Watts Link vs J- Bar

Discussion in 'Tech Talk' started by GothicRose07, Sep 8, 2005.

  1. GothicRose07

    GothicRose07 JBELL RACING

    Does any one out there know anything about the adjustments on a watts link set up, I change my dirt mod over to a watts link instead of a J-Bar, we have work with it all season thru trial and error, seems to have fantastic forward bite, but is lacking in side bite, I have been told to keep the angle of both bars the same, wether up or down, but I am not sure how to add side bite, The old J-Bar set up was easy, but no one seems to remember or have never seen a watts link, I know they were quite popular several years back and are still used down south, but could use some help if anyone knows,
    THANKS

  2. little302

    little302 Nut behind the wheel

    Jim

    There was a small section on it in the Steve Smith set up book, I'd let u know what it said , but I loaned the book out, never to return..
  3. Gettin Dizzy

    Gettin Dizzy Rational Racing

    What are you using to locate the rear end laterally then if you have no panhard bar? Perhaps you aren't meaning watts link, and are referring to a torsion bar setup, of which I am completely ignorant of, but all of the watts link (z-link, swingarm) cars are using a panhard (or j-bar) bar or it has a mono leaf with it for lateral location in the rear. Perhaps there is something I am missing here.
  4. CC-28

    CC-28 CC-28

    I think he means 2 short bars, one going to each side off the pinion.
  5. Motorhead

    Motorhead www.workmonster.com

    Since we have never used a Watt's linkage, I cannot give you any real tuning advice, just speculation, but I can tell you why you are seeing what you are, and maybe you can take it from there. That is, if you don't mind listening to an asphalt guy.

    I assume you are a dirt track racer, and your J-bar was mounted on the drivers side of the frame. As the car rolls, several things happen. 1) The rear end is pulled to the left, tucking the right rear in, compared to the front. This helps to plant the right rear. 2) A force is generated thru the J-bar, and this force has 2 components, 1 of which forces the rear tires into the ground, generating more side bite. The more the car rolls, the roll center rises, and the greater this force(jacking force) becomes.

    A tire can only generate so many pounds of grip. That grip can be in any direction, but what you gain in 1 direction takes away from grip available in all other directions. This is never more evident than on dirt, where the coefficent of friction is so low.

    A Watt's linkage reacts the cornering force thru the rear end as a pure lateral force. There is no vertical component to this force. Neither does the rear end move in an arc as the body rolls, so the RR does not tuck in. The roll center does not change when the body rolls, it is always at the center pivot point of the linkage. Since there is less jacking forces at the tire patch, there is more grip available for forward bite, unfortunately at the expense of sidebite. The rear end is not as "bound up". This is why a Watt's linkage is at it's best on a road course , because there is no rear steer induced by the linkage, and all reactions are equal in left and right turns.

    I would think you would need to reduce rear( possibly all) spring rates with a Watt's, and perhaps try a little more split, with the LR stiffer. you may be able to induce some lateral movement by altering the angles of the links unequally, but I would have to 3D model that to be sure. All 3 mounting points need to be adjustable. I can see a problem with getting the rear roll center as low as it needs to be, and it probably needs to be lowered compared to the J-bar setup(front RC too). You are looking to get more body roll.

    We race at some southern paved tracks(No dirt, no more!), and I have only seen 1 car with a Watt's linkage, coincidentally(maybe not!) at a "stop and go" type track, where forward bite was critical. It was a old school car "freshened" by a Busch shop for a rookie driver. The car was better than the driver.

    Hope this helps.

    Mark
  6. GothicRose07

    GothicRose07 JBELL RACING

    Thanks for the reply, You are correct in your theory of what is happening in the rear suspension, The car is a standard old 3 link, I tried this set up for a full season thru trial and error methods of adjustments, what seemed to work the best was angleing both bars upwards toward the frame mounts at about 10 degrees and and the center mount to it's lowest position, which was 1 inch below the center of the axle center, probaly could have used more, The angleing of the bars actualy created a slight shift in the axle to the left, I figured this set up would work very simular to a leaf spring car, and it had fantastic forward bite, but the car would not turn under throttle, coming off the corners, we lowered the cross to about 44% and increased stagger, the side affect to this the car tracked sideways down the straight aways and was very unstable on turn entry. I also lowered the left side lower control arm from 10deg. to 5deg uphill. drove better but lost forward bite.We were running a 25 lb split in the rear left side heavier, and 50lb split in the front, right side heavier, it was reccomended by an older driver who had used a watts to run a reverse spring setup left front heavier than right and right rear heavier than the left, he said this would help the car turn and increase bite on the right rear coming off the corners, We ran out of race season, before I could could try this, I am always looking for something to try on the car, just to see if it works, you never know when you will find something and you won't know if you don't try it. Once again thanks for your reply

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