aklackner wrote: ↑Wed Feb 27, 2019 4:49 pm
Since it was mentioned I figured I'd try to share some of the information I've played with a bit. Apologies in advance to OP and generally for length:
Not many seem to tune Honda suspension by frequency but looks like some in Miata space take it pretty seriously and many OEM suspensions fit within recommendations.
Some links:
https://rqriley.com/automobile-ride-han ... -vehicles/
http://www.autospeed.com/cms/article.ht ... s&A=112279
http://www.autospeed.com/cms/article.ht ... e&A=112686
It probably makes more practical sense to just take a well established setup, drive it a lot, study the dynamics, and plan to make adjustments.
The potential gain from frequency tuning, from what I understand, would be a reduced need for harsh damping rates (so unless you're getting custom valving it may not make much improvement, since most ots sport dampers are designed with relatively high rates, in part, to give a pronounced stiff "sports" feel).
http://www.kaztechnologies.com/wp-conte ... sprzak.pdf
For a real approach you'd need to establish sprung\unsprung corner weights. You'd also probably want accurate effective (at the wheel) ARB rates both single and double sided) to get a complete look at NFs since we don't tend to hit much beyond speed bumps evenly with both wheels.
That being said I have tried to do some very rudimentary calculations. Also from what I remember the "flat ride" target is to have a slightly higher (~10%) effective frequency in the rear so basically the rear catches and syncs up with the front as the vehicle crosses a bump and rebounds instead of trailing behind, pitching the car back and forth.
The DC2 LCAs have an motion ratio ~.667 (1.5) in the front and .74 (1.3) in the rear.
https://eibach.com/us/p-101-suspension-worksheet.html
This and the 60/40 weight distribution means you'll tend to have a comparatively high natural frequency in the rear.
Wheel Rate for Stock
Front @~240in/lbs = .667^2*240*Cos10 = ~105,
Rear @~240in/lbs = .74^2*240*Cos10 = ~129
NF (simplified: w/o driver or ARBs, using 60/40, even side/side weight distribution, 2600lbs as total unsprung mass)
Front (187.7* SQRT(105/780))/60 = 1.15 hz
Rear (187.7* SQRT(129/520))/60 = 1.56 hz
If linear, the OEM rear would have nearly 36% higher NF compared to the front, much larger than the target 10% target for "flat ride".
It's probably worth noting that the front does have a larger ARB than the rear, so would even this out some but this would be further pronounced if using an upgraded rear ARB.
However, taking the OEM progressive rear spring into account the rear could actually be closer to 150in/lbs under static weight or at least as it starts to unload.
WR for Stock @~150in/lbs = .74^2*150*Cos10 = 80.89, NF = (187.7* SQRT(80.89/520))/60 = 1.23 hz
or about 7% higher than the front much closer to "flat ride " target.
According to the same oversimplified math, if you run a 550 in/lbs front spring (about the max I've heard for OTS koni sport valving) you'd want to run ~350 in/lbs (linear) rear, or in metric something like 10k up front and 6.5k rear. This would yield about 1.74hz NF in the front and about 10% higher in the rear. This is above the average OEM suspension but still below 2hz guide for "harsh" feeling. Keep in mind that the OEM design stiffened the rear progressively under load. You'd lose that dynamic response with a linear setup so you may still want\need to explore closer front\rear rates to find a similar balance\feel..
Other General spring Info (mostly based on my poor guesstimates so use at your own risk):
Static load (@spring): ~1,188lbs/side Front, ~712lbs/side Rear
This means:
(with no preload) A little over 2" of spring free height is compressed at static on 550lbs\in F and right about 2" with 350lbs/in R
You should have ~3" of wheel droop in the front, ~2.5" in the rear before you'd come off the spring.
Koni Sport (yellow) total travel: ~5" front, ~6" rear
Many springs are designed to mainly see 20%-80% compression (where they will be most linear\accurate) you'll want to select spring length accordingly for best results.
Some dampers also have a "sweet spot" that tends to be ~50% compressed.
Vertical Accel. due to speed bump (up to ~ 1g= 9.8m/s @ ~15mph)
https://journals.sagepub.com/doi/full/1 ... 014/736576
This means you should probably plan for at least an additional 2" of damper compression (more to allow for driver, passengers, and cargo weight) with 550F/350R to avoid running out of spring\damper or make sure bump stops are incorporated as part of your suspension design. In reality dampers will limit this type of sudden movement but it's better not to plan to rely on the dampers to limit travel..
As a final note none of this has taken into account bushings but they can have as much or more impact on ride than fine tuning spring rates and damping. Softer rubber bushings will help absorb more of the higher frequency vibration but will break down more quickly and degrade ride quality when subject to higher rates. Stiffer bushings\solid bearings will translate more of the vibration but should handle higher rates for longer and deliver more accurate\performance handling. Harder\solid bushings will also limit the dynamic design of the OEM suspension which also impacts handling.
