Protoform P-3 Bellcrank Angle

[fvee62]

How does one determine the optimal bellcrank angle when adjusting the rear suspension of a P-3? I currently have my uprights adjusted to 11 1/2" and have a 225lb. spring installed.
Just trying to get a better understanding of how to adjust the rear suspension/camber properly.

[Hardingfv32]

The angles are used to determine the wheel rate. The changes that you can achieve in wheel rate adjusting the rocker angle are too small for the driver to notice. Simple trig calculations if you want to put numbers to it.

It takes a very short/small rocker with high angularity movement to provide meaningful wheel rate changes. Something like a Citation rocker system. Even then I am not sure the driver is going to sense the changes. You are talking about changing the wheel rate which changes the tire 's operating temperature. Differences between the front and rear tire temperatures are what cause balance changes.

Not sure you could say that there is any effect on rear camber assuming one adjusts the droop after changing the rocker angle.

Brian

[Matt Clark]

Greg,
We run our rockers so they work the shock *to* 12 o'clock, at what we figure is max compression normally. And we do not even concern ourselves with pushrod length (aside from making them equal), since that is camber-dependent. That makes the shock work the truest you can. Spring rate is obviously dependent on your car vs. mine, and I am not sure what the latest Protoform trend is, but I think you are a bit stiff.
Also, on 2nd thinking, what shock do you have on the rear now? Be careful not to get the dampening too mis-matched with the spring... I did that years ago & the rear of the car was literally pogo'ing into the first corner at Mosport.

Edit: Ed is correct down below... thinking about it after reading, my original post is how *I used* to do it before we learned... with "we" being mainly Dad. lol
We have changed a couple things, including our shock dampening setup & plan, once we made that adjustment. We upgraded to a 3-way adjustable damper on the rear while it was being rebuilt, but we still used the same spring successfully.

[fvee62]

Thanks for your replies to my inquiry Matt & Brian. Much appreciated!

[Ed Womer]

The best way is to make sure the rockers are always working towards straight up and don't go over center which will cause decreasing rate on the spring. Also I tell my customers to make the distance at ride height to a minimum distance between shock bolts so the shock usually can not bottom out which most likely bend something.

Ed

[Bob Posner]

The best way is to make sure the rockers are always working towards straight up and don't go over center which will cause decreasing rate on the spring. Also I tell my customers to make the distance at ride height to a minimum distance between shock bolts so the shock usually can not bottom out which most likely bend something.

Ed

We have found that a p3 likes 12.5 inches at ride height fully loaded as the dimension between the shock eye centers. 200 pound spring and less total camber than you may think.We run 3.3 degrees

[fvee62]

Matt, I have a Penske two-way (6 settings bump canister/rebound hex nut) adjustable rear shock. I am assuming from your post that you use the uprights (not the spring) to adjust rear camber - correct?
Also, someone had installed three shims on the spring seat, so I will remove the spring and test it to see why they did this (fatigued, or increased spring weight tension?).
Ed, thanks for your input - makes a lot of sense.
Also, thank you Bob for giving me a starting point on the rear shock dimension.

[Bob Posner]

Matt, I have a Penske two-way (6 settings bump canister/rebound hex nut) adjustable rear shock. I am assuming from your post that you use the uprights (not the spring) to adjust rear camber - correct?
Also, someone had installed three shims on the spring seat, so I will remove the spring and test it to see why they did this (fatigued, or increased spring weight tension?).
Ed, thanks for your input - makes a lot of sense.
Also, thank you Bob for giving me a starting point on the rear shock dimension.

Adjust camber with the links to the axle and check camber often. We went through a period of maddening repeated camber gain which caused a lack of turn in. Finally took the spring off and measured length. It had compressed 1/4” and obviously weakened throughout a session with camber gains up to 2 degrees.

[Matt Clark]

Matt, I have a Penske two-way (6 settings bump canister/rebound hex nut) adjustable rear shock. I am assuming from your post that you use the uprights (not the spring) to adjust rear camber - correct?
Also, someone had installed three shims on the spring seat, so I will remove the spring and test it to see why they did this (fatigued, or increased spring weight tension?).
Ed, thanks for your input - makes a lot of sense.
Also, thank you Bob for giving me a starting point on the rear shock dimension.

Correct, the pushrods are what we adjust camber with.

Adjusting the spring seat will change the preload on the spring, which may or may not be what you want, based on your droop amount. But I have seen some guys with crazy preload, to the point I am not sure they didn't coil-bind the rear on bumps.
https://www.springrates.com/blog/how...the%20vehicle.

