BRZ as daily driver?

[serialk11r]

I think electronic stability control stuff only corrects after it detects slip, so if you get stickier tires then the intervention just kicks in later.

[Margovincent_22x]

Hope that's the case cuz I'm planing to change to high grip tires due to road conditions

[Corey]

Originally Posted by fatoni

not only did i explain it, i showed them this thread. i know what happens when you brake and gas at the same time. thats my point. you cant just go adding the forces the isolated forces like that. its not how that works. 1g is 1g. 1g isnt 1.6gs. that data shows that power is important simply because without it you arent at the edge of grip anytime that car is accelerating. i think we are kind of in agreement and to be honest am surprised this has stayed pretty civil. the bottom line is that a tire only has so much grip in any given set of conditions. no matter how much force you try to exceed grip is fixed by the shape of the circle. cornering and accelerating doesnt magically change that. you cant judge a net vector by its constituent parts. im chalking it up to miscommunication but combining forces isnt making more grip. its just the thing to do at a particular place on a particular race track

Ok, I think see where the confusion is. Like I said, the grip circle is a graphical representation of the forces of the tires. I guess I made this unclear by referring to braking, accelerating, etc. in reference to the illustration. It is not necessarily a measure of those forces, but rather an illustration of the forces on the tires produced by those actions. So for the example of braking and accelerating at 100% at the same time yes, you are producing some power with the engine and quite a bit of braking force to fight movement of the wheels, but if the car isn`t moving then despite the power and braking you are still at the origin point on the grip circle; 0,0. The tires themselves are doing nothing as long as the car isn`t moving and that is all the grip circle is: a graphical representation of acceleration conveyed through the tires, both lateral and longitudinal.

Despite our miscommunications I pretty much agree with what you`re saying. On an accelerometer a driver trail braking isn`t going to have a wider grip circle than one who only brakes in a straight line. The only way to change that is to get better tires (assuming your setup makes the best use of the ones you`ve got. The difference is just how you use the available grip of the tires. All I am saying is that it is a better use of the available grip of the tires to combine longitudinal and lateral forces when possible and practical because that will produce better lap times. As for why, that is what I have been trying to illustrate above.

Originally Posted by serialk11r

I haven't really thought much about this, but isn't there something missing from the "grip circle"? That is, depending on the weight distribution of the car, the tires are loaded unevenly, not to mention the tires are affected by suspension changes and stuff...

You are correct, what the grip circle actually looks like for a given car is dependent on that car. It is generally quite close but reality usually ends up looking closer to the accelerometer plot above because as Dennis Grant said it takes quite a lot of power to use much of the available longitudinal grip of the tires for acceleration. You could say it is an ideal, and as an engineer or driver it is your job to 1. ensure the car setup can make use of the entire potential of the tires or 2. drive well enough to keep the tires as close as possible to the perimeter of the grip circle respectively. If you can achieve those two things, and your car has enough power, actual accelerometer data will look remarkably close to the theoretical grip circles above.

[Want.FR-S]

Just to chime in w.r.t. the "squash" circle. In order to fill in the top portion of the circle, you need to accelerate fully while making small steering angle. Would it be the case because this scenario does not happen frequently on a track? Thinking like a long radius curve with a bank or something so that you can keep accelerating.

[gdi2290]

[storkfacekiller]

[Corey]

Originally Posted by Want.FR-S

Just to chime in w.r.t. the "squash" circle. In order to fill in the top portion of the circle, you need to accelerate fully while making small steering angle. Would it be the case because this scenario does not happen frequently on a track? Thinking like a long radius curve with a bank or something so that you can keep accelerating.

You are right that track layout plays some role but it`s generally the case that the car does not have enough power to create that much longitudinal force due to lack of power (in relation to available traction) in most areas of a track. I`ll try to explain what I mean although explanations are apparently not my strong point

The car in question used to make that plot was an AWD Talon with about 350 whp and racing tires, and the plot was taken from a ProSolo competition (basically autocross with a drag style start). The biggest factor is the tires; expensive racing tires provide an obscene amount of grip and although it`s comparatively easy to go into a corner faster to use the lateral grip, it takes a LOT of power to make use of all their longitudinal grip under acceleration.

So to start us off, the top of the `stem`comes from hard straight line acceleration aided by AWD at the beginning, and the points below illustrate how longitudinal force (that feeling of being pushed back in your seat under acceleration) tapers off as the car gains speed. It`s for this same reason that the graph appears smushed on top. If the car had enough power you`d expect it to follow half of the grip circle, from bottom to top, through the course of taking a given corner. At entry you`d begin with maximum braking, transition to trail braking as you approach the apex, achieve max cornering grip crossing the apex, then transition into acceleration as you unwind the wheel towards the exit. At every point of a corner you are creating some combination of lateral and longitudinal force and further than that, you are creating them in proportion to each other. You increase steering angle which in turn increases lateral force as you release brake pedal pressure while trail braking, decreasing longitudinal force. After crossing the apex you do the opposite; add throttle and thus longitudinal force in proportion to how much you`re unwinding the wheel which reduces lateral force.

