coming out of corners

[Cr250r]

Hi all

just like to throw this subject open

Would like to brainstorm the following , Turnability and Driveability

i.e turning into the corner and getting drive on the exit

its a MX I am thinking about , but the concepts should apply to all
PS ANY Idea is a good one !

Stephen

 

[ctmtwilliams]

Berm or no berm? Blue grove or soft sand? There are kind of a lot of different types of turns in MX. Why don't you start and people will respond to your idea.

 

[ctmtwilliams]

Oh yeah I forgot what type of bike? A little YZ 80 with a "light switch" power band or a 450 thumper that pulls stumps? Each is ridden differently and different technique are applied.

 

[thundair]

Here is one to use on blue grove.
Turn in and just before the apex turn the front wheel toward the apex and as the bike tries to lift up, turn on the throttle and the back end will swing out. When you get it just right both ends will be slipping but you corner speed will go up by 10%. Then as you past the apex you are already turned in so stand it up let it hook up because the throttle is already on....yaaa!!!

I don't know anything but the people that do.

 

[Heckler]

Before we broach this topic you should have an understanding of the Gyroscopic Forces (angular momentum)and its components which allow us the ride such creatures of fun. An important component to of angular momentum is the rate of change of Angular Momentum or Torque. Angular Momentum is a vector having both a magnitude and a direction which both have to be conserved for little johnny to be able to ride his bike. The direction of torque and angular momentum can be vizualized by using the right-hand-rule.

http://hyperphysics.phy-astr.gsu.edu/hbase/tord.html

http://www.pa.msu.edu/courses/1997spring/PHY232/lectures/magforces/righthandrule.html

http://mathworld.wolfram.com/Right-HandRule.html

Best Regards,

Heckler
Sr. Mechanical Engineer
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Never argue with an idiot. They'll bring you down to their level and beat you with experience every time.

 

[Fabrico]

Isn't that all assuming there is a moment of inertia? A motorcycle negotiating a turn does not always have a moment of inertia or torque. If there is a birm or the bike is sliding it would all seem awash. I would think attempting to break it down like that would introduce innumerable variables.

 

[Scoobystu]

Every single corner is different in mx. Even when riding on a track a corner will change every lap because of the number of bikes that have just blasted through it.

The difference between Turnability and driveability are simply a compromise and is generally down to rider preference. You can have a bike that turns sharply but won't handle well on the straights or the other way about. Depends how brave you are. If you could design a bike that did everything you could make a fortune. That is generally where steering dampers come in. I ride off road and I like bikes that turn sharply but that means a lot of head shake and the possibilty of tank slappers and has led to a number of crashes. Generally it is technique that helps when riding bikes that are a bit unstable at speed in a straight line. Weight back and allow the front wheel to float over the bumps so you are not putting too many demands on the front suspension. Slowing down is always interesting tho.

The techniques for riding corners varies depending on it's nature. Flat sweepers are best tackled with your outside peg weighted and your weight as far forward as possible.

Berms are different as you can be a bit more neutral on the bike but still with your weight forward to keep grip on the front wheel.

With any corner in MX (in my opinion) you always go in standing slightly to soak up braking bumps with your legs, weight back and brakes on. Then Get right up front as you enter the corner and weight the front wheel. As you exit you want to be leaning back or even move back in the seat slightly to get your weight on the rear as you power out.

To try and calculate the forces involved in a MX corner would involve an infinite number of variables.

Riding a MX bike requires a lot of physical movement and consequently a lot of fitness.

Riding a road bike is a different kettle of fish altogether. Having limited road riding experience I would say that you can't really apply the cornering principles of MX riding to the road (unless you are riding a MX bike on the road). As a rider you are a lot more static on a road bike and the cornering techniques are different.

 

[Fabrico]

Then there's variables to the variables. One of the best ways to leave a birmless corner is with the rear wheel slightly sliding, the front wheel a bit off the ground, and both feet on the pegs. This can happen on pavement too. At any rate, to quantify the situation in math, one would have to be extremely skilled and have nothing better to do.

birm:

No birm:

 

[Heckler]

I have a feeling their are a few supported factory teams have a good handle on these parameters.

 

[Scoobystu]

You will notice in both photos the riders are sitting forward weighting the front wheel.

 

[Cr250r]

Gosh turn you back for a while !!


My local track is tight and twisty, so I need a bike that turns in easily and then when I open the gas ,,it to dig in and go!
My aim was to lower the centre of gravity, by fitting an 18 inch rim to the rear and a 19 to the front, then set up the shim stacks so that the wheels actually make contact withthw surface
Stephen

 

[Scoobystu]

Save yourself the bother and buy a KTM! Not sure if fitting smaller wheels is the way to go. You might encounter some wierd handling over the bumps. Also 18" off road tyres generally have a larger profile as people use them for enduro to lessen the chances of getting punctures. You might end up with a wheel that has the same overall dimension as a 19" with a standard tyre.

You could drop the forks in the triple clamps by 5 - 10 mm. That would sharpen things up as it throws a bit more weight over the front wheel and will make your bike turn in better. Before you do anything though you should check the sag on the rear suspension and make sure it is right for your weight. When you have done that you can then start playing about with everything else.