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Frequently Asked Questions



What are the Corvette generations?

Since its inception in 1953, the Corvette has had seven major design upgrades in both its platform and styling.


What is meant by a C5 / C6 Corvette?

The C5 Corvette was produced from 1997 to 2004 – 238,215 in total – and the C6 from 2005 to 2013 – 215,125 in total.


What is an I R S?

An Independent Rear Suspension.


What is an I F S?

An Independent Front Suspension.


What does WMS stand for?

Wheel Mounting Surface. The flat area on axles where the wheels mount.


What does OEM stand for?

Original Equipment Manufacturer, which is usually a company that made parts for a factory-produced vehicle.

What components are considered as part of an automobile's suspension?

Auto suspensions are commonly referred to as any component that separates the main body of the vehicle along with the driver and/or passengers from the pavement.

Typical suspension components include the springs, the control arms, the shock absorbers and the related linkages that connect the wheels and tires to the vehicle, while allowing some motion between the two.


What is the main purpose of a suspension?

A vehicle's suspension serves a dual purpose. Not only does it help to absorb the harshness of the road and allows the occupants to have a smoother ride, but it also contributes to the quality of a vehicle's overall handling and braking


What factors should be considered when selecting a suspension?

One of the first considerations when designing a suspension system is calculating the right compromise between the occupant's comfort and the car's ability to keep contact with the road surface under constantly varying conditions.


Although comfort is a concern, a race-tuned suspension may take away from the ride quality and concentrate more on keeping the tires in contact with the road surface.


Keep in mind that the only contact with the road surfaces and the forces acting on the vehicle are done through four relatively small contact patches on the tires – literally where the rubber meets the road. So anything the suspension can provide to increase the size of these patches will increase the handling of the vehicle and therefore its safety and performance.

What is a Dependent Suspension?

Front or rear suspensions that are joined together from side to side through a 'live' or 'solid' axle or tube are referred to as dependent suspensions. This simple design has been around long before the introduction of the automobile.


For many years, auto manufacturers preferred the dependent suspension design because of its simplicity – and nearly all of the dependent systems still utilized today can be found exclusively at the rear of the vehicle – in combination with an independent suspension system in the front.

The exceptions include some 4X4 and heavy-duty trucks, as well as some old-school hot rods that still utilize dependent suspensions in both the front and rear.


When one wheel hits a bump in a dependent suspension system, it effects both wheels, This will compromise the traction, the smoothness of the ride and, in severe cases, cause a dangerous wheel shimmy at high speeds. Taking a hard corner with a dependent suspension and hitting some bumps in mid-corner can be unnerving.

What is an Independent Suspension?

Front or rear suspensions that are NOT joined together from side to side are referred to as independent suspensions. Performance is greatly improved, especially over uneven road surfaces, because the movement of one wheel will not effect the other.

Another advantage is the independent suspension's wheels to move up and down while still remaining vertical, again resulting in a superior grip on the road.


A rear independent suspension, or IRS, typically incorporates a differential that is solidly mounted to the frame and drives the wheels, which are mounted to the outer subframes, through the use of jointed drive shafts, or 'half-shafts'.


An IRS system also offers an advantage in lowering a vehicle's unsprung weight, partially due to the differential being mounted to the frame – and lowering the unsprung weight is always a good thing.

What is Unsprung Weight?

Simplified, a vehicle's unsprung weight is considered to be the weight of the components that is not supported by the suspension. This includes the wheels, tires, brakes and axle, plus a portion of the springs, shocks, suspension links and driveshaft.


When a tire hits a bump in the road, it reacts by recoiling upward.  The less the unsprung weight, the less the tires will react to a bump and the more grip they will keep on the pavement.  A lower unsprung weight also results in a better ride because the ratio of the unsprung weight to the sprung weight is increased and will therefore have less effect on the occupants.

What type of springs do Corvettes use?

Both the C5 and C6 front and rear suspensions are equipped from the factory with single composite transverse leaf springs attached to the cradle.  The springs attach to the lower control arms.


Can I use other types of springs?

Yes.  Coil-over shocks absorbers can be used instead of, or in combination with, the factory leaf springs.

What is a Double-Wishbone?

The term 'wishbone' is derived from the familiar shape of the upper and lower control arms.


Corvettes have utilized this simple but effective design on every corner of every Corvette from 1997 on – and this is a contributing factor to the Vette's legendary handling characteristics.


The upper and lower 'wishbones' are mounted nearly parallel and use two mounting points to attach them to the frame and a single ball joint at the outside knuckle to attach the spindle.


The springs and shock absorbers mount directly to the arms and control the vertical movement.  This design allows for easy adjustments in camber, caster and toe in.

A C5 Corvette Upper 'Wishbone'

The Cradles are available in 13 widths. How are they narrowed?

The Cradles are available from 66.75" all the way down to 54.75" in 1" increments, based on the Wheel Mounting Surface to Wheel Mounting Surface Dimensions.  The different dimensions are accomplished by removing a section of aluminum from the center of the lower cradle.


Next, the cradle is secured to three welding jigs and welded back together.  Finally, it is braced with two aluminum plates.  This way, all of the control arms and their mounting points remain stock, with the proper suspension geometry intact.  The geometry of the shortened axles will change slightly, but the CV joints can easily handle the difference – and it will not effect the other suspension components.

