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Old 05-16-2007, 02:05 AM   #1
Scooby Newbie
Member#: 107389
Join Date: Feb 2006
Chapter/Region: TXIC
2014 Honda Odyssey

Default How to choose your own spring rates (and get the spring frequencies correct)

I made a spring frequency calculator in Excel. Unlike anything else I've seen out there, this automatically selects a rear spring rate so that the spring frequency in the rear is appropriately higher based on the vehicle speed you want to optimize for. From there, one would dial in over or understeer using sway bars as needed.

You pick the front spring rate according to the ride comfort you would like- use the calculated spring frequency as a guideline here. Generally speaking, you'll want the front spring frequency to be around 1.0-1.2 for a family sedan, 1.5-1.7 for a sports car, and 2.0-2.2 for a race car.

Download the spreadsheet: http://putstuff.putfile.com/79647/6261372

For more reading on spring frequency selection, I recommend this: http://www.optimumg.com/techtips/Spr...Tech_Tip_1.pdf
Another good link: http://www.wincom.net/trog/autocross_secrets5.html
Yet another: http://www.smithees-racetech.com.au/...cefactors.html

I'm not suggesting this calculation is smarter than human trial and error since it certainly cannot account for other limitations or circumstances on the car. It just follows the guidelines taught at the above links, so read them to understand this calculation. The default values in the spreadsheet are for an STI; we see the rear spring rate is optimized for a "flat" ride at 70mph.

Anyway, let me know what you think! The subject of spring frequencies is certainly one that is wide open for discussion.
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Last edited by stretchsje; 05-16-2007 at 02:21 AM.
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Old 05-16-2007, 10:10 AM   #2
Scooby Specialist
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Join Date: Mar 2006
Chapter/Region: MWSOC
Location: Chicago, IL
2002 Old and


So what about choosing which speed you want to maximize for ?
for autoX speeds: ?
for DD-occasional Auto-X speeds: ?

Which do you choose ?
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Old 05-16-2007, 01:55 PM   #3
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2014 Honda Odyssey


I'd really like to defer your questions to someone else- I made the spreadsheet to learn about spring frequencies, not to share what I've already learned. So really, I'm not an expert. However, since nobody else is chiming in, I'll take a stab.

Optimizing for really low speeds is nearly impossible because by the time a bump reaches your rear tires, the front tires will have already settled. This is expecially true when running high spring frequencies- since at 2hz the front of the car will have fully oscillated in only half a second, the rear doesn't have much opportunity to catch up. This would mean running much, much higher spring frequencies in the rear (as the spreadsheet shows). Maybe that would work very well, but I doubt it.

So, depending on your chosen spring rates, I don't think it'd make sense to optimize for under 60mph. You want to optimize for the average speed you find yourself driving at, so if you optimize for 70mph, both 60mph and 85mph will still feel pretty good. Maybe road race cars would optimize for a slightly higher speed, but 60-80mph is a pretty typical speed for hitting rumble strips, right?

That's about what Subaru optimized for in the STI (and even the JDM Pink springs): 70-80mph. I've read the generalized rule-of-thumb for street and race cars alike is to make the rear 0.1 to 0.3 Hz higher than the front, and again, both the USDM and JDM STI spring rates follow this guideline.
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