Project log: Prius base suspension upgrades

Hi all,

I recently purchased a 2008 base pkg 6, and, as I do with all cars, am in the process of improving the handling capabilities of the car. I've owned a series of race cars over the years, and driven many more than I've owned. I do almost all work myself.

Objective:
With this car, I want to create a competent handling daily driver which remains comfortable for passengers and retains stock utility and maintains or improves upon gas mileage

With my other cars, I've gone farther towards ultimate handling, which has created extremely competent, exciting cars, but cars which our guests don't enjoy riding in and require disclaimers before I let anyone drive them (tendency to oversteer, so be careful on corners; lower (but retain suspens travel with matched springs), so watch out for curbs and speedbumps; super stiff, so try not to drive over large potholes, etc)

Main complaints:
1) Excessive lean in corners - causes slower corner entry, mid, and exit speeds overall
2) Mushy turn-in response - results in uninspiring corner entry and evasive maneuvers
3) Extreme tendency to understeer - limits corner entry and exit speed, can cause wash-out in mid-corner

Plan (to be revised as I tune the car):
0) Touring wheels/ tires (DONE - see report below)
1) Stiffen the rear sway bar (DONE - see report below)
2) Add BT chassis stiffening brace (DONE - see report below)
3) Convert to touring rear struts/ spring (DONE - see update 5/7/2013)
4) New tires - likely Yokohama dB Specs (DONE - see report below)
4) Alignment (to be planned)
-------optional if still not satisfied---------
5) TOM's front strut tower brace (DONE - see below)
6a) Stiffen links/ bushings on front bar (e.g. urethane)
6b) Stiffen front sway bar (OE touring received, to be installed)

Results

0 Touring wheels/ tires:
-Marginal increase in steering response
-No noticable change in ride quality in normal driving conditions

Verdict: worth it, but not a big bang for the buck. Do only when you need to change tires anyway, and can find reasonably lightweight 16" wheels at a good price
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1 Stiffer rear sway bar:
I replaced the stock 19mm hollow bar with the solid 24mm TRD Matrix bar (PTR11-02060) available for $170 shipped at Carson Toyota (TRD source - do a google search). This is a 15 minute job - everything you need is included with the bar you order.

- Greatly reduced corner lean. Car retains balance towards understeer. No throttle lift oversteer at reasonable to quick cornering speeds
- Improved turn-in response
- No noticable change in overall ride quality (not harsher)
- UPDATE: I had a chance to drive in the rain - the car maintains its balance towards understeer under normal driving. I tried several abrupt lift-offs at moderate (but not autocross) speed mid corner in the rain (after the car had set up) and did not induce a loose condition.


Verdict: Worth every penny to improve handling while maintaining a safe and comfortable ride. Excessive lean is gone. Easy enough to do on your own, even if you have only basic mechanical skills.
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2) BT chassis stiffening brace
I replaced the stock mid-chassis under-carriage brace with the aluminum BT chassis stiffening brace I ordered from PriusChat.com for $165. Very simple install (less than 15 minutes from start to finish) assuming you have:
a) Torque wrench to tighten the 4 bolts to 17 ft lbs
b) Metric allen socket (I believe 6mm)

I took the car on a 200 mile roundtrip highway driver, averaging ~65 mph on the highway but ranging up to 75 mph in higher limit areas. Trip was through fields and windy.

- Overall, car seems slightly more connected to the road - inputs are marginally crisper and more predictable
- Surprisingly (to me) the car seemed to track better during gusts of wind. It seems to be more stable in responding to corrective inputs
- Update: My wife reports that she perceives a big difference in stability at highway speeds in the wind. I did not tell her I made the mod, she asked if I had done something

