A Beginners Guide to Twin-Tube Shock Technology

Depending on who you ask, twin-tube shocks can be seen in very different lights. Some drivers see twin-tubes as an older technology, with better choices out there. However, many drivers and crew chiefs swear by twin-tubes as a great option for drivers. To a certain extent, both are right. It’s true, the twin-tube shock is an older shock design. However there is still a lot to like about the twin-tube design, and it gets proven time and time again.

Shocks can make or break your weekend at the local track, however for some teams it’s more of a pitfall for them. Despite their best efforts, it turns in a way for them to tune themselves out of the ballpark. But if you understand what is going on inside your shocks, and what to look for in the track, you can prepare your shocks correctly and ultimately be more competitive.

What are the differences between monotube and twin-tube shocks?

A typical monotube shock on a modified

Shock technology can be difficult sometimes to understand, so we’ve enlisted the help of AFCO Racing Shocks to help make things simpler. AFCO explained to us how Monotube shocks feature a single tube that has a working piston and a floating dividing piston that separates a nitrogen chamber from the hydraulic oil that fills much of the rest of the housing. The monotube design is seen as a more modern design, but just like the twin-tube shocks it has its advantages and disadvantages.

Twin-tube shocks are technically an older style of shock. They have an outer tube that acts as the shock body and the second or inner tube houses the working piston. Both designs work by restricting the flow of oil through a piston, however, the twin tube design also utilizes oil control valves. Quite simply you can think of the twin-tube shocks having two cylinders that work together, and the monotube simply has one that houses all of the components.

Advantages of Monotube

  • A larger piston design allows for better control and consistent valving.
  • Resists heat buildup and cavitation.
  • Absolutely best choice for rough track conditions

Disadvantages Of Monotube

  • Drivers tend to complain of a loss of “feel” when using monotube.
  • More expensive to replace or repair.
  • Slight damage can impact the shock’s  performance.

Advantages Of Twin-tube

  • less expensive to replace or repair
  • twin tube designs allows for bumps and dents on shocks to not impact shock performance
  • ideal for slick and smooth tracks

Disadvantages To Twin-tube

  • twin-tube design produces more heat and friction
  • rough and bumpy tracks produce heat resulting in a loss of performance and cavitation.

How to choose between the two?

Like we’ve stated the twin-tube shock’s design makes them susceptible to heat, and a rough track will produce a lot of movement for the shock that will build up heat and cavitation.

“The twin-tube shocks will build up heat and risk cavitation, but that’s not the reason I would be switching to the monotube shocks,” says Eric Safell of AFCO Racing Shocks. “The monotube design is just a superior shock for the rough track conditions. The larger piston is ideal for absorbing the ruts and bumps that the rough tracks produce.”

Rough track conditions or a lot of shock movement can make the twin-tube design susceptible to fatigue and cavitation

AFCO explained to us how the larger piston of the monotube shocks allows for the heat buildup to be less severe and provide driver’s with a better option for when the track get’s rougher. “In dirt racing we see a lot of a conditions, and we’ve found that the gas shocks are awesome when the track conditions are really aggressive – Big cushion, heavy, rough stuff,” explained Bill Workman of AFCO. “In the slick conditions our very popular edge and standard shocks are really good, even into the moderate conditions.”

Quite simply the monotube shocks are more consistent when it comes to the rough track conditions. Like we mentioned before, some driver’s report a loss of feel when using the monotube shocks. So AFCO explained to us how some drivers will experiment with monotubes on the rear, and twin-tube shocks on the front or vice-versa.

Beginner Shock Adjustments

But what happens when your series or track mandates that you have to use a twin-tube shock? Some tracks and series will help teams by forcing them to use the twin-tube design that in their eyes saves teams money by not allowing them to purchase the more expensive monotube design.

Make sure you check with your track and series before trying any adjustments or builds with the twin-tube shocks. Here are a couple of reminders and tips that you can try to help dial in your car and find the grip that you’re looking for.

AFCO kept reminding us, while adjustments to the shocks will help you dial in your car; you might have larger problems that are causing the bad handling of your car. Teams might start examining chassis, spring, or tire choice before looking at the shocks, you might have a larger problem that is causing the bad handling.

When the track is wet, and does not have a lot of bite you are trying to assist the car in creating weight transfer.

There are some things to remember when analyzing what corner of the car you want to make an adjustment to. When entering a corner or decelerating, your chassis is affected by the shocks compression rate in the front, and rebound rate in the rear. But as you accelerate or exit a corner, it flips. The chassis is affected by the shocks rebound rate in the front and compression rate in the rear.

The other thing you need to remember is as the track hardens and dries up throughout the event you need to stay on top of your shocks and make the necessary changes to be able to pull in to victory lane. When the track is wet, and does not have a lot of “bite”, you are trying to get the shocks to assist with weight transfer. Teams can accomplish this by running more compression in the left side shocks then on the right. But as the track hardens up the weight transfer will happen naturally from the added grip or “bite” in the track. So as the track hardens up you need to be removing the compression from the left sides and start feeding it back into the right side shocks.

AFCO went on to explain to us how the left rear shock setup is extremely crucial to your success on the dirt tracks. The left rear shock helps determine how much forward bite you will be producing versus how much side-bite you will have. Increasing the rebound in the shock will free the car for corner entry, and provides you with more forward bite. But it all comes with a price, as you increase the rebound in the left rear shock you will lose the “side-bite” throughout the corner. So it takes a delicate balance to dial in the car.

What about when you have to run non-adjustable (spec) twin-tube shocks

To help limit costs for teams some series or tracks will force teams to use spec twin-tube non-adjustable shock. the debate will always rage about whether or not this is a good thing for teams. One of the great things about entry-level racing is learning more about what it takes to make your chassis turn left and find bite. So by forcing a spec shock, that might even produce an ill-handling car, how is that teaching anything to anyone?

Regardless how you feel about it, more then likely you will be faced with a similar scenario at some point. “I would advise teams that are faced with that dilemma to dyno their shocks when they first get them. That way you have the dyno sheets on your shocks and no exactly what your running,” Says Saffell. “If you start encountering a problem with the handling of your car and suspect that something has happened to your shocks you can go back to the dyno and run the shocks to see if any thing has changed with them.” This is a good practice even if you don’t have a spec rule. Always take advantage of every resource that you have around you.

Conclusions

In dirt track racing there is a lot of assumptions made about shocks. One of which is that twin-tube shock technology is a dying technology. This just isn’t true, yes, it is an older technology, but it can provide teams with an inexpensive competitive option for certain track conditions.

Let us stress, this is just an introduction to the twin-tube technology, if you have questions about choosing the right shock we suggest you speak with your local shock builder, or speak with shock experts like our friends at AFCO Racing Shocks that helped us with this article. AFCO Racing has a great line of twin-tube shocks that range from non-adjustable, independent rebound and compression adjustable, or double adjustable.

Ultimately a good rule of thumb is: twin-tube shocks can still be very competitive, but when the track starts to come apart and get rough, you need to start bolting on the monotube shocks to be competitive in those conditions. If you have sworn off twin-tube shocks, it’s time to take a look back at them. It might just be the thing that your program has been missing.





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About the author

John Gibson

John has been around dirt track racing his entire life. In fact, he was almost born at Monett Speedway in Monett, Missouri. He has raced everything on dirt and asphalt from karts, to Indy cars, to 650 horsepower stock cars in the USAR Pro Cup where he currently races.
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