A question about "rear steer"

Discussion in 'PSI Superchargers Tech Questions' started by Kendrick Roberts, Jan 31, 2012.

  1. Kendrick Roberts

    Kendrick Roberts Member

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    In another thread I saw that Mike Canter mentioned rear steer as a way to adjust a car driving to one side.

    I didn't want to hijack that thread so I am starting a new one. I have used rear steer in some of the circle track things I was involved in, but it never occurred to me to try it in a drag car.

    So when we talk about putting 1/8" or 1/4" in, are we saying to actually lengthen the wheelbase on the left side by that amount, or we saying move the thrust angle at the front axle axis, where you would normally want it centered, to the left (or would it be the other way?). You've got me quite curious about this, but it sounds like it might be an "if all else fails" trick.

    Even so, I am nearing "if all else fails" on our altered at very high power levels so I am game.

    Kendrick
     
    #1
    Kendrick Roberts, Jan 31, 2012
  2. Mike Canter

    Mike Canter Top Dragster
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    The thought is by putting preload by adjusting the upper right bar in a 4-Link that you actually put the suspension in a bind. By setting the upper bar at the neutral position and adjusting rear steer the 4-Link is free of binding. Normally you just move the rear axle. The common way is to move the right side forward. I guess you could move the left side back but I do the right side because of the way a car tends to push going down the track.
     
    #2
    Mike Canter, Jan 31, 2012
  3. jay70cuda

    jay70cuda Well-Known Member

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    So would I set the pinion angle first then move the right side forward to set rear steer. by adding rear steer makes the car more stable on top end ? About how much to add when you have a 2800 hp car true double frame rail car ?
     
    #3
    jay70cuda, Jan 31, 2012
  4. Mike Canter

    Mike Canter Top Dragster
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    Normally it is from 1/8 to 1/4.
     
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    Mike Canter, Jan 31, 2012
  5. Kendrick Roberts

    Kendrick Roberts Member

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    So, if I understand correctly, you are balancing the thrust angle created due to more grip on the left rear with an imposed thrust angle created by angling the rear end.

    If so, would the amount of rear steer be at all dependent of the wheelbase, as it seems as though this would cause a "dog track" condition once you weren't making enough torque to create the extra left rear bite?
     
    #5
    Kendrick Roberts, Feb 1, 2012
  6. aj481x

    aj481x Member

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    If you lengthen the left, watch your overall wheelbase and stagger. I guarantee you Collins will send you back to the pits for adjustments. :)
     
    #6
    aj481x, Feb 1, 2012
  7. Kurt - Prostart Race Cars

    Kurt - Prostart Race Cars Member

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    You boys be careful! A lot of this is a "Band Aid" for an underlying problem. If you are having such a problem I suggest contacting a qualified chassis person for assistance. With proper alignment built in to a chassis and a "GOOD" set of tires, only a small amount of preload should ever be needed in even the fastest of cars.
    Kurt



    www.prostartracecars.com
     
    #7
    Kurt - Prostart Race Cars, Feb 1, 2012
  8. Mike Canter

    Mike Canter Top Dragster
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    Sorry Kurt but all high powered fast 4-Link cars like a blown promod are going to need some correction/preload in the rear suspension. I don't care how great the chassis is or who built it. Maybe you can get away with none in a fixed rear but not in a 4-Link Promod. Using 1/8-1/4 rear steer is not a "Band Aid". Just as using a flat of preload in the upper bar is not. It is physics. I bet you that over 90% of the top promods in NHRA and ADRL are using rear steer. I will say that if you need more than a 1/4" rear steer then you may have a problems and need to get it fixed. And to answer the other question you will not see the car dogleg with that small of amount of rear steer.
     
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    Last edited: Feb 1, 2012
    Mike Canter, Feb 1, 2012
  9. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    rear steer

    i'm not a suspension guy by any means, but i was told by a fast pro mod team that when they went to penske shocks on the rear they were able to get rid of rear steer....
     
    #9
    Will Hanna, Feb 1, 2012
  10. Mike Canter

    Mike Canter Top Dragster
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    We got Penske shocks on the promod and we still have rear steer. Not much but a little. If somebody says that he has no preload in the upper bar or no rear steer then his chassis or his corner weights are off.
     
