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 Post subject: Re: spring rates
PostPosted: July 25, 2017, 10:36 pm 
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Driven5 wrote:
Tundra 7 wrote:
One thing I have noticed is that Bruntons worksheet in D2 is pivot point to center of wheel. The other calculators I found go to center of ball joint. Whats going on here?
Center of ball joint = correct
Center of wheel = incorrect

Thanks Justin I figured as much. The one reason I liked the excel program is because of the frequency value. I haven't found that on any other calculator. Being able to have the ability to TRY and have a shot at developing a flat ride is cool.

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 Post subject: Re: spring rates
PostPosted: July 25, 2017, 10:39 pm 
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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.

Listening to a few videos from Shake at Fat Cat Motorsports that didn't seem entirely true. So then how do you attack developing a flat ride. A coordinated effort between front and back?. I figured the tools are there i may as well try.

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 Post subject: Re: spring rates
PostPosted: July 26, 2017, 4:40 am 
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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'm curious what method of determining ride stiffness you better understand the logic behind, and why? The only other one I'm familiar with is zero-preload static compression, aka droop travel. But that's still just a different way of displaying the same basic data as frequency, and likewise is just as meaningless until you similarly put it into some type of (comfort/sport/race) frame of reference based on field testing and experience.

Also, if you plot it out, adding damping to the representative sine waves is actually when 'flat ride' really starts to make sense. Trying to understand it from undamped sine waves only tells half the story.

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 Post subject: Re: spring rates
PostPosted: July 26, 2017, 9:17 am 
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Driven5 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'm curious what method of determining ride stiffness do you better understand the logic behind, and why? The only other one I'm familiar with is zero-preload static compression, aka droop travel. But that's just a different way of displaying the same basic data as frequency, and likewise is just as meaningless until you similarly put it into some type of (comfort/sport/race) frame of reference based on field testing and experience.

Also, if you plot it out, adding damping to the representative sine waves is actually when 'flat ride' really starts to make sense. Trying to understand it from undamped sine waves only tells half the story.

I just Want to get close without having this thing ride like its a 2ton truck. I really don't understand it fully because I don't have history to compare it to. I've driven a couple of these cars and contacted the guys to see what they had for any of this criteria and they don't know. So I have my 2013 Civic with low pros and 17" wheels :D . Thats the best handling car I have. To me setting up a ride frequency so the front and back have a 10-15% offset makes sense. I"ll at least do that. I did find another calculator out there last night and skewed the numbers on Bruntons Excel calc to represent center of ball joint instead of center of tire and the 2 matched so that makes me feel better going in that direction. Excel is just so much easier to use than the others. I am going with the GAZ GP series shock and springs in the front are coming out at 275#spring on a 42degree angle , 1.72hz ,50%(droop), 5"travel. Wheel rate 106
The rear 160# spring on a 20 degree angle , 1.98hz, 50%(droop) 5" travel, Wheel rate 140
When You read these what does it tell you to a trained eye?.

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 Post subject: Re: spring rates
PostPosted: July 27, 2017, 8:12 pm 
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Just drove the Locost up from the Bay Area to Sacramento, a drive I make 3-4 times a month. The car felt great, as usual. I sometimes complain about the stiff ride, but honestly, it's not harsh, just firm. The tires and seats absorb a lot. Better a firm ride than the suspension bottoming out from too-soft springs.

1.72/1.92 sounds good to me, although I don't think there's much logic behind ride frequency either. It's a place to start, but there's a lot more to ride comfort than just the spring frequency. The only logical way I know to measure comfort is to go for a ride.


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 Post subject: Re: spring rates
PostPosted: July 27, 2017, 9:13 pm 
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I typically start with weight transfer and size springs and bars appropriately to make the chassis do what I want in terms of roll, pitch, and balance. Once I'm happy with that I'll double check ride frequency to make sure it's nothing crazy and move on.

