Center of gravity location

[adouglas]

It occurs to me that @Motofool might have a graphic of this... Google isn't being all that much help.

Anyone have an image that shows the longitudinal center of gravity of a typical unladen sportbike?

The reason I ask is that I want to move the chock on my trailer back. I'd had it pretty far forward and it was loading the rear suspension of my car too much.



Knowing the c.g. would help me gauge how far aft to relocate it.

I could weigh each wheel of the bike and calculate, but that's a PITA and a reliable image would suffice. Doesn't need to be precise, as long as I don't go too far to the rear.

I did find this, of the Honda RC213V... seems reasonable Puts the c.g. in the vicinity of the crankshaft.

[choneofakind]

Use a scale under the tongue of the trailer as is.

Move the bike a known distance and do it again.

Do some maths. (Or post the data and one of us can do the maths for you)

[choneofakind]

Option 2: use a bathroom scale and some blocks to determine the tongue weight, move the bike backwards until your tongue weight is at something reasonable, like 100 lbs.

Your trailer and bike combo is what, 900 lbs? So 100 lb tongue weight seems reasonable.

Per GMC, a good target tongue weight is 10-15% of the total trailer http://www.gmc.com/trailering-towing/tongue-weight.html

[adouglas]

Yeah, I know how to measure, both mathematically using the bathroom scale method and via trial and error... but frankly it's a lot less effort to get a ballpark CG and just move the thing. No need to turn this into a big production.

[rojoracing53]

Originally Posted by adouglas

Yeah, I know how to measure, both mathematically using the bathroom scale method and via trial and error... but frankly it's a lot less effort to get a ballpark CG and just move the thing. No need to turn this into a big production.

But your still going to get out there and test it in person so cut out the middle man and just get out there and start D*cking around with it. just remember to keep enough positive weight so even when the trailer rocks back and worth it doesn't go to the negative side and underweight your rear tires and jack knife you.

I know these are all thing I shouldn't have to tell you.

[choneofakind]

Cinder block and a bathroom scale. You got this.

[csmith12]

My best guesstimate is... it needs to go back about a "fist" length. lol

[SLOWn60]

I think I get to use my favourite internet cartoon again!

[Motofool]

Originally Posted by adouglas

It occurs to me that @Motofool might have a graphic of this... Google isn't being all that much help........

Sorry, Douglas; I don't have a graphic of that.
The dominant masses are the engine and the fuel; hence, the center of mass should be around there.
Consider that the weight of a gallon of gasoline is 6.2 pounds.

Just to have an estimate, I would temporarily attach a piece of pipe or wood stick half-way under the plank used to push the bike on the trailer.
Would place plank over middle pivot point on a flat surface.
Then, holding the handlebar, I would roll the bike over the plank to find an approximate point of balance, which vertical line would indicate the longitudinal location of the CG.
The tank should contain the usual amount of fuel that you use when trailing that beauty.

[csmith12]

Originally Posted by Motofool

The tank should contain the usual amount of fuel when trailing that beauty.

Which should be a full tank. Just in case you need to fill the tank because you forgot your gas can (been there, done that) or because you have extra gas in the can that you didn't pour into the haul vehicle. Lol... On the haul vehicle side, Assuming at some point there will be a fill up along the way as well. Meh... I guess I should have said just max fuel weight for both bike and cage. Man... I just aint with it like normal, sorry.

[dcj13]

Engineer Chris has the simple and elegant solution.

[corksil]

More tongue weight is better than less tongue weight. Coming from someone who hauls 14k pound trailer from a bumper pulled F350 crew cab short bed. It's a dual axle trailer, but given the geometry it might as well be a single axle.

Too much tongue weight and you feel like a tadpole swimming down the road. Bumps cause the tow vehicle to be yanked left and right (from the rear) and you must countersteer into the turn to correct the jostling of the trailer.

Not enough tongue weight, and you will pull a load up a hill, hit a bump -- rear axle will get light, traction loss, and perhaps sliding backwards down the hill with all four vehicle brakes locked up. The sliding backward down a hill while being dragged thing... it's not a nice feeling. It has happened in 4wd as well, due to poorly engineered differentials.

