How fast have you taken the prius?

I did not run mine that hard until it was near 16,000 miles

Mine gained a little MPG as it worked it's way to 10,000 miles, but the power increase as the driveline freed up was very noticable.

I love the passing power in the 50-90 range with the electric and gasoline engines in tandem at full power

 

I understand the unusual nature of your situation but if your memory is accurate it may help us figure out a technical question about the Prius.

Michelin Primacy MXV4 195/65R-15 91H is 834 RPM
Cold PSI=42/40 on a 2010 Prius

I can't say exactly how the PSI affected RPM in those tires but I'd assume slightly lower RPM maybe 1% giving a effective RPM of 825? 115 on the display, 113 on the GPS. That suggests 820 RPM (1.7% below 835) for accurate speedometer at high speeds. I'd be curious how the GPS and dash display compare at 55 MPH.

My prior theory was that the accurate RPM is 845. If you could test with similar cold PSI at multiple speeds (35, 45, 55, 65) it would be even more helpful.

 

15" Rims (standard alloy rims in the US 2010+)
195/65/15 (2010+ OEM tire size 1 Goodyear Assurance Fuel Max at 836 RPM)
195/65/15 (2010+ OEM tire size 2 Bridgestone Ecopia EP20 at 833 RPM)
195/65/15 (2010+ OEM tire size 3 Yokohama AVID S33D at 829 RPM)

Should be easy enough to tell if your tires match one of these three choices.

 

There are 15 different Bridgestone Turanza's on tirerack. If you had specified which Turanza I would have looked up the revs per mile and used it to consider speedometer accuracy.

Its no big deal if you don't want to help but I'd like to know which turanza from this page Bridgestone Tires Available at Tire Rack

and if you can give any info regarding speedometer accuracy you've noticed/measured I'd appreciate it. The more scientific/accurate the data the better.

and here is a chunk of a prior post of mine from another thread

In the U.S., manufacturers voluntarily follow the standard set by the Society of Automotive Engineers, J1226, which is pretty lax. To begin with, manufacturers are afforded the latitude to aim for within plus-or-minus two percent of absolute accuracy or to introduce bias to read high on a sliding scale of from minus-one to plus-three percent at low speeds to zero to plus-four percent above 55 mph. And those percentages are not of actual speed but rather a percentage of the total speed range indicated on the dial. So the four-percent allowable range on an 85-mph speedometer is 3.4 mph, and the acceptable range on a 150-mph speedometer is 6.0 mph. You're allowed another plus-or-minus two percent near the extremes of 20-to-130-degrees Fahrenheit, and yet another plus-or-minus one percent if the gauge was ever exposed to minus-40 to plus-185 F. Tire error is excluded from the above, and odometer accuracy is more tightly controlled to plus-or-minus four percent of actual mileage.

The European regulation, ECE-R 39, is more concise, stating essentially that the speed indicated must never be lower than the true speed or higher by more than one-tenth of true speed plus four kilometers per hour (79.5 mph at a true 70). Never low. Not even if somebody swaps a big set of 285/35R-18s for stock 255/45R-16s.

with credit portions of this info taken from a 2002 article from http://www.caranddriver.com/features/02q2/speedometer_scandal!-feature

I was surprised to see that they can modify the output of the speedometer so that it isn't a linear scale but I had suspected as much from prior experiences.

 

GPS 75 = Vehicle Display 77
GPS 70 = Vehicle Display 72
GPS 65 = Vehicle Display 66
GPS 60 = Vehicle Display 61
GPS 55 = Vehicle Display 56
GPS 50 = Vehicle Display 51
GPS 45 = Vehicle Display 46
GPS 40 = Vehicle Display 40
GPS 35 = Vehicle Display 35
GPS 30 = Vehicle Display 30
GPS 25 = Vehicle Display 25

I'm using a Garmin Nuvi 266W but I have also seen the exact same numbers using my laptop with a USGlobalsat BU-353, SiRF star 3, -159 dBm GPS puck.(very good and very sensitive) It matched the Nuvi numbers.

 

Interesting that the speedometer was accurate at 40 and below. Possible that the Gen III Prius speedometer goes non linear at 40+ MPH.

It also seems that your tire is a good match, enough so that I'd say I was wrong guessing 845 for the Gen III. I'm going to have to say 835 for dead on Gen III now. Gen II is still unconfirmed but assumed to be 845.

I guess I need to grab a GPS and do the same tests with my Gen II to see how it compares. I'm running a tire rated at 850 RPM so if I got similar accuracy on my Gen II I'd have to say that there are two different speedometer ratios. If mine were off at both low and high speeds we'd need more data to find out if Gen II and Gen III have similar/matching RPM targets.

If it turns out 835 works for both I'll have to eat crow. I'm still holding out for the possibility that gen II wants higher than 843 but I'm not willing to bet much on that.

I don't currently have access to a GPS so it might be a while before I can check it. Luckily my tires are fresh (less than 8000 miles on them so if I get my hands on a GPS it should be a valid test).

 

I'm going to wager that the GenII needs somewhere between 840-843RPM to be dead on accurate. If the speedo read in one or two decimal points we could pinpoint the number. I would borrow my Timble Nomad GPS ($3000) from work if that was the case. I think we are close enough though. Most people don't care that much.

 

I have got up to 176kph on gps/ the dash was showing 183 at the time.

 

Fastest I have gone is 112 on Interstate 5 just south of 580. Amazingly I was going with the flow of traffic and being passed by other cars. Only did it for a few seconds as I can't imagine the Prius was designed for speeds over 100 mph

 

15" dealer cheapo tires on a 2006 over a 25 mile measured distance on US50 in Nevada, flat and level, no wind to speak of. 105mph because my wife wouldn't let me run faster. Smooth and wasn't really straining. Felt like 110 - 115 wouldn't be a problem.

 

the tyres are Turanza ER30 but I could not find them in the 195/55R16 size on Tire Rack's web site to look up their RPM value. Can I proceed to measure the displayed speed and true GPS speed at the pressure that I am running them currently?

 

I was on a road trip traveling near Hell, Michigan one night just before dawn when I came upon a group of bats that were racing away from the city I was near, after a short period I passed them as "we" were headed the same way (away from Hell), never looked at my speedometer but I'm absolutely certain that the prius goes faster then a bat out of "Hell".

Hope I didn't threadjack a downward spiraling thread

 

It will exceed 100 mph and is sold in Germany. I would hope they took that into consideration.

 

Please do. We can get the tire data later.

 

Did you send postcards from the post office in Hell? They burn the sides of the postcard!

 

Sure, test away.

I tried the bridgestone website and they didn't list specs for a ER30 at 195/55/16. Is it possible you have a ER300 instead? FWIW even if you do, tirerack doesn't show revs per mile on the ER300 at that size nore does the bridgestone website. So we would just have to go by tire diameter and guess the RPM.

 

The fastest that I have driven my 10 was 75 mph in the Dakota's which was the speed limit. Also, it was into very high gusty winds. I got 50.2 mpg for that tank which was the lowest that it had ever done.

I was very pleased with that usage for the conditions.

 

Hi there, the data for my tyres are in the attachment. I think the way that the numbers are rounded or truncated may have an effect on the results. I have included the Prius' own GPS speeds as well.

 

195 Km/h, on my way to the airport.
I missed the flight that day...