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wrs986 · 05-28-2019, 02:58 PM

I replaced the 12 year old tires that came with my recently purchased 99 boxster. The wheels are 18” off a cayman. The tires on the back were 265/40/18. I replaced them with what was suggested by this forum and tire rack. I put 265/35/18. With the 40’s my speedometer was 1 mph off. Now it’s constantly 3 below what my Garmin says. It’s not even a percent of the speed. From 20 mph to 80, 3 mph lower. After reading some posts on this forum 3mph seem to be in the “normal” range. The quick fix would be to go back to 40’s when these need to be replaced. Short of pulling out the instrument cluster and sending it to be recalibrated are there any other methods to fix speedometer?

05-28-2019, 02:58 PM	#1
wrs986 Registered User Join Date: May 2019 Location: Kalamazoo Posts: 47	Recalibrate speedometer? I replaced the 12 year old tires that came with my recently purchased 99 boxster. The wheels are 18” off a cayman. The tires on the back were 265/40/18. I replaced them with what was suggested by this forum and tire rack. I put 265/35/18. With the 40’s my speedometer was 1 mph off. Now it’s constantly 3 below what my Garmin says. It’s not even a percent of the speed. From 20 mph to 80, 3 mph lower. After reading some posts on this forum 3mph seem to be in the “normal” range. The quick fix would be to go back to 40’s when these need to be replaced. Short of pulling out the instrument cluster and sending it to be recalibrated are there any other methods to fix speedometer?