Tire size change and MPH (calibration)

OK, I know that when tire size changes it can alter the speedo calibration. My 2012 Tacoma Pre-Runner lists 245/75/16 tires on the original Window Sticker however it also has the XSP-X package which is listed on the same Window Sticker indicating the factory wheels were replaced with 18 wheels and BF Goodrich tires (although it doesn't state the actual tire size). Regardless of the tire size there would have likely been some diameter difference and therefore a speedometer calibration issue. Is it possible there was any re-calibration of the speedo done by Toyota or the dealership due to the 18" vs 16' wheels?

Fast forward to today and I'm running it with 275/65/18 since I had it lifted 2" and it can now take a larger tire. When using to understand just how much the speedo is off, I plugged in the original 245/75/16 vs. 275/65/18 (current tire) and it's amount to 5.2% over what the speedometer is actually showing. So when it reads 50 mph I'm actually traveling at 52.6 mph.

I know I could get a Hypertech to correct the speedometer but in order to accurately make adjustment I'd have to be certain if the the factory speedometer calibration was left untouched for the 245/75/16 or re-calibrated for some other size tire put on with the XSP-X package.

Do you think the speedo would have been recalibrated or not prior to delivery?

 

The 18" wheels came with lower profile tires, so the outer diameter should be the same or very similar to the standard tires that came on the 16" wheels. So, no calibration would have been necessary.

The speedo should be close to accurate when running any tire size offered from the factory.

Or, just a bit fast as seems to be the case with my '15. My GPS speed is always a pinch lower than the speedometer is reading

 

My 2010 Prerunner brand new came with P245/75/16's and it was off by 2 mph on the slow side. Speedometer reading 60, but I was actually doing 58.

 

Two mph isn't enough to worry about. In fact as your tires wear down they get smaller and the speedometer will be accurate again by the time you replace them. If you were to re-calibrate now, they would be showing you 2 mph faster by the time they are worn out.

My truck with stock tires was always showing me about 2-3 mph slow compared to my GPS. When I went to a 1" larger tire the speedometer was in sync with my GPS. At least when the tires were new. The last 10,000 miles on those tires showed me 2 mph slow again.

When you make extreme changes in tire sizes and you're speedometer is off by 10 mph then it might be worth re-calibrating.

 

This site has a tire size calculator, Put in both tire sizes & it will compute everything, total cri., total outside dia, how many revolutions per mi. for both sizes, including how much the speedometer will be off. Really interesting, Check it out, I love it.

 

Speedometer is correctly calibrated at the factory accounting for factory packages.

PS factory calibration is 2-3% off from the factory for liability reasons.

 

Holy cow those hypertechs are pricey. I'm lifted and on 35s and my speedometer runs about 6mph slower than what I'm going. I wouldn't mind correcting it, but not for $200 lol

 

I'll save you some time and $$$$, use GPS speedometer.

 

Wow! With 35.4" tires, (real world) when speedometer reads 71MPH, GPS reads 80MPH. And, OEM, from the factory, when speedometer read 70MPH, GPS read 68.5MPH. Only 6MPH off with 35's????

Anyways here's the standard calculations for 35's.

 

The window sticker should read in the first column, standard options.... Basic tires and wheel sizes. The right column shows packages, features, etc. In that list it should show the tire and wheel size. Also, if your tires and wheels where part of any original package, the sticker at the drivers door will state the tire size. If the dealership swapped out the tires and or wheels... That's another story. But door tag will match OEM shipped tire size.... It's the law.

 

So, mine are the Nitto Terra grapplers, and as I recall- correct me if I'm wrong- those are 34.8ish and not true 35s. That said, it is consistently 6mph slow regardless of speed when compared to my gps (phone gps and actual navigation gps). Which is pretty weird.

 

My stickers on the door jams are incorrect. I tried to buy tires from my local Walmart for both my 1998 Tacoma & my 1999 Dodge ram 1500. I personally ordered the Dodge Ram, back in "98". I ordered it with the bigger tires. Walmart looked at the door sticker & told me they couldn't put the size tire that was on there now, they said they had to go by the door sticker. The door sticker shows the base model tire size. Luckily the original window sticker was, & still is, in the glove box. I showed the window sticker to the worker, who in turn called the store mgr., who came & verified the VIN on the window sticker was the same as the VIN on the truck, then advised the worker to put that size tire, but no bigger on my truck. A few yrs later, appx. 2010, I bought my used "98" Tacoma. When putting the reg. papers in the glove box, I noticed the orig window sticker was in this glove box also. I went thru the same thing again, at Walmart. The sticker on the door jam has the tire size for a base model "98" Tacoma, the window sticker shows it was bought, new, with the larger tires & alum. wheels. Walmart manager did the same thing again, verified the sticker VIN was the same as truck VIN &advised them to install that larger tire, size indicated on window sticker, but no larger. Most of the time, the door jam stickers will be correct, but neither of mine are correct.