Register now to get rid of these ads!

Technical Need Pre- war race car handling help! Understeers badly

Discussion in 'Traditional Hot Rods' started by panheadguy, Jun 17, 2019.

  1. oldtom69
    Joined: Dec 6, 2009
    Posts: 383

    oldtom69
    Member
    from grandin nd

    open diff or locked?if you have the rear end locked,you are going to push the hell out of the front end!I can hardly test fire my sprint car on pavement without scrubing the front tires off
     
  2. Gasolinefed
    Joined: Apr 17, 2018
    Posts: 104

    Gasolinefed
    Member
    from OR

    I don't have a ton of experience in this as every car I've built the under over steer hasn't been bad but I believe you want more sway bar rear for understeer.. transmits more of the chassis load to the back.. or find a way to soften the front... all this assuming the rest of the engineering on the car is sound..
     
    chryslerfan55 likes this.
  3. panheadguy
    Joined: Jan 8, 2005
    Posts: 950

    panheadguy
    Member
    from S.E. WI

    Thanks guys for all the input. My next race is in July At Road America in mid July. Before that I will try to get more info and try to determine if the rear end is "Free" enough. This week I need to get ready for family vacation in N. WI. All my kids and G.kids come from all over the country and "Grandpa" brings the boat, water toys, fishing gear, etc. So I'll be busy rounding it all up. Then the grandkids come to stay until after the 4th.....challenging but it's the best.
    I'll be back!
     
    chryslerfan55 and 302GMC like this.
  4. panheadguy
    Joined: Jan 8, 2005
    Posts: 950

    panheadguy
    Member
    from S.E. WI

    Old Tom, It's an open diff. '40 Ford Banjo no Q/C
     
  5. panheadguy
    Joined: Jan 8, 2005
    Posts: 950

    panheadguy
    Member
    from S.E. WI

    Zigster, The tires are Stahl Excelsior from Coker. 7.00 x 16" radials.all around. The durometer seems pretty soft and sticky. I played with TP a bit. Started at 28# and went to 30# I'm getting TP inreases of 5# just off the track. Not lifting an inside tire.....wish I was!
     
    chryslerfan55 and Just Gary like this.
  6. So there are left and right hand turns? If so, rear tire stagger goes out the window. What is the toe-in set at? I'd think that 1/4" to 3/8" out is a start. Talk to the other guys that go fast, sounds like a more gentlemanly event as opposed to Saturday Night warriors I drove against.
     
    dirty old man likes this.
  7. stubbsrodandcustom
    Joined: Dec 28, 2010
    Posts: 1,057

    stubbsrodandcustom
    Member
    from Spring tx

    I personally never go extreme toe out... 1/16" out max, I like how toe in drives to me but for corners straight to out is good. The push your having can be dialed back with tire pressure adjustments maybe. I think the other issue your having is the car isn't able to weight transfer like it wants... Meaning going into a corner the chassis gets unbalanced then you push the weight on the subsequent front wheel, apex of the turn the weight is on both side wheels on the outside, exit of turn more weight back to the rear... So If I am getting this... The main problem sounds like turn in to the apex? How does it drive out? (squirly or straight and hard)

    Test for you to do... Put the jack under the Right rear and jack up... see how much movement till the other wheel lifts or the front on same side lifts... Measure that... Shock values can also have a very pesky way of being on rebound when one side is unloading. If using lever action shocks... Change the viscosity to a little thinner shock oil to free up the shock faster on rebound... The will loosen up the chassis to swing in, weight transfer and do its thing. But this is more for fine tuning on shocks.... If friction shocks you can tune by tightening or loosen etc... But hold on that for fine tuning trying to get it faster... You have to get the push taken care of mostly first!

    The camber can be messed with but I would hold that till later, (reason being you don' have dynamic camber issues) till you have exhausted some of the other small changes that cost very little. Tire pressure can be everything to a car... I can make a ok car great with just tire pressure.. 2-5lbs makes a shit ton of difference in handling. But If it were my car, I would work on trying to lower the rear spring rate. Not too much but could be as simple as removing 1 leaf would let the car loosen up a bit... that rear on a prewar racer should be at the edge of kicking out and front planted as hell. Lets get you there! The split rear bones will hurt you some but can be overcome with some tuning, and quarter elip. front isn't a death sentence either... This just requires some fine tuning to get right but end of the day... the effort you put in will deff show in the amount of speed and fun you have..

