What's new
  • If you don't frequent the chat forum, make sure you read this post regarding land usage. It would be great if we could get everybody to send a comment in before Oct 7th!

Motorcycle Weight Distribution Mesurement?

DJ_MI

Well-known member
Joined
Feb 7, 2022
Member Number
63
Posts
529
Location
M
I come from the automotive performance world where we "corner balance" a car with four scales to measure weight distribution front to rear and side to side.

For a motorcycle the front to rear is easy. How do you measure weight distribution side to side?

KLX300-Scale.jpg
 

Yinzer Moto

Well-known member
ADV+
Joined
Jan 25, 2022
Member Number
4
Posts
2,783
Location
Pittsburgh
I come from the automotive performance world where we "corner balance" a car with four scales to measure weight distribution front to rear and side to side.

For a motorcycle the front to rear is easy. How do you measure weight distribution side to side?

KLX300-Scale.jpg

Use a bubble level to stand the bike straight up and then place the scale against the end of the handlebar, to see how hard it pushes to one side? F/R weight is adjustable by moving our bodies around, this is how we can make a bike drift in a corner. It is also important not to pin our bodies in one position with bulky bags.
 

EGR

Well-known member
Joined
Feb 9, 2022
Member Number
474
Posts
219
Location
TN
You don’t. It’s not a thing for two wheels inline. Bikes are radically different. Some of the worst dead end roads in bike GP development were when big deal car engineers came on to bike teams.

Starters. Bikes intrinsically have weight distribution capabilities beyond cage set-up wet-dreams. Driver is small part of gross and is strapped down. Rider is large part of gross and can, routinely is, all over, side to side, up down, front to back.

The entire point of cage suspension is to keep wheels vertical with vertical load on a maximum contact patch. At , say, 45 degree lean turning a bike about half of vertical “suspension” travel is actually in bike structure flex while springs and dampers are dealing with lateral force against small contact patches. Crazy complicated compared to a car. Almost nothing translates.
 
Last edited:

nmroadrunner

Reevaluating Reality
ADV+
Joined
Mar 4, 2022
Member Number
837
Posts
117
Location
Enchanted Mountain
The general principle of keeping the weight as low as possible still applies. I've witnessed more than a few riders who attached a honking big heavily-loaded top box on the rear rack and experienced poor handling issues as fuel load decreased and tire pressures were not closely monitored. YMMV
 

Yinzer Moto

Well-known member
ADV+
Joined
Jan 25, 2022
Member Number
4
Posts
2,783
Location
Pittsburgh
Thanks for the interesting info.

At this point I am primarily interested in static weight distribution w/o a rider. I was initially curious about F/R distribution and got me thinking about side to side also and how it could even be measured.

I wonder how close to a perfect 50/50 lateral balance the manufacturers shoot for when designing a bike. 49.9/50.1 or is 47/53 close enough?

I replaced the exhaust on my bike with a lighter one which saves 5.9lbs. Assuming the bike was perfectly symetrical originally, here's what the exhaust has done.

Lbs-Screenshot 2022-04-14 00.55.41.png



I'm not stressing over this, I'm just having fun over-thinking it. :D

That 5.9 pounds is pretty close to the center line. I think it would be very difficult to represent the effects on paper. 5.9 pounds in a pannier, on the outside of the bike would have a greater effect.

A couple years ago, I bolted a 1 gallon Rotopax to my rear rack. The effect on handling was shocking. As you can see, it is way up high and almost behind the rear axle. It made climbing steep grades more difficult. It also made it more difficult to step the rear out in a turn and hold it there. We did a back to back test on the same road. 20 miles of twisty and smooth dirt, with the load and without.

32004F96-DD3F-4E7F-A95B-CACF150D13A2.jpeg
 

EGR

Well-known member
Joined
Feb 9, 2022
Member Number
474
Posts
219
Location
TN
Static unloaded bare bike sort of is what it is.

Rider weight, pillion weight, position fore/aft matter a lot. Getting loaded spring setting, sag, for the given load is BFD. Bike wheel geometry is radically more complicated than car. Acceleration rear swingarm squat can extend wheelbase millimeters. Front fork extension will also extend wheelbase. Deceleration forks shorten and pitch will alter steering head angle and contact patch trail. :rofl Now tip in to a turn… That only happens after a lateral change in center of mass. You. You were vertically in line with contact patches. Stand up by moving body back on exact top.

That’s all with tires in rolling mode. Barber T1. Tires go instantly to slip mode, center decel and then over to left side lateral. Track surface dropping away. Fore and aft contact patch loading balance becomes really, really important. Rider will be measuring and adjusting in real time. I’ve read that Matt Mladin’s crew had a set of saddle butt shim pads, 1/4 inch increments to do quick balance adjustments.
 

Yinzer Moto

Well-known member
ADV+
Joined
Jan 25, 2022
Member Number
4
Posts
2,783
Location
Pittsburgh
Wait, you actually have a WRR? Do you regret getting it? :D

That's very interesting that you tested it with and without the Rotopax. On an unladen WRR can you feel a difference between a couple of gallons (~12.2lbs) in the fuel tank?

I do have one and do not regret it. I treat it as an adventure bike that can occasionally do dirtbike things.

I have never done any testing to see if I can feel a weight difference with the main fuel tank. I do actively try to watch the amount of fuel I run in the tank, if I don’t need it, I don’t fill it. I know the bike gets 60mpg and I am only going for a 20 or 30 mile ride, I’ll just put a splash of fuel in. There is something to be said about the larger fuel tanks, in that they can hold the same fuel, in a much lower location. I were to run a larger tank and only put 2 gallons in, it would be in a better spot.
 

Top Bottom