Cars balance
 

just wondering, if you do minor mods like changing the exhaust or adding carbon fibre bits, would that throw the balance of the car off quite a bit?
I remember doing centre of gravity calculations in school, and it can change it a lot, so I just want to see what everyone else thinks.

also, beginner rwd question. I've only had a bit of seat time in a 335i and c63 AMG, so I'm not too familiar with rwd since I daily drive a fwd. I understand that the frs and brz have amazing handling and balance, but what happens if you accelerate in a turn? wouldn't the back end always come loose?

Not impressed with carbon fiber. As a structural material, sure it has a lot going for it. As an aesthetic material - not impressed at all.

the back end doesnt always come loose, if you do a corner right youll notice the back end will push the car tighter through the corner without loosing grip, you have to learn what unsettles the back end of the car and the proper time to brake in and accelerate out

The balance front to rear is typical RWD balance 55/45.

I think the balance will depend on how much weight and your intended purpose for the car. If you just do spirited driving on backroads you may not notice anything. However, if you're a seasoned vet at the track, there may be a bigger difference.

I wouldn't be too concerned with minor weight differences here and there. Things may change when you start removing seats and other hefty items.

Honestly, if you enter a corner quickly a bigger danger to the rear is letting off the gas entirely than it is adding gas (to a certain extent of course). As long as you aren't way too fast to begin with, you'll actually feel the car hunker down as you power through the bend.

That's in this car. Now in something high-powered you do need to be more careful. You don't want to just step on the gas.

I always had the impression where adding gas in a turn would result in oversteer.
when I drove the c63 I didn't really experiment cause I didn't want to hit a curb.

what is the reason that so many new rwd drivers lose control?

No

Sorry if I sound a bit harsh. But I think you should save your money. Not use them on carbonfiber (if you are planning to) and use them on track days. Just learn to drive on and beyond the limits of grip in a safe environment. That will teach you what happens when you step on the accelerator in a turn and it will teach you about weight shifting to adjust the balance. A 1-2% change in front/rear weight distribution does not do much.
But as you say. Adding weight to the rear will generally result in more oversteer, in theory. Most people will not be able feel the difference between full and near emty tank. Im not able to feel the difference in a normal (FR) car. The differences are subtle. Some may be able to feel the difference in balance better than others tough.
But if you are on the road you normally would not push the car to notice the difference. On the track you usually want to keep weight low by only having about a quarter tank of fuel. So balance would not shift much there either.

Maybe they turn of all driving aids after watching tokyo drift and think they can do the same without having a clue about what happens when the car steps over the limits??
Don't fully disable driving aids if you don't really know how the car will behave when going above the limits.
Take it do the track.
You could also find a big empty abandoned parking space and learn how the car handles in different conditions (dry and wet) without ESP on before going to a track. Then you could have a bit better starting point when going to a track.
And remember, handling in the wet is very different to handling in dry conditions.

Oh my.. This is why OP needs to gets some real life experience. And should not learn driving theory from a forum.

I honestly don't know if I should laugh or cry..

It's pretty simple really. Overdrive this car and you back into whatever you're gonna hit. Overdrive your FWD car and you head on whatever you're gonna hit.

RWD cars are metric asstons more fun to drive. You have to learn to drive with the throttle as much as the steering wheel. FWD you drive with the brake and the wheel.

Enjoy

you can feel the back end come out anyway, its got progressive break of traction

oh im never going to get after market carbon fibre parts. it was just used as an example for mods.

in my limited experience with rwd cars, I've never been in a oversteer situation cause I was just test driving. I guess I am just wondering why all reviews say the handling is amazing, when I would assume awd would be better (no im not saying this car should be a awd car).
as mentioned above, the car gets more planted when turning, I never knew that. I need to experiment

IMO what makes the FR-S handling special is (1) how neutral the chassis is setup from the factory, (2) how progressive the rear end will step out, (3) how low the center of gravity and overall curb weight are, and (4) how quick and precise the steering is.

Unfortunately AWD usually results in understeer. I used to own an STI hatch and even with 3 limited slip differentials (F,R,C) when you applied power out of a turn, you would get power-on understeer. Pretty annoying. Basically tires have a limited amount of grip and asking the front tires to turn the car AND pull the car through a turn will result in the front tires losing grip before the rears (i.e., understeer). AWD will also add about 200-300 lbs of additional weight, and in most cars, in a front-heavy weight distribution. The only AWD car I've driven that handles fairly neutral is the Evo X, which uses a torque-vectoring differential in the rear to overcome the chassis' inherent understeer. Feels a bit artificial like the rear end is coming out, but very effective.

To your original q about the FR-S about when the back end comes loose under power, that depends how close you are to the limit of your grip in a turn. The closer you are to that limit (i.e., near maximum speed you can hold in a turn), the easier it is for the rear end to come out under power. The further you are from that limit (i.e., going slower in a turn), the more power you would need to apply to break the rear end loose. One thing that might help you visualize this is the concept of the traction circle:

http://www.autospies.com/images/user...tioncircle.jpg

If you're already near the limit of traction in a turn (i.e., 3:00 position in a right-handed turn), the less grip you have for acceleration. Applying power at that point would break the rear end loose. But if you're well within the traction circle, the more power you can apply without breaking traction (e.g., 1:00 position in a right-handed turn).

nice diagrams, now go find a big wet parking lot and jerk the wheel and jam the throttle. It's 90% feel, and 10% knowing what's going to happen. Go learn the "feel" :P

-Rich H.

