upgrade suspension

Rear adjustable camber links and new adjustable swaybar endlinks will do more in the rear for you. If you really want to get down and dirty to stiffen handling, then you need the Energy Suspension Master Bushing Kit. Wider tires and more downforce are your next targets.

If you are talking about the rear strut bar, then you are absolutely correct, at least, for the tC. If you are talking about rear coilovers for a FWD car, then you have a misunderstanding of how suspensions work. It matters not which wheels drive the car in the overall scheme of suspension setup. Only when you are powering thru a corner does this come into play in a road race vehicle. At this point the vehicle will behave differently with understeer/oversteer characteristics. This where you can fine tune your suspension and aerodynamics to get the most gain from the drive type. Further, where the center of gravity of a vehicle will matter more for suspension setup on most vehicles. Once the CG is accounted for, then powertrain and driven wheels need to be tuned for. A mid-engine RWD car will most likely handle differently than a front-engine RWD one. Just look at World Racing's road racing tC's. They are into there 3rd version (AWD) after they beat up most RWD cars on the track.

If you are looking for a better handling tC, I would do a front strut bar, rear sway bar, lowering springs, shocks/struts, wider wheels and stickier tires, rear spoiler/wing, front wind splitter. There is a rear strut bar that Agency makes, but I haven't used it, nor am I convinced that it works the way it says it does. I know several people on other Scion related websites that have and love it. I would also upgrade my braking system to slotted rotors, ceramic pads, stainless steel brake lines and an approved DOT 3 brake fluid like Motul.

I bought the Megan C-Pillar Support 2 yrs ago and come to find out I would've had to delete my rear air bags. I wasn't about to do that and put my passengers in jeopardy, plus I have 2 kids. Megan products in our book are cheap, and not worth buying. A spoiler may be dead weight to some, but they also help in aiding in rear down force and aerodynamics. Plus IMO the tC looks naked w/o a spoiler. If you look at NASCAR, F1, NHRA and others they have wings/spoiler and they serve a purpose, not just for added weight. Wind tunnel tests have proven this.

For an auto-cross/road course event I can clearly see your point. Yes the spoiler would be added weight and wouldn't aid very much in down force. My comments weren't based on auto cross or road course racing, hence I don't do either of those as it is. If you want to know more about Megan's products, ask NavyLife, he will clear up more points than I can. I mean you no disrespect either, just expressing my points as well.

I sent the C-Pillar bar back to Megan a long time ago for a refund.

Megan Racing! Did someone say Megan Racing? Let me at them!!! Why I ought to ..... They are like Ebay, hit or miss. Best to stay away from them.

connman429 has some good points about aerodynamics meaning nothing below 50MPH. Some aerodynamics (depending on the vehicle design) don't come into play till 80MPH or even 100MPH. Just like short course work, aero on most 1/8" track cars are useless. Cadence and myself have had to argue too many times about the importance of proper aerodynamics on cars no matter which wheel drives the vehicle. If the back end can't stay planted in relation to the front, then the car will be out of balance during the turn-in and, if in like a high speed S, during translation. Over compensating poor aerodynamic balance with suspension tightening only serves to put the car out of balance in the suspension. It all is based on what you are wanting to do with the car. That is my first question that I ask when people are looking for suggestions. Ever watch those automotive challenges where they pit top cars against each other in various sport driving events? Few can come out ontop in all categories. For that, you would need to ask Pops if he will loan you the Mark V.

Ok, now to the rear stiffening. I can attest that hatchbacks have notorious body flex in the rear. This is a problem on the tC just as it was with my Fox Body Mercury Capris. You take a sub-frame vehicle with a large open section of the body (hatch) and it is gonna twist. The Fox Body Stangs/Capris had a flex problem with the disjointed sub-frames. Sub-frame connectors were a must. The tC employs a nearly full length sub-frame with a full front clip and complete rear clip that mate thru the body just behind the B-pillar. If you really wanted to stiffen body flex, it would be sub-frame connectors at this point.

The rear floor plan and strut mounts are firmly welded together to form the rear sub-frame. The rear strut mounts are interconnected by 3 layers of thick steel spot-welded together. The open ends of the rear frame are attached to the bumper and rear floor wall pan.

Note: Toyota claims the glass roof is stiffer than it would be if it were a standard steel roof.

DME - Amazon.com: DME NEW 2005 2006 2007 2008 SCION TC ALUMINUM REAR STRUT TOWER BRACE BAR BLACK(05 06 07 08): Automotive
Ingalls - RoBear Racing. INGALLS REAR STRUT BAR: SCION tC 05-08
GReddy - Greddy 14013032 GREX Rear Strut Tower Bar OS Scion TC
Some Knock Off - TCS 05-08 Scion tC Rear Strut Tower Brace -Aluminum
Weapon R - Scion 05-07 Tc Weapon-R Stress Braces (Rear)
Megan Racing - Megan Racing C Pillar Bar, '05-'10 Scion tC : WOTMStore

Let's look at these in detail. I have the Weapon R (MMW) rear strut bar. It was the first on the market if I remember correctly. I felt absolutely no change in cornering or feel. My suspension at the time was the Hotchkis Stage I TVS minus the front sway, Hotchkis front strut bar, and OEM tires. The GReddy, DME, and the Knock Off mount slightly differently but utilize the same geometry. The Ingalls piece seems to go a step further by tying in the rear floor pan but from the above schematics, one can plainly see that the rear floor pan is already attached to the rear frame members. The small extruded tubing of the Ingalls unit is not going to add any appreciable support. Attaching to the rear floor pan is not going to stiffen up the upper body section which is where the most flexing will be occurring. This is visible as a vertical row of indentations (typically 3) just below the rear of the quarter panel windows.

You may find what I am about to say a bit unnerving so please take a seat and breathe deeply. The Megan Racing C-Pillar stands the best chance at stemming upper body flexing. Don't fret too much as it too falls short in tying the correct points. Combine the Ingalls piece, the Megan piece, and do some refinements and you will have something that actually might work. Only skid pad testing and track times will confirm this.

Good discussion! Sorry if I missed this but, did anybody else recommend changing the springs at the very least? I know the OP started this superrrr long ago, but to anybody else reading this thread interested in autocrossing; there are better springs out there than S-techs. Of course new full on coilovers would be best, but S-techs with OEM struts might even perform worse on the course then the OEM setup. Front bottoms out as the weight bias is already front heavy. S-techs has the front at -2.4 while rear is -2.0 which is just horrible with such soft springs.

Edit: Just to make sure; Tein S-techs are great springs, but definitely not something I'd recommend for autorcrossing.

I take it that you were talking about the front strut bar, correct? I took mine off to polish it and did not notice a change on the street. I still find it hard pressed to believe that the Ingalls brace does anything either based on the complete rear structure of the car and the attachment points made by the Ingalls. The front strut towers are not connected while the rears are. Connecting the rear floor pan behind the rear member just does not make any sense structurally. I am not knocking anyone for running this piece nor discounting what your perception of it's performance is. I am only stating the facts that are known compared to it's design and implementation. Only skid pad testing can settle this debate.