We all know the Prius is a silent vehicle at low speed. Recently, I traveled to California, rented a car and drove around. Because there are so many Prius out there, I could observe something I could never do at home because the Prius is rather rare around here: the noise created by a Prius at high speed (on the highway). I was driving on the right lane of the highway, at a lower speed than maximum. So other cars could overtake me on the left. When I looked in the side mirror, I could see cars approaching. Whenever I could see a Prius in the line, I was careful to listen the noise of the vehicles passing by. Whenever the Prius passed, I could hear that the noise it produced was clearly not as loud as the other cars preceding or following it. I guess we can attribute this to better aerodynamics and low friction tires. Note that I have not compared the noise level produced by the various Prius models (I, II and III). For that I would have needed to be overtaken by 2 Prius models following each other, which did not occur during the 4 days I drove there.
The engine would've been spinning at a lower rpm as well so you may not hear the engine compared to other cars which would have then engine spinning anywhere between 2,200rpm to 3,000rpm.
They're so quiet I heard a couple of them sped through the Sepulveda pass undetected during yesterday's Carmageddon.
Interesting. Although probably not the case for all cars. My civic (automatic transmission) spinned at 2000 rpm @ 100 km/h. However you are right, rpm very likely has an effect on noise level too.
That's pretty good. I aim for about 2,000rpm at 100km/h for regular automatic transmission cars. That's for fuel economy and engine noise. The Gen 3 with a torquier 1.8 litre and a reduction gear may allow a lower spinning engine. I don't have a scangauge so I can't confirm it but I do know that I have done 75mph with the iMPG showing 47mpg or higher which is remarkable. This is without cruise of course. That's pretty amazing. I'd say most cars will spin around 2,000-2,200rpm (esp. those with more gears) and maybe 2,800rpm at 120km/h. Anything over 3,000rpm will be noisy. Of course I'm generalizing but that's the rule of thumb I use.
It's spinning much lower now that I put the 15" tires back on. I'll check it but it looks like it runs around 1650-1800rpm at 65mph and at about 17-19 horsepower. Whereas the 17s required about 22-25hp to maintain 65mph. I think the GenIII suffers less from the larger wheels due to the extra HP/TQ.
Not likely. It has to do with tire design. Some manufactures will design a tire to reduce noise. A good case in point is the Hydroedge tires. They are LRR yet they are pretty darn loud compared to other LRR tires. I think there may be a closer correlation between noise and high treadwear tires but since my Michelin MXM4s are high treadwear and VERY quiet I'm not sure I am correct.
As F8L mentioned above, LRR doesn't mean it's quiet. The Nokian WR that we have mounted on the 2005 is LRR but because of its aggressive design, it does make a whistling noise as you approach 70mph. It's more noticeable in the 2005 Prius because of less sound insulation. I'm sure you won't notice in a Camry for example. Yeah but think about it. say 1,700rpm at 65mph? It's 2x the idle speed. That's pretty incredible. I was carry a good deal extra weight on the return trip (how much do 4 steelies weigh?) and I swear the Prius was getting better mpg because it was lower to the ground lol. The iMPG was alternating between 4.5 and 5.0L/100km at 120km/h. Using the poorer of the two, that's 47mpg at 75mph.
Now the question is, why? lol. I'm sure it wouldn't be that mpg with cruise (it will probably flicker between 5.0 and 5.5L/100km (or 43 and 47mpg)
Although I don't know the numbers, energy expended by friction as tires move air and by road friction that also produces noise, is energy that is no longer available for kinetic momentum. Friction from a rolling tire that makes noise is parasitic. The question that remains is how much energy is lost to momentum by friction that produces noise.
If your mean to ask why cruise control would cause the instantaneous mpg flicker or vary so much I would think it is due to the ECU trying to adjust to road conditions as best it can. The driver can foresee the road condition changes before the ECU can so is better able to control throttle response. Some drivers anyway. That is a good point although I wonder how much noise affects mpg. I do see many LRR tires that are also designed for low noise so maybe there is more to this idea. We know that sidewall deflection and tread squirm increase rolling resistance and steal energy that could be used for forward motion and both of those could cause noise.
I suppose. I was cruising such that I was losing 1km/h every 20-30 secs so that might account for the slightly better mpg. Cruise would've kept that speed.
