Front suspension - some general basic questions

[erikhoel]

I have been unsuccessfully searching the web looking for information with regard to the front suspension of streamliners. The requirement to minimize frontal area creates some very interesting problems given the limited area (space between the two tires) in which to work with. Presuming that you want a front end with negative camber and positive caster:
 
 - are A-arm suspensions the way to go?
 - should the steering arms be ahead of the axel centerline (front vs. rear steer)?
 - is rach & pinion or worm & sector preferable?
 - what are the advantages of going with a tandem wheel configuration
 
 Thanks for any insight,
 Erik

[John Beckett]

How wide is this car going to be? Treadwidth?
 
 JB

[John Beckett]

Erik
 
 The first Bonneville car I ever built had solid rear suspension. Didn?t like the ride or the handling very much. Converted that one, and every one that I have built since has had suspension.
 
 Independent suspension in the front is OK, so are solid axles. Have run both. Depends on what fits your application, and Streamliners don?t have much room.
 
 Have used rack & pinion and worm & sector box type steering, both work fine. Also front and rear steering, no appreciable difference to me.
 
 Usually run 0 deg. camber, 10 to 15 deg. caster, watch out for your scrub radius.
 
 Tandem wheels fit a very narrow package. Personally don?t see the advantage since I can?t get my shoulders into a 16? car.
 
 JB

[Sumner]

Usually run 0 deg. camber, 10 to 15 deg. caster, watch out for your scrub radius.  

I worry about this (scrub radius), maybe too much.  I'm making a straight front axle for my lakester using the ends from a '37 Ford dropped axle.  I'll use '37 type Ford spindles with mopar rotors (cut down so they are just a hub).  I have a bearing kit from Speedway.
 
 I need to order the front wheels soon and I can't change the offset much, but want to try and use the offset to help with getting correct scrub radius.
 
 Should I try and get as close to a zero scrub radius as possible?  How much negative and/or positive scrub radius can I get away with and still have the car drive in a predictable manner?
 
 I'll be running 5 X 15 inch wheels, with about a 25" X 4.5" tire.
 
 Thanks (and I don't mean to steal this thread),
 
 Sumner

[4janey2]

What is "scrub radius"?
 In setting up the turning angle of the front wheels, what steering ratio is recommended? What turning radius or how big a circle should be designed into the front axle for steering? How many degrees of turning from straight ahead to a full left or right hand turn before hitting the stops? If this is in relationship to the wheel base, what is the minimum and maximum recommendations? This would apply to roadsters or comp coupes.

[Sumner]

What is "scrub radius"?

The following is from a site on the internet and not my wording, but probably worded better than I can:
   

Definition: The distance between the extended centerline of the steering axis and the
 centerline of the tire where the tread contacts the road. If the steering centerline is inboard
 of the tire centerline, the scrub radius is positive. If the steering centerline is outboard of
 the tire centerline, the scrub radius is negative. Rear-wheel drive cars and trucks generally
 have a positive scrub radius while FWD cars usually have zero or a negative scrub radius
 because they have a higher SAI angle. Using wheels with different offset than stock can
 alter the scrub radius

With a straight axle project the king pin angle down onto the ground.  Hopefully it falls under the tire in the tire patch area.  I've heard that it is best if this point/line is in the center of the tire patch, but I asked the above question to see if there is disagreement with this.  If it is inside or outside of the center the tire will want to be turning on the inside or outside of the tire and not the center.  I would think this wouldn't be much of a big deal going straight on the salt, but I talked to a couple people who didn't get this right and said the car didn't want to run straight over 150.  They corrected it and said the car was much easier to drive.
 
 I'm still interested in some opinions on this.
 
 The rest of your questions I'll leave to someone else as I only want to botch one up today   .
 
 c ya, Sum
 
 Lakester Construction In
 Progress

[4janey2]

With most straight axle cars the tire patch is outside of the center of the king pin, so this must be positive? A 4" wide racing wheel/tire could not get enough offset to center the patch with the king pin. So how does this affect the handling?
 
 JT

[Sumner]

A couple of other things besides the wheel offset will effect this.
 
 More caster will move it out and a taller tire/wheel will move it out.
 
 c ya, Sum

[4janey2]

In setting up the turning angle of the front wheels, what steering ratio is recommended? What turning radius or how big a circle should be designed into the front axle for steering? How many degrees of turning from straight ahead to a full left or right hand turn before hitting the stops? If this is in relationship to the wheel base, what is the minimum and maximum recommendations? This would apply to roadsters or comp coupes.

[John Beckett]

A nice slow steering ratio works very well. My current car is 26 to one.
 Turning radius is basicaly whatever fits the body your using. Previous car had stock stops on the steering. My current car has one inch spacers added to the stops to keep the tires from rubbing on the body.
 
 JB

[4janey2]

How many turns lock to lock is that?
 JT

[John Beckett]

Hmmm...never measured it that way. Dont have it handy to check right now. It's approximatly half of what I started with. Lock to lock will also be effected by the ratio of the steering.
 
 JB

[Stan Back]

4janey2 -- Jim, stop by my place in Highgrove and I'm sure Al Simon can help you.  He's set up shop in the first row.

[JackD]

The steering wheel travel should be limited to the amount you can control it without going hand over hand. If you need more, you have lost it anyway.
 How many times does it have to go around before it breaks your wrist when you instinct is to not let go ?
 Bump stops should limit the travel to the amount required to move it around when you are pushing it and clear the course when it is over. How much extra do you need to go straight anyway ? If you think more will help to recover from an out of shape pass, you are better off dealing withthe reason for the sideways view and let the vehicle come back.
 Scrub steer is a product of tire contact offset from the hinge point of the steering. Each wheel width will produce a different scrub with the same spacing from the bolt surface to the hinge point.
 To best understand it's effect, imagine what would happen if you had an extreame dimention like 24". The distance will amplify the conditions that occur when a wheel is loaded by going over a bump for example. The load is sent back into the steering and the travel will be duplicated on the other side. The question is how much of that do you want or put up with ?
 Scrub in a front wheel drive is the same reasioning and in that case the drive will pull one way or the other if the wheel is offset. If you want the wheel with the most traction to take off, you know how it will.

[4janey2]

Stan Back,
 Are you a member of the San Berdo Roadsters? If so is Al in the same row as your in?
 JT