Realibrating ECU for different tire size Revolutions Per Mile??

My OEM integrities read 2 to 3MPH high at 65 MPH. I put on 205/60/15 Michelin Primacy MX4 and the speed is now right on the money. The MPG was unchanged. Actual MPG might then be a few % higher, since car was originally going slower then indicated (fewer miles). Recalibration is probably not practical, if at all possible.

 

We either need a co-operative leak from Toyota or someone needs to reverse engineer the computer that makes the calculations and figure out which value to change.

Then we need someone who can go into the Prius software and make the desired change. There have been other cars with enough info out to do that, but I don't expect it to happen soon for Toyota.

 

It wouldn't be released as it would allow -more- dishonest behavior (some would change it so the car would show lower mileage over time).

 

OK Pat, your a clever guy. Design a circuit to intercept the speed sensor and put out a signal that is X times the input signal. Now you can "calibrate" your spedometer to whatever you require.

 

If it's that simple, you can buy one of these
Official home page of the Yellow Box Speedo Recalibrator

Unfortunately, there is a good possibility that the speedometer uses all 4 speed sensors (one per wheel) and sends a composite signal to the speedometer. Maybe someone here knows for sure?

On my Gen 3, the Odometer is just about spot on, within 1%. Also, my ScangaugeII shows actual speed, while the speedometer reads 1-2 mph high at highway speeds. That means that if I did use a Yellr Box type device to correct my speedometer, the odometer would then be off as far as the speedometer was off before I corrected it.

Since the game with Prii is tracking MPG, I would rather have a spot on odometer than a spot on speedometer. My Prius speedometer is within 2 mph at any quasi-legal speed.

 

Cool, just what I had in mind. Yes, you will need 4 of them. The ABS pickups appear to be the only speed sensors. The cost would be nearly $500. Seems easier just to buy good tires that give the correct speed. There seem to be enough options.

 

Considering that and my desire to have the odometer remain accurate, I will learn to mentally subtract one mph at normal highway speeds.:cheer2:
If I want to see the correct speed I can select speed as one of my ScangaugeII readouts. Or turn on a GPS.

 

More than close enough when you consider that the 1/4 inch of rubber that is there to be worn off the tire tread reduces the tire radius by about 2% so causes your speedometer & odometer to read 2% higher than they did when the tires were new.

A stock 855 would be about 872 revs miles when the tire was worn enough to need replacing.:cheer2:

 

Good plan!

 

I use a Garmin nuvi as a GPS speedometer:

I also use the accumulated distance to correct the distance when I enter my data into the MyHybridCar.com database:
2003 Toyota Prius - Hybrid Fuel Economy Data - NHW11 2003

Now that cooler weather is returning, I can conduct 'standard day' mileage tests to compare:

• 195/70R14 - currently front tire
• 175/70R14 - currently rear tire

However, there is one thing I can tell where the 195/70R14 goes where smaller tires can not follow, up to 40-43 mph with 'hybrid mode.' That means I can travel at traffic speeds on 40 mph posted streets, keeping up with traffic, and the ICE will shutdown when it can. With smaller diameter tires, we meet and exceed the 42 mph threshold and the ICE runs even if not needed (aka., descending a grade with traffic.)

My preliminary data suggests the tire drag is not a significant function of tire diameter but the ability to travel a little faster with the ICE off helps in an urban, per-tank, basis.

Bob Wilson

 

Has there been any more headway in this area of questioning? Does the small percentage of difference in the tires size as Ken mentions below fall within the percentage of allowed error? Or is there a chance the touring ECU is programmed differently?

______________Touring__________Base
size__________195/55R16______185/65R15
sidewall height__107.25mm______120.25mm
inner diameter___406.4mm_______381.0mm
overall diameter__620.9mm_______621.5mm
circumference__1950.61mm______1952.5mm
ride height_____310.45mm______310.45mm

Just wanting to know for those including myself that may make any changes to the tire size...could effect correct odometer reading, mpg...ect.

 

This is not the kind of response i was hopping for.... Nothing in Torque to make adjustments..or the sort?

Don't think they make LRR or Energy Saver tires in 215/35/19... :Rollin'OnRubberBands:...