Does spring length matter?

[Mac Attack]

I applaud you for actually using numbers this time, but you'll see that you over-complicated the motion ratio aspect when it is a constant factor for each scenario that gets cancelled out when comparing the delta's in compressed height. Why get into an explanation of that and confuse the person asking the basic height question when it is irrelevant for the height comparison? We both ended up with a delta of 0.5" which is what I was originally proving with my simplification. Good engineers can communicate ideas simplistically, yet get the correct values because they know what factors actually are important when getting a point across.

BTW, you've posted incorrect statements in the past about the NSX suspension geometry (toe-in/out under load and the incorrect statement about toe arm location), so excuse me if I take what you write with a grain of salt. I'm 99.99% sure you're no engineer and are just repeating things you may have heard or using other internet calculations. Please tell me if you're an engineer. If you bothered to do the analysis or measurement of the front and rear suspension instead of simply repeating what you've heard, you'll find that the front motion ratio varies between ~0.75 to 0.7 as I stated above. It's a function of position due to the non-linearitity of the design. Because he wants it low, I used the more appropriate ~0.7 value, which yes, is close to 0.67. That's what the ~ means in engineering. Try to keep it simple yet effective because I'm pretty sure by this point, no one else on this forum cares about what we are writing :biggrin:

We seem to have a fundamental disagreement about whether or not simply switching to the same length spring yet softer will work for him. That's fine, I know it works because I've done the math and have used it in my application. No, I don't have a KW setup. Mine is actually pictured above, but you must have missed that since you're asking. You don't seem to comprehend what others write - only what you're thinking about. You have personal experience with swapping to shorter, stiffer springs. Whatever works for you and you're happy with that's cool. I agreed that a shorter spring (ideally stiffer as you write) is an appropriate approach IF he wants a stiffer, harsher ride and cut into his bumpstops.

So yeah, those are the two choices....

Actually, there's the third that you wrote earlier in this thread about going to a thinner helper Hyperco spring than what KW supplies their coilovers with. That was a pretty good idea that I was unfamiliar with as I don't have the KW's. If he can get the block height measurements between what he has now and the Hyperco option, that may get him what he wants. I don't know, he's got some measuring to do to determine how close he can get between what he wants and what he can get with the options laid out here.

 

[stuntman]

I needed to post detailed calculations in order to point out the errors in your simple math and understanding of motion ratios, and how far springs will compress for a given corner weight.

At the lower ride height that he is looking for, I measured the motion ratio at 0.67 so our numbers are pretty close. What exactly have I said wrong about toe arm location and bumpsteer?

I've had an NSX taken to Morse Measurements to have a full CMM done to map the geometry of the NSX to run simulations on. Have you?

You seem to focus too narrowly on spring travel and don't consider the effects of the damper's actual travel before hitting the bumpstop.

I really don't care to compare "personal measurements" with you, not do I care to continue a pissing match with someone who does not consider 11mm of rear toe-in as "excessive".

In the end, your recommendation of a softer spring rate at a low ride height will cause him to slam against the bumpstop and have a very harsh and jarring ride. I wouldn't recommend it.

I know you don't have KW V3s. It's obvious from the photo as well as your clear lack of understanding of the effects of your recommendations on his setup because you have not tested it. I have. The question was facetious.

 

[Mac Attack]

I needed to post detailed calculations in order to point out the errors in your simple math and understanding of motion ratios, and how far springs will compress for a given corner weight.

At the lower ride height that he is looking for, I measured the motion ratio at 0.67 so our numbers are pretty close. What exactly have I said wrong about toe arm location and bumpsteer?

I've had an NSX taken to Morse Measurements to have a full CMM done to map the geometry of the NSX to run simulations on. Have you?

You seem to focus too narrowly on spring travel and don't consider the effects of the damper's actual travel before hitting the bumpstop.

I really don't care to compare "personal measurements" with you, not do I care to continue a pissing match with someone who does not consider 11mm of rear toe-in as "excessive".

In the end, your recommendation of a softer spring rate at a low ride height will cause him to slam against the bumpstop and have a very harsh and jarring ride. I wouldn't recommend it.

I know you don't have KW V3s. It's obvious from the photo as well as your clear lack of understanding of the effects of your recommendations on his setup because you have not tested it. I have. The question was facetious.

I simplified and provided the delta's in ride height that could be expected with the options (which was correct as your laborious explanation later demonstrated). My apologies to anyone I confused trying to keep it simple. If folks want to learn more about suspension design, please consult the appropriate references and not over-simplifications like this in internet threads.

The other thread I'm referring to your suspension mistakes is the one that currently can't be accessed at the moment due to a glitch with Prime. You misstated that the generic location of the toe control arm determines whether or not a suspension toes in or out in compression. It does not - It is much more complicated than that. You also stated that the front toes out which it does not under compression. Furthermore, I've personally measured the NSX geometry changes with the same setup F1 cars use for alignment - strings. :biggrin: No need to pay for CMM's when I can do it in my garage very accurately for just a bit of labor! You also might want to get your money back as it sounds like they did it wrong. In the same thread I did agree that 11mm total toe in for the rear was excessive, but hey, I temporarily experimented with it since it's only 3mm more than what the OEM designers originally had and not really that big of a deal. Once again, your reading comprehension skills (or memory perhaps) have failed you.

I don't need to have a KW coilover in front of me to be able to provide input on ride height. As a nuclear physicist that's done work for NASA, the largest defense contractors in the nation and so on, automotive suspension work is simple and I treat it as such. That pioneering innovation has led to the coveted Mac Attack F1 exhaust with the first to feature tuned resonators and active valves, a semi-sequential semi-compounded twin-turbo setup with 90% of the peak torque available between 2500 RPM and 8500 RPM, DLC-coated engine internals, custom re-welded heads with flow tweaks after observing and modeling combustion patterns, custom dry sump, and soon active aero.

