Choosing the Right Springs and Shocks For Your Hot Rod
Not all hot rods are created equal, and neither are their suspension systems. With each rod build being a statement of the owner’s personality and preferences, you’d be hard pressed to find two rods that are the same. That’s part of what makes our hobby and this passion that we share so interesting.
With those previous statements in mind, it stands to reason that a cookie cutter or one-size-fits-all approach to components on your car may not always be the ideal way of building it to get the most out of your suspension and handling. The suspension system is one area where many classics and customs fall victim to that approach, specifically when it comes to their springs and shocks.
Suspension manufacturers do their best to engineer components for mass production. Custom tailoring parts for each application can be costly and from the perspective of a company that may build thousands of systems a year, it can also be prohibitive from a supply and demand standpoint as well. As such, many suspension systems come with that one-size-fits-all approach or at the most, there are limited options when a customer is ordering.
The result of all this is often a car that has neither the correct shocks or springs to give it the best ride and handling characteristics specific to its exact weight and setup, which can greatly affect your enjoyment of the finished product. A car that rides and handles poorly is not very much fun to drive. It might be ok for a quick trip down the street, but long cruises or hours spent traveling to car shows can become a tiresome affair.
Custom Tailored Options
RideTech has been in the suspension system business since 1996. This Jasper, IN company started off as a manufacturer and supplier of air suspension systems. However, in more recent years they’ve started offering coil over kits, control arms and many other suspension components to better suit their customer’s needs. Their years of experience in fine-tuning suspension systems can offer rod enthusiasts a great number of options in terms of how their car rides and handles allowing customers to literally dial in the exact combination that best suits their individual needs.
“We started out just sourcing shocks from the local auto part stores, but as our customer’s demands changed, so did our business,” says Brett Voelkel President of RideTech. The company now offers a vast array of custom tailored options and can deliver a spring and shock package to meet most customer’s demands.
We got together with Voelkel and the RideTech staff to walk through the helpful website navigation and outfit our project ’37 Ford with a better handling spring/shock package. This car, like so many out there, was outfitted with the standard one-size-fits-all shocks and springs that came with it’s suspension kits. The end result was a car that handled poorly, and rode terrible in most normal driving situations – and became unmanageable during performance driving so a change was needed as these driving characteristics were seriously limiting the enjoyment of the build.
Selecting the Right Parts
We used RideTech’s Spring Rate Calculator to calculate the specific springs and shocks needed for our Ford. This online application uses calculations developed by both RideTech and their spring supplier Hyperco to determine the best spring and shock package available. Like any computer program the outcome is only as good as the data that you enter so you will need to be as specific as possible to get the most from this application. You will need to use the calculator twice to determine the spring and shock package your car needs – once for the front and then again for the rear. There is a selection button at the top of the calculator for selecting the front or rear and at the end we will show you a few of the added options.
Monotube Vs. Twin Tube
At the top is a disassembled RideTech monotube coil over shock. At the bottom you see a typical twin tube shock. Notice the difference in the piston sizes, a quarter has been placed next to each as a frame of reference. The larger piston size of the monotube measures 1.8 inches in diameter, three and a half times the size of the piston in the twin tube shock. This allows for better control of the shock oil, better ride characteristics and better handling with the monotube.
Weight is perhaps the most critical factor in determining the proper shock and spring package. The springs will support the vehicle’s weight and the shocks will dampen the outside forces acting upon your suspension. “We see it all the time, there are so many cars out there that are over sprung. They’re running 300 lb springs in the rear, and we switch them over to 180 lb springs, though many guys protest because they don’t think the spring will support the car’s weight. Then they’re amazed when it does, and even more impressed with the ride quality improvement,” said Voelkel.
We used a lift and a set of race scales to accurately check the weight. When it comes to weight you have two options, you can either use a set of race scales to get exact measurements of your current setup, or you can use RideTech’s extensive database. Voelkel told us “We’ve literally weighed over 1,400 cars in the last year, everything from street rods, muscle cars and modern cars, to a dump truck.
We can get the customer pretty darn close if they can tell us what their car is and how it’s setup.” What you don’t want to do is go to a trucking scale, while these are fine for eighteen wheelers moving freight down the road, the accuracy may be off quite a bit for a car weighing under 4,000 lbs on a scale that was designed to weigh rigs weighing in excess of 50,000 lbs loaded.
When weighing the car it needs to be as close to how it will ride down the road as possible. So make sure you sit in the car when it’s weighed. The same idea applies to cars that are raced, you need to have all the racing gear and yourself in the car when it is weighed.
