Scrub Radius

[Var]

I'm at another modification crossroad. I've run into a little problem called knowledge. I just started to learn about scrub radius. I read a few articles on the net and pretty much all of them say that positive scrub radius is no good. Then i called the people at a rim company that make racing wheels. They said "people are blowing smoke up your ass" and when it comes to performance you want to get the car as wide as possible cause the pros always outweigh the cons. (disreguarding increased loads on suspension parts and the hub/bearing and only considering performance.) So i have articles telling me one thing and some other guy telling me something different. I'd like to you hear you'z guys's opinions.

[RBS14]

neither are correct. As you could probably imagine, it's somewhere inbetween. when you have none, you can't feel what the car is doing much of the time. For example, with no scrub radius, when the back of your car loses traction and starts rotating, you can't hardly feel it because the front wheels don't react whatsoever. with positive scrub radius, they will countersteer a little bit and you can feel what the back of the car is doing better via how the steeringwheel feels. However, a hugely positive scrub radius is bad. You don't want the car as wide as possible. A really wide scrub radius creates instability at high speeds. the front wheels tend to shimmy a lot and track weird. Ever wonder why so many lifted trucks have "steering dampener" shocks? it's to minimize the afore mentioned shimmying caused from the extremely low offset wheels they put on. The bigger the scrub radius, the higher one side of the car raises when you turn the wheels to full lock too. For example, with my stock wheels, I would turn my wheel to full lock in the left direction at a stop and the left side of the car would raise slightly. But when I put my 17x9 +15 fn's on, it raised a ton more when I turned the wheel to full lock. This is because of the increased scrub radius.

In context of the wheels you were thinking about getting, they will definately give you a big scrub radius. Too much IMO. With too much positive scrub radius, the steering feels "dead" and unresponsive. To me, I'd rather have the steering feel precise and accurate than have that extra couple inches of wheel lip. One important thing to remember with suspension setups, front suspension especially, is that when you change one angle, many others are affected. So when scrub radius is changed, other things are changed too.

[Var]

I understand what you are saying. More specifically i need to know where a bad range is on our cars. . I dont know if this makes a difference or not but i only use this car for dorifto. I park it in my garage until there's a track day or a car meet. My rim will be 16x10 offset undecided. I will do some measuring to find out my ranges to make sure there is no rubbing on the fenders @ full lock or otherwise. But i would like to go with extreme sizes just for the fuck of it. my car looks funny with the paint, may as well make it look even more ridiculous.

[RBS14]

As for a rediculous scrub radius, it's all opinion. I've got pics of a S14 in japan that is running 17x10 -15 front wheels. It's a drift car, so you know the wheel doesn't have any clearance issues with the frame at full lock. So I'd say go wit that. He also has massive over fenders. Get the wheels then the fenders, make them fit. The only thing I can't say is how it feels. maybe you'll get a response from someone running front wheels like that, maybe they could give you some imput. However that is highly unlikely, and moreover, are prolly not knowledgeable enough to know when it's too much.

[that180guy]

rbs14: can you elaborate more on exactly what the "scrub radius" is?

from what i read it has to do with wheels with too low offsets being too far apart? :confused:

[Var]

cmon alex..google the term "scrub radius"

[RBS14]

I suck, as stated below. read below for a good explination on scrub radius.

[Var]

DAMN! before your explanation i knew what a scrub radius was. that was way confusing. i just unlearned everything i read about today. here it is in a picture. pictures are fun

http://www.familycar.com/classroom/Images/Align_Scrub.gif


http://www.datsuns.com/Tech/scrubr.gif



First picture is positive scrub radius, the second picture is 0 scrub radius

[that180guy]

cmon alex..google the term "scrub radius"

silencio vargina! :fawkd:
zilvia can be a learning experience too instead of just random shit and flames. and i already understood the concept b4 hand, i just didnt know it was called "scrub radius"

[SilviaSativa]

Hopefully this clears up any confusion, just a summary from my Automotive Suspension & Steering Systems classroom manual.

Steering Axis Inclination - Angle of a line through the center of the upper strut mount and lower ball joint in relation to the true vertical centerline of the tire viewed from front.

Scrub radius is the distance between the SAI line and the true vertical centerline of the tire at the road surface.
Postive scrub radius occurs when the SAI line meets the road surface inside the true vertical centerline of the tire at the road surface.
Negative scrub radius occurs when the SAI line meets the road surface outside the true vertical centerline of the tire at the road surface.
(+)
http://www.familycar.com/classroom/Images/Align_Scrub.gif

[kazuo]

Scott's explanation sucked. It was way too confusing and long.

Pictures are better. +2 pts for VAR and SILVIASATIVA.

SO now we know.

[RBS14]

I suck. I'm sorry. I'll edit it.

[that180guy]

sweet. one of the few techincally informative threads on zilvia!! maybe well compete with fa on whose more informative....nooooooooot!

but really good intel guys