Originally Posted by steve_the_greek,Dec 8 2004, 07:50 PM

It really bugs me when I hear "Car X has got stacks more torque than an S2000, so it must be faster". It shows a lack of understanding of torque, power, rpm and gearing, so let me explain ...

Torque is what provides acceleration. Power is simply torque x RPM. Torque at the crank - which is what mfrs quote - is pointless, it's what's at the wheels count. Think about it, why does the Z4 not blow the S2000 away when it's got 50% more torque ? Why are diesels so slow when they've got so much torque ?

Before we go any further, it's important to understand the importance of the gearbox in all this. A gearbox converts between torque and RPM. If your gearbox halves the torque, it will also double the RPM and vice versa. Remember cycling ? If you're using the big cog at the back, for the same RPM at the pedals, you'll go slower, but with less effort (torque) required than if you use the big cog at the back - faster, but more effort required.

So, how about an example. Take a diesel with 244lbft of torque (e.g. Seat Ibiza TDi PD Cupra ) that redlines at 4500RPM (just a guess here, but peak power is at 3750RPM). Also take the S2000, with its 153lbft, redlining at 9000RPM.

Now, most cars are geared so that you need to change up to second at 30-40, and 3rd at ~ 60, etc. So, in 1st, each of our gearboxes is converting whatever the engine puts out at its redline to whatever it takes to spin the wheels at 30mph which is approximately 400RPM.

The Ibiza is gearing down from 4500RPM to 400RPM (11.25 times), which multiplies the torque up from 244 to 244 x 11.25 = 2745lbft AT THE WHEELS. The S2000 is gearing down from 9000RPM to 400RPM (22.5 times), and the torque goes from 153 to 153 x 22.5 = 3442lbft. Less torque at the crank, but more at the wheels - see ?

Now I've deliberately simplified things here. As we know, the VTEC kick only appears half way through the rev range, so that 153lbft isn't always available. Its poor low rev torque explains why it's relatively crap at traffic light racing unless you drop the clutch.

A true picture of an engine's capabilities requires you to look at not just the headline torque and power figures, but the whole torque vs RPM graph. In the real world, it's the area under this graph that counts.

Originally Posted by dreamer,Dec 8 2004, 10:48 PM

Ok before anyone starts on the usual lines of - but it's proper driving that's fun, how a car handles that makes it etc., anyone who knows me, knows I am not out for straight-line-speed, this is just pure curiousity about a straight line....

Oh and hood speed

Originally Posted by Jamies2k,Dec 8 2004, 10:49 PM

Didnt you see the hood speed race on top gear? The S2000 won hands down