What causes Hike in the rear?? and other questions...

#1 So what causes the HIke in the rear? 4 link bar locations on the chassis and the birdcage? Jbar angle? Ive been thinking alot about the new droop rule and had some ideas other than ride heights for getting "around" certain areas but I wanted to pose that question to everyone to see the answers that I am given. #2 Does "excessive" hike in the rear help or hurt on a bigger track? I know it puts the spoiler in the air and the interior of the car directs air to the spoiler but on a track of say 1/2 mile would the benefits out weight the negatives? In this instance should the spoiler be layed back further?#3 Taller, softer LR springs. Is that actually solving anything other than keeping the spring in the bucket of the coilover upon hike? Ive seen springs as tall as 20" out there now. Wouldnt a shorter (10") heavier spring be better for left rear traction. You would have to compress the 20" spring 4 times the amount that you would a 10" spring to achieve basically the same force as the smaller spring would put on the LR tire. Im not an engineer by far. Just asking questions as to why maybe some people are running the extreme tall springs.Just some food for thought and discussion points. Thanks ahead of time guys.

You can't have too much downforce.

Your heavy, unloaded lr spring, is gonna cause you issues when you slow for the corner.

Hike is caused by mechanical lift, the front dropping, and weight transfer from a jack in the box rate spring.

Some only think in terms of spring compressing.

Think of a 400# spring and a 100# spring each with 600 lbs on them at ride height. Tthe 400# spring is compressed 1.5 inches. The 100# spring is compressed 6 inches.
Now remove 300# thru weight transfer..
The 400# spring extends by.75 inches. The 100# springs extends 3 inches.

Both springs are still holding up 300#

Hike on throttle comes from the left (and right) rear trying to move faster than the car. The suspension links and springs/shocks turn forward movement into partial vertical and partial longitudinal vectors into the chassis which causes the wheel to walk ahead and separate chassis from spring until a limiter is engaged. (Talking about most typical dirt 4 link setups LR especially but the RR hikes too) Lift arms and/or pull bars or whatever combination of both will typically assist this movement as well by removing some of the weight off the links/springs making that movement easier and more instant. That's just on throttle. When you turn, the j bar applies a jacking force that unloads the left spring and can cause hike up. Also as has been mentioned... The spring rate. A soft enough spring will promote hike better than a stiffer one. While a stiffer spring will "load and unload" quicker... A softer spring will maintain more consistent load during its stroke and wants to travel more distance to unload the same.... Because the car will always want to transfer, relatively speaking, the same amount of weight, when you turn with a soft spring versus a stiff spring with the same static load, the soft spring will promote left rear travel upwards. As 95shaw mentioned... The force remaining in the spring at a higher amount of travel compared to a stiffer one allows it to maintain not only a better contact with the spring seat and better hike down control as the spring pressure is still helping hold the car up at the upper limit of travel... It still has more energy getting back up if for some reason it does settle some, compared to a heavily loaded LR that was stiffer. Also a heavier loaded stiffer LR would likely make the car more loose on hike down as well... One thing that's nice about the soft LR is that in order to get your extended loads you don't need to crank a bunch of extra spring load into the RF either, which helps with RF travel. If we used a 275LR for example linear... To get 200# drop load with 6.5" of drop.... And let's say the shock travels 6" You'd need to crank in about 1800 pounds into the spring, in order to keep close to 3/4" spring load in it. This would bury the RF static, and you'd likely need to add a bunch of load to keep the car from digging into the track. This would also make it harder for the car to roll over onto the RF, and on entry the RR would roll over the left front would lift and the entire front of the car would want to come off the track. By using a softer LR either through stacking, lockout, softer progressive or just softer linear.. you can control the extended load but keep the deck down in the back to pass tech. So while to a degree a stiffer LR would give you more traction in the LR on hike up and from indexing into it, that's just one part of the picture and I believe someone in here has been known to say "what you gain on hike up you lose on hike down"

What Kennedy said

Mr. K , thats was a good explanation above , I,m curious to your opinion on which is better to get a soft rear rate , the stacked set up or the long soft tornado spring ?

Stacked digressive is my favorite way of running soft lr.

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Originally Posted by fastford

Mr. K , thats was a good explanation above , I,m curious to your opinion on which is better to get a soft rear rate , the stacked set up or the long soft tornado spring ?

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Why would you limit yourself to a single spring rate?

its working pretty well on a car at tst right now , it is a 16" barrel type 80# spring from swift , but i do know that several big names are running it also , i personally have not tried it , we still on stacked , i was just looking for input from some one else that has tried it......also , the car im talking about is on a bump stop on left rear to hold car at static ride height....

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Originally Posted by fastford

its working pretty well on a car at tst right now , it is a 16" barrel type 80# spring from swift , but i do know that several big names are running it also , i personally have not tried it , we still on stacked , i was just looking for input from some one else that has tried it......also , the car im talking about is on a bump stop on left rear to hold car at static ride height....

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Regardless of how it works, it is limited, compared to a dual spring setup. That is my whole point.

