cAstro my Prius c: Project thread

This will be my project build thread for cAstro, my 2012 Prius c Two. I bought the car to be my daily driver commuter car and cargo hauler.

Thanks to Micro Image for all the help in getting this project off the ground. The intent is simple; maintain comfortable but taut ride comfort yet inject some legit chassis control and handling prowess. This will let me enjoy my corners, and a benefit is not slowing down for corners always helps fuel economy.

Here are the ingredients to date:
*KW Variant 3 coilovers from the 2nd gen Yaris, yup they fit.
*Powergrid front anti-roll bar adjustable drop links
*SPC EZShims literally dial in the rear toe and camber correction.
*A real alignment.

Aesthetic tweaks:
*XenonSupply H11 low-beam HIDs
*Pilot chrome amber turn signal bulbs [no more egg yolks]


Here are some pictures:

The first step is to remove the wipers, cowl trim and metal cowl tray. Then you can finally get to the front strut top mounts.


Here's the front with the strut removed


Here's a front strut disassembled.


Here's a little snag; I had to improvise a light press to remove the upper strut bearing from the spring hat. Good ole 7/8" socket


The KW Variant 3 front strut next to the factory strut. Note the assembled length difference. Of note, the KW damper has 0.6" more stroke, despite being shorter overall. Also of note, the stock damper runs what I'll call "typical" FWD strut stroke ratio, which runs crap-tons of droop and puts the ride height very near bumpstop contact. Stock free compression stroke from ride height is a paltry 0.35", which I hate. Thankfully KW did their homework and fixed this. Lowering the car 1.125" positions the stroke such that you have 1.2" free compression travel, which is much more like it!

 

...continued.


I drilled a small hole in the damper dust cover to create clearance for the rebound adjuster and also to thread it into the damper shaft like stock. This gets hidden under the metal cowl tray and is out of the elements anyway.


Front KW strut installed with Powergrid drop-link. Powergrids links are legit-strong and impart a noticeably more precise transitional feel to the chassis.


Close-up Suspension pron


Here's the rear dampers and springs, yellow are KW and black are stock. Curiously, KW went with less stroke than stock, which still has me scratching my head. Even so, the TUV certification gives this suspension greater GVW than stock, which is can only imply notably stiffer spring rates.


These KW Variant 3's are actually built for the 2nd gen Yaris. Since the Prius c is about 200 pounds heavier, I knew I'd have to adjust the KW assembly manual recommendations for spring pre-load to obtain an appropriate ride height. Curiously enough, compared to the Yaris, the Prius c's ride height ended up being 1/8" too high in front and a solid 1/2" lower in back. This means the Prius c is actually lighter than the Yaris up front, and probably about 250 pounds extra is saddling the rear axle. I had to retain the factory rear spring upper rubber isolator to give me enough preload to get the ride height I wanted. Thankfully the metal locating cone is long enough to maintain positive engagement of the KW spring perch along with the rubber isolator. Whew!

 

last bit for now:


This is the KW suspension installed in the back. The bottom of the damper has a little plastic cover that hides the compression adjustment from the elements. I ended up dialing in the dampers significantly different from KW's recommendations, which is unusual but then again I'm adapting the Yaris setup for the Prius c. Out-of-the-box recommendations are 6 clicks from hard for rebound front and back, and 5 clicks from hard for compression front and back. I ended up settling on 10 clicks from hard [out of 15] on both rebound and compression, front and rear. This gives the car a taut ride without being harsh or jarring. It's firmer than stock, but not unacceptably so. The body control is vastly improved, but not hardcore racecar-esque like the out-of-the-box settings, which were needlessly aggressive for the character of this car.


Here's a shot of the SPC EZShim [in red]. There's an online app and also the included chart that lets you rotate the two concentric circles to dial in the toe and camber adjustment you want. You have to do a baseline alignment to understand the delta you're looking for.

Speaking of alignment, it turns out my Prius c was poorly aligned from the factory [or dealership, not sure]. Front toe was actually toed-out, which is virtually unheard of. This explains why the car had a darty and unsettled feel down the Interstate. The rear toe was IMO too aggressively toed-in. I ended up setting up the car like this:

Front camber = -1.0 deg
Front toe = 1/16" in total
Rear camber = -0.5 deg
Rear toe = 1/16" in total

This alignment gives the car a confident feel; it actually tracks straight down the Interstate now. It's really a revelation...it's always a revelation how a good alignment transforms any car from mediocre to fantastic. The added camber gives the tires a fighting chance when I carve some corners, yet it's not too much camber to make the car tramline on the straight-ahead or add funky tire wear.


