I like to know the hand on experiance on a hotrod front suspention what is working best when we dealing with scrub radius ( distance ) -Try explain it easy and what work from experiance on this cars. I ask just the information as I cant do much to change it in reality. Lets start that draw a line from king pin down to contact area on wheel to ground. Then minus (-) scrub is more out to end of wheel and positive (+) is more to inner part of wheel. I dont know here on experiance what is prefered, is it zero or minus 1-2” or positive 1-2” ? In my case I has a 34 axle dropped 4” and 32/34 spindles and Ford 40 brakes and Ford 40 wheels ( 4x16 ) and Firestone 4.50 tires. I might change to Lincoln 1942 brakes, the model that has a semi offset. The 1939/40 has the most offset, 1941 has a zero offset and 1942 has something in between. I would for the ’look’ use the 1941 ( flat ) as then I can use my Ford drums/hubs. But I found a decent set of 1942 and seller told me it gets me a ’better’ scrub. In use the 1942 model I need to use the Lincoln drums. Note. I guess drum location change it some. So what scrubs normally this cars like to has to behave ’decent’ ? I show 3 pictures and one must has a huge positive scrub ( big finned drums ) and one more normal or around zero scrub and also normal but maybe a say 2” positive scrub.
Your pictures show Camber, the pic with the lines show positive camber, (wheel is out at the top) Not sure what pic# 2 is. Not sure why the wheel is out so far on the blue car. Scrub or scrub line refers to anything that hangs below the bottom of the wheels. Let's say your car has 4 flat tires, does any part drag on the road? If you can push the car with 4 flats and nothing touches the road your scrub line is ok. The other pic you posted shows Toe-in
The pictures above was not mean to show toe in or camber, just show spindle vs wheel centre ruff. Here is my set up on a Ford 4” 1940 wheel, Ford 1934 spindle and Ford 1940 brakes. It show a positive scrub say ca 2”. I dont know yet what a Lincoln 1942 brake will get me at scrub ( + or - ) at same spindle. I hardly think I can get a negative number at 1-2” if that is prefered. My guess we like to see a positive number at 1-2”.
Hank, I think "zero" scrub radius would be preferred. Where the center of the tread would pivot on a point. Tom
I feel most hot rods get a positive radius scrub whatever spindle/brakes and wheels used. I think its hard to get to centre of wheel or get into a negative radius scrub. If I got this correct a negative radius get a better "road feeling". But from what and where on this types of cars/frontends I cant say - thats why I ask. The question do come to me when I hear by using a Lincoln deeper offset 39/40 or the 42/48 gets a 'better' scrub. The Lincoln 1941 has a flat backing plate ( the 2 others has a deeper offset ) In reality what happens when mock this up use a Lincoln, I cant say.
If you use either '41 or '42-'48 (with a spacer) Lincoln brakes, a Ford hub & drum, along with a normal wheel the scrub is the same as Henry designed it and be just fine. It's when people use goofy combinations of brakes and wheels that the scrub gets moved way outside of where it is supposed to be.
That’s true in theory but sure does hold much when a hot rodder or guy want some new wheels and tires…. it’s the first thing thrown out the window.
Most cars have a small amount of scrub radius. One of its jobs is to put the steering linkage under some tension or compression to compensate for the minute amounts of clearances in the joints. Most rear wheel drive cars have positive scrub radius. This causes the front tires to want to toe out when the car is moving forward, hence the need for a toe in setting. This allows the tires to run at 0 toe dynamically, reducing tire wear. If you have too much positive scrub radius, like the picture of the car with the Buick drums, the tire moves in an arc when steering the car. This causes excess tire wear. It can also cause tire rub issues at full lock on a full fendered car. Other than initial design, (What 3w Hank is contemplating.) other things that can affect scrub radius are wheel offset and tire diameter and width.
Refer to the above to start, will anything on the chassis drag the ground if just on wheels? If no, off to a good start. Past that, the closer to center you can remain at tire contact using the imaginary line you reference the better off you'll be for road feel. A little bit 1 way or the other, no big issue. Too much, make changes. The blue one looks odd, I never liked that look. You said keep it simple.
That very thing is a law here in Pa. for hot rods registered as a street rod like most 1948 and back hot rods are. Not a lot of restrictions on street rod plated cars here, but the SCRUB LINE is a pretty big one. And yes, I am a Pa. certified safety inspector.
