Back in the days before our phones did everything for us except actually make telephone calls, before the interwebs put the entirety of human knowledge on our desktops, even before we could buy a pocket calculator at the dollar store, there was the slide rule. These devices were the constant companions of the engineers who put men on the moon, and variations on the idea of a mechanical analogue computer found their way into all sorts of specialized uses.
For a large part of the history of flight, the E6B circular slide rule was in every pilot’s flight bag, and even racers had their own “dream wheels” that could calculate RPM from drag strip trap speed, gear ratio, and tire diameter, or estimate elapsed times based on known weight and horsepower (or vice versa). The name “dream wheel” comes from the fact that thanks to often over-optimistic estimates of horsepower, the results from those calculations could be a bit… fanciful.
Still, they were useful tools for coming up with the right gearing and tire size, and it’s fun to play a little bit of the “what if I put a 100-shot of nitrous on my car?” game. The modern day equivalent can be found on Nitrous Express’ calculator web page, where you can calculate rearend ratios, figure out tire diameter based on width and series, and find RPM versus road speed for any combination of tire diameter and gear ratio.
But best of all, it’s an online dream wheel – Plug in weight and horsepower, and it will estimate your quarter mile time, or stick in your actual trap speed or ET and car weight over the scales, and it will come up with an estimate of how much power you’re making.
It might not be totally accurate, but it’s fun to play with. Plug in the numbers for your own car and tell us how close (or not!) it is…