can't complain, great "rubber"

 

i runnin

215/45/17 front
255/40/17 rear

615s run wider than the average tire

 

Dont confuse the subject


Grassroots Motorsports is racing them in the rain .When they compare tires they are comparing 10ths of a second . While trying to push the car to its limits . I am sure when it is raining Jim is not trying to beat the land speed record

We are talking about the streets here with some weekend auto-xing I am sure . I try to get my car to hydro every chance I get and being only 2000lbs would be easier than the S .When I got my first set I too thought they would suck in the rain . I am more than pleased with their performance . Also I will put it up against a SO2 in the rain anyday ....... Much better , you will not have the twitchy ass the S has in the rain with SO2's

 

I don't know... Jim drives pretty quickly.

 

255 might be to big as you dont have the most perfect offsets .

might want to stick with 245's .

might want to search thread widths

 

Are they better than S02s in the dry?

 

When I had to go to court for my accident. I was going to use the formula for hydroplaning. But it didn't help my case.

MPH = (9 * (√PSI)) * 1.15077945

If your running the same tire pattern it shouldn't matter how much your car weights it's how many psi your running. The more you run the less contact patch you have the faster you can go in the rain. Again there are other factors too. The actual specific gravity of the fluid that you are driving over. How deep the treads are etc...

Scott your probable able to run some really low PSI with the width of the tires you have on your Miata.

 

twice the width of the factory's and yes 28psi

Which by your statement would increase my chances of Hydroplaning . So that alone should attest that the tires are fine in the rain

That formula I would assume is just a basic formula to test tires , by not having the car weight in the formula gives them a control to test all tires .

From what you say it is all about surface area , and I agree but weight is still a factor . Thats where the MPH will change per Vehicle . To get the same tire to hydro between to different vehicles will take two different speeds .

Think of it this way if weight was not a issue keeping something afloat you would be able to get a weight of a 30ft boat to float or plane across the water on a jet ski hull . Wont happen unless you can get the speed up fast enough . But by saying weight is not a factor then technically if the jet ski can plane the water at 10mph so shouldn't the 30ft boat mass. I am no engineer, but that's my theory anyway

Other things that can contribute to hydroplaning is whether or not you are on the throttle or coasting , which is not in the formula either . If you hit the water at the same speed coasting than you did under power , you increase your chance of hydroplaning because you can stall the tires rotational speed and its ability to shed water .

not arguing here , just voicing my thoughts


Kev , I agree I don't think it would of helped your case . Posted speed limit is if road and weather conditions allow set speed limit (sunny , dry , traffic ) I believe the law states you should be in control of your car at all times and should not be driving beyond those limits dependent on conditions . Does not mean you were speeding or messing around . But I have been to court enough to know that they like that argument and they say it with a yes or no option only .

 

Hard to say as I have not put them head to head on the same car. I have never had the chance to run the two in a auto-x and compare the differences.

I auto-x on the 615's now , but different car , and I leave them on as my daily street tire . On the street I dont think you would tell the difference as you are not driving the car past its ability's as you would on the track or local auto-x

Two pros of the 615 are they are better in the rain and they cost half the price .

They were designed to run in the dry as the weekend club racer tire . But seeing that they are DOT legal you see more and more on the street .

 

This is the same formula that airplane pilots use when it's raining out. It is very accurate.

Your car weighs 2000lbs and your running 28psi in each tire. That means your contact patch per tire is 17.85 inch^2.

A S2K weights 2800lbs and they are running the same 28psi in each tire. The contact patch per tire would be 25 inch^2. (40% more surface area)

I would usually run between 31-32 psi in my S. The contact patch per tire was only 22.6 inch^2. (Only 25% more surface area)

In order to run the same PSI in a S2000 you would need a lot more rubber than what you are running on your car. Say your tires are 195 width and S2000 Would have to be running 275 width tires. A 25% (s2k @ 31 psi) increase would be 245 width.

See how it has everything to do with PSI and not just weight. Again PSI is determined by weight.

Same thing works with your 30ft boat vs Jet Ski. There weights are way different but there surface area are proportional to there weight.

I'm not an engineer but I DID stay at a Holiday Inn Express!