cAstro my Prius c: Project thread

Thanks.

Good question, however it's also one that haunts the outlaw world of automotive aftermarket. Very few companies are willing to disclose any information, and just as bad, very few enthusiasts are capable of making competent measurements to help the community. As such, we have to scrap together whatever minimal information we can get. From what Micro Image & I have accumulated to date, it appears the stock dampers have the most total stroke, the KW's trade rear stroke for more front stroke [a curious choice], then Cusco shortens up stroke everywhere, then Megan's with their usual short-stroke. That's all I have for the Yaris/Prius C at the moment.

I'll be contacting Fortune Auto shortly to try to get information from them, as they seem up-and-coming and look to be genuinely interested in performance and not false-hope fake marketing. I've had marginally mixed results with Tein; they're not usually held with high regards, so I wouldn't put all your eggs in their basket. BC's are forgettable [based on experience], Nitron's are amazing [have them on my Lotus], and brands like Penske, JRZ, and Ohlins cost waaaay more money than most sane people are willing to spend, Semi rule-of-thumb, you get what you pay for. You can still spend lots on junk, but cheap suspension is almost always junk. Suspension Techniques is an anomaly; if they ever offer a coilover for our chassis, that would be a great entry-level choice. Ditto V-Maxx, though they end up being more comfort oriented and not track-worthy at all. The two things V-Maxx and ST give up are longevity and the utmost in desirable damper curve, which are incidentally the two things that make dampers expensive.

I hope that helps,
Ryan

 

I agree that the "modding for the sake of modding" days are behind me. Most aftermarket suspensions eliminate precious travel for no good reason other than to provide a harsh visceral ride and give a false impression of performance. A stiff suspension does not automatically equate to handling performance, you have to balance damping force and wheel rate with the specific tire you're using, suspension geometry, vehicle weight, and of course application.

I wish V-Maxx made a set of coilovers for the Prius C, because I'd recommend those first to those that simply want less wheel gap and very good ride comfort without breaking the bank. The KW V3's have [IIRC] 16 clicks of adjustment for both compression and rebound. Their install guide recommends 6 clicks from hard, which I found objectionably firm, which is ironic given the recommendation is for the lighter Yaris. I'm now at 10 clicks from hard and find it acceptable, but certainly not soft by any normal street car definition. I'll push them softer just to experiment and see how they respond.

I'll report back soon.

I'm familiar with FCM, Shaikh has been a great trailblazer for the Miata [and modern performance] suspension systems over the years. It'd be great to get him on the job sorting out this chassis, but I have a feeling there just isn't the volume interest to rationalize a new project budget.

 

How's this for low?





Naw I'm just kidding. That's where the rear axle starts contacting the bumpstop on the KW's. I was just double checking where that happened. Amusingly, the tires have about a piece-of-paper clearance between the sidewalls and the fender seam. That's tight fitment!

Here's what I was doing. I found out that if you remove that little donut looking rubber spring isolator [in bottom of the frame] you end up with hella-squeaking from the KW aluminum adjustable spring perch, so I was putting it back in. Same ride height, but no more squeaking.



I was using the floor jack to raise the rear twist-beam axle until the dampers hit the bumpstops. Obviously the springs were out of the car at the time. This car is SO easy to work on, this took me as much time to photograph as to accomplish.

Cheers,
Ryan

 

There are designated lift points in the front and back of the car, as shown in the Owners Manual. The rear lift point is behind the spare tire well, and the front lift point is the subframe-side of the lower engine mount. Be sure to chock the tires when lifting the car, as always.

 

Thanks

I would presume 14" wheels would clear, as the front brakes are very small and I don't recall any brake clearance yellow-flags [let alone red-flags] when bolting up the 949's. 14" rubber might make things difficult-to-find unless you're looking for small overall diameter for auto-x.

Thanks. That's my thought exactly. As the saying goes; "it's more fun to drive a slow car fast than a fast car slowly."

 

Thank you

That tire size is perfectly taut looking on my 7" wide wheels, however they'll be bulged out on the stock 5" wide steelie. It's not a problem per se, it primarily changes the aesthetic. You won't rub at all with stock suspension or stock wheel offset; the stock suspension simply doesn't have enough compression stroke to put the tire in a position to rub anything, even at full lock. Why Tire Rack says otherwise is simply showing their inexperience with this car, which seems to be at an all time high compared to their typical knowledge base.

You may recall that I did a test-fit with a set of Kumho XS in 215/45-16 on stock suspension and I couldn't get them to rub even at full lock with an et37 wheel. There's lots of room in the wheelwells.

