Hi Guys After fitting my front end back in my finished (Mod A) chassis, my i beam sits at 10 degrees. I may be able to adjust it a bit with the split wishbones. Ive read and been told that 5-8 deg is the go so what will the ride be like at 10? Im figuring itll be a handfull manouvering at low speeds... Cheers Steve
Most have experienced a god awfull rattle between 25-35 mph. Did you read the thread from Clark here? Good info. http://www.jalopyjournal.com/forum/showthread.php?t=60986
This was scanned from an old Motors manual. Other reference books list the same 4.5-9 deg. I doubt you'll have any problem with an extra deg. It's not like 9 deg. is fine but 10 deg. is dangerous. Try it you might like it. It may be a tad harder to turn around in the 7-11 but it should run staight as an arrow.
I ended up with 9 deg.CastEr,in my mod. A sedan. '65 mustang box flipped on it's side. steeres great Sparky
I think the only time you will see much effect with ten degrees will be when trying to turn the wheels at a stand still or near that, on pavement especially if your running fairly small tires on a light car. The upside will be that at highway speeds It'll have nice feel and run like a dart. I wish I could get more in my A but I'm stuck with six unless I cut the bones.
Ten is too much. You will get caster wobble and when you do you'll know it. It has popped the headlight lenses outa the buckets it shakes so bad. Try to stay with 7ish.....Shiny
In my experience, the problem can be reduced by standing on one of two pedals. The choice is yours... Seriously though, fixing the geometry now is probably smarter and less frustrating than fixing misc. broken parts later.
Seems to be a big differences in option on this one. Lots of folks think over 7 is bad and lots of folks think 10 is fine (but alot of have had to use a stablizer)..
me = experienced race kart designer me = no experience designing cars for the road with that out of the way, i would say that 10 degrees is too much. what does caster do for you in a car? largely, it's there to self-centre the wheels when you let go of the steering wheel. on a go-kart, you use it (lots of it) so that the wheels travel vertically as you turn the steering wheel, which unloads the inside rear tyre aiding cornering (as karts don't have a diff). most karts have about 14° of caster, adjustable down to a bit under 12°. i would suggest a car with caster anywhere NEAR that of a race kart would handle like a pig. not only, as suggested above, will you get a headshake reminiscent of a dirtbike at 60mph (which gave me one of the scars on my face). with that much caster, as you dial in steering input, the inside front wheel starts loading up, the outside front starts unloading, and the opposite side rears do the same. on a kart, you do that deliberately to COMPLETELY unload the inside rear. on a car, the best grip is achieved when every single tyre carries the same amount of weight - ie = weight transfer is bad. methinks less caster would, in your application, be gooder...
and i say, when in doubt, look to the experts. find me a production road car with 10° of caster, and i will be VERY surprised. i tend to trust the judgement of the guys designing and testing a car that will be duplicated and sold a million times, than the guy that built his own car and says it drives great. like, how often do you hear someone say "this trailer i built tows like a fucking pig!!" ? yup, never.
We put 17 degrees of caster in the BFD roadster... she goes real straight, but you cannot back up very well, and with the licked rear end, forget about turning it in a tight radius! It will also give a hellacious wobble if yiou hit a bump at low speeds... but on the drag strip, it works fine! You can always try 10 degrees... and then change it if you do not like it... but if you're starting from scratch... I'd go with 5 to 7 degrees. Sam.