Finally, here's the rear rebound damper adjustment, hidden under the damper cover in the trunk.


This is a really crappy picture of the final ride height; 13 1/8" from fender arch to axle, front and rear. This is 1 1/4" lower than stock up front, and 1 1/8" lower than stock in back.

Onto the aesthetic tweaks!


Chromed amber turn signal bulbs, no more egg yolk, yay!


Find the HID ballast! Honestly it's just a temp location while I shake down the system. If it stays reliable then I'll pull the bumper and permanently mount them 100% out of sight and nice-n-low.

These are the XenonSupply.com "Prius Featured Bundle" with H11 bulbs and slim digital ballasts. The ballasts are nice n small, but they do buzz a little bit when you have the hood open. With the hood they're virtually unnoticeable.


4300 Kelvin color is OEM proper. No ghetto-bling here. The HID's match the H11's optics very nicely, and the light output is typical of HIDs, which is awesome. There's a little bit of color fringing from the optics, but IMO it's endearing and doesn't affect anything.


Other notes:

Things on the shelf:
*A set of Continential ProContact EcoPlus in 195/60-15. Hopefully adding LRR will keep FE up despite the added tire width, which I'm hoping will add some cornering grip. Have my cake and eat it too? We'll see
*Whiteline front control arm bushings, both the lateral and the rear, which I got the offset one that adds 0.5 degrees caster. I don't have a press so I need to carve time to remove the arms and have a shop swap them out. I wanted to do the coilovers first and be able to appreciate the change in caster later.

On Order:
*949 Racing 15x7 et36 on pre-order, due end Aug/early Sept.
*McGard splinedrive lugs from Good-Win-Racing.
*Opti-Coat 2.0 and other detailing goodies from Detailed Image.

See you soon!
Ryan

 

Yup, but just FYI, they're a very tight fit in the connector base, and they're sold individually. They're not OEM quality, but they get the job done. IMO if you can find better quality, get something else instead.

Amazon link

 

Just so I have it on record, KW Variant 3 stroke information:

Front: MacPherson strut w/0.99:1 motion ratio
6.8" total stroke w/bumpstop removed
theoretical bump height w/100% bumpstop compression = 9.45"
1st contact w/bumpstop height = 11.9"
current ride height = 13.1"
droop height = 16.25"

Rear: Torsion beam w/approximate 1.25:1 damper motion ratio
7.5" total stroke w/bumpstop removed
theoretical bump height w/100% bumpstop comrpession = 9.9"
1st contact w/bumpstop height = 12.1"
current ride height = 13.1"
droop height = 15.9"

 

Thanks. Bummer on curbing yours. If you want to simply try out something relatively quick and easy, go for some black Plasti-Dip. Clean and mask off the area first. It won't fix the scratches per se but will give a protective coating that can be removed if you don't like it. I've been considering doing something similar like a couple fellow forum members have done to give their Prius c a 'big mouth" look by blacking out the front end center beam.

 

Just a quick update.

Rolling Stock: 949 Racing is taking forever to get their 6UL's made. Konig is taking forever to get the specific Daylite's I ordered in-stock. So I have two sets of tires sitting in my basement ready to go; the Continential ContiPro Eco+ in 195/60-15, and Michelin X-Ice Xi3 in 185/60-15. Curiously, the Michelin 185's appear to have the same contact patch width as the Conti 195's, which is odd but typical for a snow tire.


Audio Upgrades:
I started designing an upgraded audio system for the car. I started off with the idea to add a small subwoofer, but then inflated to a medium sized project. It'll go down like this:
*Stock head-unit. The Bluetooth is my primary source and it's too good to give up. I also can't tolerate laggy aftermarket steering wheel control adapters.
*Alpine MRX-V70 5-channel class-D amp is reasonably small, light, and efficient. It also accepts speaker-level inputs, which is important for retaining the stock head unit. 90W RMS per door plus 350W RMS for the subwoofers.
*JBL Power series 6.5" component set up in front doors and 6.5" 2-way coaxials in rear doors.
*Two Dayton 8" subwoofers occupying half the spare tire well; horizontally opposed to cancel out mechanically-induced vibrations. This will be made from a proprietary enclosure construction in separate Qtc=0.71 acoustic suspension chambers.
*10 pounds [12 ft^3] of NVX damping material, no more. I'm not trying to add a ton of weight to the car; I don't find the stock noise level objectionable
*remainder of spare tire well will have a small tool kit and flat tire puncture repair kit to counteract the lack of a spare tire.

