Look! It's very simple. You measure from the center of the of the hub "front wheel" to the center of the rear axle "rear wheel" both sides. Thats how you measure wheel base! NOT TIRES.
Art "The TECH DUDE" Savedra
Actually Art, there is more than one way to measure the wheelbase and you can measure the tires because the front of the front tire
to the front of the rear tire is the same distance as center to center.
I would have to disagree with your method of measuring wheelbase IF ANY of the following conditions are met:
1. Dissimilar track widths comparing front to rear.
2. Dissimilar measuring points relative to the vehicle centerline plane (laterally)
3. Bent or sprung frame
Wheelbase is defined as (paraphrased here) the longitudinal distance between the lateral, normal (meaning mathematical "normal" or at 90 degrees to base) centerline of the front hub and the lateral, normal centerline of the rear hub, taken parallel to the vehicle centerline (See the SAE standard definitions for complete definition). This is the spec the FIA, NASCAR, SCCA, etc all use to define the measurement. If measuring by your procedure on a wide front or rear track (condition number 1 above) vehicle (wider track in front increases front "bite" in a corner, wider track in rear increases the "looseness" of the front end in a corner) by:
"...measure("ing"-added by RWS) from the center of the of the hub "front wheel" to the center of the rear axle "rear wheel" ("on"-added by RWS) both sides"
...your are getting a false measurement, one that represents the hypotenuse of a triangle, and not the base (parallel to the vehicle centerline plane). This number will be some amount LONGER than the actual wheelbase, depending on the height of the triangle (offset between measuring points, or condition number 2, above), possibly leading to a disqualification in a wheelbase limited class, due to a "too long" situation. The wheelbase MUST always be measured parallel to the centerline of the vehicle.
In condition number 3, above, the act of loading a frame will introduce variance into the suspension geometry, "moving the tire"' with relationship to the design position. For this reason the 2 sides must be averaged together to determine the actual "wheelbase" OR a vehicle layout (NOT a drawing, but a "string, plumb bob, and chalk" layout) must be done on a flat surface to determine, at the VEHICLE CENTERLINE, the distance between the 4 measured points, representing the wheelbase.
I would also have to add that measuring from tire edge to tire edge will not work if the front and rear tires are not the same size or if the front and rear rims are not the same size. Other than that I concur with Bob, generally.
I apologise if my intent was not clear. I was commenting (indirectly) that a tech official of a racing organization that wishes to attract big name (meaning MANUFACTURERS) money to this sport, should, at the very least, be VERY precise when giving a technical method that has application to his sanctioning body. I am aquainted with 3 seperate issues (one Jeep and 2 Chevy) of precicely this vagueness (from the late 80's).
When the "big boys" get involved and spend $250,000 (or more in some cases) on a single truck, precision is essential- where even a one eighth inch difference counts.
An old joke from GM/Military Vehicles goes like this.....
"If you want to run with the big dogs, you have to learn to pee on tall trees."
Taking full advantage of the rule definitions (whatever those opportunities are) is essential when you move to the big leagues.
I see your point Bob. I remember getting teched after Parker one year and they checked wheel travel. This was on a 7S truck ( Ford Ranger ). The rules stated 12" max front wheel travel. Bill was inside drinkin warm coffee I am sure because it was freakin cold out. So he had one of his cronies out to do the dirty work. Once we had the truck ready to measure he came over and started to measure. One small problem, this was a 4x4 truck and he was going to measure from the end of the hub. I jumped right on his case. I knew we were barly legal and if he did it that way we would not pass. Lucky for me the 2nd place truck was a ford also and he jumped right in to help defend my point. The tech guy then saw it our way and all trucks passed and keep there postions.
My point is you are right that how you measure thingscan be important when it comes to getting the most and staying within the rules!!!