We often get questions about spring pre load. We also see coilovers that have improper spring pre load set. So we wrote up a quick guide on how to properly set spring pre load on your coilover kit. Hope this helps!
So you’ve purchased a set of coilover shocks for your car with spring pre load adjustment, but do you know how to properly set it? Maybe If your coilover system does not have independent ride height adjustability, you may have just set it to yield a desired ride height and are now just hoping spring pre load is within proper range. Or maybe, your coilovers do have spring pre load adjustability that is adjusted independent of ride height adjustability, but you are unsure of how spring pre load affects performance. In this article we will describe the effects of spring pre load and how to properly set it.
Having too much or too little spring pre load will negatively affect suspension performance, but in different ways. Too much spring pre load can make your suspension feel like it is topping out. This happens because too much spring pre load will make the shock extend to its maximum length too suddenly, and this may unload your wheels from the road surface. Not enough spring pre load can make your suspension bottom out excessively. Knowing these effects can help make the correct adjustments to spring pre load. It is important to understand that spring pre load does not affect spring rate of a linear spring (most coilover systems come with linear springs). For example, increasing spring pre load WILL NOT increase the firmness of your linear spring. Increasing spring pre load WILL increase the amount of compression stroke you have which increases bottoming resistance.
Let’s define a few terms to help understand spring pre load effects.
The amount of stroke the spring consumes at static ride height from the weight of the vehicle is called “droop.” And the amount of stroke left over at static ride height is called “compression stroke”. The total shock stroke is droop and compression stroke combined.
Total Shock Stroke = Droop + Compression Stroke
It is important to understand that spring pre load does not affect the spring rate of a linear spring (most coilover systems come with linear springs). For example, increasing spring pre load WILL NOT increase the firmness of your linear spring. However, increasing spring pre load WILL increase the amount of compression stroke you have which increases bottoming resistance.
Springs on most coilover systems have to be pre loaded in order to retain a desirable amount of compression stroke at static ride height. For example; if you have a coilover with a 200 lbs/inch spring rate carrying 800 lbs of weight, without any pre set spring pre load, the coilover will compress 4” just from the static 800 lbs of weight acting on it. If this coilover has a total of 5” of stroke, this only leaves you with 1” of compression stroke left over! In this scenario you must pre load the spring to insure you have more than 1” of compression stroke. There is way too much droop in this scenario.
So we now know that spring pre load affects droop. But what is the proper amount of droop you should have? This varies depending on how much total stroke your coilovers have, so we treat the desired droop as a ratio of total shock stroke. In order to have an appropriate amount of droop, we recommend setting droop to be 30-40% of the total shock stroke (see equation below). Now you know that you have to pre load the springs on your coilovers to yield 30-40% droop!
Desired Droop = Total shock stroke x .35
How to set spring pre load:
You must first measure the total shock stroke of your coilover (including the bump stop length). Then measure how much the coilover compresses when the vehicle is at static ride height. Subtract the total shock stroke from the compression stroke at static ride height from the total shock stroke to find the droop amount. Adjust spring pre load until suspension droop is between 30-40% of total shock stroke.
Droop = Total Shock Stroke – Compression Stroke
How did you get started tracking your car, and get involved with performance driving dynamics in general?
When I was a kid, I used to live near a go-kart track. I didn’t have my own Kart, but my Dad worked out a deal with the track owner that allowed me to come in several times a week and do laps. Ever since then I’ve always loved going fast. In the late 90’s and early 2000’s, I was into Sport Compact Drag Racing back when the big shows were the NHRA Sony Explode Series, IDRC, and BOTI. But, then my car got stolen, and I called it quits for a while and focused on other priorities that I had at the time. Then one of my friends got an Evo, and I just loved it even after just riding in the passenger seat. Reading all the magazines that covered events like Redline Time Attack and seeing Evos dominate, just made it a no-brainer for me. Plus, the cars just take very well to very little modifications, and the cast iron 4G63 block is a work horse. I always had the intention of competing with the car even before I stepped foot on a track! Time Attack to me is like drag racing with turns, except it requires more balls and more driver skills. I always did alternative sports and dare devil type stuff growing up as a kid, so the adrenaline rush associated with Time Attack and High Performance Driving Events just made sense to how I’m wired.
