A question regarding wheel/suspension aptitude.
 

I couldn't decide if this topic would fit well in the wheel section or the suspension section-- but i think it fits here.

I'm seeing a lot of people getting large wheels; sizes such as 17x9.5, 17x8.0 and so on. Even getting a wheel like the Enkei RPF1, the weight and price of wheels in this size can get up there.

So, i'm assuming people are going for those size wheels to increase grip and to control oversteer. Now, my topic question is, instead of getting these large wheels, making them wider and wider, adding weight. . .could you not do a suspension/aero set up to make those large wheels less necessary?

For instance, could you not just add a GT Wing and adjust the rear toe to Toe Inward 0.5 degrees, leave the rear sway bar alone or remove it, while stiffening up the front a bit? I would think that setup would control your oversteer enough to be able to benefit from smaller lighter (and cheaper) wheels.

Am i wrong in this?

- - -

My history has been with small FWDs and trying to fit the smallest possible wheel over the caliper (typically 15'') and only going for a 205/50/15 tire, as to keep the overall weight of the wheel/tire at around 33lbs. Not to mention the effect smaller wheels have on acceleration and top speed.

People are adding large wheels and so on because they do help grip. And we race in classes that have rules. Not all the classes allow aero mods or large gt wings. So we do what we can with the money we have and the rules set forth. Some track the car some autocross the car and each has different needs.

I see. I hadn't considered the rules you have to abide by-- i typically run my car on open-track, i apologize for that.

However, as it's burning my curiosity, could you also comment on the validity of my logic behind my alternative to larger wheels, objectively?

It depends on what you are trying to accomplish. Adding negative rear toe and a big wing adds drag, more drag than a bigger tire patch would, so this is something to weigh the cost/benefits. Aero also has substantially less impact (some would lobby none) at lower/autocross speeds. Adding rear toe will also increase the wear on the tires.

Wider tires/wheels coupled with stickier compounds is the easiest way to increase grip with minimal sacrifices... steering feel and turn-in being 2 of the bigger sacrifices when increasing tire width.

Thank you very much for painting an objectively sound picture. I appreciate it.

You have to balance output with grip to find the ideal setup for your application. For most people, this involves wider rims and tires. Remember, this car likely has substantially more output than your FWD. The fast FWD guys I know all run large rubber (usually the largest that will fit or allowed by the rules) to match their output (B18, built K20/K24, etc.)

One could argue that oversteer with this car is a setup or driving error, and using an alignment and aero to bandaid that doesn't eliminate the source of the oversteer.

Or preference. I like a little oversteer in my cars.

I've noticed all the really fast FWD guys that are local to me are a bit nutty and have their cars set up loose... :respekt:

They also run suspensions that are worth more than the cars themselves... :eyebulge:

I suppose the nuts behind the steering wheels may have a screw or two loose... :lol:

I'll also point out that based on the information provided in one of the early marketing videos put out by Subaru, they specifically mentioned that the wheel/tire package was one of the places they sacrificed on to keep the vehicle cost down with the assumption that owners would be replacing them.

I'd suggest based on this info and the other usage of the primacy tires, the OE wheel/tire package was specifically aimed at maximizing the EPA economy label.

Gotta love Motons on a mid 80s civic :lol:

Also to address your questions RE wheel size... smaller overall tire diameter changes the drive ratio at the wheels, meaning you will be at higher RPM in the same gear going the same speed (I know, this is a 'duh' statement, but stick with me here)... in older econobox FWD cars, close ratioed gear boxes were not common, they had wide ratios and typically 4 or 5 speed transmissions, so when you reduce the tire OD, your gear box can still reach a decent top speed in the same gear. drastically changing this ratio on a close ratio gearbox will get you in trouble with being between gears too much, so you hardly ever see that practice anymore unless someone has changed their trans or diff gear ratios as well.

Why does increasing width affect turn in?

It's due to the way the tire responds to a change in heading as it is rotating. The tire flexes creating a difference in inner and outer sidewall speeds (the sidewall which is running the shorter radius is turning at a slower RPM than the outer sidewall and the tire patch becomes more teardrop shaped. As the tire rotates it creates a pneumatic trail, with larger tires, there is more deformation, which translates to a "numb" steering feel and a less responsive turn in, assuming you don't exceed the potential grip of the smaller tire and all other variables are constant (sidewall stiffness, no discernible difference in tire pressures, temperatures, etc...) the narrower tire will feel sharper. This also works in opposite effect as the wider tire will also not auto-center as well. Driving with the wider tire is just something you have to adjust to, it means you turn in a hair earlier, a hair faster, a hair further, and reduce the steering input a a hair sooner as the bigger tire catches up and reaches steady state.

Edit: my image link wasnt working so I removed it.

Thank you for your detailed reply.

Well, to be honest, my FWD has better power-to-weight-ratio and torque-to-weight-ratio than the stock FRS.
My PTWR = 190hp@2400lbs: 12.6 / 140tq@2400lbs: 17.1
FRS PTWR= 200hp@2700lbs: 13.5 / 151tq@2700lbs: 17.9
Now, those are just numbers and the FRS has well proven that it doesn't play the numbers game.

Forgive me if this comes off as stupid, but i've done the aero/suspension tweaking in Forza 3 and 4 and it's done me really well. (the concept made sense in my head so i tried it in the game and it worked.) This in itself is not much of a credential, seeing as it's just a game. I concede that.

Although, i'm not necessarily trying to delete the oversteer completely-- a little can be useful for rotating the car. In your post you mentioned FWD guys you know keeping their cars loose; that's a typical thing to do in FWD. You stiffen up the rear sway bar, raise the PSi, and add a little toe out and you can typically rotate like a champ with a slight oversteer and lift the inside rear off the ground.

My whole assertion was merely to rid the car of any excess oversteer. I just feel like there is something to be gained by the lesser unsprung weight. Also, i'm setting aside the rules by which SCCA and NASA guys have to abide by. Please rebut as though we're not penalized by such modifications.

What is the ultimate goal? Under what kind of conditions are you driving?

To me, the was was never very loose; I'm pretty much WOT everywhere, and any rear end action is a direct result of driver input, at least, on a stock FRS. If you keep that rear tucked in, it's FAST.

The larger wheels aren't stabilizing the car. Rather, they're increasing the cornering limits, and driven the same, effectively "more stable". Sure, you could make suspension changes to make the car less pushy. You could also play with aero.

I'd be wary of making any drastic aero changes to the car, as its already rather underpowered.

Then again, I seem to have a bias toward loose cars. I think the stock FRS understeers (and it does at terminal; oversteer is always driver induced in my observations).

I suppose the best way to figure this out is to determine what you consider excess oversteer, as each driver's preference is different.

The goal is just to make a very competent car for HPDE and Open-Track. I am not competitive and don't care about comparing times. However, improving my own lap times and/or making the car more intuitive, fluid, and/or responsive.

Also, thank you for your responses-- they have been educational, non-biased and overall pleasurable.

A wing will make high speed tracks easier, while making the car bias toward understeer. Before putting on a wing, I'd ask, does the rear end ever want to actually come out during a high speed corner?

The "corrections" are to correct the rear getting loose, but the rear is getting loose because I'm testing the front traction (this was the first hot lap I have ever done at this track in the BRZ).

[ame="http://www.youtube.com/watch?v=2yik-oAVm3U"]BRZ Willow Springs International Raceway 1:38 - YouTube[/ame]

Turn 2 is over 85 mph, and Turn 8 is over 120.

Zero aero, stock suspension.

Yeah wow, the car seemed well planted nearly the entire time. Stock wheel/tire size as well?