4.88 gear question... How to calibrate the speedometer? (1 Viewer)

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Perhaps I'll be corrected and learn something but my understanding is that speedometer is affected by tire size, not by the gear ratio.
 

Markuson

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Pretty sure speedo is based on wheel speed sensors...not the transmission.
So...tire diameter (rotations per mile, etc) creates the speed reading and nothing else. Problem is, there is no simple way to adjust the speedo (that I know of) except in your head.

If it drives you crazy, download one of a zillion GPS-based speedometers on your phone long enough to get a sense for it. With a decent sky view, they are pretty dang accurate.
 
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Pretty sure speedo is based on wheel speed sensors...not the transmission.
So...tire diameter (rotations per mile, etc) creates the speed reading and nothing else. Problem is, there is no simple way to adjust the speedo (that I know of) except in your head.

If it drives you crazy, download one of a zillion GPS-based speedometers on your phone long enough to get a sense for it. With a decent sky view, they are pretty dang accurate.
Ahhhh good to know. Thanks!
 
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Pretty sure speedo is based on wheel speed sensors...not the transmission.
So...tire diameter (rotations per mile, etc) creates the speed reading and nothing else. Problem is, there is no simple way to adjust the speedo (that I know of) except in your head.

If it drives you crazy, download one of a zillion GPS-based speedometers on your phone long enough to get a sense for it. With a decent sky view, they are pretty dang accurate.
There is a way to adapt a Hypertech speedometer calibrator. I did short write-up in a previous thread HERE.

Took more time to research than install.
 
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TeCKis300

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There is a way to adapt a Hypertech speedometer calibrator. I did short write-up in a previous thread HERE.

Took more time to research than install.
Thanks for the research and info!

Am I understanding that this mod only effects the dash speedometer readout? And it does not rectify the speed within the various ECUs?

As I'm on 35s now, the speedo reads about 10% low. No big deal but it does impact several of the auxiliary systems such as AHC. AHC lowers the suspension at highway speeds, ~60mph. This is useful for gas savings but also when I tow as it has the dynamic effect of increasing hitch weight distribution tension for more high speed stability. Or things like the range miles to empty (which this may fix as it's in the gauge cluster?).
 
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Thanks for the research and info!

Am I understanding that this mod only effects the dash speedometer readout? And it does not rectify the speed within the various ECUs?

As I'm on 35s now, the speedo reads about 10% low. No big deal but it does impact several of the auxiliary systems such as AHC. AHC lowers the suspension at highway speeds, ~60mph. This is useful for gas savings but also when I tow as it has the dynamic effect of increasing hitch weight distribution tension for more high speed stability. Or things like the range miles to empty (which this may fix as it's in the gauge cluster?).
It will correct any of the functions calculated/displayed within the speedometer cluster. So speed, distance, MPG, Miles to Empty have all be 100% since the addition of the calibrator. What's particularly useful about the Hypertech computer is that it will correct by a custom % (or change in tire size), and is not locked into a 3%/6%/9% that some of the similar products out of Australia are limited too (Marks4WD).

I'm sure if you intercepted each of the wheel speed sensors independently prior to the ECU/Instrument Cluster you could correct all of the speed-dependent functions. However I imagine that would require substantially more work.
 

Eric Sarjeant

Ed Martin Toyota (Indianapolis)
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@Eric Sarjeant

Hey Eric,
Would be interested in any info re installing these on 200’s if you guys have done it... Info on their site seems a little vague on vehicle specifics.
I heard about these years ago because my buddy @Higgin told me about them way-back-when he had his 80. I have never used one, but I do own the device for a 200 still sitting in the packaging. Since I was only 1-2 MGP off with my 285/65/18 tires I never felt the need to install it. I am gearing up for some major upgrades over the winter, which will include some 35s and I'll definitely want to get the Yellr installed. I'm happy make a video or post up feedback.
 

sdnative

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Markuson

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I had one of these on the 80 years ago. Super simple to install. It did affect the cruise control as I understand.

No experience with the 200 I would imagine a little more involved with everything being computer controlled and "by wire".
I wonder about it’s speed sensor focus... since we don’t just have one sensor.
 
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Looking at the yellow box site and the 200 wiring diagram it seems like it would work if we installed 4 and synchronized the offsets; otherwise not sure how we get the corrected signal out onto the can-bus from the Skid control ECU.

Although 4 would be a bit of an investment, it does look like this would 'treat the source' and thus put all systems downstream of the speed sensors themselves back on the same page for 'stock' functionality.

Screen Shot 2020-11-22 at 2.33.59 PM.png
 

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