About Buells...

[James Deuce]

Huh? You might want to re-visualise that.

It will rotate around the tyres' contact point with the road. The center of mass determines the speed of rotation around that axis given any particular tipping force.

That's about perception I think. The axis of rotation determines how the cycle parts are distributed on a MotoGP bike and is typically linked with a forward centre of mass. Fuel is mostly at the rider's crutch and under the seat because it is close to the axis of rotation to minimise the effects of liquid arcing through a large moment, and so that it can be reliably used to help load the front under braking.

[James Deuce]

Tut, Jim.

To repeat the Feynman quote in that article:

"In case the object is so large that the nonparallelism of the gravitational forces is significant, then the center where one must apply the balancing force is not simple to describe, and it departs slightly from the center of mass."

A motorcycle is not so large that when it rests on the surface of the earth, gravitational forces differ meaningfully across it.

From the same article:

"Even when considering tidal forces on planets, it is sufficient to use centers of mass to find the overall motion."

So, yes, for this topic, COM and COG are equivalent.

You've managed to contradict your own argument.

[Big Dave]

See above.

Why is your rep thingy black?

[Pussy]

Why is your rep thingy black?

He's probably disabled it

[Big Dave]

I now note that the the site is able to install a scrolling label with 'sycophant' on a member's posts - and find that quite preposterous.

Hitch - what is going on there?

[Duc]

My mates Buell has been reliable for 20,000ks +

As far as my humble opinion of the bike. (I have ridden it open road only)

Its kind of fun (for a short while) but kind of boring because of its "lazy" engine. Feels over geared to hell at 100-150kph.
Its tiringly loud (w./Drummer fitted) and the sound always surrounds you.
It vibrates heavily which is also tiring after a 100kms or so .
The mirrors vibrate so much that they are useless. (multiple images) .
The gyro effect on the wheel due to the large front disc brake, takes a way feel for the road but also is (dangerously) confidence inspiring at the same time
It looks too small under any rider (like a clown bike). The design is o.k though.

Just my opinion.

[Sidewinder]

Are They Reliable?

people say there meant to be good! well good compared to a harley maybe..... but there still crap! snap goes the belt drive!

[Big Dave]

people say there meant to be good! well good compared to a harley maybe..... but there still crap! snap goes the belt drive!

I've busted a belt. I could bust two more this week and I'd still rather it than a chain.

[ajturbo]

i enjoy mine.. i wont be selling it in any hurry...

not too keen on the 1125's but they are a great bike, love the slipper clutch!!!
and IF i had the money i would have BOTH in my garage

[Taz]

I found the 1125R to be ok...... But not really my style. Have sold my last sportsbike (Ducati) and will never buy another sports bike they are just too narrow in their focus.

[jrandom]

You've managed to contradict your own argument.

You should probably point out how I did that.

[jrandom]

Nope, i think you'll find the a bike will rotate around its centre of mass

*goes outside*

*stands bike up*

*tips it over*

Uh, nope, it rotated around where the tyres were touching the ground. Two contact points that form a line which is the axis it rotated around.

It can't 'rotate around the center of mass' anyway. That's a point. One dimension. It rotates around an axis. Two dimensions. Where are you getting the rest of that axis line from if the center of mass point is on it?

I don't think y'all have very clear mental pictures of any of this. Correct me if I'm wrong.

Bike stands up.

Bike tips over.

Axis of rotation = the two points where the wheels were touching the ground. (Barring any sliding tyres, of course.)

Whether or not it's rolling forward at the time makes no difference.

[dipshit]

*goes outside*

*stands bike up*

*tips it over*

Uh, nope, it rotated around where the tyres were touching the ground. Two contact points that form a line which is the axis it rotated around.

Wow, that was a thorough and in-depth analysis of cornering physics. You should go and inform all of the bike designers of your research findings and superior knowledge. After all you have done several track days and are the best thing since carbon fibre was invented.

Any reading on the subject will soon fill you in.

http://www.sportrider.com/bikes/2003...ent/index.html

"One of the central concepts that drove development of the CBR600RR and the RC211V is mass centralization; that is, concentrating the component masses as close to the motorcycle's center as possible. When a rider initiates a turn, the motorcycle rotates around its roll axis--an imaginary fore-and-aft horizontal line drawn through the center of mass of bike and rider--as it leans into the turn. Placing the major masses (engine, fuel, rider) closer to this roll axis results in a motorcycle that reacts more quickly and smoothly to control inputs at the handlebars. The concept of mass centralization has been a guiding principal at Honda for decades,"

Wayne Gardner has just recently told storeys to the press of the trouble they were having with Honda's 500's during the 90's. Honda kept trying to lower the COM and the bikes were complete pigs to race as they just didn't have decent cornering speed. The bikes simply would not go around a corner the same as their competitors at the same lean angles.

It wasn't until one day when Suzuki was setup next to his motorhome and he could see straight in the side of the Suzuki tent and see their bike stripped down to its frame. A team of Honda photographers spent all weekend photographing the Suzuki through his mirrored motorhome windows shooting rolls and rolls film. They printed them out at lifesize and measured the Suzuki dimensions and realised they were completely wrong about their low mass centralisation.

Their new bikes that soon followed after having a good look at the Suzukis improved matters drastically.

[jrandom]

Honda kept trying to lower the COM and the bikes were complete pigs to race as they just didn't have decent cornering speed. The bikes simply would not go around a corner the same as their competitors at the same lean angles.

... once it's done tipping, it'd turn faster at the same lean angle with more mass further away from the center.

So, yeah. Righto then.

I'm not sure that we're actually disagreeing on anything.

Other than where the roll axis is.

I'm quite prepared to admit that it may well not go through the bottom of each tyre.

I suppose the key to visualising that is to remember that since the bike is changing its velocity (speed and direction) at the same time it's tipping, the roll axis is different to what it is when the bike is at a standstill. Fair call.

And so, yes, of course, if the axis isn't actually at the bottom of the wheels, lowering the mass as much as possible wouldn't always be the best idea.

Awesome. I learn something every day.

And hey, if Honda's racing engineers made the same mistake of (presumably) assuming that the roll axis was at the tyre contact patches, I don't feel too embarrassed.

[Ocean1]

Awesome. I learn something every day.

Yeah. We’re to be concerned that you found some discomfort on an XB12, a bike somewhat closer to the handling characteristics of a GP bike than… some other, heavier, less performance oriented machines.

Nah.

I look forward to the day you learn your perceptions about Buell's handling characteristics and geometry are at odds with those of most GP bike design engineers. Yes, they can feel seriously twitchy and they can feel unstable if attempted to be managed like a cruisier. It took me a while, but I believe I’ve got the required technique sussed, I find problems only when attempting to use the bike for things it’s not designed for. In their correct application they’re not only very good they’re simply unbeatable.

And lets be clear about that correct application eh? If you want to navigate sub-100k curves as quickly as possible consistent with a modicum of safety, on a reasonably affordable road legal motorcycle, and you’re prepared to learn what technique that machine demands in order for that to happen, then a Buell will be on your shortlist. It’s that simple.