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Free spring rule


enginerd
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4 minutes ago, turbogrill said:

Ouch!

 

What was that?

IRS swap. Was valued at 50, then tech article removed silently, charged per suspension item, then when tech/Dana saw the fab work to make it fit in our s10 it’s a “tube frame” and only in EC
 

Have an entire thread I started on it a while back if you want to see/hear the entire story. Still bitter about it if you can’t tell 😂😂😂

Edited by mgoblue06
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3 hours ago, mcoppola said:

If you input the wire diameter and OD, you can play with # of active coils to see how much change occurs for the amount of coils cut.

Part of my calculations also involved determining "how many coils per inch" a spring has, as it helped to predict how the rate changes when you cut them shorter.

 

We quantified all the predictions with actual spring rate checks using a press and load cell. Another benefit to the rate checks was compressing your current spring to ride height and noting the load on the load cell. You can then take your new spring, compress it that same load rating, and note the height. If it's over your current ride height, cut a bit more. If it's shorter than your current ride height - you know the old saying "I cut it twice and it's till too short!" 

To add to this. If the the springs are constant rate then the length you remove is linearly related. So if you take 25% of the length out you increase spring rate by ~25%. It is slightly more complicated because sometimes the 1st coil are dead by being connected to another part of the coil. 

 

I am 6+hrs from the closest track so I went very deep into the math world to work out balance (oversteer and understeer) with different swaybars and such. I don't have enough test track time to really experiment. Maybe enough to fine tune. So I went way deeper then most would need. Balance was close to calculated on the versions I tested. Most of my fine tuning was finding the right spring rates and roll bar combinations for wheel traction. Going too far on springs to try and not use a 20 point rear bar resulted in poor behavior when the rear of the car skipped. That is more of platform problem...

 

In my examples below you just need column G * column k / (column K - column L) to get your new spring rate. Wire width and inner and outer calcs were to stay legal. Height change is just spring rate x weight. Mostly simple math. 

 

Last year I tested my calculated spring rates vs actual springs. 1 set was way off, cut they were less the OE rating; bad springs. Everything thing else was within 20lbs/inch of what I calculated. This works well. It is also a good way to understand how front, rear, and swaybars effect the car. Atleast if you go deep enough.

 

image.png.d8f8f957d4005876d1cc81a7bd4eb3f9.png

 

 

 

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34 minutes ago, mgoblue06 said:

IRS swap. Was valued at 50, then tech article removed silently, charged per suspension item, then when tech/Dana saw the fab work to make it fit in our s10 it’s a “tube frame” and only in EC
 

Have an entire thread I started on it a while back if you want to see/hear the entire story. Still bitter about it if you can’t tell 😂😂😂

I'll have to go find that. I would be livid.

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27 minutes ago, karman1970 said:

I'll have to go find that. I would be livid.

This '50 point value' was never a part of the rulebook.. it mysteriously appeared out of nowhere in the tech help desk and sparked a ton of outrage on the forum including by board members. I knew it wouldn't last but it's unfortunate that others acted on it so quickly and sunk time and money in such a project.

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32 minutes ago, enginerd said:

This '50 point value' was never a part of the rulebook.. it mysteriously appeared out of nowhere in the tech help desk and sparked a ton of outrage on the forum including by board members. I knew it wouldn't last but it's unfortunate that others acted on it so quickly and sunk time and money in such a project.


Was literally the worst time to start a build when that all went down. Oh well. 


GBU lives on raging inside me forever 😂😂😂

 

 

Edited by mgoblue06
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59 minutes ago, enginerd said:

This '50 point value' was never a part of the rulebook.. it mysteriously appeared out of nowhere in the tech help desk and sparked a ton of outrage on the forum including by board members. I knew it wouldn't last but it's unfortunate that others acted on it so quickly and sunk time and money in such a project.

I remember the beginning of the fiasco.  I agree on the 50 points, ridiculously cheap. 10 per part made sense, plus points for the diff and materials for a subframe.  But straight to EC for too much fab work after the official unofficial rule book says I can?  Seems wrong to me.

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2 hours ago, veris said:

To add to this. If the the springs are constant rate then the length you remove is linearly related. So if you take 25% of the length out you increase spring rate by ~25%. It is slightly more complicated because sometimes the 1st coil are dead by being connected to another part of the coil. 

Inversely proportional.

 

If you cut 25% off, you have 3/4 of the spring length left. Invert that and you get 4/3 or a 33% increase in spring rate.

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I thought the purpose of the spring rule was to help new teams and budget teams. You see the rule, go buy some H/R or other drop in springs for $150-200 and you are done. Simple and easy and a huge amount of teams are doing just that.

 

Then there are the ones who buy a few sets of cheap ones, cut them to make them stiffer and figure out what they feel is best for their car, zero points. The series is about creative solutions.

