Installed 37" tires- speedo correct now?

[Conejoracer]

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?

 

[farman]

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?

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

 

[JDUB]

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.

 

[hagak]

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

 

[Conejoracer]

Installed 37" tires- speedo correct now?

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

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.

 

[LekRap]

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.

 

[Conejoracer]

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.

 

[KaiserM715]

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).

 

[Huck]

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

 

[str8fast]

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


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