After switching to taller winter 19” tires, the speedometer is wrong by about 4-6mph. Is there anything I can do to fix this?
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Speedometer wrong after changing tires? How to fix?
- Thread starter Venom
- Start date
The fix is to use a wheel/tire combination that overall maintains the exact same diameter, within 3%. Using a taller tire REQUIRES a smaller wheel.
EDIT: along with the speedo, you've changed your overall drive ratio.
EDIT: along with the speedo, you've changed your overall drive ratio.
There are many good resources for calculating tire sizes. Here is one. The closer you get to the total diameter the closer the spedometer will be to accurate.
www.tyresizecalculator.com
Tyre Size Calculator - Calculates Tyre Dimensions for Plus Sizing - TyreSizeCalculator.com
Find the perfect tire size for your larger wheels with our Tire Size Calculator (Tire Plus Sizing Calculator) while keeping proper car performance, handling, and a comfortable ride. Don't let a tire mismatch ruin your car's sleek new look.
Gotcha, so basically there’s nothing I can do unless I replace all 4 of the new tires?There are many good resources for calculating tire sizes. Here is one. The closer you get to the total diameter the closer the spedometer will be to accurate.
Tyre Size Calculator - Calculates Tyre Dimensions for Plus Sizing - TyreSizeCalculator.com
Find the perfect tire size for your larger wheels with our Tire Size Calculator (Tire Plus Sizing Calculator) while keeping proper car performance, handling, and a comfortable ride. Don't let a tire mismatch ruin your car's sleek new look.
You could just drive with it and make a mental note that the speedo is off. Both of my BMWs prior to getting the Tesla had the speedometer read low by about 5% when brand new. I kind of think they do it on purpose. It really wasn't a big deal. I basically knew that at highway speed the speedometer read 3-4 mph slow and adjusted accordingly.
I don’t mind the speedometer being off, the issue is that autopilot is currently limited to 80mph on highways (down from 90mph), so my autopilot speed is limited to 74mph on the highway. I’d rather it be inaccurate in the opposite direction since it’s unusable on the highway now haha.
Not sure what you can do about that one. Here in the east we only have a few roads with 70 mph speed limits, so 74 would be enough for me. I usually like to set the speed to 1 or 2 mph slower than the average drivers. I find NOA to be happier if it isn't having to pass too many other cars. I usually set at 72 in a 70 zone and relax.
I don't understand. You say you are limited to 74mph instead of 80. That means the car indicates 80 but you'Re really going 74 when you look at your phone/gps? That would indicate that the wheel does more rotations for the same distance than the original specification. If you kept the same wheel, you have less sidewall than before. You said you had more sidewall, which should have made for a bigger wheel that does less turns, and a car that indicates slower than you are really going.
What are the original and current full tire dimensions?
What are the original and current full tire dimensions?
Here's a good calculator to show differences in tire sizes. Of course it's helpful to use these tools PRIOR to buying any wheel/tire combo
Tire Size Comparison
IamGaryGnu
Endless IBS
FWIW if you "underreport" your tire size, that should reduce your reported speed and more importantly, odometer. just saying.
I ended up changing my wheel size from 19” to 21” even though they’re 19” and now my speedometer seems to be accurate!
Too bad with all the technology available that the speedometer isn't controlled by satellite/GPS.
Important point, the warranty expires faster if you use smaller tires. And they do not look good on the car. I learned that from a friend… who then decided to sell his smaller winter tires he bought by mistake after just two winters and get regular ones. He wanted narrower 225 but forgot to adjust the aspect ratio. And 225 had no benefits in stability, sometimes it slips due to not enough contact area.
Midnightsun
Active Member
There are many places where one looses the GPS signal not to mention tunnels and really bad weather. Speedometer readings need to be available all the time not just when the weather permits.
Using larger wheel diameters will hurt the car in general as the motors need to work harder to do the same work they were designed for, similar to being over-propped on a boat. The bigger the diameter the more damage will be done. Not really a good idea in the long term.
All available choices when ordering on all vehicles when it comes to wheel diameter have the same outside tire diameter regardless if it is an 18" wheel or a 21" wheel.
Good point about GPS not always available!There are many places where one looses the GPS signal not to mention tunnels and really bad weather. Speedometer readings need to be available all the time not just when the weather permits.
Using larger wheel diameters will hurt the car in general as the motors need to work harder to do the same work they were designed for, similar to being over-propped on a boat. The bigger the diameter the more damage will be done. Not really a good idea in the long term.
All available choices when ordering on all vehicles when it comes to wheel diameter have the same outside tire diameter regardless if it is an 18" wheel or a 21" wheel.
I just put 18" with 235/45-18 tires and programed this size tire. But now my speedometer is reading 1 mph more than actual. Prior with the 20" Uberturbine it was dead on. With the 235/35-20 factory tires program it was 1 1/2-2 mph off. Kept switching back and forth.
metroplex
Gearhead
You'd think with Teslas advanced software they'd allow us to calibrate the speedometer or have a function where it would self calibrate upon request by comparing GPS over a set time on a flat road. Not that hard to do.
On Fords made after 2005 with an electronic vehicle speed sensor, you can go in and tweak the ECU to adjust for tire circumference. I think with Fords made in the past 10 years there is a setting in the Body Control Module where you can use FoRScan to adjust it directly. I just had to do this with aftermarket tire size on my 2017 Fusion Sport, and the speedometer is dead even with 10 Hz GPS. In my 2014 SHO and 2007 Mustang I changed the tire circumference in the PCM tuning because I didn't know about FORScan or being able to adjust it in the BCM.
On Fords made after 2005 with an electronic vehicle speed sensor, you can go in and tweak the ECU to adjust for tire circumference. I think with Fords made in the past 10 years there is a setting in the Body Control Module where you can use FoRScan to adjust it directly. I just had to do this with aftermarket tire size on my 2017 Fusion Sport, and the speedometer is dead even with 10 Hz GPS. In my 2014 SHO and 2007 Mustang I changed the tire circumference in the PCM tuning because I didn't know about FORScan or being able to adjust it in the BCM.
airborne spoon
Active Member
i remember my 88 mustang i had to go to a speed shop and buy a few different speedo gears and swap them out till i got it dialed in with the right gear. later on my 2006 mustang i was able to just quickly program my new tire size and the car auto corrected the speedo itself.
But tesla doesn't want us fiddling around in the software
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