Landracing Forum
Tech Information => Technical Discussion => Topic started by: JohnR on May 31, 2006, 02:18:33 PM
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I am building a roadster (30 A) that will see some running in SCTA XF/STR class as well as use on public roads.
I am getting ready to set the front caster (castor?) and want some input from guys who have roadsters. For a street vehicle, I am leaning towards 4-5 degrees but for the race usage I'm thinking 12-15 degrees. Of course, I want it to do both and can only set it once. Anybody have a vehicle with alot of castor for racing but then run it on the street? benefits? drawbacks?
Thanks,
John
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John, I don't have a roadster, but this much I know. The greater the caster, the harder it will be to straighten out after a turn. You better keep it under 6 or 7 degrees , or you are courting disaster..............
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I am building a roadster (30 A) that will see some running in SCTA XF/STR class as well as use on public roads.
I am getting ready to set the front caster (castor?) and want some input from guys who have roadsters. For a street vehicle, I am leaning towards 4-5 degrees but for the race usage I'm thinking 12-15 degrees. Of course, I want it to do both and can only set it once. Anybody have a vehicle with alot of castor for racing but then run it on the street? benefits? drawbacks?
Thanks,
John
Are you running 4-bars, split wishbones, etc.. Why not figure out a way that you can change it back and forth?
c ya, Sum
c ya, Sum
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I am building a roadster (30 A) that will see some running in SCTA XF/STR class as well as use on public roads.
I am getting ready to set the front caster (castor?) and want some input from guys who have roadsters. For a street vehicle, I am leaning towards 4-5 degrees but for the race usage I'm thinking 12-15 degrees. Of course, I want it to do both and can only set it once. Anybody have a vehicle with alot of castor for racing but then run it on the street? benefits? drawbacks?
Thanks,
John
Are you running 4-bars, split wishbones, etc.. Why not figure out a way that you can change it back and forth?
c ya, Sum
c ya, Sum
Split wishbones. I guess I could just have two sets of wishbones, but I guess I'm lazy and want something to do all of it.
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Invent something and call it "Adjustable Ends".
Also remember the settings for the drag link so you can center the steering each time you change it.
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John, I don't have a roadster, but this much I know. The greater the caster, the harder it will be to straighten out after a turn. You better keep it under 6 or 7 degrees , or you are courting disaster..............
:x don't know where this came from??? my brothers had so much caster the fenderless front wheels looked like a road grader in a turn & never gave a problem on many years of street use,it turned a little harder but it was like power stearing when it came time to straighten out, let go of wheel & watch it spin to ctr.. on mine I just went to motors manual & set for 40 ford and never had any trouble either, course never went much over 150.
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Invent something and call it "Adjustable Ends".
Also remember the settings for the drag link so you can center the steering each time you change it.
Jack, I want to keep the stock wishbones for the original look. So that rules out a 4 link or a hair pin style with adjustable ends. I just like the look of the split stock wishbones.
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Invent something and call it "Adjustable Ends".
Also remember the settings for the drag link so you can center the steering each time you change it.
Jack, I want to keep the stock wishbones for the original look. So that rules out a 4 link or a hair pin style with adjustable ends. I just like the look of the split stock wishbones.
:lol: : :? where the split wishbone attaches to frame use several vertical mtng holes.
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You can "pie cut" the radius rod and reset the angle right behind the front forging that attaches to the tube to put more caster in. Al Simon did it that way on our race roadster with, I believe, '46-'48 radius rods. Gives you a nice "stock" appearance with more caster, yet keeps to rods parallel to the ground so springing up and down has minimal effect on the caster setting, especially if you keep the rods long.
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John R,
Picking the right caster setting has been a confusing study for me!
Some of the information I think is right:
Most of the excessive caster that you see on many of the salt flat cars is probably done to lessen the tire scrub.
Excessive caster has a tendency to lift one of the rear wheels up when you turn the front wheels. Not good if you are sprung and have a long wheel base. Bad if you have a rigid short car.
Some of the people on this forum have had good handling with the smaller numbers 6 to 8 degrees. One of the things that popped up while I was building my fat fender pick up front end was, some of the factory Camero caster settings were 0 degrees.(zero) :shock: go figure.
You might give a thought to using Henry's stock setting. It is a early ford spindle ,isn't it? Take your time on the line up. Scatch that. That wasn't necessary. I've seen pictures of your Honda.