I'll be doing the audio stuff over the next few weeks. Lots is going on in the home front so the car can't be my sole focus at the moment.

Here's a how-it-sits picture in the meantime:


Cheers,
Ryan

 

After seemingly never-ending manufacturing delays, I finally got the 949 Racing wheels! Thanks to Good-Win-Racing for the prompt shipment. The wheels are 15x7 et36 with a 67/54 hubcentric adapter mated to Conti EcoPlus in 195/60-15. I also changed to McGard spline-drive lugs that have the rotating seat to not scratch the wheels and torque up smoother. The fitment is excellent, the rolling resistance appears comparable to the stock tires [obviously TBD long-term], and the cornering grip is massively improved.

Let me know what you think. I'm considering lowering the car another half inch to improve the stance. The KW's allow me to do so and still have more compression travel than stock.





Yes, I know I'm shadowing my own shot. Forgive me




Cheers,
Ryan

 

It's amazing how it's 1.25" lower than stock and it still looks jacked up. We all know that "Wheel Gap Kills". LOL




*Also*
I've started installing the stereo bits. The rear door speakers are in, as is the front right component set. It's incredible the improvement in frequency response & resolution between these JBL Power's and the OEM flimsies. At the moment I'm simply using the included JBL brackets, which requires drilling new mounting holes in the sheetmetal, as Toyota decided to use some very odd bolt pattern. Also, I needed to double-up the adapters up front to clear the speaker magnet from the window glass when its fully rolled down. Mounting the component set crossover also required some careful placement and wiring management to not interfere with window operation. I'm using gasketing foam to seal the speaker and brackets to the sheetmetal. I've also added some NVX sound damping material to the doors where I could reach without removing the vapor barriers' messy glue.

With any luck I'll start pulling the interior this weekend to install the subwoofer enclosure [which is built] and the amplifier.


*Double Also*
I took the car on a road trip this weekend. I hosted the Michigan MINI Motoring Club fall color/wine tasting tour up in the Leelanau & Old Mission peninsulas of beautiful northern Michigan. The vehicle makeup consisted of a pack of MINIs, a Mazdaspeed3, a '62 Bentley and an '88 Rolls Royce. The Prius C acquitted itself nicely on the fun peninsula roads, being a reasonable pace car. The Prius C had no trouble dispatching the Bentley and Rolls through the twisty bits, but of course the MINI's & MS3 weren't a fair match. The stock tires definitely were the weak link, and I'm bummed I didn't get the 949's in time to have them on the car. I gave the car a significant dose of Welly, likely driving the car far beyond its typical demographic intent. I found out that if you keep it floored long enough [we're talking 15+ seconds here], the revs will keep rising to what seems to be peak engine Power instead of peak Torque. Nevertheless, I still got 50 MPG for the tank, which is awesome given how hard I was driving it [which was deep in the "red" every acceleration and through every corner]. The modest power was definitely apparent, and the car was giving its entire bean to stay on pace up the steep hills. In all, the car did the job and remained amusing to drive.

 

I got the door speakers all finished. Goodness, the sound quality is a revelation compared to stock! It's obvious the head unit at the very least puts a low-pass or some sort of high cut on the rear door speakers, but otherwise I'm not hearing the head unit being a significant detriment to front stage sound quality. The doors don't rattle like they used to, which is a nice surprise given I didn't use even a square foot of sound damping material in each door. Yay for keeping things light and still effective.

Yup that's me. Are you there too?

 

Here are some updated pics of the new ride height. I lowered the car down to 12.8" susRH [suspension Ride Height from axle to fender arch apex], front and rear. It looks mucho better with the more-flush rolling stock setup, you can barely fit a little finger in the wheel gap. Let me know what you think.

Please ignore the filth, it rained like mad the past couple days and it's just now magically nice out, so a proper sudsing is forthcoming.





Cheers,
Ryan