How Much Front Castor???

[scotts216]

How much front castor is considered appropriate or ball park for a vintage Formula Ford????

After driving my newly finished F2 car, the stteering and handling was phenominal compared to my FF - Same manufacturers. The F2 car has had the castor taken out by lengthening the front and shortening the front upper a arm rod ends. Until I drove the new car, I never realized how hard the Ford steering was. Maybe we should all drive each others' cars to learn more.......

My Ford has these rod ends at equal length. When I was a beginner quite a few years ago, I had the initial set up checked by a prep shop and I was told that the Ford had 8 degrees neg. castor, which I was told was a lot. This car has always been hard to steer, and I am now wondering if that is way too much and that easier steering is just a few adjustments away???? I always thought that symmetrical was best. I'm wondering if I should change the rod ends to try to dial some of it out??? Anybody have a thought on the "proper " amount of castor to run???

The bottom a arm rod ends are both screwed all the way in.

Any input or ideas on the subject appreciated.

Thanks, Scott

[Todd TCE]

I'd say 3.5 to 5.0* max.

Keep in mind that many of the older FFs running Triumph parts may then rquire some tinkering of the steering arm, steering arm pillar or in some cases; moving of the rack to get bumpsteer where you want it.

How you go about setting the caster vaires from car to car.

Pick either the upper or the lower arm to be your reference. Don't adjust both unles you do the same to both sides or you'll alter the track and wheel base. (well, we're talking ideal world here, older cars don't always work out quite that way)

If the upper is the fixed point then pull in the rear lower rod end and stand up the upright. Moving the rear will likely net you more gains than the front. And not effect camber as bad.

Now, camber...if this car is one of those messy 'if this/then that' English set ups with no method of changing one without the other...find a shop to help change this for you. And soon. Common is conversion of the upper outboard to a rod end for camper changes.

Send me some pics and I'll see if I can brainstorm some more ideas for you.

[James Hakewill]

Hi,

A monster 8 degrees of castor would make the car almost impossible to steer, surely!

I've normally set my cars (late 70's/early 80's FFs) up with between 3 1/2 and 4 1/2 degrees of castor.

However:
- I've driven a '78 Van Diemen with 2 degrees of castor which was super-super light and oh so easy to drive - on Vintage-style tall ACB9 tyres. Made my Crossle with 4 1/4 and American Racers feel like a tank. I'm now back to 3 3/4, which is noticably lighter.

- I've driven a '85 Formula Atlantic with 5 degrees of castor (and wide front tyres), which was pretty heavy, but not too bad. I'd like to take some castor out, but the owner says that it's set up like that to keep the wide tyres on the ground at big steering inputs. I need to go back to my books to argue about that one.

Anyway..

For a vintage FF I'd start with 3 1/2 degrees of castor and go from there.

James

p.s. remember when you change castor it will also change the bumpsteer adjustment a lot - as well as camber and toe.

[scotts216]

Thanks guys......Now I know where I got those "java Man" forearms!

Funny how you don't know what you have until you have something to compare it to.......

Todd, I will take some pics of the front end and post here. Hoping others can learn something also.

I do OK setting up the car. Never had any bump steer problems (that I know of), so I am a bit nervous about getting lost when it comes to that. I will have to fina a castor gauge, then try. I assume the way to do it is to set car on ride ht blocks and check toe at 1 inch of bump and droop? I do not have any idea of what parameters to adjust to get rid of bump steer?
Any hints appreciated. Todd, you mentioned fiddling with the steering rack? I can see that by adjusting the upper a arm rod ends that I can tilt the upright forward some, but looks like it will increase neg camber, and will also toe in, and also change the angle of the steering arm. Perhaps the adjustment is multiple..... Gues I will just have to play with it and see. I can always put it back to where it was. It works good there, just really hard steering. Looking forward to trying to figure out trying how to "lighten the load"

Thanks for your comments, and I will post some pics tomorrow.......Scott

[James Hakewill]

Hi,

Bump steer at the front is adjusted moving the outboard end of the steering rod up and down - either by a whizzo adjuster or more often by spacer washers.

In theory, you can also adjust it by moving the steering rack up and down, but this isn't likely to be practical on a formula car.

On the front you want to get pretty close to zero bump-steer, but erring on the side of toe-in in bump.

On the rear end, you adjust bump steer by changing the rear upright inclination. Again, a tiny amount of toe-in in bump is much better than toe-out in bump.

Badly adjusted front bump steer will make the car unstable under braking as the front loads up and the wheels change direction!

