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 Post subject: Re: spring rates
PostPosted: February 12, 2018, 1:08 am 
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TRX wrote:
a.moore wrote:
I never entirely understood the logic behind using frequency - its getting shot to hell as soon as you add any sort of damping.
I don't think damping was a big factor when those frequency figures were enshrined.
Which "frequency figures" are you referring to?

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 Post subject: Re: spring rates
PostPosted: February 17, 2018, 11:19 pm 
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Tundra 7 wrote:
turbo_bird wrote:
I went fairly stiff with my suspension. It's currently at 2.4 Hz front and 2.66 rear. I started out at 1.96 and 2.38, but had way too much body roll for autocross, plus was bottoming the suspension a lot. Check out page 9 and 10 on my build log for a discussion on it, and the online calculators that I used to figure it out. It's definitely a firm ride, and I'd maybe go a bit softer for the street, but it isn't terrible the way it is now.
Kristian

The picture with your out of control sway is crazy. I don't think I've seen a 7 with that much roll. It must have changed quite a bit.

When I bought stiffer springs I went 50% stiffer front and rear. I don't have any pictures to show the roll, but I'm pretty sure it's a lot better. I'm pretty sure I was on the 10" wide slicks when the body roll pictures were taken too, so there was lots of stick.
Kristian

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 Post subject: Re: spring rates
PostPosted: February 18, 2018, 12:46 am 
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My coilovers showed up last week. I went 425# front and 300# rear. I think the fequency is 2.10 front 2.4 rear. So we’ll see how it works out. I bought QA1rebound adjustable.

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 Post subject: Re: spring rates
PostPosted: April 14, 2020, 11:36 am 
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Another rule of thumb is that the wheel rate for a performance vehicle is one half of the static load. A 2000-lb car has approximately 500-lb one each wheel and hence requires a 250-lb per inch spring rate.


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 Post subject: Re: spring rates
PostPosted: April 14, 2020, 1:21 pm 
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Bobber wrote:
Another rule of thumb is that the wheel rate for a performance vehicle is one half of the static load. A 2000-lb car has approximately 500-lb one each wheel and hence requires a 250-lb per inch spring rate.


Oh no kidding. That is a first. It’s a little bit easier isn’t it. You still have to factor in shock angle and add in the factor. I ended up getting a good match the car performs really well.

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 Post subject: Re: spring rates
PostPosted: April 16, 2020, 6:53 am 
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I have always used sprung weight, adjusted for motion ratio squared for that "rule" Might give you a similar or different answer depending on motion ratio.


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 Post subject: Re: spring rates
PostPosted: April 16, 2020, 10:18 am 
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Tundra 7 wrote:
Bobber wrote:
Another rule of thumb is that the wheel rate for a performance vehicle is one half of the static load. A 2000-lb car has approximately 500-lb one each wheel and hence requires a 250-lb per inch spring (wheel) rate.
Oh no kidding. That is a first. It’s a little bit easier isn’t it. You still have to factor in shock angle and add in the factor. I ended up getting a good match the car performs really well.
While Bobber got the verbiage mixed up in the example, the initial explanation is entirely reasonable and has been brought up here multiple times over the years. Also note that it should ideally be the sprung weight, and not the total car weight. This would get you a 2.2 Hz natural frequency. it's on the stiffer side, but is still a perfectly reasonable starting point depending on the intended usage. In my opinion, most people building these types of cars would be well suited with the wheel rate in the 1/3 to 1/2 of sprung weight, with 1/3 (1.8Hz) being on more the sporty street side and 1/2 (2.2Hz) being on the more track performance side.

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 Post subject: Re: spring rates
PostPosted: April 16, 2020, 2:23 pm 
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I shot for 1.9-2.2. With the adjustable rebound on the QA1’s I can stiffen them up so it handles like a go cart. I cranked them up one day and could barely hold a straight line. The car was so tight it was crazy.

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 Post subject: Re: spring rates
PostPosted: June 17, 2020, 12:52 pm 
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Your tires are softening your springs.
I never worried about this before but ideally you should consider your tire spring constant in series with your wheel spring constant. So with a tire spring constant of 1600 lb per inch combined with a spring constant of 300 lb per inch at the wheel, your effective combined spring/wheel constant is around 250 lb per inch.


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 Post subject: Re: spring rates
PostPosted: May 10, 2023, 9:51 pm 
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Location: Carlsbad, California, USA
This is an older thread, but appears to be monitored still by many of the previous posters, so I'll try for answers I need here.

My situation is:

1) I have an on-paper estimate for my finished build and from it (and my estimated weight distribution) an estimated weight at each wheel.

