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High speed bobbing



I've been to Willow Springs several times and have now gotten to the point of well, fear on turn 8. I am at approx 120 mph and the front end is bobbing considerably. I've got the stiffest springs John offers up front and Koni's.

I am afraid I may not have the shocks set to the harshest setting (firmest). How will I know I have set them correctly?

If I have, is there something else I can do to help the bobbing?


What shocks?

What is your front setup?

Alignment settings?


my front shocks. They are Koni reds and I believe I have adjusted them for the firmest setting.

Regarding alignment specs, here ya go.

Camber: - 3 degrees on both sides
Caster: +2 degrees
Toe: 1/8" IN


Well, compare my setup to yours.

620 springs (560# actual)
1 1/8" solid sway bar
Adj strut rods
Stock upper & lower control arms
ORP dbl roller spring perches
ORP camber adj set
ORP roller bearing idler arm
Quick steer kit
Flaming River close ratio steering box
Koni Reds mid setting
I have the rubber gasket on top of the rad support to seal at the hood
Stock drag link, pitman arm, crossmember and tie rods
12" Lincoln big brakes
Cooling ducts

Rear setup is:
4.5 mid eye leafs (175#) with poly bushings
Panhard bar
Koni Reds, set to medium
9" rear, drum brakes and 4.11 gears

Alignment settings are:
+2.5 Caster
-2.5 Camber
+3/16" Toe out
I have not experienced anything like what you are describing. Alignment settings don't seem out of whack. At what speed does it start "bobbing"? I've run mine up to 127 so far at PIR and it was OK. That was on street rubber too! My gearing and tire size now limits me to 118.


Active Member
Sorry I got here late. I would say it's the shocks that are giving you that bobbing or porpoising. It wouldn't be the springs or suspension pieces since you have roller parts. We do have customers call us about the cars porpoising and it is corrected with a stiffer shock. Your Koni's may be worn. I too have never had that happen on any of our cars and we run it the 130mph range a lot.


My Koni's have less than 12 months on them and less than 2 open track sessions. If the shocks are the culprit, maybe it is due to them being set too soft.

When I am at Knotts, maybe I can take someone with some knowledge out for a spin. 8^)

It also might be a combination of the track and the car. At 120 mph, it does not take much to get things moving....