Before somebody says just buy a made for asphalt chassis, this is just for information purposes only.

We've got an older Harris combo car (dirt or asphalt). Currently, it is a 3-link with fifth coil (ladder bar) with brake floaters. We can mount shock and springs on either front or rear of housing. Springs are coil slider type. Panhard bar behind rear end.

Besides adding a sway bar, what else should be done to CONSIDER running this chassis on asphalt (i.e. how should trailing arms and panhard be in rear, lenghts of bars, types of springs, should we have screw jacks in rear, etc.)???

We are curious to figure stuff out.

Personally I don't think there is anything wrong with those combo chassis. There used to be a lot of them running around. Anyhoo..



What has worked for me is this: Currently I run an Eagle chassis. It's a 99, with a 72 chevelle front clip. Hopefully some of this helps.

Springs on sliders (or coil overs) in the front of the housing. The newer chassis are going back to screw jacks. It's an opinion kind of thing. As far as sway bar I have ran everything from 1 1/8" to 1 1/4". Good starting point for the trailing arms could be 0 degrees on the left and up 4 degrees on the right, that's with driver in the car. No sure about the ladder bar. Could work on asphalt but could get bound up, tough call. I've seen it done before. My old Dowker chassis used something similar, just with rubber biscuits instead of a coil. Something else you could do is call Harris up and ask them for some suggestions, I'm sure they'd be glad to hear from a chassis owner. Oh the panhard bar. As long as you can get it, and with the rear side about 9 1/2" off the ground with a about an 1 1/2" split uphill to the chassis. Granted that's assuming it runs to the right of the chassis. Typical asphalt cars run with rear side on the left and the chassis side on the right.


Any further questions feel free to pm me anytime. I'll answer the best I can.

Good luck
Perry

which side of the panhard bar connects to the frame and how long is it?

Otherwise you might want to lower the uppper a-arm mounts depending on how they are, and get the bumpsteer and ackerman tweaked into place.

Thanks! That's the kind of info I'm looking for.

The panhard attaches to the left side of the chassis. A mount can easily be added to the right side of the chassis and a new mount added to the left side of the rear end. There is room to slide the rearend to the right to allow room for the new panhard mount without compromising the trailing arms on the LR but might push the trailing arm on the RR out a bit too far. Should the trailing arm mounts on the rear be a floating birdcage or welded mount? Also, if the ladder bar isn't needed, is anything used as torsion besides the 90/10 rearend shock?

SFRacer55,

Welded trailing arm mounts would be ideal for asphalt. For the third link I would suggest one from Quickcar. It's a steel rubber biscuit mount. Also Howe sells one, There is one from Sweet but I don't think it's legal in the mods. Basically all of it has to be steel. Also I would use a biscuit bar with a 90/10. Some still use a solid bar. With a shorter bar the traction happens much quicker and harder so instead of all of these cars using 3 ft long bars they've gone to 15" long with more angle. It's worth experimenting with. But that quickcar mount is like $119 almost anywhere you find it and works real nice. You can also use a spring loaded pull bar but it must be a 5" coil. I'm not up on those though. Tried it once, it got good bite but I couldn't keep the back of the car down under power.

Question: Is this Harris car early enough that the RR trailing arm could be really long? For a while they were building cars so that the RR trailing arm extended half way up the car with a shorter LR to control roll steer. But the RR would not move as much because of the larger arc. I'm pretty sure the earlier Windpusher chassis did that as well.

Thanks PFD. The RR trailing arm can be the really long one or short (still about 20"). We've only used it on the short length on dirt. the chassis is a '95.

Does the biscuit bar run to the same mount as the 90/10 shock on the chassis? If not, does it run to a bar next to the driveshaft (which we would need to weld one)?

I would stick to the short trailing arm on the right. I've never ran a long one, but it doesnt make sense to me to do it. Most of the cars that had one have switched back as far as I know.

The toplink can go in place of your 90/10 shock if it was on top on the rear end and angled down to the frame... preferrably with some adjustment. Ideally it would be located to the left, at about 58%-60% of the treadwidth... assuming that you can get the left side weight that high. I'm not sure that I've ever noticed much of a performance advantage to it, but I did switch all of my mods over to this type of bar and one of them got a lot better, unfortunately several other changes were made at the same time, so I can't be sure that was a big change.

I would also ditch the brake floaters, mostly just to lose the weight and complexity.

If you have mounts to run the LR spring forward and the RR spring back I would do that with the "biscuit bar". If not I would put them both back and run a solid upper link.

I used to run a lot less angle in my trailing arms than what Perry said, but that's going to be driver preferrence. Just keep in mind how the axle is going to steer under roll and squat, and concentrate on what you are feeling on the track. The RR arm makes bigger changes in roll steer because it travels more than the LR (in compression) through the middle of the corner.

Another thing you can try with the biscuit bar is changing the distance of the axle mount to the center of the axle tube. This will make torque steer, and as the axle stretches the biscuit bar it can be used to steer the axle. I would run the LR in a lower hole than the RR to steer the axle to the left and tighten the car on exit.

Honestly, if I were to do it again, I would probably just put a solid link in and put both springs behind the axle. That would be the simplest and easiest to feel and understand. The ladder bar wouldnt be a bad way to go either, some cars have used variations of that with success, like the trailer load leveler springs and half leafs and stuff like that.

