Technical PtII-Ratio of Spring weight to unsprung weight unfavorable, what helps?

As an aside...

We usually think that a stiff frame is the best, yet when Ford designed the Model-T he made it flexy on purpose. That way he could keep it light without it cracking right away. (Flexy things crack eventually...)

So it didn't last as long as it might have, but while it did last, it had better traction because the tires stayed on the ground.

 

There's a commercial someplace for the Reese hitchs and load lever bars. They took a FWD tornado or eldorado and hooked up a trailer with the bars, then took the rear wheels off the car and towed the trailer. Obvious weight transfer (foward to the cars front axle and rearward to the trailers axles) there and the bars put a static torque force against the hitch.

 

31Vicky, I don't understand your questions below. As for reading my sketches - I originally misunderstood your question - I thought the hole in the concrete was just big enough for your spud bar - and then thought you were pushing horizontally to "tip" up the concrete block. So to make the FBD easy I "faked" it and pretended that the bar was on a hinge and rotated the bar 90 degrees so it was horizontal and you were now pushing straight down. Effectively making your problem into a "teeter totter" of sorts. I did this so I could easily throw in some numbers and get some answers and so that you could see the difference in force needed to lift the concrete. I threw in the one reaction point and labeled it "0" because at that point it would start to LIFT up. With the way you ACTUALLY intended it to be drawn doesn't really change anything - the resulting FBD will be the same. Numbers of course would be affected but the general thought process is the same. If I could understand your question I would at least attempt to take a stab at the answer.

 

A trunk full of moonshine might help. ;-)

 

Oh man, here comes another hack sketch.
LSandA is going to be so proud.

Basically i was working up to the engine on a levered motor mount coupled to the frame rail.

Give me a min, ill get my good crayons and sharpen them up. Lol

 

I'm thinking a belly full of moonshine

 

You know sometimes it take a belly full of moonshine to figure things out.

 

Ok here's the pic,
In this there are 4 separate motor mount scenarios & they are color coded.
One is facing rearward, next is straight under, the next is facing forward and the last is longer facing forward.
The frame is a rough sketch of a regular old 33/34 frame and the engine draw above its resting place, to be lowered down.

With concrete and bar demonstration, you showed me how I moved/lifted one end of the slab by applying my weight thru the bar into the slab. It was torque created by my weight on the bar generating the force, torque.

So when I said put 800-900 lbs on a 12" bar I wanted to see the torque applied to the slab and what would move ( read transfer weight). Then When I said make the slab 10 feet long I wanted to see how that increase would effect the out come. And all of that was working up to this pictures representation of levered motor mounts creating torque and transferring weight.

Man I hope that makes sense.
thanks for your help!!

 

This got me thing about what actually happens with this style rear spring and suspension
The weight pushes on the spring hangers, The hangers try to spin (torque) the housing, the p&j style ladder bars are loaded because of the weight on the rearend. This has got to be doing a lot of weight transfer just sitting there too, no?



Nobody wants to tell me this isn't transferring weight ? Or how much ? Or where its going ? Or where I should go ? Lol

 

I give you an A-.....drawing skills are average for a man of your skills and knowledge, but the use of colors like that is ingenious.........I just had to come back and say something.....I love hearing you hands on guys make the pencil pushing pencil necks that wouldn't know doodly if they hadn't read it in a book.......I remember my mentor telling me one time..."That looks good sitting in the shop, but that 1/2 mile dyno will prove your work fruitful or dumb"...talking about the Circle track we ran each weekend.

 

Lmao !
You really should see some of my artwork. There's down and dirty back of a napkin stuff that suffices most of the time. But then there's other stuff that a drawing is all you have to sell it with. Some guys have a natural talent for it, I need to coax mine to flow and that takes time. Obviously a sign painter would be extremely easy going about doodles and make them nice without trying. With some of the sit I do, they say that " I make it look easy" I always tell them that making it look easy is the hard part.

