How do you measure for coil overs?

[Over2tonsoffun]

I am looking to do coil overs on my new project. Viking has them for the front but not the rear. So I figure to use a set of universals ( if there is such a thing) for the rear. Only problem is how do I know which length to get. What measurement do I use, The factory coil, the shock, other????

Thanks
Tim

[Tim john---]

Perhaps reach out to one of the manufacturers of the brand you intend to use, ask them how to determine accurate measurements for their particular brand/model.

Tim john---

[David Pozzi]

Each shock has a manufacturers recommended installed length/height.
Shocks with limited travel have less ability to vary ride height without topping out or bottoming, so I prefer a shock with 5.5" to 6" travel on the rear if possible. If I want to raise or lower the rear 1" the longer shocks will allow that. If buying a rear suspension kit, the mfr will have a suggested shock length at ride height. Just make sure his design ride height is close to what you want to run your car at.
OR:
Set your car at it's desired ride height and pick a shock that fits that space. Assuming you have shock mounts in place to measure from.

Once you know the shock length at ride height you can pick a coil to fit it. Estimate the load on the coil and how much it will compress and pick a length that will still allow adjustment room up or down. A first or second gen Camaro will have about 800 to 850 lbs on the rear wheels. The weight of the wheels, tires, brakes, and axle housing are all un-sprung weight so subtract that. It's about 175 lbs per side on the rear, so 850 minus 175 = 675 lbs load on the coil. A 300 lb/inch coil will compress 2.25" so a 10" coil will compress to 7.75". 300lb/inch divided by 650 = 2.25" compression, 10" - 2.25" = 7.75". There are shock motion ratios that throw that calculation off, but on a leaf spring, 3 or 4 link suspension, it won't change much. I like to run a 10" coil and jack up the spring perch a bit to set ride height. Then to remove the spring, I can take the shock loose and unscrew the spring perch enough to get the upper spring seat off without having to compress it with a tool.

[Rod P]

Originally Posted by David Pozzi

Each shock has a manufacturers recommended installed length/height.
Shocks with limited travel have less ability to vary ride height without topping out or bottoming, so I prefer a shock with 5.5" to 6" travel on the rear if possible. If I want to raise or lower the rear 1" the longer shocks will allow that. If buying a rear kit, the mfr will have a suggested shock length at ride height. Just make sure his design ride height is close to what you want to run your car at.
OR:
Set your car at it's desired ride height and pick a shock that fits that space. Assuming you have shock mounts in place to measure from.

Once you know the shock length at ride height you can pick a coil to fit it. Estimate the load on the coil and how much it will compress and pick a length that will still allow adjustment room up or down.

What he said!

[rodney@ridetech]

You need to size up the shock at your intended ride height.

Your intended ride height needs to have enough room for the suspension to compress, 2 1/2" - 3" of compression travel as a minimum. The bigger the vehicle, the greater the compression travel needed. For instance, the 71 Buick Sportswagon you have in your signature, you wouldn't want to get under 3" of compression travel. You also need to look at total suspension travel. Total travel is the amount the suspension moves at the wheel. Since we are discussing the rear, it's close to the same as the shock travel. We typically shoot for a minimum of 5" total travel, anything less sacrifices overall performance. If you have more than 5" total travel, that's even better.

With the above in mind, set your suspension to your desired ride height and measure mount to mount. Use this dimension to help determine the correct shock. We typically run our shock travel at 60% compression, 40% extension. What I mean by this is, we use 60% of the total shock travel for compression and 40% of the shock travel for extension. For example, We would run our 5.2" travel shock with approximately 3" compression travel and 2" extension travel.

I hope this helps you. I have posted a link to our CoilOver page to help you chose a length. http://www.ridetech.com/store/coil-overs/

What kind of vehicle are you working on? We may have a rear setup for it already.

Rodney

[marolf101x]

I would like to add one thing I have to explain to people all the time. . . motion ratio.

The front of most cars have a motion ratio as the shock/coilover is located on a control arm somewhere between the frame and the wheel/tire, NOT located directly over the wheel/tire. Typically this is around 2:1. . . meaning for every one inch the shock/coilover moves, the wheel/tire moves two inches.

The rear of most of these cars has a motion ratio very close to 1:1 as the shock/coil over typically sits just behind the rear axle. In this situation when the shock/coil over moves one inch, the wheel/tire moves one inch.

As Rodney stated, we shoot for a minimum of 5" of wheel travel. If you were paying attention you now know you don't need a shock with 5" of travel for the front. . .you really only need a shock with 2.5" of travel.

I hear it all the time. . ."I want a really long travel coil over in the front". That's great, but even if you get a coil over with 10" of stroke in there the wheel/tire will still only move around 6" as it's limited by ball joint bind, which is not what you want limiting suspension travel as it will result in a catastrophic failure.

[BMR Sales]

Originally Posted by Over2tonsoffun

I am looking to do coil overs on my new project. Viking has them for the front but not the rear. So I figure to use a set of universals ( if there is such a thing) for the rear. Only problem is how do I know which length to get. What measurement do I use, The factory coil, the shock, other????

Thanks
Tim

What kind of car?

[Josh@Ridetech]

Originally Posted by marolf101x

I would like to add one thing I have to explain to people all the time. . . motion ratio.

The front of most cars have a motion ratio as the shock/coilover is located on a control arm somewhere between the frame and the wheel/tire, NOT located directly over the wheel/tire. Typically this is around 2:1. . . meaning for every one inch the shock/coilover moves, the wheel/tire moves two inches.

The rear of most of these cars has a motion ratio very close to 1:1 as the shock/coil over typically sits just behind the rear axle. In this situation when the shock/coil over moves one inch, the wheel/tire moves one inch.

As Rodney stated, we shoot for a minimum of 5" of wheel travel. If you were paying attention you now know you don't need a shock with 5" of travel for the front. . .you really only need a shock with 2.5" of travel.

I hear it all the time. . ."I want a really long travel coil over in the front". That's great, but even if you get a coil over with 10" of stroke in there the wheel/tire will still only move around 6" as it's limited by ball joint bind, which is not what you want limiting suspension travel as it will result in a catastrophic failure.

Agreed. Definitely something that needs to be understood.

[Over2tonsoffun]

The car I am looking at coil-overs for is a 1985 Ford Crown Victoria 2 door. So it is a coil sprung rear

Tim

[David Pozzi]

Also look at how much the bump rubbers take up in travel. You don't want an installed shock that is 1/4" off the bump stops.