This will just confuse the already confused. Scrub line and scrub radius are horses of a different feather.
One you scrub in a straight line, the other you scrub in a circular motion...sorry, I couldn't help myself
I’m a little confuse ( guess its normal ) Key here what works on this cars. I’m not building a roadrace car, I only try to build it as they was done in the past. -I will drive this Ardun head 3.5” chopped coupe very mild. Question is, I has a 34 dropped axle and 34 spindle and a 40 4” wheel and now I has 40 Ford brakes but it will change to a offset brake shield from Lincoln with Lincoln drums/hubs. -This must been done many times in the past. If I got my test correct today I has a 2” positive scrub ( but is that scrub radius or scrub line = I cant say = help needed clear that out ) But the overall question is the seller of the Lincoln 1942 brakes said the offset get the scrub better. What it mean in the test I did on mock-up I guess I will se on the Lincolns soon. But asking just to has a reference on what experiance told on this cars. So far I’m all over on 2” positive, 1” positive, 1”, zero or 1”negative etc. Now it come up radius and line. But all this is VERY good learning = so big thanks on inputs so far So put a spacer and ’get back’ to Henry, that is not what I was told, as the offset and the drums on the Lincoln was the key to get the scrub better ( from Ford 40 brakes ) -Maybe question like this simple cant be asked as to many ways to see it. I’m not really ask on the best, just what has worked. Or maybe just bolt it on and see. Maybe I first need claar up ”radius or line” or where is that line on 34 spindles and 1942 Lincoln brakes and this wheels.
No, you are correct with the question and pics you supplied. It is some of the other replies that are confused and have it wrong............ You want a little positive "scrub radius" to stop wandering/tramlining. Half an inch, or close to it, is generally seen as good (10 to 15mm positive). This will make the front wheels want to "toe out" while rolling down the road. "Toe in" is added and counteracts this so the wheels actually point straight at road speed, but the whole steering system will be in a state of opposing tension. This takes most of the wobble out of it all. Too much scrub radius will make the steering heavy and over-reactive to road surface irregularities. It will also chew out your tires over time. We will leave "scrub line" for another day..........
You actually need a bit of positive scrub radius to counteract positive caster. The longitudinal forces [or drag] cause toe-out which counteracts vertical forces [from caster] causing toe-in. But if you go too extreme with both, you will get death wobble , because these forces can exceed the mass of the vehicle
From what I heard on seller on the Lincoln brakes was 30-60 mm positive. ( or say it in inches a tad over 1”- 2” ) and there I’m now on the Ford brakes ( = 2” ) and that set up is very common. But I will clean and mock up the Lincoln 42 brakes and get back to thread as soon as I know. -Maybe it get me to 1/2”, I will let you know. Then on driving experiance will take several years as this is huge project to learn on the style, collect all parts, fix all damage as all parts is old, then frame and body works and headers and engine works and paint and chrome and get the car togheter plus a ton of money to make it happens. I’m maybe is close to a deal on a old kit Ardun heads and a Ital supercharger. That get me to has maybe 75% of the parts. It shore is very expensive and complicated and time consuming to build up a ol racer coupe ! I hope I can make it to end.
Off topic vehicle but a good explainaton in small words. Steering You Straight: What is Wheel Offset and Scrub Radius? | DrivingLine Truthfully on that car with your wheel and hub setup you probably aren't going to be off enough to write home about. the guys who run into the issue are those who run a hub that places the wheel further out towards the end of the spendle or those who run deep reverse wheels. If it is off the leverage from the tire contacting the road further out from the 0 point is going to give you more feedback when you hit a rough spot in the road. It's also going to be a bit harder on wheel bearings. Other than that it is right there with Ackerman in that scrub radious is another thing that some of these guys who want to sound knowledgable because they read "how to align your race car" toss out in an attempt to impress the natives. All of our hotrods that have a wheel base a tad different than what the chassis left the factory with have Ackerman a bit off but go to the parts book for front spindles for any brand of truck that has a standard cab short box, standard cab long box, extended cab short or long box or crew cab with short or long box and check for front spindles, There is only one spindle for all wheelbases in the same weight of truck, they don't have a different spindle for the long bed crew cab than the do for the short bed standard cab. Back to scrub radious . This well known Pacific North West car is a pretty good example of being way off from what the book says is good scrub radious. Still I have never heard that it drives bad. On this one with a dropped axle and probably 40 drums the scrub radious is pretty close to text book right on. Side shot of the black 32. Then we have a good number of members who run Buick drums and 35 Wires and have to have a spacer to move the wire out to clear. All of them will tell you that their cars drive great and don't have and issue. I just flat would not get my nickers in a knot and worry about it. Let the self styled experts rattle on and have fun.