Seems like a lot, to me, but on the other hand...it turns out to be virtually Ford endorsed! Here's a snippet from that 1936 best seller, "Ford Service School: Wheel alignment": "...The amount, however, can vary up to 25% without any noticeable effect on the performance of the car. Thus, with 8 3/4 degrees caster, a change of up to 2 degrees would have practically no effect of itself on the Ford car, providing the change were equal at both wheels." Ill effects listed in this section are just the increased difficulty of turning wheels with car at standstill, a problem that would presumably be somewhat worse with modern tires and post-'36 spindles...I'll read some more in this gem and see what else they say about caster difficulties. Two thoughts: You are working with a chassis?? Seems like there's no good way to know for sure what angle is going to result once car is complete and set on its own springs at full weight...in other words, don't change anything until car has found its stance. Second, you don't need to hack the radius rods--caster is adjusted by bending the axle between perches and kingpins. I don't know if this can be applied to streetrod cast axles! Scary thoughts, there. Since no one has the set of jigs and hydraulic jack Ford dealers used, it seems to me that what is needed is simply a helluvalong lever with jaws like a monkey wrench. I'd like to know more of "field expedient" axle adjusting--seems very doable, but I've never tried it. A fierce magnet holding a long rod axially aligned with the kingpin on each side would allow you to sight across a fenderless car to observe change and symmetry.
Ok lets go again, after this week every reader should be well versed on caster. First lets assume that all steering parts are new and tight , I stand that on a street driven car, 10* caster is way to much. The principles of caster are two fold, one, to create a trailing action, making the vehicle go in a straight direction and two, to aid in returning to neutral or straight position after cornering. Insuffficent caster leads to wandering, or continually chasing the track of the car when driving. Excessive caster is evidenced with hard steeering or difficulty steering in tight spots. Excessive caster is sometimes masked by the exchange of steering boxes with different gear ratios, thus making the car appear to steer easier, yet hiding a design problem. The most common effect of excessive caster is a low speed shimmy. With excessive caster, when a bump is encountered the excessive caster will cause the spindle to deviate from its normal track and then to return too fast and go past its netural point. Tire harmonics will make it seek its neutral point and set up a shimmy or side to side vibration until the forces disipate or the vehicle is slowed down. Because of the quick violent vibration it is sometimes remagnified by turning the steering wheel and mistakenley called bump steer, which actually something else. Since the length of the radius rod controls caster change the longer the radius rod the less the caster change and since most vehicle being built have only 2"-3" of travel, most experience minimal caster change during operation providing it has been set correctly at ride height. 5*-7* is adequate. Unless you have an original axle I would not put caster in by bending the axle. Whether reproducton axles, cast, forged or welded tube they do not like the use of a press to reshape their design. In addition even original twisted axles have a tendency to return to their original set and continual stressing is not good for the metal, (heating/ bending). Adjusters allow you to modify caster angle on a 4 bar but if you have 1 piece radius rods, cutting and rewelding is best. Heating and bending radius rods is difficult due to design and position of bend. What you are trying to do is come up with a caster angle that suits the combination of, spring travel. tire size, tire construction and suspension design you have built. This is a road car not a race car and different suspension principles apply to them and are used to achieve different results. Dick
The way Race Suspension Expert Arthur Mallock explained it to me, the vertical travel you talk about does pretty much the same on a Sprung Race Car. But he used it mainly to get Weight transfer to the inner Front wheel, Sharpening the Turn In. But it only works if you have a lot of Offset beween the Centreline of the Kingpin and the Thread of the Tire. And most traditional Hot Rods with skinny Tires dont have that much offset...
I did a quick google for the specs on a Citroen 2CV, because I remember seeing some extreme angles on those. It seems they had 15 Deg... Unless you are building something for Bonneville, I wouldn't try that on a Hot Rod.
At 10 deg I thought the fuckin wheels were going to pop off with a bad case of the wobbles when I hit bump at about 20mph.... whooooa scared the shit outa me. I have it at about 6 and it is way better!
glad i read this... I just recently lowered the rear of my car another inch and forgot to check the front caster..Im at exactly 10 degrees as well. Gonna have to raise the front radius rod mounts on the frame.. No big deal cause I was thinking of remaking them anyways. Fixing the caster should be relatively easy if your still in the build phase.. Just raise your mounts 1/4" or so.. As long as the angle on your spring perch isn't too far out of wack this shouldn't cause any binding... Git her done!!!!!!!!!!!
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