wheel hop durring Acceleration

[T.B]

Looking for some help to get rid of wheel hop during acceleration. I think its caused from the rear moving forward, normally fixed by swapping to a stiffer bushing or heim joints (witch i think this is my problem that the heim joints are bad). It's a 1971 Camaro with a g-bar that we made are own upper and lower links with heim joints. would i be better to try a jonny joint are one of the spohn joints? Are can there be another problem im not getting?

[exwestracer]

Did you just build the links, or design the whole system? I'm asking because I'm wondering about geometry. Has it always had wheel hop since you put it in, or is this something that just "happened"?

Unless you can reach under there and move the links around by hand, I wouldn't condemn the heims JUST yet...they usually don't allow wheel hop until they are worn out.

[T.B]

YES i just built the links it started out as a tri- 4link from air ride or chassis works but i think air ride designed it, and when chassis works took it over they just added a set of vari-shocks instead of air bags. No the wheel hop just started. The car only has about 800 miles and 2 track days. i thought the heims would last longer than that. o and i did just change spring rates i went up to a 200lb spring from 175lb but i don't think that would cause the problem.

[exwestracer]

...duplicate

[exwestracer]

Tim, did you reset the ride height when you changed springs, or is the rear sitting higher now? Did the wheel hop start at the same time?

I never assume ANYTHING will or won't cause a problem...

Can you "rattle" the suspension links by hand?

[Bryce]

If you raised the rear of the car with the new stiffer springs you would have changed your IC and A/S.

What kind of rod ends did you buy. I would recommend the chromoly with teflon kevlar race. I am running those on the front of my falcon and I have no wear issues after 2.5 years. I am using the same on my 3-link in the back I only have about 100 miles but no wear issues either. Also I have no wheel hop and 225 pound springs.

[T.B]

Yes I did raise the car by 1/2" or so with the new spring's it was lower in the back than the front, now it's level.

No I can't rattle the rods. Yes the first time I noticed it was after the springs were changed, but it was a few 100 miles after we changed them.

[exwestracer]

Yes I did raise the car by 1/2" or so with the new spring's it was lower in the back than the front, now it's level.

No I can't rattle the rods. Yes the first time I noticed it was after the springs were changed, but it was a few 100 miles after we changed them.

This is the setup we are talking about, right?


With that short of an effective upper link, the IC will be very sensitive to ride height changes, as Bryce mentioned. I would put the rear axle on stands (weight on axle and car level to floor), and measure the distance from the upper mounts on the axle and frame down to the floor. The height number itself doesn't matter, but if the frame mounts are equal or higher than the axle mounts, the car will be very prone to wheel hop. <This is a gross over-simplification of a complex calculation, but I would start there. If the car has adjustable shocks, also make sure one of the adjusters didn't get backed off all the way somehow. About the only other thing I can think of that would cause this problem is a dead shock; and even so, correct geometry should eliminate it.

[T.B]

Yes very simular.Thanks Ray i will give that a shot.

[T.B]

Thanks for the info guy's the frame mounts are equal on one side and a slight higher on the other. Is there a magic number i need to be at with the upper links between the axle and frame mount? the lower links are equal.

[exwestracer]

Thanks for the info guy's the frame mounts are equal on one side and a slight higher on the other. Is there a magic number i need to be at with the upper links between the axle and frame mount? the lower links are equal.

Ok, here's where it starts to get complicated... With the lower links level, you are technically at the "correct" ride height. With the top links level (I'd try to figure out why they are different, too...), you have NO instant center, and therefore no anti-squat on launch.



The more down angle you get in the upper links, the harder it will plant the tires under acceleration. Now, how you get them there is another story...and it IS possible to go too far on a street car.

[Bryce]

This is a general statement which may apply to your set as well.

With a stiffer spring you will need a stiffer shock, otherwise this becomes an underdamped system, which can lead to oscillation or wheel hop in your case.

A tire with too little air pressure can also lead to a oscillation and eventually wheel hop.

In your case: can you please measure all the link pivot points left and right and post up, with your weight in the drivers seat. Ray or myself can run them through a suspension calculator and tell you the A/S.

1) lower links should be horizontal
2) the upper should point slightly down towards the front of the car.
3) the rear end should be centered and the links should be centered in the car aswell
4) the lower links should be parallel to the car's longitudal centerline
5) the upper links should have an equal angle to the axle centerline.
6) both sides should be the same with your weight in the drivers seat.

[exwestracer]

I do think the problem is ride height related (if only because it didn't appear until you raised the car with the stiffer springs); however, be sure to check all the items Bryce mentioned, as well as the shock adjusters for correct settings.

[T.B]

Thanks Bryce and ray I will check all the dim tomorrow and post them. I'm going to re fab the upper frame mounts to fix the passenger side being a little off. And It would be nice to see were I'm at before having it all welded up.

[T.B]

Here's A quick sketch on were I was able to get at with a few mod's. I can get more angle down in the uppers if needed.

Attachment 53053

[Norm Peterson]

Do you have the elevations of those pivot points and a rear tire size? I'm guessing that the uppers are at about 3" above the axle centerline and that the lowers are at 4", maybe 5" below, with about a 13" tire loaded radius.

What I am seeing is that starting from a relatively low amount of anti-squat with the previous springs, you lost about 1/3 of that just from the 1/2" ride height change. Your IC is probably way out around 10 feet ahead of the front axle line.

A rough plot of your anti-squat (rough because I am working from at least 3 guesses here) is suggesting that the antisquat increases rather rapidly as ride height is lowered (it gains over 20% inside the first inch of squat). I'm not sure what that's trying to tell me, but it's a lot higher rate of A/S change around the static ride height than I'm used to seeing with either OE triangulated 4-link or 3 link arrangements. Definitely a function of those short uppers and their length relative to the length of the lowers. Roll steer looks minimal, though.


FWIW, at ±20° plan view skew (I think that's what I'm seeing), if the rod ends in the uppers were fried badly enough to cause the hop all by themselves, the axle would probably be moving around laterally enough to make the car feel a bit woozy.


Norm

[T.B]

Hi Norm, the uppers are 4 3/4" up from the center line of axle and 4 1/2" back of the center line
the lowers are 5" down from center line and 1/4" back from the center line.rear tire size is a 335-30-18 witch i think would be around 26" dia.

thanks

[exwestracer]

According to your drawing, your IC is out at about the front axle centerline and about 8" above ground...WAY below the neutral line.

On a typical 110" car, the neutral line would fall somewhere about 50" ahead of the rear axle C/L at that height.

[Norm Peterson]

. . . 4 1/2" back of the center line

??? (doesn't appear to agree with the earlier sketch).

If the '4' isn't there, A/S is under 15%. Might be a little higher if the '4' is and the length is still 9-7/8", but not by much. No matter where the UCAs start, 2° down angle from there isn't much at all, and it takes quite a distance to converge with the LCA line in side view.


Norm

[ochohill]

This is the setup we are talking about, right?


With that short of an effective upper link, the IC will be very sensitive to ride height changes, as Bryce mentioned. I would put the rear axle on stands (weight on axle and car level to floor), and measure the distance from the upper mounts on the axle and frame down to the floor. The height number itself doesn't matter, but if the frame mounts are equal or higher than the axle mounts, the car will be very prone to wheel hop. <This is a gross over-simplification of a complex calculation, but I would start there. If the car has adjustable shocks, also make sure one of the adjusters didn't get backed off all the way somehow. About the only other thing I can think of that would cause this problem is a dead shock; and even so, correct geometry should eliminate it.

Is there anything wrong with the 2 upper arms being all heim joints in this design?