Well I'm gonna counter that ideal. "...would say their cars drive great..." and not that some wouldn't, but I've found more often than I'd like to that so many don't really know what great is. They put up with wander, suspension limits, ill handling, tires that squeal as they navigate tight parking because "...and this old stuff just does that..." is the urban legend that comforts. I think the more you understand in basic terms the better the outcome. Do we need a PhD in suspension geometry? No, but we can't just play copycat either. After all the investment in time and asset perhaps more than a coin toss can help determine ride and drive quality. I vote worry about it just a little vs ignore it and have fun.
I believe at some point even natural differences in left/right braking power can make the steering pull fairly hard on the steering wheel too, if the scrub radius is "too much.".
I was wondering if there would be "witness" marks on the tires over time if the scrub radius was an issue.
not withstanding......... don't forget the unseen line between the centre of the wheel bearings the two taper rollery bearings I reckon want the load in the middle of them = { \/ } that is the thing that will make you snigger under your breath when perusing the picturds as its when you realsie for the first time that a wheel is sitting outside the outer bearing for example you will . also for example IF a 1940 ford hub has the same dimensions as a f1 hub and they are both 16'' one is a 4j one a 5j or 6j? do they share the same offset? NOT backspace
I’m building my first traditional hot rod but from past experience with race cars, ATVs, and other go-fast toys, scrub is pretty important to me. I’ve driven/ridden a few built vehicles with excessive positive scrub and it was always a bad experience with excessive steering feedback, which in a few cases was dangerous. Surface irregularities (ruts, potholes, etc) yank on the steering wheel, and striking an obstacle could rip the steering wheel right out of the drivers hands. Even under normal driving the feedback is excessive. I know we aren’t building off-road racers here, but the fact remains that with excessive scrub a force that your wheel encounters has leverage against your steering control and those forces are going to be transmitted to the steering wheel, probably not in a way you like. It just makes for really bad driving in my experience.
airsix, -Are you into some negative scrub radius ( lets talk radius ) as I dont yet know diffirence on line and radius ( even if my test was done with a ’line’ ) But as I try to say, the combo I use is not new but I did like hear on experiance what works best. So far a zero scrub migh sound nice but it sounds more ( from most ) to go a positive scrub. But building a traditional hot rod one cant change that much anyway. So my major question I has was ; as I was told, the Lincoln 1942 semi offset gives a ’better’ scrub over thd Ford 39/40. This 42 Lincoln backing plate has a offset but so do the Ford 39/40 backing plates ( I throw in pictures just show this ) Whit that said, its 3 Lincoln models on ’offset’. But so far I has not test in a mock-up it and compare to the Ford 40. Lincoln 39/40 = deep offset. Lincoln 41 = less offset Lincoln 42/48 = semi offset. Note. Once install it, it is what it is since I will not change spindles ( 34 ) or wheels ( 40 )
So very much all of this. I have been told that hot rods are supposed to ride and handle poorly, and that is just the way that it is. If looks could kill, I would be long dead from pointing out a build error.
I'm thinking that you are going to have to live with it and be done with worrying about it. As Airsix very well said in post 26, you may get more and stronger feedback than you want but with the tires you will run that may not be all that drastic. It's just going to want to have a bit more wiggle in the steering wheel than you want on rough roads. There is a lot of extra space between that wheel and the drum but we all have to live with our personal choices. It is what it is unless you are afraid it won't pass inspection because of the offset. Truthfully if I was not going through everything you have been doing I'd think you have a spacer or adapter between the wheel and the hub by the loks of things.
Mr48chev, Your absolutly correct. And I also said it. I’ll just ask on experiance what scrub numbers do works best in this type cars ( no matter of combo, spindle, brakes, wheels ) The mock up I did is not very serious just a ruff one but I has NO adapter. If bolted on with bearings my scrub test might change some but in big picture it shows what this combo will be and that is around 2” positive. My next question, why ( if why ) a Lincoln 1942 will has a better scrub ( I showed the backing plates )
The Jalopy Journal
