The Science of …Base Valves and Taking Away a Win

Brad Wilson asks: “The NASCAR Camping World East Series is a regional tour that is merely a blip on the radar that is big-time racing, but NASCAR changed a precedent this Tuesday. They stripped driver Peyton Sellers of his win completely and put him in last place, instead of fining the team like they do for the big three. The reasons: 12-4-A (actions detrimental to stock car racing); 12-4-Q (car, car parts, components and/or equipment used do not conform to NASCAR rules); 20C-12.3 C(7) (Shock absorber base valves will not be permitted: Right rear shock absorber had a base valve installed).

t two are NASCAR’s blanket offenses, but the last one is peculiar. Is there any any you could explain what a shock absorber base valve is and why it would provide an advantage?”

Thanks, Brad, for the question. I have been happy to see EPSN’s NASCAR Now devote a little time to the touring series, even when there isn’t a major controversy like there was last week.

Last week, Andy Santerre’s car, driven by Peyton Sellars, was stripped of its win due to the aforementioned shock violation. The ubiquitous rules 12-4-A and 12-4-Q cover everything from cussing to fuel additives; however, you don’t see rule 20C-12.3 C(7) cited very often. As Brad pointed out, this rule says that the right rear shock had a base valve installed, which is not allowed. So what exactly does a base valve do and why are they not allowed?

A shock absorber provides damping for the springs. When a wheel goes over a bump, the spring on that wheel compresses. If there were no shock absorber, that corner of the car would bounce up and down like a bobblehead. A tire doesn’t have much grip when it’s not in firm contact with the track. The shock absorber damps (reduces the size of) the up-and-down motion of the spring.

Imagine submerging a bobblehead in a container full of a viscous fluid, like syrup. If you pushed the bobblehead’s head down and let go, it might go up and down a few times, but the fluid will stop its motion pretty quickly. That’s called damping and that’s basically how a shock absorber works: The stored spring energy is transferred to the shock, where it is dissipated by friction and heat. By damping the up-and-down motion of the car, the shocks help keep the tires in contact with the track, and that improves grip.

A monotube shock absorber (the type used in NASCAR) is a piston (a disc with holes in it, shown below from the RE Suspension catalog) moving up and down in oil. The holes are very small, which means that you need quite a bit of force to move the piston. The holes in the piston are covered by shims (very thin washers) that bend when the piston moves up and down. The shims bend more when the piston moves faster, uncovering more of the holes and allowing more oil to move from one side of the piston to the other. (At very low speeds, a valve in the shaft allows direct flow.)

Oil is relatively incompressible, which means that when you press on it, it doesn’t change volume. Gases, on the other hand, are compressible (to some extent). They expand and contract to fit the container in which they are contained. A marshmallow is a combination of sugar and air pockets. When you press on a marshmallow, the first thing that happens is you press all of the air out of the air pockets. Only then do you compress the sugar that forms the rest of the marshmallow. A shock has to be filled with an incompressible fluid for it to work.

The volume inside the shock that can be filled with oil changes as the shaft moves in and out of the shock. You can only put in as much oil as there is space when the shaft is entirely in the shock. When the shaft is pulled out of the shock, there’s going to be some space left.

In some shocks, that space is filled with air; however, the motion of the piston up and down can incorporate air into the oil. That air forms very small bubbles that make the oil the equivalent of a liquid marshmallow. When the piston tries to push on the oil, it first has to push the air bubbles out of the oil. The shock can’t respond quickly, because the oil doesn’t offer resistance until all the air bubbles are pushed out.

This problem is solved by using a pressurizing gas and floating piston. The floating piston separates the oil from the pressurizing gas, which usually is nitrogen. If you just put nitrogen gas in at atmospheric pressure, you wouldn’t solve the problem; however, if you pressurize the gas (usually ~15-40 psi), that pressure forces gas bubbles out of the oil.