    Almost forgot, you can loosen up the rear spring by adding the nylon slippers in between the springs.... If you don't have them already it may be enough to help solve the understeer.
     
    chryslerfan55 and pitman like this.
  8. trollst
    Joined: Jan 27, 2012
    Posts: 1,440

    trollst
    Member

    You still haven't said what you're using for power, does it have enough power to make it oversteer? We also don't know your driving style, balls out, or cautious? Maybe you're afraid to wreck that beautiful baby, and are under driving it, not being critical, just wanting more info, sometimes you can negate ill handling with a more aggressive style.
     
    dirty old man likes this.
  9. panheadguy
    Joined: Jan 8, 2005
    Posts: 950

    panheadguy
    Member
    from S.E. WI

    The engine is a 235 Stovebolt. Probably one of the most sophisticated domestic engines from the pre- war era.60 over, balanced, zero decked and .100 off the head. Some port work, split dual tubular exhaust. and rocking a mean old Rochester monojet on a stock intake. Backed up with a Camaro IROC T5 tranny.
    I left the engine out in earlier posts because I don't think it's a factor for now. I plan to make a manifold for 3 S.U. side drafts once the car is sorted. There is plenty of torque to break the rear loose... but it will just keep plowing ahead straight. It starts to gasp for more fuel and air at 4500 rpm but I'm at 105 mph in 4th so I'm not sure how much faster I want to go until the car is sorted.
     
  10. X-cpe
    Joined: Mar 9, 2018
    Posts: 605

    X-cpe

    Remember only one change at a time so you can assess the outcomes of each and start a notebook to keep track of the changes and outcomes.
     
  11. panheadguy
    Joined: Jan 8, 2005
    Posts: 950

    panheadguy
    Member
    from S.E. WI

    Yes. I made too many changes. Without much thought I changed my radius rod end points, and stiffened the shocks all around. Going to disconnect everything and then start jacking.
     
    chryslerfan55 and lothiandon1940 like this.
  12. What do you mean by "end points"?

     
  13. Gasolinefed
    Joined: Apr 17, 2018
    Posts: 104

    Gasolinefed
    Member
    from OR

    You do realize that if you split the bones front/rear your turning the axles into sway bars right? and sway bars affect the over under steer of a car.. if you change the at chassis mount point of the radius rod especially the length your changing the leverage point which could change the cars steer characteristics.. And are you running a tube axle, increases the roll resistance more than an I beam..

    Just a guess but is sounds like your over swayed to the front from the torsional resistance of the 1/4 elliptics and the radius rods turning the front axle into a sway bar..

    If it were me I'd try removing some leaves from the elliptics (if possible) for testing and possibly the front shocks.. try the car and if the problems better then you know...

    And you have split bone rear right? that will transmit some of the chassis load rearward if you soften the front..
     
    Last edited: Jun 19, 2019
    pitman and chryslerfan55 like this.
  14. Yeah! I've been lurking for a few days....I'm not sure if I can be much help. Fur Biscuit, Dirty Old Man and others have pretty much hit most of the considerations where problem may lye, I think it's matter of where to start.

    Set out a plan and stick to it! What you want is a car that is balanced. 50/50 is ideal! (not often completely achieved) To the extent the balance of weight is out; you have discovered one of your problems: A Bad Design for a cornering race car is an out of balance (more than 40/60) chassis! Weigh each of the four corners..If they're off you know that your chassis is "Off"! You want a "Stiff suspension in front ; Soft in the rear.

    I suspect those quarter elliptic s in the Front will do better on a course like Road America. Parallel leaf sprung chassis do better in a straight line (they don't want to turn). As far as radius rods four bar all around seem geometrically to be best. I use Dunlop Racing tires (bias ply) with set at 18# all around filled with Helium (doesn't expand with heat). Make sure your tires and wheels (and brake drums) are true and balanced. I haven't found that "off the Shelve" tires and wheels are consistent

    With a straight front axle, for ease of turning without excess "scrub" the centerline of the kingpin should hit the ground just inside the front "Tire patch". Some say it that it should be centered on the tire. This is probably true for stronger walled radial tires (which are difficult to use on PreWar race cars because they "stick" the release suddenly).

    If you use racing events to "Test" the changes to your car; you'll end up like me....A broken, dirty old racer! Seriously drive or tow your car to a large vacant parking lot (usually Sunday) and do "Figure Eights"! I taught my youngest daughter how to approach racing corners that way. It works!

    Incidentally, if it make you feel any better I don't consider my car one that handles perfectly!

    BE2019.jpg
     
  15. Pete1
    Joined: Aug 23, 2004
    Posts: 1,644

    Pete1
    Member
    from Wa.

    "I did recently move the rear radius rods to the outside of the frame rails and I think this screwed me good. I don't think I'm getting and roll in the back and am unweighting the front because of it.."

