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I took my 996 cup to the track yesterday...the main straight is 1 km (.6 mile) long and I was well into 5th gear before the braking zone, yet the digital speedo was only reading about 135 mph. My buddy in his 06 997 cup was hitting 156 mph. Now I don’t believe 10 hp and the squential gearbox is worth 21 mph. Nor would a minor variation in exit speed from the final turn result in such a discrepancy in top speed.
This got me thinking, is the speedo in the cup car calibrated to the larger rear tire of the cup or the smaller tire of the street car? Has anyone checked the accuracy of the speedo against GPS data?
What I can say is that the speedo in our 996 gt3 is very optimistic, meaning 20 to 30 km/h above my gps speedo around 210 km/h. Street car, stock wheel sizes...
What I can say is that the speedo in our 996 gt3 is very optimistic, meaning 20 to 30 km/h above my gps speedo around 210 km/h. Street car, stock wheel sizes...
Yes, I found the same with my 996 GT3 road car. Speedo would read 215 km/h when actual speed according to GPS was 202 km/h. No GPS in the cup car yesterday unfortunately though.
My 996 cup car speedo reads 20km slow at 200kph. This is based on the motec data that is much more accurate. There is no way to adjust this. The tyre size is the reason why.
I took my 996 cup to the track yesterday...the main straight is 1 km (.6 mile) long and I was well into 5th gear before the braking zone, yet the digital speedo was only reading about 135 mph. My buddy in his 06 997 cup was hitting 156 mph. Now I don’t believe 10 hp and the squential gearbox is worth 21 mph. Nor would a minor variation in exit speed from the final turn result in such a discrepancy in top speed.
This got me thinking, is the speedo in the cup car calibrated to the larger rear tire of the cup or the smaller tire of the street car? Has anyone checked the accuracy of the speedo against GPS data?
Many thanks.
Is the 996 cup transmission and final ratio the same as a regular 996? If yes, max speed in 4th gear is close to 124mph and 5th is close to 150mph.
My stock 996 speedo reads precisely 3mph higher than any GPS device.
My 996 cup car speedo reads 20km slow at 200kph. This is based on the motec data that is much more accurate. There is no way to adjust this. The tyre size is the reason why.
This was exactly my thinking, thanks for confirming it. If an 06 997 Cup is doing 245-250 I’d expect a 996 to be around 235-240 at the least. It was touching 220 on the speedo just before the braking zone so your findings are pretty much in keeping with mine. I need to access my data!
Is the 996 cup transmission and final ratio the same as a regular 996? If yes, max speed in 4th gear is close to 124mph and 5th is close to 150mph.
My stock 996 speedo reads precisely 3mph higher than any GPS device.
The cup car final drive is 4.0:1 so shorter than the street car. Also cup transmission has shorter 3, 4, 5 gears than the street car too. I *believe* 1, 2 and 6 are the same as the street car but someone please correct me if I’m wrong. My road car speedo always read higher by about 5%
Only 5th gear? On s 1 km straight, I'd expect you to be in the upper third of 6th
as mentioned, 997.1 cup cars are doing 245-250 km/h (top speed around 280). Even 240 in a 996 is no where near the upper third of 6th? The other 996 cup out there yesterday was just getting into 6th before having to brake for turn 1, but the rev limit on that car was set at 7300 and the owner told me he deliberately short shifted 5th to 6th so to allow an easier down shift to 2nd (by skipping gears) in the braking zone.
996 Cup pulls speed off one of the wheel speed sensors, if it is running the MS 3 ECU (2002 and newer). If you are running different size tires from original, it will not display correct speed.
996 Cup pulls speed off one of the wheel speed sensors, if it is running the MS 3 ECU (2002 and newer). If you are running different size tires from original, it will not display correct speed.
Mine is a 2003. So you’re saying what is displayed on the speedo is accurate provided I’m running the correct tire size? I had a 250/640 on the front and 305/680 on the rear.
05-24-2018, 05:36 PM
My 996 cup is SLOW - speedo accuracy?
