5th Coil angle

[JDracing57]

What is the effect of moving the top 5th coil mount forward or backwards. Also what is a good angle to start with and does anybody use spring rubbers in they're 5th coil spring?

Thanks

[MasterSbilt_Racer]

What is the effect of moving the top 5th coil mount forward or backwards. Also what is a good angle to start with and does anybody use spring rubbers in they're 5th coil spring?

Thanks
You change the angle, which changes the rate. You also move the point where it lifts the chassis forward. Some people like the
top forward so that it straightens up during hike. Not necessary, IMO.

You can use spring rubbers for a quick and dirty adjustment just like any other place on the car.

[TheJet-09]

Mine is straight up/down at ride height. I've also had it about 1* leaned back, figuring the bottom is coming forward during acceleration I wanted to start it out on that side of its arc (I can't say that I noticed any difference in either).

[jesel45]

what if it was angled back at the top close to 2"? have a buddy that continues to argue with me saying it makes no difference on how it works, seem to me that if the spring is already angled backwards at ride height that when the car starts getting up that the 5th coil isnt really doing anything as it is moving forward pulling out on the shock therefore not allowing the spring to do its job, am i wrong in my thinking?

[TheJet-09]

2" sounds extreme. With mine being 1* (degree), it equates to around 1/4" or so set back at top. My thinking was to not go over center on the lower shock (5th coil) mount's arc/curve, taking into account that it is moving forward.

[Matt49]

Three things you have to consider:

1) Adding angle decreases the effective spring rate felt at the upper and lower mounts.

2) Moving the bottom mount changes the amount of rear-end torque felt by the spring and therefor changes the amount it will travel under a given amount of torque. Remember: travel changes the height of the j-bar on the pinion side.

3) Moving the top mount changes the lift point which is why moving it too far forward can cause an on throttle push. It is trying to lift the front of the car too much.

[billetbirdcage]

Torque arm 101:

You guys are missing the basic points of the torque arm and sort of need to forget about the angle of the 5th coil for the most part (this has an effect on things but mostly from a different aspect then mentioned).

2 basic things you need to pay attention to: Lower mounting point and upper mounting point

Lower mounting point: Mostly effects the spring rate the arm see's during acceleration. The farther forward the stiffer it reacts to the arm.

Upper mounting point: The farther forward the more weight is removed from the front of the car and transferred to the rear tires.

When the arm lifts it removes weight from all 4 springs of the car, how much off each one is dependent on how far forward/back/left/right the top mount is. Then applies that weight to the rear end via the torque arm. Say the top 5th coil mount is exactly in the middle of the COG of the car (this isn't going to happen cause typically it's 45" or so ahead of the rear axle).

Example 1: Lets just say the torque arm is lifting 1000 pounds total so 250# off each spring. So basically (over simplifying here for discussion) it's removing 500# from the front and back of the car off the springs and applying 1000# to the differential thru the torque arm mounting points on the rear end.

Example 2: If you move the top 5th coil mount back it removes more off the back then the front of the car, lets say the same 1000# total but now 600# from back of car and 400# from the front of the car. The difference between the 2 is this:

Again taking some liberties to help explain this and disregarding some things and forces going on to make the point clearer:

Example 1: Removed 500# from both front and rear and but added 1000# to the rear, for a net gain of: Rear -500 +1000= +500# on rear tires / front -500# = -500#


Example 2: Removed 600# from rear and 400# from front but added 1000# to the rear, for a net gain of: Rear -600 +1000= +400# on rear tires / front -400# = -400#

You need to think about the top and bottom locations as separate and the top mount location being the most important and the lower mount more of a spring rate change then anything. Now granted angling the 5th coil will make the arm see a different rate, but unless you angling the 5th coil a far amount the change will be small and therefore arguable to whether it effects the car enough to notice. Again talking a small change.

