In my experience working on suspensions for almost 40 years I've learned there really is no set rules to vehicles. Sure there's experience, guide lines, etc but every car is different. Had 2 set up identical and one drives great and one like hell. Whether it be the weight distribution, front axle load etc that makes the difference I can't say. Had a early 80`s t-bird that wouldn't wear tires unless you set it up at -3/4 camber with fat 1/8" of toe in but every other same year thunderbird worked with 0 camber 1/16" toe in. I wish there was a 1 formula fits all but there isn't. That's why as I build mine I try to eliminate these problems that I've had to deal with for years going into mine. Example: I've seen the small tube cross over tubes bend when bumped against a curb hard enough, not really hard hits just that perfect bump with all the angles just right, I also think on some of the heavier cars they may be the cause of some small vibration at higher speeds so I build mine out of heavy wall tube (.120) also went from 1" tube to 1 1/8". I've built 8° of caster into the front 4 link frame brackets, the stock brackets and set up run about 4° caster. This way my suspension is at 8° with all 4 rods in a neutral position on threads giving me numerous amounts of adjustment. And absolutely no bind in the front suspension. Went to the same trouble on the rear end. All suspension components built and installed with frame at ride height and suspension at ride height. With the rear triangulated 4 link the lower bars are parallel to the ground, pinion angle set with all 4 bars showing equal thread count again allowing for maximum adjustment. Upper bars slightly down with 37° angles outward. Again the details are in the building on what may help the drivability and handling but even then there is variables that come into play.
Now I know why those Mexican dudes used to drive so slow in those low rider, wide reversed rim, small wheeled sedans. Because their scrub ratio was way off...
It seems the easy way to poor scrub radius is to reverse the front wheels. Been happening a long time, it may be "traditional" but it's a bad idea.
So just out of curiosity, how bad is this setup for scrub. To me it looks to be about 1" out of the tire tread contact
pretty bad. However it's a good example for this scrub radius thread to show that disc "kits" and Ford wire wheels with their spacers simply don't belong together. I believe Ray mentioned these wires w/discs earlier, and on other threads. This is also a perfect example of copying what people have seen done time and again, and therefor simply don't have a reason to "think it over first". A few hambers that try to point any major issue out on somebody's build, often take verbal hits from keyboard warriors. The bad part is that you have painted yourself into a corner as far as you are now questioning your own build that is now a finished chassis..... even as far as custom built cycle fenders to fit that incorrect offset. The good part is that perhaps this thread is why you and others might benefit in the future from Blake's scrub radius thread here. My own personal take on the current misdirection of the hamb: Let the hate begin, but somebody needs to say it on the only traditional hotrod site on the web... when we stray away from the old ways, things sometimes just are done for looks without research and then problems develop.(such as Ford wires w/discs) I cannot believe some of the things I've read or saw on hamb just in the last week. People read it and take it as fact sometimes, and if someone disputes it, they look like a shit starter. Example...A thread popped up where a member wanted to switch from an off topic GM HEI distributor and go to a points distributor...and one person insists that you then need to put new plugs in every 10 to 20k miles...which is a pretty ignorant statement. See? if a person wants to go "old ways" on a traditional site, he usually gets misinfo from the modernists. The hamb is not about building stuff that has 12 heated cupholders and outperforms, and out-handles a Mercedes. .
I've got a better idea, let's NOT let the hate begin. If it does start this thread will go away and I'm learning here! Tire diameter has been mentioned a couple times, so far. If I'm understanding right, even with the same rim different height tires will have different scrub radius. One other question: how thick is the typical adapter for Ford wire wheels on '40/48 brakes? -Dave
You are sooo not embracing your inner Jerry Springer. Some of the posts on here remind me of this picture I stole off the internet a while back. Sometimes we need an engineer on a ride along, sometimes we don't.
It's a combo of parts up with the compromises made stacking up wrong. Looking at it from the only vantage point I have,, it seems like the problem begins with the brakes. If I were standing in 1950 it might look different. There's no question that disc brakes are superior to drum brakes. The question rests on whether or not disc brakes are needed, and many variables there. The first being available traction for braking because no matter what you'll never exceed that traction by increasing the brake force. The next variable is going to be weight- GWV of donor vehicle vs GVW of the hot rod being built. For example : If you've got f1 or F100 brakes designed to stop a loaded 6000# truck on your #2000 lb hot rod there's way more than enough brake force. The other end would be Motorcle disc brakes and calipers designed to stop a 600lb MC trying to stop a 2000# hot rod. My opinion is that we probably and most likely do not need disc brakes nor can we use their superiority but really do need good geometry.
