Power hop problem

[Fahlin Racing]

I have a friend with a Dodge pickup he uses for driving often and pulls in a 'work-truck' class when he competes. When he isn't under the weight of a sled, the truck hops under power during a burnout. Now would it be easier to perhaps stiffen the rear suspension or could we control this with a longer ladder bar set?

Thanks, Jim

[crazyman]

I had a S10 v8 that hopped like a rabbit. I cut the panhard brackets off a Chevette, welded them to the axle and frame, used the Chevette rod, and my wheel hop was gone and ride was greatly improved. His results may vary, but a panhard rod does tighten up the rear of anything, except IRS..

[Fahlin Racing]

Thank you for the input, I will ask him if he would want to go the panhard route. I was going see if Billy Shope's website had some to read on this power hop situation but I can't seem to access it. There is plenty of this power hop with agriculture tractors in the fields though. If you know of any suspension literature or a good website, please do let me know. I haven't found much yet.

[ZIGGY]

I was going see if Billy Shope's website had some to read on this power hop situation but I can't seem to access it.

Shope mentioned in a recent post that he was not able to contact his provider & he might be out of business.

What kind of rear suspension does the truck have?

[Fahlin Racing]

The truck has the basic factory leaf spring and solid axle. Nothing fancy.

[ZIGGY]

I'd bet some of the drag guys will tell you to just clamp the springs and maybe use a pinion snubber, like the old Mopar stockers used to do.

[Bubstr]

Wheel hop is oscillation pure and simple. There are a lot of ways to cure it. Spring wrap up or high anti squat value is usually the cause. Spring / shock values and tire pressure perpetuate it. Since changing IC on a leaf spring is hard, using something to stop the front half of that leaf spring from turning into an S, would be a good start. Some kind of traction bar or clamping would be a good start. MOPAR's with leafs generally have a higher anti squat than needed. Clamp it, snub it and shock it and it will do fine. Clamping both springs in front of axle at each leaf end and right rear behind axle is usually the way to go on them.

[Fahlin Racing]

Alright, sounds fairly easy.

Bubstr, what is your view on ladder bars and power hop. is the condition able to be controlled by changing the length of the ladder bar? I read that brake hop could be settled down with adjust the length of the arm in a swing arm style rear setup, I am just curious as if the ladder bar length would work in the same manner. I haven't dealt with the ladder bar before, or run into a power hop situation so its new to me.

Thanks again!

[Bubstr]

Alright, sounds fairly easy.

Bubstr, what is your view on ladder bars and power hop. is the condition able to be controlled by changing the length of the ladder bar? I read that brake hop could be settled down with adjust the length of the arm in a swing arm style rear setup, I am just curious as if the ladder bar length would work in the same manner. I haven't dealt with the ladder bar before, or run into a power hop situation so its new to me.

Thanks again!

To get to oscillation, (Hop), You need a cause. Most times this is a high instant center, (front of bars or spring mount too high). This not only drives rear contact patch into pavement but also lifts rear, (separation at tire to body). Ideally we would change IC height, but due to body restrictions, I can get hard to do. If the IC is right at 100% You get no separation or compression and this makes your other suspension parts, such as springs and shocks work so much better. Mostly because they have little to do. In these cases, you have to lean on them a bit. Higher spring rates and shock values to suppress the oscillation.

Ladder bars usually have this high IC problem also. You are correct, a longer ladder bar will lower IC. Not only because of length but the farther forward the lower the intersection point is in relationship to center of gravity height at the front axle. This is a line drawn from the rear contact patch, threw the front mounting point and extended to the front axle. At that point if it is higher than the center of gravity height, you have a high IC or anti squat value. This is one of the reasons 4 bars are popular, the seat gets in the way of the left ladder bar on most cars. It takes your adjustabillity away.

There are always more than one way to skin a cat. That is why double adjustable shocks are popular. Get IC as low as you can and suppress oscillation with spring and shock. Ride height can change IC to some extent also. Don't let the kind of suspension scare you, they all can be made to work. They all work off the same Physics. It's just that some are easier to work with. Too bad you can't get into Billy Shope's site. good diagrams and pure basics based on physical law.

[Fahlin Racing]

Thank you very much, great explanation! The truck is a stock 3500, Dodge's pickups tend to have more ground clearance than others which probably is the reason for the problem as far as the Instant Center position.

I have seen some ladder bars with a slot around an inch in length for allowing movement where they fasten to the frame, wouldn't we want a rigid mount for a pivot point? I think this would allow even more room for hop.

[Bubstr]

No need to make this too difficult. What are you willing to do to get it right or just close and what do your rules allow. To optimize your combination may take rebuilding the whole truck. I was under the understanding this was a work truck class? other than reframing and balancing weight out for power and traction, your going to have compromises, or build a real race car. The leaf springs can serve you just as well as a ladder bar, unless your making a ton of horsepower. You have options of lowering truck, with lowering blocks in the rear and softer springs in the front or dropped spindles or both. You can clamp leafs in the front half and the rear half of the right one and install an adjustable snubber, to limit wrap up. If your still getting hop then, it would probably be in the tire side wall. If you don't like clamping Idea, there are a multitude of traction bars, slappers or the adjustable ones.

These are easy fixes. If you was to build an all out race car, would you want to start with a Dodge Truck and tie one hand behind your back to start? That front mounting point on a ladder bar, leaf or 4 bar better be tuff. All the power is pin pointed there at the leave. I don't think I'd like a slot.

[Fahlin Racing]

Yeah, when my friend told me about that slot some other guys have used, I kind of cringed some which I thought was odd. He currently has 48" ladder bars on it thats why I am asking about them. The class is pretty much off the dealer lot with some mods to the engine (havent read the rulebook), supposedly, but a lot of the competiton he rolls against trailers their rigs in when he and a few others actually drive theirs to the pulls. I will mention the clamping of the leafs since that seems to be less labor intensive than adding a leaf. I will mention everything we have conversed about though.

Thanks

[Fahlin Racing]

Finally able to update. My buddy built some 72inch ladder bars and his truck doesn't hop at the start of the pull anymore or unloaded. He is pulling consistently high 200s now every event he goes too. He actually placed first earlier this week too. Thanks for the help!