How to weigh motorcycle.

[corksil]

Let's pretend that an individual was trying to weigh a motorcycle.

Let's also pretend that the individual only had a scale capable of weighing one tire per measurement.

Could you put a scale under each tire and add the two numbers to determine the total motorcycle weight?

I think the reading would be inaccurate due to the fact that fuel and oil slosh around if the motorcycle is tipped.

[cbinker]

it would work.

or if you have a scale that can weigh over 500# you could place a 6 foot piece of plywood on the scale where it is balanced and roll the bike onto it.

[Snake]

Yes that will work. D.O.T. inforcement cops do the same thing when they randomly stop big rigs.

[Triple Jim]

You can also use one scale to do the job, and put the other wheel on a block of wood to get it to the same height as the scale top. Weigh both wheels separately and add. You can balance the bike upright carefully by hand without pushing up or down if you're halfway careful. You'll see that the scale reading doesn't move around much if you do it right.

[Mohawk]

You don't need the block of wood. Assuming your scale is like 2" high the CofG moment is less than 1/2Kg per end. Just make sure you have a ramp up to the scale height that will NOT move, or the scale may tip as you try to roll on to it.

[Motofool]

You will introduce a bigger difference by having more or less fuel in the tank.

There is wet weight and dry weight for each motorcycle.

[Triple Jim]

I suggested the block of wood because my old scale is something like 3" high, and when I calculated the error, it was a couple pounds. Yes, you don't have to use the wood if you're not going for high accuracy. Not that bathroom scales have high accuracy in the first place.

Of course fuel level is very important. 5 US gallons of gasoline weigh about 30 lbs, so if you're trying to lighten the motorcycle and are going to weigh it more than once, have it empty or full each time.

I just did a rough calculation, and it looks like if you weighed a 250 on my scale that's 2.5" high without the other wheel being on a 2.5" block, you'd be about 5 lbs low after you add the reading from each wheel. As stated, this isn't a big error, but it's an error.

[Alex]

Pick it up with both hands, estimate. It works great when I'm trying to win a free lunch at the buffet.

[Triple Jim]

For me it would be pick it up with both hands and start shopping for an artificial spine.

How's yours doing, by the way? Any improvement?

[Alex]

Not much change, but I haven't tried lifting motorcycles recently. I can suggest it to my PT guy.

[empire00]

If you have front and rear stands you can just pick the bike up and set it straight down on the scales if they are narrow enough.

[corksil]

Originally Posted by cbinker

it would work.

or if you have a scale that can weigh over 500# you could place a 6 foot piece of plywood on the scale where it is balanced and roll the bike onto it.

Good info. All the bikes are under 300lbs. Obviously I'd need to subtract the weight of the plywood for an accurate measurement.

Originally Posted by Snake

Yes that will work. D.O.T. inforcement cops do the same thing when they randomly stop big rigs.

I've looked into those scales for my towing rig and they are in the ball park of 2-5k. For motorcycle, something more simple should work.

Originally Posted by Triple Jim

You can also use one scale to do the job, and put the other wheel on a block of wood to get it to the same height as the scale top. Weigh both wheels separately and add. You can balance the bike upright carefully by hand without pushing up or down if you're halfway careful. You'll see that the scale reading doesn't move around much if you do it right.

I will try this with a bathroom scale. Very smart to put block of wood under adjacent tire to keep wheelbase level. Otherwise bike would tilt fore or aft and give lesser scale measurement. Thanks.

[corksil]

Originally Posted by Mohawk

You don't need the block of wood. Assuming your scale is like 2" high the CofG moment is less than 1/2Kg per end. Just make sure you have a ramp up to the scale height that will NOT move, or the scale may tip as you try to roll on to it.

Yes, center of gravity would shift without wood block under opposite tire from scale. Not sure how much but it would certainly affect the measurement. Tipping the scale could damage it so smart of you to recommend ramp for scale. Thanks.

Originally Posted by Motofool

You will introduce a bigger difference by having more or less fuel in the tank.

There is wet weight and dry weight for each motorcycle.

Yep yep. Noted. Thanks hernan.

[corksil]

Originally Posted by Triple Jim

I suggested the block of wood because my old scale is something like 3" high, and when I calculated the error, it was a couple pounds. Yes, you don't have to use the wood if you're not going for high accuracy. Not that bathroom scales have high accuracy in the first place.

Of course fuel level is very important. 5 US gallons of gasoline weigh about 30 lbs, so if you're trying to lighten the motorcycle and are going to weigh it more than once, have it empty or full each time.

I just did a rough calculation, and it looks like if you weighed a 250 on my scale that's 2.5" high without the other wheel being on a 2.5" block, you'd be about 5 lbs low after you add the reading from each wheel. As stated, this isn't a big error, but it's an error.

I agree with everything you said. You must be a wizard if you know the formula to calculate the weight difference WITHOUT using a wood block to keep the tire that the scale ISN'T under at the same height as the tire that the scale IS under. Hopefully that made sense. Thanks.

[corksil]

Originally Posted by Alex

Pick it up with both hands, estimate. It works great when I'm trying to win a free lunch at the buffet.

