Installed 37" tires- speedo correct now?

I just put on a set of Toyo RT tires, 37x12.5x17 on my Raptor. I expected the speedo to be off, but I've passed three radar speed signs that indicated my speedo is correct. I tried 4 different GPS apps for speed, all indicated speedo was accurate or indicated up to 2mph slow.
If my gearing is stock (CPO truck with 17k when I bought it), how is the speedo accurate with "true" 37's?

Conejoracer said:

I just put on a set of Toyo RT tires, 37x12.5x17 on my Raptor. I expected the speedo to be off, but I've passed three radar speed signs that indicated my speedo is correct. I tried 4 different GPS apps for speed, all indicated speedo was accurate or indicated up to 2mph slow.
If my gearing is stock (CPO truck with 17k when I bought it), how is the speedo accurate with "true" 37's?

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Did you test your speedo before you put on the 37s. My truck when it was completely stock always read about 2 mph faster then what I was actually doing at around 70-75 mph.
Also the truck could have been tuned for 37s before you. But you probably know if the truck was tuned

My speedo is only off by 4 mph @ 70 with 37's. So when doing 70 mph I'm actually doing 74.

Also, I guess mine aren't "true" 37's though lol.

Most speedo will read a faster speed than actual. So if you go larger tires you are just moving closer to actual speed.

Installed 37" tires- speedo correct now?

farman said:

Did you test your speedo before you put on the 37s. My truck when it was completely stock always read about 2 mph faster then what I was actually doing at around 70-75 mph.
Also the truck could have been tuned for 37s before you. But you probably know if the truck was tuned

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I never really tested it, but over the last 76k I've put on it, I have occasionally thought my speedo read faster than I was really going. Now, at 70 on the speedo, GPS reads true or up to +2 depending on the app. It's the same at 35, 45, 55, 65.
I'm pretty sure there is not a prior tune installed, the dealer would have caught that at some point.
Other than the slight power loss, the upside is my speedo is apparently good to go.

I would be curious if this effects the onboard MPG estimates too? What is it saying your MPG's are looking like?

I know "the tune" by SVC makes it easy to adjust tire revolutions. I love the tune and maybe it'll help compensate for the slight loss of power your reporting too.

Installed 37" tires- speedo correct now?

I'll report on the milage after I put some addition miles on it. I may go to a tune, or just regear depending on how well I can deal with the power loss.

I have noticed that my speedo with the factory tires is about 3 mph off when compared to GPS data (speedo shows 70, actual speed is 67).

Yon can adjust for tire size without tuning. It's a calibration adjustment and would most likely go unnoticed to a dealer

Got any pics of ur truck I'm about to pull the trigger on some 37 rts


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