NORTHWOODS PERFORMANCE NEWSLETTER

‘I just don’t like the idea of spacers. Can’t I lift the front of my RAV just using longer or bigger springs?’ We get that question quite a bit. There are a few folks out there that offer spring only lifts for the front, but that may have some drawbacks, and the solution is not really that simple. So let’s dive into the overall design of struts, and how we can modify them for lift and driving performance.

If we asked what the purpose of an automobile suspension is, and you answered ‘to absorb the bumps in the road’, you would be correct, but only half right. By design, the primary purpose of suspension is to keep the tires in contact with the road surface. And that can either be while rolling over a bump, or when dropping into a dip or pothole. The main objective is to keep the tires in contact with the road surface at all times for total control of the vehicle.

To accomplish this, a suspension has to have up travel—the ability to absorb some BA bumps as the wheel and suspension travel up, while keeping the chassis level. But it also means the wheel should be able to travel DOWN into some big holes and dips, while still keeping the wheel in contact with the road for control, and keeping the chassis (and those leather seats and that kickin’ stereo system) level.

The down travel is called DROOP, or sometimes SAG during initial suspension setup. If you jack up a car on a lift, and then settle it down slowly until the suspension and springs take the load and weight of the car, this is called the RIDE HEIGHT of the car—the position where the car settles under its own weight. This point should use up about (for a good rule of thumb for most cars) 40% of the total travel of the suspension. So if your total suspension travel is 8”, then you need about 3.2” of droop, or sag, or down-travel. What this means is that when you are driving (quickly!) down your favorite two-lane twisty, and there is a 3” pothole or drop in the pavement, you can still maintain total control through the turn without your front tires losing contact with the road, and then having an abrupt visit with the outside guardrail (or oncoming traffic!). If you are traveling off road, this could instead lead to an unfortunate meeting with a stump. Either way, it will not end well for your Sunday drive, or your RAV.

I’m a fan of off road racing, and the big desert trucks have perhaps the best example of what we are talking about:

Here is a Trophy Truck at normal ride height:

And here is a great example of how the suspension should stroke. The front of the Monster truck is at full compression, and the back end at full droop, but still in contact with the dirt and providing traction!

And if you are just hanging it all out, here is one in full droop!

So our suspension needs to travel up to absorb bumps, but it is also critical it can travel down from the ride height! 

In a strut system, the upper and lower spring perches are fixed. The distance from the strut mount on top to the spindle mount below, and the angle of the strut mount and the lower spindle mount for camber and caster alignment, as well as the overall length of the strut are all fixed by the original design. Unless you change to a different strut design, or even a coilover along with the other required structural changes (that’s a topic for another article). So the total height of the spring, once installed and compressed within the strut, are fixed too. If you put in a longer spring, this just means you have to compress it more to get it within the strut (called pre-load), but once there the overall length of the strut, and the installed spring, is still the same. You just don’t get more travel out of it.

So if you design a spring, by making it much stiffer or longer, and compress it into the strut, it can in fact give an increase in vehicle ride height—or a lift. But that just means the vehicle is not settling into its original ride height, has essentially no more droop, and is riding at the top of its overall travel. What does this do? With any little drop in the road surface, be it an expansion joint on the freeway on-ramp or a wicked pot hole on your favorite dirt road, the tire will lose contact as the suspension tries to drop into the hole, but reaches the end of the strut travel long before reaching the bottom of the dip. In real world terms, you hear a big ‘clunk’ as your suspension hits the lower stops, and if you are on a freeway on-ramp, you may well be heading towards the outside guard rail before your front tires make contact and steer you around the turn again. It can be spooky.

So what’s a better way? In short, we do not get any of our Northwoods lift in a strut system with the spring. Yes, we have a 10 to 20% stiffer spring than stock, depending on the application, but we design it to give the same ride height as stock once installed within the fixed dimension strut. Don’t get in front of me here—yes this means we still have about 40% droop designed into our strut systems to maintain total control under all driving conditions. Stiffer spring, less body roll in the corners, less braking dive, better off road composure, eats up the bumps, and still has enough droop to maintain tire contact under most all conditions. Win-win with a Northwoods spring.

So how do we lift the front of our Northwoods strut vehicles anywhere from ½ to 2 inches? That is a story for another article.

Until then, adventure on…