My lakester is set up with 18 degrees of caster 8-[ . It has no suspension but am making provisions to install it later. It has a designed(eye ball) wheelbase of 192". I'll put scales on the rear wheels when I have the differential mounted and see if the wheels have a tendency to lift when the frt.whls. are turned. If it doesn't I'll let you know and you can ignore this long-winded post
Harv
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IMO the class and speed you want to run does not require as much castor as one may think. Personally I would try a few runs at 4-5 and see what happens. Your first runs are trials to begin with. I have 8 with a 28" tire a less with a 32" tire and been 216. Good Luck...
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I set my caster at 10 degrees +/- on a Studebaker with 120" wheel base and a straight axle, 26" front tires, I drive it some on the streets and LSR, goes real straight, so far up to 228 mph.
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(http://purplesagetradingpost.com/sumner/temp-pictures/Beatty%20Lakester-1.jpg)
John why not copy one of the most famous lakesters out there, Tom Beatty's 1950's lakester frontend (see picture).
He used an "A" axle as it is flatter. Turned it upside down and re-bent the ends so that the camber would be right. This then allowed the axle to be pretty close to the arch of the transverse spring for better aero. The axle was now almost a straight axle.
He also reversed (swapped side to side) '40 ford ('37 to '48 are the same) spindles so that the drag link would be in front of the axle and close to the same plane as the axle/spring was in, again for better aero.
The wishbones where split to the sides of the car and he used center steering with a right side pitman.
From the picture it doesn't look like he is running that much caster. The car ran 188 mph in it's first trip to the salt (1951) with a 296 Merc flathead and a 3-71 Navarro blower setup. He entered the 200 mph club in '55 with a 211 2-way average. In '62 he bumped his B Lakester record to 243 mph running a blown Olds, so the caster seemed to work fine for him.
If you can find "THE RODDER'S JOURNAL" Number 12 there are lots more pictues of the car and a good article on him and the car.
They also mentioned he ran this car at high speed on a dirt oval for an exhibition and mentioned how he would make 200 mph U-turns on the salt :D .
The other thing is these front end pieces aren't that expensive if you hunt around as not many rodders want the "A" axles so you could easily set up 2 front-ends. One for the street and one for the salt.
c ya and have fun,
Sum
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Sum,
Looks looks like zero camber to me on Beatty's tank! I was confused before and am more confused now.
JohnR,
If you know what to set the caster at now after all of this information it would suprise me. The only thing I've come up with is, there's a whole lot more to make a car go straight than caster! Good luck with your roadster.
Harv
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John -- I'll show you a similar (as I described above) set-up on my Sedan at the lake on Sunday. I'm not techie enuf to snap a picture of it and post it. But I think what I have used on two cars will suite your purpose. Stan.
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Sum,
Looks looks like zero camber to me on Beatty's tank! I was confused before and am more confused now.
Harv
It looks like zero in the picture, but looking at other pictures I would say it is 4-5, probably about what was stock back then.
Stan if you can take some pictures and e-mail them to me I'll be glad to post them.
c ya, Sum
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You need some caster just to make the steering "stable" i.e. the caster preloads all of the steering connections and gear and caster makes the steering want to go to straight forward so if you run lots of it the car really wants to go straight but will also add a "cross jacking" affect if you turn the wheels alot. Cross jacking can also be increased by using a spindle with lost of king pin inclination, which is why spring cars run 10+ deg. king pin inclination and 7-10 degress of caster. When they back it into a turn and then "steer right to go left" the right front wheel picks up the front end and also this causes the left rear to carry more weight which is just what a sprinter wants. BUT sprint cars have fairly rigid frames so this jacking cause by lots of caster and king pin angle actually does something. Most of the cars at B'ville are long, narrow and or have fairly flexable frames so the cross jacking affect of the added caster is not as prominate. Give her 10 degress and if she don't go straight give her some more!
Rex
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Some additional thoughts on the subject-NOSE HEAVY cars seem to require less caster than tail heavy.Those of you that may have Fred Puhn's '70s book "How to Make Your Car Handle" will recall a chart that shows late model Lincolns of that time actually having POSITIVE caster (top of kingpin leaning forward) and Porsches-with their overhung engine- having a lot in the opposite.
Top Fuelers exceed 30 sometimes. Funny Cars around 12 and Pro Stocks 9-but the violent acceleration required may dictate those numbers.
I'm amazed at the lack of caster on Beatty's tank- and recall my first trip to El Mirage in the mid-50s wen his and Earl Evans tanks battled for top time till dusk!
El Mirage cars maybe should be set up more like sprint cars- lots of being loose on dirt!