The first step in the spring rate calculator is to enter a corner weight. In our case we can look at the front corner and determine the weight readout from each scale. If you are weighing each end of the car separately (the total front end, total rear end) then you will need to divide that weight by two to approximate the corner weight.
Most car’s will have approximately a 55/45 weight bias, or for this application we can at least assume that. So if we were to multiply the car’s total weight by 0.55 we end up with the approximate total front end weight. We can now divide that number by two to get the approximate corner weight. This method is more of an approximation and might be helpful if you don’t have access to scales. Our front corner weight was 815 lbs while the rear corner weight was 715 lbs This gives us a front to rear weight ratio of 53/47, pretty close to the 55/45 average.
We also need to determine the unsprung weight. This is the weight of everything not supported by the spring. The wheels, tires, brakes, hubs, knuckles, perhaps a portion of the control arm. This part may be more difficult to determine if your car is already assembled. RideTech says you can safely assume anywhere between 70-120 lbs depending on your wheel/tire combo.
To help, many wheel and tire manufacturers have this data available on their websites. The same may hold true for your suspension components and brake suppliers. For our ’37 the front unsprung weight was 115 lbs and the rear unsprung weight was 105 lbs.
Once all of this data is entered the spring rate calculator will come up with a figure for “sprung weight” shown at the bottom of step one. This is what is used to determine the spring rate needed for the car, since the unsprung weight will not be supported by the car’s springs. Our car had a front sprung weight of about 700 lbs and a rear sprung weight of 610 lbs.
Motion ratio is the lever effect or mechanical advantage that a wheel has on the suspension with respect to it’s compressing the spring. This is another key factor, as the control arms have a lever effect on the spring. That effect will influence how fast or slow and how much the spring is compressed when the suspension is acted upon by the wheel.
In most cases, this will only be calculated for front suspension unless you are running an independent rear suspension. In the case of a solid axle the motion ratio is typically going to be assumed at 1:1.
To determine the two numbers you need to enter for this step, you will need to measure a front control arm in two places. The first measurement will be from the pivot point of the control arm where it attaches to the frame at the center line of the control arm bushing. You will measure from here to the centerline of the spring or if your car is already equipped with coil overs to the center line of the coil over assembly. Then, measure again from the center line of the pivot point on the frame (same one you just used), to the centerline of the lower ball joint. Once both of these numbers are entered the motion ratio will be calculated and displayed in the yellow box. We entered 8.5 inches for dimension A and 11.25 inches for Dimension B. This results in a front motion ratio of: 0.756.
Coil Spring Angle
The next factor will be coil spring angle. This again affects how the spring will compress when acted upon by an outside force, such as the wheel moving. Coil spring angle can also be a contributor to spring bowing or even coil bind in certain setups or when using springs other than the Hyperco sourced units from RideTech.
To measure this angle you can use a protractor or other device that will read angles. Measure the angle of the spring or coil over in relation to the horizontal of the control arm, or in the case of a rear spring, in relation to the rear axle (if solid axle equipped). Typically, this measurement will fall somewhere between 70 and 90 degrees. Our front suspension was 85 degrees, and our rear because it’s solid axle can be assumed to be at 90 degrees which is correct in this case.
Shock Stroke and Spring Length
This last factor is also critical in creating a package that will allow a car to ride comfortably. “One of the greatest atrocities that I see – cars that are too low to allow the suspension to work properly, they’re either on the bumpstops or just an inch or two above them,” Voelkel told us. If ride quality is what you’re after you may have to give up a bit of ride height to affectively achieve it.
Allowing the suspension system adequate room to compress and react as it encounters changes in the road, as well as changes in how you are driving will allow it to perform as it was intended. Ideally you want 2 1/2 to 3 inches of compression space or stroke for the shock absorber so your shocks have adequate room to do their job. On larger vehicles this ideally should increase to 4 inches or more. The database contained in the Spring Rate Calculator contains every spring and shock combination offered by RideTech.
There is more than one way to determine the correct shock stroke and spring length that you’ll need. It’s important to note that because the body of RideTech’s shocks are generally larger than other brands spring length and the ones they specify in many cases may be longer.
We see it all the time, there are so many cars out there that are over sprung. -Brett Voelkel
If your car is in the build phase or you’re not equipped with coil overs yet, you will need to mock up the car at ride height. Next measure the distance between the shock mounts. You can now make a shock and spring selection. RideTech can help you with this part of the process if you’re unsure of the needed selection after taking your measurements.
