Lowest Speed for Hydroplaning?
 

What's the lowest speed at which you've ever hydroplaned? Not on slicks, but rather on street tires.

Yeah, yeah, I realize there are several factors that combine to lead up to this type of event. But in general, on a street-driven car on street tires, what's the lowest speed at which you've felt that "oh bleep" feeling of disconnect from the tires skipping along the water surface?

For me, I think it was about 50-55 mph.

That sounds about right.

water hydroplaning occurs at 9X the square root of the tire pressure; roughly.

reverberated rubber hydroplaning is a different dynamic.

I've noticed it above 55 mph just like stated in the drivers manual (if I remember it correctly from 30 years ago).

The old rule of thumb I learned from an engineer is simple.

The square root of your tire pressure times 10 is the speed you would hydroplane if the water is deeper than the tread.

The easiest one to calculate is 36 PSI Square root is 6 multiply bt 10 and bingo 60 MPH.

That is one reason big 18 wheel simis with tires running 90 PSI can blast bast you in the rain.

It is not a hard and fast rule but a good guide. If it is raining much at all I slow down to 55 maximum.

9 x square root of tire Pressure for typical (dynamic) hydroplaning. I'm not aware of a published formula for reverted rubber (steam) hydroplaning or viscous (thin film) hydroplaning.

Disclaimer: it's been a while since I went through the Gleim or Jeppesen books on this stuff so someone (preferably another flyer or CFI) check me but this is what I recall.

I've hydroplaned twice...once in a downpour on an I-95 bridge in south GA (no where for water to go) at approx 55...fortunately, I had both lanes to myself to regain control and no other traffic. Once in my SC400 at approx 60 around a gentle curve...(probably more oil than water on the road)...One and a half spins across a grassy median coming to rest facing oncoming traffic. I was just along for the ride on that one...just damn lucky both times. Each could have easlily been "the one" :(

Never put that much thought into it. I don't think I have ever hydroplaned in my F-350. It has 235 85-16's with a little over 5000# on the front axle and 85psi in the tires.

Not that I don't appreciate the engineering input, but the question wasn't: What's the theoretical speed at which one would hydroplane?

Rather, for those of us who have actually hydroplaned in a car, what's the lowest speed at which that occured? I'm just asking out of curiosity (which is why I don't mind the theoretical stuff, though it doesn't answer the question).

I've had worn fronts lose it while accelerating at about 45MPH. Providing the road went straight, I could go faster, steering wheel wasn't worth much. I had to be very calculated based on the banking of the road how fast I went. Rears had more tread, and the fronts were plowing some of the water away. I looked at the tires the next day, and ordered a new set for the front.(Was a new to me car, that is now my parts 944)

Tire contact patch, width, and tread shape will change it quite a bit. On my skinny wheels and tires, I've never hydroplaned my '44. On my regular, or fat sets, with decent tread, its around 50-65MPH depending on how deep the water is.

Slowest though, was apparently drains that couldn't handle it on the roads outside down town. The road dipped down a few inches, and all of it was water. No grip to slow down at all, aside from when my car finally sunk to bottom. I was already going slow because of conditions, so I was in conditions that felt like I "hydroplaned" for a few seconds at sub 30MPH. Brakes did nothing either from getting soaked, that was awesome at the next stop light right after. :\

Not that much different than lubrication regimes...

http://forums.pelicanparts.com/uploa...1359581654.jpg

I don't know how fast they were going... would imagine 35-40... or what condition their tires were in, but I once had two women coming at me across a paved median in a small car.

It was during a downpour on a four lane and they were in about 3 inches of water coming down a 4-6% grade. It looked like they were trying to use the front tires as rudders.

I was in the left lane, saw it happening, and just accelerated past them... the water wasn't that deep on my side. Looking in my mirror, I saw them finally come to a stop halfway into my lane.

Extremely tire and weight dependent question.

My experiences in a 2900 lb Boxster on:
Worn NT-01 tires- 35mph yikes!
Hankook RS-3s- 55mph
Michelin PS2s- 65mph

3500lb Lexus RX 330 on Yokohama A/S tires- 80mph+ (never got there)
5500lb Chevy truck on Bridgestone A/S tires- 80mph+ (never got there)

I guess you could say hydroplaning speed varies widely.

I'm trying to get my mind around the influence of tire pressure on hydroplaning. At first blush it would seem that a highly inflated tire would provide less surface area than an under inflated one and that a bald tire would provide more surface area than a grooved one...but maybe thats it...maybe its about the surface area? The weight is the same but if you reduce the surface area with grip asperities or increased hardness than you increase the force per area of contact thus requiring less residence time of the surface in order for the water to develop a film? Is that it?

If so, then ride with spiked tires in rain ( while tearing the crap out of the road) would be near impossible to hydroplane .

Ok, thanks guys...I think I now understand. You just witnessed a monkey learning to use a twig to snag termites! ;)

Around 45-50mph with heavy rain and bad drainage in 1965 Corvair, factory steel wheels with 205/60-13 "bargain" tires.

Around 45 mph in a 1962 Corvair back in 1968. Scared the ****te out of me as the car spun off the highway.

There is also a temp factor. You can hydroplane most easily around 36F. This isn't an black ice issue, but water viscosity. You can also "hydroplane" more easily on mud.

At 30 in a Chevy Vega. Oily, greasy wet road. Nearly hit a tree.

A friend of mine has a Viper he autocrosses. He was driving home on his DOT rated autocross tires when the rain started. He said it was the most terrifying drive in his life. The rears would spin if he gave it any gas at all. The fronts would not handle 30 MPH. He just idled over to a gas station and waited for the rain storm to pass.

As I understand it, lbs per square in. of surface area determines hydroplane velocity along with tread design and the ability to shed water quickly. I can feel this when running different size front tires. A 255 R-comp will lift off at much slower speeds than a 225 R-comp. A 205 A/S tire will keep road contact at much higher speeds.

We had a downpour at one of our DE events in SoCal last year with lots of standing water and it turned into a hydroplane test lab. R-Comp tires were completely useless but quality street tires were revealing. We could charge down the back straight at 70mph, the front tires would lift off, and as long as you made no sudden moves, the car was pretty directionally stable at full plane. As we approached a corner, gently adding brakes increased the effective weight on the front, the tires made contact and you could make the corner only to lift off in the next straight. It was a pretty wild experience and I learned a lot about the hydroplane threshold that day.

Very interesting! I looked it up and it sure does thicken (like many fluids will) when temp drops, the fact that it may provide an increase in hydroplaning makes sense too...provides more body so to speak?

BTW - I got the below graph from this website - its pretty cool, I've used this in the past ;)
Engineering ToolBox

http://forums.pelicanparts.com/uploa...1359648501.jpg