Speedometer calibration after adding 35” tires

[Sal731]

Picked up my rebel from the shop. Had a six inch Bds lift kit installed. Added 35x12.5 tires. When I left the shop I had to take the highway home. According to Waze when I was doing 70 I was really doing 74. I kept an eye on Waze for the correct speed I was traveling. When I got off the highway I stopped at a traffic light. Once moving I realized that Waze and my truck were now exactly reading the same speed. Before going home I took her back on the highway so I could get her going fast again and the speedometer either recalibrated herself or Waze somehow is copying the speed from the trucks speedometer. According to Waze they will read your speed and not what your vehicle is saying. If this is correct than the 21 rebel recalibrates it’s own speedo

 

[Idahoktm]

No, your truck will not self calibrate. You need to disconnect your mobile device from your truck and then you'll see that your speedometer is off by 3-6 mph.

 

[MikeyHo808]

Picked up my rebel from the shop. Had a six inch Bds lift kit installed. Added 35x12.5 tires. When I left the shop I had to take the highway home. According to Waze when I was doing 70 I was really doing 74. I kept an eye on Waze for the correct speed I was traveling. When I got off the highway I stopped at a traffic light. Once moving I realized that Waze and my truck were now exactly reading the same speed. Before going home I took her back on the highway so I could get her going fast again and the speedometer either recalibrated herself or Waze somehow is copying the speed from the trucks speedometer. According to Waze they will read your speed and not what your vehicle is saying. If this is correct than the 21 rebel recalibrates it’s own speedo

Let’s not ignore the elephant in the room…
DUDE…that is beautiful!

 

[penguinphan]

Love those wheels. I got the same thing in grey.

 

[SKT Customs]

Yeah if it’s plugged in then it reads what the truck says; unplugged it’ll show your difference. At 70 I’m actually going 79mph with 37s lol

 

[bigdodge]

this is the thread for wheels and tires
you will need alphobd and lots of reading

Wheels and Tires

Wheel and tire discussion forum

5thgenrams.com

 

[SKT Customs]

this is the thread for wheels and tires
you will need alphobd and lots of reading

Wheels and Tires

Wheel and tire discussion forum

5thgenrams.com

Or a simple calibration tool or go to the dealership!

 

[MikeyHo808]

I too have a question regarding speedo recalibration. Although a very different issue, my apologies to the OP if I hijack this thread just a tad.

Went from the stock Falken’s AT’s to Toyo 33x12.5. First recalibrated with AlphaOBD, and then again with my Pulsar. Although the Toyo’s are listed as 33’s, overall inflated is 32.5”, according to website. Have recalibrated using both sizes, and still sit about a 2 mph slower than actual (speed gun at front gate says 25 when speedo reads 23). Shouldn’t it be the other way around, faster than posted? Would using the 2 methods conflict with each other? I returned the AlphaOBD setting back to stock when I used the Pulsar, but the difference remains.

Alrighty…thread un-jacked…thank you.

 

[SKT Customs]

I too have a question regarding speedo recalibration. Although a very different issue, my apologies to the OP if I hijack this thread just a tad.

Went from the stock Falken’s AT’s to Toyo 33x12.5. First recalibrated with AlphaOBD, and then again with my Pulsar. Although the Toyo’s are listed as 33’s, overall inflated is 32.5”, according to website. Have recalibrated using both sizes, and still sit about a 2 mph slower than actual (speed gun at front gate says 25 when speedo reads 23). Shouldn’t it be the other way around, faster than posted? Would using the 2 methods conflict with each other? I returned the AlphaOBD setting back to stock when I used the Pulsar, but the difference remains.

Alrighty…thread un-jacked…thank you.

If your truck is reading slower it’s because you’re inputting a tire size that is too large. Your actual inflated diameter on that tire is probably about 31.5”. Try that measurement and it should be dead on.

 

[SKT Customs]

Here’s a pro tip for everyone who’s trying to calculate their tire’s actual diameter under the weight of their truck. The sizes listed online for the tire is a “ballpark” and is always listed for a tire that is not actually being weighed down by a vehicle. To find the true diameter, take the number 63,360 (the # of inches in a mile) and divide it by the “revolutions per mile” listed on any given tire (its always listed for every tire out there), and then divide your answer by Pi. For instance, the 33x12.50r22 Toyo AT3 mentioned above does 639 revolutions per mile. So 63360/639=99.15 / 3.1415= 31.56”.

A perfect example of how tire sizes are a “ballpark” number, is the Toyo MT vs Falken MT in 37x13.50r20. The Toyo MT does 560 revs/mile, which is a true 36.01”; whereas the Falken MT does 573 revs/mile which is 35.21”. So 2 tires that are listed as the exact same size, are actually .80” different once they’re mounted & under the weight of the vehicle!

Hope that helps

 

[Idahoktm]

I too have a question regarding speedo recalibration. Although a very different issue, my apologies to the OP if I hijack this thread just a tad.

Went from the stock Falken’s AT’s to Toyo 33x12.5. First recalibrated with AlphaOBD, and then again with my Pulsar. Although the Toyo’s are listed as 33’s, overall inflated is 32.5”, according to website. Have recalibrated using both sizes, and still sit about a 2 mph slower than actual (speed gun at front gate says 25 when speedo reads 23). Shouldn’t it be the other way around, faster than posted? Would using the 2 methods conflict with each other? I returned the AlphaOBD setting back to stock when I used the Pulsar, but the difference remains.

Alrighty…thread un-jacked…thank you.

If you did nothing, this is what your readings would be:


I went from the stock 32's to 33's like you. I measured the tires and they came out to 2567mm's of circumference. I entered that number in AlfaOBD, finished the calibration and my speedometer was still off by 1 mph at 60 mph. I went back and bumped the tire circumference up to 2625mm's. My speedometer was spot on.

It sounds like you entered a number that was too small or you didn't do the calibration correctly.

 

[SKT Customs]

If you did nothing, this is what your readings would be:
View attachment 129959

I went from the stock 32's to 33's like you. I measured the tires and they came out to 2567mm's of circumference. I entered that number in AlfaOBD, finished the calibration and my speedometer was still off by 1 mph at 60 mph. I went back and bumped the tire circumference up to 2525mm's. My speedometer was spot on.

It sounds like you entered a number that was too small or you didn't do the calibration correctly.

Actually you’re right, I had it backwards in my previous reply. If his truck is reading slower than it’s actually going then his number is too small. I said too big. Weirdly that kinda throws off my whole follow up post - even though the math on my post is correct lol. Plus there’s no way his 33” tire is actually larger than 33” so that makes no sense lol. Sounds like the hardware is programmed weird or something

 

[MikeyHo808]

Appreciate the info, guys. No way these tires are bigger than 33’s, so looks like a recalibration of the recalibration is the call. Thanks.

 

[Sal731]

Let’s not ignore the elephant in the room…
DUDE…that is beautiful!

Thank you brother