Inaccurate speedometer
#1
Rennlist Member
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Inaccurate speedometer
The speedometer in my Cayenne reads 2-3mph slow. I've compared it with my phone and with my GPS enabled radar detector and it is consistently slow. It is bang on with my 911 and my other car.
I noticed in the TPMS settings that you can specify the wheel size and tire type. I have it set correctly but if I changed it from 19" to 18" would the computer recalculate the speedo for the wheels spinning faster?
Anything I can do or must I just live with it?
I noticed in the TPMS settings that you can specify the wheel size and tire type. I have it set correctly but if I changed it from 19" to 18" would the computer recalculate the speedo for the wheels spinning faster?
Anything I can do or must I just live with it?
#4
Rennlist Member
That is interesting. Mine is shows about 7% fast. That is, at 60mph showing on the speedo, I'm really going about 55-56 according to the GPS.
Last edited by skiahh; 02-17-2017 at 12:38 AM.
#7
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It's a euro law that they can't read slow - only high (and a somewhat complicated formula, allowing for a certain percentage of the speed plus a base offset.) The idea being that no one should be deceived into speeding by a slow speedometer.
If you use tires with the same rolling diameter as the tire sizes specified by Porsche - the "size" (ie - diameter of the wheel they fit on) shouldn't matter. So - changing the size setting on the computer won't change anything. The tire diameter is used by the TPMS to set the range of acceptable pressures.
If it was me - you're under warranty - see the dealer.
If you use tires with the same rolling diameter as the tire sizes specified by Porsche - the "size" (ie - diameter of the wheel they fit on) shouldn't matter. So - changing the size setting on the computer won't change anything. The tire diameter is used by the TPMS to set the range of acceptable pressures.
If it was me - you're under warranty - see the dealer.
Last edited by deilenberger; 02-17-2017 at 12:52 PM.
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#8
Racer
I believe the rule in Europe is that they cannot read low, and on the high side the limit is no more than 110% plus 4kph(2.4mph). Mine seems to read about 7% high, so within that tolerance !
#9
RL Community Team
Rennlist Member
Rennlist Member
You could play around with tire width and aspect ratio at www.willtheyfit.com to find a combination with a slightly smaller rolling circumference which will add a little speed to the gauge for the same distance, or you could leave it be as the odometer is also probably a little low keeping a few miles off the car each year, or at least off the odometer.
#11
Instructor
My 2016 Cayenne S eHybrid reads 4mph slow (came with 21" wheels from the factory). I validated this with GPS as well as a recently calibrated Truspeed S lidar (used by CHP to write tickets)