If you are on dry pavement and the hill is steep, you may only slide for ten feet with all four truck tires locked. If the pavement is wet and the hill is steep, consider 25-30 feet of sliding backward. If there is mud/grass involved, you may very well slide backward to the bottom of the hill. If you find yourself in this situation, do your very best to reverse-steer the rig perpendicular to the hill. Gotta let on/off the brakes because you lose your steering ability if the tow vehicle has locked up tires. Try to get it done before your nuts disappear up into your abdomen. Things are harder if you panic.

Don't ask me how I know this. Something about pushing limits. Not recommended.

My point --- more tongue weight is better than less tongue weight.

Good luck and don't underestimate how a tiny bit of moisture can throw everything you know about traction out the window. As for ice... I can only imagine. I don't have that where I live.

[corksil]

After looking at your picture -- I can't tell if the trailer has it's own brakes or not. If so, probably electric but it doesn't look likely. If so, be aware that many electric brakes are engaged only in the forward direction.

In simple terms -- most electric brakes are very simple mechanisms. Picture a drum brake, but instead of a slave cylinder which forces the brake shoes out against the inside of the drum, there is an 'arm' with an electro-magnet on one end which engage/disengages -- and on the other end, an oblong shape which transfers the motion of the 'arm' into force applied in opposite directions against the brake shoes causing them to contact the inside of the rotor.

Most people aren't aware that the most common form of electric trailer brakes.... do NOT work if the trailer is travelling in reverse.

Test this stuff out in a safe place and get familiar with your setup. I'd also double up on ratchet straps. Try to predict the nastiest and most horrible panic stop imaginable and then over-engineer from there.

[choneofakind]

No brakes in reverse, eh?? That never would have occurred to me. I always assumed those little brake solenoids were triggered by the tow vehicle's brake light circuit, regardless of forward vs backward travel.

One more thing to keep in mind and check before driving.

[choneofakind]

Just a thought while I re-visit the OP. Maybe look into a hitch that raises your ball relative to your receiver. You might want to level out that trailer a touch. They make drop balls, you usually can just take the ball off, flip the mount, and reinstall the ball. Insta-raising ball.

[rojoracing53]

I like electric trailer brake controllers because you can touch your brake pedal just enough to activate your brake lights but not really your brakes and your trailer will brake on it's own. This will bring the load taught and stabilize most stability issues caused by poor driver input or poor roads.

We're the racer types that pass EVERYONE between event's pulling our 14,000 trailer and have perfected special cornering and excessive down hill speed techniques because RACERS.

[corksil]

Yeah the trailer brakes are certainly 'triggered' .. activated.. engaged.. when braking in reverse, but due to the design, they don't 'work' properly. Maybe technology has improved since last year when I rebuilt my electric trailer brakes, but I doubt it.

[jkv45]

Originally Posted by choneofakind

Just a thought while I re-visit the OP. Maybe look into a hitch that raises your ball relative to your receiver. You might want to level out that trailer a touch. They make drop balls, you usually can just take the ball off, flip the mount, and reinstall the ball. Insta-raising ball.

I think this is a good idea to do first, then calculate the weight of the trailer and cargo, then find the recommended tongue weight, then measure the actual tongue weight and adjust the position of the cycle to get the correct amount.

You don't really need to know the CG of the cargo, just the actual tongue weight its position produces.

[SLOWn60]

You guys are WAAAAAAAAAAY overthinking this! (Unless this is a winter thread in which case; carry on! )
1: Hook up trailer to car.
2: Roll bike onto trailer.
3: Slowly roll bike forward until trailer teeters.
4: Roll forward an additional 8 inches.
5: Secure at that location.

I own 3 trailers. 2 utility and a 24' enclosed.
You do not need a load levelling hitch on a utility trailer.
If your rear end is squating then move the load back a few inches.
If your hitch is bouncing on the ball; move it forward a few inches.
If you're still having issues when towing a small utility trailer then you need a better tow vehicle!
A quick note: load levelling hitches have their own dangers if not sized properly or used overzealously and they probably cost more than that trailer in the photo above!

[adouglas]

Originally Posted by SLOWn60

You guys are WAAAAAAAAAAY overthinking this!

Yep.

All I was looking for was a generic, ballpark c.g. location so I could go down to the garage, eyeball how much I need to move the mounting plate, drill a couple of holes and be done with it.

What I wasn't looking for was what I already know - namely, three or four different ways to figure out the c.g./ideal location for the chock. All of which are good ideas, don't get me wrong... just not what I was asking for.

