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Helper/Tender springs

 
Old 04-24-2019, 06:19 PM
  #21  
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I think I demonstrated pretty clearly above why there could in fact be a difference between 0 and 100 and 200, and that there could be benefits beyond simply keeping the spring seated. If you're going to write that off as overanalyzing while also contradicting it, I don't really know what to say! You're welcome to do as you like, and I'm sure zero rate helpers work fine (as do none at all in my experience). But I'm interested in actually understanding this stuff as much as possible, and determining whether non-zero tenders could be useful. I'd call that analyzing, no 'over'.
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Old 04-25-2019, 07:53 AM
  #22  
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Originally Posted by Nate Tempest View Post
I think I demonstrated pretty clearly above why there could in fact be a difference between 0 and 100 and 200, and that there could be benefits beyond simply keeping the spring seated. If you're going to write that off as overanalyzing while also contradicting it, I don't really know what to say! You're welcome to do as you like, and I'm sure zero rate helpers work fine (as do none at all in my experience). But I'm interested in actually understanding this stuff as much as possible, and determining whether non-zero tenders could be useful. I'd call that analyzing, no 'over'.
How is a 200lb helper spring per corner going to offer anything supportive to a 750lb corner to make the spring rate progressive? Especially when its tied to a sway bar? The only potential slight effect would be aiding in more body roll, which I don't see as a positive. Analyze away. I'm just sayin

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Old 04-25-2019, 08:02 AM
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Originally Posted by Nate Tempest View Post
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.
I can't comment on whether the numbers are accurate (although check out farnorthracing.com's dynamics calculator and see if they come out in the ballpark).

Edit: Made a conjecture here I second-guessed, so I removed it.

If you do consider adding in the effect of a a thick front bar paired with softer main springs, it might mean there is so much resistance to droop on the inside when cornering that the inside wheel lifts without the main spring ever fully unloading in the first place, and so any change to tender/helper rate has no impact.

Personally I like to over-analyze everything, even if I'll never be a good enough driver to turn it into laptimes.
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Old 04-25-2019, 08:13 AM
  #24  
 
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Unless the helper/tender spring is more than 3.5 inches tall (which it would not be) it would be fully compressed with a 700 lb corner setting on it as S2000 Junky alluded to. So you effectively have a thicker perch and shorter springs at rest or under any compression. The helper would only come into play at all when the corner was unloaded so would not really make a progressive rate. Not sure how much effect it would have at all really beyond just acting as a regular helper spring.
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Old 04-25-2019, 08:24 AM
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Originally Posted by s2000Junky View Post
How is a 200lb helper spring per corner going to offer anything supportive to a 750lb corner to make the spring rate progressive? Especially when its tied to a sway bar? The only potential slight effect would be aiding in more body roll, which I don't see as a positive. Analyze away. I'm just sayin
That's the big thing he's missing too. The tender might only come into play when the unloaded side's travel is beyond what normal spring length will give you in droop. Not only that, but it still has to overcome the shock's rebound valving. In large dips, etc I don't see a 250lbs tender overcoming the valving for a 700lbs/in spring.
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Old 04-25-2019, 08:28 AM
  #26  
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Exactly
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Old 04-25-2019, 10:30 AM
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Originally Posted by s2000Junky View Post
How is a 200lb helper spring per corner going to offer anything supportive to a 750lb corner to make the spring rate progressive? Especially when its tied to a sway bar? The only potential slight effect would be aiding in more body roll, which I don't see as a positive. Analyze away. I'm just sayin
Under normal circumstances, the 200lb/in tender would indeed be fully compressed, as you would want it to be. Assuming your car is well set up without the tender, with the damping matched to the main spring, you wouldn't want the tender spring to start expanding under regular cornering (or on the flat) since that would just increase body roll. The situation where it could be potentially useful is when you hit a dip with one wheel larger than that main spring can handle. IE, if you are pulling 1.3G around a corner and you have a square spring setup and no sway bars (to make things simple), the inside corners of the car aren't going to have 750lb on them anymore, they're going to have about 150lb. So if your springs are 600lb/in, they're only going to be compressed by about 1/4". Hit a dip that large (and even most bumpy curbing is more than that) and that wheel will be completely un-loaded.

So, if you add a tender spring, you have something to push down that corner to maintain contact. (In this case you wouldn't want it to be 200lb/in, but more like 75, so it's still compressed under normal cornering.) True, it won't push nearly as hard as the main spring, so it will act slower against the rebound damping that is tuned to the main spring. But it will still do more than no spring at all, so at the very least your tire will make contact again sooner than if you didn't have the tender, and you'll absorb the dip better than without it.

That's as straightforwardly as I can demonstrate how they could be helpful. I'll also say I'm not just making this up—this scenario was first described to me by Bryan at JRZ when I questioned why they recommend tenders; I just thought it through and added the math in order to understand it. I'm also not saying they will always be helpful. As I mentioned earlier, at least using rough numbers it looks like in the front of the S2000 due to the stiffer springs and bar it may not be possible to use a stiff enough tender to actually have a useful effect, while also keeping it fully compressed under normal circumstances when you don't want it to act. If you're not running Hoosiers though, or certainly in the rear, it looks like they could have some use.

Last edited by Nate Tempest; 04-25-2019 at 11:31 AM.
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Old 04-25-2019, 12:09 PM
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With the rates you suggest and a connected F/R sway bar, the S2000 suspension doesn't travel enough in compression and droop to make use of any helper or tender spring in regular motion. You would have to soften the main spring and up the tender spring rate in order to start using it, and at that point I think you're moving more toward a plush street setup rather than a track or autocross focused setup.

Of the track-focused JRZ's I've seen, the majority have zero rate helpers.
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Old 04-25-2019, 12:15 PM
  #29  
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Originally Posted by massiah86 View Post
With the rates you suggest and a connected F/R sway bar, the S2000 suspension doesn't travel enough in compression and droop to make use of any helper or tender spring in regular motion. You would have to soften the main spring and up the tender spring rate in order to start using it, and at that point I think you're moving more toward a plush street setup rather than a track or autocross focused setup.

Of the track-focused JRZ's I've seen, the majority have zero rate helpers.
Again, the tender is not intended to expand during regular motion, it's intended to allow the inside wheels to follow mid-corner dips beyond the range of the main spring. Such a dip would only have to be a fraction of an inch, so it's certainly not unheard of.

I'm certainly not saying they're vital—I've run happily without them for a couple years now. Just that they were recommended to me so I did some thinking on it, and I can see how they could theoretically be helpful. Whether the difference would actually be noticeable, I don't know.
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Old 04-25-2019, 02:00 PM
  #30  
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Originally Posted by Nate Tempest View Post
Again, the tender is not intended to expand during regular motion, it's intended to allow the inside wheels to follow mid-corner dips beyond the range of the main spring. Such a dip would only have to be a fraction of an inch, so it's certainly not unheard of.

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In order for this to work, the helper spring would have to be a high enough spring rate to force the sway bar down on the inside wheel overcoming the sways spring rate in that situation. So depending on the rear sway bar weight that would need to be stiff enough that you may be running risk of influencing damping and potentially ride height and then re adjusting bump travel and going around in circles. Your better off running a stiffer main rear spring with 0 rate helper and removing the rear sway bar all together so you can get independent articulation for maintaining forward traction, if that's the new goal. You could run a 50 or 100lb helper in that case since you don't need to overcome a sway bar and get potentially more inside wheel force without influencing your static ride height or total spring rate.

Last edited by s2000Junky; 04-25-2019 at 02:05 PM.
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