Highsides. They’re violent, they’re unexpected and they’re spectacular to witness but they’re not something any rider wants to ever experience firsthand. So what causes a motorcycle highside? Can you do anything prevent them? And is there anything you can do to stop a motorcycle highside if you feel it happening?
We’ll get a little bit technical in this article, so if you prefer moving pictures instead of big words, check out the video we created below, called “Dance of the Highside” which shows some of the most spectacular examples of highsides we could find.
In simple terms, a highside occurs when the rear tire loses traction and then regains traction – the rear tire biting and gripping onto the road. Counter intuitively, you’d think that regaining traction would be good but the problem is that in the small fraction of a second between losing traction and then regaining it, the bike has rotated along its axis. When the rear tire regains traction, it causes all sorts of physics to occur – none of it generally very helpful to staying upright.
When this happens, you essentially have two forces working in different directions. The front wheel is pointed one way and the rear wheel another. The one that wins is the rear wheel, where all the power is being delivered.
Here’s a slightly more technical explanation courtesy of Wikipedia:
When going through a curve on a motorcycle, centripetal force (added to the other lateral forces such as acceleration or deceleration) is transferred from the road to the motorcycle through the contact patch, and is directed at a right angle to the path of travel. If the net force is greater than the static friction coefficient of the tire multiplied by the normal force of the motorcycle through the tire, the tire will skid outwards from the direction of the curve. Once a tire slips in a curve, it will move outwards under the motorcycle.
Below is a perfect example. These series of photos was captured of a rider at turn 9 at Chuckwalla (courtesy Triumph675.net). As you can see in the animation below, the rear tire loses grip and rotates to the left of front wheel which is pointing in a different direction. As soon as the rear wheel grips the road again, the forces at play throw the rider and cause the motorcycle to take a tumble.
So what are the actual causes of a highside? A highside can occur from any of the following:
- locking the rear wheel through excessive braking
- applying too much throttle when exiting a corner
- oversteering the bike into the turn by shifting weight to the front wheel and using balance to drift the rear wheel sideways
- exceeding the lateral grip through too much speed (although, this is more likely to result in a lowsider), or too much lean
- an unexpected change in the surface friction (water, oil, dust, gravel, etc)
- reducing the friction on the rear tire by scraping the bodywork of the motorcycle on the road surface
Of the causes above, the only one that you as a rider really have a hope of saving is when you lock the rear wheel. Most of you probably remember in your motorcycle licensing/traning course that if you lock the front wheels, get off the brakes as soon as possible but if you lock the rear wheel, keep that rear wheel locked until you come to a stop (or to a fairly low speed). And that’s because you don’t want to let the rear tire grip again as doing so can cause a highside.
But what about the massive highsides that we showed in the video above? Those weren’t caused by rear wheel locks but usually by a loss of traction from too much speed in the turns. What are you as a rider able to do to save yourself from such a highside?
The only cure is prevention – don’t ever let the rear wheel lose traction because once it does, it’s nearly impossible to come back from. It should be evidence enough that the best of the best in Moto GP and WSBK can’t stop highsides but in case you think you’re better than them, take a look at the animated gif below. The time between when the tire loses grip and regains grip is probably 0.10 to 0.20 seconds. As a human being you just can’t recreate quick enough to do anything about it, especially at the speeds and forces at play.
The only piece of advice that we can really give you is that if you have superhuman reflexes and believe you can save a highside, remember the age old phrase – when in doubt, gas it. By intentionally getting on the throttle you’ll hopefully continue to break traction at the rear wheel and maybe, just maybe you’ll save it (or at least lowside instead of highside).
The good news is that highsides are much less frequent than they used to be with modern technology – both on the track and the road. In MotoGP (especially the premier class), despite the sheer amount of horsepower being transferred to the rear wheel and the incredible lean angles acheived, highsides are actually fairly rare. Due to electronic aids like traction control, slip control and so forth, highsides only occur in extreme circumstances.
On the road, highsides generally don’t occur too often anyway as you won’t be (at least you shouldn’t be) hitting speeds in corners where your rear wheel loses grip. With ABS and traction control becoming increasinlgly common, you’ll have to be pretty unlucky (dirt, gravel, oil or some other substance on the road) or maybe just a little bit stupid (the roads aren’t a racetrack for good reason).