Rear Sway Bar

This is the main reason I am not installing my new front sway bar until I can get a better feel for how the rear sway bar has affected my car.

 

Which front bar are you going to install? I have a touring front bar already. Are you going to get a Corolla bar? How much bigger is that one?

 

The Corolla front bar is 24mm. The Prius Touring bar is 22mm. I already have the Corolla bar but have not installed it yet. I picked it up at a salvage yard for $50. I didn't want to go larger than 24mm though as that may cause increased understeer.

 

This is off-topic but is there a way to tighten the play in my steering wheel? I'm not talking about a modification...I'm talking about taking it to the dealership for them to fix. My mother's Prius, I noticed, is more responsive when you turn the steering wheel side to side.

 

I have a similar problem with my car. It is in my case, the tires. Since I put my new Hankook Optimo H727s on, I have very poor response to turning the steering wheel, and at high speed the car becomes unstable (but that's a different thread). As the tires are new, I did not want to replace them - I drive a lot of miles, so I'll replace them soon enough. Anyhow, I thought maybe putting the rear sway bar on might make the car more stable, which it did.

So what kind of tires do you have vs. what your Mom has?

 

Now that's an interesting point. I have stock 16" tires (Bridgestone Turanza EL400). Of course hers is the stock 15" (Goodyear something?). Does tire size and profile have something to do with it?

 

Neo is probably right.

Stand beside your car and bridge from the rear of your left front tire to the fender with one hand so you can feel small tire movements. Then reach in the window and see how far you can move the wheel in both directions before the tire moves. Try that on both cars.

They will probably be about the same.

There is a pre-load adjustment on a Gen III steering rack (most likely yours too). I really doubt that's a problem though.

Tires can make a big difference in steering response, even tires of the same size and rating. You can have a tire that feels like a complete flabby POS and another tire the same size that give nice crisp steering response.

 

I'll defer that one to the tire experts. Is this something you noticed just since installing the new rear sway bar, or has it always been the case?

 

I will have to try that steering test. Off topic, but that flabby POS response is actually what motivated me to add the sway bar. The bar did not fix the flab problem, but it did make the car more stable in spite of it. Is there a particular tire specification that characterizes steering response of one tire vs. another? I don't want to make that mistake again.

 

I've never seen a spec like that. When I'm buying tires I don't have experience with, I use the Tire Racks detailed survey results and pay attention to the "steering response" rating. It's mostly a function of sidewall stiffness, but other things count too so don't completely ignore them

 

It was always the case since the day I bought the car. My mom drove it a couple times and noticed it. Then I did too. For the longest time, I've ignored the problem and I still doubt it's an issue. This was more of a "just wondering..." thing.

 

You could swap tires/wheels with her and find out for sure.

 

That is about the best you can do. The Tirerack tests are helpful for learning about tire characteristics that the specs can't tell you. The Hankook H727, for example, rate well in snow conditions but Tirerack testers did knock it for sluggish steering response and not so great handling. It's a good tire but not one that should be chosen if you want crisp steering and balanced handling. This is why I created the Tirerack test report thread.

 

Smaller sidewall size (Low profile tires) increases cornering and turn-in response, as there is less sidewall to flex while turning.

It’s one of the major reasons to plus size the tires up to a 16" or 17” rim.

The faster turn-in rate makes the car corner and steer better, which is why most auto-cross, road racing cars have them, low profile tires are installed for a purpose, and it's not just to look cool.

The down side, is that the smaller sidewall tires give a harsher ride, because there is less sidewall to cushion the bumps and potholes. But honestly, I’d prefer a harsher ride to have the increased turning response.

Check your mom’s tire pressure, make sure it’s at the recommended specs. If it is, then try increasing the pressure. The increased pressure will help minimize sidewall flex, but you will get the most results from plus sizing the rims and tires.

If your mom doesn't want to have to buy new rims and tires, another option is when her OEM tires wear out and it's to change tires, she can switch to a wider tire on the 15 inch stock rims.

I changed my OEM 185/65R15 tires to 205/60R15 General AltiMax HP at 44psi in the front tires and 42psi in the rear tires and I've noticed an increased turn-in response. I've read that I'd take a mpg hit, and so far I haven't. I was getting 57mpg yesterday when the weather was 70 degrees out.

 

Detailed tire articles can be a help.

Do you remember way back when, before the Goodyear Aquatred came out the first time?

Back then Goodyear was in a slump and had been getting poor reviews/ratings/losing business. They couldn't seem to engineer a good passenger car tire but they had some good truck tires. So they took a truck tire design and changed the tread on it from an off road suited tread to what is now known as the the original Aquatred.

Good news was it performed well. Bad news was the sidewalls were stiff like truck tires and on lighter vehicles some people complained the ride was too stiff.

Unrelated the Aquatred first gen (early 90s) also had a problem with the center channel not being deep enough so the wet weather traction didn't degraded heavily as the tread wore off.

Eventually they redesigned the Aquatred who knows how many times (by the mid 90s it was Aquatred II) and many other tire companies copied the design. I have no idea if their tires are still stiff sidewalls like the early aquatreds were but reading that story obviously stuck in my memory and way back when (maybe that also says something about how much I read and how well I remember what I read).

point is if you read the press release (the tire PDF nowadays), the CR, autoblog, tirerack reviews you might see someone mention something relevant to the origin of the tire design that might clue you in to the stiffness or softness of the sidewall.

 

It's interesting that you all think it's a tire disparity. If that's the case, then it doesn't really bother me. I just wanted to make sure there was nothing wrong with the car itself.

 

Try nudging the car sideways by leaning into the fender (don't bend anything ). Try it on both cars and notice the amount of give in the tire as the car wiggles.

There is no guaranty it's a tire thing, but odds are it is.

 

If you're worried about nudging the car just open the hood and grab a solid chunk of metal and push and pull the car side to side and watch for how much the tire flexes and bends vs. the suspension.

You have 16" tires so they are not that bad but compared to a 17" low profile tire the difference can be quite large depending on the sidewall construction for each tire. There really is not much sidewall to flex on a 45 series tire. You're more than welcome to borrow my 17s for a week or two if you really wanted to test this out.

 

I looked around on the web a bit. Found this, but seeing as how you're driving a 2009, it's probably not worn out rack bushings.

 

Just a note on the sway bar. There's one favorite part about my morning commute that I now love. This s curve:



I know it doesn't look like much from an aerial view, but because it goes downhill and has some blind curves shrouded by trees, its a lot more fun than it looks. Most cars brake through this section at about 30-35mph, and I used to too. Now braking isn't even on my mind. I want to accelerate. I can comfortably take it at 50 mph and I bet I could even push 60 if I tried.

Just today during this stretch, I was sandwiched by 2 late year black BMWs. The BMW far in front of me wasn't braking (props to BMW for great stock handling). Meanwhile I accelerated and nearly caught up to him by the time we merged. The BMW behind me was left way behind, but after he merged, he accelerated, changed lanes, and overtook me. I saw him look my direction and he was probably thinking "Wth a Prius?"

That's right.