Top speed

[bam_bam]

There's some nice Arthur going on in this thread.

[RossDagley]

top speed is irreverent. What does it quarter in?

[PetrolDave]

top speed is irreverent. What does it quarter in?

Quarter times are irrelevant too - a vehicle with huge power but handles like a jelly can do a fantastic quarter time, but will be hateful to drive in the real world.

A better measure is the Nordschleife lap time, that at least takes into account power, drivability and handling (so how the engine and chassis work together as well as absolute numbers).

[bam_bam]

top speed is irreverent. What does it quarter in?

Quarter times are irrelevant too - a vehicle with huge power but handles like a jelly can do a fantastic quarter time, but will be hateful to drive in the real world.

A better measure is the Nordschleife lap time, that at least takes into account power, drivability and handling (so how the engine and chassis work together as well as absolute numbers).

STOP SAYING SENSIBLE STUFF!

[JCviggen]

Of course you're correct, but you can see air temperature and road gradient have very little effect on top speed. Drag is king.

I can't make any pretty graphs on my phone but it doesn't look right to me. Air temp is OK but gradient is way off.

A 20 percent gradient (1 in 5) with a 1700 KG car (published is 1620 which is optimistic and without a driver) is 3335 N as far as I can tell with my smartphone. Car weight in N 16, 671 multiplied by a 20 percent gradient.

So...quite a lot. More than the total aero drag force at 190 mph! Probably why you could not, in fact, go up a 1 in 5 hill in 6th gear as there isn't nearly enough torque available. I realize you used 20 degrees rather than percent but that's a lot more still so I assume that was accidental. I think 20% is about as steep as you'll ever find a road on.

What figures did you use for Cd and frontal area by the way? I found 0.31 and 2.17 sq.m giving 2916 N of drag at 190 mph (85 m/s)

Calculating only the power to overcome that drag I got 2916 * 85 equals 247,860 Watts or 337 metric horsepower (20 deg C and 1 atm)

Real life constraints are the gearing of the RS4 which will be revving really rather high at 190 and well past peak horsepower.

[fredjudd]

Glad you call my graphs pretty.

Without wishing to start an internet argument or sound like a total pr*ck that isn't how you calculated the force required to push an object up a slope. We are only talking top speed here which means the engine power has to effectively a small component of the car mass. This has a huge affect on acceleration but not top speed.

I used;
Cd 0.31
Area 2.52 m^2

Since these are constants when varying air density, wind and gradient for the purpose of this experiment the absolute numbers are less important.

Either way they're fast enough!

[taylora]

if i was going to ever do a top speed run it would of been this morning.
found myself on the M69 about 8am. dry and clear, and 3 lanes of almost completely empty straight 3 lane motorway.
saw about 2 cars over a mile for 15 miles and no lorries, the road goes Leicester to Coventry so is never full. but a sunday morning and its just about begging to be a raceway. i'll never know what it would of topped out at, but i'd of bet it would of made the local paper if i'd been caught!

i grew up in those parts and it wasn't unheard of for a parents car to be borrowed with the express purpose of finding out just how far round the clock it would go on that very road. it wasn't me, but there were a number of witnesses to >140 in a rover 600 something or other. goodness knows how accurate the speedo was, but that was the winning number for that road.
and thats how stupid teenage boys are. in retrospect very glad i didn't have an rs4 when i was 18!

nb, so i settled for a mildly illegal 3.5k rpm in 6th and got left behind by some with bigger wotsits than me....

[Covkiller]

My best ring time is 8:43
Did 9:04 two weeks ago on a lap with more traffic than the M6 on a Friday afternoon.

[boombastik]

My best ring time is 8:43
Did 9:04 two weeks ago on a lap with more traffic than the M6 on a Friday afternoon.

well done with that times, I managed a 9.12 on my 3rd ever lap and repeated it on my 4th looking forward to going back again next year

[RossDagley]

My best ring time is 8:43
Did 9:04 two weeks ago on a lap with more traffic than the M6 on a Friday afternoon.

Very similar to mine - well done mate. I'm at 08:30 exactly (in the B7 RS4) but more proud of sub 10 in the wet. (And a sub 12 in the snow!)

Back there in 10 days time - this time in the B8. I'll probably bottle it though and rent another swift lol

[andyg72]

My best ring time is 8:43
Did 9:04 two weeks ago on a lap with more traffic than the M6 on a Friday afternoon.

Timing on the north loop is bad for your health

[RossDagley]

My best ring time is 8:43
Did 9:04 two weeks ago on a lap with more traffic than the M6 on a Friday afternoon.

Timing on the north loop is bad for your wallet

Fixed.

[JCviggen]

We are only talking top speed here which means the engine power has to effectively a small component of the car mass. This has a huge affect on acceleration but not top speed.

Correct for a level road - where increasing the mass of the vehicle has a negligible effect on top speed contrary to popular belief. Because gravity is exerting a force on the mass 90 degrees to the direction of travel/propulsion. If this weren't true then trains wouldn't be able to get any kind of speed with their power to weight ratio.

However on a slope this changes massively as gravity starts to work against (or for) you and there is no way you can get those speeds on a 20 degree uphill slope. It's called gradient resistance and I'm pretty sure I calculated it correctly http://www.thecartech.com/subjects/auto ... rmulas.htm

This is why you're forced to downshift driving up a steep hill. Overcoming the gravitational force requires increasing the force at the wheels of the car which means shifting into a lower gear where you trade speed/horsepower for an increase in force. You cannot go up a steep hill in 6th gear and 20 degrees is beyond steep.

But yes, we're well into pedantic territory here

You really notice this effect on the Nordschleife as well. Driving downhill towards Schwedenkreuz you easily get up to 150 mph and climbing rapidly but on the longer slightly uphill straight the car is pretty much static at 135 at the end of it.

My 1995 front wheel drive Volvo did an 8:04 by the way chaps

[andyg72]

My best ring time is 8:43
Did 9:04 two weeks ago on a lap with more traffic than the M6 on a Friday afternoon.

Timing on the north loop is bad for your wallet

Fixed.

Ha cheers

[SuprSi]

My 1995 front wheel drive Volvo did an 8:04 by the way chaps

F**k!

Vids or it never happened lol.