In a recent thread about mounting my split wishbones F&J said this: I've been thinking about this for the past few days. I've heard people say set it between 5*-7*, others have said as much as 10* I've always followed the 7 degree crowd, because thats what I've always been told it should be. How's about a civil discussion on caster angles in a street driven hotrod?
I did the 'somewhat' vote because the caster is actually set by ford in the spring crossmember. I match the axle caster to the spring caster so there isn't any misalignment/binding when i slide the bolt thru the shackle and perch - i think ford sets them at 5-7degrees.
Ford said 4.5 to 9. More caster will give you more camber gain in turns, this could lead to shoulder wear at the high end. Caster increases trail, meaning the contact patch center is behind the spindle, this increases self aligning torque or steering effort. Some say it increases wobble. Caster gives more "bite" in turn because it jacks weight (adds wedge) onto the LF/RR on left turns and vice versa. Steering effort and tire wear are the most noticeable negatives, until they show up the more the merrier. 7 seems a safe neutral number. Baaaah Baaaah
I believe caster on an I Beam is subject to car weight, spring action, wheel offset and the kind of Tires you are running. Also drag link or cross steer in same conditions will take a different set. The real question is how Heavy do you like your steering wheel action? The Wizzard
the more + caster the heaver the car drives up to a certain point , high speed police cars LTD and vic 6.5 to 7 +
Very true...and trail isn't often considered when setting caster. Why should it be considered? Because 7* of caster on an axle with tall 16" tires has a good bit more trail than a 7* caster axle with short 14" tires. Puts a whole different spin on things when thats considered! Maybe the old 60's/70's standard of 7* isn't really needed with the tall tires of yesterday and today. Just something worth thinking about in the scheme of things...
I'm in the process of figuring out my caster angle now. I'm running hairpins on the wifes 33 coupe (Chevy). Where is the place to pick up the caster angle and what method do you use to accurately measure it IE: Method and instruments needed? And for anyone that wants to know in order to make the degree symbol you hold the alt key down, then type 248 I vote close to 7°
I agree with this! No one ever thinks of the difference in tire dia when they set up a front end. BUT, the 7* ballpark is a solid starting point.
Well when building, you have to start someplace with a target caster. If and only if you have adjustable perches on bat wings with either a 4 bar or adjustable radius rods will you have any tune-ability in the front suspension after its built and road tested. If 4 is your target or 12 is your target you need to know before you start fabing. Also should know your tire sizes before hand. So seven is as good of a target as anything else but if you wind up close it will be ok. The other thing is 90% of hotrods have the entirely wrong offset on the front wheels . Theoretically this should cause more problems than it does and be of more concern than not being at 7 caster
Not saying that less than 7 won't work. IFS set ups usually run much less, but 7 has always worked well in mine. My model A had much less than 7 when I first got it. It drove terrible would get the death wobble occasionally and wondered all over the road. It drives much better now but I also changed other things too so I can't say its all due to the caster change only.
I drove a Model A that I traded for about 200 miles when my towing truck broke down. It had virtually no caster. Had to drive with both hands and no flinching. Got home, pie cut the wishbones and got the caster about 7 degrees and lived happily with it.
The reason I replied to that thread in a strongly worded post, was that you did say where your caster was if you did not cut the bones. I could be wrong, but I don't think anyone said that "hey, you are within factory specs, so why cut/weld if you don't need to" ...and you also bring up the point I was trying to make about ; "I've always followed the 7 degree crowd, because thats what I've always been told it should be. ". I have seen this question so many times about "where to set my caster", and not one person asks about details of the build. Instead they mostly all will say 7, without a reason why. I have even seen people with solid axle parallel leaf spring cars ask, and they get the same 7, which is totally wrong. Show me just ONE stock factory spec on a twin sprung I beam car that is anywhere near that. I can put up pics of a Motors that only goes back to 1935, but a few of those cars were still on solid axles, and they are anywhere from 1 to 2, and some cases 3 max. I just did not want you to think you had to cut your bones, without a good reason why the 7 is needed, with your type of build,........ motor weight, box ratio, tire type, and sizes F to R, as well as scrub radius and other things.