When I first got my Locost on the road I tried cranking the damping to the hardest setting. I made it 100 feet and had to stop - it was unbearable. A few clicks from soft was perfect.

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 Post subject: Re: spring rates
PostPosted: July 28, 2017, 2:40 am 
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Tundra 7 wrote:
...the front are coming out at 275#spring on a 42degree angle , 1.72hz ,50%(droop), 5"travel. Wheel rate 106
The rear 160# spring on a 20 degree angle , 1.98hz, 50%(droop) 5" travel, Wheel rate 140
Generally speaking, that looks pretty reasonable for a street driven Locost. If the one you're using doesn't already do so, try to take a look at spreadsheet/calculator that will help you get an idea of load transfer (handling balance) to see what you might need for roll bar(s) on the car to balance it out. You might want to check how full droop and full compression both affect your suspension rates too. I'm guessing you'll have a falling rate on at least the front. While certainly not ideal, not necessarily the end of the world either...Especially since it's pretty common on Locosts due to the way they're designed. Just something you may want to consider. Also make sure you account for the bump stops when looking at travel as well.

As has been said though, obiously this is just a starting point. Your actual weights as they affect the ride will not be exactly the same as your predictions, and will be variable as depending on passenger status, cargo, and fuel level. Also, as has been noted, damper tuning will certainly play as much a role in ride comfort/control as anything.

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 Post subject: Re: spring rates
PostPosted: July 28, 2017, 4:16 am 
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And since I finally figured out how to get this to work in (the nowhere near as good as MS Excel, but it's free) Google 'Sheets'...

Regarding why adding damping to a basic frequency analysis actually helps with explaining what is happening to the suspension, and bolstering the case for a 'flat ride', consider the following two plots (Blue = Front, Red = Rear) and try to determine which one a road disturbance would tend to upset the chassis less:
Attachment:
Flat Ride Undamped 1.png
Flat Ride Undamped 1.png [ 22.9 KiB | Viewed 4103 times ]

Attachment:
Flat Ride Undamped 2.png
Flat Ride Undamped 2.png [ 22.35 KiB | Viewed 4103 times ]

On the one hand, the rear catches up to the front faster in the first case. On the other hand, the rear eventually becomes more closely aligned for a brief period in the second case.









....Now consider the following two plots (Blue = Front, Red = Rear) and try to determine which one a road disturbance would tend to upset the chassis less:
Attachment:
Flat Ride Damped 1.png
Flat Ride Damped 1.png [ 16.97 KiB | Viewed 4103 times ]

Attachment:
Flat Ride Damped 2.png
Flat Ride Damped 2.png [ 16.84 KiB | Viewed 4103 times ]

This one kind of explains itself, not leaving you wondering whether the rear is catching up to the front too quickly or not quickly enough.

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 Post subject: Re: spring rates
PostPosted: July 28, 2017, 6:18 am 
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Driven5 wrote:
And since I finally figured out how to get this to work in (the nowhere near as good as MS Excel, but it's free) Google 'Sheets'...

Regarding why adding damping to a basic frequency analysis actually helps with explaining what is happening to the suspension, and bolstering the case for a 'flat ride', consider the following two plots (Blue = Front, Red = Rear) and try to determine which one a road disturbance would tend to upset the chassis less:
Attachment:
Flat Ride Undamped 1.png

Attachment:
Flat Ride Undamped 2.png

On the one hand, the rear catches up to the front faster in the first case. On the other hand, the rear eventually becomes more closely aligned for a brief period in the second case.

One of the guys with a stalker I've goiten to know I talked to him in the last couple days and he has just pirated his springs. He said the car has actually smoothed out and lost a lot of the harshness. I thought I rode fine, but that's a limited experience too. To me it's weird that it would happen but I can kinda see it here. I think that's what you were doing here. Stiffer spring makes the dampening happen faster. Good point on bump stops. I have to add an 1" if not mistaken







....Now consider the following two plots (Blue = Front, Red = Rear) and try to determine which one a road disturbance would tend to upset the chassis less:
Attachment:
Flat Ride Damped 1.png

Attachment:
Flat Ride Damped 2.png

This one kind of explains itself, not leaving you wondering whether the rear is catching up to the front too quickly or not quickly enough.