Thanks Gavin. I appreciate the detailed info. The panhard bar is 25". If we move the panhard bracket on the chassis to the RR and welded a new panhard bracket on the rear, the panhard bar will end up being a bit shorter.

The 90/10 shock and mount is just about level and can only go up. The toplink on the rear isn't very tall though. We can either add a new taller toplink on the rear to create downward angle for the biscuit bar or simply weld on a new chassis bracket with more adjustability to a downward angle. Either way, it should work.

When you mean solid top link bar, does it have a little rubber bushing where it attaches to the rearend toplink bracket and uses the same mount as the 90/10 shock? This is a short distance (14" or so). Is the biscuit bar in lieu of the solid toplink bar mounted to a further forward bar from the same toplink mount?

Keep the answers coming, this is tremendously helpful!

Nope I just mean to not run a biscuit bar or any other "spring" toplink. Just a sleeve and 2 heims. It would have the same downward angle as the biscuit bar. It needs the angle to help the car transfer weight. The more I think over these types of suspensions in my head, the more I think we've managed to over complicate them.

25" seems short for a panhard bar to me. If there's room to clamp an axle bracket to the left side axle tube and run a bar to the right side of the frame you should be able to get a longer bar in there.

Gavin said:

"Nope I just mean to not run a biscuit bar or any other "spring" toplink. Just a sleeve and 2 heims. It would have the same downward angle as the biscuit bar. It needs the angle to help the car transfer weight. The more I think over these types of suspensions in my head, the more I think we've managed to over complicate them."

I've run both a spring top link and a solid "sleeve" toplink, and have found out what Perry did also, with the spring link I would get good bite off, but it wouldn't hold down the stretch.

Not sure about the biscuit, could see where it may work better than the spring top link, might try it next year, not sure yet.

Also, with the spring top link, I run left front, right rear spring mount set up. With the solid top link, ran both on rear.

Driver choice as to feel with those set ups.

Sounds like we all have some work to do on test and tune days, eh?

have a good day,

schinde

I'm not saying that that doesn't happen, I'm saying that I don't know WHY it happens. It is a spike in the torque curve of the engine, or is the "spring" deflecting further and letting the rear end wind up more and turning the rear end? That's why I'm starting to believe that simpler is better. 3 solid links and a panhard bar = K.I.S.S.

You do get the advantage of adding "dynamic" wedge with the staggered springs though, maybe that is better? I don't know, but it is how all of my cars were when I sold them, and it is how my dad's car is now.

gavin said:

"I'm not saying that that doesn't happen, I'm saying that I don't know WHY it happens. It is a spike in the torque curve of the engine, or is the "spring" deflecting further and letting the rear end wind up more and turning the rear end? That's why I'm starting to believe that simpler is better. 3 solid links and a panhard bar = K.I.S.S."


Nor do I. One of the fun parts of this game, trying to figure it all out.

I myself wondered if it had to do with the torque curve also as to the car not keeping the bite. Had not thought of the axle wrap, good point.

I agree w/ the K.I.S.S. theory, just haven't tried a biscuit yet, wonder if that would limit the travel of the axle better, yet ease the initial shock of putting the power down when your foot is too antsy to feather it in.

have a good day,

schinde

True.

I also have a problem when I think about the biscuit (which is still just a spring with a progressive rate and different damping properties) because the tires need to grab to apply the reaction torque (or tendency of the pinion to climb the ring gear) that causes that toplink to stretch. Makes me think that its only benefit is jacking wedge and trying to steer the rearend if done correctly... but that's easy to do incorrectly also. I wonder about adverse effects of the bisquit bar when rolling out of the throttle too... seems you might HAVE to be smoother off the throttle with it.

All in all, anything CAN work... but what is the easiest to work and the most consistent.

thanks again gentlemen. I believe I got it now, or at least much better than a few days ago.

Here is what we got:
put panhard mount on right side of chassis and put a clamp bracket on left side of rear for panhard bar (which we can do) - I'm not sure what the length will end of being.

Remove brake floaters

Use solid LR and RR trailing arms; keep RR trailing arm on the short mount on the chassis

Remove the ladder bar/fifth arm altogether

On the toplink, replace 90/10 shock with a solid bar (or biscuit bar if you dare) mounted to the same spot as the 90/10 shock would go on the chassis, except need to add more downward angle than current mount allows (degrees or inches down?)

Either put RR and LR springs behind housing or in some configuration that we feel comfortable with (which we can do as we have both mounts front and behind).

okay, last couple questions: 1. What is the pinion angle of the rearend? and 2. What wheel offset for base set up?

Don't let me scare you away from the biscuit bar, tons of people use them, and have good success. Which would account for more than "theory".

If you run the biscuit bar, put the LR spring in front of the axle and the RR behind.

Toplink angle should be adjustable from uhh... 5-15* I guess. (What do you think Perry?)

Also, your short RR arm isn't shorter than the LR, is it? Hopefully they are the same.

If the car is light I would run 1" offset wheels all the way around, if not 1" on the right and 2" on the left.

You'll need more pinion angle with the biscuit bar, because it will lose some as the axle wraps up. I would run 6* down with the biscuit bar, and 2-3* down with a solid bar.