Wheels and Steering and Shocks, Oh My!

Yes, I was assuming on both examples that the maximum angle done by drive wheels was the same.

If two given cars have the same maximum angle at the wheels, then the one with the more direct drive ratio will have the smaller lock-to-lock turns.

 

You're right about the amount the wheels turn being important in the equation. But for the most part, the differences between the amount the wheels can turn is insignificant to the differences in steering ratios, so a car with a lower ratio almost always has a lower lock-to-lock as far as personal production vehicles go.

In the 2010 Prius, and simplifying slightly, the Prius models 1-4 can turn the tires 74.8 degrees total from one extreme to the other. The Prius 5 can turn 69.3 degrees. That means you get a couple more degrees of turn at maximum on each side with the Prius 1-4, but again this simplifies things like the fact that the wheels do not turn in parallel and have camber and whatnot.

The formula is (steering wheel lock-to-lock) * 360 / steering ratio. Previous posts have the numbers.

The Prius V has faster steering, meaning it has a lower ratio (14.6 in the V and 17.6 in the rest) and in real world terms this means you have to turn the steering wheel less to move the tires a given angle. In the Prius 1-4 you're turning the steering wheel more to get the same effect, though you can get a slightly bigger maximum turn angle, taking more turns of the wheel in the process of course.

 

Surprisingly, the 17" tires have a slightly smaller outside diameter than the 15" tires.

The 17" tires are 215/45R17 - which comes out to 24.62 inches
The 15" tires are 195/65R15 - which comes out to 24.98 inches

Formula is width X aspect ratio X 2 + wheel diameter = total diameter

Width is the first number (in mm), aspect ratio is the second before the R, and the last number is the wheel diameter in inches.

The 17" tires are .79 inches (20mm) wider however, which is the reason they cannot turn as far without rubbing.

There is actually one 195/45R17 tire made by Yokohama (on TireRack at least), but it is a summer tire. You could swap out your 15" wheels for 17" quite easily with this tire and not worry about the rub.

 

It would not be a surprise for you if you had read this thread entirely before posting.

I just said the 17" are smaller a few posts earlier on this very same thread:
http://priuschat.com/forums/2010-toyota-prius/60065-wheels-steering-shocks-oh-my-5.html#post862832

 

See if it has something to do with driving wheel size. Probably you're not yet "at home" with the larger wheel?

 

ummm...didnt engineer mention a slightly greater turning radius? that would explain it. less angle for tires to travel would explain less steering wheel angle

 

I know LoL, I was referring to the placebo effect, to your "feel"

 

I didn't read through all the pages. But, I picked up my V ATP last night and this morning took it too work. With the gen II I was able to do a u turn with out having to do a 3 point turn. But, with the gen III I had to. I was a bit dissapointed.

 

gen 3 is reported to have bigger turning radius... at least pretty sure it was mentioned. was thinking about going thru all the videos, but no time for that...tuesday is pretty much errand day

 

That's correct.

2009 has a curb-to-curb radius of 34.1 feet.
2010 has a curb-to-curb radius of 36.8 feet (39.2 feet in the 17" wheel model).

 

FINALLY!!! From the is 2010 not ready for prime time thread:

I think I'd pass on the upgrade as the assist is already too great for me. I don't think it's the damping that's the issue, when enthusiasts and reviewers talk about road feel they don't mean the wobble feedback of the uneven road that dampeners suppress- it's the feeling of your hands directly controlling the tires and feeling the torque response on a turn. High ratio and high assist are pretty much the opposite of a responsive steering system. But I guess I'd have to drive it to feel. In reality I don't think I'll be able to really notice anyhow, but I guess now it looks like having the option may be better.

I wonder when they will begin to offer steer by wire, as it will get rid of the wasteful continuously running power steering motor and increase MPGs. Seems like a natural for the Prius, especially considering road feel is not one of the strong suits anyhow.

 

Doug may not have described the tweaks correctly. I agree that it seems that reducing the boost would be better but Toyota has to be aware that the "numb" steering is the most criticized feature of the 2010. Hopefully the engineers/programmers will be able to make it a little less numb somehow.

They did say that they would get back to us on how an upgrade would work. You may be right that buying soon and having the option to upgrade is the way to go.

Roy