[Tim Corcoran]

I want to fine tune ride height and extension and rebound rate. I would like to know about using coil overs with double adjustable shocks on a 65 LeMans bracket car. I would like to hear from anyone who has done this and which ones you would recommend. Thanks

[firechickenman]

Look into the Viking hybrid coilover system. The upper end of the spring seats in the OE spring seat. Lower end of the spring sits on the adjustable shock collars. I have the double adjustable Crusaders on my Firebird and they are great street and strip!

[HWYSTR455]

Just to say it out loud, 'technically', you shouldn't adjust ride height using the spring preload. You should be adjusting the spring preload to make the travel of the piston centered on the shaft.

In other words, you want the shock to be roughly in the middle of the travel at rest, and it should reach the end of the shock travel at either end.

If you have it centered properly, and it is bottoming out, then you need more spring rate, and visa-versa.

That technically how it should be with conventional coil springs as well.

The effect of it bottoming or slamming the extension, is it destroys the shock.

If you can't get it centered and the spring is correct for the app, you need either a longer or shorter stroke shock.

To calculate, you can mock up the control arms without a shock/spring, cycle the suspension in both direction, measure the total travel, and go from there. Make sure you have both upper and lower bump stops in place when doing so.

At rest, you can measure the distance from the lower bump stop to the contact point for a compression measurement distance.

(if you get what I'm trying to say)

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[HWYSTR455]

Interesting, there are calculators online to determine optimal shock length:

https://calculator.academy/shock-length-calculator/

I just found that, there may be better ones out there, just posted that one as an example.

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[HWYSTR455]

Here is the how-to from QA1:

https://qa1.net/resources/how-to-mea...custom-shocks/

That's probably an accurate method for this particular conversation.

Front/rear weight of vehicle is needed to properly provide info when selecting springs.

The shock itself in an app with a vendor that offers control arms usually have specs for free travel of certain makes/models to determine shock lengths.


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[Tim Corcoran]

Thanks for the info, I guess I need to weigh the car

[HWYSTR455]

A local truck scale works for front/rear weighing, many are self-serve, drive up, and unmanned.

Cat Scales is a nationwide scaling company with a locator service to weight anything, you can punch in your zip code to find the closest:

https://catscale.com/cat-scale-locator/

They also have phone apps to locate scales, and give step by step instructions. It's pretty easy.

They are surprisingly accurate. Basically, there are 3 pad sections you drive on to, and just position you front tires on one, rear tires on the next. Some have a ATM style walk-up, swipe a card, and it prints you a readout. I think when I did my car it was like $15.

Here's the readout from my GTO. And yes, it's a porker!

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[HWYSTR455]

You can look around for a 4-corner scale place, many chassis shops have scales, and 4-corner is the best. You can actually dial a chassis in per-corner that way.

You can load weights on the front seat to mimic you being in the car, too.

Don't forget to calc weight of gas, try to go with a full tank.

With 4-corner weights, you can load sway bar ends, change shock valving, and springs rates to get it perfect, but usually close is 'good enough'.

Keep in mind most 4-corner scale pads have a max load of 1000lbs each. So if you suspect you are over that, you are basically left with going to a truck scale.

You can start at a truck scale to get your total weight, and then determine if you want to do a 4-corner or not.

As a note, 90% of all the vendors that offer springs are not going to recommend rates very accurately, they are lazy and just give you a choice of 3 or 4 rates. That way they don't have to order/stock as many. And, sadly, they are generally SBC-type recommendations.


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[KGTO]

Back when I was racing my 65 I switch to QA1 double adjustable coil overs and was very happy in how much I could control the hit. Not only for the front, but also the rebound on the rear. It gave me a wide range of adjustments for different tracks with just a turn of a knob. It launched pretty violently (ladder bar) , and I did scale the car at the time too. I think you'd get the best results using them on all four corners.