The Ever-So-Dangerous "Tank Slap"
Mar 30, 2009, 02:52 PM
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The Ever-So-Dangerous "Tank Slap"
Tank slap, fishtail, whatever you choose to call it - it's dangerous, it's scary and for some reason, the oil on the roads here make it a reality, particularly on cold days and/or cold tires.
What am I doing incorrectly to cause this? Is it addition of too much throttle too early in the turn? There seems to be such a fine line of too much throttle and too little throttle - too much and the rear end comes out (hence the propensity for a tank slap); too little and the car just pushes wide.
Suggestions? Lower the rear tire pressure? Currently running RE-01R on 32F/29R.
Constructive driving techniques and suggestions welcomed. Idiotic, one-line comments ("dude, the car's just too much for you"; "just learn how to drive"; "go take a class") ignored.
What am I doing incorrectly to cause this? Is it addition of too much throttle too early in the turn? There seems to be such a fine line of too much throttle and too little throttle - too much and the rear end comes out (hence the propensity for a tank slap); too little and the car just pushes wide.
Suggestions? Lower the rear tire pressure? Currently running RE-01R on 32F/29R.
Constructive driving techniques and suggestions welcomed. Idiotic, one-line comments ("dude, the car's just too much for you"; "just learn how to drive"; "go take a class") ignored.
Mar 30, 2009, 05:57 PM
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None of those one liners here...
Honestly, the fishtail or tank slap is waaay past the problem. The car sliding shouldn't be a dangerous issue if you have the driving technique to catch it, a tank slap would mean that it already went through the initial slide and is now on the way back past center the wrong way. There's a dozen reasons why the car will initially go sideways, most of them begin and end with the driver and not the car.
Are you on the street or on a race track? I recommend playing around at a car control clinic or track day a bit and get used to sliding the car around without it tank slapping.
Honestly, the fishtail or tank slap is waaay past the problem. The car sliding shouldn't be a dangerous issue if you have the driving technique to catch it, a tank slap would mean that it already went through the initial slide and is now on the way back past center the wrong way. There's a dozen reasons why the car will initially go sideways, most of them begin and end with the driver and not the car.
Are you on the street or on a race track? I recommend playing around at a car control clinic or track day a bit and get used to sliding the car around without it tank slapping.
Mar 31, 2009, 09:06 AM
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Thanks, Matt - it's just just on the street through very tight corners. I'm not sure if a "slap" is the right characterization; it's more of a quick wiggle more than anything else. If I had to guess, I'd say that the rear end is only moving side to side less than 24 inches.
Totally agree it's all about a problem between the seat & the steering wheel (driver).
I'm going to have to find somewhere safe like a CCC to try to induce the slide in a turn and how to catch it.
Thanks again, Matt.
Totally agree it's all about a problem between the seat & the steering wheel (driver).
I'm going to have to find somewhere safe like a CCC to try to induce the slide in a turn and how to catch it.
Thanks again, Matt.
None of those one liners here...
Honestly, the fishtail or tank slap is waaay past the problem. The car sliding shouldn't be a dangerous issue if you have the driving technique to catch it, a tank slap would mean that it already went through the initial slide and is now on the way back past center the wrong way. There's a dozen reasons why the car will initially go sideways, most of them begin and end with the driver and not the car.
Are you on the street or on a race track? I recommend playing around at a car control clinic or track day a bit and get used to sliding the car around without it tank slapping.
Honestly, the fishtail or tank slap is waaay past the problem. The car sliding shouldn't be a dangerous issue if you have the driving technique to catch it, a tank slap would mean that it already went through the initial slide and is now on the way back past center the wrong way. There's a dozen reasons why the car will initially go sideways, most of them begin and end with the driver and not the car.
Are you on the street or on a race track? I recommend playing around at a car control clinic or track day a bit and get used to sliding the car around without it tank slapping.
Mar 31, 2009, 12:45 PM
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Well a wiggle on an Evo could be just the diffs working on really tight and slippy corners. But still go to a CCC, it'll be a ton of fun and you'll learn a lot. Where do you live? I can probably find you a good one to attend.
Apr 2, 2009, 11:20 PM
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Nothing with cars is cheap. The BMW ones are usually around $110 per day. I know there's a number of schools that go on around Vegas, just have to look. Do one and you'll have the confidence and skill needed to control that Evo of yours!
