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Helper/Tender springs

 
Old 04-23-2019, 01:23 PM
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Originally Posted by s2000Junky View Post
Too much over analyzing here for something that offers a real function with no draw backs other then a few bucks. The idea is not too add spring rate altering the shock dynamics, but rather just keep the spring seated on the perch at full droop, picking up the gap between your spring and perch retaining the ride height flexibility you want. Its possible not just when jacking up the car but on more abrupt elevation changes to pick up both wheels enough to unseat the springs. I added some Eibach 0 rate helper springs to my coilovers when I changed the springs out for the shorter stiffer ones and needed them at that point. Just get them and forget about it. Could save you some annoyances or problems down the road.
That's likely true for helper springs. Although you are adding a bit of weight as well as cost, it's minimal. Question is whether you'd ever actually use them outside of lifting the car. However, what JRZ is suggesting are tender springs, not zero-rate helpers.
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Old 04-23-2019, 02:58 PM
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Originally Posted by Nate Tempest View Post
That's likely true for helper springs. Although you are adding a bit of weight as well as cost, it's minimal. Question is whether you'd ever actually use them outside of lifting the car. However, what JRZ is suggesting are tender springs, not zero-rate helpers.
Well I know I don't like hearing my springs rattle around or become unseated when I lift my car in the air and then worry about them not seating properly again. Up to you.
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Old 04-23-2019, 03:09 PM
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Originally Posted by s2000Junky View Post
Well I know I don't like hearing my springs rattle around or become unseated when I lift my car in the air and then worry about them not seating properly again. Up to you.
Totally, and that was my original reason for looking into this in the first place, along with running into that line in the JRZ manual. For whatever reason, I've never had a problem with my fronts moving around or jumping back into place, even when the car is lifted, but it does happen with the rears.

So at the very least I imagine I'll get rear helpers. Going to take a closer look at the front to see if I can figure out why they're not doing it, and if I can count on that. But having learned more about this, I'm also interested in whether tender springs (rather than just helpers) could be beneficial in more ways than just keeping the springs seated, as I got into above.
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Old 04-24-2019, 11:06 AM
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What you went into above is basically the lite version of why you'll see even stiffly sprung rally cars with tenders - otherwise all that droop travel you have on the damper is wasted and you may as well fit shorter units.
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Old 04-24-2019, 11:20 AM
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So the more I learn about this, the more it seems like I might as well go with actual tender springs. They should be sized such that under normal cornering and braking loads they will still be fully compressed on the unloaded side, so the only time they take effect is in these situations where you hit a dip on the unloaded side. That way there won't be a reduction of spring rate (and resulting body roll) under normal conditions, but we'll get a bit of a benefit in the situation described above.

So I guess I need to work out how much max weight transfer these cars have with sticky tires and ~13" ride height.
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Old 04-24-2019, 01:56 PM
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Edit: this post doesn't account for sway bars or motion ratios so isn't very accurate. More accurate calculations below, starting here: https://www.s2ki.com/forums/s2000-racing-competition-11/helper-tender-springs-1193570/page6/#post24597213ggg

Just ran some numbers. Lowered S2000 has a center of gravity of about 18", or 0.457m. Weight (mine) is 2965lb or 1350kg, split pretty evenly to about 750lb per corner.

My max acceleration around corners is around 1.1-1.2G; I'm guessing with R-comps you'd be in the 1.3G range, so using that to be safe.
So, cornering force = 1.3*9.8*1350 = 17,200N
Torque on the lever from CG to ground is then 17,200N*0.457m = 7860Nm

For a track width of ~58", or 1.47m, that means a weight transfer of 7860/1.47 = 5347N, or 1200lb.

So if you assume equal spring rates front and rear and no sway bars for simplicity, that would mean 600lb per corner gets transferred from inside to outside, meaning you would have about 150lb remaining on each wheel, and would want to size your tender springs such that they're still fully compressed at that weight. IE maybe a 50lb/in spring with 2" of travel.

In reality, front springs will be stiffer than rear, which means more of the weight transfer will occur in the front, and so the front tender should probably be softer than that, and the rear could be stiffer. IE if front springs are 700lb/in, and rear are 500lb/in, you're going to get roughly 700lb of weight transfer in the front and 500 in the rear, ignoring sway bars, so you would only have around 50lb on the inside front. A big front sway bar will also move more of the weight transfer to the front, but it does so by effectively increasing the load on the unloaded front spring, so I don't think it should affect front tender sizing. It should allow rears to be stiffer though. So it definitely seems like one could put some significant spring rate rear tender springs on, and not have them interfere with dynamics during normal roll under cornering—as long as they're fully compressed with ~200-250lb on them, they should only expand if the wheel hits a dip. In the front though, if my math is right, the inside wheel does get very light when cornering with sticky tires. In that case, anything more than a very soft tender spring (ie 25lb/in with 2" travel, or less, using the numbers above) will begin to expand under normal cornering, which will increase body roll, as well as shifting more of the weight transfer to the rear.

I'd be very interested to hear from someone who races S2000s in a serious way and knows more about this stuff than I do (that wouldn't be hard!) as far as whether these numbers are close to what's seen in the real world. I can certainly see why autocross guys don't tend to run tender springs, as this isn't going to be beneficial on a flat surface, and could cause issues if your tenders are too stiff for the Gs the car is pulling. It does seem though that properly sized tenders could be beneficial on the track in certain circumstances, without sacrificing roll stiffness in normal cornering.

Last edited by Nate Tempest; 05-05-2019 at 01:19 PM. Reason: formatting was messed up for some reason
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Old 04-24-2019, 03:16 PM
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For your calculations -- from my data, 1.2G is sustained on level ground for an NT01, with sustained 1.7G in a certain banked corner out west (Chuckwalla bowl).
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Old 04-24-2019, 03:18 PM
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Originally Posted by Chibo View Post
From my data, 1.2G is sustained on level ground for an NT01, with sustained 1.7G in a certain banked corner out west.
Thanks, fits with my data on flat. In a banked corner much of that cornering force will be normal rather than lateral force, so the weight transfer shouldn't be higher.
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Old 04-24-2019, 03:49 PM
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I'm on 200lb eibach 175-250-200 helpers in the rear since thats what my car came with. I've also run on 0 rate and 150lb helpers on other s2000s. All have been compressed at ride height and my car is an autox car only.
Not sure what sites you run on, but at packwood and even at pitt meadows, some spots you can catch air or hit bumps in a straight or in a corner that would unload the rear. At lincoln at us nationals, the ridges between the concrete pads there are some big ass bumps and cracks in the concrete that could unload the rear too.

I couldn't say for sure if the higher rate helper did anything at all. I have run a back to back event with helper no helper and not noticed a difference really but i'm busy worrying about other things.

I only care about not chewing up my spring caps if the spring gets unloaded enough.
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Old 04-24-2019, 05:52 PM
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Still way too much over analyzing here. Whether its 0 rate or 100lb or 200lb, if it cant support the weight of the car... or overcoming the rebound damping setting (which I can say it wont off the top of my head without any calculating) its a moot point,.The only goal here is to keep the spring seated when its unloaded. If you want to run a dual rate spring set up for a progressive ramp up, then your in the wrong car and doing the wrong Motorsports. You should get into off roading. Think about it, you have approx 3" of piston travel, half of which is taken up with the weight of the car, you don't have room to develop a progressive spring rate, you will ruin the ride/performance.
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