Speedometer

[regachoz01]

i just changed from 18” to 19” wheels and I also just found out that I also need to recalibrate my speedometer? Any tips on how to do that?

Sponsored

 

[BEERCHAMP]

i just changed from 18” to 19” wheels and I also just found out that I also need to recalibrate my speedometer? Any tips on how to do that?

I put 20"s on from 19"s, my speedo is 1 1/2-2mph off, but my ESCORT Redline Radar detector reads the correct speed. I'm ok with that and don't plan to recalibrate over 1 1/2/2mph difference.

 

[cactus_kid]

I wouldn't worry. The error will be in your favor. I've checked using several GPS apps.

 

[m3incorp]

Plug in your original rear tire size here and your new rear tire size to see the new speedometer reading.

https://tiresize.com/speedometer-calibration/

 

[m3incorp]

That depends. Going from a 235/50R18 to a 345/35R20 would cause the speedometer to read 5 mph slower than actual speed.

My tech called himself doing me a favor by updating the calibration in my speedometer to fit my larger wheels and now my speedometer reads 6 mph slower than the actual speed. Not good when driving at that 15 mph above speed limit threshold here in Georgia where the ticket becomes and "excessive speeder".

I wouldn't worry. The error will be in your favor. I've checked using several GPS apps.

 

[ORRadtech]

That depends. Going from a 235/50R18 to a 345/35R20 would cause the speedometer to read 5 mph slower than actual speed.

My tech called himself doing me a favor by updating the calibration in my speedometer to fit my larger wheels and now my speedometer reads 6 mph slower than the actual speed. Not good when driving at that 15 mph above speed limit threshold here in Georgia where the ticket becomes and "excessive speeder".

Our "super speeder" law is not as simple as 15 over. What it actually is is over 75 on a two lane road or over 85 on any road or highway. So you could actually be 30 mph over on a 55mph highway and not get a super speeder citation. Further, the agency who issued the citation only gets whatever fine their court imposes. The super speeder fee ($200) is separate and is paid to the state DDS. You get that fine/notice in the mail a couple of weeks after the citation is settled in court. And, oddly enough, there are no additional points on your license for the super speeder citation, just the extra $200.
As for the speedometer being off I believe I've read that the car has the ability to self correct within certain small differences. Or a dealer can adjust it correctly for you. Or if you're willing/ able to use Forscan it can be corrected in there. I know I've read the instructions on the Forscan mod on this forum.

 

[m3incorp]

I was referring to what the DA told me when I went to court last month for speeding.

Interestingly he told me that you do get points and reported to insurance when you receive a super speeder ticket. I will try to stay away from that so I won't have to personally find out which it is

I have not come across anyone that actually had their speedometer self-correct, so can't comment on that. I do agree 100 percent with your last two sentences. My dealer adjusted mine using the wrong values for "tire rpm" and caused my speedometer to go from reading 2 mph lower than actual speed to reading 6 mph lower. If they were not over 2 hours away, I would have them go back and make the correction. I doubt if my local dealer will do it without charging me, since it was another dealer's mechanic mistake.

Our "super speeder" law is not as simple as 15 over. What it actually is is over 75 on a two lane road or over 85 on any road or highway. So you could actually be 30 mph over on a 55mph highway and not get a super speeder citation. Further, the agency who issued the citation only gets whatever fine their court imposes. The super speeder fee ($200) is separate and is paid to the state DDS. You get that fine/notice in the mail a couple of weeks after the citation is settled in court. And, oddly enough, there are no additional points on your license for the super speeder citation, just the extra $200.
As for the speedometer being off I believe I've read that the car has the ability to self correct within certain small differences. Or a dealer can adjust it correctly for you. Or if you're willing/ able to use Forscan it can be corrected in there. I know I've read the instructions on the Forscan mod on this forum.

 

[17Magnetic5.0]

It’s pretty easy to do with forscan. There should be a spreadsheet somewhere that shows how to do it.

 

[Rick#7]

Our "super speeder" law is not as simple as 15 over. What it actually is is over 75 on a two lane road or over 85 on any road or highway. So you could actually be 30 mph over on a 55mph highway and not get a super speeder citation. Further, the agency who issued the citation only gets whatever fine their court imposes. The super speeder fee ($200) is separate and is paid to the state DDS. You get that fine/notice in the mail a couple of weeks after the citation is settled in court. And, oddly enough, there are no additional points on your license for the super speeder citation, just the extra $200.
As for the speedometer being off I believe I've read that the car has the ability to self correct within certain small differences. Or a dealer can adjust it correctly for you. Or if you're willing/ able to use Forscan it can be corrected in there. I know I've read the instructions on the Forscan mod on this forum.

Here in FL, 30 over the posted limit is an automatic court appearance, at least that's what the cop who gave me a warning for going 32 over told me ;-)

To the OP, changing rim size doesn't automatically change the speedo accuracy, it depends on overall tire diameter. Going from 235/50r18 to 255/40r19 will make no difference in the speedometer since both tire sizes have essentially the same outside diameter.

Use the link in post #4 and see if your new tires really make that much difference. I wouldn't worry too much about 2-3 mph error. My speedo reads about 2 mph fast from the factory. If you do need a correction the dealer can do it, or if you plan to get a tune you can correct it yourself with the tuner.

Sponsored