The amount of weight saved by these type of parts does not significantly affect the 'balance' of vehicle. "Adding carbon fibre bits" will in fact add weight. Not to mention most carbon pieces are carbon in look only. True, engineered, light weight carbon parts are not the kind where you can see a pretty weave pattern under clear coat. A good aftermarket exhaust will only save you a handful of pounds as well. We're talking about a nearly 3,000 lb vehicle. The weight of the driver, or the fullness of tank has more of an effect than than the weight of most other pieces.

No. The rear wheels will only come loose when they overcome the kinetic friction between the road and tires. In fact, when racing you ideally want to have completed all of your breaking prior to the turn. That way you can be on the power through-and out of the turn. RWD is typically the preferred setup in race cars because then the wheels each have separate jobs. You see, with a RWD car the front wheels steer and the rear wheels provide power (all wheels brake). With a FWD car, the front wheels steer and have to provide power (as well as brake). An AWD car is great for low traction situations because all wheels can provide power, but you're still taxing the front wheels by asking them to do three things at once.

As others have mentioned, FWD typically understeer or "push" through corners with the nose of the vehicle pushing wide through turns. AWD also usually do this because of what I said in the earlier paragraph, as well as the fact that most AWD systems are based on a FWD layout. The beauty of RWD is that they tend to oversteer, where the rear of the vehicle will tend to swing wide. ***Caveat: there are MANY factors beyond FWD/RWD that affect over/understeer characteristics, these are generalizations.*** The tendency to oversteer can help the RWD drive car to steer through a turn by applying a bit more throttle, to break the back loose a bit and turn the car a bit more.

As another poster mentioned, a common mistake people new to RWD make is letting off the throttle in a turn. This can be very bad. This induces "throttle-off-oversteer" in which the rear suspension becomes unloaded (weight is transferred forward) and the rear of the car looses grip. This typically induces a catastrophic spin.

Other factors: tire grip, road surface, weight balance (FWD tends to be front heavy, RWD tends to have a better distribution), camber, caster, mechanical and pneumatic trail, suspension type, roll center, c.o.g., etc!!!

great replies! thanks a lot
now I understand rwd way more (in theory)
just have to go get this car now!

and correct me if I'm wrong. from the comments I gather, it seems as though rwd cars have A LOT more room to work with in a turn.

In general I would say a RWD have more room to work with considering it is easier to adjust the balance. But since you have more room to work with its harder to drive on the limit. But when you do its so much more rewarding.
A FWD/AWD is for the average person easier to drive faster. It is easier to utilize most of the grip. But less fun and generally less work.
Many people find less work and just going fast to be more rewarding without having to balance the car that much.

That's not an unreasonable way to look at it. In FWD the car is being pulled by the front wheels, whereas in RWD it's being pushed by the rears. The reason you spin if you decelerate rapidly in a turn (this can be by braking or simply by lifting off the throttle) is that the deceleration causes the mass of the car to be thrown forward (picture what happens to occupants and loose objects inside the car, well the same thing happens to the car itself; animators often way exaggerate the effect so picturing a cartoon car coming to an abrupt stop gives you a good idea of how it works). When this happens, the traction wheels (rears) lose traction and swing around. Conversely, if you accelerate in a turn, mass goes to the rears and away from the steering wheels so they lose grip and the car straightens out. If you go to a car control clinic or other event where a skidpad is available, you can try this out for yourself.

im not so sure i agree with that. cars like the frs and the miata are easy to drive and thats the reason why spec miata is more popular than spec focus. with these cars that are balanced is is more dangerous to drive at the limits but many inexperienced drivers in fwd cars just drive too hot and end up pushing off so much speed without learning the lesson.

whhhattt? im curious as to what kind of carbon fiber applications u have seen. the high quality stuff is beautiful i.e pagani & lambo superleggera.

As I said, it is an impressive structural material, as in the examples you cited. I just don't much like the look of exposed carbon fiber as trim pieces.

you would be in the minority then.

Let's say the car is 2800lbs, and is a perfect 50:50 split. That means that there's 1400lbs in front, and 1400lbs in back. That means every 50lbs you take out of 1 side will increase that ratio by 1 point to the other side. For example, if you take out 50lbs from the exhaust at the rear, you change the balance to 51:49 F:R

Math:

1400 (rear) - 50 (weight reduction) = 1350 (new rear)

1400 (front) + 1350 (new rear) = 2750 (new total)

1350 (new rear) / 2750 (new total) = 49%

true to an extent.
based on what I learned in school, the shape of the peices play a big part. I forgot the formulas but it gets a little
complicated. your COG can get put to the left or right side too.

Right, I was just trying to make it as simple as possible. Basically, any MINOR change will have next to no effect...nothing that any normal driver would ever be able to tell. You'd have to start shifting hundreds of pounds for it to become really noticeable

OP, do you have anything like SCCA solo II autocross in your area? Great way to learn. You can read all this theory, you need to experience it to truly know.
And then you'll be able to start feeling what difference mods you make do.