Shock Travel Mounting Placement

[Wbulk]

Let's say you are using a shock that has 1.5" of shock travel which results in 3.25" of wheel travel. You are trying to determine the upper mount location. Should the shock be located in the center of travel at ride height, for 50% up and 50% down travel? Or should the travel for a Cobra be 60% up (compression) and 40% down.

Opinions?

Wayne

[Richard Hudgins]

Wayne,

I would go with 60% Bump and 40% rebound.

Depending on your wheel rate the 3.25 total travel might not be enough.

2.5>3 inches bump is the minimum I would design to for a road car.

A 1.5 stroke damper is going to be hard to valve correctly as well since

shaft acceleration and velocity is going to be quite high.

[Wbulk]

Richard,
Are you suggesting that I go with another shock? The most total wheel travel I have is just about 4.5 inches without rubbing the fender or putting the ball joints in a bind at full droop.

Wayne

[strictlypersonl]

I'm with Richard. 3.25" is too little for total wheel travel unless you're using very high (track only) spring rates. Where did you get a shock with only 1.5" of travel? Is there a bump stop built in?

I would mount a shock to limit travel to eliminate ball-joint bind at full droop but allow at least 2.5" jounce travel from ride height. The ERA has 3.5" jounce travel and 3.25" droop travel at normal ride height. That allows those who like their car really low to retain reasonable travel when the car is "non-standard". Which seems to be the standard.

(Tomorrow I'm going to get a call: "Bob! Just how low can I make it?" )

[Wbulk]

It's a QA1 ALN3855P. Yes it does have a built in bump stop.

Thanks.
wayne

[strictlypersonl]

The ALN3855P has a 2 5/8" stroke, which is somewhat better than the originally stated 1.5". Now the question is what is the wheel travel resulting from the full stroke of the shock? Was 3.25" calculated or measured?

Is this shock for the front or rear suspension?

[Wbulk]

The specs on the shocks do show about 2 5/8" but you have to subtract the 1 1/4" bump stop, so actual travel really is about 1.5". The total wheel travel was measured. With the shock disconnected I have just about 4.5" travel from not quit rubbing to ball joints hitting.
The shock is for the front.

Wayne

[strictlypersonl]

You'd be surprised at how much those rubber bumpers can be compressed.

For any further analysis, we'd need some more information. (Illustration at ride height.)

[Clois Harlan]

Wayne,

These guys are two of the best with information regarding suspension travel and set up. Both have helped me on other issues in the past. Good luck and as you know I am following your build pretty close. Wayne show them some of your pictures, I think that would help a lot.

[Wbulk]

I will get those measurement this morning.

Thanks.
Wayne

[Wbulk]

I did a little testing on the rubber bumpers without the spring installed and sure enough that thing compresses to the point where I had to stop or I thought it would split. I don't know how you would calculate for that with travel. But if you hit it often it would be destroyed.

Measurements:
The Lower A arm pivot point to balljoint center is 12.87" and it is 4 deg. down on the outside at ride height.

The lower A arm pivot point to shock mount is 7.87".

The shock it presently at 15 deg. with the angle between the A arm and the shock = 19 deg.

I believe the intention would be to relocate the upper mount and use shock QA1 4855B.
It is 10.130 compressed and 14.25 extended. Then subtracting whatever for the bump stop that is about 1.25".

The other measurements are:
1. I would like ride height to be at 27" from ground to lip of the fender.

2. At just about 25.5" to lip of the fender the tire is just about as high as it can go without rubbing. That is without a load on the tire with spring removed. That may bring it to 25" with weight on the tire. But then there's that bump stop.

3. At 30" from lip of fender to the ground the ball joints hit.

So which way do you figure it from? Do you set it at from the bottom up, say 29.5", and so it doesn't hit the ball joints? Or do you set it from the top most compression and and let the extra shock on the down side and then maybe add a droop stop under an upper A arm so you don't damage the ball joints.

Wayne

[strictlypersonl]

This is my approximate recommendation for a workable suspension with your shocks. If the tire hits, then frankly I would say you have a wheel-offset problem that should be corrected.

Damper installed length at ride height is 12.7" at the original angle.

[Wbulk]

Thank you very much. May I ask would this set up use the shock as the droop stop to keep the ball joints from hitting at full droop, or would a stop have to be added under one of the upper arms.

Wayne

[strictlypersonl]

Frankly your measurements got so complicated, I didn't check the rebound bind within my limited timeframe. You'll have to test whether this setup stops the interference. If you need to move the upper shock mount up to do it, that's a good thing: It gives you more upward travel.

My design was optimized for suspension travel, not mechanical limitations.

[Wbulk]

I will test it out.

Thanks again.

[Richard Hudgins]

Originally Posted by Wbulk

Thank you very much. May I ask would this set up use the shock as the droop stop to keep the ball joints from hitting at full droop, or would a stop have to be added under one of the upper arms.

Wayne

Wayne,

Dampers are not designed or built to act as droop stops. You can damage the piston and the top of damper body.

Always use a droop stop.

[Wbulk]

Richard,
I went over the calculations that "strictlysersonl" gave me and it appears like there is more shock travel with this shock than the suspension has. I was thinking that I might as well set this up with the suspension at full droop and the shock fully extended minus say .37", or at 13.88" QA1 ALN4855B, that way the shock would stop the suspension from hitting the ball joints at full droop. I would have plently of travel on the compression (top end) side. I may end up rubbing the body on a really hard bump though.

Are you saying the shock fully extended should not be used to limit the suspension? Are we talking apples?

Wayne

[Richard Hudgins]

Originally Posted by Wbulk

Richard,
I went over the calculations that "strictlysersonl" gave me and it appears like there is more shock travel with this shock than the suspension has. I was thinking that I might as well set this up with the suspension at full droop and the shock fully extended minus say .37", or at 13.88" QA1 ALN4855B, that way the shock would stop the suspension from hitting the ball joints at full droop. I would have plently of travel on the compression (top end) side. I may end up rubbing the body on a really hard bump though.

Are you saying the shock fully extended should not be used to limit the suspension? Are we talking apples?

Wayne

Wayne,

Correct. You should never use the damper (Shock) as a droop stop. You can easily damage the piston, the shaft, the "O" ring seal, and the valving from piston top impact with the damper body top nut.

[Wbulk]

Richard,
Would you have any pictures of how it should be done by chance. My suspension is a basic Mustang II clone. Tubular A arms with coil overs.

Wayne