Maximum Speed per Lean Angle?

I've got a V Star 650 Classic. I made a slow speed (15 mph?) turn and
the floorboard scraped the ground. It got me wondering - What would be
the maximum speed one could do this before the back tire washed out?
Assume a good street surface and fair to good technique used. Or in
general, how do you know when you are nearing the maximum lean angle?
Is there any control feedback short of washing out?

Make simplifying assumptions as necessary. I will not be testing
anyone's theory out on the street, but it would be good to have an idea
of the limit of performance.

"Lean until you low-side. It's a little less lean than that." Ok I
got that one out of the way. Continue on...

Regards,
JaxSeagull

 

Jax,
Its not speed. - If you ground hard enough at low speed
you'll lift the rear and drop it, - just not as hard.
You already know the limiting angle.
Grinding off the boards on the pavement is not an approved
modification technique.
Lean is a function of speed and turn radius so either stop
grounding the boards or install a set of high rear sets if you
want to push it.
MadDog
-" R75/5 forever!"

 

What would be the maximum speed one could do this before the

Depends on the radius of the turn and the speed you're going...

If you should happen to be around a sportbike, look at its rear tire's
edge. You may notice that there is a distinct lip at the edge, and that
lip is well-buttressed by stiff rubber pieces reinforcing the
sidewalls. You can feel this edge when you reach it by leaning, it
gives the rider a lot of confidence...

The rear tire has less profile, IOW the curvature across the tread is
less, than the front tire. If you keep trying to lean a sportbike
further and further and steer tighter, the front tire will wash out
first, warning the rider if he has any sense at all. If he doesn't,
he'll apply more throttle, and this will load the front tire even
harder as he tries to steer tighter, and the machine will start speed
weaving and maybe spit him off...

Front tire have more curvature, they usually don't have the buttressed
edge, and you can go off the usable part of the front tread sooner than
you'll go off the edge of the rear tire...

Sport riders talk about "chicken strips", that part of the trad that
has never been used, it's still black and shiny. The buttressed edge of
the rear tire may have a chicken strip 1/8th to 1/4 of an inch wide.
But the really round profiled front tire may have chicken strips 3/4ths
to 1 inch wide, the rider cannot lean the bike far enough to use the
tire all the way to the edge...

A sportbike has all the hard parts tucked up so they won't drag, and
the sportbike can easily be leaned to a 45 degree angle, going around a
450-ft radius turn at 81 mph. That's 1-g lateral acceleration and this
can be accomplished on street tires, you don't need super sticky race
rubber to do it... IOW, the motorcycle is accelerating toward the
center of the radius of the corner at 32.2 feet per second, while it's
going forward around the turn at 119 feet per second...

All out race bikes have sticky rubber tires on both ends, and they can
achieve over 1.5 g's lateral acceleration, while leaned over to an
angle of 55 degrees from the vertical...

Tires on cruiser bikes often don't have the lip in the rear tire's edge
that I mentioned. So, when you lean further and further, you don't get
the reassuring feel of being on that heavily-buttressed edge. Instead,
when you lean the bike too much, it feels like the rear end is falling
out from under you. It will recover, though, when you stop trying to
lean the bike so much, and the front tire will push the motorcycle back
to toward the vertical position anyway...

If your Yamaha didn't have low pipes and floorboards to drag, you could
probably lean it safely to about a 40 degree angle fromthe vertical
with cruiser style tires...

 

Get off the seat and get an ass cheek off the inside of the saddle. The
shift of your weight into the inside of the turn will help keep the bike
more upright while maintaining the same speed on a given turn. Thus,
carrying more speed through a turn before you start scraping hard bits.

However, 15 mph is so slow that moving the bike under you (instead of
you over the top of the bike) is usually the technique used. Floorboards
tend to reduce clearance angles. However most cruisers aren't too
bothered by it as they aren't looking to carry speed through twisties in
most cases.

Get out and do some slow speed practice in an empty parking lot and
learn what your bike will do. It could save you some broken bike bits
(or worse).

 

How far do you want to hang off?

It's useful to think of motorcycles as having _two_ distinct lean
angles.

The first one is the center of mass lean. This is always required to
maintain balance. But, the mass has two parts, the bike and the rider.
As Brownse points out, the rider can lean differently from the bike.

The second lean angle is dictated by the steering geometry. Lean
a bike (pedal or motor) and the forks turn in the direction of the
lean. When the lean angle matches the curve radius there's no need
to apply force to the bars and the bike can be ridden without hands.

This gives what you might think of as a "design speed" for a particular
bike: At some speed the center of mass lean and steering lean will match
and the rider can sit bolt upright. At lower speeds the bike will want
to be leaned more than the rider, to keep the steering in equilibrium.
At higher speeds the rider will have to lean more than the bike, to avoid
dragging things. This requires some extra force on the bars, to keep the
bike in the turn.

Tire profiles have an enormous influence also, I'm assuming a fairly
"neutral" tire, with a round cross-section, which I imagine would be
customary on a cruiser.

hth,

bob prohaska

 

Rear sets on a V-Star -- cool!! ;-)

The floorboards fold don't they? As long as they're folding and not
carrying weight you should be fine as long as traction holds. You'll
wash out -- maybe the front -- when you lean so far that something
touches down hard enough to start reducing the weight on either tire.
And it may be something else that does it -- case guards, pipes, etc.
Footpegs or floorboards generally fold for this reason; it's solidly
mounted parts that'll put you down.