Q: “What causes the phenomenon known as “fishtailing” and how do you stop it? I was at a HPDE event at Road America many years ago and the instructor said a quick stab of the brakes would stop it. I’ve have only gotten to use it when towing an unstable race car trailer, and it did work on that. Should that work in a race car or on the highway?”
A: “Fishtailing” is oversteer. Think of oversteer as the car steering more than you wanted it to, so it has over-steered. In other words, you’re going around a corner, turning the steering wheel the appropriate amount to make the turn, but the rear of the car swings out and makes the car turn more than you wanted. It has oversteered. Another way to think of oversteer – or fishtailing – is that the rear tires have less grip than the front tires do, and therefore they slide more than the front tires.
Note that oversteer is not what you, the driver, have done – you haven’t turned too much. Oversteer is what the car is doing. See the Oversteer: What It Is & How to Control It video.
Why has the car oversteered or fishtailed? Again, it’s because the rear tires have less traction than the front tires do. What could cause that? Ultimately, speed is a factor – if you were going slower, the tires (in this case, the rear tires) would not have reached their limit of traction and begun to slide. Usually there is more than one factor at play here. Often the car is not balanced – the main thing that you, as a driver, can control at the moment in time. When you brake, what happens? The car’s nose dives because weight has transferred to the front; the rear tires have become less loaded, and therefore their traction/grip level has been reduced. I hope all of that makes sense because it leads to the answer to your question – but it’s important that you understand that first.
If your car is fishtailing, or oversteering, it’s because the rear tires have less traction than the fronts. A quick stab of the brakes will put more load on the fronts, and less on the rear, making the problem worse.
There is one other scenario that could lead to something that seems like fishtailing, and that’s “power oversteer.” If you drive a rear-wheel-drive car with enough engine power to cause the rear tires to begin to spin (wheelspin) while coming out of a corner, you will cause the rear tires to break traction and the rear of the car will begin to slide sideways. This is oversteer, but in this case it’s caused by extreme power being delivered to the rear tires – you were too hard on the gas pedal. To control this, you should simply ease up on the gas pedal. I would definitely not recommend stabbing the brakes, as that’s going to cause too much load transfer to the front, and could cause the car to spin around. And again, to control power oversteer, simply ease up a little on the gas pedal to reduce the power to the rear tires.
As you can see, neither situation would be cured by a quick stab of the brakes. In most cases (there could be an exception to this, but it’s extremely rare – I can’t think of one right now!), the last thing in the world you would want to do is stab the brakes. Modulating the throttle is the only thing you should do. If you’re dealing with oversteer from the rear tires not having enough load on them, gently squeeze on the gas to transfer weight to the rear; if you’re dealing with power oversteer, gently ease up on the gas pedal to give the rear tires more cornering grip. Notice the word “gently” in both scenarios.
I’ve driven many tow vehicles with trailers that were unstable (unfortunately!), and never once has braking helped stabilize it. Sure, slowing down can help, but that must be done very gently, otherwise the trailer will try passing the tow vehicle! In fact, I remember sleeping in a van on the side of a highway one night after my co-driver overreacted to a swinging trailer and braked. The trailer swung around, spinning both trailer and tow vehicle – and blowing out the tires on one side of the trailer. In most cases, if a trailer begins to swing, gently easing on the gas pedal will pull it out of that situation. The problem with this is that it was too much speed for the stability of the trailer that caused the problem in the first place – and it’s not instinctual to accelerate when the vehicle is feeling slightly out of control.
All of this comes down to basic physics and vehicle dynamics. Of course, it’s one thing to understand it at an intellectual level, and another to actually do the right thing when faced with what feels like an upcoming near-death experience!
I think that the best thing to stabilize a swinging trailer would be. as you said, apply a little throttle to “pull” it out of the swinging motion, and, if possible, apply trailer brakes only to pull back against the forward force of acceleration. Both force vectors would be in the longitudinal direction, like tightening a string. But I don’t think you can apply trailer brakes only.
Exactly correct. Also, you should have a trailer brake controller with all but the very lightest trailers, unless they are using surge brakes like a U-Haul trailer does. They all allow you to apply the trailer brakes manually for just that reason.
I think this is why he said stab on the brakes, so the trailer brakes are activated, but that should be done when car and trailer are in a straight line, in a swinging motion, that’s a very dangerous thing to do, the trailer could push the car around.
“Oversteer scares passengers, understeer scares drivers.”
Speaking as a rally driver, oversteer is used all the time to rotate the car in negotiating turns. There isn’t enough grip on gravel, dirt, snow, ice, etc. for the tires to do the turning through a corner at speed. Getting back on the throttle, transferring weight back to the rear tires, is the primary mechanism to settle it out.
Sounds straight-forward, but doing so is a reflex that has to be trained into your brain. Panic reaction for the average driver when the car gets loose is to pull the foot off the throttle – creating/exacerbating the oversteer and sending the car into the bushes, unfortunately. Or, chasing the ensuing rotation with significant steering wheel input – loading up the springs on one side and flipping the car back and forth…and into the bushes. I’m slow, so it took me about a half dozen races to fully program the reflex. Thankfully the engineers have tried to design this out with stability control for the average driver in a street car.
For the racer, oversteer can be a fantastic tool. In my mind, in the context of the rally racing I do, I like to think that “the hands merely suggest, but the feet do all the steering.” Even through the tightest hairpins and acute intersections my hands almost never move the steering wheel more than a quarter of a turn.
I have consider buying a new Mustang GT (pp1) or a Camaro 1ss 1lE but coming from a FWD Fiesta ST I think V8s are still out of my skill when driving on track
I’m new to HPDE (1X laguna seca 1x buttonwillow) but after watching lots of HPDE crash videos it seems that folks can loose control of just about anything out there
My hearts says V8 but my brain says use ND miata or 987 cayman
From the videos below, could you tell us what do you think went wrong
on some of this crashes the cars look like they were going straight
this one looks too much speed out of turn 11 at Laguna
It’s hard to say what happened in the first video – the one at Mid-Ohio. It could be a tire/mechanical issue because his brake application didn’t look so hard that it would upset the car that much. I don’t know. The second video – at Laguna – looks to be too much throttle application for the amount of steering he still has in. If he’d unwound the wheel more, or been smoother with the throttle application, that might have helped. But I’m speculating without all the info…