The Science Behind the Calculator

September 25, 2008 by Steve Wortham

Introduction

I created the 0-60 calculator back in 2004. At the time I couldn't find anything quite like it so I built my own. It's a bit of a toy that I still use to this day. Since I created it, it's been linked to from hundreds of websites and I figure it's about time to explain how it works, why it works, and just what you can and can't expect from it.

How it works

It's a rather simple Javascript calculator that works off of power/weight ratios and rating factors. The idea is this: take sample data from the 4 most important points of analysis (horsepower, weight, drive wheels, transmission type) and then write a formula to best fit the 0-60 calculations based off of that data. So when I started out I tried to make the calculator work for everything from a Ford GT to a Subaru WRX to a Hyundai Elantra. It didn't take me long to come up with a formula that fit quite well for all of these cars. And to my surprise, it only required a small amount of fine tuning after that as I continued to test other cars. And every "normal" production car I tested from that point on was quite accurate according to their published 0-60 times.

Why it works

It's my belief that horsepower, weight, drive wheels, and transmission type are the most important factors.

Some have asked me, "What about torque?" Well, torque is a factor and obviously torque is needed to move the car. But the peak torque number really doesn't tell you much. You'd really need the full torque curve to get much benefit and that would add to the complexity of the calculator. The peak horsepower number, however, tells you a lot. That's because horsepower is derived from torque and RPM, hence the formula: HP = Torque x RPM / 5252.

I'll give you a couple of examples to illustrate my point. A '99 Honda Civic SI is famous for it's high-revving motor but also infamous for its lack of torque. As you may have picked up by now, high-revving motors tend to have more horsepower than torque. In this case the Civic has 160 hp and 111 ft-lbs torque. But, because the motor revs so high, Honda has the freedom to change the gearing accordingly which almost makes up for its lack of torque. In just the opposite fashion, there's the '97 3.8L V6 Mustang I used to have. It had 215 ft-lbs of torque but only 150 hp. It was not a high-revving motor by any means. Those two cars are examples of very different approaches for affordable sporty cars of their time. Sadly though, even though my Mustang was RWD and had much more torque than the Civic, the Civic was actually faster since it had 10 more horsepower and weighed less.

When is it inaccurate?

There are plenty of scenarios where you can find inaccuracies. Gear ratios are a big factor, of course. Some cars can get to 60 mph in one shift, some in two shifts, or there's some like the Ford GT that can get to 60 in 1st gear. But grip is perhaps the biggest issue. The calculator isn't going to do so well with extremely high-horsepower cars or high-horsepower cars with skinny tires. The old Corvette Sting Ray is a good example of that. Back when they had the 427 in that car, its puny tires were so over-powered it was ridiculous. So if you put the parameters for that car into the calculator I'm sure you'll find the result a bit optimistic.

But as I said, it is a toy. I find it helpful to get a vague idea of how fast my project car ideas would be if I ever built one, or how much faster my Subaru will be after shedding 100 pounds. I hope you can find a similar use for it yourself. Enjoy.