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PostPosted: July 31, 2008, 10:00 am 
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Spring Rate Calculator (Excel worksheet)

Got this at http://locostbuilders.co.uk/index.php from user MikeCapon. You specify weights, wheel travel, shock travel, and percent 'sag' (portion of shock travel used at ride height), and it gives you the spring rate required to hold to hold the chassis at ride height.

Adjusting the spring preload will alter the wheel frequency. The sheet could be rearranged to input frequency, if anyone is so inclined.

Great little worksheet for someone with a finished car, pondering the eternal question of what spring rate to use.


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 Post subject: Re: spring rates
PostPosted: June 28, 2009, 11:45 am 
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If it matters our car uses 225 front and 300 rear. Which seems about right according the thumb rule of half the corner weight. Our car rides quite comfortably almost better then my civic with lowering springs and adjustable shocks. This is with the shocks full soft mind you but the spring rates seems quite good.

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PostPosted: June 28, 2009, 12:10 pm 
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Pete B wrote:
Spring Rate Calculator (Excel worksheet)

You specify weights, wheel travel, shock travel, and percent 'sag' (portion of shock travel used at ride height), and it gives you the spring rate required to hold to hold the chassis at ride height.

Ack. This seems about as helpful as a software tool that calculates how much air to put in the tires to set ground clearance. While it might do that, the result has nothing to do with making the car handle, which is the whole point - I thought. Maybe I'm completely missing the point... it can't be for setting ride height only, that's silly.

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 Post subject: Re: spring rates
PostPosted: February 4, 2010, 9:53 am 
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here's a nice spring calc, seems to be fairly close. It's aimed more at off-road racing, but I would imagine it gets you in the ballpark. http://f-o-a.com/calculator.html

I like this one even better... http://www.gorancho.com/docs/spring_selection_guide.pdf


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PostPosted: March 7, 2010, 9:53 am 
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KB58 wrote:
Pete B wrote:
Spring Rate Calculator (Excel worksheet)

You specify weights, wheel travel, shock travel, and percent 'sag' (portion of shock travel used at ride height), and it gives you the spring rate required to hold to hold the chassis at ride height.

Ack. This seems about as helpful as a software tool that calculates how much air to put in the tires to set ground clearance. While it might do that, the result has nothing to do with making the car handle, which is the whole point - I thought. Maybe I'm completely missing the point... it can't be for setting ride height only, that's silly.


No your not missing the point at all and springs are another headache that takes days and a bucket load of springs to get close and then you got to balance front to rear.

The problem with static calculators is that they don't take into account what happens for the second inch of travel, then the 3rd etc.. The chart may say a 220lb spring but what wire diameter, coil number and spring diameter 220lb spring should you choose? Do you choose a 220lb spring thats 300lbs or 400lbs at the 2nd inch?

Hands up all those who have actually changed the springs on their car even though it's "good handling"?

And then theres bump stops ........


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 Post subject: Re: spring rates
PostPosted: March 7, 2010, 9:56 am 
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russellmn wrote:
here's a nice spring calc, seems to be fairly close. It's aimed more at off-road racing, but I would imagine it gets you in the ballpark. http://f-o-a.com/calculator.html

I like this one even better... http://www.gorancho.com/docs/spring_selection_guide.pdf


Actually I would tend to trust off roaders more than the others, these guys would have a better basic understanding off the amount a spring rate should increase through it's motion.


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PostPosted: March 11, 2010, 8:55 pm 
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No your not missing the point at all and springs are another headache that takes days and a bucket load of springs to get close and then you got to balance front to rear.

The problem with static calculators is that they don't take into account what happens for the second inch of travel, then the 3rd etc.. The chart may say a 220lb spring but what wire diameter, coil number and spring diameter 220lb spring should you choose? Do you choose a 220lb spring thats 300lbs or 400lbs at the 2nd inch?

Hands up all those who have actually changed the springs on their car even though it's "good handling"?

And then theres bump stops ........[/quote]

Isn't that why you should be using linear rate springs?,same rate up untill coil bind right?.

Progressive rate is dandy for the daily driver but....


