Top Speed Research

[agent_zed]

you should be able to work out the absolute top speed assuming no drag by working out the gear ratios. Since these are fixed the car can only ever achieve a given speed for a given engine.

 

If the car has an engine that red lines at 6000rpm and a 1/1 top gear which is being reduced by a 3/1 dif the wheels are now doing 2000rpm. Lets say you have 205/55/15 which have a rolling diameter of 1850mm (185cm).

[agent_zed]

If we times the rolling diameter by the rpm so 1850mm times 2000 equals 3,700,000mm per min ( /1000 to get metres)

 

so 3700metres per minute

 

x 60 for an hour

 

equals 222000

 

/1000 for kms

 

equals 222kmph

 

convert to mph (thanks google)

 

equals 137.94mph absolute top speed.

[agent_zed]

I think my maths is correct but prob best to check

 

But as said above drag plays a massive part. I'm sure i read that over 55mph drag becomes the main factor, whereas below that rolling resistance is greater.

 

Weight could be argued to play a part as you will get clutch slip with a heavier vehicle.

 

As for drag i read that the sierra was something like 0.35 drag co-efficient and the caterham is 0.7. with 1 being a brick

 

hth

[agent_zed]

got there in the end. I think it didn't like the equals symbol as when i changed it to the word equals it allowed me to post. very weird.

[Bob Tucker]

http://locost7.info/gearcalc.php

 

This saves all the mental shenanigans..

[Guest whiz]

my ST Zero went off the clock last weekend. oops did I just say that

[Snapperpaul]

Weight is most certainly a factor as it is the mass of the vehicle that the power must accelerate

Yes drag is a factor but not the whole picture

[Bob Tucker]

I had one of the first Sierras produced...unfortunately only 1.6

& I have it on very good authority that it was capable of 103 mph, slightly downhill.....oops

[Grim]

Can someone please explain to me how a 2B with a standard Pinto and an MT75 (which I'm not sure was ever fitted to the Pinto but that's no matter), would be as fast or even faster than a Sierra given the shocking aerodynamics of a 2B compared to very (in it's day) slippery Sierra.

 

The drag is based on the coefficient of drag (which for our cars is much worse) and the cross sectional area (which is smaller). So it works out that has more drag than the sierra but probably not as much as you'ld think. The sierra has much more air to shift, albeit that it does it more efficiently.

[richyb66]

I've had our aerdynamicist at work looking at this and he confirmed that the drag / frontal area comparison would even out the high cd of the kit and the greater frontal area of the Sierra.

 

The fact that some kit go faster in 4th gear then 5th suggests that the drag is a big factor because the car needs to be revving higher (nearer peak power) to reach Vmax. This probably explains why my car runs out of steam at about 85mph in 5th (on my private stretch of road) but would possible go faster in 4th.

[keith kelly]

i only have 4 gears and mine gets to 110 at good acceleration and then wont go no further. I did have a ratio calculator some where which let input your diff and gear box and it would work out your speed based on your revs and 110 was about the max for a four speed on a 3.62 diff at safe revs

[philshelton]

i only have 4 gears and mine gets to 110 at good acceleration and then wont go no further. I did have a ratio calculator some where which let input your diff and gear box and it would work out your speed based on your revs and 110 was about the max for a four speed on a 3.62 diff at safe revs

Yours is always in bits Keith :rofl: :vava:

[keith kelly]

True! But it does go on the road sometimes.

[Bob Tucker]

See my previous post..GEARCALC does just that, input wheel size, engine revs, gear ratios diff ratios etc.

[Guest luke2152]

Weight is most certainly a factor as it is the mass of the vehicle that the power must accelerate

Yes drag is a factor but not the whole picture

Weight and acceleration have no bearing on top speed just how long it takes to get there.

Power and drag is the whole picture. Drag can be aerodynamic or mechanical and it could be argued that extra weight puts more mechanical drag on the wheel bearings etc but this is negligible.

This is why turbocharged land speed record cars can afford to carry several hundred litres of iced water to efficiently cool the intercooler - the extra weight has no ill effects on top speed but the cold air increases the power