I don't trust my estimation skills to be that accurate. In my mind, it would either weigh more or less than a 80lb bag of concrete and if it's more, I would quickly drop the weight and run off to fetch my excavator.

Originally Posted by Triple Jim

For me it would be pick it up with both hands and start shopping for an artificial spine.

How's yours doing, by the way? Any improvement?

Spines are serious business. The older I get, the more I learn that firsthand through direct [unpleasant] feelings.

Originally Posted by Alex

Not much change, but I haven't tried lifting motorcycles recently. I can suggest it to my PT guy.

Dude don't mess around and lift motorcycles for fun. I used to lift heavy weights due to an excess of spunk and testosterone but then I got a [little] older and realized that I was using up my body prematurely. Serious business.

Originally Posted by empire00

If you have front and rear stands you can just pick the bike up and set it straight down on the scales if they are narrow enough.

"Fish scales" are cheap and easily available online, and they measure hanging weights but it's tricky to hook up proper rigging in a manner that I'd feel confident about. It's all fun and games until a bike is hanging from rope and a knot slips. Rubber side down, shiny side up.

I like your idea much better. Tomorrow I'll see if I can fit a bathroom scale between the front and rear paddock stands that I have.

Thank you all for the intel. Somehow you guys think in ways that I don't, and save me a lot of [potentially expensive] trial and error.

[Triple Jim]

Originally Posted by corksil

You must be a wizard if you know the formula to calculate the weight difference...

No, the calculation is like a lot of things... it's really not difficult, it just seems that way.

[choneofakind]

The sum of the moments about the non-scale side wheel is equal to zero. Boom. Just remember that your scale is measuring normal force (always perpendicular to the floor, in this case directly up), but because your bike is at some small angle, you're actually looking for a component of that to get the weight on that wheel. The angle can be calculated with a triangle made up of rise and run, where rise is the height of your block and run is the wheelbase. You'll need basic trig and some drawings to make sense of it and keep all your conventions straight in your head, that's it.


or... skip the hard stuff, assume a small angle approximation of 1 for your cosine (perfectly legitimate option), and say, "good enough for government work" and take the scale reading for its face value. if your scale is 2" tall and you have this many questions on the math already, the 2" thick scale will make an insignificant difference.

or... just put the other wheel on a block that is of similar thickness to the scale. This is likely the easiest method to avoid doing math. Then swap the scale and block to opposite sides so you can get the weight on each wheel. Add them together as a quick double check to make sure your total weight makes sense.

#wizardry

it's really not that hard.
https://en.wikiversity.org/wiki/In_s..._equal_to_zero

[Triple Jim]

The biggest source of error comes from the center of gravity being something around 18" above the floor, so that when the motorcycle is higher at one end, the CG moves toward the low end.

[choneofakind]

The cosine involved in the sum of moments calculation takes care of that. As the angle of incline approaches 90, cosine goes to 0. So.. For example, if we have the rear on a scale and the front on the ground, if the scale were so thick that the angle of the motorcycle approached 90 degrees from level, the cosine of 90 is 0, so there would be 0 weight on the rear wheel. But that's just an explaination of how cosine works for this. obviously we're dealing with a small angle because the scale is only a couple inches thick, not several feet.

Do one wheel at a time. Sum the moments about the opposite wheel, keep your convention straight and it will get you the weight on each wheel. Add them together and you get the weight of the entire bike. I'm not sure what your method was, Jimjimjim.

[Triple Jim]

Originally Posted by choneofakind

The cosine involved in the sum of moments calculation takes care of that. As the angle of incline approaches 90, cosine goes to 0. So.. For example, if we have the rear on a scale and the front on the ground, if the scale were so thick that the angle of the motorcycle approached 90 degrees from level, the cosine of 90 is 0, so there would be 0 weight on the rear wheel.

You're leaving out the fact that the CG is not in line with the contact points. The weight on the rear wheel goes to zero well before the angle gets to 90 degrees. Balance a motocycle (or model of one) on its rear wheel and you'll see that its wheels are not forming a 90 degree angle to the floor. It's balanced when the center of gravity is directly over the contact point of the wheel on the floor.

[choneofakind]

No, I'm intentionally ignoring it to make things simpler. Make the CG inline with the axles (which are what, 11 to 13" off the ground as well?) and the number of equations in your system is greatly reduced because the x component ends up going through the pivot point when you sum your moments and therefore causes no moment.

The block under the other wheel makes this weigh easier, (see what I did there?) but it will be good enough for what it's for if you just assume the CG is inline with the axles of the wheels and everything is square.

I guess that's the most pressing question of this whole thing for the OP: how accurate does this weight estimation have to be and what's it for? Because that tells you how in depth you have to go with it.

[Snake]

Keep
It
Simple
Stupid

[Ninjinsky]

Stoppie onto the scales glance down real quick.

Seriously I have done the scale under each wheel thing and it should work but it is inaccurate (or the bike weighs less than spec) and I don't know why.
Most councils have a public weighbridge that they use for vehicle laden weight checks etc'. As a taxpayer you should be allowed to use it for ten bucks or so
Here is the west of England list. Hawaii resources I cant find googling from here
http://www.devonsomersettradingstand.../weighbridges/

[choneofakind]

Originally Posted by Ninjinsky

Seriously I have done the scale under each wheel thing and it should work but it is inaccurate (or the bike weighs less than spec) and I don't know why.

