Center of Gravity

[RedShift]

I'm rebuilding an old tent trailer into being a bike trailer for my GS500.

It may be an obvious answer, but my question concerns locating the center of gravity of the bike so I can position it over the axle and get a balanced trailer with minimum (20-30 lbs) tongue weight.

Would spotting the bike so the transmission is over the axle be close enough?  Would aligning the axle with the case caps be a better choice?

Has anyone towed their bikes?

My reason to do this is to travel with the family, then ride the bike when the roads get interesting.  My wife doesn't like driving for more than about an hour where as I could ride or drive all day.  This seems like a great compromise.

Comments?

[Kerry]

I don't have a trailer, nor have I towed my bike (yet).  But as far as the center of gravity goes....

When the bike is on the centerstand, the bike tips forward, so the balancing point must be a little forward of the center stand pivot.  Your trailer tips forward when empty too, right?  So you need to coordinate 2 centers of gravity.

If it were me I would take a few experimental passes at it.  I'd start by giving a best guess for the CG of the bike, then strap the bike down and use a bathroom scale to determine the tongue weight.  (Find my weight   first, then my weight while holding the tongue up at bumper height.)

More than 30 lbs extra?  Move the bike back.  Less than 20 lbs extra?  Move the bike forward.  Repeat until satisified....

Can anyone think of a better way?  I'm just brainstorming here!

[yamahonkawazuki]

ive towed mine, (how i got it home), i put it in center of trailer, 6' by 12' in a piece of steel fashioned into a gutter like shape to keep the wheels from sliding out. and strapped down at four corners. pulled perfectly, most of the bikes weight is around the engine/tranny. by the time you figure the front end of the bike into this, it puts that right around, or close to the  axle(s).

[RedShift]

Thanks for your post, Kerry.  I'll take your advice and install the hold-down rings and straps and balance the trailer's tongue weight before I install the front wheel chock.

Frankly, most of the construction was eye-balled so why not introduce a little experimentation to balance the bike.  I'll shoot for 20-30 lbs of tongue weight.

Yama, I've also been thinking about putting a gutter down to keep the bike aligned.  I've also thought about putting a rubber mat down where the tires meet the trailer.  Strapping it tight at four points should keep it spotted.

Roy...

[Pkaaso]

Having towed many things.  Here is what I'm reading.  Kerry is saying, the empty trailer tongue weight should be measured and when bike is loaded, measured again.  You want to add more of the weight to the tongue or toward the front.  If you have too much weight toward the rear, the trailer will become tongue light, and this is BAD.  It will cause the trailer to not track well and may cause high speed swing or whipping.

Now the bike weighs 417lbs wet.  It's my guess that the tongue should increase by more than 20 - 30 lbs.

I have a small trailer that I haul my bike in.  I have to hook it up to the truck in order to load and unload it.  If I don't, it will teeter-toter.  It is not the design that the axle on the trailer take all the weight, it is designed so the weight is distributed between the rear axle of the car/truck and the axle of the trailer.  

Finding the happy medium is the trick.  I would guess 60/40 the most forward and the less rearward of the trailer axle.

Paul

[Kerry]

Here is what I'm reading.  Kerry is saying, the empty trailer tongue weight should be measured and when bike is loaded, measured again

Actually, I said what I meant.

I'd start by giving a best guess for the CG of the bike, then strap the bike down and use a bathroom scale to determine the tongue weight. (Find my weight  first, then my weight while holding the tongue up at bumper height.)

I thought of two reasons not to measure the tongue weight directly - with a bathroom scale, at least:
 1) You don't want to ding up your bathroom scale, and
 2) You should get the most accurate measurement when the tongue is at trailer hitch (not "bumper", sorry) height.

So, I suggested the method that I used to use to weigh my big Labrador who wouldn't even FIT on the scale, let alone STAY on the scale.  I would get on the scale by myself and find MY weight, then I would pick up my Lab ("Ooof!") and find our combined weight.  Subtract MY weight from OUR weight, and I had my answer.

This procedure might work best in a closed garage or a back yard.  You wouldn't want the neighbors to wonder about the weirdly diet-conscious weight-lifter out on the driveway with his bathroom scale, right?  

Caveat: I was only trying to help with the method of measurement.  I do NOT claim to know the appropriate front-to-back weight ratio or trailer-to-truck ratio.

[Pkaaso]

Ah, OK!  I read that wrong.    I see what you ment, to find the weight of the tongue not the difference loaded and unloaded.  Makes sense now i've read it with my glasses on.

Sorry to miss quote you Kerry.

Paul

[yamahonkawazuki]

should be alright to put bike in mid of trailer, strapped down. worked great for both my gs and my frontier. went up to 80 trailer made no attempt to do anything but follow my truck. also take into account, hauling extra gear, parts etc.  

[Pkaaso]

Just be careful not to have "negative tongue weight."  Meaning if the trailer lifts in the front when loaded.

Just my .0002 cents worth,
Paul

[RedShift]

I appreciate the dialogue.  

Just be careful not to have "negative tongue weight."
Paul

I hear this loud & clear.  I've trailered other things and know what happens when there's not enough forward weight.  Tossing the bike from side to side at highway speeds is not my idea of travelling across country in style.

As Kerry suggests there should be a healthy tongue weight after the bike is on.  I've got some 30 lbs already (at hitch height) so I should be able to target the bike's engine over the axle and expect to be close to balanced.

At my rate of progress, I should have an update by mid- to late-July.



Roy...

[Pkaaso]

Good luck with the trailer project.  I really like your idea of pulling the bike and then riding sections with the wife driving.  BRILLIANT!!!  

Enjoy, be safe, and take lots of pictures.

Paul

[RedShift]

Paul, I'll let you know how it turns out.  Should be early-August, but yea, I kinda think it a neat idea myself.  Drag the bike on the flat, boring roads, and then when they become twisty, hilly, or otherwise interesting, boom, I'm off on the bike with my chase team (wife & daughter) behind me.

Or at least that's the plan.  The interesting roads are at least an hour away, and all it costs me is gas and lunch for the family someplace interesting.

Tie-downs, wheel chock, fenders, lights and trailer hitch are on order.  

Stay tuned...

[Pkaaso]

Cool, thanks.

Was thinking last night about how fun it would be to rent a small motor home, drag the bike in my trailer and do the same as you.  Just sounds better and better.

Look forward to hearing more.

Paul