Speedometer Correction After Larger Tires? (1 Viewer)

[r2m]

Just curious what all of you out there that have gone with larger tires are doing about your speedometers being off?
After mounting BFG LT285/75R17 (33.9") size tires and regearing both front and rear diff's, my speedo is just about a perfect 10% off. Reading 50 mph on my binnacle, per the gps on my phone, I'm at ~55 mph, my speedo = 70 mph, real speed = ~77 mph, etc.
Same for my MPG on my dash. When I'm reading 15.5 mpg, I'm actually getting 17.05 mpg.
So what I'm saying is, it's easy enough to calculate in my head what my real speed and mpg are, but I'd much rather not have to do that.

Has anybody addressed this themselves??
Some time ago back in the Fall of 2019 I emailed Yellow Box (Official home page of the Yellow Box Speedo Recalibrator - https://yellr.com/index.htm) and their reply was:
"Yellow Box is likely compatible with your Lexus, first we would need to confirm the type of speed sensor used.

Attached are some photos if your Lexus has this same 3-pin plug set at the Output Speed Sensor, then Plug-n-play Harness is available. The Output Speed Sensor is typically located on the transaxle/bell area of the transmission.

If your Lexus has a "2-wire/2-pin" Output Speed Sensor then it will require "2-wire" unit and Splice Harness only."
here are their attached photos:

Has anybody used them or any other vendor? If so, comments??

 

[MrTorgue]

Watching thread. Both of our GXs are slightly off. I’ve been using Waze/torque on the 470 for GPS speed

 

[Acrad]

Unfortunately....I've followed threads on this for years and haven't seen someone post a verifiable reprogram of speedometer.

 

[r2m]

I may bump this a few times in the next couple of weeks for the occasional lurkers, just to give everyone a chance to read it.

 

[Acrad]

I threw in another inquiry to Hypertech... and Rough Country Suspension Systems - https://www.roughcountry.com/contact/

just said "No"

 

[MrTorgue]

I threw in another inquiry to Hypertech... and Rough Country Suspension Systems - https://www.roughcountry.com/contact/

just said "No"

Boooooooooo!!!!

 

[jmanscotch]

I just live with it. I keep highway speed corrections in my head for long trips, but for the most part I just aim to go with traffic. Around town the speed isn’t off enough for me to worry too much.

You guys are calculating MPGs?! Why would you do that to yourself! I just fill up when it gets to half a tank and think no more about it.

 

[MrTorgue]

You guys are calculating MPGs?! Why would you do that to yourself! I just fill up when it gets to half a tank and think no more about it.

I could give a crap about MPG. It’s a large thirsty V8, who cares! I usually fill up around a quarter tank. I also keep the speedo difference in my head and adjust accordingly. It also helps that I try to stay within 1~4 MPH within the posted limit.

 

[yeos]

I originally bought it to monitor my transmission temps, but if you have an Ultragauge you can set it up to read out the correct speed. I'm 5mph off on the cluster at 70mph with 33.5" tires.

 

[Tex68w]

I do my calculations with the calculator on my phone. I don't bother checking fuel economy every tank but if I were pushing some heavy head winds or hills I'll run the numbers to see what I was getting. I don't care much about the speedo, occasionally I'll drop my speed 1-3 mph at 70 otherwise I just set it to the speed limit and forget about it.

 

[r2m]

I usually only look at mpg on trips to get an idea of where we will plan on getting gas and want to expect for gas prices. So if necessary, we'll lean it out to when the gas light comes on if we know there's cheaper gas ahead. But those are known locations and not just guessing.
Otherwise I don't really check mpg.
As far as highway speeds, my father always told me to be the second fastest person on the road. Although when there's not a lot of traffic, I've found that on the highway between towns I can easily be 5-10 mph over the posted speed and still have highway state patrol pass us with no problems. When we're slowing down having to go through small towns, then I stick it right on or even a little under the posted speed. The local police are generally real sticklers about travelers speeding through their towns.

 

[Acrad]

Perhaps an option for someone to work with

Speedometer Correction Device Installation

www.tundrasolutions.com

SpeedoDRD

 

[r2m]

Perhaps an option for someone to work with

Speedometer Correction Device Installation

www.tundrasolutions.com

SpeedoDRD

Wow, that's a great detailed install description!
(too bad it's for a Sequoia...)
Looking at their vehicle selection it was all for motorcycles and I think side-by-sides. Nothing for cars, SUV's or trucks.
Wonder how that fellow with the Sequoia figured to use the model he did? I'm guessing he bugged their tech support.

 

[jmanscotch]

Just a note to think on; I noticed my Scangauge displays a different MPH than my speedo and via a GPS app on my phone, it'd seem the scangauge is rather accurate to actual GPS speed with my 33's. Read correct on a trip I took recently with highways speeds between 75-90 where the speedo would read up to 6-7 MPH slow. Not sure where it's pulling that information from.

 

[re_guderian]

Just curious what all of you out there that have gone with larger tires are doing about your speedometers being off?
After mounting BFG LT285/75R17 (33.9") size tires and regearing both front and rear diff's, my speedo is just about a perfect 10% off. Reading 50 mph on my binnacle, per the gps on my phone, I'm at ~55 mph, my speedo = 70 mph, real speed = ~77 mph, etc.
...

I'm surprised you're that far off with a re-gear? I was less than 5% off with 285/65/18's and stock gears.

 

[SmithGX]

Lutz Auto is willing to provide a product if they can get a donor vehicle to validate the install in central CA.

Lutz Auto - Speedometer Correction Device

We are pleased to bring you the fully plug-and-play Lutz Auto Speedometer Calibrator for 80/100 series landcruiser's/LX's. This speedometer calibrator is fully adjustable and has no latency issues. After installing and calibrating it, you will forget that it exists! Ships quickly from the...

forum.ih8mud.com

 

[r2m]

Lutz Auto is willing to provide a product if they can get a donor vehicle to validate the install in central CA.

Lutz Auto - Speedometer Correction Device

We are pleased to bring you the fully plug-and-play Lutz Auto Speedometer Calibrator for 80/100 series landcruiser's/LX's. This speedometer calibrator is fully adjustable and has no latency issues. After installing and calibrating it, you will forget that it exists! Ships quickly from the...

forum.ih8mud.com

SHOOT!!! I'm in So. Cal otherwise I'd let them use mine!

 

[lgorman]

Here is a write up on a Speedohealer successfully installed in a 120 series 4Runner:

Speedometer and ABS Adjustment? - Toyota 120 Platforms Forum - http://www.toyota120.com/forum/showthread.php?t=4369

 

[BigSwede]

Here is a write up on a Speedohealer successfully installed in a 120 series 4Runner:

Speedometer and ABS Adjustment? - Toyota 120 Platforms Forum - http://www.toyota120.com/forum/showthread.php?t=4369

That thread is 12 years old... might be something better out there now, but I dunno.