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 Post subject: Re: spring rates
PostPosted: March 12, 2010, 12:54 am 
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Considering that vast majority of springs available for use with the types of shocks most people will be using in their Locost builds are linear rate springs (regardless of what wire diameter, spring diameter, or number of coils is used to achieve said spring rate) I'd say we don't have much of a choice either way.

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 Post subject: Re: spring rates
PostPosted: March 13, 2010, 9:12 am 
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Driven5 wrote:
Considering that vast majority of springs available for use with the types of shocks most people will be using in their Locost builds are linear rate springs (regardless of what wire diameter, spring diameter, or number of coils is used to achieve said spring rate) I'd say we don't have much of a choice either way.


Don't know where you live but in Australia King Springs and a few others will wind you progressive springs to your design at little extra charge. If you ask nicely and give them more money they will grind a tapered wire for you too. Theres no reason you can't use dual springs on a typical coil over, motorcycles have been doing by the millions for 50 years.

http://www.kingsprings.com/


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 Post subject: Re: spring rates
PostPosted: March 13, 2010, 12:42 pm 
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According to the information directly beneath my avatar, I live in Wisconsin. And in the USA, where most people on this site happen to be based, yes there are a handfull of variable rate springs available. And I'm sure that you could also cough up the money to have custom progressively wound springs made too. However there wouldn't be much point for a home hobbyist performance road/race car application. I'd also hate to think how expensive, challenging, and time consuming it would become to keeping changing out custom wound progressive springs as you try to tune the car...As opposed to paying ~$50 to go to a different spring that is still a completely 'known quantity'. There are many suppliers that carry standardized sizes of linear rate springs in a wide variety of rates, designed to match the relatively standardized sizes of race-type shocks. As was mentioned by L8 apexr it's nice to know your spring rate at any given point in the suspensions range of motion on a performance road car, as that's pretty critical information when tuning the suspension. Then if necessary it's just a matter of tuning the wheel rate progression through the shock actuation geometry. Sure there might be a benefit to a professional race team or mass market manufacturer with cubic dollars, gobbs of tuning data, and nearly unlimited resources...But that doesn't apply to many people on this particular web site, so it's not actually a point worth dwelling on for very long.

Since I'm not building a motorcycle or an off-roader, I would also certainly forgo the dual spring setup with it's relatively sudden increase in spring rate as the softer coil goes into bind. While again probably fine when applied correctly for long travel/softly sprung vehicles seeing certain specific conditions, like trying to maximize droop to prevent lifting a wheel in widely varying terrain...It's generally not a very good situation to have happen in a short travel/stiffly spring vehicle when hitting a bump mid-corner at speed on a comparatively smooth/flat surface. One of the keys to getting the performance out of the car, even at the professional racing level, is handling characteristics that the driver can predict.

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 Post subject: Re: spring rates
PostPosted: March 14, 2010, 1:51 am 
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So you just want a pissing contest, fine.

Dual rate springs (2 springs on one shock).

(example figures only) - How about using a 200lb and a 170lb on the one shock, not only gives a moderate rising progression but also helps damping as the springs differing oscillation rates help cancel each other out (the reason they use double or triple springs on an engine valve). A big benefit also is makes the suspension more tuneable as you have the option of changing either (cheap) spring.

(example figures only) - A 170lb with 3" may move say 1/2" and then the pressure has reached 200lbs and has started to slowly accelerate the 200lb spring in difference to your "the sky is falling" one soft/one hard spring nonsense. If I bother to go to work today (Sunday, raining, cold) I'll grab pictures of a dual rate strut I'm playing with at the moment and how simple it is.

Since you mentioned droop there is less extending spring pressure with this setup so you have less body roll (the inside wheel isn't pushing up as hard) and less crashing through potholes (the wheel wont extend as fast and the softer spring at full droop requires less energy to compress initially when it hits the far edge of the hole).

If you think this isn't relevant to Locosts and othe rroad vehicles then 1/ You are against the thinking of every car manufacturer in the world (all who use progression of some type)
and
2/ Speaking mostly for yourself - "But that doesn't apply to many people on this particular web site, so it's not actually a point worth dwelling on for very long" - It applies to anyone interested in increasing the roadholding, handling and comfort of their road based performance cars.