    As others noted, that was the wrong way to go. Put them back to a pivot point directly under the front U-joint and as close to it as possible.
    As a side note, be sure they are super stout because in that setup, they not only locate the rear end but 95% of the forward driving force is through them. The other 5% is through the spring. It is a good idea to have a safety strap around the connecting joint so the wishbone can't drop if the joint breaks. Most race associations require this.
     
    chryslerfan55 and Old Dawg like this.
  16. I should have added that tire adhesion with the surface of the track (dirt or pavement) is paramount.. A race car designer/builder MUST consider ALL elements that effect that adhesion (say "Grip"). Suspension geometry is a good start (camber, caster an toe-in). Toe-In; NEVER Toe-out! And yes: The Akermann IS important so that the turning radius of both front wheels being on different radius', are tracking with no "scrub" thus not loosing "Grip".

    Bottom line: A reasonably weight balanced chassis, with a properly geometric suspension WILL tend to lose "grip" with weight shifts due to braking, turning and acceleration. It's up to you to get the aforementioned elements in reasonable relationship so that the race car will act in a predictable manner.

    To get this all together you may have to replace wheels and tires; move front or rear axles, springs and radius rods. You might even have to move the heaviest element: the engine! If not you may have to replace that big hunk of iron with a smaller, compact engine such as a Ford four banger, a Chevrolet 490 or a Dodge Bros four Banger! Even a Ford "Flathead" V8 might be lighter.

    Remember: "To keep racing upfront; you're NEVER done!" I've been doing this (as an amateur) off and on since I was 16! I just turned 80!
     
  17. dana barlow
    Joined: May 30, 2006
    Posts: 3,444

    dana barlow
    Member
    from Miami Fla.

    Lot of good ideas from others..Have more to work with;Getting info on what you have;;Any car;Basic handling ( there are a few exceptions/like over HP to wheel or braking) is when in a turn,the end of car that slides first,is the end that is over loaded the outside tire grip.
    ? A four wheel car is like a four leg chair,?are all four legs being loaded the same? Or is there a higher load on two? Know how the lbs. are placed. Race cars we each wheel scale to find,but there is a farmer way of finding how car is standing on its four tires; be sure tires are at same psi at the end they are on F or R, put driver lbs. in seat{ bag of BS same lbs. as driver can work an get drivers head into smaller hat}. On straight axle set ups;Get a floor jack with about 6in part of 1in. X 1in. angle iron on jack pad with V pointed up=find dead center between rear tires an jack up rear end tell both tires are off the ground= look to see if one tire is higher then other tire and by how much ?? It shows you your car is out of balance in cross lbs. Adjust tell wheels lift same time off ground.*{for road racing both left an right turns/not for oval one way only}
    To check front to back % ; Start by jacking to frame one side of car tell both tire are off the ground=look at witch end came up first/move jack closer to other end,do again tell you get both on that side coming up same time=That can tell you front to back % of lbs. if you size WB and size from jack to each ends axle center.
    #1 That can be alinement of tire to road and or, #2 lbs. transferred by speed/centrifugal force. #3 Or/and tire is not responsive to bumps{no matter how small/no road is smooth)= #3A Tire dose not follow road, it's movement is too stiff ,so will not grip down side of bump. #3B Or too soft an bounces from bump so will not grip down side of bump. Keeping these ideas in head may help find what makes it push/plow/understeer=same rose
    .
     
    Last edited: Jun 20, 2019
    pitman and chryslerfan55 like this.
  18. Mimilan
    Joined: Jun 13, 2019
    Posts: 143

    Mimilan
    Member

    That advice ^^^^ would cause more understeer , you've got it the wrong way !!
     
  19. Ned Ludd
    Joined: May 15, 2009
    Posts: 3,845

    Ned Ludd
    Member

    A lot of the above posts are pointing you in the direction of more front roll stiffness. This is backwards. The only time adding front roll stiffness reduces understeer is when you have IFS with less than optimal camber recovery – which is pretty much any IFS – because reducing roll overall reduces front camber gain.

    All else being equal, you need to soften the front.
     
  20. Best advise that I can give, boys is "Don't get hung up on just one element"! "Roll Stiffness" front OR back, for example, depends on a lot more considerations; not the least of which is the basic design of the automobile, I've found (the hard way) that canards leading to "Band-Aids" often lead to going the wrong way! Just saying
     
    chryslerfan55 likes this.
  21. Mimilan
    Joined: Jun 13, 2019
    Posts: 143

    Mimilan
    Member

    You would be referring to total roll stiffness . The relationship between front and rear roll stiffness [or roll couple] is how the understeer/ oversteer can be dialed out.
    These issues only happen at the absolute limit of a tyres adhesion [ either Fr or Rr] . The OP could simply slow down a little.
    [But with men being boys this would be an impossible request]
     
    chryslerfan55 and SquintBoy like this.
  22. 270ci
    Joined: May 17, 2010
    Posts: 346

    270ci
    Member

    How about your "ackerman"? Surprised no one mentioned it, but maybe I missed it.
    Is ackerman set up properly for your wheelbase and track? Something I'd check out. If it's off the front tires will not be working in tandem during turns. My 2 cents.

