Maximum speed

StillIC · Postby **StillIC** » Sat Jun 18, 2011 12:17 am

Sorry, that should have read cubed root of velocity.

rjastra2 · Postby **rjastra2** » Sat Jun 18, 2011 3:50 am

StillIC wrote:Sorry, that should have read cubed root of velocity.

Let's work these figures backwards

Corvette ZR1 = 450kw and 330km/h top speed
So at 110km/h it would only need about 17kW (1/27th)
220km/h would require 133kw (8 times 17kw)
Sound about right?

Postby **NitroDann** » Sat Jun 18, 2011 10:15 am

In not sure what ive done here. Are you saying you need 4 times or 8 times more power to do 2 times the speed?

Dann

StillIC · Postby **StillIC** » Mon Jun 20, 2011 10:08 am

Yep, sounds about right. But remember there is an 'overhead' in the power requirement to turn and distort the tyre rubber. It is a pretty linear 'curve' when plotting power V velocity, however....a small percentage of power at 330km/h, a much larger one at 110km/h.

Read it again Dann. Twice the speed = 8 times the power to overcome aero drag.

If 80kW ATW gives you 200km/h (say, my Celica), you can do 100km/h with just 10kW ATW. And you therefore need 640kW ATW to do 400km/h....which is about what a Veyron has.

Scott

Postby **NitroDann** » Mon Jun 20, 2011 12:09 pm

yep your right. Seems I was off by a ^2

Thankyou.

Dann

Postby **NitroDann** » Tue Jun 28, 2011 1:27 pm

So....
A friend of a friend of mine who apparently has a black and white na6 recently sent me a few videos he says he took on his phone regarding the 185kmh max speed question.

He didnt have a long enough road but his car goes from 160-170 in about 2 seconds so it wasnt having any issues at all. It looked like the needle was just going to fly past 180.

Dann

MX5-SP · Postby **MX5-SP** » Tue Jun 28, 2011 1:40 pm

NitroDann wrote:So....
A friend of a friend of mine who apparently has a black and white na6 recently sent me a few videos he says he took on his phone regarding the 185kmh max speed question.

He didnt have a long enough road but his car goes from 160-170 in about 2 seconds so it wasnt having any issues at all. It looked like the needle was just going to fly past 180.

Dann

Your friend used his phone to video his speedo at 170kph!!... :shock:

It sounds like your friendship might be of a temporary nature.

Postby **NitroDann** » Tue Jun 28, 2011 2:55 pm

Why? A phone is easier to tape to the dash than a camcorder is.

Dann

manga_blue · Postby **manga_blue** » Sun Jul 03, 2011 10:50 pm

Logged a 193.4kmh before turn 1 at PI yesterday with a 15kmh tailwind and everything else much the same as usual. That's 7kmh better than anything previous and the first time I can recall having the wind behind us like that. 5th gear took the car from 179 to 193 when usually it gives me no speed increase at all. Nice to see the speedo over 200 too

Certainly demonstrated the impact of wind drag. Ultimately it made little difference to lap times since you've got to beat upwind out of the Southern Loop and Siberia anyway.

It was interesting to apply some of StillIC's formulary. Using Dynamic pressure = 1/2 air mass x velocity squared only gives you 0.22 psi at 180kmh and 20degC. So just a trumpet sticking way out the front really would give you buggar all boost - you must find a high pressure zone somewhere on the car.

greenMachine · Postby **greenMachine** » Mon Jul 04, 2011 12:01 am

manga_blue wrote:Certainly demonstrated the impact of wind drag. Ultimately it made little difference to lap times since you've got to beat upwind out of the Southern Loop and Siberia anyway.

Nope, it did make a difference.

Think about it. Drag increases as the square(?) of speed, that means you are using more power at 200kmh to increase 1kmh, compared to 100kmh. So if the wind is behind you at the highest speeds, you will be going faster (lapping quicker) than if the wind is behind you on slower parts of the circuit. This is magnified by the length of the PI straight, and the high entry speed.

If your lap times did not reflect this, there was something else at work offsetting this gain.

:mrgreen:

manga_blue · Postby **manga_blue** » Mon Jul 04, 2011 12:50 pm

I'm afraid you're right, GM. I did a PB there late in the day. I would have preferred to put that down to great driving rather than wind assistance. :roll:

Averaged about 5 kmh faster than the old PB down the main straight, 2 km slower from Southern Loop to Honda and 2 kmh faster upwind from Siberia to Lucas, probably because of a bit of shelter from the ridge.