Your information below your avatar does not say Wisconsin it says WI and I don't have a clue where that is and yes this is an American based forum (why I like it here, mostly you American Guys are great) but a lot of international people come here too. I linked the King Springs website as an example for people to search in their own countries for similar.

There, I just wet the fence 5 feet up, your turn - nah don't.


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 Post subject: Re: spring rates
PostPosted: March 14, 2010, 5:23 am 
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Because I'm sure there are people of many different levels of technical knowledge here, I'm going to point out a couple of things that people sometimes understandably misunderstand.

About 99% of the "catalog springs" (or "catalogue springs" for furrners) listed for race car coil-over shocks are linear rate.

What does that mean?

A 200 lb spring will compress 1" if you put a 200 lb load on it. At that point it is still a 200 lb spring, i.e. it still has a 200 lb per inch rate.

A 200 lb spring will compress 2" if you put a 400 lb load on it. At that point it is still a 200 lb spring, i.e. it still has a 200 lb per inch rate. It has not become a "400 lb" spring.

A 200 lb spring will compress 3" if you put a 600 lb load on it. At that point it is still a 200 lb spring, i.e. it still has a 200 lb per inch rate. It has not become a "600 lb" spring.

It will be a 200 lb spring right up to the point it's not a spring... its coil bind or solid height.

==============

Misunderstanding #1: A 200 lb will not compress until there is a 200 lb load on it. Wrong. If you put a 100 lb load on it, it will compress a half inch.

==============

Misunderstanding #2: If you stack a 170 lb spring on top of a 200 lb spring, the 200 lb spring will not compress at all until the 170 lb spring is coil bound. Wrong. The 200 lb spring is supporting the 170 lb spring, so it has load on it. Since it has load on it, it is therefore compressed by some amount (see Misunderstanding #1 above).

In fact, since they are in series, they both are seeing the SAME load.
==============

Misunderstanding #3: Stacking two springs of different rates will create a progressive rate spring. Wrong. It creates a linear rate spring softer than either of the two springs involved. Consider #1 and #2 above, plus the fact that, all else being equal (coil diameter, coil spacing, and wire size), a longer spring is a softer spring... to understand this.

So what's the new linear rate?

The following is verbatim from Hyperco, right up the road from me... whose "Hypercoils have been utilized by every Indy 500 winner since 1965"

Combined Spring Rate

This is used when two springs are stacked on top of each other.

Combined Spring Rate =
(Spring Rate 'A' x Spring rate 'B')
÷ (Spring Rate 'A' + Spring Rate 'B')


For example if the rate for spring 'A' is 200 and the rate for spring 'B' is 500, the combined rate is calculated as follows:


Combined Spring Rate =
(200x500) ÷ (200+500) = 143


Plugging Cheapracer's 200 and 170 lb springs into this yields a linear spring rate of 92 lbs per inch...

UNTIL one of the springs is coil bound.

How do you know when/where that happens to which? It's not as hard as you might imagine when you keep in mind that both springs at all times have the SAME load applied to them. If there is 100 lb load, the 200 lb spring will be compressed (100/200) a half inch and the 170 lb spring will be compressed (100/170) 0.588" ... the shock travel is 1.088". Cross check that against a 92 lb spring... (100/92) = 1.087" (slight error, 'cause the 92 was a rounded figure). The free height and solid height are usually known from the catalog... subtract solid from free and you know available deflection, so you can easily figure out what load it takes to bind each spring (I'm too tired to decide if it will always be the softer first, I think spring dimensions come into that too).

Here's the rub. Cheapracer implied, I think, that there would be a 30 lb jump in spring rate (or none?) when the 170 lb spring goes solid. Wrong (please don't piss on me!). It jumps from 92 lbs to 200 lbs suddenly... not gradually. That's probably not good. :cry:

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 Post subject: Re: spring rates
PostPosted: March 14, 2010, 11:19 am 
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Having run dual springs on my 280Z for literally years I think I'll chime in here. First let me say that this is more of a race car suspension rather than a street suspension and has limited travel (I shortened the struts 1.5") but still more travel than a Locost.
I don't have the spring rates in my head but I can get them later if needed.

