# Question about motorcycle physics **URL:** \ **Category:** Factual Questions\ **Created:** [May 25, 2004, 5:22pm UTC](https://boards.straightdope.com/t/question-about-motorcycle-physics/247014 "2004-05-25T17:22:44Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![KidCharlemagne](https://avatars.discourse-cdn.com/v4/letter/k/ed8c4c/32.png) [@KidCharlemagne](https://boards.straightdope.com/u/KidCharlemagne)\ **Post date:** [May 25, 2004, 5:22pm UTC](https://boards.straightdope.com/t/question-about-motorcycle-physics/247014/1 "2004-05-25T17:22:44Z")
Jerry Palladino, a respected motorcycle riding instructor says this about doing a U-turn: > [@](#): > > As I have stated before, just about all production motorcycles are capable of making a U-turn in well under 20 feet. That means that you can U-turn on just about any two lane road including the narrow streets in Ybor City. Here’s the technique you need to apply. If you are about to make a left hand U-turn, keep your foot firmly on the rear brake, keep the clutch in the friction zone and roll on the throttle. Dip the bike towards the right curb, then quickly and smoothly turn your head completely around to the direction you want to go. At the same time you are turning your head, you should be pushing on the right grip turning your handle bars as far as possible and leaning the bike to the left. He also says, > [@](#): > > [In addition to turning head in direction you want to go and using the friction zone,], the third technique is the proper use of the rear or controlling brake. With the motorcycle in the friction zone, keep your foot on the rear brake and feather it as the bike starts to move. By doing this you are making the motorcycle think it’s going faster than it is. When you apply power and keep your foot on the rear brake, it keeps the motorcycle from falling over at low speeds which is where most people have a problem. I’ve never heard of anyone having problems balancing their motorcycle at 50 or 60mph. If you don’t use these techniques at 5 or 10mph the motorcycle feels clumsy and wants to fall over on it’s side. Why does the motorcycle “think it’s going faster than it is” by using the throttle and rear brake, rather than just a little less throttle? I thought maybe it had something to do with a gyroscopic effect of the spinning crankshaft, but you’d have to be slipping the clutch, correct? ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [May 25, 2004, 5:34pm UTC](https://boards.straightdope.com/t/question-about-motorcycle-physics/247014/2 "2004-05-25T17:34:49Z")
If this causes the wheels to spin out a bit, that will increase their angular momentum, thus making the bike more stable. If you are “feathering” the breaks, maybe you are interspersing a few burst of higher veolocity in there, thus creating some instances of higher angular momentum in the wheels. That’s all I can think of… ---
**Author:** ![cornflakes](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@cornflakes](https://boards.straightdope.com/u/cornflakes)\ **Post date:** [May 25, 2004, 7:02pm UTC](https://boards.straightdope.com/t/question-about-motorcycle-physics/247014/3 "2004-05-25T19:02:48Z")
I think he means that you should keep the rpms up to increase the gyroscope effect while feathering the brake and clutch. It’s been years since I rode (so don’t hold me to this), but I think I did the same thing by keeping a couple of fingers on the clutch and front brake levers and holding the engine at around 3000rpm. ---
**Author:** ![Edward\_The\_Head](https://avatars.discourse-cdn.com/v4/letter/e/ce73a5/32.png) [@Edward\_The\_Head](https://boards.straightdope.com/u/Edward_The_Head)\ **Post date:** [May 25, 2004, 7:38pm UTC](https://boards.straightdope.com/t/question-about-motorcycle-physics/247014/4 "2004-05-25T19:38:31Z")
> [@cornflakes](#): > > I think he means that you should keep the rpms up to increase the gyroscope effect while feathering the brake and clutch. I can’t imagine that keeping the RPMs up is going to chage the gyroscopic effect. I would say that if what he says is true it’s more because when you give the rear tire more gas you are creating the downward force and that’s giving more grip on the road. I know you can do this without using the rear brake at all as I do this all the time on my bike. It’s mostly how you sit on the bike, hang off the other side and you change the center of gravity making it easier to do. I know this has been talked about in a few motorcycle magazines and books. It’s also part of the newer MSF course. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [May 25, 2004, 8:11pm UTC](https://boards.straightdope.com/t/question-about-motorcycle-physics/247014/5 "2004-05-25T20:11:16Z")
