ADOGNY

Why did that chicken cross the road Rob?

Mr. RS

I would be interested if anyone has varified their speed with a GPS system or the like as I am unsure as to what the margin of error is when you start getting to big numbers.

193MPH by the way, absolutely rock solid and still going...

GTGTGT

So, I am impressed that people have taken there cars to the limits! Although I am waiting to get my GT3 in the next month (it is somewhere in production), I have taken my 2002 C4S into the 160's quite frequently.

As a follow up question - are people concerned about their tires? I have heard of xraying tires to ensure that there are no blemishes.

What precautions should be taken before driving your car at 190 mph?

GuyR

Precautions.........

I'm running on a 2 mile+ runway in a month or so and aim to hit the rev limiter in 6th in my GT2.

The preparations shall consist of:

1. Checking the tyre pressures.

2. Turning off the radio.

3. Asking the passenger to get out.

Seriously though, most times you run that fast are momentary opportunities on the right road, so you invariably just hope the car is OK. Best not to do sustained speed above 180mph and avoid corners, since its high speed laterall loads that damage tyres (hence why so many blow-outs occur on tests at high-speed ovals).

P.S.

Indicated 190mph in dry in GT2
Indicated 180mph in wet in GT2
My best is 199mph on GPS in Skyline GTR R34 with 700bhp.

Bentley

Make sure you have 'Y' rated tires before you hit those speeds!

MetalSolid

How long does it take the GT2 to stop from 197mph...?

Bentley

Negative acceleration [deceleration] figures can be ROUGHLY determined using the '1.6 Formula'. To utilize this racing tool merely multiply the negative acceleration [in miles per hour] by 1.6 to determine the APPROXIMATE stopping distance. For example, 70 to 0 times 1.6 gives you a stopping distance of 112 feet in your Porsche. 197 to 0 times 1.6 would give you a stopping distance of up to 315 feet!
There are MANY variables to consider when using this GENERAL TOOL: mass of the vehicle, size and shape of the car [aerodynamic drag], condition of rotor and pads, brake fluid, condition and size of the tire footprint, road surface, wind, temperature, altitude, etc.
The '1.6 Formula' does give a street racer a indication of how much distance to allot if something goes wrong. It is very useful in E & E driving.

Steve Conley

197mph to zero in 315ft?! You would have to scrape your face off of the windshield if you stopped that fast.

I am an engineer that failed physics, but I can tell you with certainty that braking distance relative to speed is not a linear relationship. Maybe the 1.6 formula refers to some other parameter?

bob_dallas

I strongly concur (not about you failing physics ) - it is most definitely NOT a linear relationship and 315ft is way too short, but I am too tired to exert much effort disproving. I trust there will be more banter on it by the time I awake in the morning anyway. I did, however, pick up the R&T that's sitting on my desk to give a reference point.

GT3 braking from 60 - 119ft
GT3 braking from 80 - 207ft

GuyR

Theres no way its linear, from basic physics since kinetic energy is the product of speed squared. Also during the 1st second of deceleration from 200mph you will cover much more distance than the first second of deceleration at say 20mph, so I'm afraid that is BS.

Lets put it this way by the 1.6 rule you would stop from 1000mph in 1600 feet, but since at 1000mph you are doing 1,466 feet per second, assuming linear deceleration (not true but I'm just making a rough point), your average speed from 100mph down to zero is 500mph ie 732 feet per second. To stop in 1600 feet would mean stopping from 1000mph to zero in just over two seconds - I don't think so.

I've down full speed stops in previous cars from about 200mph and you need a lot more than 315 feet, more like 600-800 feet.

Bentley

You gentlemen apparently suffer from selective reading! You state that the 1.6 Formula is pure linearity which it is not. Let me repeat my exact words so your selective interpretations may hopefully be adjusted:

"There are MANY variables to consider when using this GENERAL TOOL: mass of the vehicle, size and shape of the car [aerodynamic drag], conditions of rotor and pads, brake fluid, condition and size of the tire footprint, road surface, wind, temperature, altitude, etc.
The '1.6 Formula' does give a street racer a indiction of how much distance to allot if something goes wrong. It is very useful in E & E driving."

Those of you who have studied Physics should certainly understand that the MANY variables of this GENERAL TOOL mentioned do NOT promote linearity at all but gives " 'a indication' of how much distance to allot".
By merely focusing in on the name some of you gentlemen have missed the point, unfortunately.

bob_dallas

OK Bentley - you've dug a hole for yourself and no amount of arrogant, belittling, superior attitude is going to dig you out of this one. Just admit it - you were so far off that you can't explain it off.

I don't believe anyone here suffers from selective reading. but perhaps you do... I've pasted your message below just in case.

You state that you can make a rough determination by multiply the negative accleration (in MPH) by 1.6 to determine approximate stopping distance.

First - since when was ACCELERATION measured in MPH? MPH is a measure of SPEED, not acceleration.

Secondly, a straight multiplication factor implies a linear relationship - even if it is an approximation you are still implying that there is a linear relationship and that it's the same relationship from 20MPH or from 200MPH - this shows a complete lack of understanding of Physics as Guy also pointed out.

Third - you do make an allowance for other factors that could affect it but those variables do not have any impact on the basic formula - it's still a fact that it's not a linear relationship regardless of if every one of those factors was equal or perfect.

Fourth - you say it's an approximation that a street racer can use if something goes really wrong...? Picture a wall in front of you, you are doing 197 MPH and you have 315 feet to stop - would you even see the wall when you are covering close to 288 feet per second?... even add in a 25% margin of error...hell - add a 100% margin of error...boom

Lastly - do a quick calculation for us... calculate the time and G forces for negative acceleration from 197 to 0 in 315 feet. Ouch.

Come on...Even a good scientist/engineer can admit when he's wrong.

Bentley

T2-T1 Divided by D = velocity is what you were trying to say?

bob_dallas

I calculated the G force for deceleration from 197 to 0 in 315 ft. 4.114G - in the reach of F1 cars (I believe) but way out of reach for most cars, racecars, etc.

BTW, a slight apology - I was a little harsh in my prior message but I still stand behind all my points.

bob_dallas

Just another interesting data point - if my math is right.... Stopping a 3000 pound car from 197 to 0 would require the brake system (and aerodynamic drag to a small extent) to absorb 3,900,304.5 foot pounds of energy.