2) I have all the measurements and the formula to calculate the wheel rate of any spring mounted on my front suspension (double A-arm with coilovers).

3) I have measurements for my coilover length at my desire ride height (6") front and rear.

4) My rear suspension is a live axle with nearly vertical (89 degrees) coilovers mounted somewhat inboard versus typical Locosts.

4) I want my ride to be reasonably comfortable (a little on the firmer side is OK) on the street, but autocross capable.

5) I have my tires and wheels, but do not know how to calculate the effective spring rate of that combination or how to apply it in conjunction with the calculated wheel rate for any particular spring.


So, I'm looking at developing:

A) a figure for the actual spring rate (lb./in. deflection) that will get me close to my goals, so I can actually order my coilovers and springs ASAP.


My take-aways from reading all of this thread are:

i) The spring rate should not be less that 1/2 the estimated weight at each wheel.

ii) The upper bound would be 1.0 times the estimated weight, which is what a race car might have.

iii) The GAZ Excel spreadsheet is a good tool and will give me a figure for suspension frequency, which in my case might be best in the 1.5-1.7 range. I'll be using some model of GAZ coilovers anyway.

I just learned about the frequency measure from this thread, so it's news to me. I don't expect my first set of springs to be my last, as I'll have the real car to weigh and suspension-tune eventually. Autocross is likely going to be my main tuning tool, but it will be a street car used primarily on open highways.

My first question is, "What additional information do I need to calculate the spring rates at front and rear and get the coilovers ordered?"

Thanks in advance,

Lonnie

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


Last edited by Lonnie-S on May 10, 2023, 10:01 pm, edited 1 time in total.

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 Post subject: Re: spring rates
PostPosted: May 10, 2023, 9:59 pm 
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<< DELETED DOUBLE POST>>

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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 Post subject: Re: spring rates
PostPosted: May 11, 2023, 3:23 am 
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Quote:
5) I have my tires and wheels, but do not know how to calculate the effective spring rate of that combination or how to apply it in conjunction with the calculated wheel rate for any particular spring.
The data is not publicly available, so for an apples-apples comparison to what data is publicly available, you pretty much have to leave it out anyways. It's not as accurate, but it's more precise.


Quote:
i) The spring rate should not be less that 1/2 the estimated weight at each wheel.
Remember, we're talking wheel rate, not spring rate. I'd also argue more like 1/2 +/- 20%, with a bit more rear than front. Adding some sway bars would more easily let you stay on the less than 1/2 side while still maintaining good roll control.


Quote:
ii) The upper bound would be 1.0 times the estimated weight, which is what a race car might have.
That would be a 3.13Hz frequency, with a natural droop of just 1 inch. That's not just racecar territory, that's high-downforce racecar territory.


Quote:
iii) The GAZ Excel spreadsheet is a good tool and will give me a figure for suspension frequency, which in my case might be best in the 1.5-1.7 range. I'll be using some model of GAZ coilovers anyway.
Make sure that their equation either includes the spring angle angle in the motion ratio when it's squared, or that it gets squared if treated as a stand-alone term in the equation. Many, if not most, online resources seem to get this wrong. https://grassrootsmotorsports.com/forum/grm/wheel-rate-calculation-discussion/241074/page1/


Quote:
My first question is, "What additional information do I need to calculate the spring rates at front and rear and get the coilovers ordered?"
Next up would be looking at Lateral Load Transfer Distribution or Front Roll Couple (aka LLTD or FRC). See the 'chassis calcs public' attachment. https://www.locostusa.com/forums/viewtopic.php?f=5&t=19253&view=next


Edit: Looks like I also need to go back and find those motion plots to repost on the previous page.

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Last edited by Driven5 on May 11, 2023, 10:18 am, edited 1 time in total.

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 Post subject: Re: spring rates
PostPosted: May 11, 2023, 10:18 am 
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Another way to compare results:
viewtopic.php?f=5&t=11815

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Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12


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 Post subject: Re: spring rates
PostPosted: May 11, 2023, 11:28 am 
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@Driven5
It looks like the ChassisCalcsPublic file is missing to from https://www.locostusa.com/forums/viewto ... &view=next, Justin.

Can you repost?

Thanks for the lookup/research on those discussions. I understand the concept of frequency, but I need to better understand the variables used to derive it for the suspension.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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 Post subject: Re: spring rates
PostPosted: May 11, 2023, 11:36 am 
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@MV8
OK, I'm going to digest that info.

It's helpful to have some qualitative estimate (e.g., 80-100: sport touring cars to sports cars) to work with. I know my first choice will not be the permanent, end result, but having something "in the ballpark" actually is the goal for this round.

Cheers

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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