 

It's a small humbling world us great people live in...hehehe

 

31Vicky, After studying your sketch there's a few things that jump out at me right away! First off LOOSE that 4 blade fan and get a good 6 blade one! Next those round exhaust port heads gotta go -not only are you missing one exhaust port but they are teeny tiny! at least step up to some triple nickles on that biatch. All the better if you can spring for them fancy "store bought" al-u-mini-um ones! Unless of course those are actually the freeze plugs - in that case I hope they are installed properly - them flat ones can be a PITA if you're not careful. Oh yeah - lastly - you aren't gonna transmit torque anywhere with that setup - you don't even have a transmission yet!!!! Sheesh

 

Pass the moonshine

 

Yeah!
See what happened ?
no more fancy doodles

 

Another hand drawn sketch. A bar with a bolt in the center. When you apply torque to loosen the bolt, the far end will try to lift. If the engine weight is applying torque to the mount, the static load is actually taking weight off the rear of the car. Under engine torque, the left side would be being pulled instead of being pushed and would help plant the left rear tire on the stock car, possibly. Just my backyard engineering opinion.

Blue

 

31Vicky, With regards to the "spring behind" setup - I tend to agree that it would put some load on those front bars - just sitting there statically. Now if you mash the gas pedal I would tend to think that the rear axle will want to rotate up in the front (for the same reason someone invented slapper bars) With the front already preloaded to go up I would think that it'd be even more likely to react upward to that throttle mashing which of course would pull the rear (where the spring mounts) down (something Newton said - action reaction mumbo jumbo) - Pulling the rear spring down - it is connected the rotating rear end - would tend to pull the frame down with it. None of this is what you want if your goal is to plant the tires for a drag race. So I would further assume that's why we don't see a lot of those setups at the dragstrip. But this is all speculation - I don't have any cars with this setup - and don't see myself trying it out anytime soon. Maybe tomorrow I will think about it again and think the opposite? That's my take on it for the moment though.

 

I have built a similar set up for a model T coupester, What is the maximum amount of travel that you are looking at? This model T will have 4 inches of travel max, I added a spring pivot like what is used on the front to help not twist the spring under travel. With a set up like this you need weight transfer to compress the spring so it stops loading the housing the holes in the end of the trailing arms for my model T raise the ground clearance and change the force on the arm and housing. How is your spring attached to the rear axle?

 

What's the down and dirty way to figure the static weight shift.
Like a for every For every pound in the spring equals so many pounds out at the bar mount crossmember. It's like prying on the short end of a lever and not much I suppose.

 

Ok, had my moonshine and the more I read this the harder it gets, been thinking how the engine mount location of Tannergang's works.
In a chassis you have 2 basic torsional effects going on, 1 from the motor trying to twist the chassis and the other the diff trying to lever the chassis up on acceleration. Now his application was on circuit cars so the right rear wheel is going to be doing the majority of traction work I think, Anyhow, by shifting the point at which the engine is mounted to the chassis further back, the ratio of the engine torque being transfered to the chassis rail is ratio'ed further rearwards toward the rear axle giving better bite on the tyres. I think this mount is just a part of his fine tuning of the chassis but am unsure whether it would have any influence on sprung vs unsprung weight

 

31Vicky, IF I understand the question, down and dirty - linear dimensions. Meaning if something is applying a force 1 foot away and I am countering that force 4 feet away then I will only have to counter with 1/4 as much force. D&D is the teeter totter example again. The Fat kid has to scoot way in to counter balance the thin kid. The fat kid will not teeter very far (up/down) movement compared to the thin kid who will move a lot. Matter of fact the amount of movement is your clue as to the leverage you get. I can remember working on some elaborate linkages and when trying to understand the leverage involved it became easier to understand when we took in the amount of movement. Am I even close to following what you are asking??

 

Great !
This example is 48/8 so a factor of 6:1 or 16%
Can you guess why I'm asking ?
It won't be today, but ill be weighing, total, sprung, and unsprung weights.
There will be a discrepancy there as the scale will be telling me what it sees not what's being transferred by this factor.

Maybe some more moonshine and ill get an idea on how to figure out where the transferred weight is going. This seems overly complicated right now but I can only weigh static. I can only drive dynamic and the more loud pedal the more weight transfer.

I'm hoping I can use this to my advantage.
Maybe this is part of the reason these cars are oversprung and the "boxed" recommendations are wrong.

 

Left over moonshine epiphany-
Not sure how to use this yet.
If I took a bar and placed it under the ladder bar mount and over the rear crossmember- when i push down I should get 16% more leverage than I'm putting in- is that right ?

