Wheels and Steering and Shocks, Oh My!

They are both directly related TP. If you have a smaller (more direct) ratio, it means you will turn the front wheels up to the maximum allowed with less turns in the driving wheel.

So, in fact, the ratio is directly related to lock-to-lock turns at the wheel. If the ratio is longer, you will have to turn the drive wheel more to reach the lock position each way.

 

I love fast steering, bring it on.
No, fast steering won't make you lose control by over steering, ask a kart driver which has about 1/4 turn lock to lock.

 

Ditto here Mate - and deciding on the V --- the steering difference / improvement (until Sept anyway) was icing on the cake.

I may have missed if posted already, but has someone driven both the Rev 3.0 V and also the non-V models? Is the ride / handling / steering THAT different?

 

My understanding of why the 17" wheel cars have a ~2.75 lock-to-lock, vs. ~3.75 for 15" wheel cars, is because the larger 17" wheels can't be allowed to turn as far or they'd rub.

My guess (not sure) is that the 2 cars might in fact have the same steering ratio, just a different lock-to-lock, with the shorter lock-to-lock on the 17"s preventing them from rubbing.

Prius Team--any input here?

 

The big difference is that the Prius goes where it's pointed, unlike the typical land yacht where you have to saw the rudder back and forth. True, there's not much steering feel, but it's less tiring, and there's a direct response to steering input. I will admit it took some getting used to, but I much prefer it now.

 

Ahhh... had not thought of that possibility, well done!

I don't know if that is the reason, but I must call your attention to the fact that one thing is to be larger, another is to be wider.

The 15" wheels are in fact larger, i.e. each rotation goes a bigger distance. The circumference of the 195/65R15 is bigger (@1993.3mm) than the circumference of the 215/45R17 (@1964.4mm).

So watch out when you say "larger wheels" because technically the 15" are in fact larger than the 17". It's the outside circumference that counts, not just the rim.

On the other hand, the 15" is not as wider as the 17", since the 17" version is using 215mm wide tire instead of 195mm, a delta of 20mm which can make it rubber the inside of the tire if the lock to lock is too big to accommodate for the wider tire.

It's the extra 20mm that make for better handling, better grip on dry surface, and of course the lower MPG value. Everything has its price.

 

This is not the case. As they have stated before, there is different hardware on the two, and after the fall, they will all be built with the same hardware and setting. The 15" tires currently have a 2 foot shorter turning radius, and that will likely be diminished or removed with the adjustment.

 

I intentionally used the word larger (didn't reference tire outside diameter), since I didn't have the specs on the 2 wheel/tire combinations.

 

It would be GREAT to have any and all of of this cleared up, but we've been asking for a while...

Anyhow, in my opinion I doubt the 17" version of the car would have restricted turning capabilities- ie not being able to turn the wheels as far to either side. However, the turning radius of the 15" model is 17.1 feet, while it is 18 feet in the 17" model so I could be wrong. However, I believe other factors come into play (wheelcut, toe, caster, tire width, etc) for the turning radius, and these are pretty close together.

In any event, the mystery of what and if the "EPS tuning upgrade" will be for those who take delivery of 15" cars this summer remains. The 15" feels mighty floaty to me because of all the powers steering assist, and coupled with the slow steering this is really my main complaint with the car. I guess someone has to carry the crappy 80s buick steering (non)feel into the next century!

The BMW method which adds power steering boost at parking or slow speeds and then reduces it as you go to normal driving speeds to increase your road feel is so obvious and simple I can't believe other manufacturers don't use it. It can't be that hard to program the EPS to reduce its boost over 15mph. Drive a car without power steering and you'll realize right away it's a lot easier to turn while moving and you don't even notice the lack of power steering motor once you're moving at a decent clip.

 

You might be right--I said I was not sure, which is why I asked Prius Team to provide some input.

Also--at least according to the doc below, the 15" wheel cars have a 0.9' smaller turning radius.

 

But that's the problem- we don't know for sure if the 15" cars will eventually come with the 2.75 lock-to-lock hardware or with the brushless motor or not after the fall. Prius team SEEMED to imply only the electrionic power steering tuning would be upgradeable, but again, since they haven't answered any questions we're all trying to decode the cryptic message about the steering changes.

If it's true that the 2.75 hardware (which I think anyone who is aware or cares at all how their steering feels would agree is superior) will be coming on the 15" models at some point, than I think it is unlikely there will be a free upgrade- replacing the rack and/or motor is not exactly cheap or necessary.

Even the EPS tuning upgrade may not be free- it's not like a safety or defect issue that MUST be fixed or anything.

 

Please read the first page of this thread over. The Prius Team tries to explain it, although they could have done a better job, as it is confusing.

 

So what are we supposed to conclude from this, regarding the direct question if the upgrade will be hardware, software or both:

The production units are here, no follow up, just speculating by forum members.

We still don't know how or even if the 15" models that are arriving can or will be upgradeable. All they have to say is "we still don't know".

Nobody has explained what exactly these software tuning differences are either.

 

OK--after further digging--here's what I found:

15" wheel cars:
steering ratio: 17.6 (source: Toyota tech document)
lock-to-lock: ~3.75 (source: Prius Team post)
turning radius: 17.1 (source: Toyota tech document)

17" wheel cars:
steering ratio: 14.6
lock-to-lock: ~2.75
turning radius: 18.0

On the 15" cars, the lock-to-lock is 36% larger, while the steering ratio is 20% less direct (requires 17.6 degrees of turn for every 1 degree turn of the tires, vs. only 14.6 degrees required for the 17" cars). So the steering wheel turns 36% more, but for each degree turned, it turns the tires 20% less, meaning it allows the tires to turn 13% more than the 17" cars.

So what have we learned?

17" wheel cars have lower steering ratio (i.e. more direct steering), smaller lock-to-lock, and the max. tire turning is less (presumably so they don't rub). This translates to a slightly larger turning radius.

 

Comments in bold below

 

Of course, but we do know the streering ratio of these cars already. That's what I meant when I said the hardware on the 2.75 car is superior, because saying lower ratio or faster steering is confusing for some people.

That's pretty much what I think too, but some people have asked if there will be production 15" cars with the lower ratio and 2.75 lock-to-lock which would mean different hardware. The prius team could just be saying the 2.75 is planned for the Pruis V, which we now know is true. The 15" version of the car I test drove had the 3.75 lock to lock rack.

I'd be very surprised if they changed the steering rack that ships on the 15" models in a few months. The software upgrade is more likely to actually happen, and that's all I infer from them saying the EPS system will be upgradeable, but then they went and said they weren't sure if there will be a hardware upgrade or not which is why people think the 15" wheel vehicles may eventually come with a lower steering ratio like the Pruis V. The big question to me is what exactly these EPS upgrades are and if they are reven going to be available.