Rear Sway Bar

it has something to do with the caster angles. might need to increase it a bit (or return to specs) to become more stable. i think they check this on that zero point calibration process.

 

Those with noises after this install, if you used the original Prius bolts that is your noise. The hole on the Corolla/Vibe/Matrix bar is larger than Prius. The bolt isn't thick enough so the bar actually shifts a bit and eventually works loose. You need to use Corolla etc. mounting bolts and that will permanently cure the issue.

 

Thanks for the heads up. How long do you think we can go before the rear starts making noise? I'm asking because I've driven several thousand miles since I've retightened the bar, and still no noise.

As for the Corolla bolts, can u verify the year and trim model we would need for the progress bar upgarde? thanks.

 

03-08 Corolla will work. Mine came loose quick due to how I used the car (autocross). The more aggressive you drive the car the quicker it works loose.

 

is OEM hollow or solid? the smaller diameter bars are usually solid.

yes it is correct it is power^4.

If OEM solid and replacement hollow the difference would be:
(27^4 - 23^4) / 19^4 = 193%

it is not apples to apples but for comparison Gen III TRD bar is 22.4mm and OEM setup does not have any bar (they made torsion beam stiffer)

 

Slight off topic, but with the TRD bar on the Gen III, it is a lot easier to break the back end loose.

MB860 ?

 

yes but I still find front is more likely to go. But I am running 38psi in the rear, 42 front.

 

Going on your advice, I switched the bolts out, and that seems to have done the trick! Images below:

The Purchased Parts
Bolt Comparison
Nut Comparison
Bolt Comparison 2
Bolt Comparison 3

Total cost was about 25 bucks. I actually had to go to a mechanics garage, as my impact wasnt strong enough to get one of the bolts off! Definitely something to do if you got the progressive bar.

 

Did you measure the diameter of both the old and new bolts? They look the same to me except for the length...

 

That's an excellent question.

Assuming the bolt is the same diameter, but just merely longer, will it make any difference?

I'm thinking not because the torque strength will still be the same. However, this is not my area of expertise.

Anyone want to chime in?

 

I have 24mm TRD (PTR11-02060) rear sway bar on my 2007 Gen II Prius and I had to retorque OEM nuts twice since TRD sway bar was installed as new part two years ago. Lately creaking noise became stronger and stronger, and I was sure that was noise only, but it wasn't. Last week I went to my repair shop and put the PriPri on the lift: where sway bar and C frame suspension come in contact there was TRD bar red paint scraped as an evident sign of relative movement between parts. We decided to retorque OEM nuts to TRD sheet specifics: 150 lbs-ft (204 Nm) using strong treadlocker. The mechanician was not able to torque to 150 lbs with one arm, he had to use two arms and full of his strenght to torque them. Now creaking noise has gone and I was surprised to rediscover full solid driving style with retightned bar. This is the prove that we not only have noise when nuts get loose, but elastic force too. Mostly at small suspension roll angles. This leads to loose solid driving sensations that 24mm rear sway bar is able to bring us on this car.
Are there news about Corolla lager diameter bolts ?

 

I bought the Progress bar and will replace the nuts with aircraft nuts that you can get at a local hardware store.
I will install it this week

 

Don't forget the bolts!

 

lol, well I think that I can do that

 

I've come up with an idea !! Those who are afraid of oversteering with 24mm rear sway bar could try to install it with bolts only. The bar will reduce its stiffness and oversteer too !! Don't forget to install bolts from top to bottom... using force of gravity the right way helps...

 

That would sound awesome. lol

 

I'll take oversteer anytime vs understeer. If you haven't learned how to oversteer a car, you haven't learned how to drive properly

 

So I just installed it and went a few blocks to the store and back. It feels solid now in the rear. Yeah!

 

I have done some homework to better understand rear Gen II sway bar stiffness matters. My stock 2007 Prius, before new 24mm TRD sway bar, had a stock rear 20mm sway bar. This bar weights 1332 grams.

Some math homework lead me to this conclusion: sure this bar is hollow and NOT solid, as we know. But not only. Avoiding the cutting of the bar, in order to calculate inner OEM bar diameter as an unknown value I went for weight and geometric measures and assumed (as very close to real) 1000mm as bar torsion working length. Well, the result for OEM 20mm hollow bar is 14mm inner diameter, and thus only 3mm of wall thickness.

Comparing stiffness between OEM hollow 20mm and TRD 24mm solid rear bar, as we go with fourth power of diameter, we have TRD bar is 2,73 times stiffer than stock hollow 20mm bar. That’s a huge amount of more stiffness !!

So why is TRD 24mm sway bar working so good on this car and doesn’t make it oversteer like crazy ??!!

In my opinion we have three matters:

# 1 Stock Prius setup understeers like crazy and there is a lot, a lot, a LOT rear roll lacking stiffness amount before we reach oversteering handling.

# 2 With front OEM 22mm sway bar and 24mm TRD rear sway bar the car is very close to neutral handling. Understeer is mostly gone, thought it remains a typical understeering FWD car behaviour. Anyway I guess not many cars out there are as close to neutral handling with their stock handling setup as Prius is with this customized setup. This is due to security reasons: factories can’t risk for rubbish drivers !! However the car still rolls a bit too much for my taste and hope the front 24mm sway bar from Corrola/Matrix (I placed an order for it at my dealer using Toyota PN, as you gave me here in PC … life may bless you !!) will help. Sure it will, but the way the car will react to increased stiffness is all to be tested on the road.

# 3 When we consider elastic roll stiffness we have to consider overall stiffness and calculate it at the wheel. So if we have overall wheel roll stiffness as summary of A+B+C+D, where A is tyre rate, B is helicoidal spring rate, C is C-beam rate and D is sway bar rate, an increase of 273% at sway bar element will not lead to the same overall stiffness increase at the wheel. It’s a lot less !!

How much is it ? I can’t calculate it as I don’t have C-beam stiffness.. and I don’t want to do any further homework.. I don’t miss school time !!

 

I also noticed the stock rear sway being hollow due to it's light weight.
So really it is more like a 15/16mm solid bar. With the Progress bar it is a solid 22mm.
Also, mfg typically setup fwd with understeer.