--In auto racing, slip angle is the angle between a wheels actual direction of travel and the direction towards which it is pointing. The more slip angle the more side force a wheel will generate - this is true up to a certain maximum, typically around 4-8 degrees, where the side force will start to drop off again.--
Hello, fellow drifting.com members. I write this today to explain one thing that is often confusing to newbies and even those who are already drifting. It is the old grip vs. drift arguement. As many of you already know, there is a time and place for each. Drifting is not just used for fun and to keep the revs up and waste gas. Drifting can be fast. It is widely known that with some slip angle, usually still considered grip by most racers, tires can really grab the road better. One basic rule of thumb is that if you can take the fastest line at near wide open throttle or at wide open throttle and keep in grip, you should never drift on that corner (dynamic drifting doesn't have much of a place here). Another rule of thumb is that (I know this thanks to malcolm, GridRaceTech, and Ryan) the best slip angle for radial slicks is around 1-2degrees, for bias-ply slicks, around 3-5 degrees, for DOT-R compound tires (rather like drag radials or street-legal racing tires), around 5-7 degrees, and for street tires, anywhere between 4-9 degrees. An example is at a chicane. If you rotate the car on corner entry where you would normally already be turning in and on the gas, you can hold this until the middle point of the chicane. Why would you do this? Well, with a simple short moment off the gas and perhaps a dab on the brakes, the car will automatically swing back around for the corner and you can slowly let off the gas and retain grip ASAP after the apex for corner exit. After corner exit, you should be flooring it, so don't try to drift here. Always remember to take the best line along the chicane, as straight as possible, rolling over both curbs (remember to keep it stable here
). Becuase of the fact that you only want a bit of slip in a straight line, at corner exit you dont want to have the rear tires hanging out, but you do want to have the car rotated which is the whole point of drifting. Well, that and fun. Unfortuneately, I had trouble while uploading a picture of this but you get the point. at corner exit the car should never keep rotating after you are facing the correct direction UNLESS you are going to the outside for the next corner going the opposite direction (like a chicane with a straight in between).
Another important thing to understand is the under normal cornering, parts of the tire are already slipping a bit since it is as if your tires is a drivetrain with a locked differential. The inside of the tire cannot rotate slower than the outside, thus causing slip. With front-wheel STEERING, the rear tire's contact patch gets this amount of slip in a diagonal pattern, starting at the inside rear portion of the tire, even moreso on the outside tire since it is travelling faster and the outside-inside of the the tire's slip ratio is the same and therefore the higher the speeds (the outside tire travels fast with a differential on the car), the faster the outside of the tire must travel and, to a LESSER extent, the inside portion of the tire (depending on camber, caster, and other alignment settings). This is an elementary version of slip angle. With HICAS (four-wheel steering), the same principle applies except the slip effect isn't as diagonal and it is moreso starting from the back and heading to the front of the contact patch. A drift is defined as the point at which the ENTIRE tire gains this slip effect and the car begins to rotate. The more you break traction at this point, the greater the slip angle.
Here are some examples of exhibition (slow) drifting. it is only done for spectators, not speed.
In the picture below, Ueo Katsuhiro (in the hachiroku) has a very high drift angle whereas the driver of the 240 behind him is demonstrating a somewhat fast but still an exhibition drift. This is quite often used to catch up to the person in front of you during Tsuiso.
The Hachiroku in the picture below is demonstrating just 1 or two degrees of drift angle, the perfect angle for most cars near corner exit.
Cars with bias-ply slicks benefit from slightly more drift angle like the one below. Keep in mind that I am NOT saying that this MR-S has bias-ply slicks, but its drift angle is about appropriate for such a tire
Can't stress this one enough people, NO.
The cars below have drift angles slightly beyond the drift angle that is desirable and beneficial to most racers. However, on lower traction surfaces or on street tires, this is the perfect race drift angle for the turn shown.
Picture this: Petter Solberg (famed WRC driver, almost killed his co-driver in Rally Deutchland; actually he escpaped without a scratch even though he was almost crushed by [this will suprise you] the rollcage) is drifting a corner (in an AWD, mind you) covered in snow. it has a 90 degree turn (which he is on), a short straightaway, and then another left-hander. What he will do is rotate the car slightly before normal corner entry and power through with minimal steering work. With the AWD system, this is all very fast and his drift angle will stay constant (by this I mean as seen from above, the angle will decrease slowly to zero in relation to the road ahead as he rounds the bend. He will almost floor it (for traction purposes), then brake for the next corner and do the same thing. This also demonstrates how on slippery, gravel, and snow covered areas with low traction, the optimum drift angle can raise up to as much as 20 degrees on some street tires.
This time a different car is on dry, hot tarmac. He does the same thing except without the straightaway in between. This is hardly a drift. It is simply a controlled spinout which also involves flooring it afterwards and travelling 10 feet to the left while he's at it.
This time a video of the same type of corner. Ignore the minimal countersteering due to AWD.
http://s92836226.onlinehome.us/filmy...owerslide.mpeg
The same type of corner demonstrated in a different car at a different angle.
This is another demonstration of an appropriate corner exit drift angle on tarmac, this also applies similarly to RWD
This is an actual, real-world use for high-angle, slow exhibition drifting. The FD in front is trying to block the other FD from passing by taking up too much space and blocking all of the fastest lines.