> [@cornflakes](#): > > I think he means that you should keep the rpms up to increase the gyroscope effect while feathering the brake and clutch. BTW, the “gyroscope effect” is angular momentum. I was talking about A.M. of the wheels, but is there significant A.M. in the engine itself at high RPMs? ---
**Author:** ![beltbuckle](https://avatars.discourse-cdn.com/v4/letter/b/3da27b/32.png) [@beltbuckle](https://boards.straightdope.com/u/beltbuckle)\ **Post date:** [May 25, 2004, 8:14pm UTC](https://boards.straightdope.com/t/question-about-motorcycle-physics/247014/6 "2004-05-25T20:14:11Z")
I think what he is talking about by using the rear brake to provide some resistance, one is keeping the rear suspension loaded and therefor steady during the turn. What a horrible way to describe it thought. I ride a large street bike (a kawasaki vulcan 1500), and I can easily make sharp U-turns. The key is practice and experience. The best way to practice is to go to a parking lot (free of oil, gravel, etc), and turn the handlebars all the way to one direction until they hit the lock and will turn no more. Then, keep working at feathering the clutch enough to keep the bars locked throughout the turn. With enough practice, you will become quite good at it. The key is keeping the balance just right at such a low speed, and to have enough speed to stay upright. ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [May 25, 2004, 9:02pm UTC](https://boards.straightdope.com/t/question-about-motorcycle-physics/247014/7 "2004-05-25T21:02:17Z")
If you’re simultaneously giving power with the engine, but couteracting that with the rear brake, the suspension won’t know that you’re doing this. The opposing forces all are contained at the hub. I think it must be that if the engine is already revved and you start to tip too far to the inside of the corner, it’s an automatic reflex to let off the brake and use the power to pull you back up. If the engine is already revved, it will be very quick. Maybe the author doesn’t realize he’s doing this. I’m not a motorcycle rider, just a bicycle rider who understands physics, and this business about “making the motorcycle think it’s going faster” is BS. ---
**Author:** ![cornflakes](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@cornflakes](https://boards.straightdope.com/u/cornflakes)\ **Post date:** [May 25, 2004, 9:30pm UTC](https://boards.straightdope.com/t/question-about-motorcycle-physics/247014/8 "2004-05-25T21:30:49Z")
> [@John Mace](#): > > BTW, the “gyroscope effect” is angular momentum. I was talking about A.M. of the wheels, but is there significant A.M. in the engine itself at high RPMs? There can be. I seem to recall that some pro riders claimed to prefer the Honda Interceptor because it’s V-4 configuration let them throw it down faster in corners than they could with inline fours. Supposedly, the shorter crankshaft helped. Of course, there can also be a lot of bullshit when talking about cars and bikes. ---
**Author:** ![stuyguy](https://avatars.discourse-cdn.com/v4/letter/s/ec9cab/32.png) [@stuyguy](https://boards.straightdope.com/u/stuyguy)\ **Post date:** [May 26, 2004, 3:18am UTC](https://boards.straightdope.com/t/question-about-motorcycle-physics/247014/9 "2004-05-26T03:18:53Z")
> [@CurtC](#): > > If you’re simultaneously giving power with the engine, but couteracting that with the rear brake, the suspension won’t know that you’re doing this… Not necessarily true if it’s a chain-drive bike. Normally the engine’s drive sprocket tugs at the top of the rear wheel sprocket to make the wheel spin, thus propelling the bike forward. With the rear brake applied, the drive sprocket will still try to tug at the rear sprocket but the wheel can’t spin. Instead the entire rear fork will try to pitch up and forward as the chain tugs on the whole rear assembly. The effect is worsened by the fact that the pivot point of the rear fork is behind and below the drive sprocket. The rear assembly ain’t going far, mind you, because the suspension will stop it. But the effect is to compress the rear shocks ever so slightly.