Cars built on an aftermarket chassis are even more fortunate in this instance. Due to their vast databse, RideTech has the specifications on many aftermarket chassis out there. Referencing that information, they can help you determine the correct shock stroke and spring that you will need. For our installation we chose a front shock stroke of 3.6 inches and a spring height of 8 inches. For the rear we chose a 4.1-inch shock stroke and a 10-inch spring height.
Once you have entered all the data the spring rate calculator will output three columns of information based on three different applications. For our purposes we will be following the recommendations for the cruiser/daily driver option. This car does not see the track or autocross, so there’s no need to use the options for performance or racing setups in our case, though the information is available.
We ended up with a recommended 375 lb spring for the rear and a preload of 0.64 inches. For the back, the spring rate calculator recommended a 200 lb spring and a 1.06-inch preload. Our actual part numbers ordered are (part numbers are different than screen shots due to a glitch that RideTech has since remedied in their database):
- Shocks-24139901 – 3.6″ stroke shocks
- Springs-59080375 - 8″ 375 lb springs
- Shocks-24149999 - 4″ stroke shocks
- Springs-59100200 - 10” 200 lb springs
Our package is a coil over setup both front and rear. Since this car is primarily a cruiser and we’re looking for optimum ride quality with improved handling we’ll be using RideTech’s non adjustable shocks.
The shock absorber is the single biggest factor that influences ride quality. By changing that we can give a whole different personality to a car
We chose RideTech’s Non Adjustable (NA) shock for our application. In our discussions with Brett Voelkel on this article he stressed to us, “The shock absorber is the single biggest factor that influences ride quality. By changing that, we can give a whole different personality to a car.” The RideTech NA shock is the company’s entry level non adjustable unit. At first glance it may seem like we selected the “cheap” option, but we can assure you – there is nothing cheap about this shock.
Built to the same standards as their adjustable line, this shock features a monotube design with a 1.8-inch piston diameter. This piston is approximately 3 1/2 times the size of those available in montube shocks. This allows RideTech to tune the shock more easily, it also allows for more consistent performance without fade, better dampening and better ride quality.
This picture shows the coil over that was originally installed on the car. Compare that to the photos of the RideTech coil overs installed. You can see that the springs we replaced clearly have a greater number of coils that are spaced too close together. This contributes to coil bind. Coil bind is a condition that occurs when the spring is compressed and the coils come into contact with one another, essentially the spring runs out of room to do it’s job. This results in poor ride quality, poor handling and can also affect braking performance..
Just like most of RideTech’s shocks the NA shock has a body made from impact forged aluminum, uses a double-sealed rod guide and a 5/8-inch shock rod. The body has a hard anodized finish to ensure it looks good and doesn’t corrode even after years of service. The spring seat area features fine thread for near infinite preload adjustments.
All of RideTech’s shock offerings are the result of years of industry experience. They’ve worked closely with companies like Delphi and more recently Fox to develop the best products for their customers. Even at the entry level NA line, this is no cheap off-the-shelf shock from the local parts store.
Other Shock Offerings
RideTech also offers several other coil over shock absorbers including:
- Single Adjustable - Features a single adjustment knob to adjust ride quality and shock performance, this knob is located on the shock body.
- Select Coil Over - This shock has a steel body and utilizes a control unit mounted in the car, you never have to get out of the car to change the ride or handling characteristics.
- Triple Adjustable - This shock features a remote mounted reservoir and is the ultimate in adjustability offerings. Featuring a single body mounted adjustment for rebound and a dual stage compression adjustment allowing independent adjustment of both high and low speed compression.
All of RideTech’s springs have a powder coated finish that should keep them looking good for years to come. They have a high resistance to bowing, and allow for increased travel. They’re constructed from high tensile CNC cold wound steel. The use of this high-quality steel allows for the actual coils to be spaced further apart, decreasing the total number of coils in the spring. This greatly reduces the chances that you’ll run into coil bind. If you look at our pictures of the parts previously installed on the car you can see inherent “coil-bind” issues which contributed to the harsh ride characteristics the car previously suffered from.
We’ve highlighted the installation in pictures throughout this article. If you’re familiar with basic hand tools you can do this project on a weekend afternoon either using a lift or on the floor with jackstands. It helps to have a friend nearby to hand you tools but it really is a job you could do on your own, as simple as replacing the old shocks and springs with the new coil overs.
We removed the old coil overs from the front and then verified fitment before we assembled the new units from RideTech. To do this we simply extended a shock and with the suspension mocked up at ride height we placed the shock where it would ride. We then inspected for proper clearance and verified that the shock had adequate stroke length. Ideally you want 40-60% of your stroke length available when sitting at ride height.
Installing the assembly is a matter of sliding the new coil over onto the mounting studs and then securing it with the nylock washers supplied in the kit.
