Can someone please explain suspension scrub line? I read some explanations online but, I wasn't getting it. Perhaps if it could be explained as if talking to a 5 year old, it might actually sink in to my pea brain. I'm more of a hands on - visual kind a guy so pictures/illustration would help. Appreciate the help. -David
Basicly scrub line is ANY point of body, frame, suspension or chassis, that would fall below a line drawn from rim lip to rim lip (side to side, front to back and diagnal) should 2 or more tires COMPLETELY dissentegrate.
hi mate, I'll draw a pic but this is the easiest way to explain: look front on to your car. draw an imginary line from the bottom one front rim to the bottom of the other front rim. this is the scrub line. its basically what your car rolls on if both your front tyes go flat. what you dont want, is for things like suspension, chassis, motor parts etc to protrude below this imaginary line because if you get two flats and these metal parts hit the road you're going to loose control and or flip the ride. Danny
Run a string from the bottom of one wheel to the bottom of the diagonal wheel (ie: rf to lr)...anything that hangs below that line will scrub the ground if you have a flat tire....not good.... http://www.nsra-usa.com/safety.htm
If you take a string, hold it at the edge of the bottom edge of the tire rim and stretch it across to the bottom of the other tire (the ground, in other words)...that's the scrub line. Anything hanging below that "imaginary line" will be damaged should you have a flat tire while moving...works for front and back. R-
any suspension or frame component that hangs below the bottom of the rim. the body and exhaust doesn't count.
So is the scrub line the line from one rim to the the contact point of the other 3 wheels ( Like it would be for 1 flat tire), or to the other 3 rims ( 4 flats) ?
Guess you have never had a dramaticly channelled body,lol. Sure counts when it digs into asphalt and does an IMMEDIATE spin
If and when the explanation is clear folks-please print it out and give it to every one you know who is building a car now-cause they either dont know or care about running aground.... I like a car low ,but- excuse me ,the cars being built [and built lately] are just fucking STUPID LOW. they're Ugly and dangerous too!
HAH!, scrub line simply is.... If yer kar gets a flat tire. the road scrubs away parts of your kar hanging below the rim. I.E. the better your kar sits the more crap you have violating the skrub angle theorum.
The worst part are "bagged cars". Guys will air them up and then measure scrubline, ummmm, not how it works, the idea is to check the safety, not justify the rules.
thanks for asking and thanks for the answers..... One more though.... So it basically has NOTHING to do with the steering or suspension geometry, it's a safety issue...... so with a flat you still have some control.....
So, I don't need to worry about positive or negative scrub and the effect on steering, tire wear, etc. but, should be more concerned simply with what'll drag if I get a flat?
The dragging part isn't as bad as the catching part... like when something catches on a bump in the road and either remove the part (and maybe a few other parts that are attached to it), or the part stays on, and the rest of the car keeps going, like in end over end or a roll.
yup...and you might want to be concerned about stuff that won't hit the ground when you get a flat, but might get broken off if you happen to drive over a speed bump, or a curb. A friend learned this recently when the back half of the brake booster came off on a curb, and his new 41 poncho got crunched and he and his buddy got hurt.
Okay... the actual term "scrub line" measures from each wheel lip to the contact patch of the other three tires. Scrub line only takes into account ONE flat tire. Common sense, however would dictate that if you plan to allow any loved ones to ride with you, or you actually value your own life enough not to risk it, that anything hanging blow the plane defined by the lower edge of all four wheel lips is a danger in a catastrophic failure. A friend of mine in high school was killed when a dump valve failed on his hydraulic-equipped Camaro while coming down the Conejo Grade on the 101 freeway. I've never considered building a car that could "lay frame" since.