F&J, I'll be cutting the bones. I really don't like how low they set, and I really don't want the super low frame mounts. I'm taking all this in as a chance to learn a little suttin'
I guess I need to go back to that thread to read what is going on, because I am confused at this point. You were 4.5 or 5 with "what" placed "where"? Yes, I know what you just wrote about not wanting low hanging mounts. but I still want to know where will you set the caster, and why BTW, you don't need to copy the angle of the spring mount area inside the front crossmember...you can mill an angled shim if needed, or some cut and reposition that area of the crossmember. I made a shim for my stock 32. I am going WAY out on a limb with my caster on my setup, as i have a very heavy early Olds, a very fast ratio box, etc. I won't dare say where my caster is set right now, except to say "it is not within factory specs" . I'll post how this car behaves in July..If all goes well.
Hoop you need to compare trail with line 7-- 7* with 26" tall tire and 7* with 24 " tall tire to explain trail. What you need to do is compare 26" at 7 vs 24 at 5* to show trail with similar tire. The problem develops when you are comparing bias ply to radials as design dictates different setting as well as tire width. In most cases with newer and wider tires you can rollout some of the caster and achieve a good tracking and stability. 5* is what I suggest.
OK, here are some facts, split model A bones running back level with the ground have 1.2 degrees, + or - 1 tenth. Now raise the frame mount end an inch and you at 0 degrees caster. I have seen cars running these setups many times. 37 to 41 bones running back level are at 7 degrees, + or - 1 tenth. Raise the frame mount end 1 1/2" and you are now at 6 degrees. Running the bone uphill with suspension and or tire rake will take away even more, how much? It all depends on many factors. I dont know if 32-34 and 35-36 and the later dipped ones have the same ammount of factory caster as the 37-41 but I would think they are close if not the same. I have driven lots of cars with measuemets as low as 1 and as high as 8, they all drove different, but again there are many factors, weight/engine size, wheelbase, tire style and width, bias/radial...etc. I drove a friends glass 32 roadster awhile back down the freeway at 65, it had model A bones mounted level, so about 1 1/4 degree caster, it drove very nice and didn't wander, however it did have radials. The answer to the question? As stated there are so many factors to figure in, it all comes down to each individual/builder...one size does not fit all.
Whats 'trail'? And since we are 'wandering' around with our steering, anybody think thru the camber? Stock ford camber made no allowance for the crown on a modern highway.
Dual spring caster I ran 2° to ease low speed/parking steering effort and it was still enough at 100 mph at the drag strip...When I put the quicker ratio power box in [Heaven!] I put it back to 4° for a little more natural return to center..
I'm with "oj", and set mine to eliminate binding in the shackle bolts.. So far, it's working just right, at a resulting 6 degrees Pos. 4TTRUK
I didn't mean for the chart to suggest any setting just showing the effect of 2 variables There are so many variables its impossible IMO to just pick a number
I have used 4 degrees for many years on many cars. Much more than 7 and you have to help the wheel to straighten it up after a turn. IMHO.
Just to make things more confusing..remember if you change the ride height in the rear, that changes your caster angle. Higher in the rear decreases the caster angle, lower increases it. Like wise if you install taller tires you will decrease your caster angle and lower profile tires will go the other way. Many years ago on my first 46 chevy truck, I bought new rear tires that were an inch taller than the old ones. I drove it home with both hands on the wheel and a certain part of my body puckered trying to keep it going in some straight direction. The next day after some thought as to what had caused such a drastic change, I drove(carefully) back to the tire store and bought the same tires for the front and fixed the concern. This is important stuff. Tossing a bunch of heavy stuff in the back of your ride can cause concerns too. As for the latest project, I set mine up with the frame level and kept the ride height set to keep the frame level with the ground with some adjustablity. I also welded the front spring cross member in with 7 degrees angle built in. Because someone(Bobby Knighton) that is much older, smarter and more experienced said to do it.
Look at the front tire from the side. A line drawn thru the center of the tires contact point at the pavement and the center of the spindle would be 90*. Vertical. A line projected thru the king pin if it had NO caster would meet the ground at the same place. Now...rotate the king pin back to create caster and the projected line moves forward of the tires contact patch center. The distance the king pin line is ahead of the center of the contact patch vertical line (at the pavement) is called TRAIL. It works like the caster wheels on a shopping cart...except it isn't as obvious to the eye. Raising the axle higher by using taller tires changes the trail because the projected line thru the kingpin moves farther forward. That description is very basic...and if you think about it more you can see other potential issues that might need correcting just by installing taller tires or offset rims. EVERYTHING has an effect on everything else and needs to be considered if going off the normal path on a build.
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