What this means is that if you`re driving well (read: smoothly) you would expect there to be a roughly equal amount of points all around the perimeter of the grip circle which represent the different phases and your smooth transition between them of every corner on the track. On a normal non-autocross track there`d probably also be a disproportionate amount of dots on the positive side of the Y axis that represent accelerating on straight sections which is where you spend most of your time.

The reality however is it takes more power to `fill in` that top area of the plot than most cars have. The smushed area then represents where the car could not produce enough longitudinal grip to follow the perimeter of the circle. This is certainly not the fault of the driver as the plot plainly shows he was driving to the best of the car`s ability, but rather is the result of a lack of power. In such a situation all you can really do is give it max throttle and adjust your steering/lines so you`re using as much cornering force as possible in combination with the power the car can produce, and this is what causes the plot to look smushed.

Now you do have a point as well. If a track were designed predominately with strange increasing radius turns and the such you might end up with an equally strange accelerometer plot showing a driver that went from full lock to straight line acceleration. I think it`s likely that given such a situation the driver would find the best lap times by finding a way to use the rest of the grip circle though.

[Draco-REX]

Originally Posted by storkfacekiller

I WANT THIS ON A T-SHIRT!

[quasi13]

My BRZ will be a year round car, but I expect most of my miles to be put on in the winter since I am mostly on a motorcycle in the summer. I almost bought a WRX: when I discovered the BRZ, I started thinking of all the great times I had in my s13 primarily because it was RWD.

As others have said, RWD + snow tires = lots of fun. The winter is when I do my drifting - I don't like the speeds required to drift on dry tar on public roads. In the snow is actually where I learned how to handle a RWD car. My advice is to embrace some RWD driving time in the snow - just go somewhere without people or telephone poles or curbs or deep ditches or... Then just play with caution. You'll probably learn a lot.

I've driven through all sorts of snow in FWD and RWD cars with all sorts of tires. I highly recommend snows! In fact, I don't plan on going through a MN winter without them again, because it makes such a huge difference in how safe and confident feel. I can't say about whether you should bother with snows in VA though, but summer tires (or bald tires) in the snow is a disaster.

[Captain Snooze]

Originally Posted by ashtray

You need to learn how to drive the car differently than a FWD car in the rain.

In a FWD car, when the roads are slick and you go around a turn a little too fast, the FRONT tires lose traction and the car pushes out of the turn. To correct for this, you reduce speed and continue to turn the wheels in the direction of the turn. (so a right turn, car starts to slide, you keep the wheel turned to the right. This is called understeer.)

A RWD car reacts differently when it loses traction around a turn. The REAR wheels push out, causing the car to start to spin. In a right hand turn, the way to correct for this is to turn LEFT during the slide. (this is called oversteer)

In EITHER case though, you pretty much always point the tires in the direction you want to go. With a RWD car that is spinning, this requires you to turn the wheel the opposite way. Watch the Pixar movie "Cars" to get it.

Pardon me but I will refute part of what you are saying. You are making broad generalisations as to fwd/rwd steering behavior. Fwd vehicle usually reduce understeer by accelerating. That is, the front wheels pull the front around the the curve. Coming from rwd cars i spun my current fwd trying to drive it like a my previous rwd cars. That is by backing off going around bends. My current car , not your typical fwd steerer, has creamy smooth lift off over steer but this will bite in the wet if you back off abruptly.What if you are going around a curve at speed in a rwd car when you hit a wet patch across the road? The front wheels hit first resulting in massive understeer. If you are going too fast for the conditions you are going straight ahead regardless of what you do. The rally basher I owned was rwd. It exhibited massive lift off over steer.Most garden variety rwd vehicles, to the best of my knowledge, understeer. It has to be severely provoked to get them to oversteer. You are more likely to plough off the road than spinning.

[Corey]

FWD cars reduce oversteer with acceleration, not understeer. The reason FWD cars are notorious for understeering mostly has to do with the fact that they use the front tires for both accelerating and turning. Combine that with the fact that the laws of physics are working against them (accelerating shifts weight off of the drive wheels) and you have a pretty poor formula for traction. This is why FWD autocross cars usually "point and shoot" by running really stiff rear springs to rotate the car in the right direction and lessen weight transfer to the rear so they can just accelerate in a straight line.

[sbxjap]

BRZ is going to be my daily driver while I redo my Civic for shows again... but I'll probably do simple mods on BRZ (always had that tuner itch).


Just don't go driving crazy and it'll be fine in snow... as long as it's not too high, that is. My Civic is a pain in snow only because of height and the city not plowing...

I plan on getting a set of rims and tires for winter anyway... and another set for summer and/or show.