So how many track days do you have under your belt, and how has your experience been so far?
About 23 events since August 2010. In 2011, I was the 2nd runner up overall for Modified Class for Extreme Speed’s Evo Competition, which was my very first year doing competition. I just kept showing up, even though my car wasn’t competitive at the time, and I was still very green driver wise. I got one 2nd place finish, one third, and a string of fourth and fifth place finishes. In 2012, I was 2nd runner up overall for Extreme Speed’s AWD Competition in Street Class with a three first place finishes, and three third place finishes. There were over 33 competitors in Street Class alone. I also have two first place finishes in Extreme Time Attack’s Street AWD Class, and was the 2012 Street Class Champ and Street AWD winner at Redline Time Attack’s big return at Buttonwillow in November 2012. So far in 2013, I have one first place finish at Round 2 of the 2013 XS AWD Comp at Buttonwillow, and one 2nd place finish at Round 4 at Chuckwalla. For RLTA 2013, I have three 2nd place finishes in RLTA’s Street AWD Class so far.
What was your scariest moment at the track?
At Buttonwillow I went off at about 105 MPH right at the exit of the esses at an angle which I was pretty much parralel with the track. The car tail whipped hard in the dirt and I fought to hard to keep the car under control and keep it straight. I shot back across the track toward the inside wall just before Sunset and the pit entrance. As the car was back on the pavement I was waiting to feel the car take a set, I then eased on the brakes when I got back on track and stopped the car from going toward the wall. That was probably the closest call I have had.
What is your biggest pet peeve when you go to the track?
People not giving point by’s, or hitting traffic when I’m trying to put in a hot lap.
If you could recommend any one thing about tracking driving, what would it be?
Start in a lower hp car, and with mid grade performance street tires. It teaches you to scrap for every bit of speed, and be smooth, versus just blasting between corners. I tracked for over a year with less than 300 whp, which in the AWD Turbo world, is not a whole lot of power. If you already have a high hp car, ask your tuner to tune a specific track map in which the hp and boost is dialed down. If a relatively low hp AWD Turbo Car still proves too much for you to develop as a driver, go with an even lower hp car like a Miata, which has a very low cost of ownership with Mazda Motorsports providing wholesale prices on parts. It will teach you good momentum dynamics in a way that is much harder to learn in a high hp car. If you think you can handle the “power”, are your lap times telling you otherwise? You might actually go just as fast, or faster with less power. Watch lots of in car video of the tracks you are about to visit. Read books about performance driving and set-up, and practice techniques like heel toe, left foot braking, trail braking, etc whenever you can, and when it’s safe. Get a lap timer with data acquisition. Talk to people with a good driving track record and lots of experience. Get at least one good instructor and or mentor. A good class for would-be AWD new comer’s is Extreme Speed’s AWD Enthusiast Class.
Any parting words for the track heads out there?
Drive fast, drive safe. There are people that love you back at your house.
Driver: Mark Jager
I was always interested in cars and working on them and once I got my license and was giving my first car (91 honda civic 4 door) I began modifying it. I spent a summer with my Dad in Michigan where we fixed up a car that he bought, it needed everything from a tune up to a paint job, but we were able to bring it back to life and then at the end sold it.
I grew up in Rosamond CA, which is where willow springs is located although I initially was not interested in road racing. Once I started modifying my car I began to take it to LACR. A few buddies and I would go every Wednesday and Friday to the test and tunes and race our cars and when you race you tend to want to go faster so motor swaps and turbos then followed. Once LACR closed down I needed to find a place where I could get my motorsports fun and with a new purchase of an STI it seemed fitting to try Willow Springs although I will admit it took my wife to buy my first track day before it happened. Then I was hooked signing up every so often and having a great time. Then I made the decision that I wanted to make this something that was more a part of my life so I pushed myself and Extreme Speed to allow me to help with their events and when I say that I mean do whatever they needed from setting up cones to directing traffic. After some time I was fully integrated into their team and began doing what I really wanted instructing and helping other drivers get what they wanted out of their track days. During my time with Extreme Speed I was able to learn from some of their amazing instructors and owners including Doug, Chris, Joel, Amir and many more all willing and able to teach me anything I wanted to know. This enabled me to accelerate my learning curve substantially. I would say if I can give any advice to a driver who wants to get better at the craft it would be to get out to the track and get a good instructor sitting next to you and remember going fast is a byproduct of your discipline and learning good technique. I was lucky to find some amazing friends along the way which encouraged and helped push my skills to new levels as well, the track is full of great people you just have to get out there and meet them. The guys I surround myself with now Ken Kasitz, Paul Leung, Rob Campbell, Gil Martin and many more are all guys that come to the track and help myself and my car go faster at each event.
