I am trying to understand the physics and the designs of a car.

Assuming:
1) You have a car that has street racing mods (performance brakes, tires, etc...).
2) The road is flat and has no debris.
3) You are driving 100 mph and the corner that you WILL take the turn is 50 mph.

Someone please inform me how someone would approach the turn and why (reason)?

Please don't respond with: "Slow car down to 50mph and take turn. After turn, step on gas peddle to speed up again".

For example
I read somewhere that, by slowing down into a corner that the weight will be on the front wheels. This will allow the car to turn better.

 

Are we talking about a FWD car?

 

yes. ill just say the the car is an Acura TL.

 

Whats the braking distance before the apex of the turn? is the max you can do 50? or is that the safest esitmate?

a heel-to from 6-4th while braking before the turn will bring you right to 50 while entering and then a downshift into 3rd right before the apex will get you into the powerband. once in 3rd you can power through the turn full throttle assuming you are NA and a 6 speed with LSD.

 

The braking distance is whatever you decide because you know the turn is coming and the max you can do is 50mph.

Could you please rephrase the 2nd paragraph into non-car jargon? I understand the first sentence but the 2nd one is beyond me.

If the turn was towards the left, from 100mph to 50mph the front right tire should take the brunt of the kinetic energy which i assume allows FWD to have better steering. At the apex, does a FWD lose some of it's forward momentum from the engine because the weight shifts towards the rear wheel?

 

u want to learn right? google heel-toe. tracks usually have a recommended braking marker thats why i asked the distance. you can decide and i was asking what distance you decided on

 

I don't understand how the weight shifts to the rear wheels? Apex is simply the straightest line you can take while turning. Straighter the line faster you can go. At least that's my understanding.

 

 

Since we're talking about a FWD car, you're going to want the least amount of understeer possible. The question is how?

Do you decrease weight in the nose? Mess with suspension settings to make the car more neutral? Electromechanical gizmos to add power oversteer? (aka ATTS) or an LSD?

 

thats why its important that he specify if he is naturally aspirated or boosted and if its an autotragic or a maual.

but its good to have some more oversteer than understeer. the lsd allows me to swing my rear out a it and punch it at the end of a corner to straighten out

 

Better acceleration. On all but the slipperiest surfaces rear wheel drive cars accelerate faster than a front drive car from a stop. This is because when you accelerate quickly from a stop the weight of the car transfers to the rear of the car. In a rear drive car this places extra weight on the rear of the car, essentially jamming the tires into the road greatly increasing traction. In a front drive car, when the weight goes to the rear, weight is taken off of the front wheels. This allows the front wheels lose traction and spin easier. If the wheels are spinning not only does this slow you down but it also makes it difficult to steer the car. In the rear drive car the front tires are available for steering even if the rears have lost traction. - http://www.rearwheeldrive.org/rwd/rwdbenefits.htm

With this in mind, with my FWD, once i step on the brakes, some of the weight of the car and momentum will transfer to the front two wheels. If i am turning left, the front right wheel is taking most of the weight. Does this weight lead to better traction since the weight will allow the wheel to have more grip?

At the apex, should i "floor" the car to accelerate? Keeping the article above in mind, would the car accelerate better if i was only on 3/4 of the throttle (to reduce tire spin)?

Lastly, let's say the turn is 500 feet away. Should i heavily use the brakes at the last minute (to optimize time and speed) while heel toe shifting OR should i start reducing speed 300 feet or 400 feet away? I ask this question because i want to understand the physics.

 

Slow in, fast out.

Depending on the turn you may want an early or late apex. Don't trail brake if you can avoid it.

http://www.wtfstables.com/rmsoloschool/

 

Don't trail brake if you can avoid it? I would have to disagree with that. You're first thought is absolutely correct, how you shape one corner is just as important as how you want to shape the next corner and how shaped the last corner.

Phee's pic is good but to really understand the art of it, you should have a few more corners to see how to correctly construct your line.


My TL loves trail braking, let's the rear end rotate around beautifully and really helps set the car up for corner exit. The best situation for it I've found is on a corner with a very late apex because you can carry more speed into the corner and it just slingshots you around and throws you out damn near already ready the next corner which is most likely the opposite direction of the first.


This is a pretty hard discussion to have online! Find a track day and learn it in the real world!

 

The problem you're having is understanding is EVERYTHING is variable. That's what makes or breaks a driver. You ask should you "floor" it at the apex? It completely depends on your car, the track, and your confidence. There is NO just standard equation for this stuff. Is the track pretty wide? Does your car have an LSD and decent sticky tires? Then the fastest way out of the corner may be to "floor" the throttle. A lesson I would challenge you to is the idea of MODULATION, both on the brakes and on the throttle sometimes too. Maybe the right word for the throttle is the idea of progressivism.


