What's the Prius III's top speed limited at?

That depends on whether the controlling ECU is programmed for max displayed mph or max MG2 rpm. If it is programmed for max MG2 rpm, which is what I would expect, then the displayed mph will change according to tire revolution per mile spec.

 

Reply to my own post: I was wrong. I punched up the speed and switched to km/hour display, and DOES go to three digits.

 

Zoinks Scoob, thats like 120mph!

 

As far as we know, that is fixed.

If you know how to tell the ECU that the tire revs per mile are different than what was programmed at the factory, please let us know. Some of us would like to re-calibrate our speedometers.

 

I really dont know, But we got ours up to 105 one time on the way to Vegas.

 

Fuzzy,

You are misunderstanding what I am saying. If the ECU is programmed for Max MG2 RPM, it does not care what the tire size is. Once it reaches Max MG2 RPM it limits the RPM. Now the MPH of the car at this point is dependent on the tire size. So the max speed will vary from 112 mph.

Is that so hard to understand?

Dwight

 

^^ But how does it know what the tire size is?

Does it have a separate speed sensor, independent of the tires? I haven't known any of my cars to ever have any speed measure independent of the drive wheel RPM.

 

Why do you think it needs to know the tire size ????

 

A fixed value is programmed in at the factory. When the tires wear or are changed out for different models or sizes, the ECU doesn't know anything has changed, so the speedometer just shows what the car thinks the speed is based on wheel rotational speed, not any independently measured or calibrated value of road speed.

Thus, when MG2 hits its RPM limit, the dashboard will display 112 mph because that is what the pre-programmed tire size corresponds to, and the ECU has no other speed information. Drivers who have fiddled with their tire sizes need to make their own adjustments to the displayed value.

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Put another way, the wheel RPM, MG1 RPM, and dashboard indicated MPH should all be locked together by fixed ratios. Adjustments for varying tire size are entirely up to the user, the car doesn't know about it.

 

Do you know for a fact that the ECU limits based on MPH? If so, I agree with you.

 

What's the functional difference if it uses MPH or MG2 RPM? When these items are locked together by a fixed proportionality constant, the end result is the same.

 

If the limit is MG2 rpm, then the vehicle speed can change based on tire size. MG2 is connected to the wheels through a fixed speed reduction gear. If the tire size changes the vehicle speed changes by the difference in tire size.

I have a document that calculates mph based on gear ratios and tire size. Let me find this file and upload it. Then you can change tire size and see how the mph changes.

 

I'm sure his dad can afford his lawyer.

 

... and "it's the loneliest number that you'll ever do."

 

I remember reading an article in the PE paper years ago on the fastest speeding ticket. You had to email your story and provide proof if possible. The paper highlighted 3 people. Evidently a Dentist from Temecula got the award and the reporter was showed a ticket that read 200 MPH. He took possession of his 2010 Viper from a Temecula dealer and later that week got the ticket out near Indio. The policeman pulled him over and asked if he was speeding. He said yes. The cop said why? He said I wanted to see how fast it can go. The cop said we clocked you at 201 with the helicopter but wanted to leave you alone for awhile and enjoy it before you went to jail. Said h lost his license.

 

Document attached.

 

How do I tell the car / ECU that the tire size has changed? Absent such updated parameters, the indicated speed at the point where the limiter kicks in should not change.

Remember that I am talking about indicated speed (displayed on the dashboard), not the true ground speed (unknown to the car).

 

OK, I finally see your point. The displayed speed may not change but the actual speed is what changes.

 

That's because no one will believe you were speeding in a Prius.

 

+1!