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May 22, 2009, 09:11 AM
#10
Simply put, a tank slap is a snap spin. Technically speaking it is caused by the natural unloading of compressed suspension (or weight transfer) compounded by the available traction to the fore or aft tires in relation to said weight shift (circle of adhesion).
In more detail, this is it...
Lesson 1 - On ANY car, front, rear or all wheel drive, the weight of the vehicle will move to the REAR under acceleration and to the FRONT under breaking or lift. The degree of that weight shift is proportionate to the amount of throttle or brake.
Lesson 2 - When there is MORE weight on a tire, the more traction it will have. Less weight, less traction or "adhesion".
Lesson 3 - The Circle of Adhesion. The amount of traction available to a tire lessons with the angle of the tire in relation to the direction of momentum. (if the front tires are turned all the way to lock and the vehicle was driving straight, the amount of grip to the front wheels is almost nill UNLESS you slow down. Otherwise you will "push" through the corner.)
Lesson 4 - Putting it all together....
If you are driving straight at even throttle, you have equal traction at all four tires.
If you are driving straight at ON throttle, you will have more traction to the BACK tires.
If you are driving straight at OFF throttle, you will have more traction to the FRONT tires.
If you TURN while driving, the more steering input you give the less speed you can carry, knowing this....
If you are turning at ON throttle, you will have LESS traction to the FRONT tires (and creat 'push' or Understeer).
If you are turning at OFF throttle, you will have LESS traction to the REAR tires (and possibly step it out or create Oversteer).
Ahhh... now we are getting somewhere. Turning in OFF throttle LIFTS weight off the rear tires and lessons the traction there. KEY POINT
In YOUR senario, you are on the freeway, arguably going to fast for the conditions, and you turn in and the back gets loose. What you ARE doing to cause the "tank slap" is to drive along, the back gets loose, start to come around a bit.... you panic, turn into the skid and LIFT the throttle or worse yet, start braking...
When you do that, you lift MORE weight off the back (which is already struggling for grip) and ADD steering (which is pointed the opposite direction of the corner).
When the weight shifts forward and front tires bite, the car rapidly turns the direction the wheels are pointing... Thus the tank slapper.
You are then most likely trying to aggressively counter steer and now WAY off the throttle or hard braking and if the weight transfers again, you will snap back the other way again.
That is what is happening.
The PROPER way to deal with this is first, not going faster than the available traction. That is a given. But for anyone that might get caught out on ice or a sudden emergency situation or just get caught out by the Evolutions's natural springiness in the rear end, the PROPER way to deal with this situation is...
You are driving along and the back end starts to step out. DON'T create a sudden weight shift forward. Don't lift all the way out suddenly or brake hard as that will EXAGGERATE the problem. Turn into the slide a LITTLE and apply throttle a LITTLE, NOT MUCH. Just enough to shift some weight onto the back tires.
As the car start to straighten out, UNWIND the wheel. In other words, get the wheel back to center AS you apply throttle and the car straightens out. It's ALL proportionate. Just enough throttle and equal amount of steering until everything is centered. THEN lift and brake.
I have been teaching private performance driving and Tactical Response for state and federal agencies for many years both on and off road and this type of spin is a big part of performance and daily driving. You see the skid marks on the freeways everywhere and it's really a combination of driving over your head and somewhat bad advice from your driver's ed teacher. Turning into the skid is appropriate, but standing all over the brakes is not. Driver's ed relys on the fact you are not going fast enough to create the rapid weight shift... which, in an EVO, you just ARE.
In on road schools, we teach to not brake the circle of adhesion. In Rally Schools, we teach students how to do this on purpose, and then we call it the Scandinavian Flick. Once you understand WHY it happens, you can avoid it altogether but if you every find yourself in an emergency, you will know what to do. Just don't put yourself in that situation.
Disclaimer: Performance Driving is for the appropriate venue. Public Roads are not the place for it.
Come to one of our schools and I'll show you personally how it happens, why it happens and what to do to control it.
Best,
Scott
In more detail, this is it...
Lesson 1 - On ANY car, front, rear or all wheel drive, the weight of the vehicle will move to the REAR under acceleration and to the FRONT under breaking or lift. The degree of that weight shift is proportionate to the amount of throttle or brake.
Lesson 2 - When there is MORE weight on a tire, the more traction it will have. Less weight, less traction or "adhesion".
Lesson 3 - The Circle of Adhesion. The amount of traction available to a tire lessons with the angle of the tire in relation to the direction of momentum. (if the front tires are turned all the way to lock and the vehicle was driving straight, the amount of grip to the front wheels is almost nill UNLESS you slow down. Otherwise you will "push" through the corner.)