During corner entry - as the suspension loads up, dodgy bump steer is also likely to make the car feel terrible during the transition phase before steady-state cornering.

Uneven castor side-to-side will typically make the car pull to one side.

You can measure bump steer with a toe-guage like you suggest, at varying amounts of bump/droop - but it's much more accurate to use a specialised bump steer guage.

This book is a classic, and contains a good chapter on setting up formula cars of your vintage!

Prepare to Win by Carroll Smith

As you say - adjusting castor is one thing, but then you'll have to re-adjust camber, toe and bump-steer; typically in that order - and then check it all again.

James

[scotts216]

Thank you James.......exactly the information I was looking for.....I don't race for a while, so perhaps I can string it up and play with it. I do Have carroll's books and remember the plate and dual dial indicator set up. Perhaps a bit complicated for me at the moment, but I will give it a try.

Thanks again for the very well put information.....Regards, Scott

[Murray]

The best starting point is the original manufactures set-up sheet. there can be quite a varation between car designs. My Lola T-200s call for 6 degrees of negative castor and the steering is very light. Were one to use 2 or 3 degrees on those cars the steering would be way too light with little self center. If you cannot find the original factory reccomendations I would go in increments and see how it feels. If you cannot find the factory settings, I would suggest you start with getting a castor that gets your steering right and then work on bump and then camber.

[Todd TCE]

As James points out to you; you must reset toe (and perhaps other things as well if the change is huge) after you make the change to the mount on your steering arm.
If you don't the 'base' setting is off so when you get it right the whole mess is out the window again.

As for the rack, some older cars used spacers, shims or pillow blocks of different heights to establish the base point of rack height. Altering this changed the toe settings. While this seems odd to some it's common practice on some street iron nowadays when lowering the car. Same reasons.

If you have Triumph ams and need to raise the steering up I'd suggest you have some tube spacers fab'd up for them rather than simply washers. The 'stanpart' arm can be drilled out carefully and fitted with a bushing to 3/8 which I've found to be ample for steering yet bendable in a crunch. Put your 'give' somewhere.

Both sides against the middle and sooner or later you'll hit on the total package!

[scotts216]

Thanks Todd, I will need to study your post and think a little, but I will eventually figure it out. Pics to follow of the suspension. Triumph uprights. Note the rod ends are the same length out on the upper a arms front and rear. It would appear that the only answer is to move the front one in.....then figure the camber and toe from there..........





Hope this works.........

[scotts216]

By the way, my rack is modified Spit, and cannot move up or down. Bolted directly to the chassis. I still have the tie rod ends outboard. I do not know if the spacers will help??? Seems that the steering links need to come upward? Note the steep angle on the steering arms...... And the car is not all that low. Perhaps I will need to get rid of the tie rod ends, drill out the taper in the steering link and add a rod end there??? That would lower the arms????? Turning the front upper rod end inward will will rotate the triangle of the arm on an arc forward and inward. Obviously camber will be more neg, and I haven't decided what I think toe will do - I would guess it would have to toe out. I will just have to fiddle, measure, record and see what happens........

[Todd TCE]

Cool. Now let's start with my basics on this if I were workig on it. Your mileage may vary.

First given there is no 'easy' camber change on this animal, (I'd change that too, but we'll get to it later) you must first, as on all cars, decide what arm will be the base or primary one. On this car I'd use the lower as the fixed point. This means both lowers would be set up identical. which then determines both track widith and wheelbase. We are making some assumptions about the frame which may or may not pan out....

With the lowers and your initial report I'd say the rear rod end needs to be 'in' about as far as you can go and the 'front' one out half way to start. This should kick the lower arm back some and reduce your caster. Looking at the tops in double shear you cannot shift it fore and aft much so we either need to do our best on the bottom as a base or may yet have to offset the top rod ends too. Messy. Everything f'in changes when you do camber changes...

Next, I'd see where this takes the caster number. While a zoomy gauge helps, you can do this with a smart level and two points on the spindle; find something you can measure the angle of with the smart level. Measure it now at whatever it is. Can be 30* or so as long as you can measure it again over and over the same way and get the change. The final caster number is not as important as the side to side and reducing what you have. Try a straight edge up on the top ball joint down to some other spot maybe? Actually if the car is square now you could even measure from the floor up to the steering arm with a tape measure, reduce the distance and call it good. We'll try to make it a bit more technical...!