Masters is right. A linear spring is a linear spring. And in order to change your drop load, you need to adjust the ride height, and if you're being teched and riding the line of passing, or trying to keep yourself riding the line of passing tech making changing to the one corner will affect the opposite corner so then you need to dink around there .. With a stacked setup you could adjust your extended numbers with minimal/no affect on static heights.

i think thats why they have a bump stop on left rear , to control static ride height....

Why would you run a bumpstop? Why not use the benefit of it sitting down even lower to your advantage and raise the deck height even more?

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Originally Posted by fastford

i think thats why they have a bump stop on left rear , to control static ride height....

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While yes it controls the Ride load/ride height that can also be controlled by the coilover nut without the bump but then you couldn't set the ride vs extended separately. Adding a bump more or less makes it similar to a stack where you can adjust the 2 separately.

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Originally Posted by fastford

i think thats why they have a bump stop on left rear , to control static ride height....

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Yup. But the tornado does nothing I can't do with 2 springs, besides separate me from some money. And ride load and droop load are still more connected than a digressive system.

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Originally Posted by Punisher88

Why would you run a bumpstop? Why not use the benefit of it sitting down even lower to your advantage and raise the deck height even more?

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To a point, that's true. Eventually, you may get too low.

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Originally Posted by Punisher88

Why would you run a bumpstop? Why not use the benefit of it sitting down even lower to your advantage and raise the deck height even more?

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Say I have the car as low as it could possibly go and can't go any lower, but it has too much extended load for what I want. The bump would allow me to keep ride there but I could unwind the coilover nut and shim the bump and have less extended but same ride

Hope that makes sense

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Originally Posted by Punisher88

Why would you run a bumpstop? Why not use the benefit of it sitting down even lower to your advantage and raise the deck height even more?

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thats why they have a min rule also now, I've seen cars dragging the frame rail under the driver, its easy to fix and tech, 3-4 in wheel to slide under the driver at ride height, then jack her up and check the deck height, but watch whats next, watch how far they get the nose down now to get the angle back, lol, there already working there butts off on it, get ready for a new chassis lmao

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Originally Posted by billetbirdcage

Say I have the car as low as it could possibly go and can't go any lower, but it has too much extended load for what I want. The bump would allow me to keep ride there but I could unwind the coilover nut and shim the bump and have less extended but same ride

Hope that makes sense

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this is how im thinking as well , also with the ride height rules starting to appear , i guess it would help meet this with a light spring and still allow more control of load at droop....

All makes sense now. I hadn't thought of it like that.

yep , every one thinks of a bump stop in the dynamic state , and MBR , that tornado and bump stop was a little over 100 bucks , a complete stacked set is heavier and cost at least double that amount , i am in agreement on the stacked being better or lets say more adjustable , but if you dont think outside the box and try things , you will fall behind....

Is there any consequence to going too soft on the left rear spring, while using a bump to maintain ride height?

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Originally Posted by fastford

yep , every one thinks of a bump stop in the dynamic state , and MBR , that tornado and bump stop was a little over 100 bucks , a complete stacked set is heavier and cost at least double that amount , i am in agreement on the stacked being better or lets say more adjustable , but if you dont think outside the box and try things , you will fall behind....

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I already have stack hardware and a 50# birdcage. Im not buying a tornado. I'll buy things if the physics make sense. I never bought a strange oval axle either.

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Originally Posted by bcarrot28

Is there any consequence to going too soft on the left rear spring, while using a bump to maintain ride height?

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A hard landing may break your shock mount off, but otherwise no. I've done it before.

The main reason to use a single spring is because you rules specify only one spring per wheel...but, just because there is a spring there doesn't mean it is functional, all I'm sayin', for you limiting rule racers. -Wink

The reason I ask about the light spring is I have been running a 50 on the lr this past year but have not been sitting on a bump, so my chain load is very high. I have also been fighting a terrible bounce on throttle all year since going to this spring.

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Originally Posted by bcarrot28

The reason I ask about the light spring is I have been running a 50 on the lr this past year but have not been sitting on a bump, so my chain load is very high. I have also been fighting a terrible bounce on throttle all year since going to this spring.

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I'm guessing you have a spring or very soft rubber on your chain?

I have tried several hard, soft and none. Still violent bouncing

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Originally Posted by bcarrot28

I have tried several hard, soft and none. Still violent bouncing

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Might be a geometry issue then. How high is your chain load?

My car is around 200lbs. Teammates car is on the same effective spring rate but stack. His has been as low as 40 and still bouncing.

The spring rate, by itself, isn't the problem. It's shock or geometry.

We've been through 3 sets of shocks and tried to work with the shock guys. No answer yet. The only thing we changed when this started was lr spring rate and percentages. The same cars had no issue before hand, has been very aggravating.

I had this problem, and i narrowed it down to indexing in the cage at the bottom of your droop travel. As MBR said, geometry. Try to get all the indexing out of the BC, zero index all the way to full droop and see if that does it.

Just by coincidence, i was running about 200lbs droop load, on a 175/175 stack.

We noticed it really bad when i was playing with indexing the top bar, aft 1" on the BC, away from CL. It indexes the cage FWD right at the bottom of droop travel, and that really made it buck coming off the corner.