3-Link Wheel Hop in 1st Gear

[silver_pilate]

First let me say that the car is driving better than ever. I did some adjustments to the front end and it's tracking great when cruising. And for most spirited and casual driving, it's great.

I took my son out for a drive around dusk and we were trying things out on a wide open stretch of country asphault with not a car in sight. The tires had been warmed up with a quick donut or two in an empty lot, so they were a bit stickier than normal. We tried a few hard launches and had some violent wheel hop in first gear as the tires tried to grab. It was really shaking the windshield. I only tried it twice because I didn't want to break anything with the shaking.

This is the only time I've noticed any wheel hop in the car and it only happens in first with purposeful hard launches, like you would at the drag strip. The pinion angle has been set and rechecked after some miles and it's set at around 1.5 degrees down.

Should I increase the angle a bit closer to 2 degrees, would that help or make things worse? Any other thoughts, or should I just try for more consistent traction on an actual track before I expect it to launch like it's on an actual track? ;)

I've not much experience when it comes to suspension setup, so talk to me like I'm a slow 7th grader :D

By the way, here is a picture I snapped from a nearly identical evening drive we took last week:

https://i.imgur.com/W3Z8GRl.jpg

[Jeff Kleiner]

You have two options for installing the lower control arms to the axle. Using the upper set of holes will provide a little more bite and the lowers will result in better handling. There's always a trade off.

Jeff

[Gordon Levy]

The other option is to replace the bushinged lrca's with a set of my double hyme jointed ones.

[silver_pilate]

I set up the LRCAs in the lower hole on the axle mount as that was what FFR suggested in the manual would give more traction. Do you think it's worth switching to the upper hole on a street driven car?

Gordon, once things settle down, I may give your hyme jointed arms a try since they seem like they would take care of any binding.

[Gordon Levy]

No, I don't see any advantage in switching the mounting.

[GFX2043mtu]

Your rear end lower control arms have rubber bushings in them and regardless of the duromete they flex and squish under hard acceleration. What happens is they can compress and uncompress when the tires break traction and the process repeats quickly giving you a shuttering or slamming (wheel hop). This is much like when a leaf spring muscle car twists the leaf springs into an “S” and the same process occurs but more violently. The best option is to eliminate the bushings completely and use hyme jointed lower control arms. These are solid joints that can’t compress. Because of this, these will eliminate the hop issue while correcting or improving other issues. These issues include, roll binding and thrust angle corrections if needed. The solid non flexing joints will also make the car track like an arrow, wheels spinning or not when set up right. Lastly the rear hole options will offer little improvement of your issue. Not that I’m one to be negative or spend other people’s money but, if you want this issue gone completely and better tracking under load spend the $250 and don’t look back.

[FLPBFoot]

Agree. A good use of $250. I had a thrust angle issue that these took care of and the ride even seems to be a bit smoother with the hyme jointed arms.

[GoDadGo]

Spohn makes some killer lower control arms for our applications.
I had some custom lowers made by the guys at Spohn so that I could shorten my wheelbase and now they offer adjustable versions.

An added plus is that their Del-Sphere Joints Are Rebuildable.

https://www.spohn.net/shop/Factory-Five-Racing-MK3-MK4-Roadster/Adjustable-Rear-Lower-Control-Arms-with-Del-Sphere-Pivot-Joints.html

Note:.. I shortened the wheelbase to better center the rear wheels within the wheel well arches:

https://youtu.be/uLmHEoWTEHg

[Gordon Levy]

The issue with the arms linked is they are still mounted at an angle in the car which is far from ideal. Ours installed and almost straight in the car which adds a lot to handling and feel.

[GoDadGo]

The issue with the arms linked is they are still mounted at an angle in the car which is far from ideal. Ours installed and almost straight in the car which adds a lot to handling and feel.

Great Information To Know!

..I'll likely move my spacers around to square things up!

[GFX2043mtu]

Levy has a good point, and is completely correct. The angled rear arms on the FFR come from the mustang design. The design used angled arms to latterly locate the rear end in place of a panhard bar. Great for cost, bad for control due to roll binding and deforming bushings due to the geometry inherent in the design. We use a panhard bar or potentially for some watkins linkage in our cars. Because of this we can run links that are Parallel to the chassis. This should be considered when purchasing this type of upgrade.

[BEAR-AvHistory]

Was a alpha tester for the Sphon bars, provided the initial measurements of the stock FFR bars. Have not had a wheel hop issue with NITTO 555R tires.

https://thefactoryfiveforum.com/attachment.php?attachmentid=125354&d=1585678415

BTW still have the unused FFR round tube bars in the box if anyone wants to make an offer.

[Todd Baumann]

Start with adding in another .5° so you are closer to or around 2° down total before you spend any money.
The only thing you will need to watch out for is that your driveshaft can go into a bind when unloading the suspension.
If that happens then just back it off a little less. If that doesn't work for you then you can go and purchase arms like
Gordon's or Breeze's where you can adjust the length on them.

[NAZ]

There are many things that contribute to wheel hop but when you break it down you are simply intermittently loosing traction. The tire bites and then loses bite in an oscillating manner which tends to bounce the tire like a basket ball. But then you knew that.

Since your FFR 3-link is based on a Mustang 4-link (the LCAs are still mounted the same inefficient way as came from Ford) the primary contributor typically is the flex in the elastomer bushings on the LCA -- as mentioned above. Your UCA should be made with heim joints which will not flex. The first change you should make is to replace the LCAs with ones that either used heim joints or Johnny Joints, a type of rebuildable non-flexing joint. I expect that will take care of your problem and also eliminate the need to add downward pinion angle. The reason we run the pinion angle a couple degrees down (at front) is as the torque is applied to the axle the pinion gear wants to climb the ring gear and this applies a rotational force on the axle housing and the elastomer bushings allow a couple degrees of rotation. But the non-flexible heim joints don't flex, therefore, the axle housing is not allowed to rotate. So, you will need to readjust your pinion angle this time to match your trans output shaft angle.



Now, here’s some other things that can contribute to wheel hop:

· * Hard tire compound – either aged or simply a higher treadwear rating.

· * Too much air pressure (most folks will run way too much air pressure in the tires on these light cars. I run 15 PSI in my radial street tires and 8-10 PSI in my drag slicks – yours may be different but the optimum pressure will be much lower than what’s marked on the sidewall and based on obtaining an even heat across the tread after driving 4-5 miles on the freeway).

· * Not enough weight transfer to the rear:
o Too little anti-squat.
o Too much rebound damping on the front shocks.
o Too much bump damping on the rear shocks.
o Not enough static weight to rear over the axle.

· * Hitting the tire too hard at launch:
o Less launch RPM.
o Move instant center closer to the center of gravity. Note: this will require some fabrication effort and if you go this far you might as well correct all the other deficiencies in the Mustang design that limit traction and cause poor handling. If you don't have the knowledge and skill to pull this off yourself there are many shops across the country that can.