[humfrz]

Originally Posted by paulca

Okay, fair point on "indicated" speed. But the stock speedo overreads by around 10%. So his 149 indicated is probably more like 136 actual.

If you don't believe this, look up the mechanical limit of 2nd gear, I believe it is 59.8mph or something similar. Now go and bounce the car off the limiter in 2nd and see what speed it reads, I've seen mine read 65mph. Then check on a GPS.

Wheels/Tyres make a difference, even tyre pressures make a difference. The speedo only counts how many times the wheels go round, via a gearbox sensor and multiply it by the circumference of the tyre. If you put smaller wheels, even by a few mm smaller the speedo will read high. Even worn tyres can add a few percent to your indicated speed. If you changed your wheels and tyres and did not match the sizes exactly to achieve the same total circumference of stock your speedo is now inaccurate. In the UK insurance companies get awful annoyed about this and refuse to pay in some circumstances.

As I worked out on another thread. The difference in horse power between 139 and 160mph is 64bhp! The car needs 264bhp to do 160mph. That is assuming the 139 is it's genuine max actual speed.

You see adding 10mph here or there is not a small thing at top speed. Every mph needs more and more power. The simple rule is, to double the speed you need 4 times the horsepower. Anyone with a basic college education can rearrange that to work out the horse power difference needed to change their vmax by a given amount.

A down hill will not make as much difference as a tailwind would. Air resistance is such a big factor that mechanical drag is all but negligible at top speed.

With that said, in theory with a constant 20 mph tailwind I suppose 150 might be achievable. However finding such a steady wind that would allow the car long enough to accelerate to 150 is going to be very hard to find.

OK.

I challenge you (or anyone else) to do the math with the formula shown in post # 272.

If you accept, please indicate what factors you used for the variables in the formula.




humfrz