Alignment vs. Dyno Numbers (theory)

New 12/18/2004

It's finals week here at V8SHO.com, and I'd like the following questions answered in short-essay form. Bonus points if you show supporting calculations or diagrams. (Keep any drawings to a very small file size! No bitmaps!)

Suppose I go to a dyno, but my front wheels' toe is in (or out) a few degrees. Wouldn't that rob some power that is intended to transfer to the dyno rollers, and give me lower dyno numbers as a result?
How much do you think a slight toe-in or toe-out might waste on the dyno (or the street, for that matter?)
How much of this would be due to friction at the wheel bearings, and how much would be due to friction where the tires meet the road?
How much of this would just be due to force cancellation from the opposing lateral components of the vectors from each wheel (due to the thrust angles not being parallel?)

On the SHO, IIRC, the toe is supposed to be slightly in for handling reasons. If you were trying to tweak out a few more HP or improve drag times, and time & money for alignment were NOT factors, would it be possible to get an improvement by setting the toe to zero? How seriously would this compromise handling in situations other than "straight line"?

I was thinking that caster wouldn't make any difference, and camber *might* hurt if it is extreme enough to reduce the contact patch of the tires and allow slippage, or if it introduced any significant mount of friction into the wheel bearings due to the direction gravity being non-perpendicular to the axis of rotation. Any thoughts?

Dan Carman
'97 PG
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Here's my 2 cents. Caster would definitely have more of an effect
on the dyno and the strip. Two wheels facing each other, pointing away from
each other or just one turned in or out is going to bind. Pushing or pulling
would not matter if the wheels are fighting each other. Camber is a
different beast altogether. I have my caster and camber zeroed out. The
car handles like a dream and my tires don't where out as quick. If the tires
last longer at these settings and I'm still carving out the curves everyday
then there is apparently minimal bind or friction. However, such settings
may have some negative impact on road course times. I have found with this
car over the 68,000 miles that I've had it that any camber will "knot" the
tires on the edge.
Jason Barker
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Probably.

OTOH, a lot of things can also affect power to the wheels, like tire brand/tread, tire pressure, etc.

Obviously there's a lot of other factors that affect 1/4 mile times, but dyno runs have their own limitations WRT determining how the car really performs.

Sure, you can set things like toe to zero to get better dyno times, but an exactly comparable car with better suspension settings will beat you on a road course where absolute HP is not as much of an issue.

Ron Porter

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