Good post Moto-P, I'm glad to see there are other people that really stay true to keeping proper suspension geometry and ride dynamics. I have been, and still am, thinking long and hard about what I want to do to the suspension since for most of us our FR-S wont be a track only car, we still have to get to work without a stiff back all day :burnrubber:

I fail to see how installing stiffer suspension with the stock tires will induce understeer. Sure, if you mess with the F/R spring rate ratio, increasing the front drastically more than the rear, then I could see this happening. But if you increase the rates such that the F/R balance stays the same, or even makes the rear more aggressive than it is now, than why would it understeer more?

Good question. It shouldn't mess with the balance, however stiffer springs can make a tire lose traction sooner. Coupled with poor driver influence, like too much steering input, can cause understeer (or oversteer).

This is a good point and something people should watch out for when buying coilovers. I've already seen some show up for this car that are way stiffer in front than in the rear. I'm guessing those are for drifting setups, but will really destroy the balance of the car if you're going for grip. Darren's guide in the suspension section lists the spring rates for the coils.

I'm trying to explain how the rsr coils work to him, but he doesn't seem to understand that they aren't ever off of the shelf unless a shop buys them that way. You talk to RSR and choose the spring rates, 6k-9k for front and back, and then they ship them to you in that configuration. Moto and I both have 6k F 7k R and it feels extremely close to stock, but better. The balance is still there, the. At really eats away at the curves still.

What's the advice on tire setup. If aesthetically pleasing springs aren't available for appropriate balance, would increasing tire width be advisable. Would a 245 tire fit well with stock suspension and maintain balance?

The front of the FRS/BRZ like any car, needs to dive, to increase the front weight distribution upon deceleration, allowing the car to grab at the front, and loosen at the rear for the car to get a firm grip of the road with the steering tire. This has a lot to do with, and depends on the ability for the tire to GRIP and CREATE the G forces that allow this dive. With stock tires, there isn't enough traction to decelerate the car enough, and thereby reducing this ability. When you increase the suspension stiffness, it takes even MORE grip to make it dive, and without this grip, the tires will not get enough weight on it to steer.

This is just an example in ONE vector and direction, but this holds true for all axis of the motion, and the car needs to transfer weight back and forth, and side to side to make this happen. The FRS/BRZ is a very light and centered car with low center of gravity, thus making this very difficult since there isn't a huge overhanging weight like most cars. While this is a trait that allows physically, a very acute and responsive car, it is also very sensitive to changes like this.

This is why, overly stiff suspension on the FRS/BRZ tends to create less ability to motion the car correctly when changing vector of travel, and also the direction of the car, and wheels, if the tires can't hold the G-forces necessary to do it efficiently and readily.

Tada's design of equipping it in such way and balancing the car, with mild grip tires is exactly this, to challenge the driver to develop the skills to do this, and to give gratifications to those who can drive it well, and be rewarded the speed that comes along with it. That is what a true sports car should provide.

Yes, again, the lack of dynamically distributed weight on the front tires is the culprit for the quick loss of steering feel, and resulting loss of traction. Stiffer springs, and shock compression settings, can prevent the car from planting the front tires to initiate a turn.

Poor driving skills is a whole different matter as this is simply the inability for the driver to feel and maintain the contact patch at nice, gradual, stable level of grip at any given speed and abrupt and violent inputs and rebound forces, creating a havoc on the dynamics of the vehicle. :D This is also why I recommend a long-stroked (taller) suspension with soft, compliant, and slow moving parts on the suspension for novice drivers, so all of the dynamics of the car are accentuated, and things happen slowly and more predictably. Fast, stiff, grippy setup requires the driver to be much more sensitive, quick, and extremely accurate, and feed-backs happen a lightning speeds where they might not understand at all, what is happening with the vehicle as controls are lost.

Increasing, or changing tires sizes both in width and diameter has consequences that change many different variables, and simply raising the contact patch should not be taken lightly or be treated as a fix-all solution. Increased tire contact patch also means less ability for the tires to reach proper temperature, and reduced grip over loose surface as rain and snow, and even dirt.

I think to keep the inherent balance of power and handling of the FRS/BRZ, the tire size change should be minimal, regardless of going with 16", 17" or 18" to keep the same diameter, and relatively small widths. 225's and 235 width should be plenty for a light FRS, to be fun and agile as universal car. Going beyond this only if there is a specific purpose in various field of REAL racing.

I feel that GRIP and DRIFT setups should be really similar. AS handling and ease of control of a car at any dynamic action, should be a very refined and singular in point. Sure in Pro-Drifting there is a big difference from standard alignment setting, but most D1 cars, in early days before entire sub-frame change was allowed, usually had similar rate equipment. Only set a little stiffer overall, to stabilize the violent flicking of direction. Drift cars still need a LOT of traction in both braking and accelerating vectors, as speed is lost more in a drift than in a grip situation, as you are taking a SLOWER approach to any corner.

Anyway, back to topic, that FRS should have a compliant balance of suspension, that is closely matched to the tires, and no more. For this car, we just need to find that balance where the driver skills are up to the task, before making anything "higher performance" as this car is so demanding of the driver, that if the car is overbuilt for the driver, he will simply be going slower in a higher tuned setup.

totally agree. my last track day all i worked on was braking and loading for cornering. this car is faster using weight transfer and tire slip without a doubt. the oe setup is very good at accomplishing this and when you do it right you know it because you get the tires singing but not screaming. i also learned this car is really good at letting you know when you do it right. if you over brake and have to unload the front a little early it totally messes up the cornering rotation and exit speed. blindly, i'll agree that 20-25 mm of drop would be ok if you're doing it for further cog reduction or aesthetic reason. i really like the stock setup, it's fun and educating. they only thing about changing to a stickier tire is if you don't have a well developed sense of weight shift, a sticky tire will stunt development of it as you'll stay closer to the grip side of things instead of walking that grip slip line. getting the car loose tells you alot about what you are doing. i spun twice on track this wknd working on my trail braking and front loading.


for my purposed the stock tires are good. when i go to a different compound i will either stay at 215 or only go up to 225. but that wont be until i get more consistent with this car. and i hope my coilover choice doesn't affect my learning pace.

I really liked progress coilovers on my B13. They are only height adjustable. Progress took the time to tune the shock and spring combo so the customer couldn't mess up the handling of the car.

To me it's not about the wheel gap... it's about the wheel being concentric with the fender! And the FR-S/BRZ does that quite well, so IMO the FR-S/BRZ isn't too high at all. The ride height is perfect. In fact, lowering the car will ruin the already concentric wheel/fender look from the side. Who else agrees with me on this? There's no need to worry about scraping your car either as a bonus! And besides, the car's center of gravity is already low enough.

yeah, that makes sense. So essentially, unless you add decent front grip with better tires, don't mess with the suspension. I suppose doing a sticky 235/40/17 on an 8" rim would do the trick, and then upping the spring rate would be ok so long as you don't go overboard.

Yes, I understand. I am a vehicle dynamics specialist. I setup and tune clients car for circuit, auto x, etc.

:respekt: I enjoy reading your posts as they are on point and educational. I believe that suspension tuning is an art, not always a science.