Regarding your question at the reference desk about F1 car gearing, here's my calculated, generic gear ratio for top gear at Monza, and how I derived it.
First off, based on past broadcasts showing telemetry data, the fastest speed that an F1 car reaches during the season (and thus the tallest gearing) is found at Monza, where speeds peak at approximately 340 kilometers per hour. Also, according to the FIA Technical Regulations (available at [http://www.formula1.com F1's official site]), two other critical figures are set by the rules--the engine rev limiter is set to 19,000 revolutions per minute, and the diameter of the tyres is set to 660 millimeters.
The basic formula is that you determine the gear ratio by dividing the engine speed by the rotational speed of the tyres. We know what the engine speed at top speed is, 19,000 rpm, but to finish this equation, we need to find the tyre speed.
Assuming that there is no wheelspin involved, every time the tyres make one complete rotation, the car will travel forward the same distance as the circumference of the tyres. Thus, we can figure out the rotational speed of the tyres by dividing the car's speed by the tyres' circumference.
Step one, therefore, is to convert the car speed to use the same units as our known figures--in this case, from kilometers per hour to millimeters per minute. 340 km/h * 1000 m/km * 1000 mm/m / 60 min/hr == 5,666,666.67 mm/min
Next, we calculate the tyre circumference using basic geometry--circumference equals pi times diameter. 660 mm * pi == 2073.45 mm
Now, we use these figures to calculate the rotational speed of the tyres. 5,666,666.67 mm/min / 2073.45 mm/rev == 2732.96 rev/min. Call it 2733 rpm, given the approximations already involved.
One step remains--finding the gear reduction. Divide the engine speed by the tyre speed, all the units cancel out, and you're left with the gear ratio. 5,666,666.67 rpm / 2733 rpm == 6.952, so the total gear ratio on a modern F1 car at Monza, in top gear, would be 6.952:1.
Note that I'm not sure whether F1 cars today use a separate differential gear, or if they use a transaxle that combines the functions of transmission and differential into a single unit; if they use a separate diff, then the ratios in the transmission itself would be much lower, as you would multiply the gear reduction of the differential gear by the ratio in the transmission to get the total ratio. However, the total ratio would remain about the same.
Hope this helps! Rdfox 76 (talk) 05:05, 21 March 2008 (UTC)
:Wow, that was very good. One thing that I'm not understanding is the very last portion. Since a transaxle combines the function of a transmission and differential into a single unit, is it not the same thing as having separate transmission and differential gears when calculating gear ratios from tire rotational speed? For both cases, doesn't the engine speed have to go through both the transmission and the differential gears, the only difference being the location of the two? Acceptable (talk) 20:46, 21 March 2008 (UTC)
::Well, the difference there is that the transaxle uses a single gear to both perform the gear reduction and to act as the differential itself; the conventional transmission-differential arrangement has a separate set of gears in the differential, which generate a further gear reduction. Normally, in a conventional transmission-differential setup, the transmission actually uses a 1:1 gear ratio in high gear, so the total gear reduction is equal to the ratio of the differential (for street applications, typically between 3.5:1 and 4.2:1). The transaxle bypasses this step, so the gears used in it are different than in a transmission-differential configuration that has the same final drive ratios. Rdfox 76 (talk) 04:18, 24 March 2008 (UTC)