Going a step further, even with my 1.5" lower-than-stock coilovers, rather aggressive wheel offset [pushing the tire a half inch out from stock] and 195 wide tire, I've only heard rubbing once. It was a light transient rub during a large bump in a banked sharp corner while at the limit of tire grip [where the throttle needed to be floored just to keep momentum around the corner] *grin* (Tunnel of Trees fun twisty road in northern lower Michigan).

Lastly, if you're using OEM Prius C steel wheels, there's nothing changing at the hub, so no need to worry about hubcentric rings. Those are only for when you're going with aftermarket alloy wheels that use generic hub bores so they'll fit a variety of cars.

 

Yes, you'll have to talk to your wheel/tire shop. I'm not sure exactly which steelies you're getting, so it'll all depend. In any case, you'll want to use steel-wheel specific lug nuts and ensure they're hubcentric.

Thanks I had an Elise with an aftermarket supercharger prior to my Exige S. They're essentially the same car with aero, power, and equipment differences, however having the soft-top on the Elise made it super-easy to drive around with the top-off, which is sooooo much fun. Curiously, early S2 Elise prices have pretty much stabilized, so if you have mid 20's to fund your dream car, you can get an n/a 2005 Elise and later on put a supercharger on it. Presto, mucho fun.


In more topical news, I can confidently say the Continental tires on my new wheels are broken-in. They feel more stable and consistent then when I first put them on. It took about 1000 miles to get them to this point and now they feel good-to-go. Just a subjective data point for those that put new tires on the car; give them some time to break-in before passing judgement. Speaking of judgement, I can now say these Conti EcoPlus tires have better steering feel than the stock Bridgestones with similar overall rolling resistance [perhaps slightly more speed in EV mode], however they do not have the gobs of wonderful steering feel the Kumho XS's had, and it seems the aero drag from the wheel offset and width change is noticeable during full-tank Interstate road trips. The overall improvement in cornering grip however is excellent and well matched to the KW coilovers, so I can now take corners without feeling the tires are the weak link. This is a better result than I expected for an "eco" branded tire.

 

Ok, audio system time!

A few weeks ago I installed the door speakers and a very modest amount of sound damping material in the doors.
*NVX sound damping material, only about 1 pound per rear door and 1.5 pounds per front door
*JBL P662 6.5" 2-way coaxial w/ 1" soft-dome tweeter and pigtail simple 1st order crossover

*JBL P660C 6.5" component set w/ 1" soft-dome tweeter and 2-way external 2nd order crossover




Because the stock speakers are larger than everyone keeps saying, I had to drill new mounting holes to mount the included JBL brackets for the 6.5" woofers. The stock speakers are more like 7", but they're an esoteric footprint, not something off the shelf in terms of available aftermarket. Also, there isn't that much mounting depth available. I had to stack up both adapter plates and use copious neoprene gasketing foam to be able to clear the speakers magnet to the front window by about 1mm when it's rolled down fully. Snug!

....

While running the wiring from the head-unit to the amplifier location under the passenger seat


The signal wiring is run from behind the head-unit, down the center stack, underneath the cupholder insert, next to the shifter, under the Eco button, down the tunnel, into the pocket of space under the passenger seat.

 

Part 2, Amplifier & Subwoofer

Using an Alpine 5-channel class-D amplifier mounted underneath the passenger seat. I'm inputting high-level signal from the stock head unit, which I found to be acceptable sound quality. I ran 4 awg power & ground from the 12V battery and encased them in neoprene foam to keep them from potentially chaffing against the cars' sheetmetal. I'm also using a 60amp fuse mounted on top of the 12V battery, to protect the wiring from over-current in case of a short.

I built my own subwoofer enclosure using two Dayton 8" 4 ohm subwoofers wired in parallel and tuned it in a 0.71 Qtc sealed enclosure. The enclosure is mounted within the back half of the spare tire well on 4 rubber pads [two of which were used for the spare tire], and then fastened to the car with the factory spare tire hold-down location. That bolt is accessed behind the terminal cup, and is rubber gasketed to maintain enclosure Ql. The enclosure is very solidly mounted, and you can literally elevate the rear end of the car by puling up on the enclosure!

Here's the shot of the subwoofer enclosure in place. The woofers are horizontally opposed to cancel out vibrations from being physically induced into the chassis. The stock foam blocks are being cut down to make clearance for the enclosure. About 1" of foam rests on top of the enclosure. Not shown is my flat tire repair kit with air compressor.




I kept the floor vent clear to retain functionality.


This is the view of the amplifier with the passenger seat all-the-way forward


View of the amplifier trim peeking out from under the passenger seat


You can't see the amplifier from this angle

 

The Alpine MRX-V70 amp I'm using has 5 channels of output, but is configurable such that you only need as little as 2 channels of input. I have it setup such that channels 1 through 4 are direct from the high-level inputs of the stock head-unit, and are then summed within the amp to create a 5th channel for the subwoofer.

I hope that makes sense!