Sponsors: Yimi Sport Tuning, Full-Race Motorsports, Borg Warner, Scat Crankshafts, JE Pistons, Supertech, Killer B Motorsports, South Bend Clutches, Wasp Composites, Swift Springs, ACL Race Bearings, Mil Spec, APR Performance, Rays, Project Mu, AP Racing, GTSPEC, Whiteline, Fuel Injector Clinic, Outfront Motorsports, SoCal Porting, Aeromotive, GSC Power Division, Koherent Chassis Workz, Cobb
Records/ Personal Bests:
Streets CW: 1:21.766 TA Overall Street Class Record
Big Willow: 1:26.566 TA Overall Street Class Record
ACS: 1:45.394 TA Overall Street Class Record
ACS Infield: 1:10.105 TA Overall Street Class Record
Chuckwalla CW: 1:55.316 TA Overall Street Class Record
Road Atlanta: 1:33.407
Nickname: Honey Badger
Class: Street AWD
Model: Impreza WRX STI
Chassis Code: GD
Engine: Subaru EJ257
Displacement: 2457cc (2.5L)
Boost Pressure: 24-27psi
Power Output: 500WHP
Weight: 3280 with Driver
Block: Subaru EJ257
Crankshaft: SCAT Crankshaft
Connecting Rods: SCAT
Pistons: JE Pistons
Valves / Valvesprings / Spring Retainers: Supertech
Head Studs: MAPerformance
Intake Manifold: OEM kind of
Turbo Manifold: Full-Race Motorsports
Wastegate: Borg Warner
Bypass Valve: Borg Warner
Exhaust: Custom Yimi Sport
Fuel Pressure Regulator: Aeromotive
Fuel Delivery: Aeromotive A1000
Fuel Injectors: Fuel Injector Clinic 2150cc
Radiator: Howe Custom
Oil System: ACL Oil Pump, Killer B Motorsport Pickup, windage tray and Pan, Accusump
Additional Engine Work: Outfront Closed Deck Block, ACL Bearings
Driveshaft: Driveshaft shop Carbon shaft
Transmission Gearing: Stock
Clutch / Flywheel: South Bend Clutch 4 puck disc, prolite flywheel
SUSPENSION AND BRAKES
Shocks: RaceComp Engineering Tarmac II
Springs: Swift Springs
Sway Bars: Whiteline Front & Rear
Additional Suspension Work:
Whiteline Steering Rack Bushings, Roll Center Kit, Anti-lift Race, Adj Lateral Links, Front & Rear Endlinks GTSpec Front Strut Bar, Subframe, rear diff brace and trunk cage
Front: AP Racing 355×32 BBK
Rear: STi Rear Brembos
Pads: Project Mu 999 Front and Rear
Brake Lines: Steel Braided Brake Lines
WHEELS AND TIRES
Wheels: Rays Gramlights 57Xtreme 18×9.5 40offset
Tires: Hankook RS-3 255/35/18
Front Bumper: Wasp Composite front Splitter and Canards
Trunk Lid: Siebon
Spoiler/Wing: APR Performance GTC300
Livery Design/Graphics: Badgertastic
Thank you to all my sponsors and supporters!
Yimi Sport Tuning
Killer B Motorsport
South Bend Clutches
ACL Race Bearings
Fuel Injector Clinic
GSC Power Division
Koherent Chassis Workz