    My bad, post #6 already mentioned ackerman.
     
    Last edited: Jun 21, 2019
    chryslerfan55 and trollst like this.
  23. Mimilan
    Joined: Jun 13, 2019
    Posts: 143

    Mimilan
    Member

    A quick question ! Is the tyre "feathering" towards the outer edge of the tyre [eg: scuffing to the Left on the L/F tyre?] or towards the centre of the car?

    Squealing of the tyres AND "feathering" towards the outer edge is caused by too much Ackerman or too much toe out [causing the unloaded inside tyre to scuff]
    Ackerman is not desirable on race cars due to slip angles at the loaded tyre [causing the unloaded tyre to turn too sharp]
    Leave the Ackerman for car park queens

    If the tyre "feathering" towards the inner edge of the tyre, this is classic overloading of the tyre which will require roll stiffness adjustment

    The rear radius rods are not allowing the car to roll in the rear would cause oversteer.
     
    King ford and chryslerfan55 like this.
  24. Torana68
    Joined: Jan 28, 2008
    Posts: 1,075

    Torana68
    ALLIANCE MEMBER
    from Australia

    an answer to the first question, where is it mounted and could you move it back? Done any corner weighing?
     
    chryslerfan55 likes this.
  25. AmishMike
    Joined: Mar 27, 2014
    Posts: 365

    AmishMike
    Member

    Ackerman only for car parks? Wow. Would love to see film of your smoking front tires
     
    chryslerfan55 and Atwater Mike like this.
  26. Mimilan
    Joined: Jun 13, 2019
    Posts: 143

    Mimilan
    Member

    Don't twist my words , I certainly didn't write "Ackerman only for car parks" [get your eyesight checked]

    I wrote "Leave the Ackerman for car park queens" which is a description of cars that are normally driven slowly around tight corners.
    We also use the term "Trailer queens" and "Show queens" to describe modified vehicles that never get used.

    Ackerman is not desirable on race cars [except for mid corner on tight corners], and can cause corner exit understeer.
    On a race car you want all four tyres helping during cornering. When a tyre approaches it's limit of traction the slip angle increases [requiring more steering input]
    Ackerman increases the steering angle too much on the inside tyre which carries less weight [the squealing you hear on road cars is usually the inside tyre getting dragged sideways]

    If the car is driven like a "car park queen" this is a moot point, but it will certainly be getting passed by cars driven at the limits of adhesion

    PS: smoke pouring off the front tyres is not caused by lack of Ackerman, but by seriously late braking into the corner entry zone when inside front is unloaded.[due to turning in]
     
    Last edited: Jun 22, 2019
    dana barlow and chryslerfan55 like this.
  27. dirty old man
    Joined: Feb 2, 2008
    Posts: 8,096

    dirty old man
    ALLIANCE MEMBER

    It is true that increased roll resistance on the rear, whether buy anti roll bar or spring rates will increase oversteer in a car with a properly and freely operating suspension.
    But when you have rear radius rods, or trailing arms positioned with the leading attachment points way outboard you have a bound up suspension whose reactions to hard cornering don't always follow the rules.
     
    chryslerfan55 likes this.
  28. AmishMike
    Joined: Mar 27, 2014
    Posts: 365

    AmishMike
    Member

    Do not road race have done some dirt racing ( real Racing - turn right to go left ) & for there & street will always want correct ackerman. Watched a street rod make 90 degree turn where outside wheel turned much sharper then inside wheel - MUCH where i half expected rim to push through the tire. That poor tire must have smoked on high speed turns & am sure showed feathering from outside edge of tire to inside mentioned earlier in this post..
     
  29. panheadguy
    Joined: Jan 8, 2005
    Posts: 950

    panheadguy
    Member
    from S.E. WI

    Again thanks for all the input. I am MIA for the next two weeks doing family stuff. when I can get back out to the garage and try to do some checking of the suspension movement I'll get back on here. Have a nice 4th.
     
    chryslerfan55 likes this.
  30. Mimilan
    Joined: Jun 13, 2019
    Posts: 143

    Mimilan
    Member

    That is "reverse" Ackerman not zero Ackerman.
    It could also be overloading the tyres due to bad understeer and the driver just adds more steering input.[overloading the tyre more]

    What you described can sometimes be observed on Autocross [slalom] tracks , with small tight corners. Ackerman helps here [Car park Racing :)]

    Your experience with dirt racing should know that Ackerman has adverse effects with opposite-lock driving. [and not desirable] but it can be overcome with "wedge" and carrying the L/F.
     
    chryslerfan55 likes this.

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2020 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.