How Ride Height Assists Suspension Diagnostics
Measuring the ride height of a vehicle can give you some important insight on the health of the suspension components.
Hi, I’m Joe Bacarella and I’m here in the Tennoco garage and today we’re going to talk about a key point when inspecting suspension systems, and that’s measuring ride height. Ride height may dramatically impact the alignment, the directional stability, stopping distances and steering. It’s also a key factor in the durability of most suspension components, including shocks, struts and tires.
It’s the key to determining whether one or more of a vehicle’s springs need to be replaced. However, properly measuring ride height can be tricky. As an example, there’s not one standardized measurement for all vehicles, and many manufacturers don’t supply ride height specifications for many of their vehicles, since they know that modern spring designs can support the weight statically, but the vehicle may see an issue dynamically as it drives down the road.
So there are two steps to determine if the springs are doing their job. First you want to measure static ride height, then we want to inspect for dynamic ride height concerns. In this video, we’re going to accomplish four things. We’re going to cover the different measuring points traditionally used, and we’ll also cover a quick reference check for vehicles where the ride height specs are just not available.
Next we’ll discuss the differences between static and dynamic ride height and how to apply this knowledge during the inspection process. We’ll also cover common mistakes made when diagnosing ride height concerns. We’ll talk about how the front and rear of the vehicle are linked together and how to determine what corner of a vehicle is causing a ride height concern. And we will identify a few inspection tips that will help you quickly determine if a vehicle’s springs need to be replaced. Are you ready to start? Let’s go.
Okay, there’s a few things to check before we get started. You definitely want to check the tire pressure, and it’s a good idea to make sure you have the same size tires all the way around. It’s really nice if they’re the same manufacturer of tire.
You want to take a look in the trunk. Make sure there’s not any cargo in there that wouldn’t normally be in the vehicle. You want to check the fuel level. It normally should be between 1/2 and 3/4 of a tank of fuel to get proper measurements. And you may even want to simulate the driver’s weight on some lighter cars.
Okay, let’s discuss some of the common points traditionally used for measuring ride height. On a lot of vehicles you would measure to the bottom of the rocker panel, both at the front and the rear of the vehicle. On many older vehicles, they would have you measure the ride height at the bumper. On a lot of newer vehicles, they have you measure the ride height right through the center line of the tire to the bottom of the fender lip opening.
Another good point, which is more accurate, is to measure from the center of the wheel, right to the fender lip opening, because that negates any issues with tire wear or different diameter tires. On many vehicles with full frames, the manufacturers will have you measure to the bottom of the ball joint and subtract that measurement from the suspension pivot point.
As you can see in this simulation, when the springs start to sag, the measurement will get smaller, indicating that the springs need to be replaced. This type of measurement eliminates any difference due to variance in compression of the body, the frame cushion.
Okay, let’s talk about the difference between static and dynamic ride height. Static height is when the vehicle’s just sitting there. It’s often called curb height. Dynamic ride height is when the vehicle’s traveling down the road. It’s seeing a lot more force as it travels that speed, and it has a tendency to bottom out if there’s a problem. So how do you know if there’s a dynamic ride height issue?
Well I like to look at the jounce bumper. So the jounce bumper limits the suspension travel. If the jounce bumper is smashed, if it’s cracked, if it’s missing, that indicates there’s a dynamic ride height issue. On strut suspensions, the jounce bumper is located right on the rod of the strut.
And it will also crack. It will be smashed and sometimes it will be missing all together. Another great indicator of a dynamic ride height issue is when the vehicle sits well statically, but when passengers get in the car, it sags dramatically.
Okay, so now let’s discuss the relationship between front ride height and rear ride height. And one of the most commonly made mistakes when diagnosing ride height issues … When I measured the ride height of the vehicle, I noticed that the right rear was almost an inch lower than the left rear, and that the right front was lower than the left front.
So how do I know if the ride height concern is caused by the front springs or the rear springs? Well, the proper way to determine that, would be to lift the front of the vehicle by the frame equally. If the rear ride height remains unequal, then we know we have an issue with the rear spring. If the rear ride height is now level, then we know that the ride height issue is with the front spring.
Okay, so I just lifted the front of the vehicle, evenly from the frame and now I notice that the rear bumper is level, so that indicates I don’t have a spring issue on the rear of the vehicle. The spring issue is with the front of the vehicle.
Okay, so now let’s talk about inspection of coil springs. Most modern springs are a very light diameter for improved ride and performance, but they have a durable coating, usually epoxy, to protect them and maintain their diameter throughout their life. As the spring gets older, the coating can get compromised, and the compromised coating will allow the coil to actually rust, which decreases its diameter, makes it weaker.
So that’s a good indication that the spring will need to be replaced because it will mostly likely fail once the coating is compromised. Another thing that we’re looking for, is the ramp angle of the coil. It should be nice and even throughout all the different coils. If there’s a kink in any one spot, that indicates that the spring has been damaged, either because of a missing jounce bumper, or it could have been damaged during service.
During service, the technician should remember to grab as many coils as possible, when compressing the spring and leaving gaps between the coil. If you only grab a few coils in the middle, and you compress them completely together, that can cause the spring to kink or be damaged.
Okay, so what do you do if there’s no ride height specifications for a vehicle that you’re inspecting? Well, although body designs vary from vehicle to vehicle, a good reference point would be to measure from the center of the wheel to the bottom of the fender lip opening, all the way around the vehicle. On most passenger cars that measurement should be within 1/2 of an inch of each other, from side to side and front to rear.
If it’s an SUV or a truck, it’s normally within 3/4 of an inch of each other, front to rear and left to right. Another good check, would be to measure from the top of the tire to the bottom of the fender lip opening. This is going to tell you if the entire vehicle is sitting low. So for most passenger cars, you’re going to see about an average of 2 1/2 inches. For most SUVs and trucks, it’s going to be around five inches.
Some other good indicators would be to look at the rocker panel of the vehicle. Most vehicles, the rocker panel is going to sit level, or it’s going to be raised slightly high in the rear. You can also look at the window sill molding. It should also be level, or slightly high in the rear. And if it’s a pickup truck, you can look at the bed of the truck, and the bed of the truck, same thing. It should be level or slightly high in the rear on most trucks.
Okay, that’s it. You should now be ready to inspect the ride height on just almost any vehicle that enters your garage. Thanks for joining us in the Tennoco garage.