Wheel weight vs. chassis weight ratio OR spung/unsprung bias

[solomon7]

It seems like there should be a direct correlation between srung and unsprung weight regarding a rig's stability. What I mean to say is if your chassis and guts (sprung) weighs let's say 3 lbs 4 oz and the axles and wheels (unsprung) weigh 2lbs, then the weight below the CoG would be less than above makin the rig less stable at sidehills and vert i/e. more weight above than below.
If the chassis/guts weigh 3lbs 4 oz. and the wheel/axles weight 4lbs, there would be more weight below making the rig more stable and less prone to rollovers.I see many with I think less below than above but can't see how it works.
The physics just make sense in my hesd. I wonder what others sprung/unsprung weight are.
Please chime in if you can. Mine is: Sprung 3lbs 1.3oz Unsprung 3lbs 7 oz (roughly) and is incredibly predictable, but seems heavy.
What about ya'll? The more info the better evidence.
AM I JUST WAY OFF HERE. Gurus, please school me:???:!

 

[Nabil]

your at 6.5 pounds, which is just about perfect for a 2.2 rig IMHO

i know just about every rig i have built has had a lighter sprung than unsprung weight. i think you are just about right where you want to be

 

[whoodie]

It is simply CG height. You are taking it too far with sprung and unsprung weight. Unsprung weight really only comes into play with heigher velocities. Crawlers are so slow you can treat the problem as static. Keep an eye on your CG height and you'll be fine.

 

[Offroader5]

IMO, you'd always want more weight in the unsprung category for the very slow crawlers like what we have. Reason is, the more weight you have there (whether it be axles, tires, wheels, foam, wheelweights, servo's on the axle, battery pack on axle), the better off you'll be. Of course go way overboard with this weight and it will start to hurt you.

The way I see it is I want to have more weight in unsprung than I do in sprung. This means it would be very tough to tip since most of the rigs whole weight is always on or very near the ground.

My new rig breaks down like this:

1. Complete chassis w/skid, trans, cobalt puller, RX, ESC, shocks, half the driveshafts, and all links = 1 lb. 7 oz (637 grams)
2. Front & rear axle assemblies w/servo, plates, steering linkage, and half the driveshafts = 1 lb. 3 oz. (542 grams)
3. Tire & wheel combo = 2 lb. 14 oz. (1290 grams)
4. Battery pack = 8 oz. (214 grams)

So the way I see it...if you add items 2, 3 & 4 (which is my unsprung weight), you get 4 lb. 9 oz (2046 grams). This is just a touch more than 3 times my sprung weight. I have a 3:1 ratio between them. I think having 3 times more weight on the ground than what is constantly moving with the suspension...is a much more stable ride than having it closer to 50/50 or even worse....more sprung weight.

 

[whoodie]

So if your sprung weight is a foot above your unsprung weight it is ok? You are all assuming that your sprung weight is above the CG and unsprung is below, that is not always the case.

You have to look at the height of the CG's for both of the sprung and unsprung masses to even begin to compare the two.

 

[Offroader5]

But the CG of your sprung weight is not as much at fault if your unsprung CG is either the same height or lower.

If I had a heavy as hell motor/trans/chassis that had a lower calculated CG than the CG of my unsprung mass...it doesn't necessarily mean I'm better off. The CG of the unsprung doesn't change height in relation to the ground that the tires are resting on. But the CG of the sprung weight is constantly changing heights.

For example, if you're running a full droop setup, the sprung CG is at the lowest point it will ever be when the rig is sitting static, and it can only rise further away from the CG of the unsprung and the ground. If I have a 3:1 ratio in favor of the unsprung...the chances decline that the CG of the sprung mass will be as likely to cause a problem.

If you changed nothing on a rig in terms of it's sprung weight, but only changed the unsprung to a MUCH lighter mass (lighter wheels, lighter tires, lighter axles...etc), that truck would now be way more likely to tip due to the unsprung to sprung weight ratios now that it's closer to favoring the sprung.

Man...this is hurting my head :lol:

 

[whoodie]

So basically what you said is that you want a low CG.

 

[Offroader5]

But he asked about the correlation between unsprung and sprung....and that's what I explained.

 

[whoodie]

Right, and what I said is that it does not matter nearly as much as CG height.

