Straight Axel Caster and Weight Distribution

[Sumner]

Sum,

I am having trouble with the Car 3 speed RPM gear chart excel format.. It will not let me change the gear ration in rear end.  Something about sheet protection,

I know the Works version allows me to do that as I did it at home and MAN  it is dead on..  I am my office and do not have MS Works..

Is there a way you can email me the excel file for 3 speed car tranny's

Charles

Hi Charles, sorry for the problems.  I don't have excel, but make the spread sheets in works and then save them in excel format.  I just load that one into works using the excel format and it seemed to work.

If it is blocking the cell with "protection" you should be able to go to the cell and turn that off using the "format" and then "protection" tools at the top of the spread sheet.

Maybe someone else wouldn't mind loading it and letting me know if there is a problem.

Thanks,

Sum

[Cajun Kid]

Sum,, I will try that.. Thanks

[willieworld]

charles  dont think that because you find a low tire that you are done ---if you were standing in front of your car look at the kingpins you will notice they arnt straight up and down but are angled  in at the top and out at the bottom --if you emagine a line through the center of the kingpin to the ground --at ground level the line should be in the center of the tire --if it isnt your scrub radis is off and will cause your car to wonder --in lsr its very important --if you cant figure it out have a front end shop do it someone that is familiar with race cars  --when i finish a race car i always get it close then it goes to the alignment shop  ---i know there are pluses and minuses in front end alignment and personal preferences but we all still need to stay in the safe zone     willie buchta

[Cajun Kid]

Willie,  my Caster  is about 4 degrees from my angle dial thing.  The toe is 1/16th in.

The scrub , I have no idea..  When I get the valves adjusted I will go to front end guy..

Does this scrub radius have something to do with back spacing on the front rims?

If the rims have more back space (narrows the wheelbase) is that a factor to reduce the scrub radius ?

[Sumner]

Willie,  my Caster  is about 4 degrees from my angle dial thing.  The toe is 1/16th in.

The scrub , I have no idea..  When I get the valves adjusted I will go to front end guy..

Does this scrub radius have something to do with back spacing on the front rims?

If the rims have more back space (narrows the wheelbase) is that a factor to reduce the scrub radius ?

Yes the back spacing, tire height, etc. will effect it.

another page to read..........

http://purplesagetradingpost.com/sumner/bvillecar/construction%20page-21.html

Sum

[RidgeRunner]

Charles,

     Quick ans, general rules of thumb: 

     When our driver increased his caster to about 12 degrees on his street roadster it handled better at Maxton in the 135-150 range. 

     Yes, backspacing is a component in figuring scrub.

     Yes, usually increased backspace is needed to narrow the TREAD to get closer to 0 scrub radius.

      Nice to meet you at Maxton, good looking car, keep up the good work.

                         Take care,

                          Ed
                     

[Glen]

Charles, another thing with a solid axle you will lose some degree of caster when the front end lifts. The 12 to 15 degree sounds good. Steering stops are not a bad idea but you can probably get by without them. Tire pressure is very important usually best checked early when they are cold. You can do a search on almost anything on the web site. The history over the years is the best, so many answers can be found or someone that can help you.

[Ratliff]

I have set up my roadster weights 65 - 35  and with 8 degrees of caster.  I don't want to start a debate but I think anything more is a crutch for the set up.  I know lots of guys run 12-14  degrees, but what happens when you have to correct the wheel.  One of the rear corners picks up and when you go to correct that.  The car comes around.  Just build a simple model out of wood and try the different caster angles and see what happens to the chassis.  But then again I dance to a different drummer.

In cars with a lot of weight on the front end the wheels have more inherent resistance to turning so less caster is needed.

[Stan Back]

It's good to check tire pressure cold --- but -- if you've been in line for a long time (say, Bonneville) and one side of the car has been in the sun for hours, the other shaded, it's good to even them off when you're 3 or 4 back.

[jl222]

222 - gonna throw some S##t in the game before I go nite-nite. I wanna emphasize - no criticism intended, cause there be a whole lot of DIFFERENT solutions out there!

 From what weight balance you've described I feel you must run a lot of body rake and run LOW to the ground with a good air dam.

I woulda thought that thing would weathervane MAJOR. I.E. swap ends.

(The old CP/ CG thing.)
                       




