Want to modify steering to decrease turning radius. Can it be done?

Not all 4s came with the 16s, first off. 2nd off... you can modify it to have the better steering radius, but you are looking at at least $1000 in modifications.

 

hey, you should straight trade for my C2. it has the turn radius you want lol jk

 

First, let me point out as an automotive engineer, you are cioncerned about too little a problem.
Any dfference between the steering ratios are likely the pinion gear to steering rack so yes, you can likely change the rack and pinion to get what you want but there's no real reason to do so. If indeed there is a significant difference in turning radius its ikely the rsult of the rack length and the diameter oif the pinuiongear limitig the trave (therefore you g less travel of the rack back and forth so the wheels won't turn as far.
Having installed severa wider wheels and tires on Prius 1 thru 4s I can verify there is no problem fitting even 7" wide rims and 205 section tires so changing wheels/tires are not your solution.
I am curious as to why youbelieve you need to change the steeing ratio,turning radius. I have a sneakin suspicion that going for the slower steeing ratio will not prvent your having to o 3 point turns and why do you have to do so many?
PS in all likehood, the least expensive change is literally sell your Prius C4 and get a C2 or 3 with the 15" wheels with the 'tighter' steering ratio but check it out first in a test drive that includes a U turn that your C4 has to do a 3 point turnaround to verify theC2 won't need a 3 point. When I tried it here in the shop lot I couldn't tell the real difference..

 

again... as I mentioned above... the C4 with the 15" wheels don't have the higher turning radius. They are the same as the 1/2/3

 

We got to bench racing the peculiar Prius C change in track and increase in turning circle when equipped with 195/50x16 tires. Its strange that the tire size should decrease in diameter, widen by an inch and the track decrease by 0.8 inch front and 1 inch rear while increasing the turn radius by spec 6 feet. It makes no sense to mount better size wheels/tires and reduce the track. We can understand increasing the offset and increase rim width to accommodate wider tires but reducing the track (distance between centerlines of front tires by .8 inch, or 20.3 mm and the rears by 1 inch, or 25.4 mm.. That’s a change of 10 mm on each front wheel and 12.5 mm on each rear wheel. Nonsense. Probably the suspension is changed to shorten track and possibly because of the change in the steering rack ratio. Next time we get the C4 in here we’ll do some measurements.
Our conclusion is you’ll be better off selling your C4 and get a C2 and add the accessories of choice if you want that lesser turning circle. These changes to go from C4 to C2 or C3 are major in scope and not readily addressed especially by garages. Its not that it can't be done, two of us are grad engineers who did this kind of projects in our careers but its not simple..

Further, we got to investigate the Yaris and we think the difference in turning radius could be the use of the Yaris closer ratio rack and pinion in a limited space. With the pinion being larger and the space for the rack being the same, that naturally means the travel of the pinion is less and thus there is less turning the wheel. Ergo, the turning radius is greater. I suspect if yu replaced the steering rack and pinion gear that would slolve your problem. Meassure the turns fully left to fully right and reverse and advise your answer. IOf its less than 3 and an eigth turns lock to olock you've probably nailed it. While you're at it measure the amount of the change in angle of the front wheels lock to lock.If its just the rack that needs to be changed figure $1000 for that including labor but get a quote first. And we still say trading is better. cheers.

 

*le sigh* ... why not just get a c4 without the 16" wheels like I keep mentioning... The C4 that comes with the 15" standard don't get the rack change... I know this... because mine has the 15" wheels standard...

 

*le sigh*

 

Which is why asking questions without listing your location yields 'wrong' answers.

 

What kind of name is John for a Canadian? Canada is nice. I'm in Toronto currently for business. Feeling bad for Alberta for that flooding.

 

I dont own a Prius c, but I would suspect that like about every other car built, the steering stops are built into the lower control arms to limit front spindle travel. The steering stops may be an integral part of the arm, or just a simple bolt on. I dont know of any situation where the turning radius is set at the steering rack, it's done at the spindle and lower control arm to avoid bending any steering rods when the limit is reached. I would bet fitting the smaller wheels and increasing the distance to the steering stops is possible at not much cost. A little time spent with the Prius parts guy to compare part numbers should reveal what would be involved.

 

Who reads posts' these days. I personally didn't know that a c4 there was that far off in difference from the ones there.

 

I'm thinking something like this.

Or, something else cheap and quick would be to watch what you're doing and don't do that any more. Drive so you don't need to do 3 pt turns any more. Perhaps it's driving style, perhaps it's where you drive. Perhaps old habits can be modified.

 

In some states, U-turns are illegal.

 

I did not find any states that prohibit u turns, certainly GA doesn't. That said, they all restrict when and where you can make a U turn.

- http://www.dds.ga.gov/docs/forms/driversmanual.pdf

(Both Taiwan and the Philippines do prohibit U Turns)
Michigan is notorious for making them mandatory. Michigan left - Wikipedia, the free encyclopedia

 

They may have changed it recently, but I know for a fact that Ohio was illegal around 5 years ago. Unless both the judge and the police officer were taking me for a ride.