Going Quicker, Faster and More Reliably with Lightweight Hardware Part 2

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In our last issue, we began our look at how you can slice and dice your ET slip by way of reducing rear end unsprung and rotational weight. Plenty of hardcore class racers (Stock & Super Stock as well as Competition Eliminator) incorporate these pieces on a regular basis, and they’ve discovered a number of advantages. Many have also found that reliability doesn’t diminish with lightweight parts. Bottom line? You can definitely use these pieces in something super competitive, like a heads up grudge car or even in something such as a small tire radial racer. Here’s the rest of the story:

Spool: Obviously, this is another good place to peel weight out of a rear end. As an example, a 40-spline spool for a Ford 9-inch weighs 11 pounds. A lightweight Profile Milled spool for the same application weighs 8-1/2 pounds. An aluminum M-W spool weighs 4.7 pounds. You can find titanium spools, but they’ll typically weigh 1/5 of a pound less than the aluminum spools (for most mortal little-guy racers, this precious metal exotica is out of the question - the weight figure is for your reference). In the case of a 12 bolt Chevy, a standard steel spool weighs 14 pounds. Meanwhile, a lightweight Mark Williams spool for the same application weighs 11 pounds. An aluminum Dana 60 spool from M-W weighs in at a mere 8 pounds, while a lightweight steel spool tips the scales at 16.5 pounds. In contrast, a standard steel spool for a Dana 60 weighs a beefy 21 pounds. The primary differences between a standard spool and the lightweight piece are the addition of lightening holes drilled through the hub and a profile milled ring gear flange.

How does this lightening process affect the strength of the spool? It doesn't. The lightened pieces are just as happy in a high horsepower car as the standard components. What about the aluminum spool? In this case, NHRA class racers are finding that an aluminum spool simply isn't a reliability factor in their cars. Many are seeing over 200 hard passes with this setup, and when you take one apart, the aluminum spool looks perfect - so perfect that the splines look like they're brand new.

Ring Gear: Ring and pinions are heavy. And in most cases, they don't need to be as heavy as they are. M-W has come up with a scheme where they can place a Ford 9-inch, Dana 60 or Chevy 12 bolt ring gear on CNC lathe to remove anywhere from 1/2 to 2-1/2 pounds of excess baggage. And it's all rotating weight. We should point out that this service is available for pro gears with ratios from 4.88:1 to 6.20:1. How reliable are these components? Class racers in the know tell us that with a 3,000+ pound Super Stocker (with a 6.00:1 gear), they can get well over 100-125 passes on the same lightened ring gear. That's usually one season of use, and if the ring and pinion are changed, it's only as part of a regular maintenance schedule.

Axle Tubes & Wheels: Axles such as the 12-bolt Chevy and the Dana 60 incorporate press-in axle tubes (which are eventually spot welded to the center section, or "coconut," by the factory). Meanwhile, most Ford 9-inch housings have tubes which are welded in place. In a lightweight application, chrome moly tubes are an efficient way to carve a good chunk of excess weight from the housing. How much weight can you save? It really depends upon the exact housing width, but there might be more here than meets the eye:

When reflecting on rear end housings, you should also think long and hard about wheels. How are they related? Consider using the narrowest housing possible, then making up the difference with wheel offset. Some sharp chassis builders set up cars with rear wheels with the smallest backspace possible (typically, drag race wheels with the smallest backspace dimension are lighter than identical wheels with a larger backspace figure). This means the actual axle housing can be physically narrower. State-of-the-art aluminum race wheels are most definitely lighter than steel axle housing tubes. By running the narrowest housing possible, the axle shafts can also be shorter. Excess unsprung weight is removed, and so is rotational mass. An important side benefit is the fact that a narrow housing also makes for a stiffer, shorter axle. Finally, keep in mind that a wheel with a shallow backspace dimension makes it easier to remove the wheel and tire.

What's It Worth? There are more than a few benefits that arise when you peel weight from the rear of a racecar. It's a well-proven fact that a low ratio of unsprung weight (which includes the tires, wheels, brakes, rear axle, and half the weight of the suspension links, drive shaft, springs and shocks) when compared to sprung weight (the rest of the car) makes for much better traction. Here's why: The total unsprung weight is what the shock absorbers must attempt to control (in the bump direction) so that the slicks remain in contact with the track surface. The less unsprung weight there is, the easier it is to control. That makes life easier on your shocks and probably makes life easier on you, since the suspension in your racecar chassis will be easier to tune. Just as important is the fact that rotating mass (wheels, tires, axles, spool, ring and pinion along with anything else that spins) posses a rotational inertia that eventually contributes to the mass of the vehicle. As mentioned previously, the heavier the rotating pieces, the more power it takes to turn them.

There is some important (and simple math) involved: Using some of the pieces shown in the photos as an example, we've carved approximately 4.5 pounds from the axle shafts. The Mark Williams profile milled spool chops another 3 pounds from the housing. Using a back cut ring gear removes another 2.5 pounds from the mix. In total, these rear end components add up to 10 pounds of weight loss. According to engineers who do this for a living, for every ten pounds you take out of the rotational mass, it's like removing 17-1/2 pounds from the racecar. Factor in the use of small backspace wheels along with other lightweight drive train hardware, and you have a car with a split personality. This means a car with lightweight hardware can statically weigh the same as a car with more conventional components, but when it's under power, it acts like one that weighs significantly less. It certainly doesn't take a rocket scientist to figure out that a lighter car is quicker, faster, easier on parts and, in most cases, more consistent than a heavy counterpart.

As you can see, it is possible to go quicker, faster and more reliably with lightweight hardware. Combined, those are strong arguments for putting your rear on a diet. For a closer look at lightweight hardware, check out the following photos:

There are three different types of spools readily available from Mark Williams. Included in the mix are a standard steel spool, an aluminum spool and a lightened steel spool.

A lightweight Mark Williams spool for a 12-bolt (as shown here) weighs 11 pounds. The primary differences between a standard spool and the lightweight piece are the addition of lightening holes drilled through the hub and a profile milled ring gear flange.

Meanwhile, a 7075-alloy aluminum spool can remove even more weight. See the text for additional info.

This is a piece we didn't mention in the text, but for some applications, there's plenty of weight savings (and/or potential strength improvements) to be found in the pinion yoke.

Pro Stock cars often incorporate billet titanium yokes. For mere mortals such as ourselves, we can opt for forged 4340 steel yokes or even aluminum jobs (second photo).