The bikes are in storage and buttoned up. There's no need to get the trailer out and load it up in the middle of winter. Nor is there any real need to weigh the bike.... though admittedly, it might be fun to actually find out how much the track bike does weigh. Feels light to me.

Sure, I could go all OCD on this, but why bother? Not really interested in making this more than a 15-minute project. "That looks about right" is entirely sufficient.

[csmith12]

Originally Posted by adouglas

All I was looking for was a generic, ballpark c.g. location so I could go down to the garage, eyeball how much I need to move the mounting plate, drill a couple of holes and be done with it.

See post #7. lol

[adouglas]

Originally Posted by csmith12

See post #7. lol

Why, I oughta.....

[jkv45]

Originally Posted by adouglas

Yep.

All I was looking for was a generic, ballpark c.g. location so I could go down to the garage, eyeball how much I need to move the mounting plate, drill a couple of holes and be done with it.

What I wasn't looking for was what I already know - namely, three or four different ways to figure out the c.g./ideal location for the chock. All of which are good ideas, don't get me wrong... just not what I was asking for.

The bikes are in storage and buttoned up. There's no need to get the trailer out and load it up in the middle of winter. Nor is there any real need to weigh the bike.... though admittedly, it might be fun to actually find out how much the track bike does weigh. Feels light to me.

Sure, I could go all OCD on this, but why bother? Not really interested in making this more than a 15-minute project. "That looks about right" is entirely sufficient.

I guess I misunderstood what you were looking for.

Based on your initial post requesting the CG of the bike, I didn't expect you to blow-off any suggestions that would require calculations, trial-and-error, or adjustments.

I still think you should level-out the trailer and measure the actual tongue weight, but it may take more than 15 minutes to do properly...

[SLOWn60]

Has no one else noticed the contradiction between Mr Fists signature and his bike on the trailer?

Enquiring minds want to know!

[adouglas]

Originally Posted by SLOWn60

Has no one else noticed the contradiction between Mr Fists signature and his bike on the trailer?

Enquiring minds want to know!

That was loadup for my first track day two years ago. Since then I've gotten a taller hitch coupler (trailer is more level now) and bought a dedicated track bike -- one with just about all the goodies.

[adouglas]

Originally Posted by jkv45

I guess I misunderstood what you were looking for.

Based on your initial post requesting the CG of the bike, I didn't expect you to blow-off any suggestions that would require calculations, trial-and-error, or adjustments.

I still think you should level-out the trailer and measure the actual tongue weight, but it may take more than 15 minutes to do properly...

Apologies for the misunderstanding, but the OP did clearly request an image showing c.g. of a typical sportbike, not a method for finding the c.g. of my own bike. It also clearly stated that such an image would suffice.

I know everyone's just trying to be helpful... but I really do know how to do this the "right" way.

As long as the loaded c.g. is forward of the axle, I'm good... an inch or three won't make a difference. To be honest, even with the bike as far forward as it is, the trailer tows just fine. Simply looking to optimize things a bit.

[SLOWn60]

Seriously; I load a lot of trailers and the simplest way to find the CG is as I said: roll it on, find the teeter point and move it a few inches forward of that. That's the location for your wheel chock. Do it when you haul it out the first time this spring and allow a half hour to drill & bolt if you're really slow.

[Somchai]

@adouglas, extra for you.
The exact measurement from the center of gravity at a GSX-R1000 (I guess the 600/750 are not far away, or maybe the same).
The center-point is "Schwerpunktlage"

[VaFish]

Move the chock back 4-6" and call it good.

[SLOWn60]

Or simply enter the known data:

[VaFish]

Originally Posted by choneofakind

No brakes in reverse, eh?? That never would have occurred to me. I always assumed those little brake solenoids were triggered by the tow vehicle's brake light circuit, regardless of forward vs backward travel.

One more thing to keep in mind and check before driving.

The brake circuit works in reverse, but the way most electric brakes work is they have an electro magnet that is attracted to the brake drum when energy is applied. When the magnet get stuck to the brake drum it is pulled in the direction of rotation and mechanical force is applied to the brake shoes. In reverse when the magnet is energized and it attaches to the brake drum the mechanical force is in the opposite direction and releases the brake shoes.

https://en.m.wikipedia.org/wiki/Electric_friction_brake

[adouglas]

Originally Posted by Somchai

The center-point is "Schwerpunktlage"

Gesundheit.

Ihre Google-Fu ist leistungsstark. Danke.