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My thoughs on wheel hop.*

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  • My thoughs on wheel hop.*

    SUBMITTED BY PRODARWIN

    Well, I've seen a lot of wheel hop threads lately, so I decided to write up my thoughts on it. Take 'em or leave 'em. Mods feel free to move this to whatever section you feel best.

    Ok, your Saturn has wheel hop, and clearly you are not alone. But before you go spending your hard earned monies on such goodies as the "earthshaker" mount, SDA dogbones, or filly things with 94a poly, do a little thinking. I believe the following misinformation is being spread on the subject of wheel hop: The cause of wheel hop is engine mounts that are too "soft". First of all, the only direct link between your powertrain and suspension is the driveshaft. While it is possible that your engine rocking back and forth could cause this motion, it is highly unlikely. How many rear wheel drive cars do you see cure wheel hop with engine mounts? Despite being RWD, they also have a driveshaft connected directly to the powertrain.

    So how do I fix it?

    There are a few things that contribute to wheel hop, but the basic premise behind all of them is your cars inability to control the up erratic movement of one or both of the front tires during low traction situations. There are several connections in the front suspension where this can come from: LCA bushings, swaybar-cradle bushings, struts, strut mounts, springs, and engine/trans mounts. The first thing you should do if you have wheel hop is check your struts. Why? Struts are direct control of the up and down motion of the wheel. Unlike most components in the front end of the saturn, they provide damping. When a strut is blown, you lose almost all control of over this motion, and regardless of the rest of your suspenion, your wheel will bounce up and down in the fender all day long.

    The next thing to check: Front end bushings. Why? Because as bushings wear, they provide far less gross motion control than in their new form. They also get softer, lowering the wheel hop frequency. Engine mounts also get softer, but pretty much only the TAM mount loses motion control as it wears. Most people don't think about it, but a lot of wheelhop is the result of the wheel moving fore/aft as well as up down. I've experienced this first hand... after I did the auto to manual swap on my 93SW2, you could see the wheels walk forward almost an inch inside the wheel wells. This is with all brand new components up front except swaybar-cradle bushings. Replacing those fixed the problem in a heartbeat.

    Other causes?

    Unsprung weight will magnify all of the above problems. Your saturns factory suspension (and most after market suspension components for that matter), were not designed to control the motion of your 18X8 Chrome plated wheels. Adding a fair amount of unsprung weight puts tons more force on each rubber connection in the front end. And remember, its not just wheels, its balancing weights, tires, rotors, calipers, etc.

    So what about engine mounts?

    I'm not going to say replacing mounts wont help... it will. Be do they need to be hard as a rock? No. Having a super hard engine mount increases the dynamic rate a tremendous amount, resulting in higher wheel hop frequency (if it still occurs), more vibration (and we all know saturn interiors need all the help they can get), and they can also break shit. Believe it or not, the shape and durometer of a stock mount is finely tuned to dampen the motion of the powertrain fairly well. And the less vibration you can feel from your engine... the less vibration reaching your wheels.


    I don't want a shitty interior, but I still want to control engine movement, what should I do?

    My recommendation: Get a 1991 center engine damper setup. Its an air piston incorporated into a mount. It has a static rate of almost zero, but a provides quite a bit of damping, especially at wheel-hop frequencies. You could also make your own very similar setup. Several vehicles use this style damper to control start up vibrations.

    Anything else I can do?

    As I stated earlier, bushing compliance is a big factor... consider poly bushings, or even replacing swaybar to LCA bushings with steel washers. If this fails, or you feel its not enough, lower control arm to cradle ties may be effective.

    Also, learn to drive it without causing hop. A simple change in driving style can easily cure hop. And its free Smile

    Lastly....

    If you are running a drag-tire setup, the above stuff still applies, but it may not eliminate hop completely. Obviously when you double the traction of stock tires, its a whole new ball game. But I can offer this... on a hard launch, allowing you engine mounts to have a lot of travel lessens the impulse of the clutch-dump, having the same effect the a "wrinkle wall" drag tire does. So once again, eliminating all compliance in the front end is not always the best solution. But, these thoughts are purely theoretical... I have never run drag tires.

    Anyways, those are just my thoughts on the matter. Take them or leave them.

    -Travis

    P.S. If you are wonder about credentials... I did spend 2.5 years doing NVH (Noise Vibration and Harshness) development of hydraulic engine mounts and bushings for Goodyear Engineered Products, along with writing a senior thesis on an actively controlled multi-stage damping hydro mount.
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