Assuming you can get the a arm to shift enough to reduce the number (caster) then you won't have to mess with the upper. Reason? Because moving BOTH of the rod ends in and out will change your camber setting. Out two on the front and out two on the rear will stand it up more for example. And not effect caster. Personally I'd shoot for zero camber while doing all of this simply for ease of reference. Caster may change a bit with the camber but not much. I'd look for caster of less than 1/2* per side difference. Same is nice if you can do it. Car will pull or wander to the side with less. Don't confuse this with road crown down a straight however.

Now for toe. I'd remove those old clunker tie rod ends. They don't allow for bumpsteer changes. Pop them out by a good whack on the side of the steering arm, they'll pop out. Drill the arm out to 1/2" and have some bushings made to convert to 3/8" (they're tapered) and then make some adjusters to replace those old ones. Me, I'd do 3/8-3/8 on all of it max. You could do a split size rod end with a fat shank but I prefer something that might bend on impact. The rod end if done in LH thread will or could screw directly to the old 1/2" steel arm via the link and be perfect right from the start to make an adjuster. Now your bump is set with spacers under the rod end. More or less as needed. Email me for some pics of what I'm speaking of if you need an example.

Lastly if it were my car...those upper a arms would be changed. I'd remove that ball joint and do a rod end there. I've got ball post replacements for the taper and this then fits a 1/2-1/2 rod end. You then set caster via bottom and or top as needed (keeping it square) and make camber changes from the outboard rod end. And depending upon your ball post height you can alter the camber gains a bit to run the tire more straight up given that it will gain more in a bump condition, such as a corner. Keeps more tire on the ground on the flat and helps with tire life. The key is just how much is too much etc. And of course how it works with the lower arms.

I'm whipped, get started and let us know.!

[Jonathan Hirst]

Todd makes some excellent points regarding working through the front end set up - and his suggestions for modifications would certainly ease the procedure in the future.

You didn't mention if you were running in Vintage (or Monoposto)but judging from the posting location you might be. If you do embark on replacing ball joints with rod ends, modifying suspension from original, etc., be sure to check with your organizing body to ensure you would still meet eligibility requirements.

It could save you a lot of headaches in the future.

Good Luck.

PS - What car are you running with a Xpit steering rack?

[scotts216]

Thanks guys. Todd, thanks for the dissertation. The car is a 1969 Alexis MK 15. I would say the suspension layout is typical of the period, and just realizing how poorly laid out it is. It was also designed with all right hand rod ends which makes adjustability a real pain.

Still in the thinking mode, but definitely excited to make some changes and drastically improve the ability to steer the car.....

I do have a set of upper A arms designed to use a rod end or male tie rod end. Problem is that I do not know who made them and the welds are suspect at best. So my plan at the moment is to have a certified welder check out the welds, and if they can't be re-welded, I will make a jig and remake them.

As for originality, I do not know that this is an issue, as I am not really changing anything other than the method of attaching one part to another, and rod ends were available in the day.
Would like to keep a male tie rod end at the outboard end of the upper arm, but the way it is designed, it may casue the arm to be at too high an angle, so I may have to use a rod end.

Also, the pillow blocks are spaced forward of the chassis with washers. I think that this may have been done to help adjust bump steer previously? Even movint the rack forward could change the length of the outboard steering arm length?

Will let you all know how it turns out as I work on it later in June.

Thanks for all the input. The racing community is filled with great folks...........

Pic of the new A Arms:



[size="1"][ June 02, 2004, 10:38 AM: Message edited by: scotts216 ][/size]

[Jonathan Hirst]

RE "period availability"- Fair enough comment.

If you do run Monoposto though be aware of this rule:

"All Historic Pre-1973 Formula Fords must compete in the identical specification as
manufactured. Updates and modifications, however "period" they might appear, are
specifically prohibited."


I have seen people given a hard time with innocent changes in the past and didn't want you to have to experience the same.
FWIW.

Jon

[scotts216]

Jonathan, Thanks for the thoughts. I am a vintage purist for the most part. I would prefer that my car run as close to original as possible. I have always believed that in vintage racing we are trying to re-create, not re-invent......

That said, I will most likely use a male tie rod at the upper outet end of the A arm. Think I will make a jig and remake the new type A arms.

I fiddled with the car a bit and cranked in the front upper rod end, and it reduced castor, and as expected, it toed it out and increased neg camber about 4 degrees........ Problem then is that there is no way to adjust out the excessive camber with the original design. So, it bacame obvious that the upper a arm design has to be changed.......

Now I just have to figure a backwoods way to measure castor......Think Todd mentioned a smart level..........