Suspension Optimization and Tuning Help

[Ron Sutton]

Tuning the split in a panhard bar for neutral handling

For most road course & autocross applications, a watt's link works well and is the preferred choice of many. I agree & support this ... but because I'm a tuner, I prefer a panhard bar ... but only if it is height adjustable on both sides & centered in the chassis. This is not a thread to steer someone towards or away from either. Just an understanding of how they work & how they can & can not be tuned.

Pros & cons of Watt’s links:
• Pro: Does not cause different roll centers, roll resistance or tire loads on LH & RH corners.
• Con: Can not be tuned to provide different roll resistance or tire loads on LH & RH corners.

Pros & cons of panhard bars:
• Con: If simply set level, causes different roll centers, roll resistance & tire loads on LH & RH corners.
• Pro: Can be tuned with simple angle change to achieve neutral & equal roll resistance & tire loads on LH & RH corners.
• Pro: Can be tuned to provide different roll resistance & tire loads on LH & RH corners.

The natural tendency for a panhard bar (mounted to the housing on the left & the chassis on the right):
• In LH turns, the left side rod end raises only a small amount with tire extension & the right side rod ends lowers significantly with suspension compression. This moves the roll center down dynamically on LH corners.
• If the panhard bar had been level at 10”, the math could look like this: LH 10.25” & RH 9” = DRC 9.625” & 1.25” split
• In RH turns, the left side rod end lowers only a small amount with tire compression & the right side rod end raises significantly with suspension extension. This moves the roll center up dynamically on RH corners.
• If the panhard bar had been level at 10”, the math could look like this: LH 9.75” & RH 11” = DRC 10.375” & 1.25” split

The split is the same both directions … at 1.25” in this example:
• But the DRC (dynamic roll center) is ¾” lower on LH corners than on RH corners.
• The car rolls more on LH corners … making the car more free or looser.
• The car rolls less on RH corners … making the car more tight or pushy.
• If the panhard bar mounting is reversed, everything above is reversed too.
• This can be corrected easily. More on the “how to” later.

The irony is … the torque steer from centered 3-link, 4-link, torque arm & truck arm suspensions … behave the opposite under power on corner exit. So under power the combination of torque steer & panhard effects are neutralizing each other to some degree … but just on corner exit. You would still have the car behaving more freely or looser in the entry & middle of LH corners … and more tight or pushy in the entry & middle of RH corners. So it’s not the ideal solution by any means.

But with an offset 3-link … if the top link is offset to the right the correct amount to counter the torque … you end up with zero torque steer under power. Combine this with a Watt’s link or “Balanced Panhard Bar” and you will have even loading throughout the corner … on both left & right hand corners.



What is a Balanced Panhard Bar?
We already know that Watt’s links do not cause different roll centers or loads on LH & RH corners … and they can not be adjusted to do so. If you’re running a Watt’s link you will have even loading. If you’re running a panhard bar … with an offset 3-link … you need to tune the panhard bar angle to neutralize the effects discussed above and have a balanced panhard bar set-up. It is easy to do, but needs to be done.

To counter the typical panhard bar effects, you simply run angle … also known as split … in the panhard bar … with the left side lower & right side higher. (Assuming the panhard bar is mounted to the housing on the left & the chassis on the right.) For discussion purposes only, let’s say you run the same 10” roll center but with a 1/2” split. The left side would be 9.75” & right side 10.25”. The dynamic results during cornering would look like this:
• In LH turns: LH 10” & RH 9.25” = DRC 9.625” & 0.75” split
• In RH turns LH 9.5” & RH 11.25” = DRC 10.375” & 1.75” split

This next part throws people off as it is a little challenging to digest:
• The dynamic roll centers do not change with panhard bar split.
• But the differences in dynamic panhard bar angles … change the chassis roll resistance & tire loading when cornering.
• The lower levels of split on LH corners & the higher levels of split on RH corners … balance the handling left & right.
• Of course the numbers above are just an example & the split needs to be fine tuned on any race or track car.

So Ron … why don’t you run a Watt’s link?
Simple answer really. There are some variables that sometimes call for the race car to load the tires more one direction of corner & less the other direction. An adjustable panhard bar lets me fine tune the balance of tire loading.

Situations to tune balance with panhard bar split:
1. Car not 50/50 balanced side to side. Some cars are left heavy due to driver placement.
2. Some tracks have more rights. Some tracks more lefts.
3. Some tracks have high speed lefts & low speed rights … or vice versa.
4. Some tracks have more banked lefts & flatter rights … or vice versa.
5. Some track have off-camber corners, combined with flat and/or banked corners.

At the end of the day, winning races is about overcoming the challenges of the track better than your competitors. If I have a tuning tool that lets me tune for any of these 5 conditions better than my competitors that don’t have this tool … that’s an advantage I’ll take.

We ran a course with 7 right hand turns and only 2 lefts. One left was banked & the other was tight & flat. We used several tools to “wedge” the opposite direction of oval track racers. This gripped up the RH turns & freed up the LH turns. We had amazing grip on all the right hand turns. The banking providing “ok” grip for the first left turn. And freeing up the other super tight left corner made us faster there too. We were faster in 8 out of the 9 corners … won a lot a of races … and won two championships at that track.

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Whew! That’s a lot to take in. Let’s summarize it.

1. Centered 3-link, 4-link, torque arm & truck arm suspensions experience torque steer under acceleration.
2. Offset 3-links, if offset correctly, do not experience torque steer.
3. Watt’s links do not cause different roll centers or loads on LH & RH corners … and cannot be adjusted to do so.
4. Panhard bars do cause different roll centers & loads on LH & RH corners … but can be adjusted back to neutral & balanced.
5. Panhard bars can be run neutral & balanced … or tuned to load the tires differently if needed.

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With a centered 3-link, 4-link, Torque Arm or Truck Arms & a Watt’s link:
• You will have even loading on entry & middle for both left & right hand corners.
• You are stuck with torque steer on corner exits.

With a centered 3-link, 4-link, Torque Arm or Truck Arms & a adjustable panhard bar:
You can use the panhard bar angle to effectively counteract "torque steer" … to a degree. The keys to doing this are simple:
• Keep the center height where you want the roll center.
• Lower the side you want to load the tire more on & raise the other side the same amount.

This strategy is always a compromise. But the suspension already had a compromise.
You’re just shifting where the compromise is.

Think of it this way:
• If you eliminate 100% of the torque steer, you will have 100% of the effects provided by an unbalanced panhard bar set-up.
• If you balanced panhard bar set-up 100%, you will have 100% of the of the torque steer.
• Most racers shoot for a 50/50 balance and then tune for track conditions.
• You can always shift the balance to gain here & give up there.

With an offset 3-link & a Watt’s link:
• You have zero torque steer and can achieve a “Balanced Panhard Bar” for even loading throughout both left & right hand corners.

With an offset 3-link & an adjustable panhard bar:
• You have zero torque steer and can achieve a “Balanced Panhard Bar” for even loading throughout both left & right hand corners.
• Plus, you can tune tire load balance with panhard bar split if the situation calls for it.

Make sense?