Scrub line??

I've done a search without much luck. I'm looking for a bit of a refresher on what scrub line is? I should remember from trade school, but I'm getting old. Any help or direction would be appreciated

 

The point where shit happens if your wheel falls off...

 

A scrub line is an imaginary surface created if lines were drawn from bottom of wheel rim on one side to
bottom of tire on other side. When lines are drawn from both sides an “X” under the vehicle suspension
is created. No suspension or chassis component shall be below top portion of this imaginary “X”.

 

So the concern is usually with cross steer set-ups?

 

Take the tires off the wheels. Install the wheels back in the car and lower it to the ground. The only thing that should touch are the wheels. Anything else that is at or below ground level is below the scrub line.
The reason this is the law in so many places is that if the worst possible thing happens and you loose 2 or more tires and anything drags, it affects control.

 

That's it? I thought it was way more complicated than that! I must have been confused with SAI

 

Beat me to it. Nice and simple.

 

SAI is Steering Axis Inclination.
Easy way to picture it is to look at a solid axle. The spindles are just about level with the ground (Camber). The kingpin is NOT exactly perpendicular. It is leaned out at the bottom a bit. The line through the middle should hit the ground at the center of the tire that is touching the ground. It's a bit harder with SLA and other IFS cars, but the principle is the same.

 

Thanks for the help. I thought scrub line was something more complicated. Hate to finish the 27 to find out it's messed up!

 

scrub line- the 40 cars waiting to get in the carwash

 

The above is 'SCRUB RADIUS'...two different critters. DD

 

This is the way the NSRA used to measure it during their safety inspections. It is a bit more forgiving than the way RodSTRace discribed...but not much.

It's a tough spec to meet if you like your cars low...not MidWest low, but California low...especially if you're running high profile tires.

So I don't even try to meet it. I design the car so that no unsprung mechanical components extend below the frame...and hope that the car skids straight if I get a flat tire.

I'll probably get a lot of shit about this...but just ask me if I care. I like 'em low, NSRA or not.

 

http://www.cdxetextbook.com/steersusp/wheelsTires/alignFund/steeringaxis.html

http://autorepair.about.com/library/glossary/bldef-748a.htm

http://www.tpub.com/content/construction/14273/css/14273_336.htm

Steering axis inclination (SAI) is the angle away from the vertical, formed by the inward tilt of the kingpin, ball joints, or MacPherson strut tube.