Verdict: Moderate increase in stability at highway speeds. Given the $165, I might make this a mid-pack mod in favor of others if you are concerned about handling.
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4) Yokohama dB Super E-Spec (Grand touring summer)
I replaced the stock touring Bridgestone Turanzas with Yokohama dB Super E-Spec's (195/55/16) purchased from TireRack at $139/each. I was after 2 main objectives:

a) Better turn-in response, transition, and overll grip​

b) Equal or improved gas mileage​

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Also, given I run a separate set of snow tires in the winter, I was not concerned with snow and ice traction. With these criteria, I eliminated wider than stock, heavier than stock, and any all-season tires that were not at least better than stock. The rest I left to research. I good place to start is TireRack's article: "When Round and Black Becomes Lean and Green"

Not sure the miles on the Turanzas - they came with the car and had been swapped from the touring with unknown miles. Turanzas were worn, but not bald, probably 4/32" left in the tread. Impressions after ~2500 miles below:

Comfort - These tires are quieter than the Turanzas, even with full tread. Quieter at steady state and quieter over bumps. I was not expecting this, but it is welcome​

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Fuel economy - I'm getting an average of 1-2 mpg better with these than with the Turanzas. This is a 2%-4% increase, consistent with what TireRack reports​

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Handling - Much better turn-in response. Car overall feels crisper and more poised. Steady state cornering ability is noticably improved. Wet handling is substantially better than stock. Overall, very happy with these in the handling department. These are certainly not the silver bullet, but a large improvement.​

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Verdict: Pricey, but well worth it for the added safety alone, particularly in the wet. Not to mention the much improved handling overall.
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5) TOM's front strut tower brace
This was a relatively easy addition to the car - 45 minutes from start to finish. I got mine from Sigma Automotive ($399). You'll need a 10mm, 12mm, and 14mm socket, 14mm wrench, 8mm hex bit, and torque wrench capable of doing 30 ft lbs. While it may look daunting given you need to take apart the front cowl and remove the windshield wipers, everything is easy to get to, remove, and re-install. There is a good how to with photos here:

[ame="

"]BT Strut Tower Brace Install (by Gadgetdad) - a set on Flickr[/ame]

I took the car around some clovers and did some quick transitions at moderate speeds (35-45 mph) to test out the impact. The Prius behaves like you would expect with a front strut brace if you've ever used one before:

- Turn-is is crisper. Entering clovers, the car feels more connected to your steering inputs. The time between your input to turn, the car leaning, and then settling is reduced, making you feel more confident in corner entry. No change in amount of lean expected or experienced.
- As with all cars I've ever put a front sway bar on, the car feels more settled and stable throughout the corner - just a more solid feeling. You can consistently and predictably accelerate to the limit of the tires
- Likely as a result of the crisper input, transition response seems to be improved.

Verdict: Improved overall feel - not much overall improvement in grip. Better responsiveness to steering inputs is good. An expensive upgrade.
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3) Touring rear struts and springs (5/7/2013)
I finally got around to installing the rear touring suspension - struts and springs. The parts were relatively inexpensive at the time of purchase - less than $300 all in. However, I had them installed by the dealer as I have just not had the time. This added nearly $400 to the total cost of this mod. Upon this writing, the front of the car remains stock save the BT strut tower brace.

Initial impressions: The rear of the car feels much more planted. Upon some low speed transitions (30mph - 40mph), the mismatch in roll between the front and back of the car if very evident. The front seems to be working very hard to keep up with the rear. That being said, the car tracks extremely well once set into a corner. Turn in is responsive, but not crisp.

I took a few higher speed corners - a clover onto the highway. Where before the car felt at the edge at ~45mph, with the rear struts and springs, the car felt very confident and tracked well. I was able to accelerate out of the corner onto the highway at full throttle with no loss of traction.

I also tried to get the car to rotate mid corner by jumping on and off the gas. Even at 40mph in the clover, the back end stayed planted. I did notice the front end struggling to keep traction in this case - there is a hint of understeer creeping back into the car. This was confirmed on a 90 degree exit at 30 mph. The car tracked the corner well, but I could feel the front just barely skating along.

I think the stiffer touring bar will even out the handling by setting up the front end faster. I will confirm Friday when I have it installed.

