Floater Rearends - Choosing The Right Rearend

Decisions, Decisions
In the planning of Project Bomber, Frank Kimmel and I both knew we had to have a floater rearend. After all, this car is being built to run in Frank's Street Stock Nationals and the rules require floater rearends largely because the series races on tracks like Kentucky Speedway, Bristol Motor Speedway, Rockingham Raceway Park, and other high-banked, high-speed asphalt tracks.

However, we would have opted for one anyway regardless of the rules. You see, floaters have both axles splined on both ends and a hub assembly with two outer bearings on it which is retained with a hub nut. The design of the floater keeps everything together in the event that you break an axle. That's a huge safety benefit. In a non-floater rearend if you break an an axle, you could lose the wheel, which can be dangerous. Imagine a wheel bouncing down the track with the hub assembly and axle still attached. That situation has the potential to end very poorly.

For Project Bomber, we settled on a 9-inch Floater from Quick Performance, the Ames, Iowa-based race car rearend manufacturer. About 30 percent of the racers who run Frank's series have Quick Performance rearends in their cars as well.

In the process of ordering up the rear we took some time out with Quick's Doug DeMoss to get a little more information to help you out when making your own rearend selection.

Spool Vs. Locker
It's a pretty common question, which should I use a spool or a locker? To answer that question, however, you're going to need a little bit of knowledge and your track's rulebook. A spool locks the wheels, so that they always turn at the same speed, whereas a locker locks only when under power and unlocks when you lift the throttle going into the corner. As you might imagine the locker is the preferred rearend on a lower banked short track. "You'll want a locker if you're going from 130 on the straights to 45 entering the corners," says DeMoss.

In Frank's series, however, the cars run in a more steady state, in other words there isn't that tremendous rpm swing and you can almost flat foot it around the track. Many of the tracks have gentle radius curves with substantial banking. That means that spool is the preferred rear.

"If you don't turn the wheel hardly at all at your track and you can flat foot it all the way around, you'll want to go with a full spool, mini spool, or even an open carrier," says DeMoss. For comparison's sake a full spool will give you weight reduction while the open carrier gives a side to side benefit of not scrubbing horsepower off in the corners. A mini is somewhere in the middle.

For Kimmel's series, DeMoss goes on to say, "I'd probably just run an open carrier, you run those tracks in steady state so you're not going to break the tires loose." DeMoss has shipped a pretty even mix of rearends to FKSSN competitors-some mini, some full, some open carriers.

Gundrilled & Polishing
Another common question the guys at Quick Performance get is 'are gun-drilled axles worth the added expense?'

"Generally, gun-drilled axles are twice the price of a regular set with about a 2-pound weight savings," says DeMoss. "If you want to get technical about it, that mass reduction isn't going to affect the moment of inertia of the turning axles because the weight removed is so close to the center of the spinning mass. Again, because the Kimmel Street Stocks are running in such steady state, gun-drilled axles are not as critical. Lightening that part is not as big a benefit and you usually won't see anything in your lap times. In fact, I don't think any of our customers who run Frank's series have ordered gun-drilled axles."