Coilover Length

[Henney]

I'm going to be running a MSII setup on the front of the '49 I'm building. The current ride height is just about where I want it but leaves very little adjustability in the coilovers. On top of that I wouldn't mind it being just a little lower. My initial thought was to change out the coilovers for 2" shorter ones but talking to Justin at Scotts he says it won't work. He knows more than I do but I'm having a hard time understanding what it'll affect. Can anyone help explain it to me?

Thanks

[PGSigns]

Most the suspension systems are designed with a shock angle and length to get the geometry they are looking for at the design ride height. The length of the shock will set its travel length. If you put a shorter shock in there it could have less travel and end up at a bad angle causing all kinds of issues. With more information about your set up a better solution to your ride height problem other than shorter shocks may be available. An adjustable top mount may be what you need.
Jimmy

[robnolimit]

Swapping to a shorter coil-over is a bad idea. Suspension manufacturers spend a lot of time trying to get the suspension to operate properly in a certain "range" Swapping in a shorter shock will change the range. From here, you could 'over-travel' a ball joint or tie rod end (which could result in a part failure). Also, you will be outside of the 'sweet-spot' for the suspension, and things like bump-steer, camber-gain, and side-scrub will be negatively affected.

When comparing 'ride height' from one set up to another, there are just too many variables to say "about an inch lower than what I got, which is about 5". the best way to go about the whole ride height deal is by comparing the SPINDLE PIN HEIGHT (center of the spindle pin or wheel) to the bottom of the FRAME RAIL (at the axle center line). This takes everything else out of the picture. I can tell you that at RH, our IFS for a 47-54 chev, the spindle CL is 1 3/4" above the bottom of the frame rail. You can move it up/down about a 1/2" and still be in the 'sweet-spot' (so from 1 1/4" to 2 1/4" above the bottom of the rail). Justin (Scotts Hot Rods) can tell you where their IFS will land, and so can many others. Here's a tip. If they can't give you this info, shop somewhere else. Measure your truck now, and compare.

[Henney]

Thanks guys. Follow up question for my own understanding. If the coilover is shortened wouldn't there be less of a chance for over-travel? And wouldn't the geometry still fall inside of the sweet spot with just less travel? Sorry if I'm being dense on this one.

[PGSigns]

The over travel of a ball joint or tie rod end is from the travel of the suspension being out side of its designed range letting the parts bind.
Jimmy

[Henney]

I pulled the manufacture dimensions up to compare them between the two shocks that would be applicable. The current shock is the 13” eye-to-eye shock. The proposed is the 11”. Using the provided dimensions the 11” shock falls outside of the original travel range by 1 5/16”. Is this really that big of a concern? I realize because of the angles it’ll be slightly more at the spindle but not that much.

Conceptually what’s the difference in changing the coilover length to running a bagged system? Bags have a much larger range that guys operate them in? Also, if the tolerances are this tight why is there height adjustment in the coilovers to start with?

[PGSigns]

The adjustment on the coil over to allow the spring to be raised or lowered to get the shock in the middle of the travel. This allows for adjustment based on the spring rate and the actual weight of the vehicle. The amount the spindle will move in relation to the shock is dependent on the ratio of the position of the shock on the lower a arm. The closer it is to the spindle the less change you have. A simple drawing with the lower control arm, the pivot and ball joint and the shock mounts can be used to show the change in the shock angle and the sweep of the A arm.
Jimmy

[Henney]

I 100% agree with what you're saying. But with that we're talking the difference in 1/2" to an 1" that the shorter coilover would travel outside of the original travel window. Is the tolerance really tight enough that this would cause an issue?

[Henney]

any other thoughts on this?

[PGSigns]

It can cause an issue. With out knowing your geometry hard for me to tell you where the issues will be. If the designer of your front end was on the edge of the travel needed with the shock he chose than an inch less travel on the coil over could reduce the travel at the wheel as much as 2 inches or more. That may allow the shock to get bottom or topped out easily while driving. Bottoming out beats up the shock and the mounts and topping out causes the wheel to lift loosing traction or even leaving
the ground.
Jimmy