    #10
    Mike Canter, Feb 1, 2012
  11. Kurt - Prostart Race Cars

    Kurt - Prostart Race Cars Member

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    This is based on a solid car, as I thought the topic was in regards to the "other" thread. Still needing "Rear Steer" is a "Band Aid" for a situation occuring in a suspended car.
    Kurt
     
    #11
    Kurt - Prostart Race Cars, Feb 1, 2012
  12. Mike Canter

    Mike Canter Top Dragster
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    LOL, this topic is kind drifting back and forth down the track from solid to 4-Link.
     
    #12
    Mike Canter, Feb 1, 2012
  13. Force Fed

    Force Fed Member

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    Hi Mike,
    Would rear steer on a 4 link Pro Mod with a RHS driver position be different than a LHS driver car?
    The reason I ask this is over the years I have noticed that left hand drive cars have the tendancy to drive left and right hand drive cars drive right.The only conclusion to why this happens is the rear is trying to drive around the drivers body mass.

    Alan
     
    #13
    Force Fed, Feb 1, 2012
  14. Mike Canter

    Mike Canter Top Dragster
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    No because you guys are on the bottom of the world and your typhoons a toilets spin in the opposite direction. Seriously "my guess" is no because it is to do with the torque being applied to the rear axle and the fact that the drivers side tire is getting more weight on it while going down the track. That is what I have always been told. You would have to spin the driveshaft in an opposite direction.
     
    #14
    Mike Canter, Feb 1, 2012
  15. Kendrick Roberts

    Kendrick Roberts Member

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    Please indulge my ignorance for another moment. I watched the PM's at the snowbirds very carefully, and most of the faster cars went impressively straight on what I considered a medium bite to marginal track.
    Among them was the one Mike has referred to (Marooon/Burgundy Camaro, 6.0 player)
    If, as Mike says, most are using rear steer, then I am in.
    I am attempting to attach a drawing of my understanding of what we are discussing here.
    I had to make a few general assumptions as there are small variations from car to car, but I am looking at this conceptually overall.
    Assumption 1: 4 Link 20 to 24 inches apart at rear (width, not height)
    Assumption 2: MAX out of square 1/4"
    This will give a thrust angle of: from 0.54 degrees to 0.6 degrees MAX
    You can see in the picture why I am asking about the effect on a different wheelbase.
    I CANT GET A PICTURE HERE< MY LINKS DON'T WORK <PDF<>DOCX<>MAC PAGES
     
    #15
    Last edited: Feb 4, 2012
    Kendrick Roberts, Feb 4, 2012
  16. Mike Canter

    Mike Canter Top Dragster
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    That was a hard time at Snowbirds because we had actually just changed the 4-Link setup and were trying to find ourselves again. We did get it figured out as you can see and also seen in the US Street Nationals at Bradenton. Credit for that car driving straight is owed to Adam Flamholc who is an excellent driver and to that beautiful G-Force car. The car was kept in the European FIA setup for both races which is basically the NHRA and ADRL PM rules. Actually that track in Bradenton has lots of traction and is very well prepared by Todd's track crew.

    You are correct in that the amount of rear steer will vary depending on the wheelbase of the car. That is why you should start off with a very small amount and see what happens.
     
    #16
    Last edited: Feb 4, 2012
    Mike Canter, Feb 4, 2012
  17. Kendrick Roberts

    Kendrick Roberts Member

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    Another attempt at pics. For some reason I can't make the editor accept any links I try so if you copy and paste this in your browser it will take you to the pic.
    The reason I am adding the picture is I remember a long term misunderstanding by many when the people at NASCAR were talking about front or rear steer. (an Ackerman angle reference)

    http://way2fast4u.wikispaces.com/file/view/rear+steer+mac.pdf

    Very PC on your Bradenton comment Mike. It is what I consider our home track, and it has been a very predictable, consistent racing surface which I prefer over many other tracks.
    My comment was not meant as a criticism, but a relative rating.
    Since we all race at different tracks with different amounts and types of preparation, I just assumed that all have run on tracks that were much tighter, as well as much looser, and I put them in the middle of those extremes. So if you had a high powered car that was set up for tighter, you would find it marginal.
    My apologies if I offended the good people at Bradenton.
     
    #17
    Kendrick Roberts, Feb 4, 2012

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