It's because of the angle. How far off was it?

[VaFish]

Originally Posted by Alex

Pick it up with both hands, estimate. It works great when I'm trying to win a free lunch at the buffet.

When I way my dog I step on the scale and weigh myself, then pick up my dog and step on the scale again. Subtract the first weight from the second one and I know how much my dog weighs.

Would work for bikes too.

[Mohawk]

Extra bonus points to the guy that can pick up a 150Kg motorcycle & still see the scale to get the weight

[corksil]

VAfish must have a small dog.

For a whopping six bucks I found a hanging luggage scale that reads up to 110lbs. It was great for weighing different wheel/tire combinations but obviously is inadequate for weighing an entire bike. However, it got me thinking (uh-oh.)

Does anyone know where I can find a load measuring unit that fits between two pieces of rigging? I know that industrial cranes have them for the purpose of knowing the weight of a particular piece of hoisted cargo.

I believe the unit is referred to as a thermocouple, because the sensor actually measures the temperature of a tiny piece of elastic material inside the unit while it stretches when a load is lifted. It's amazing what you can find on ebay from overseas if you use the correct search terms but that is not my specialty.

If I could find a unit, about the size of a volleyball or smaller which would fit between two pieces of rope or nylon webbing -- and could measure the force between those two materials for purpose of determining weight, I would be keen on buying it.

Basically a "luggage scale" but bigger and with.... say... a 500 or thousand pound weight limit.

I could easily construct a sling to lift motorcycle with my excavator, and with a special load measuring unit, I could accurately determine the weight of the bike without any maths.

As far as I know, if an object is dangling from an overhead lift point, and the force through the string that the object is dangling from is measured, this will always be an accurate measurement. [Obviously the measuring implement could be miscalculated but let's not over think things.]

Thanks for the help and this is all very thought provoking.

[Motofool]

Check these ones out:

http://www.ebay.com/bhp/crane-scale

For less money, you can use your hanging luggage scale if inserted in the pulling leg of rope coming from a pulley system:

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

[empire00]

Alternatively find a warehouse or shipping department somewhere that will let you roll your bike up on one of their shipping scales. Or use a truck scale at a truck stop or scrap yard.

[adouglas]

Inspired by this thread, I just weighed my track bike using the bathroom scale method.

Amazing how much weight all the street stuff adds. My R6 in track form with a dry tank weighs just 360 pounds, give or take a couple.

[dcj13]

So just how accurate does one have to be when weighing a motorcycle?

Plus or minus a couple of pounds? Or ounces?

[Alex]

[corksil]

The main reason I asked is because I've been trying different tire/wheel combinations on various bikes and most of the PUC [public utility commision] scales here have incrementations of +/- 20lb. That's not precise enough.

Anyways.. thanks!

[VaFish]

Originally Posted by Mohawk

Extra bonus points to the guy that can pick up a 150Kg motorcycle & still see the scale to get the weight

Talking scale

[DEFY]

water displacement:

[adouglas]

Originally Posted by dcj13

So just how accurate does one have to be when weighing a motorcycle?

Plus or minus a couple of pounds? Or ounces?

Depends on why you're weighing it.

Example 1: In F1, there's a minimum weight limit and every gram counts. So they ballast the cars very precisely to avoid disqualification. There, precision is vital.

Example 2: If you're just doing it for chits and giggles, then who cares? When I got my track bike, it felt really light. "Gee," I said to myself, "This feels lighter than my old Ninjette." So I weighed it and found that yeah, it is. There, spitting distance is good enough.

[corksil]

Originally Posted by VaFish

Talking scale

Yeah okay, you win. Nowadays scales talk. I must be getting behind on the times.

Originally Posted by DEFY

water displacement:

Is that the travis pastrana x-games bike that was crashed in SF bay? I heard that travis almost re-negotiated his riding contract with suzuki after that stunt and the resulting fine.

Things have certainly changed between now and 1999.

http://www.sfgate.com/sports/article...es-2919840.php

Originally Posted by adouglas

Depends on why you're weighing it.

Example 1: In F1, there's a minimum weight limit and every gram counts. So they ballast the cars very precisely to avoid disqualification. There, precision is vital.

Example 2: If you're just doing it for chits and giggles, then who cares? When I got my track bike, it felt really light. "Gee," I said to myself, "This feels lighter than my old Ninjette." So I weighed it and found that yeah, it is. There, spitting distance is good enough.

Hold up a second... you have possibly re-arranged my entire world and perspective. Did you say that your inline-4 yamaha 600 weighed less than your ninja 250 twin? Suddenly I feel so out of touch.

Maybe I need to buy new motorcycle. Again.

["A"]

Go to your local recycling station:

[corksil]

+/- 20lbs ^^^

[corksil]

Originally Posted by adouglas

So I weighed it and found that yeah, it is.

06 R6 - 161kg

08-12 250r -151kg

...according to wikipedia.