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Drag Racing Story of the Day!

Dragster Front End Specs Q&A

By Jim Hill and Pat Foster

OK you savvy front-motor digger experts, here's a question I'd like to place in front of you chassis types:

Front-end geometry is of course known to be critical to the ability of a high-speed race car, like a dragster, to maintain steering control and handling. What were the specifications for adjustment typically used for these applications? Camber, caster, and the angle at which the front axle was typically "laid-back"? Also, the "offset" front axles that were popular for staging roll-out advantage, what effect does this offset have on front-end alignment numbers?

I learned from my doorslammer racin' days (see, everyone does have a skeleton or two in their closet!) that front-end alignment specs were very important in getting an a-frame front-end car like my '57 Chevy Gasser to "go straight" as well as run more mph. I also found out how much these numbers can slow a race car if they're "out."

Foster and Fuller: (Hmmm. Sounds like a brand of scotch or a law firm) Do you guys have any specific specs you liked to see in a front end, or is this still a "speed secret" best kept under wraps?

I had the front-end alignment done on my truck this morning, and after the tech that did the job gave me the computer print-out of the "before and after" specs it got me to thinking. He used a computerized Hunter machine, a far cry from the trusty length of string and homemade front-end gauge common to many home shops.

Jim Hill

Jim - Good question. Passenger cars present problems in this area that have little or no effect on dragsters. (Note the word "dragster"). This problem is improper or premature tire wear. Not a problem in dragsters, at least front tire wear. <g> Handling in a dragster is affected little by front end alignment. Again, this is because of the tire "patch" on the ground, very small indeed. 

The contact provided by the front tire means the car is in a state of terminal "push" at all times. The rear of the same car is in a state of terminal "loose" at the same time. Not the best situation going, but works well enough to keep her between the guard rails most of the time.

One area I have always paid close attention to is the geometry that can cause the dreaded "bump steer." This happens when as the suspension goes from full bump (up) to full drop (down) as at the finish, or for that matter at the starting line. The steering geometry forces the car to "steer". That is what has happened to most of the cars we have seen in those old photos that show a car engulfed in smoke with the front wheels laid over, one way or the other. Makes for bitchin' photos but starts the car on a "snake" around run. Look at the tire tracks in some of the old photos. 

When the funny cars started hauling ass, geometry reared its ugly head as never seen in a dragster. The reason being was weight and aero-effect on the front end. Suddenly we had a lot more tire on the ground and steering was greatly affected by turning the steering wheel (what a concept). The result was much improved geometry, eliminating all traces of "bump steer," or crash -- that simple. 

None of this is rocket science and was and is easy to accomplish. This is not the place to go into detail. If I did, someone would surely post it over at Cole's place and then all the armchair experts over there could beat me up for weeks to come. I'm too old to get beat up or to fight back. (Don't book that last statement!)

Pat (I'll fight in a heartbeat) Foster
http://nitroparts.com/diggers-profab.html

 

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