Without seeing these "shims" myself, did you disassemble it yet? Or just seeing something in there?
I ask, because if you did not disassemble it, I am guessing you see the Torsion Relief Bearing.
https://www.walmart.com/ip/Eibach-ER...0A70/967950984

I don't know how old your spring is, but as Bob said, they can age and/or sack out... so I would see about having the rate checked also.

[fvee62]

Matt, You are correct, the "shims' I was seeing are actually the torsion plate assembly you were referring to.
Any suggestions on a method for measuring my spring tension - or is this a job that needs some kind of specialized rig?
Thanks again to all for this very helpful information!

[Matt Clark]

Matt, You are correct, the "shims' I was seeing are actually the torsion plate assembly you were referring to.
Any suggestions on a method for measuring my spring tension - or is this a job that needs some kind of specialized rig?
Thanks again to all for this very helpful information!

I would guess there is some way to test it yourself, but I am not sure what is "proper" to get a true reading. Probably involving a bathroom scale & levers.
I would look into sending it somewhere, personally.

[veeten]

Any stock car shop or Race team will have a rate checker. Get a accurate measurement.
I have old chrome coil springs loose 1 inch in length and 50 Lbs. on rate.
It should only take a few minutes to check them.
Measure the total compress length before spring off the shock

[FVRacer21]

I slightly disagree with using the push (or pull rods) to change camber. When you change the length of the “rods” you also change your droop. If you set your car up with a good spring and the chosen rocker angles (distance between the shock mounting bolts) then set the “rods” to get camber, then the droop, you should leave these alone and just adjust the spring to compensate for sag. Unless something wears out or is bent, the only variable will be the spring - and BTW shock pressure.


When tuning, you always want to change one thing at a time, and if you use the push or pull rods to change camber AFTER the initial settings, you could change droop also. And if you are doing this to compensate for shock pressure or spring sag you would be essentially changing the rocker angle.

Measuring and documenting everything is a good way of making sure nothing is worn or bent.

ChrisZ

[Matt Clark]

I slightly disagree with using the push (or pull rods) to change camber. When you change the length of the “rods” you also change your droop. If you set your car up with a good spring and the chosen rocker angles (distance between the shock mounting bolts) then set the “rods” to get camber, then the droop, you should leave these alone and just adjust the spring to compensate for sag. Unless something wears out or is bent, the only variable will be the spring - and BTW shock pressure.


When tuning, you always want to change one thing at a time, and if you use the push or pull rods to change camber AFTER the initial settings, you could change droop also. And if you are doing this to compensate for shock pressure or spring sag you would be essentially changing the rocker angle.

Measuring and documenting everything is a good way of making sure nothing is worn or bent.

ChrisZ

Would you not just need to adjust your droop limiter at that point?

[FVRacer21]

Would you not just need to adjust your droop limiter at that point?

Matt,

Yes, if you are doing a complete alignment. But say the spring sags or the pressure changes and you do a quick change to the camber, you might not remember in the heat of battle. I am not sure if the rockers are close, if the change makes much difference, but a car like the BRD that has very short rockers, might have a larger effect.

when I worked for Skip Barber Racing School, we ran all pull rod cars and had a jig for each end and never touched after that. If anyone who works with FF can chime in how they do I since most FF are push rod at this point.(?)

ChrisZ

ps - if it works for you, I would not change, but I have been caught out before.

[problemchild]

When tuning, you always want to change one thing at a time, and if you use the push or pull rods to change camber AFTER the initial settings, you could change droop also.

ChrisZ

I could not disagree more. Of course you have to reset the droop after adjusting the pushrods. Because droop and camber effect different dynamics in the FV rear suspension, it is logical to adjust each independently to improve the handling in different parts of corners. Adjust your pushrods for camber first, then reset your droop.

Any car that I have worked on for decades, you got the desired bellcrank angle by setting the spring perch and shock length, then leaving it alone, and adjusting only pushrods.

[FVRacer21]

I could not disagree more. Of course you have to reset the droop after adjusting the pushrods. Because droop and camber effect different dynamics in the FV rear suspension, it is logical to adjust each independently to improve the handling in different parts of corners. Adjust your pushrods for camber first, then reset your droop.

Any car that I have worked on for decades, you got the desired bellcrank angle by setting the spring perch and shock length, then leaving it alone, and adjusting only pushrods.

Greg,

I don't think we are disagreeing. Once the camber is set, if it changes it has to be a issue with the spring/shock. So you have to check the bellcrank angle first to see if it has changed before going back to then adjusting the pushrods. And at the track I have seen people (hand raised) forget to check the droop. You tend to only do it one though...

ChrisZ

Off Topic 1 - not FV related - but on a FF do you do corner weights with the spring perches or with the push rods since it does not affect the camber? Thanks.

Off Topic 2 - Your car won the NEFV championship this year.