If I move 1 pound from the area of the ladder bar crossmember mount to the rear crossmember or behind it it like I moved 1+16% - Is that right ? Or is there some compounding or canceling or another step in the equation that I'm missing?

 

Where's all the tinkers today

 

This is 203 posts in and I still dont know what you are trying to achieve. The suspension pictured generates a torque on acceleration as the axle torque pulls upwards on the radius rod, the amount is unknown as there are too may variables in the positioning of the angle created by the radius rod front pickup point as well as the length of the radius rod arm. As I stated before the torque load changes based upon the tire traction so you are shooting at the moon with a BB gun to try and come up with an accurate answer on the amount of weight transfer.

if you want to get an idea of what is happening and have access to 4 race car scales you can place your car on 4 wheel scale pads, take a 3" diameter water pipe and span the frame pickup points of the radius rods, place a floor jack mid point of the pipe span and slowly jack the car up and read the differential in the wheel weight readings. This will tell you if you are transfering weight to the front or to the rear and save a lot of speculation and then you can approximate based upon inches of upward travel verses weight moved readings.

 

When you build something that is purpose built.......you wanna think about everything during the entire build as you already know........The real trick is knowing what to adjust and change after you established the baseline after that first pass or drive ect. To make it all work........

Too many factors change after you run and determine all the static #'s......Like the torque and movement produced from your engine ect. and every other factor.......I like to see cars that have thought put into them......not too many of them around.........

Anyone can plug a Hemi into anything........that does not mean it will be fast.....I seen that proven.....so much more to it.....its fun...My Model A Pickup ran 9.50's thru a boxed stock frame rails..over time as I introduced more HP and torque...That thing would leave the line twisting in anger.....and still no traction issues, only problem was...you did not know which way it was going to go.......would it have worked better if it was tied together more than it was ?........or would that have made it blow the tire ? I still think about that eventhou it's retired from the track............Dave

 

Shooting at the moon with a BB gun I like that one.
Dick, as I said before in an earlier responce to you- I'm trying to achieve a deeper understanding. My edification.
Maybe guess in the right direction.
Bark up the right tree
Understand how changes effect things and go in the right direction.

So take this rear suspension design and the scale dilemma.
Maybe its just brand spanking new to me and I'm like a guy who just found religion and its centuries old stuff. Funny thing is most guys say their shit is too stiff out back and yet nobody says why or why thier calculations were off. Not ever once in any magazine I've read or reading posts here or suspension theory books have I saw mention of the static weight transfer if a spring behind buggy spring axle. And to take that further, the front axle spring behind or in front weight transfer that must be there too. 80 some years worth of acumilated info and I haven't seen it mentioned.

Simply Weigh the sprung weight of the rear, pic a spring right?
Well when you set the car down, the sprung weight will be different because of the static weight transfer in the design- so the first guess is automatically wrong and the spring is too hard. To me that's a bunch of money I don't have, more parts on the shelf I don't need, and more work id rather not do. It would be different if I took a walk out back and found what I need behind the shed, but I need to find it on a computer, trust someone, give money, pay for the ride, depend on a crew of misfits to get it here. I know how that work and know it well because I wasn't sure which way direction to guess.

Hopefully this kind of thread helps anyone build a better car, i know it will for me.

 

I agree.
First roll out should be within a "zone" and you should have adjustment either way to get where it is best. First roll out should tell you that you are in the wrong state and need a redesign. That does happen but it shouldn't be a standard of operation.

 

Weight doesn't transfer. Again, WEIGHT doesn't transfer. LOAD does, so the trick is to get the rear axle loaded when you want it to do more WORK. Axle TQ is greater than flywheel TQ by perhaps 400% or more due to multiplication of available flywheel TQ through the trans and rear axle gears. The rear axle wants to twist counterclockwise as viewed from the rear. It also wants to wrap up at the pinion from the same forces. I only say this to help view the forest instead of the trees. The WORK will be done at the rear axle. Sprung and unsprug wt can be shifted some but the forces will remain.

 

That's a very good distinction.
Molecules of mass are not transferring position, where and how their load is carried does.
That Clear distinction may have helped even more 9 pages ago - lmao
Still glad it's here!
Thanks