There is also another variable here. With all the weight shifting and slip being uneven throughout the tires under grip, traction can be upset very easily from (and I'm quoting Malcolm here) a small crack in the pavement or a little pebble. This sudden onset of oversteer or understeer or excessive four-wheel sliding isn't as violent when drifting. The higher angle the drift, the more this is true. But, because of reduced grip, there is a dropoff point when these benefits become useless and, in fact, damaging to your speed and possibly to your car.
Yet another reason to drift slightly is weight transfer throughout the contact patch. Yes, weight transfer throughout the contact patch. Picture the tire as mostly gripping. There is a diagonal path of where the slippage passes the point on the tire with the most work being done. During a full drift (at a few degrees of yaw) the weight is evened out much better and the uneven speed of the tire is essentially fixed. This can be compared in the exact same way to giving some gas to a car with a locked differential. And that, my friends, is how slip angle works. Plus, you get the benefit of rotating the car without some ridiculous 90 degree four wheel steering (well that's a thinker, I wonder if that would work. You would need two steering wheels but that's no problem. If you have multiple arms like that dude in Spiderman 2 or whatever).
If you want more reasoning, lets look at the traction circle.
As you can see, 1g of braking, acceleration, or raw turning can be used at once on this hypothetical car. However, you cannot utilize 1g of braking force and 1g of turning force at once, amounting to 2gs. This would make some people assume that the cornering force and braking or acceleration force can only amount to 1g. WRONG. If you look at the square in the top right quadrant of the traction circle, you will notice that if you are to use around 65% (0.65g) of your cornering force, you can use up to 75% (0.75g) of your potential acceleration force! The reason behind this is that a tire can potentially, in a perfect world with perfect conditions (not seen on ashphalt) generate full potential in all directions at one time. However, to harness this and essentially "line up" the traction circle with your car, you need some slip. Now I know what you are all thinking: 2 things. #1: if you can only utilize 65% of your cornering force, then won't you run off the road/track? #2 What about the rules of dynamic and static friction? Won't the slip just cause you to slide away into the junkyard? Well, in regards to #1, you just need to brake earlier. If you brake later then a pro racer does, you won't be able to use any throttle and you will run to the outside of the turn and, as you slow down from cornering and friction, you will run back to the inside and you should be fine. If you brake earlier, then you can utilize the entire potential of the traction circle if done correctly. Now why would this slow entry speed, high exit speed pay off in the long run? You will take the proper line. You won't slowly run to the outside and back in again. You won't hit an early apex on a regular turn. That is what will shave precious seconds off your lap times. #2 This is the reason why you can't have the best of both worlds: 1g of acceleration + 1g of cornering. Because of the necessary slip, you can only corner (with the car demonstrated by the traction circle above) with up to 1.4g as opposed to 1.42g approx. (once again, thanks for clearing this up malcolm, I was quite tired when i wrote this section). It is 1.42g because of the approximate 45 degree angle between the acceleration and cornering force in the traction circle therefore you can add 1g + 1g together to get 2g, and then find the approximate square root, giving you about 1.42g. However, this is where the slip is required. This is also why it is not a traction square
.
I hope this has been helpful to you all in understanding the dynamics, reasons, and overall science behind drifting. You must also made sure that you do not mix up AWD and RWD, although, as you can see, there are very striking similarities since AWD drift is basicalle a useful form of partial understeer. In a way AWD is like having high grip with low traction.
My conclusion is that, in reference to the idea in the beginning of this writeup about slip angle under complete grip (along the contact patch), small amounts of drift essentially help straighten out this contact patch thus increasing lateral traction therefore allowing for tighter steering angles. This is the concept behind the four-wheel slide. That, coupled with the rotation of the car, is what makes drifting faster on some curves.
To sum it all up, go out there and try grip first. Once you have learned about taking correct lines, practice these techniques to find appropriate angles on each corner. You will find your lap times disappearing like Eddie Murphy after Delirious. After this you can learn how to use multiple angles on different corners and take advantage of late and early apexs and keep in control and, most of all, have fun!
Note: Some cars don't require such slip. For instance, Formula 1 cars never drift; not just because of near-perfect traction control coupled with drivers like Schumacher but they are set up perfectly within the restrictions and guidelines (I hate those). They also lose 50% of their downforce at 5 degrees yaw. A car that performs best under grip is a VERY good car. Yet another bunch of elements contribute to optimum slip angle and turning technique:
alignment settings. These include steering axis inclination,
Dave Point/steering axis point, camber, caster, toe, and individual toe on cornering. Although the Dave Point has to do with what kind of slip angle you want, I mentioned already how camber, toe, and other alignment settings change your optimum slip angle and how your contact patch is not always even. We racers sometimes like to call it the steering axis point or simply refer to the adjustment necessary if the SAP is offset, an adjustment to the "steering axis inclination". This can help scrub radius and many other handling characteristics of the car, or make them worse if you don't know what you're doing. Always remember to trust your mechanic because something might happen on the track one day and you front brakes will fail and the rears will lock and you will lose control like that one day at the track a few years back. Anyways, I am going on a tangent now so if you want more alignment info, check out this site. It is a must-see for newbies:
http://autotech-training.com/Alignment/Alignment.htm
Anybody volunteer to make a glossary for this thread?
Special thanks to malcolm and Ryan for helping me improve this thread with their helpful posts in other threads as well as this one. Also, thanks to Craftsman and Dave Coleman;
Dave Point.
what pricks.
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