My question concerns SAI(steering axis inclination): How much SAI is "too much"? I know this depends on other design and adjustment variables, especially camber & caster, but just curious, since I know that SAI helps the most to center a car(straight line) and doesn't have the same negative effect on backing up as does high degrees of caster.
-ChrisCoaster
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Hmmm. I was right. Too scientific for this NG. I'll ask elsewhere.
Bye
>
You appear to have answered your own question...or maybe you should learn how to ask an intelligent, comprehensible question instead of just posting to show off your limited knowledge.
Steering axis inclination is set so that the axis passes through the lateral center of the tire's road contact area. If the tire hits something, it won't yank the steering wheel out of the driver's hands. People who put wide wheels with their attendant outward offset (or just offset wheels of regular width) on their cars often find them unpleasant to drive, as every little irregularity on the road wants to make the vehicle pull one way or another. Fashion over function again. Just like politics. Why would anyone want to increase SAI unless they wanted to recenter the axis on offset tires? And why mess with SAI if it's going to upset the camber?
Is that scientific enough?
Dan
___________________ Sorry Dan(and others). It's just that I post to a lot of forums out of curiosity and a willingness to learn or enhance what I already know. It's frustrating when I ask a question and it takes days for a reply to show up, when most other posters' questions are answered within hours of being posted. Nothing personal.
So basically SAI is designed to aim an imaginary steering axis through the midline of a tire specified for a specific vehicle - correct? Makes sense, and it's not something usually considered by customers who want to "plus-size" their factory tires, unless the rim offset allows for the tire's width to be distributed equally on both sides of that center axis.
You are posting through 'Google groups' on the World Wide Web or WWW by the looks of your header. This means it can take days for your post to show up on some 'Usenet' newsreaders.
If you were posting through a Usenet server instead of a web page, your post usually shows up instantly and can be replied to instantly.
A lot of Google folks and WebTV'ers get their noses out of joint because they think they are being ignored due to the propagation delay.
Then again, maybe you 'were' just ignored.... ;-)
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06
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A better picture:
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____________ Ahh, now I get it. So the axis of the SAI might be designed to fall slightly inside or outside of the centerline of the tire to give a particular vehicle a certain feel and handling.
FWIW, front-drive vehicles are a lot more persnickety when it comes to scrub radius than RWD. I think most people interpret a scrub-radius effect- the wheel jerking to one side or the other if a front wheel passes over a slick spot or loses traction during hard acceleration- as torque steer. That effect does not, of course, exist with a rear-drive car. I can imagine that the trend of tiny donut tires on huge offset (outward) rims on front-drive econoboxes a few years ago made those things virtually un-driveable on slick roads. I certainly always gave them a wide berth....
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Handling, yes to a degree. But the single most obvious effect of a non-zero scrub radius is to increase the sense of steering input ("pull") during braking (and acceleration on front-drive cars) when the front wheels have unequal traction or unequally performing brakes. Take, for example, a right front brake that is not working. IF the car has a positive scrub radius, the car will pull toward the working brake on application of the brakes. A zero scrub radius- no pull (and incidentally no direct indication that the brake is not working!) And a negative scrub radius will cause the car to pull toward the DEAD brake.
>Byeeee,,,,, tell her I love her. cuhulin
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________________________ Now if one of you could explain to this dyslexic ole' fool the difference between positive and negative scrub radius. Is it negative when the steering axis hits the road outside the centerline of the tire and positive when the steering axis hits the road inside the center line of the tire, or vice versa?
In either case, theoretically I could design enough SAI into a car depending on how far in(toward the car's center line) the upper and lower links can be positioned. That of course in turn depends on how big the engine is and how much offset the wheel rims possess. Ahhhh science.... : )
-CC "Who needs SAI to stay in his lane on the purntike, nyuk nyuk..."
Doggy,she needs to take me out in the front yard now,for ''whatever''.Byeeeeeee,,,,,,,, cuhulin
Its the way you said it- negative when the axis is OUTSIDE the center line of the car.
I apologize.I guess I had one beer too many.I only drink two six packs every week and a half. cuhulin
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