Well, it appears the way I learned "scrub line" is totally different from what has been posted. As I learned it -the scrub line had more to do with the LOW points on your chassis. The context it was used in was typically describing how to route important features (brake lines, fuel lines, trans lines, etc) ABOVE the scrub line in an effort to prevent (running over) a foreign object from damaging any important system of your car. Until now I had NEVER heard of a flat tire determining what the scrub line would be. I can see where this is important, but it seems to me that it is only the tip of the iceburg IMHO. The problem with the way I see it being defined here (and I don't mean to debate the definition - but instead the practical application) is that to define it simply as a line defined by the lower edge of the rim suggests anything ABOVE that is "safe" territory. Which would be true I suppose if your world was perfectly FLAT. Given this I suppose one might be inclined to mount a brake line on the BOTTOM of a frame rail so long as it was ABOVE this magical line. The problem as I see that definition is when you encounter real world issues such as CURBS, CHUCK HOLES and other road side nasties. Last thing you need is to run over a curb and find out that the frame bottomed and PINCHED your brake lines flat and tore off your trans cooler lines - you know junk like that. Now granted I have heard of other "scrub lines" but these were in a different context - steering geometry and such.
Much clearer now. Thanks to all for the help. It actually makes sense now in a real world, practical sort of way. -David
I don't want to confuse things but just to clarify. Of course there is some thing called "scrub RADIUS" that refers to the arc that the wheel moves in when making a turn. I don't think most of us will have to deal with that. Pretty sure that is some thing that is dialed into the spindle axle/A-arm relationship. Woody
you haven't been paying attention to what I build have you?!?!!! "any suspension or frame component that hangs below the bottom of the rim. the body and exhaust doesn't count" Thats a direct direct quote from one of the big name street rod associations when one of my customers went for a "safety inspection"... he got the sticker. I was taught scrubline is a line from the bottom of one rim to the contact patch on the other tire diagonally across. No frame or suspension component should hang below that line... whatever. BTW, yes I've drug body. For long distances and on purpose.
I think it's not so much the exact definition that's important....instead, it's the fact that you've looked under the car and thought about what might happen when you get a flat or something else happens. So many people don't, I don't know how many cars I've seen with lowering blocks and the ubolts poking an inch or two past the rim.
Why wouldn't the body count? If the body is sliding on the pavement you still will loose control. I always thought the scrub line was if you took all 4 tires off the rims and sat the car down on all 4 rims with no tires mounted, nothing should touch the ground. With that said on the MSRA web page it says "No steering suspension or chassis components should be below the scrub line".
Killer has the "simple" explanation. I added the "tire(s)". (meaning the other three) A "quick and dirty" way to check to see if your going to have a "scrub line" problem; is to REMOVE ONE WHEEL from the front of your vehicle, and lower the car on to the brake drum or disk, (GENTLY!) if ANYTHING ELSE touches the ground FIRST; YOU HAVE A SCRUB PROBLEM! It's a SEVERE test, but every once and a while cars have lost a wheel.
Maybe its just me, but it seems this scrubline rule was invented to regulate Big Trucks. And then kept alive to mess with Hot Rodders. A softly sprung car with good ground clearence can still bottom out, or hook or snag something on, say, a rail road crossing... From what I've read and heard, getting a flat in a SUV can be a real big problem too. And they have plenty of ground clearence... I'm not saying bottoming out isn't a problem, i'm just surprised it seems to be singled out...
you haven't been paying attention to what I build have you?!?!!! Nope, could care less what you build, it was a joke anyway "any suspension or frame component that hangs below the bottom of the rim. the body and exhaust doesn't count"Thats a direct direct quote from one of the big name street rod associations when one of my customers went for a "safety inspection"... he got the sticker. My channelled 34 pick-em-up DIDN'T get the sticker because my body sits 3 inches from asphalt at ride height (everything else clears). I was taught scrubline is a line from the bottom of one rim to the contact patch on the other tire diagonally across. No frame or suspension component should hang below that line... whatever. NSRA told me it was "rim lip to rim lip as to replicate the worst possable conditions". Not that I woulda got the sticker anyway going by your definition. BTW, yes I've drug body. For long distances and on purpose. Lol, who hasn't???
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