Any angle is just going to change the motion ratio of the arm vs what the spring sees and just alters the effective spring rate slightly. I have purposely left out acceleration weight transfer, anti-squat, speed of tire loading, and several other things. Not saying angle doesn't matter, it's just that the upper and lower mounting locations are more important and have a bigger influence on car handling then the actual angle of the spring and should be treated as such. You should be selecting where you want them the upper/lower mounting points off these 2 basic theories and not off position to get an certain angle.

[TheJet-09]

Thanks to both of you for the info/perspective. Billet - Based on what you've said/learned, if the top mount were 2" back from the bottom mount (as Jesel posted) and you moved only the bottom mount back 4" (so the top is now 2" forward of the bottom), increased the spring rate the required amount to maintain the same overall effective rate (based on the change in lift arm "length"), would there be no difference in the overall effect on the car?

[billetbirdcage]

Thanks to both of you for the info/perspective. Billet - Based on what you've said/learned, if the top mount were 2" back from the bottom mount (as Jesel posted) and you moved only the bottom mount back 4" (so the top is now 2" forward of the bottom), increased the spring rate the required amount to maintain the same overall effective rate (based on the change in lift arm "length"), would there be no difference in the overall effect on the car?

With ruling out other things happening, theoretically yes if you where able to change the spring so the effective spring rate was the same it would be very similar handling wise. You may notice a change in the amount of time for the traction (instant traction) to come in from the different length on the arm but after that they would be very similar.

As matt said: 3" of travel at 32" vs 3" of travel at 40" will put the rear end side to side at a different place under throttle thus changing handling just from dynamic rearend placement

[TheJet-09]

Good stuff! Thank you.

[billetbirdcage]

Good stuff! Thank you.

One part I left out is the force at the lower mounting point.

Say you have enough traction for 600ft pound from the engine with a 6.00 gear so basically you have 3600 ft pounds at the tires. As the lower mount is moved forward you have less pressure to lift on the car given then same traction at the tires.

That force would be 43200 in inch pounds to make it easier to figure the foot pounds at the lower mount length. So 32" would be 1350 ft pounds and 36" would be 1200 ft pounds and 40" would be 1080 ft pounds, so farther back you will actually have more force to lift on the car.

I purposely left this part out to get the basic idea across, but this can throw a monkey wrench into my whole explanation. Have fun

This is part of the reason I said to treat them as separate adjustments, I prefer to only move the top mount and leave the bottom one alone unless moving the top a fair amount. I'll move the upper around 2" either way without worrying about the lower. This way you get the desired effect on where your lifting on the car without changing the rate or amount of force the arm is doing.

[Austin34471]

Billet, how much worth do you put in the lateral location of the liftbar? I can see it making a difference as far as the direction the lift bar is pushing up on the car right to left. Obviously you are going to need it to migrate a good ways to the right if you want the 5th coil shock perpendicular to the ground (if that's indeed what you want) once roll and dive are taken into consideration.. Which do you think is more effective at controlling this migration, having the 5th arm locator that goes back to the rearend or to the side of the chassis like a rocket/club 29?

[25drtrkr]

One part I left out is the force at the lower mounting point.

Say you have enough traction for 600ft pound from the engine with a 6.00 gear so basically you have 3600 ft pounds at the tires. As the lower mount is moved forward you have less pressure to lift on the car given then same traction at the tires.

That force would be 43200 in inch pounds to make it easier to figure the foot pounds at the lower mount length. So 32" would be 1350 ft pounds and 36" would be 1200 ft pounds and 40" would be 1080 ft pounds, so farther back you will actually have more force to lift on the car.

I purposely left this part out to get the basic idea across, but this can throw a monkey wrench into my whole explanation. Have fun

This is part of the reason I said to treat them as separate adjustments, I prefer to only move the top mount and leave the bottom one alone unless moving the top a fair amount. I'll move the upper around 2" either way without worrying about the lower. This way you get the desired effect on where your lifting on the car without changing the rate or amount of force the arm is doing.

Thanks for posting about multiplying your torque by your rearend gear, been preaching that for years, and no one wants to listen.

Rearend gear is the great equalizer in dirt track racing!