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 Post subject: Re: spring rates
PostPosted: July 29, 2017, 4:41 pm 
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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

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 Post subject: Re: spring rates
PostPosted: July 31, 2017, 9:01 pm 
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This is really good stuff. I think I have a good place to start based on others experience. Thanks everyone. Next month ill be placing my order.

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 Post subject: Re: spring rates
PostPosted: November 13, 2017, 11:23 am 
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I am playing around with actual weights now. The car was scaled this weekend with race scales no passengers 1322#. Front corners with 2 people and full fuel are 400lbs front and rear corners are 440. its really well balanced 49.7% front and 50.7% rear.
My front mounts are 14" center to center at RH. I forced the droop and travel to get the max bump I can stand and not drag my pan, because of the 1" bump stop I would actually have a 2.5" bump not 3.5.

I forced the variables to 4.5" bump and run with a full 3.5" where the pan drags. with either of these I am in the frequency I think I want to be in. By the way I am at the 45degree point on the chart. I am getting caught with a shorter shock length on the program than what I need to mount, unless I am making this harder than what it is. The chart says required travel 3 or 4.4 you have to add 1" for bump stop then pick the shock for your set up. Can I use the first senecio with the 35% droop with a 14.1" shock??. The second one if I use the 5.5" shock its the right one for the chart, but i end up with 5" of bump OUCH!.

Any good guidance. By the way I have noticed I'am right at design limits with the shock angle. I'll have to live with it at this point. the only other calculator i found was hypercoil. I think its giving me completely different answers.


Attachments:
File comment: This would be the second.
photo1-23.jpg
photo1-23.jpg [ 1.45 MiB | Viewed 3779 times ]
File comment: The first senecio I came up with
photo1-22.jpg
photo1-22.jpg [ 1.5 MiB | Viewed 3779 times ]

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 Post subject: Re: spring rates
PostPosted: November 13, 2017, 12:30 pm 
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Tundra 7 wrote:
I am playing around with actual weights now. The car was scaled this weekend with race scales no passengers 1322#. Front corners with 2 people and full fuel are 400lbs front and rear corners are 440. its really well balanced 49.7% front and 50.7% rear.
My front mounts are 14" center to center at RH. I forced the droop and travel to get the max bump I can stand and not drag my pan, because of the 1" bump stop I would actually have a 2.5" bump not 3.5.

I forced the variables to 4.5" bump and run with a full 3.5" where the pan drags. with either of these I am in the frequency I think I want to be in. By the way I am at the 45degree point on the chart. I am getting caught with a shorter shock length on the program than what I need to mount, unless I am making this harder than what it is. The chart says required travel 3 or 4.4 you have to add 1" for bump stop then pick the shock for your set up. Can I use the first senecio with the 35% droop with a 14.1" shock??. The second one if I use the 5.5" shock its the right one for the chart, but i end up with 5" of bump OUCH!.

Any good guidance. By the way I have noticed I'am right at design limits with the shock angle. I'll have to live with it at this point. the only other calculator i found was hypercoil. I think its giving me completely different answers.

OH great I just read a previous post on this thread and my measurements are all wrong. I went to center of wheel. :BH: :BH: Someone can erase all this garbage.

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 Post subject: Re: spring rates
PostPosted: November 13, 2017, 2:13 pm 
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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.

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 Post subject: Re: spring rates
PostPosted: February 11, 2018, 12:13 pm 
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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.

Those target frequency numbers probably date back to the 1940s or 1950s. Shocks didn't damp much; I could work a typical 1960s or 1970s replacement shock back and forth without trouble, and the "heavy duty" replacements were usually no better.

Remember the old-school "count how many times the car bounces" way to check shocks? Nowadays, any noticeable bounce would indicate a problem.


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