 

[solomon7]

Which is derived from the ratio of sprung and unsprung weight to each other, hence the less sprung weight , the lower the CG and more stable the ride. Insane ride height/breakover could be achieved as well while still maintaning stability i.e. "sticks/berg/clod" and the like.
I'm sure there is a mathematical formula to it somewhere.
This is good stuff guys! Well articulated also.
PS Yeah I'm really happy with the performace and balance of my setup now. Just wanted to see what others thought on the matter.
Good stuff!

 

[whoodie]

Draw a diagram, do a moment balance and tell me it is not CG you are ultimately looking at.

 

[solomon7]

Totally. It is the CG ultimately but when clearence is an issue as with crawlers if all the "guts" and any weights that were in the wheels were place as low as possible on the sprung section of the vehicle, for it to have a low CG the belly would have to be considerably lower than a rig with most of weight on the unsprung parts?
A stock Ax10 kit has all the electronics mounted on the chassis and very little weight unsprung plus insane ride height= high CG.
Another has all the electronics on the axles; same ride height.
The latter will go steeper safer than the first Unless the first lowers itself some to compensate for weight up high. My wifes mostly stock WK can go up the same stuff as my comper that has 3" clearance. The catch is she has to lower it to under 2" and add more weight in the tires to compensate for all that stuff sprung up high. Even if she mounted the tranny upside down to get the motor lower, without dragging belly its CG is just too high with all the sprung weight. If the trans was strong, I bet with a pound n each wheel the CG ratio would be off set enough to be as stable as any other crawler. It'd just weigh a ton.
I see the points being made, and perhaps sprung and unsprung are too literal a term, but there is a distinctive correlation between them and the CG., I think. Aren't semantics fun lol? It's nice to see other opinions from you guys and yes it's more than I need to be worried about. My CG is 1.9" over the axle:mrgreen: but it's in my nature to perfect stuff; always room for growth. Feedback rocks"thumbsup"
Good night all, Solomon

 

[RCMFMaxxMan]

the words "sprung" and "unsprung" are being used inappropriately. there is a lot of sense here but some irrelevant terminology. you are all on the right track. just get rid of the two words, sprung and unsprung. change them simply to lower and higher haha. it seems that we want more unsprung weight but that is only because our unsprung weight locations are usually the lowest locations to locate weight NOT because they are unsprung weight locations. Sprung weight and unsprung weight has to do with how the suspension responds when the entire vehicle is in motion and is met by another object (like a truck flying through the air and meeting the ground). rarely in crawling does a circumstance come about. the most common suspension cycling that occurs in the crawling world is not due to impact, but merely a change in the ground beneath the vehicle. Therefore, sprung and unsprung weight is quite irrelevant to crawlers. the suspension will cycle the same (for a crawler) whether the weight is supported by the spring or if the weight is unsupported by the spring. If you want to get into rock racing, then we can talk more indepth about sprung and unsprung weight, but for this topic you are merely talking about how high the weight is. For example you said if you take the wight from the sprung location (chassis) and make it unsprung (axle), then you can raise the chassis and not lose cg. That is true, but has nothing to do with if the weight is sprung or unsprung. For example, you could move the weight from the unsprung (axle) to the sprung (chassis) and raise the height of the axles (larger tires, maxx axles, poulson style, etc.) and not lose cg. so, as you can see the ability to raise and lower ride height without increasing cg is independent of sprung weight and unsprung weight. The only thing that is dependent here is how low or high the weight locations are. If you have a high chassis and chose to move weight from the axles to the chassis and raise the axles, you probably aren't doing yourself any good.

Well, this was long winded but I wanted to get the point across. I hope that all makes sense. whoodie was on the money. don't over think it. low weight is better than high weight. and parts with less weight can be raised higher than parts with more weight.

i have said sprung way too many times :lol:

 

[whoodie]

...

Thanks, perhaps I should scan in a free body diagram to show it graphically.

 

[Kamikaze]

My truck is 6.5 lbs, my unsprung weight it 5 lbs. I'm good."thumbsup"

 

[Offroader5]

I had a long winded post I was writing here...but I held down the backspace key figuring it was not going to do any good to continue the debate.

Yes, it does all center around the CG...but where you distribute the weight, whether it be above or below the "springs" really does matter. I know what works for me and everyone else knows what works for them whether the official wording or vocabulary was right or not. I'll just leave it at that. "thumbsup"