Your braking points are just as variable to the things I listed above. Depending on the speed of the corners, most tracks will start marking the braking distances between 300 and 500 feet before the corner. Again it really comes down to what your brake setup is, what kinda corner your braking for and big your gonads are to brake as late as possible.


You have to get on the track and try it for yourself. There are certainly PRINCIPLES for racing, but is there an exact science to it, Hell no. Again that's what makes a racing driver and racing driver.

Hope that helps!

 

Perhaps. But your car is heavily modified for the track, right? And you're quite expereinced on the track, right?

So are you sure you want to be advising the OP to trail brake in order to hang his ass end out?

 

i have a general question: what about rwd cars? i can't seem to get the line right...the rear end tires seem to constantly slip out. do you guys actually let off the gas? hold steady?

 

For me, Yes and Yes.


I see your point about a newbie trail braking but it probably won't take him long to pick it up. But yes, its definitely something that has to felt out.

 

That's where the idea of progressivism really comes into play. If you're talking about corner exit? Just remember that the principles are the exact opposite of fwd cars. Meaning that on an fwd car, lifting off the gas in a corner will "most" of the time result in oversteer as the center of gravity is shifted forward and the rear end lightens up. Whereas on a rwd car, lifting of the gas in a corner will definitely make most cars "push" or understeer wide through a corner.

I can go on and on with all this stuff but I'll try to keep it short and sweet.

What are you tracking that's rwd?

 

Is diffcult to answer this question as cars are set up differently, typically the fastest is to follow the driving line that Phee had suggested. But I've seen race driver defy that logic by having the car slide slightly, also some really good FWD driver utilize left foot braking to slow the car while keeping the car in/close to vtec range. And alignment setup plays big part too which I could go on for days.

 

Best way to optimize speed on the street: Drive the speed limit, you never know what is going to be in your way or coming at you on the other side of the turn.

Hopefully this is meant for autox or a real track, though.

 

I'm assuming this is your G coupe. My recommendation is get stickier tires. The G's are set up to be quite tail happy. You can induce oversteer by either too much throttle application or letting off mid way through the wider turn. On really tight, slow turns, you can induce terminal understeer. Luckily these cars are easy to steer with the throttle.

I auto-x my G and I've found tires are key. With my OEM 17s and high performance all seasons, it's a complete handfull in the turns. With my aftermarket 18s and summer rubber, it's a completely different car and has far higher limits. Oversteer isn't nearly the issue.

 

remember, its never safe to say you can take a turn at X mph. what you need to say is how much centripetal force your car can give. while centripetal force is proportional to velocity(Fc=mv^2/r), when you only say "50mph turn" there can be too many factors. for example, 50mph may be the turn in velocity but most of the time a turn is not 100% uniform and i can guarantee that you will not be holding the steering wheel at a constant position the whole time. so therefore when your steering wheel moves even the slightest amount during a turn, you will have increased/decreased your centripetal force which may push your car's grip out of limit and you will spin out.

if you really want to understand physics and design of the car, take some engineering classes in college.

 

that makes total sense. i've had more experience with my recent rwd purchase (g37 6mt sedan). what you mentioned, is EXACTLY what happens; not sure why i was so surprised to read it the first time around. you'd think it'd be common sense to let off the gas during corners - it took me a while to ease myself out of it; was used to holding the gas constant or pushing around corners in the previous fwd car i had.

if the OP doesn't mind, can you expand on the thought? great stuff...and easy to understand for the non-car literate owner

 

Great information Dave! Appreciate the pointers. I haven't yet pushed the limits of the G as of yet...so I'm a little unfamiliar with how the car handles under heavy throttle in the corners; waiting for spring for Pacific Raceway opens - that and I'm still not the best with the MT.

I have a sedan by the way we're one of the same!

 

You better stop talking and more doing.

 

whoa, that is a loaded question. well, i haven't seen anyone talk about slip ratio yet, so i guess i'll start.

so you should learn something about tires first. It is best to have a slip ratio of 10 to 15 percent because this is when your tires have maximum grip. Say the circumference of your tire is 2 meters and as your tire rotates forward. After 1 full revolution, the tire travels 2 meters, you would have a slip ratio of 0%. Now let's say after 1 full revolution, your tires only travel 1 meter (circumference of your tire is still 2 meters), your slip ratio is 50%.

This is why when you see professional drivers accelerate, brake, etc, there is some minor chirping sound coming from the tires. Of course if there is too much chirping your tires are losing grip.

well, that's all i have time for right now, but you should really learn more about tires first and how good tires affect your handling of your car before learning about the layout of your car, etc....