There is, however, a catch. There always is. The additional pressure from the nitrogen gas increases the force needed to make the shaft move. At low shaft speeds, it is hard to get much damping. This is where a base valve comes in. A base valve is similar to a piston in that it has holes, shims and a jet in its center; however, it functions differently than the piston. The base valve is fixed in the shock, usually between the piston and the floating piston. This creates a third chamber in the shock.

The base valve’s construction essentially allows the displacement of a volume of oil equal to the shaft volume entering the shock, which moves the floating piston; however, the base valve also maintains the resistance necessary to force oil through the piston. When the shaft is in rebound (the shaft is being pulled out of the shock), the gas behind the floating piston presses outward and oil is allowed through the base valve back into the compression chamber.

The base valve (also called a base plate) allows you to decrease (or even eliminate, depending on the design) the pressure of the gas in the shock. Having a base valve prevents gas bubbles in the oil, but doesn’t increase the force necessary to move the shaft. This allows the shock to respond better at low shaft speeds, which increases grip and therein lies the advantage of having a base valve. This would be especially noticeable on a smoother track, where the shock shaft isn’t moving as quickly as it would if you were going over a lot of bumps.

NASCAR shock rules are very restrictive and do not allow base valves. Shocks are very complicated and NASCAR already has a challenging time policing the current shocks. Quarter-midgets, however, are allowed to use shocks with a base valve, and the design by Chet Fillip of ARS is one of the few monotube designs I was able to find advertised on the web.

Santerre said, as reported in an article by David Poole, that they had gotten the shocks from another team (in another series) and used the shocks in a test. Three of the shocks were removed prior to the race and the fourth–which apparently was the illegal shock–was not. It’s entirely conceivable that there was some miscommunication and someone thought someone else removed the right rear shock after the test. Time is short and patience is usually pretty short as well at tests, especially when there is an upcoming race. The shocks of the top five finishers are routinely inspected in the Camping World East Series, so they knew the shocks would be broken down. That makes it hard to believe someone put the base valve in on purpose.

Santerre objected to the penalty, which can’t be appealed, asking what the difference was between him and Jack Roush except for money. Without getting into the question of whether this was cheating (I still haven’t mastered mind reading), this is something of a different situation than the migrating oil box cover. The possible advantage gained (and you would have to know more about the specific configuration of the shock and the gas pressure used to know) probably wasn’t all that significant. This an explicit violation of a very clear rule. It’s not in the ‘grey area’. It is hard to claim that it happened because something fell off, got knocked loose, or got damaged during the race. Someone put the base valve in the shock. This is more analogous to adding something illegal to your fuel tank than it is to having a oil box cover not covering the oil box.

I have to agree with Dave Moody, who opined that this ruling is going to have absolutely no impact on the top three NASCAR series. The one thing that NASCAR is usually consistent about is that they don’t consider intention when making penalties. For them to say that this is clearly an innocent mistake and therefore they won’t penalize the car opens the door for other teams to see what they can get away with claiming are ‘innocent mistakes’. The next time something happens, how do they decide that it was or wasn’t “innocent”?

Thanks again for the question, Brad.

1 Comment

  1. The Camping World East and West series are even treated very different from the ‘big boys’ during the race as well. Race control will send drivers to the back for ‘rough driving’ at a much higher rate than the premier series ever would think of doing. (if the premier series would ever consider that)

    And this can only be looked at as a good thing especially with the influx of ‘obsolete’ Car of Yesterday parts and chassis making their way to the CW Series.

    There is a much greater need for a stronger arm of the law and Nascar is doing the right thing.

    I watched post race inspection that same weekend in the West Series, and it was interesting to see the Crew Chiefs looks as Nascar was removing the rear ends from the top 5 cars. It made you wonder if these CCs were thinking to them selfs of ‘I hope we have removed everything we were supposed to’. I guess Santerre’s team may have ‘missed’ one of those shocks, but Nascar still has to take a hardline approach and did.

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