Lesson 4 - Putting it all together....
If you are driving straight at even throttle, you have equal traction at all four tires.
If you are driving straight at ON throttle, you will have more traction to the BACK tires.
If you are driving straight at OFF throttle, you will have more traction to the FRONT tires.
If you TURN while driving, the more steering input you give the less speed you can carry, knowing this....
If you are turning at ON throttle, you will have LESS traction to the FRONT tires (and creat 'push' or Understeer).
If you are turning at OFF throttle, you will have LESS traction to the REAR tires (and possibly step it out or create Oversteer).
Ahhh... now we are getting somewhere. Turning in OFF throttle LIFTS weight off the rear tires and lessons the traction there. KEY POINT
In YOUR senario, you are on the freeway, arguably going to fast for the conditions, and you turn in and the back gets loose. What you ARE doing to cause the "tank slap" is to drive along, the back gets loose, start to come around a bit.... you panic, turn into the skid and LIFT the throttle or worse yet, start braking...
When you do that, you lift MORE weight off the back (which is already struggling for grip) and ADD steering (which is pointed the opposite direction of the corner).
When the weight shifts forward and front tires bite, the car rapidly turns the direction the wheels are pointing... Thus the tank slapper.
You are then most likely trying to aggressively counter steer and now WAY off the throttle or hard braking and if the weight transfers again, you will snap back the other way again.
That is what is happening.
The PROPER way to deal with this is first, not going faster than the available traction. That is a given. But for anyone that might get caught out on ice or a sudden emergency situation or just get caught out by the Evolutions's natural springiness in the rear end, the PROPER way to deal with this situation is...
You are driving along and the back end starts to step out. DON'T create a sudden weight shift forward. Don't lift all the way out suddenly or brake hard as that will EXAGGERATE the problem. Turn into the slide a LITTLE and apply throttle a LITTLE, NOT MUCH. Just enough to shift some weight onto the back tires.
As the car start to straighten out, UNWIND the wheel. In other words, get the wheel back to center AS you apply throttle and the car straightens out. It's ALL proportionate. Just enough throttle and equal amount of steering until everything is centered. THEN lift and brake.
I have been teaching private performance driving and Tactical Response for state and federal agencies for many years both on and off road and this type of spin is a big part of performance and daily driving. You see the skid marks on the freeways everywhere and it's really a combination of driving over your head and somewhat bad advice from your driver's ed teacher. Turning into the skid is appropriate, but standing all over the brakes is not. Driver's ed relys on the fact you are not going fast enough to create the rapid weight shift... which, in an EVO, you just ARE.
In on road schools, we teach to not brake the circle of adhesion. In Rally Schools, we teach students how to do this on purpose, and then we call it the Scandinavian Flick. Once you understand WHY it happens, you can avoid it altogether but if you every find yourself in an emergency, you will know what to do. Just don't put yourself in that situation.
Disclaimer: Performance Driving is for the appropriate venue. Public Roads are not the place for it.
Come to one of our schools and I'll show you personally how it happens, why it happens and what to do to control it.
Best,
Scott
Last edited by RallyDSM; May 22, 2009 at 09:13 AM.
May 29, 2009, 02:33 PM
#14
OP, I don't think you're getting tank slap/spin. I think you're just losing traction on the rear end.
It can also be your car's setup. Before the last autocross, I installed a rear sway (stock front) and had the rear camber reset from -2* to -1.5*. Multiple times, I had tank slapper, off throttle snap spins happen or almost happen -- and I was driving the car the same way as I always had!
It can also be your car's setup. Before the last autocross, I installed a rear sway (stock front) and had the rear camber reset from -2* to -1.5*. Multiple times, I had tank slapper, off throttle snap spins happen or almost happen -- and I was driving the car the same way as I always had!
May 30, 2009, 04:21 AM
#15
For real guys, if you can put together about 20 - 30 students that would like to take a basic Performance Rally or Solo Driving School, let me know. We can take our school on the road and Vegas isn't to far to go and we're based on Washington State/Oregon so Canada is close too, eh?
I also do private bookings
Seriously though, I gave you the basic theory for performance driving.... which is true for any wheel configuration or any suspension setup or tuning.
Obviously, bad tuning or fine tuning will change the limit of adhesion and the time weight transfers but generally speaking, you can drive an average or even poorly tuned car with these basic principles.
I'm glad to help
Scott