How will I know which width kit is right for my project?

The starting point in determining the proper width is to measure the distance between the WMS (Wheel Mounting Surfaces) on the axle hub from one side to the other.  (More information in Section 12)


We base all of our measurements on the wheel mounting surfaces, so you can always be sure in ordering the proper width cradle.

Can I measure the vehicle's track instead of the wheel mounting surfaces?

No!  Because there are too many variables – and there is a lot of misinformation regarding what a vehicle's track actually is.


A vehicle's track width is properly measured from the centerline of a tire to the centerline of the other tire on the same axle.  So, if your wheels have any positive or negative offset, which they usually do, the track width and the wheel mounting surface measurements will be different.

What if I require a width that isn't offered in the kits?

The best way to 'fine-tune' the wheels and tires for your particular project is to research the different widths and offsets offered by today's wheel manufacturers.


Some of the positive and negative offsets are a bit confusing, especially when many of them are metric. Then the offsets must be calculated against half of the actual width of the wheel, instead of its advertised size and so on.


Whenever possible, I always try and find a wheel manufacturer that still includes the old-school method of indicating offset, which is Backspacing.


Then just subtract the Backspacing from the actual width of the wheel to calculate the Frontspacing – and that's all you need.


Remember, a 17” x 8” advertised wheel size is taken where the tire meets the rim – so that wheel will physically measure about 18” x 9”.

Can I use my car's stock frame for the conversion?

Usually not.  As with many suspension upgrades or when larger than stock tires are being installed within the confines of the stock body lines, modifications usually begin with the installation of a new rear subframe, sometimes called back-halfing a frame.


What exactly is back-halfing a frame?

It entails the removal of the vehicle's factory rear frame, near the back of the passenger compartment, and replacing it with a new, usually narrower, frame to accommodate an upgraded suspension and/or wider tires.


There are several companies that offer frame rail kits – and fortunately, it's a lot easier than it sounds – and can usually be accomplished by the DIY auto enthusiast.

How can the Corvette Interface IRS be easier to install than a 4-Link?

Once the rear frame rails are secured to the vehicle the only thing left to do with the Corvette Interface IRS system is to raise it up, slide it back and forth until the wheels are centered in the wheel wells and drill six mounting holes on each side.  Done.


However, with a typical 4-Link suspension once the frame rails are secured to the vehicle, a lot of the work is still ahead.  First and foremost, there is the task of laying every component out and locating the proper placement for all of them.

Next, the 4-link and coil-over shock brackets have to be welded to the rear axle.  Then the brackets for the 4-links have to be welded to the frame.  Next, a crossmember needs to be welded in for the coil-over shocks, along with the shock mounts.


Finally, a panhard rod, or cross-link must be installed to keep the rear axle from moving from side to side.


For high-horsepower drag cars, the 4-Link, or ladder bar setup is still the way to go – but for handling, nothing beats an independent rear suspension.

Can I install the Corvette Interface IRS System in a Pickup Truck?

Certainly.  In fact, a pickup truck conversion is one of the simplest swaps there is.  Once the bed is removed, installing a new rear frame and the IRS can literally be done in a weekend.


The new frame can be installed inside the original frame before the original one is removed, therefore all of the bed and bumper mounts can be transferred to the new frame and everything will remain aligned.


Once the new frame is secure to the original front frame, the old frame can be cut out and discarded.  Next, the entire Corvette Interface IRS system – including the wheels and tires can be rolled under the frame.  Then set the bed

Then set the bed onto the new frame and roll the suspension until it's correctly positioned in the wheel wells.  Next, mark the frame, raise the bed and drill the mounting holes.  Done.

How much room do I need from the back of the seat to the center of the rear axle for a Type IV kit?

If you have 38” or more, the conversion is a GO!


Are there any ways to reduce the 38” needed to fit the Type IV conversion comfortably?

Sure! First of all, if you're using a Chevy LS engine, the intake manifold can be mounted on the engine backwards, with the throttle body to the rear.  Another trick is to use some racing seats, which are usually quite a bit thinner than the original seat. Finally, you can move the entire drivetrain back, so the centerline on the differential is an inch or so rearward of the rear axle centerline.  The CV joints won't mind this at all.


What makes the Dobbertin Performance Innovations Corvette Interface Kits unique?

Unlike the other Corvette suspension adapters, our heat-treated A356-T6 aluminum castings have all of the mounting points built right into them.  There is no guesswork when locating the control arms, the shocks, the spring or the Corvette cradle.  A drill and some basic hand tools is all that you need for a professional looking installation.


What gear ratios are available?

Factory gear ratios for the Corvette differential include 2.73, 3.15 and 3.42, while other ratios of 3.73, 3.90 and 4.10 are available from aftermarket manufacturers.


What difference will a Type IV kit make to my car?

This will transform your car.


It will single-handedly re-define your ride.


You'll no longer own the 'Blue Chevelle', or the 'Blown Chevelle' – but from the day of the conversion – on – you'll own the 'Mid-Engined Chevelle' – so be prepared for that!


Is there anything cooler than a mid-engine conversion?

It all depends on your perspective, but I don't think so.


When someone looks under the rear of the car, does it look High-Tech?

You be the judge –

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