Since this car has a solid rear axle the rear shocks are a bit easier to gain access to. After removing the old coil overs, the rear suspension should be mocked up at ride height and a bare shock test fitted to check for clearance and interference. Once this is verified, the rear coil overs on this kit are assembled in the same manner as the fronts. We also installed these with the preload set to zero.
Checking and Setting Ride Height
Ideally, with the preload set at zero if we ordered our shocks and springs correctly then we should have the correct ride height. In a muscle car or other applications at this setting the ride height is approximately two inches lower than the stock height. To check ride height lower the car on the ground and jounce the suspension. Simply place some weight firmly against it, pressing down and releasing, do this at both the front and rear, then roll the car back and forth a few times. Now you can measure the ride height. If the height is too high at zero preload then a different spring might need to be ordered and another shock length may also be needed.
Fortunately for us, due diligence on our end allowed for the perfect shock/spring combo the first time out of the gate. But if the ride height is too low the springs can be adjusted by rotating the adjusting collar using a spanner wrench. RideTech sells the spanner wrench for $20 and it’s available on their website. Up to 1 1/2 inches of preload can be added to systems with a shock stroke of 2.6 inches to 4 inches and up to 2 1/2 inches of preload can be added on 5-7 inch stroke shocks. If more preload is needed to achieve the desired ride height then a different spring and shock combination would be necessary.
Verifying Proper Shock Extension
Another key measurement after installation is to verify that the car will not bottom or top out the shocks when going over bumps or pot holes. Generally, if the shock has 40-60% of it’s travel available at ride height then it should be able to travel over the worst bumps. Our front shocks have a 3.6-inch stroke and the rears have a 4.1-inch stroke, this should be plenty for our application.
The easiest way to verify extension is to measure with the car on a lift. Measure from the center of the fender lip to the ground with the car at ride height, using the center of the wheel as a reference point. With the car on the lift slowly raise it until the tire is just about to come off the ground. Measure the distance from the fender lip to the ground again and subtract the previous measurement.
Ideally the number should be greater than 1.5 inches but less than 3 inches. If it’s less than 1.5 then the shocks are in danger of topping out and a number greater than 3 inches means you’re in danger of bottoming out the shock. In either case a different package would be needed to correct that problem.
As Voelkel told us, “Ride quality is a whole lot easier to achieve than good handling, but the two don’t have to be mutually exclusive.” The difference in driving the ’37 is night and day. As Rocky Nash, the owner of our test rig explains, “The ride quality went from being like a dump truck to riding like a newer sports coupe. The handling has also dramatically improved, the car is precise to control and while it’s not new Corvette like around the corners, it offers plenty of confidence.” And we had to see for ourselves, having taken a cruise in the ’37 prior to the install, we wanted to see just how dramatic of a change a RideTech coil over swap could make.
Night and day indeed! Before the car was slow to react, clunky, and stiff. Now, the ’37 was nimble and comfortable, and while it’s not designed to be a track car by any measure of the term, this Ford is ready to clock some miles both near and far. In short – it’s now enjoyable to drive, whether going down the street to the local cruise night or hundreds of miles away to attend the next big event.
While the springs and shocks have the most dramatic affect on how the car will ride and handle there are a few other factors that you should take into consideration with your current car or build.
Wheels and tires will play a key role in how well your car rides and handles. The tire is the first part of the suspension to be acted upon by an outside force. As such, selecting the proper tire for your car is crucial if you want to meet your goals. Just putting on the cheapest thing at the local tire dealer is not going to yield great ride or handling. Conversely, the most expensive low profile tire out there may offer phenomenal handling characteristics but a less accommodating ride. Your best bet is to consult an experienced professional and perhaps even discuss with some of your fellow enthusiasts. In the end, ride quality can be very subjective, what feels good to you may be terrible to someone else and vice verse.
Voelkel and the crew at RideTech have encountered and resolved many suspension issues that were the result of too little ride height and travel.
Ride height and suspension travel also play key roles in determining how your suspension system reacts and how well your car performs. As we mentioned early, Voelkel and the crew at RideTech have encountered and resolved many suspension issues that were the result of too little ride height and travel. Suspension systems need adequate room to react to conditions. If the spring is already heavily compressed, or the shock close to bottoming out where the vehicle is set to ride, then the ride is going to be harsh. While sitting low gives good appearance, it needs to be done properly with the correct suspension setup.
We included a video above where RideTech team members, including Voelkel, explain some more about what they do regularly at shows and how they make determinations of the correct spring and shock combination for customers cars. They also explain some of the mistakes and dangers they find as well so it’s definitely worth a watch.