patch equals tire pressure. So by increasing tire pressure, you are reducing the contact patch area. That's the correlation, that's the assumption, that's as far as it goes.

If you want to provide where you got that data on airplane hydroplaning, I'm sure I can tell you why they're both the same. I'm going to take a guess and assume that they aren't using the exact same tires or number or tires. And I will also guess that the ratio of contact patch area to weight is the similar for both.

I know you didn't say to over inflate the tires, but you should also know, and I'm not talking down to you, that not everyone on here always thinks before they do things. I could just picture someone reading that, seeing that it's raining, bump all their tire pressures up to 60psi and then crash their car. Just because one of the SME's said that they could. But sure, if you're going straight and never turning at any kind of speed, then do whatever you want, I wouldn't suggest it though.

And I never meant to talk down to you. I knew I shouldn't have even said anything and let everyone think what they want, but sometimes I can't help it.

All I'm saying is that the equation does not apply to automotive tires. There are some common principles, but it's not a direct application. But with the tread designs and water evacuation and all that other fun stuff that gets introduced when you're talking about normal tires on car, it gets a little more complicated than just saying that it's the inflation pressure that will tell you when a car will hydroplane.

For example, take two tires, one wide, one skinny, both on cars of the same weight and running the same inflation pressure, so both will have the same overall contact patch area, but different contact patch shapes. The wider tire will hydroplane before the skinny tire. This is because it is much harder for the water to evacuate from the center of the contact patch due to the greater width.

If you're interested, here's the report:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19640000612_1964000612.pdf