SAAB 95/96/97 RPM to speed calculator

The racecar doesn't have a speedometer...

People kept asking me how fast I was going and I would answer "Oh, about 5500 rpm."

*blank-stare*

Not quite a quick change.

Also, theres a great opportunity for tuning the gearing to different tracks if you swap gearboxes with different final drive ratios.

Before doing that though, you want to make an informed decision. Part of the information you need is the available final drive ratios.

Model	Pinion gear teeth	Ring gear teeth	Final drive ratio
SS&R	6	35	5.83:1
??	7	40	5.71:1
96 (3 spd) 95	7	38	5.43:1
grp 1 (SS&R) GT 750 '65 Sport	7	36	5.14:1
'66 MC 850	8	39	4.88:1
Sonett V4	9	42	4.67:1
??	9	38	4.22:1
"Nurburg-Ring"	9	36	4.00:1

If you aren't sure what final drive you have in your old Saab gearbox (were talking V4 and 3 cylinder two-stroke here)... Simply pull the fill plug for the transmission out and shine a light in there. Spin the ring gear around and look on the edge of it until you see a series of numbers. For example, on the ring gear in Dad's Quantum Formula S it had the number 481 scribed into it. Then, stamped into it was the sequence (with spaces): 800373 42-9 9 67.
The scribed number 481 is probably the adjustment tolerance for the ring and pinion gears, which are sold as a matching set. The stamped number 800373 is the part number of the diff set. 42-9 is 42 teeth on the ring gear and 9 teeth on the pinion gear. 9 67 is September of 1967.

Sweet... But now what?

Then you need to be able to convert arr-pee-emm (RPM) into road speed using the final drive ratio you've chosen. Just plug in the appropriate numbers and click the calculate button.

Tire diam:		in =		m
Circumference:		in =		m
Engine RPM:
Differential:	standard 95/96			Sonett or?
# pinion teeth:
# ring teeth:		speeds			speeds
gear ratios diff. 1:		km/h	M/h		km/h	M/h
1 st gear 1:
2 nd gear 1:
3 rd gear 1:
4 th gear 1:

What the numbers mean.

Tire diamter: A 25" diameter is a fairly rough estimate of the standard tire for a vintage SAAB. 24.8" is the actual diameter of the Dunlop "L" Series 500-15 tire that I run on the rear (drive wheels) of the Formula S.
Engine RPM: Put in your max RPM at the fastest point of the track, or whatever the heck you feel like.
# pinion teeth: Under where it says "Sonett or ?" you can change the number of pinion teeth to match whatever you've got. 9 is what the Sonett box has.
# ring teeth: Under where it says "Sonett or ?" and under the # of pinion teeth field, you can change the number of ring gear teeth to match whatever you've got. 42 is what the Sonett box has.

Decision time.

If you have been to a few tracks and know your RPM at the end of the longest straight, you can make a judgement as to whether or not you would like a taller or a shorter overall gearing. Certainly, there will be compromises at many tracks, if not all of them. I could use shorter gearing at Pittsburgh, but wouldn't want to go much shorter at tracks like Summit Point or VIR.