 

I think there is a huge difference between drop in springs or cut springs that do not have ride height adjustability. That is the key.  On my own car, I have adjustable coil over type of spring setup. I have multiple sets of springs and can and do run different springs at different tracks, WGI is stiffer and Nelsons is softer. Then you install, put on scales, corner balance to your desire and race. This makes a massive difference and a few turns on the adjust makes a really big difference to get the corner balance just right.  The 40 points on this makes total sense as it makes a big difference. When I had drop in replacement springs it was not the same league.

 

I like the idea of keeping drop in replacements as is that is what a lot of teams on a budget to, it keeps it simple and it is what we have.

 

We want rules stability, and we should have it, but a rule change like this would really affect a huge portion of the field. When we put rules forth we really need to think about that first. Sure, a team might take advantage of that, but trying to punish a team with a rule change that will affect a huge portion of teams is not the answer. There are better ways to do things.

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On 10/28/2021 at 3:25 PM, veris said:

I am 6+hrs from the closest track so I went very deep into the math world to work out balance (oversteer and understeer) with different swaybars and such.

 

I think it is cool you put this level of effort in. If you are not familiar with the Milliken book on vehicle dynamics then you should look it up. Has all of the equations worked out for you. I could send you an excel sheet if you want that has all this work in it, you would just need to clean it up and make the inputs match your car. Includes damping targets as well.

 

It is over 15 years old, from my FSAE car design days..... damn it hurts to say that out loud. 

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21 hours ago, veris said:

I'm read most of the Smith books. Haven't read Milliken. Smith isn't big into the frequency tuning idea, but he had much more test track time then I do. 

 

Thanks. PM sent... 

 

Smith is from an interative growth era of motorsports. Lots was changing but you could be a great practitioner and still advance the movement. 

 

Milliken brothers came in a era of little science in the sport. Negative camber wasn't a universal truth in setups yet. 

 

Like comparing Picasso to Michelangelo. 

 

The Milliken book equations I am thinking of get you close from a blank sheet, and offer you good ways to compare magnitude of changes. You might still need some Smith in your life to know which way to turn the knobs, but at least the math can tell you how far you went (and scale to a similar car that is bigger, smaller, etc).

 

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FWIW I have used ride frequency to select spring rates and roll couple to calculate desired roll couples / roll bar rates for idk maybe 3 builds now? Every one of those turned out very good on the first iteration. I've never even tried a different spring rate on the NC.

 

I'm sure trial-and-error works too, but I've had success with math.

I own all the To Win books but tend to refer to RCVD more often.

Edited by Grant
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I don't feel like I've ever gotten a performance advantage from coilovers vs. cut or custom springs. A spring is a spring. I only did coilovers on the NC because it was cheaper, easier, and I thought I'd be running the car in WRL.

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2 hours ago, Grant said:

I don't feel like I've ever gotten a performance advantage from coilovers vs. cut or custom springs. A spring is a spring. I only did coilovers on the NC because it was cheaper, easier, and I thought I'd be running the car in WRL.

What do customs generally run per spring?

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Race Car Vehicle Dynamics takes a lot of time to gain an understanding and the benefits can't be understated.  I recommend the hard cover version for wear and tear.  I take time to reread it every day.  I'm anal so it is my bathroom book.

 

FYI: The Milliken's are father and son.

 

Another good source is https://performancetrends.com/SuspAnzr.htm

 

Kp

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On 10/30/2021 at 7:11 PM, Grant said:

FWIW I have used ride frequency to select spring rates and roll couple to calculate desired roll couples / roll bar rates for idk maybe 3 builds now? Every one of those turned out very good on the first iteration. I've never even tried a different spring rate on the NC.

 

I'm sure trial-and-error works too, but I've had success with math.

I own all the To Win books but tend to refer to RCVD more often.

I love this stuff,  my problem is I read it and by later that day if someone asked me a question about it I'm back to "its vodoo and witchcraft".   

 

 

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On 10/30/2021 at 7:11 PM, Grant said:

FWIW I have used ride frequency to select spring rates and roll couple to calculate desired roll couples / roll bar rates for idk maybe 3 builds now? Every one of those turned out very good on the first iteration. I've never even tried a different spring rate on the NC.

 

I'm sure trial-and-error works too, but I've had success with math.

I own all the To Win books but tend to refer to RCVD more often.

 

Some of the NC coilovers are being sold with a 700/400 spring rate.

 

Given the close to 50/50 weight distribution I would assume this means different ride frequencies for front and back? Or how does that work.

 

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14 minutes ago, turbogrill said:

 

Some of the NC coilovers are being sold with a 700/400 spring rate.

 

Given the close to 50/50 weight distribution I would assume this means different ride frequencies for front and back? Or how does that work.

 

e30 suspension has vastly different motion ratios for front and back. NC may be similar.

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39 minutes ago, enginerd said:

e30 suspension has vastly different motion ratios for front and back. NC may be similar.

Good point, they are 0.8 / 0.9 according to Fat Cat Motorsports.

 

So a 500/400 spring rate would have even frequencies.

 

(Also it seems common to have a stiff front and no rear sway if that has anything to do with it.)

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