jelliotlevy

Maybe someone can help me. I am trying to get estimates of road speeds in the various gears. The brochure gives all the gear ratios, but the calculations seem to come out wrong. Example: they say that 6th is 0.81:1, with a 4.1:1 final drive ratio. Given the 225/50*16 rear tires (works out to 811 revolutions per mile for the rear wheels), I get, rounding off a bit, 2700 revolutions per mile in 6th gear, or 2700 rpm at 60 mph. The tach looks more like 3100-3200. Somewhere, in my other poking around, I found a web site that refers to the S2000 also having a 1.16:1 primary gear reduction, whatever that is. Applying an additional factor of 1.16 to the revs/mile in 6th gives me 3125, which seems to more correctly match my speedometer observation. Am I right? If I am, then what is the so-called primary gear reduction.
If I have this basic number correct, then I can also get estimates of mph in the lower gears near redline. Using that additional 1;16:1, I seem to be concluding that 8000 rpm occurs at 40, 61 and 84 mph in 1st, 2nd and 3rd respectively. I know that when you are accelerating briskly, you need to watch the tach rather than the speedometer, but it does help to know what the corresponding speeds are, if for no other reason, speeding ticket avoidance.
Can one of you super wrench-heads help me with this bit of gear theory?

Tanqueray

Josh did work on this and provided this handy spreadsheet:
http://hackforfood.com/s2000.xls

RedY2KS2k

I can't vouch for the accuracy, but one Car and Driver roadtest listed the following mph/1000rpm and top speed for the various gears:

mph/1000 top speed
1st 4.8 43
2nd 7.3 65
3rd 10.1 90
4th 12.9 115
5th 15.5 138
6th 18.5 146 Their observed top speed. Peak torque is 7500 rpm, peak
power at 8200. This represents about 7900 rpm. As
speed increases, drag (force slowing car) increases and
torque (force accelerating car) decreases after 7500 rpm.

Please don't start a flame war over the top speed number. It's what one magazine tester observed on one car.

I'd run the numbers on my calculator, but I don't know where to verify the exact number of tire rotations per mile for the rear tires, so I'd only be duplicating your work.

However, 3125 rpm * 18.5mph/rpm would be 57.8 mph. By the chart above, 70 mph should be 3,780 rpm, which is seems about what I remember it being in my car on the freeway.

cmnsnse

The tranny has a Secondary reduction of 1.16:1

Secondary because its at the output stage, the mainshaft with your primary drive gears is 1:1 with the engine.

jelliotlevy

Josh did work on this and provided this handy spreadsheet:
[url]http://hackforfood.com/s2000.xls
...............
That Josh is an absolute genius. His numbers match mine exactly, when I change his driveshaft ratio of 1.2 to the 1.16 value which I had found. Very handy spreadsheet, since you can put in whatever engine rpm you want, and whatever tire size you want, and can adapt it to any car for which you know the tranny ratios. As I said before, that Josh is an absolute genius!!

stockae92

based on Josh's spreadsheet ... :
Max speed in different gears

The Reverend

You all owe me so big. I made you all a gear calculator:
My gear calculator

Here is a link to stock gear ratios:
S2000 gear ratios