Weight Debate

[ubbb69]

I have been thinking about this subject for a while. I think that the choice in tires have alot to do with how much weight you need. I have a set of panthers on order to test this. Im thinking that with such a soft sticky tire im goin to make my rig as light as i can. I know that i might have to play with the foams to get the traction needed for such a light rig. Im planning to cut the foams enough for tire wrinkle without the sides folding.

Having a light rig will have some advantages but i will prob have to lighten up my springs to allow enough flex with such a light rig. I have just the standard axial kit tires and losi rock claws now. The kit tires require massive weight to work decent. Since putting the claws on i have dropped some weight and like the agility of my rig. The panthers should be just right to get my rig to as light as i can and still get good traction. Might even work with an m3 proline compound but dont have the cash for 2 diff sets of tires at this time.

[engineerjoe]

Right now I have 3oz in both fronts and nothing in the backs.

I think my rig weighs in around 6-7 lbs.

From an engineering perspective I dislike putting weight in the wheels for a couple reasons:
1. weights increase rotating inertia making it accelerate slower, drawing more amps
2. weights increase the likelyhood of breaking during a fall
3. they put more stress on the drivetrain
4. weights in the tires makes it more critical to properly tune your foams (to get more traction)

The purpose of weights in the tires is to lower the CG. I just like to find other more creative ways to lower the CG (flipping shocks, droop, lightening items mounted up high, etc.)

really it comes down to personal preference. I like having a light rig so I don't break and surprisingly, what I can't get up with grip, i just punch it and use momentum to get me up.

[LoveToROCK]

In the spirit of experimentation I added a quarter pound of weight to each axle and then tested the climbing ability against the crawler without the added weight.

I setup my test rock at an angle that the crawler would just make it up and then gave it a little more steepness until it would not make the climb.
The rock is leaning steeply, it ends and the rest of the climb is almost straight up for 8" and then a ledge. A tough climb but I was able to make it once without flipping backward without the weight added to the axles.

With the weight added it had very little trouble making this climb. The weight down low really helped by lowering the COG allowing it to make this climb without flipping backward. I was also able to make it going real slow since the weight also added to the traction.

Yes, not very scientific of a test but it did prove to me that adding weight down low improves the climbing ability. Just how much weight to add and where is the tricky part.

Here's what I did to add weight low. I had some 1/16" sheet lead that I formed to the axles sort of like a lead skid plate. I used a small hammer to form it tightly to the shape of the axles and zip tied it on. This was done just for testing but I wonder now if I might keep these lead "skid plates" in the tool box just in case I need to use the extra weight someday. These do lessen the ground clearance by a 1/16" which isn't much.

I'm sure there are situations where this added weight would make things worse. I'm test climbing ability only right now.

I did take a few pictures before I removed them.

[mmbackpacker]

That's a pretty cool idea right there...I really like the thinking outside the box-ness of it.

The idea of putting the weight inside the wheels ahs never really appealed to me for the reasons stated by engineerjoe..... all said, I preffer a light nimble rig to a heavy one.

[rockspider]

I like to have a behaviour that is similar to that of a real 1:1 rig. That means heavy. But how much?
I did some thinking and measuring, and the conclusion was that most our rigs use bodies in 1:8 scale. Tubers without a body also are 1:8 scale. Check width and wheelbase: a 10 inch width axle in 1:8 means a 80 inch real axle, which ain't that far from a Dana60 width.
A 5" tire on a 2.2" rim is close to a 40" tire on a 17" rim.
So what?
If scale is 1:8, weight must also.
Weight is related to volume, so must consider 8 at cube, 8x8x8=512
Now take this magic number and the weight of the model and the weight of a 1:1 rig and follow this equation:
model weight x 512 = real vehicle weight
or
model weight= real vehicle weight / 512
It works!
For example a light rig like a Jeep TJ weights somewhere around 3500 lb (give or take) which divided for 512 gives a model weight of 6.8 lb, a heavy fullsize pick-up weights somewhere 5500-6000 lb which translates into 10-11 lb.
Don't know the real weight of a competition rock-buggy, but given the weight of steel tubing, engine, tranny, heavy axles and so on, I don't think they can be much less than 3000 lb, if at all. And that would anyway means about 5,8 lb.

Conclusion, adding weight on models is a good thing, the general behaviour becomes more real and less bouncy, and the rubber of the tires can actually develope much more traction.
Personal preferences and driving style will favor more or less weight, but a little bit of weight is always needed.
A stock Axial weights 3,5 lb, that means a real rig barely weighting just 1800 lb. Too light. Even with soft tires and zero pressure, a rig that light would spin tires endlessly on the first dirt climb.


Wow can't believe I wrote almost a book, LOL! Sorry!

Cheers

Alex
from Italy

[frdtrkguy]

The sheet lead is a good idea for lowering the CG but I bet it doesnt slide across rock as good as the stock plastic axle cases.

[LoveToROCK]

Originally Posted by frdtrkguy

The sheet lead is a good idea for lowering the CG but I bet it doesnt slide across rock as good as the stock plastic axle cases.

As I said...I was experimenting with weight, never said it was the cats butt for a skid plate. But actually it did slide better than I expected it to. Also the lead does harden from the hammer shaping to fit the shape of the axles. The rock scrapes are just hammered away and it's was smooth again. I did setup a few rocks last night to see how it worked as a skid plate. I agree though, not the best material for a skid plate but better than I thought.

If I were setting up for a comp where there were steep climbs and ledges I might try them out again. Having a 1/2 pound of weight down low like that does help a lot.