Pull or Push Rod Suspension?

... The week that was and what's on the horizon?

Jim Gould

Jun 08, 2024

and his amazing Cardinal

… A Webinar Soon

We are Planning Something Special!

and You Are Invited

… Stay Tuned!

Understanding the Pull Rod Suspension

by Aric Streeter

(as posted by Aric Streeter on Facebook)

"As a suspension nerd, one of the coolest things to me about the Fields Auto Works Cardinal Coupe that I drove with Scott Robertson on the Tire Rack One Lap of America this year is the pull rod style suspension on both the front and rear of the car.

As opposed to the more common push rod style of suspension - often seen on formula cars and some high end road cars - where a rod (the push rod) from the lower outer control arm actuates a bell crank and then the damper / spring assembly, the pull rod style takes a slightly different approach.

Instead of pushing / compressing a rod as in the push rod configuration, in a pull rod system the actuation rod “pulls” on the bottom of the damper / spring assembly, with an extra (usually shorter) link attached to both the bottom of the damper and the chassis to make the free body diagram happy.

There are pros and cons to both styles, but there a few distinct advantages a pull rod suspension has over push rod.

The first is that at no point are you putting a thin and long actuation rod in compression.

In a push rod system, the actuation rod is in compression on bump, where the highest forces occur, and depending on the angle of the rod, often its material and diameter (and wall thickness) needs to selected to prevent buckling, and the effects of buckling if a failure were to occur.

I’ve seen more than one push rod fail in buckling due to binding and shock loading over curbs.

With a pull rod arrangement, you don’t have that problem.

The next advantage is that given the places that components of the suspension naturally want to be, its relatively easy to ensure that each articulating joint is in double shear - or supported on both sides of the pivot.

Double shear is FAR stronger given the same materials as compared to single shear, and as such, single shear joints, as are common on push rod bell cranks, need to be oversized to both support large forces and to allow large enough bearings to support those forces.

Oftentimes heavy hardened shafts are needed for the bellcrank pivot as well, which can complicate assembly methods, as these shafts aren’t an integral part of the typical chassis.

Another advantage is that a pull rod configuration more evenly distributes forces amongst the suspension and chassis pivot points, so the material sizes, choices, and assembly methods become more uniform and straightforward than with a pushrod style.

Lastly, a pull rod arrangement not only moves the damper assembly inboard - like a push rod system does - it also moves the damper center of mass downward, helping C of G height.

In all, it’s a cool, if uncommon arrangement.

With cars like the Cardinal out there, maybe it will become more common in the future!"

Are you:

. looking to buy a Track Car?

. Would You Like to Know More about how a Pull Rod Suspension System works?

. The Cardinal is Light, Quick and it really Sticks!

. an amazing car with fabulous technology throughout.

Stay tuned!

The Week that Was

… and it was Fantastic

Hi All,

This is just a note to offer a huge Thank You to John Minion, Trevor Rolfe, Jack Wood (editor of Complete Kit Car), Paul Wylde, Craig Hutchison, Mike Ruff, Trevor Harmer (in absentia), all of the manufacturers, and all of our interview guests who helped make our coverage of the National Kit Car Show in the UK such a success!

Thank you all!

7Spot Jim

Here is some more live and recorded media from Malvern.

From Trevor Rolfe of Oscars Garage

Extra From Malvern

We also streamed Live from Malvern and had a MiniKit interview with Paul Wylde (while searching for Trevor Harmer), had a pre-view of Motofest in Coventry with Craig Hutchinson and had a terrific time catching up with Locost Builder, Mike Rupp.