It is next to impossible to tell the precise moment the suspension changes from dual spring to single spring. Before I bought them I had thought that the suspension ran on the softer spring until it bound and then switched over to the harder spring so I envisioned it as more or less a roll bar in that engaged once I had the car in lean or a bump. I was ever so glad it didn't work that way since I couldn't figure out the handling issues at change over, but I was eventually talked into it.

I absolutely love it!!

I have a softer spring which really makes it hug the road a whole lot better on the rough country roads around my house. No more skittering around on the surface of the road. But as expected if I hit a bigger bump or get the car leaning into a corner then it firms up and holds the roll down.

Let me say that this is better on the road and on the track than on an autocross course. That little extra bit of roll (as I like to think of it) makes it take a millisecond to take a set when I'm doing hard, fast, quick inputs like is needed on the autocross course. it's kinda like the difference between a 60 series tire and a 35 series. The 35 series responds more quickly to quick inputs. I have found the 35 series is better on an autocross and the 60 better on the track.

I never played with spring rates, but just ran what GC sent me, but that was back in the day when GC was actually responsive and helpful. I wanted to do the same thing on my S2000 and after 3 months of waiting for GC to calculate the best combo I gave up. They'd say they could do it and would do it, but it kept being bumped to the back shelf.

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 Post subject: Re: spring rates
PostPosted: March 14, 2010, 12:33 pm 
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Excellent post there Sports car designer. In case nobody figured out what he was saying, unless your car goes into coil bind you still have a linear rate spring. Using his formulas and the suspension travel with your car as well as the point of coil bind that you have calculated, YOUR DUAL WOUND SPRING WILL NEVER BE TWO RATES IF ONE DOESNT GO INTO COIL BIND. The reason the oem,s do this is strictly to prevent bottoming.It allows for a cushy ride without bottoming on the pavement.

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 Post subject: Re: spring rates
PostPosted: March 14, 2010, 12:50 pm 
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And if your dual wound springs never go into coil bind, leaving you with a linear spring rate throughout the suspensions full range of motion...Then you might as well save some time/money by using a single linear rate spring. If bottoming the shock is your primary concern, there are very good (even progressive rate) bumpstops readily available too. Which is another trick used by many OEM's.

It's worth noting for those that might not fully understand, that SCD's post also only applies to having two springs mounted in series. Progressively wound springs are a different animal all together, and do have a smooth progressing from the initial to the final spring rate, and when used correctly by somebody who has the resources to do so, can be a very good and effective suspension.

Since it was brought up, I also wanted to mention that dual valve springs work in parallel, which is completely unrelated to the way dual suspension springs work as so eloquently described(I couldn't have said it better myself) by SCD. Parallel springs are always being displaced an equal amount, so their individual spring rates are add to get the combined spring rate. The side beneift, which is why they are so effectively used as valve springs, is that the natural frequency of the system is significantly increased due to the fact that when one spring is in it's natural frequency range, the other isn't...Thus helping maintain control of the overall system.




cheapracer wrote:
If you think this isn't relevant to Locosts and othe rroad vehicles then 1/ You are against the thinking of every car manufacturer in the world (all who use progression of some type)
and
2/ Speaking mostly for yourself - "But that doesn't apply to many people on this particular web site, so it's not actually a point worth dwelling on for very long" - It applies to anyone interested in increasing the roadholding, handling and comfort of their road based performance cars.
And 3.) You didn't actually comprehend what I was saying, which boils down to the fact that these things can absolutely be useful in certain specific applications, but due to the relative complexity are generally best left to being developed by a person/team/company having significantly more technical and financial resources than the average Locost (Low-Cost) builder doing all of the development work for them self.



cheapracer wrote:
Your information below your avatar does not say Wisconsin it says WI and I don't have a clue where that is
WI =
cheapracer wrote:
Google or maybe I can come around to your house make your coffee and give you a foot massage as well?
:roll:

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