weight distribution vs "sags"

[docc]

Setting up sports cars is so about "weight distribution" (50/50, and all that).

 

With sporting motorbikes, we often talk of "weighting the front." And with these bevel drive Guzzi, the worry about the rear weight bias.

 

So, another member and I are looking to compare "sags" and weight distribution, but what to expect?

 

Not 50/50 like a sport car? 60/40? What?   

[JBBenson]

That's a good question. With my slightly lower clip-ons, and raising the forks a bit in the triples, I think I have done what I could to counter the "ass-heavy" V11. But I really don't know.

 

But, motorcycles are such a dynamic environment, especially front to back, with accelerating and braking forces, much more so than cars, not to mention the rider shifting back and forth.....also, the rider's weight is a factor too, being a much larger percentage of the total weight than with a car.

 

I guess holding a "normal" riding position when measuring....? 

 

Let us know what the results are.....in any case, I am sure the red-frame Sports are better at it....

[footgoose]

To what end docc? This is new subject matter to me.

 

using the halfway point between the axles, and just eyeballing it, it seems the front would weigh more. I dunno, just me. Looks 60/40 front.

[docc]

I'm assembling a platform to (attempt to) put my Sport up on two classic Fairbanks-Morse physician's scales. One of the other forum members has a Sport1100 that may be getting new front end, and this is one way to try and assess the changes.

 

Looking for a third hand, or some method, to have the rider in place while the measurements are taken.

 

This could certainly go all hair-brained . . .

[gstallons]

Maybe....

[JRD]

This is obviously an example of a person with entirely too much free time on his hands!    Just jokng Docc.  The NASCAR boys have spent untold millions of dollars trying to figure out how to make their cars just turn left.  And they have specific rules determining front to rear and right to left weight bias. 

As motorcyclists, we are asking even more of our suspensions since our center of gravity and weight distributions are constantly changing as we "lean" into the corners, slide back on acceleration and slide forward under heavy braking.  I think that a properly "tuned" suspension, eg.- sag, preload, rebound and damping will have a greater benefit than attempting to change the weight bias since our bias is never constant.

If you watch a NASCAR race pit stop, often times a pit crew member will place a wrench in a hole in the back window.  He will then turn the wrench to add or take out "wedge" or pressure on the spring of that particular wheel. Basically they are either adding or removing pressure on that wheel.  I would be interested to see if adding or removing preload to the rear shock spring has any effect on the weight bias of your bike while it is on the scales.  It looks like your system just might work, put a block under the side stand to keep the bike as vertical as possible.

 

Please keep us posted.

[footgoose]

Interesting JRD. I always wondered what effects were at play with a front end that has damping on one fork and rebound on the other.

[JRD]

Footgoose- that is an excellent question and I hope someone much more familiar with suspension set ups can answer.  Maybe someone who races, not necessarily road race but also moto-cross  since they are continuously working with different set ups for the various tracks. 

The Ohlin forks and shock on my Aprilia seem to work fairly well (:-D) with damping and rebound adjustments on each individual fork leg.  Recently I rode both bikes to top off the gas tanks with ethanol free.  Took the LeMans first.  Came back to the house and immediately jumped on the Aprilia.  Took the exact same route and was amazed and the difference in comfort of ride.  As smooth a ride as the LeMans has, the Aprilia was like riding on air!  

[docc]

[docc]

Revealing results. We all know the big block Guzzi are "rear weight biased." I thought I addressed this by setting my sags (32mm front/ 25 mm rear) and dropping my triples 5mm. Yet, I carry a good bit of kit in the Tekno panniers (about 18 pounds) behind the rear axle.

 

With Mistral carbon fiber canisters (saves 5 pounds per side) and no US evap system (another 5 pounds), this 2000 V11 Sport weighs 543 pounds/246 kg. Weight distribution, with rider/ Aerostich/ helmet on board: 43/57% front:rear.

 

Curiously, the Sport 1100 showed identical distribution even with sags 25/31mm front/rear.

[czakky]

That's not too bad, eh?

[docc]

That's not too bad, eh?

I wasn't sure what to think. I knew it wouldn't be 50/50, and 40/60 would be a disappointment, so I suppose 43/57 is pretty decent, especially with the Tekno panniers in place.

 

And the weight, also. I used to say the bike would be out of gas at 500 pounds (227 kg). Looks more like 515 is run dry, but again that's with kit in the panniers. So, not too bad?

[docc]

Wheelbase measurements were somewhat mystifying, though.

 

The early RedFrame V11 Sport is a full inch (24mm) shorter than the Sport1100/1100 Sport-i: 1471 vs 1495mm, 25º rake vs 26º. (The later V11 "long frames" of 2002 on are 1490/25º).

 

Yet all of our axle to axle measurements are 6 or 7mm (~1/2 inch) shorter than the published specification. Hard to comprehend that dropping the tiples and increasing the rear pre-load/ spring rate could shorten the bike a half inch?

 

Not that I speak any calculus. Could be vagueries in the method . . .

 

"You're a poor scientist, Dr. Venkman."

[GuzziMoto]

That does sound like a lot of difference from published specs from just fudging the geometry, but I would expect some difference.

Also, aside from affecting the geometry, messing with the preloads / sags/ fork heights does not really change weight distribution much. This was noted once or twice way back when in one or two of the argument threads on the subject of front ends and stability.

Cars are different in this regard, you can adjust how much weight is on each wheel by adjusting the spring preload for that wheel. It is something very different from the way motorcycles work.

 

Did you measure weight distribution both with the rider and without? I assume the "rider" is of "average" weight?

What about measuring the rake? Both with a rider and without....

[docc]

Funny thing, when we weighed the two bikes without the rider, they, again, had identical distribution: 46/54

 

The Sport1100 with about a half tank of fuel weighed 483 lbs/219 kg and its rider 189 lbs/86 kg in a leather jacket and helmet.

 

The V11 Sport with about 1.5 gallons of fuel weighed 524 lbs/238 kg and its rider 175 lbs/79 kg with helmet and Aerostich Roadcrafter 1 piece suit.

 

(The Tekno panniers and their daily load-out added 18 lbs: 45/55 distribution)

 

We did check the rake but one bike was free standing and the other with rider (more *poor science, Dr. Venkman* ) just to confirm that the earlier Sport has an extra degree of rake (V11 are 25º).