Georgia to Michigan Commute I-75 80mph

Thanks for sharing. It's good to know it still yields ~43MPG driving at 80MPH. :thumb:

 

Think of what you might have gotten for MPG numbers if you left the cruise control off!
I never use CC, I get better numbers without it!

 

That sounds about right. That is what the GenII would achieve at that speed on a long trip.

 

That is my finding of late as well...

 

I got similar results from a 2010 Toyota Prius III (44mpg @80mph) going along I-70 from Missouri to Pennsylvania using cruise control most of the time.

 

Thanks.
This information is helpful to me. I'm considering a c and spend a fair amount of freeway driving at 70+mph. (but not all the hills you've described)
I notice that you have the 15" alloys - how do they handle through the hills and turns at that speed?
My biggest decision at this point - is whether to get the 16" wheel upgrades or stay with the 15"'s.

Thanks for posting.

 

Umm...handling has little to do with tire size and a lot to do with sidewall stiffness and rubber compound.

The reason why 16" wheels, by many people, are perceived to "handle better" is because they are usually shorter sidewall tires which naturally won't flex as much.

If you where to drive two cars back to back, one with a set of tires with decently stiff sidewalls (like Falken Azenis), The other with stickier, but softer sidewall tire (like Hankook RS3's) both of the same size: the stiffer sidewall tire would "feel" like it handles better, even though the skid pad and lap times would say otherwise.

The 15" tires on the C have a sidewall that is 113.75mm tall, the 16" tires have a 97.5mm sidewall. 16.25mm shorter sidewall will cause a huge difference in "feel", but not an actual change in handling.

(in reality, the 16" tires on the C are 195mm wide, the 15" are 175mm wide, so the 20mm extra of tire on the ground will help with lateral acceleration, which only perpetuates the "16s are better" idea)

On my track car, by the way, I sold my 16" and 17" wheels in favor of 15" wheels. Absolutely no speed difference on track between the 3 (all had Toyo RA1's), but the 15" tires are FAR cheaper. The whole setup is lighter by several pounds also, which extends the advantages of the 15" tires.

On side note, the 16" tires on the C4 have a smaller rolling diameter than the 15" tires, so the tires are turning more RPM to go the same distance.

 

You have to think in practical terms and non-modified suspension systems.

The fact is, the Prius being a relatively heavy car does not corner well with a tall sidewall tire and the problem is exacerbated by a soft sidewall. My GenII did not handle/corner well at all with the 185/65/15 tire. Sidewall flex was pronounced and in hard cornering the tire had a tenancy to roll over which is evidenced by sidewall scrubbing. They would howl fiercely when pushed hard. I ran 3 different brands and models of 15" tire on that car at numerous pressure settings from 35psi to 60psi. Higher pressure helped but there was a limit to how hard you could take a corner. A simple swap to a 17" wheel/tire (215/45/17) instantly transformed the feel of the car in terms on handling, steering response and cornering ability. I could take corners MUCH faster with the 17" tire. I ran two different brands/models of 17" tire on that car.

The GenIII with its 195/65/15 has a much better suspension setup and the even the 15" tires allow for decent cornering ability once you set the suspension in a corner. MUCH better than the GenII on 15s. I can only imagine, however, that upsizing to a 17" or even 16" wheel/tire will have the same net effect on the GenIII. Lap times do not tell the whole story. Sometimes people just don't like feeling the tall tires rolling out from underneath the car. LOL