Suspension tuning - dampers, spring rates, etc.

[aklackner]

I think this sounds similar to issues Xian warned me about with running soft dual rate\progressive rear spring with a stiff rear bar.

When the total force from the rear bar is exceeding the rear spring rate to the point it's pulling the rear inside LCA toward the body more than the rear spring is pushing away, to keep the wheel down, the wheel will lift. This would also be the case if you're rolling to the point of exceeding the primary spring length since helper springs would be very low rate compared to force from the rear bar at that point.

I think he said that higher spring rates would be needed to support more rear bar or possibly more front bar to help limit the weight transfer away from the rear inside?

[PatHidden]

That all makes sense to me. Plot twist tho: He was running a no sway bar setup. So probably a stiffer front spring would help?

Maybe Xian can chime in on that interesting setup, no sway bars. I've only seen like 3 cars on the west coast go with this kind of setup.

[Xian]

I’ve never tried a legit no bar setup. Always seemed sorta silly to me unless it was just a “let me see what it’s like” sorta thing. Bars are a GREAT thing to use for tuning; no reason not to have one unless you’re constrained by rules.

Having said all that, West Coast Scott (Rinde, the Soooper Genius, RR98ITR on HT) tried it fairly extensively on his ITR. After doing a buncha wacky stuff to get the roll rates where he wanted, he came away with the realization that it wasn’t as fast/good as running bars. IIRC, he was north of like 1200-1400# spring rates at the front and the car had picked up all sorts of nasty habits (snappy over curbs, darty under braking).

As far as the question on lifting a rear tire and flat spotting it, you’d need to either:

1- not trail brake as much
2- add more front roll rate via spring or bar and thereby keep the inside rear tire on the ground.
3- add more rear spring/bar OR soften the front so it lifts earlier in the corner (and for longer).

I guess you could also try using rear toe out, reduce camber, increase rear pressure in an effort to get the rear sliding earlier... if you get it loose enough, you really can’t trail brake like that anyway. Ideally (IMO) you want the car loose on anything less than full throttle. This lets you brake, bleed brake pressure as you turn in, and then use the throttle to balance the car while the SlipAngle helps to scrub speed on corner entry.

PS
With no bars, you also need to pay more attention to low rate, tender springs so the main spring doesn’t decouple at full droop. It may be a case where something like these would help your buddy with the flat spotting?

PPS
Some (most?) of this sorta stuff is floating around on HT or RRAX if you spend some time searching it up. Unfortunately, the old threads from the ITR forum got nuked I guess.

[coolhandluke]

Cross-posting from another thread:

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.

[aklackner]

Don't remember seeing numbers on these before and stumbled across them today. thought I'd share
Spoon Progressive Springs
SPOON: FRONT: 6.5 kg/mm (~364lb/in) REAR:5.5 kg/mm (~308lb/in)

Spoon fixed Dampers (I'd be curious where these are compared to Bilstein, Koni Sport, race, or elsewhere if specs.are avail.)
0.05m/sec ： F 92/-57kgf R 36/-24kgf
0.1m/sec ： 145/-90 80/-55
0.3m/sec ： 290/-190 150/-90

[coolhandluke]

The Spoon dampers were similar to Mugen Showa IIRC. Thank you for posting rates.

[Chase_acura]

Ordered corner balance scales so will be showing/testing that out shortly. Have a track day at COTA next month so eager to see how my setup in sitting now and how it can be improved.

[Chase_acura]

Setup came in, tested out. NSX sitting pretty good already but will make adjustments for driver weight
Glad I spent the money on a full wireless setup, super convenient

[coolhandluke]

Writeup recapping the impact of switching from rubber/urethane bushings to Kingpin Machine spherical:
https://nasaspeed.news/tech/suspension/ ... -bearings/

[aw614]

Good article, I like Chris recommendations from the old forum about staying with OEM for street cars, but spherical for full on track cars. He was right about the issues with hardrace bushings, a friend of mine had his front bushings fail after 3 years, the first year was 6mo of autocross, but after that, his eg was a daily driver and the bushings basically fell apart. Needless to say my friend was pissed that they fell apart so fast. I heard the same issue from Dave-ROR at a local autocross.