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Old 05-28-2019, 02:58 PM   #1
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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?
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Old 05-28-2019, 03:30 PM   #2
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It's normal and there is no way to change it.
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Old 05-29-2019, 06:29 AM   #3
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Quote:
Originally Posted by wrs986 View Post
After reading some posts on this forum 3mph seem to be in the “normal” range.
The "normal range" is the speedo reading 3 - 4 mph high, not low.
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Old 05-29-2019, 06:45 AM   #4
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Originally Posted by BoxMann View Post
The "normal range" is the speedo reading 3 - 4 mph high, not low.
+1

Who needs a speedo anyways except my wife. Every time we drive I have to reminder her that the speedo displays 25mph over. We aren't going 95, we're only going 70.

I so rarely look at the speedo that it doesn't bother me anymore.
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Old 05-29-2019, 09:10 AM   #5
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In 2003 the digital speedometer was moved from the bottom of the center tachometer to the bottom of the speedometer on the left, making it more difficult to look at. I generally keep my phone in a RAM mount on the center of the windshield just above the dash with Waze open and use that for my speedometer.
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Old 05-29-2019, 09:44 AM   #6
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Originally Posted by kk2002s View Post

Every time we drive I have to reminder her that the speedo displays 25mph over. We aren't going 95, we're only going 70.
LOL !!

I gotta remember that one.
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Old 06-01-2019, 08:23 PM   #7
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The dash speedo is merely a suggestion and heavily influenced by tire wear and tire choice. If you *must* know your precise speed +/- 2mph, only trust a GPS receiver.
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Old 06-01-2019, 10:44 PM   #8
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my 99 2.5 tip has a difference of 5mph over compare to phone speed.
Tires are all stock sizes per front hood sticker.
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Old 06-02-2019, 04:36 AM   #9
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Quote:
Originally Posted by ndfrigi View Post
my 99 2.5 tip has a difference of 5mph over compare to phone speed.
Tires are all stock sizes per front hood sticker.
My 99 tip is also 5 over.But I drive off of the tach so ?
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