The verdict: Pricey, but well worth the investment. The margin of safety added to the car is quite large in cornering. The excitement factor is much higher, as is the confidence you gain while driving. Less roll is clearly evident and appreciate. If you can do this one yourself, it is a no-brainer. If you have to pay to get it done, I would think about how much you really want to push your car and if you would benefit from the added enjoyment of a markedly better handling car.
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I will continue to add to this as I execute my plan.

 

I had tried to respond earlier, but my computer froze.

Drees is correct - under normal driving, there should be very little to no change in tire wear. I've put stiffer bars on all of my cars, and have had them for over 100k miles combined. No tire wear difference on any of those, so I am confident that there should be none here either.

As for ride comfort, I reiterate nothing perceptibly different was noticed in normal driving conditions with this bar. In theory a stiffer bar does add to the spring rate slightly, which could cause a slighlty stiffer ride. However, in this application, neither I nor my wife have perceived this.

Jonathan

 

Dan,

Tires do make a huge difference in turn-in, overall grip, cornering stability, and balance. I'm glad you found a set that you are happy with. I run a set of high performance summers on my other cars, and swap out with winter tires in the cold season.

As for the oversteer - it does seem like a big change to go to the larger bar, but the suspension is still very soft overall. While lean is reduced, it is certainly far from eliminated. I have not yet tested in wet conditions (I will post if I get a chance before it snows), but I doubt to experience oversteer. In fact, even on my much more aggressive setups, oversteer on front-wheel drive cars has never been snap - I tune for lift-off, controllable oversteer, which only really appears near the limit (e.g. in autocross events). The setup I've got now on the Prius feels nowhere near what would be required to achieve consistent lift-off oversteer, and certainly not snap oversteer.

I'll continue to update as I learn more about this setup on this car.

Jonathan

 

I'll definitely post my results, although I don't have high expectations for it reducing wander and sailing. As you state, the Prius is tall and flat from the side. On the plus side, it is very heavy! Can you image what would happen with a 2500lb car!

Wander can be reduced by alignment settings, but I haven't tried those yet. On my daily driver, I run -2.5 camber in the front, and it tracks all the groves on the highway - you have to pay attention when you are driving. Put on 8" race slicks and watch out!

 

Drees,

Absolutely alignment is a big deal! It has made a world of difference on my other cars in terms of balance, turn in, cornering force - you name it.

I haven't fully decided on alignment yet on the Prius. I have two concerns:
1) Tire wear - the Prius is VERY heavy for its size
2) Gas mileage - I need to study the geometry a bit and decide what makes sense as far as camber and what this means for contact patch in a straight line. I'm less concerned about toe in this respect.

Jonathan

 

I haven't come across any sidewinds of any strength since the bar, so no comments there.

I run -2.5 on my dd neon also. My FSP car runs -3.2 degrees up front. Tire wear on both is good, but both are light (FSP is <2200lbs!)

Jonathan

 

Update: 4/28/10: BT chassis stiffening Brace

I've edited the post above. Relevant excerpt:

 

1) Not sure I understand - are you answering the question from above? I have not installed yet so cannot comment

2) TRD solid sway is stiffer than touring - should make it flatter

3) Yes - in the end, the Prius is not a race car, but can certainly handle better than stock and be a good, comfortable, DD

4) Complicated question. Are you looking for dry, wet, summer, all-season? Falkens are great dry summer tires. You could try Fuzion ZRI's if you want an "extreme performance summer" - they are relatively cheap and should last 1 maybe 2 summers. If you want more options, Sportscar Magazine (SCCA publication) did a review of "extreme performance summer" tires last fall. I think it looked at 8-10 different soft but DOT legal street tires.

5) You live in CA? I used to live in Pasadena. The 2 up the mountains was my test track for mods back then. I did not have the Prius then, however.

I've got the touring front bar in my garage, the strut tower brace on its way, Yokohama dB spec tires to put on, and the touring rear suspension to install. I'll be busy in the next few weeks!

Jonathan