Explain to me how leaf springs relate to traction.

[Yeahrightgreer]

I’d like to get a better full understanding on the Mopar rear leaf suspension.

I understand in theory that when you’re lined up and punch it; the axle is trying to rotate and push into the ground. And obviously since it can’t go down it must go up, pushing onto the car and lifting the rear end up.

But a few questions I have.

Would adding more leafs to a car ALWAYS help it hook better?
If so - why don’t you see a car rolling around with 20 leaf springs. (Besides the fact that it would look absolutely silly and be way too high)

Is there a point where rear ride height or maybe even spring stiffness counteracts your ability to actually hook?

Does the tightness of the leaf springs matter that much? Meaning why do racers have to factor in vehicle weight and just don’t buy the tightest sprints available.
(Let’s pretend that ride comfort is completely irrelevant and only looking for performance)

Finally - what advantages, if any, does location the rear end under the springs have as opposed to above the springs.
I know on the trucks they are under the springs. Is that simply for ride height or is there something more ?

 

[BeepBeepRR]

Axle wrap has a lot to do with traction. Thats why your 8.75 has a pinion snubber to reduce the amount of axle wrap. Another way to reduce axle wrap is with traction bars or cal-trac style setup. It just helps plant the tires. otherwise you are going to spin through the wheel hop of the rear springs unloading the wrap. This is my guess. Others that drag race will have better information.

 

[BAFRAID]

I skimmed through a lot of this but my basic thoughts related to physics are the energy Has to go somewhere. so it either goes into your car raising up so you’re losing the energy that actually raises the car, or you somehow control the car raising up and force that energy into the wheels which then lock up and propel the car forward. I think that’s where you walk the fine line of balancing the amount of energy you’re putting through the wheels and the amount of traction you have. Obviously if you have more energy then you have the ability to control the traction you’re going to spin the wheels. I think that’s probably a key part in racing is finding that balance. The axle twist is another place that you could lose energy. It takes energy to wrap that axle up. If you can keep that from twisting up and force that energy into the wheels again you have more propulsion.

 

[coloradodave]

Axle wrap has a lot to do with traction. Thats why your 8.75 has a pinion snubber to reduce the amount of axle wrap. Another way to reduce axle wrap is with traction bars or cal-trac style setup. It just helps plant the tires. otherwise you are going to spin through the wheel hop of the rear springs unloading the wrap. This is my guess. Others that drag race will have better information.


View attachment 1036594

Picture's upside down...

 

[BeepBeepRR]

Its a picture off a website.. I just linked it. But its just for reference. I downloaded it and flipped it and reposted it.

 

[33 IMP]

A rearend wants to do two things when a lot of power is applied. The nose of the pumpkin wants to tip up, as an opposite reaction to the tires trying to turn forward, which can cause the front segment to go "s" shaped, and cause wheel hop. And the ring gear wants to "climb" the pinion, which means the rearend is trying to unload the passenger side, and add load to the driver side. Mopar dealt with both these reactions, in the design of the track pack springs and the ss springs. Mopar's front sgment of the spring is much shorter than the competition (read naturally stiffer) and they use extra half leaves on the front segment to make it stiffer yet (the long ,soft rear segment provides the soft ride.) Then, to counter the ring gear climb, they have more leaves on the pasenger side than the drivers. Thats why mopars dont need the old slapper bars that the chevy and ford leaf spring cars do.
There is lots more to making a leaf spring work for LOTS of power, however. (And jacking up the rear end, or mounting the rear under the springs is NOT the way to do it!)

 

[BeepBeepRR]

 

[66Satellite47]

Big HP & torque Mopars benefit from a good leaf spring combination. The stiffness of the front half of the leaf makes a major effect on the chassis reaction. With more power the effect of the proper shocks becomes even more important. The specific leaf spring design for a particular car is a bit tough to figure out.

 

[R413]

This will help

 

[MoparLeo]

"you are lined up and punch it" tells me your an up and comer. Good for you. Welcome to a lifelong learning experience and fun hobby.
Race cars don't have to worry about ride quality and going over bumps in the road.
Most street based cars used for racing generally use the springs primarily to setup the height of the rear of the car. The coil spring is the easiest/cheapest way to adjust height and uses up the least amount of room, general wrapped around the shock absorber. Various types of bars are used to control weight transfer, stability. A leaf spring is not the most desirable type of spring for "racing" but that is what we have to work with. Mopar stayed with the rear leaf long after the other 2 major mfgs. went to coils. Most every car and most light duty trucks use coil springs today. Compact, softer riding, easier to service.
Race cars don't make good street cars and vice versa.

 

[tmaleck]

If you can find it, go read the old Direct Connection racing manual. It covers everything from engines to suspensions and and ton of stuff in between.
Anyway, it lists factory and DC parts numbers for performance mods.
In terms of suspension under acceleration, you actually want to see the car come up evenly on all four corners (according to the DC manual). This has the effect of pushing the tires into the pavement, giving more traction. Think of it this way. Imagine the body of the car is fixed and does not move. If the car squats under acceleration, it actually has the effect of lifting the tire off the pavement, reducing traction. In addition to this effect, the other points about axle wrap and wheel hop also come into play. Spring rates, shock valving, pinion angle, weight transfer all factor in as well.

 

[Steve009]

Look up uncle Tony’s garage on YouTube. He does a great video on pinion snubbers. When to use them and when not to. Explains how suspension affects hook up as well and does it in a way that is easy to understand.

 

[33 IMP]

That dudes arm is bigger than my leg! And i'm 6'3, 200

 

[66Satellite47]

Great video.

 

[Yeahrightgreer]

Appreciate the knowledge. Lots of learning occurring. I'm building my '67 Satellite and want to replicate the old school S/S racers of the 80's.

A bit off question - but how does the front suspension relate to the rear during a launch? I know obviously a lot due to weight transfer but I've read that you want approx. 4-5 inches of front end upward travel? Is this to load the rear with a kind of slingshot method? Finally - as awesome as it looks, is the ultimate goal to decrease the amount the front tires pull air?

 

[BLK 68 R/T]

[QUOTE
If so - why don’t you see a car rolling around with 20 leaf springs. (Besides the fact that it would look absolutely silly and be way too high, plus ride like a bulldozer going over boulders[/QUOTE]
Fixed

 

[66Satellite47]

Appreciate the knowledge. Lots of learning occurring. I'm building my '67 Satellite and want to replicate the old school S/S racers of the 80's.

A bit off question - but how does the front suspension relate to the rear during a launch? I know obviously a lot due to weight transfer but I've read that you want approx. 4-5 inches of front end upward travel? Is this to load the rear with a kind of slingshot method? Finally - as awesome as it looks, is the ultimate goal to decrease the amount the front tires pull air?

A really good, consistent working suspension needs both the front and rear setups to work together. The proper amount of rear spring separation to plant the tire, without wasting the movement on upward motion, not forward motion. Rear shock selection is important. Front suspension is the same, generally big wheel stands are going up not forward. If the car carries the front tires about equally (2 to 6 inches) for about a car length or so, that's in the ball park.