Well, if you believe the speedo, it's 194km/h or 121mph. [ame=http://www.youtube.com/watch?v=BOP-ExEj8KM&feature=related]YouTube - Autobahn Topspeed Prius[/ame]
Top speed of my Prius is 115 by speedometer (tested last month) which would be about 112 actual. It feels very stable at that speed and really didn't take to long to get up there, I only stayed at 112 for a few seconds and then slowed down to a stately 65 again. Completely empty stretch of road in eastern Washington where I could see in both directions for miles.
Then there must be differences between the U.S. and Euro versions (cause you can see 194km/h on his speedo). Could be simply a value difference (i.e. it shows a higher number in Europe even though the real top speed is the same) or it really is faster in Europe.
Yes ours are definitely electronically limited, you drive right up to the top speed still accelerating pretty good then at an indicated 115 it's like you hit a wall of pillows, just won't go any faster. I'm sure if it were not for the limiter the car would go quite a bit faster. Could be the European version is either not limited at all or has the limiter set to a higher speed. I was very impressed by the stability. As I was slowing there was a bit of a corner I went through at about 100 and it really felt good, more like a sports sedan than a economy car.
Remember that you do have 215 width tyres and that definitely helps. Could be. In that video, he was accelerating decently at 180km/h
So I guess that means That_Prius_Car and Brad_Rules_Man weren't lying about their Fear and Desire in Las Vegas-like trip overtaking a butthole truck at 116 mph after all.
Tires. The Prius is limited due to the speed rating of the no-seasons provided in the NAR. EU-spec vehicles come with specific summer (or winter, depending on the season in which the vehicle is purchased) tires. Summer tires tend to carry a higher speed rating that no-seasons. It is incumbent upon the owner to make the switch between the two different tires based on the season of operation.
Could it be that our speedo reads about 5-10 mph (and the relevant amount in kmh)higher than the actual speed? I believe this is some European requirement and I know mine reads different to my TomTom sat nav. The car will show 70 mph but the satnav shows 65 mph.
The Toyo A20 all season tires (215/45-17) that came on my Prius are V rated, 149 MPH. I am not sure what the speed rating is on the 15" wheeled cars.
Next time you try a speed test be sure to look in the third direction, upwards too! I've heard the use of light airplanes to check for speeders is a common practice in E. Washington.
That's what I'm leaning towards. Euro-spec cars tend to read the highest, followed by Asian-spec cars then American-spec cars (also applies to the manufacturer's home country) Another possibility, yes but that's assuming Toyota outfitted the Prius with H-rated tyres or higher. Most are S or T because they don't expect a Prius to run at that sort of speeds. A summer tyre doesn't necessarily mean a higher speed rating.
Unfortunately the EU speedometer is "a bit" optimistic .... even the EU 3 Gen Prius top speed is electronically limited to 181 kmh (i.e. 112 mph), it is necessary in order to protect the MG1 from overspeed. So there are no differences between US and EU Priuses, in term of performances. IMO the tyres have nothing to do with this matter, here are sold Priuses with 17" tyres and W specs (>240 kmh limit) and with 15" and H specs (>210 kmh limit). But the declared performances (specs sheet) are the same....
Any tire correlation would be based on the lowest speed rated tire that comes standard on a new Prius. There would not be different top Prius speeds for different tires.