Switching from 18's to 19's
06-15-2018, 09:04 AM
#1
Rennlist Member
Thread Starter
Switching from 18's to 19's
I picked up my CD from my dealer yesterday, and I showed him the 19 inch OEM wheels I had bought (same wheels on one of his loaners), and he told me my speedometer would change. I thought that the sidewall change would compensate for that, and thus there would be no change to the speedometer. When Porsche builds a Cayenne, surely they don't build a different speedo based upon the wheel size on the build sheet? Is he correct or no?
06-15-2018, 09:28 AM
#2
Burning Brakes
Your dealer, or whoever you spoke to is just ignorant.
There is a menu in the computer/whatever the hell it is called in our dash display, where we can tell the vehicle what size wheels/tires we are running as well as if they are all season or summer tires. I went from 19" to 20" and told the vehicle what I now have and I'm sure it had adjusted as I have a GPS HUD and the speed is right-on with the GPS speed.
There is a menu in the computer/whatever the hell it is called in our dash display, where we can tell the vehicle what size wheels/tires we are running as well as if they are all season or summer tires. I went from 19" to 20" and told the vehicle what I now have and I'm sure it had adjusted as I have a GPS HUD and the speed is right-on with the GPS speed.
Last edited by BenCD; 06-15-2018 at 08:29 PM.
06-15-2018, 02:46 PM
#3
Racer
Tell your dealer, he is an idiot. Sidewall change will compensate for that.
There are online calculators that will help you choose the right tire size to keep the outer wheel diameter constant. You can usually keep the difference in wheel size within 1%.
There are online calculators that will help you choose the right tire size to keep the outer wheel diameter constant. You can usually keep the difference in wheel size within 1%.
06-15-2018, 03:20 PM
#4
Rennlist Member
Your dealer, however you spoke to is just ignorant.
There is a menu in the computer/whatever the hell it is called in our dash display, where we can tell the vehicle what size wheels/tires we are running as well as if they are all season or summer tires. I went from 19" to 20" and told the vehicle what I now have and I'm sure it had adjusted as I have a GPS HUD and the speed is right-on with the GPS speed.
There is a menu in the computer/whatever the hell it is called in our dash display, where we can tell the vehicle what size wheels/tires we are running as well as if they are all season or summer tires. I went from 19" to 20" and told the vehicle what I now have and I'm sure it had adjusted as I have a GPS HUD and the speed is right-on with the GPS speed.
But he's an idiot for not continuing on to say you can change tire sizes in the vehicle menu, like Ben noted.
06-15-2018, 06:41 PM
#6
Instructor
Why is everyone so concerned about the speedo changing. Do any of your's actually reflect the vehicle's accurate speed, even after selecting the right tire size out of the cluster's menu options? It's a common occurrence these Porsche vehicles that the speedo reads about 5 mph faster than you're actually traveling. There's tons of threads on it here and on Sixspeedonline. Mine is consistently 4 mph higher than actual speed. Always has been apparently. I envy you guys if you've figured out a way to actually calibrate it perfectly. For what it's worth, I haven't found a single instrument cluster repair shop from California to New York that is willing or able to touch these clusters yet.
06-17-2018, 08:41 AM
#7
Drifting
Bottom line, as long as you.....
1) select a correct 19” wheel that fits the Cayenne (bolt pattern, offsets, accommodates TPMS, strength, etc.)
2) select an OEM sized 19” tire w/ correct specs for the Cayenne
3) ensure compatible TPMS sensors are fitted to each wheel
4) make the proper changes to the tire/wheel info via the user interface settings in the vehicle, specifying 19” and the type of tires (performance, all-season, etc.)
....your vehicle will be fine.
1) select a correct 19” wheel that fits the Cayenne (bolt pattern, offsets, accommodates TPMS, strength, etc.)
2) select an OEM sized 19” tire w/ correct specs for the Cayenne
3) ensure compatible TPMS sensors are fitted to each wheel
4) make the proper changes to the tire/wheel info via the user interface settings in the vehicle, specifying 19” and the type of tires (performance, all-season, etc.)
....your vehicle will be fine.
Last edited by CarGuyNVA; 06-17-2018 at 08:43 AM. Reason: additional info
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06-17-2018, 10:50 PM
#8
Rennlist Member
Thread Starter
The 19's I bought are are the Cayenne II wheels (OEM). I like the 19's but now I 'm thinking of going to 20's.....may not be as comfortable as a ride, but it will look good. Making these changes is fun....sort of like a motorcycle. You do all kinds of things to make it your own. I want those exhaust tips that BenCD described in another post.
06-18-2018, 04:20 PM
#9
Burning Brakes
The 19's I bought are are the Cayenne II wheels (OEM). I like the 19's but now I 'm thinking of going to 20's.....may not be as comfortable as a ride, but it will look good. Making these changes is fun....sort of like a motorcycle. You do all kinds of things to make it your own. I want those exhaust tips that BenCD described in another post.
I have the 19's in the Design II wheels and think that they are ok but 20's are better and I can't tell the difference in the ride at all. I'm going to put snow tires on them for this upcoming winter.
My farm-beater.
06-19-2018, 04:06 PM
#10
Advanced
I can't remember which magazine I read concerning speedometer readings, either Panorama or Excellence. Porsche purposely built the speedometer to read two mph faster than your actual speed. Supposedly this helps people keep from receiving speeding tickets. I can attest that my CS speedometer does read two mph higher based upon the radar speed signs I pass almost every day. But, really, two mph faster?! I'm driving a Porsche! Two mph is nothing! LOL 