Disc brakes are not about increased braking force, they are about improved control & feel, especially at the limits of tire adhesion. Self actuating drum brakes are about the worst at this, with lack of both feel and control. Under hard/emergency braking they tend to lock up and slide. The best braking comes from slowing down the rotation of the wheel without prematurely locking it up. If you lock up the wheel and the tire slides you both increase stopping distance AND lose control of the vehicle. This is where disc brakes excel and self actuating brakes are at their worst. Do you really need good geometry over control and feel of the brakes? I question that. Which is more dangerous, an extra inch of scrub radius, or brakes with reduced feel and control at the limits of tire adhesion? Which has resulted in more crashes over the years, cars locking up the brakes in a panic stop and slamming right into whatever it was they were trying to avoid, or a driver losing control of his car due to an extra inch of scrub radius? I think you have a tough argument from either a safety or performance aspect. And I'm not talking about poor designs with several inches of extra scrub radius, which we see even with some drum brake systems, I'm talking about a system that may add an extra inch, maybe even 2 inches, of scrub radius. IMO, that's still a fair trade off from a safety and performance perspective. From a traditional styling perspective, no, it's not. But if the discussion is about performance, I'll take that extra scrub radius and deal with it in exchange for better braking performance.
Your entire post is dead on, but I quoted the most important sentence to me.^^^ That sentence won't go over well with the people who have been mislead for decades, especially the ones who actually have said on hamb, that just by switching to a single circuit drum braked car to a dual circuit with the same drum setup will make it stop better. There is just so much misinfo around. Sure, I know that if you run through 2 feet of standing water, the discs will stop far better, but do we need be concerned with that odd event Are we "still ok" if I don't agree with most of your post? I just don't have those brake "feelings" you speak of, or the other issues you posted, with mine as a daily in modern day hectic traffic conditions. It has 40 front drums and 55 Olds rear drums, 6:70x 15 bias fronts and 7:60x 15 bias rears. It has great feel and neither end will lock unless I force it to. Yes, I've had people pull out in front of me more than once. My car is somewhat better at defensive driving, as I run a 1950's super fast ratio Ross steering box that only turns 2.5 turns lock to lock on the stock Ford axle stops. I could switch lanes in a bad situation by barely moving the wheel...and I also run super low caster so it takes little arm effort to avoid something happening that is in your path. I refuse to build a front end with incorrect geometry. Seems like if a person "does not get it" at that first part of a chassis mock up, or is willing to trade off geometry?...then the rest of the build will be more to follow trends or misinfo, rather that doing what is really needed, or not needed.
Scrub radius is just one part. Think of it as tire contact area and these pictures have been looked at as if you had zero caster. When you turn the wheel with no scrub radius the contact stays in the same place but having some KPI induces a camber (contact area) change in the tire when turned. If you add a scrub radius the contact area is going to rotate forward or back effecting the wheel base and track width. If you add caster it moves that imaginary line infront or behind the contact point and now when you turn the wheel the caster creates more camber (contact area) change and jacking effect on the car. This just by turning the steering wheel and we haven’t got out of the driveway yet. Add camber, toe, Ackerman percentage and tire pressure, As F&J and others stated it’s a balancing act the manufactures did for us. At speed I want as close to zero as possible and in a parking lot I’d take more scrub radius but overall a neutral turning car. Just as I have inputs on the tire, the tire has inputs on me.
Absolutely! Disagreements on things like this are no big thing. Discussions are how we work things like this out, and I'm big enough to admit I'm wrong too when I'm convinced about it. At this point I'm not. Anyway, I fear pursuing this further is a distraction from the main topic of the thread, so I'll drop it.
It is and it isn't the main topic/issue. The thread is scrub radius, particularly on solid axle and the quickest way to throw it out is the very common brake setups. It's almost as if you shouldnt talk about one without the other. The quickest way to compromise back out of created shitty scrub radius is to put a FWD style offset wheel on your hot rod. Yuck! We put disc brakes on a 59 Mercedes 190sl and kept the original track width and used the factory wheels and had great geometry. It wasn't a kit sold by every store with an internet shingle though. The same is doable on a straight axle but it doesn't use the absolute cheapest rotors and calipers known to man. We also got a fantastic disc brake set up on a 54 Chevy truck with all sorts of trick shit on the non wearing parts to use off the shelf rotors, pads and calipers and great geometry. Plus we knocked 4 lbs off the unsprung weight on each side. Once again, in case you missed it I stated in that post that without question disc brakes are far superior to drum brakes. You mentioned quite a few ways. One really cool thing you didn't mention is there's usually no periodic maintainence or adjustments needed between pad changes. That's not the case with drum brakes and they shouldn't be treated the same.
As you saw, I posted my tire sizes and that they are bias. Carry that thought out logically, then you should, or already do understand that if I was to decide to run performance type radials of certain sizes on both ends, my current brakes might not then be not as well suited/matched... IMO. I knew what tires I wanted to run in the beginning, then kept that in mind during the rest of the build. A little off this topic but follows the thought of tailoring the chassis parts/design to what other things you do use... I use 35/36 rear trailing arms, but set in a true wishbone design by using a 1932 front bone yolk center piece. Any person asking on hamb as to if a torque arm is required with rear 35/36 arms, he will get the "yes" nearly on every response. Mine does not have one, as I run skinny tread bias on the rear, and the tail end of this car has so little weight that you simply will break the tires loose before stressing the bones which are also running with "lowered mounts on the axle tubes". << that "lowered mounting" reduces stress on the bones. If I ran slicks, then the build must change to that change. "Tailor the whole car", is my point, not just using blanket statements that cannot possibly cover all the possible variables on our hand built cars.
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