REX, BLUE, DAHLGREN? Opinions?  - Even Willie!


   

   Thank God we didn't know anything about center of pressure-center of gravity theories when we built the 222 car, or we would have a lot of wheelspin [resulting in  oversteer and possible spinout] like a lot of other cars i know of.
   Yes the car is low and has 1'' of rake under the rocker pannels.
                         
                                     JL222
             

[Cajun Kid]

Willie,  I just did the imaginary line thru the king pins to check scrub radius.  The line hits the ground inboard of the center of the tread/tire center line.  I would say the line intersects the ground 1/2 way between the inner edge of the tire and the center.  So it looks like I have the wheels out to far (not enough back space

The rims are 15x7 with 4.5 back space..  I want to go to  15x 5 rims

What can I do to get the center of the tires in?  Or am I close enough now ?

Charles

[willieworld]

charles i would try to get the scrub down it sounds like you have about 1 1/2 inch i would try to get it down to about 1/2 inch (at least below 1 inch) you can do that by changeing rims -tires-machine work  --first though take some accurate mearurements you may be closer or farther than you think ---what happens when you have to much scrub on uneven ground the wheels will try to steer the car its worse if you hit a pot hole or loose salt   --i think that more caster will help too --on our dra cars we would run 10 to 12 degrees---------------------             just some thoughts  willie buchta           

sumner had the same problem you might want to check his website

[Sumner]

   Thank God we didn't know anything about center of pressure-center of gravity theories when we built the 222 car, or we would have a lot of wheelspin [resulting in  oversteer and possible spinout] like a lot of other cars i know of.
   Yes the car is low and has 1'' of rake under the rocker pannels.                         
                                     JL222

Like someone has mentioned earlier there is more to it than just CP/CG.  Obviously your combination has worked for you, but I still wouldn't say that it is correct for everyone.  You do have a lot of mass up front in your car and in the middle which I'm sure helps your situation.  If you took a lighter car and just hung weight at the rear bumper I don't think that would be a good deal.  Now a lot of weight in the back doesn't hurt a thing if the car is never upset and doesn't have wheel spin.  Your car must be in that operating mode now.  The CP is only going to come into effect if the car does start spinning the wheels and is upset to the point that it wants to turn.  A lot of cars that don't get into this situation don't need to worry about it probably.

The point you made about the F1 cars I feel actually probably shows what does happen with the weight in the rear.  These cars along with a lot of other circle track cars use a lot of aero work for downforce and to help them handle.  Their main purpose is to corner and not go straight so they work toward a neutral balance where they aren't pushing or loose.  We would like our cars to push if anything.  Once the F1, NASCAR cars do start to spin you can see them spinning like a top in most cases exactly what we don't want to happen. 

John when some of us bring up CP and CG we aren't criticizing your setup as it has worked for you and you are happy with it, we just want some of the people that are considering this for the first time to take a look for what has worked for a lot of other people, in fact airplanes use the concept every day  .  They should also take a look at your car and make a decision what is going to work with their car, their HP, their body style and the speeds they expect to run.

c ya,

Sum

[Cajun Kid]

Willie,  when you say get the scrub down, I assume you mean bring the wheels in more towards the center of the car ?  Narrow the overall width (track) 

I can do that by increasing the backspacing or keeping the same back spacing and narrow the rim ?  Correct?

The reason I ask is I have 15x7 rims now.  I want to go to 15x5  but that narrow I can not increase the back space, so by reducing the rim width (from space, does that help too ?

Sorry to be so bothersome,, but scrub radius is a new term/concept to me,,,

Charles

[willieworld]

sorry charles  with a scrub radius of 0 it would be in the center of the tire any thing outside of that would be positive anything inside the center of the tire would be negetive     willie buchta 


yes more backspace    narrower will also work   if you have a 6 in wide tire and rim now and you changed the tire and rim to a 4 inch with the same backspace you would move the scrub closer to 0  --for every inch that you narrow the tire and rim but keep the backspace the same you move the scrub radius in by 1/2 in --i know it sounds goofey but say you have a 6 inch wide tire and rim with a 3 1/2 in backspace  and 1 1/2 inches of positive scrub if you narrow the rim and tire to 4 inches and keep the 3 1/3 in backspace you will now have 1/2 inch of positive scrub   much much better