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iTrader: (3)

In my readings about wheel hop, I've noticed that there are some variations in peoples' stories. Specifically, the part that solved their problem (LCA's, shocks, poly tranny mounts, etc.) and the situations in which they experienced wheel hop varied (high traction and low traction situations). After a great deal of thought, I've come up with a conceptual theory about this, and I'd like to hear what you experts think about it (since I'm a total newbie and may be just talking out of my ***).

It would seem that there are three links in the system of getting the energy from the wheels to the car. First, the tires must keep traction and hook up to the cement in order to transfer the energy to the axle. Second, the suspension must be strong enough and stiff enough to transfer the energy from the axle to the chasis. Finally, the energy transfered through the suspension must be great enough to overpower the inertia of the car.

First, let's consider the individuals who do not experience wheel hop even in a high-traction situation. In the first link (tire traction), they have a great deal of capability to transfer energy. Therefore, the suspension (mainly the LCAs) has to be able to transfer that large amount of energy to the chasis. As the axle tries to move forward, the LCAs push down on the axle and remain firm enough to transfer all the energy to the chasis, which then moves the car.

Now, let's look at someone who does experience wheel hop in a high-traction situation, but not in a low-traction situation. When they have good traction, again, there is a large amount of energy to transfer to the chasis. However, in this situation, the LCAs are not up to the task and they absorb energy rather than transfering it by flexing and failing to plant the wheels on the ground. This only happens in a high-traction situation, though, because in a low-traction situation they will not be overpowered before the tire traction is overpowered. Thus, in a low-traction situation the car will spin its tires (as they are the weakest link in the chain) before the wheels will hop (because the LCAs can overpower the tire traction).

Alright, what if you have wheel hop when you do not have good traction, but you don't have wheel hop when traction is good? When traction is good the axle tried to force itself forward, the adequately-firm LCAs force the axle down to the ground and transfer the power appropriately to the chasis. But, what if traction is not so good? At this point the axle is not forced forward very hard, and thus the LCAs do not force the axle down. The wheels hop. But why didn't they hop in the above cases when traction was poor? The shocks. If the axle isn't lunging forward due to high traction then the LCAs are not planting it downward in reaction. The only thing to hold the wheels down now is the shocks and springs (which basically just means the shocks).


Cliff's Notes: I'm theorizing that if you get wheel hop only in high-traction situations, then your LCAs are not doing their job either because they are weak or because they are not angled properly. I'm also theorizing that if you get wheel hop only in low-traction situations that your issue lies in the shocks, as the LCAs will not force the wheels down as hard in a low-traction scenario.



Again, I'm not saying this is definitely true. I'm just kinda thinking out loud. Like the title says, what do you guys think?

BRENTT94Z

iTrader: (3)

Good Theory!
I have a low traction wheel hop right now. Im running Nitto Drags 315-35-17's. Before I swapped back to stock suspension and the new homemade control arms, I had great traction. Now I have a nasty wheel hop. The shocks im using are QA1 adj, behind a T56 and 12bolt 4.11 gears. Only thing Im thinking thats left to check is the drop down bracket. Now that the car sets higher, Ive changed the angle of the control arm due to the drop down bracket. The control arms I had on the car before had poly bushings and were made by SPOHN. The ones I have now are much stouter but have no give like the old poly bushings. I made them double adjustable. Each end are mounted by rod ends.
Any Ideas?
Brentt

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iTrader: (3)

Maybe my theory isn't so great. If it were right, then your problem would be somehow related to your shocks. It just seemed to me that if you have low traction (and thus, low amounts of force forward against the LCAs), the LCAs wouldn't push down much, and then you're basically relying on the shocks to keep the wheels down. *shrug* I'd be interested to see what others have to say.

BRENTT94Z

iTrader: (3)

That being the case, and now that I have the weaker stock spring, maybe I should adjust my shocks to a stiffer ride.

jimmyblue

iTrader: (11)

Here are my opinions on the theory...

LCAs do not push down. They push forward, but from an
offset position so the axle wants to rotate top-forward
and crawl over the end. The torque arm snubs this rotation.
Where better LCAs play, is in maintaining a stiff and consistent
geometry. If the arms bow or flex (as the stock stampings
might) the rear geometry can change jerkily.

The instant center of the 3-link system can be adjusted so
that the axle torque reactions drive the axle downward. The
stock setup is a pretty neutral compromise, I think it is a
little too biased toward traction lift (so as to absolutely
avoid brake hop). Acceleration hop and brake hop are
your two "walls" but brake hop is where you get lawsuits.
Anyway, with a hard torque arm mount your acceleration-
hop and brake-hop are coupled. Separating things so you
have a torque arm that binds on acceleration only, and
another that binds on braking only, can let you separate
them but that's for crazed enthusiasts.

LCAs or a torque arm that flex and store energy can be
a source of bunching-up-and-releasing, wheel hop. But
I believe it's usually another mechanism.

When you push torque through the axle you have several
torque reactions. You have the wheel torque, LCA pitch,
torque arm snub going on. You also have axle roll in reaction
to the driveshaft torque. This is what makes the right tire
want to lift and the left tire plant (roll CCW). If you can
balance the LCA pitch reaction to counter the driveshaft
roll (ideally, overcome it) then you will get a tire that plants
harder, the more you drive it. This is good.

If your LCA pitch down force (let alone up-force, ick) is
less than the driveshaft roll up-force then every time the
tire sticks well, the force goes into lifting it (net). This is
where you can get an oscillatory sequence going (stick,
lift, unstick, drop, stick....). A weak LCA that lets the
LCA down-force wimp out, is bad. A weak TA that lets
the axle rotate rather than push down, is bad. You can
offset the geometry more to the good by LCA relocation
brackets but they will only help you to a degree, against
bungee parts elsewhere. Same for each of the other bits.
Weakest link, etc.

I'm a little bit suspicious that the Torsen plays in this too,
I have an upgraded one (T-2R) and it's great but at its
bias limits I do get some bang, bang, bang. I think it's a bit
laggy in throwing the bias around and lag in a feedback loop
makes oscillation.

DONAIMIAN

iTrader: (18)

i have the poly tranny and tq arm mount and bilstiens and a pro kit and control arms nd relocation brackets. Only thing left to do is tq arm, hopefully that will help me end this.

BADZ

iTrader: (5)

I did my lca's and phr and it helped quite a bit with the stiffness to the 12 bolt, then the adj big sway bar, shocks, adj big tq arm and fine tuning it and 750hp to boot. Then the consistent low 1.30's 60ft's were there... Its killer when the car rides a small wheelie out of the gate 80ft out....

Any give or flex from rubber bushings will allow wheel hop...

John_D.

iTrader: (2)

Agreed, the lca's don't push the axle up or down directly. The angle will lift or lower the car though. And the opposite reaction will plant or lift the axle.

If the lca's are angled down (standing at the rear of the car looking forward), on launch the lca's will try to push the rear of the car down. That "squat" looks like it would give you traction, but it takes downforce off the axle.
(and it wastes some energy compressing the rear springs)

So with downward angled lca's, I think shocks could make a big difference in managing hop. Springs/sway bars maybe.

With straight lca's, I think lca bushing "give" is where hop comes in. Not flex in the metal.

A soft or torn torque arm mount can let the diff housing wrap up and unwrap repeatedly, regardless of lca angle.

BRENTT94Z

iTrader: (3)

I did forget to mention, I dont even have a sway bar on the rear. Ever since I installed the 12bolt, It required a bigger tubing clamp and I didnt think the sway bar in the rear would effect the traction, only handling. Can anyone explain the logic to the reason you need a sb for the rear to have better traction?