Look below for the extensive work on my setup maximizing compression travel, droop travel, ride, ride height and so on with a custom lift system too. No, it's not with mediocre KW's but the same techniques apply. The damper body length, piston length, bumpstops and so on were optimized for my setup. Furthermore, we even incorporated the correct load orientation for top spherical bearings that unfortunately reduces the available travel. All that necessitated an inverted clevis top mount to maintain the desired suspension travel which was another new innovation that hasn't been done on a NSX before. The result is a race damper (Ohlins TTX) that rides very smooth on my crappy roads, is the lowest ride height I want, and incorporates a lift kit. Pics below for just the front setup.

View attachment 160835

View attachment 160836

View attachment 160837

For anyone considering lowering their KWs with slightly softer springs and worried about running into issues with stroke limitations and bumpstop interference, look no further for real-life experience on an old popular suspension mod on our cars - Using H&R springs to lower the car about 1.5" and still using softer spring rates than what I proposed. From the NSX wiki https://www.nsxprime.com/wiki/Suspension, the H&R springs had only a 260 lb/in front rate and lowered the car about 1.5" on the long, OEM dampers with its long bumpstops. I've never heard anyone complain that they were getting beat up from bottoming out as alluded to by one particular poster here.

I've rationally explained as much as I can, and I know someone will want the last word here because that's their nature, so this will be my last post here.

Peace.

 

[docjohn]

I ran the HR springs on koni yellows and the track/street performance was sub-optimal due to what I felt was complete compression of the spring under load/bumpy surface and effective spring rate going to infinity and beyond....:tongue:

 

[stuntman]

A shorter spring won't reduce the compression travel of a suspension if you get into the bumpstop before either spring option coilbinds. This is what you were incorrectly claiming.

I had OEM length koni yellows with threaded spring perches running a similar ride height as the KWs and they, along with 1.5" lower H&R springs do hit the bumpstops, hurting the ride quality, predicability, compliance, and response of the car; while my KWs at that same ride height do not.

Edit: docjohn isn't the only other person I've heard this from; I've also driven multiple NSXs with this setup and they all do it.

Your lack of understanding of basic motion ratios, of how complex systems work together, and drawing incorrect conclusions from looking at one aspect of a system makes me fear for the results of your day job.

Please provide your hand measured bumpsteer curves.

The location and relative angle of a toe link, as well as the UCA & UCA absolutely determines the bumpsteer curve of the suspension. Changing the location of the outer Link's pivot point is a very common and fundamental way to affect the response and loading of a tire (the bumpsteer of a tire).

You yourself have issues with reading comprehension. Its not the glitchy thread that you and I talked about bumpsteer. I said if the toe link is parallel with the ground (assuming an already low ride height), the NSX front suspension will toe-out in compression.

 

[goldNSX]

Furthermore, I've personally measured the NSX geometry changes with the same setup F1 cars use for alignment - strings. :biggrin:

Same here. (already out of this thread).

 

[Mac Attack]

:biggrin: Darnit, guess I have to hop back in and acknowledge this impeccably-timed bit of info:

I ran the HR springs on koni yellows and the track/street performance was sub-optimal due to what I felt was complete compression of the spring under load/bumpy surface and effective spring rate going to infinity and beyond....:tongue:

OK, so I now know of ONE reputable person running HR springs on OEM-length dampers that was hitting the bumpstops. What kind of doc are you? Should have done a nip/tuck to your bumpstops as is apparently common for lowered KWs :wink: Again, the H&R 260 lb/in rate is still 40 lb/in less than I recommended in this thread and apparently with a trimmed bumpstop should be acceptable.

 

[goldNSX]

One last post here.

Hitting the bumpstop is mainly a dynamic thing, not a static thing. Unless someone lowers the car too far, then it's both.

Hitting the bump stop is mainly determined by the shock compression forces, not the spring rate unless you replace the springs by steel sleeves.

I've seen many cars going too low and a lowered NSX might look cool but the lower the worse the ride and predictability. H&R springs were letting the shocks sit permanenly on the OEM bumpstops.

Someone can trimm the bumpstops a little bit (I did that, 0.5'') but there are certainly limits doing so.

If anybody puts this in question, YES, I did all the measuring up and down on the NSX. :wink:

 

[docjohn]

haha I have a high post count....but my reputation .....open to debate....:tongue:

 

[stuntman]

:biggrin: Darnit, guess I have to hop back in and acknowledge this impeccably-timed bit of info:

OK, so I now know of ONE reputable person running HR springs on OEM-length dampers that was hitting the bumpstops. What kind of doc are you? Should have done a nip/tuck to your bumpstops as is apparently common for lowered KWs :wink: Again, the H&R 260 lb/in rate is still 40 lb/in less than I recommended in this thread and apparently with a trimmed bumpstop should be acceptable.

Ah yes, because according to a nuclear engineer: I'm not reputable when it comes to suspension despite setting up arguably the fastest "Time Attack" car in the world (that happens to be an NSX) as well as being hired by race teams and OEM companies to set up and help develop road cars and (even LeMans-winning) race cars.

Depending on the desired ride height, cutting down the bumpstop to increase compression travel still may not be enough to prevent hitting the bumpstop and causing a harsh ride. As I said earlier, in this situation, a stiffer spring rate that prevents hitting the bumpstop can actually create a far better ride quality in lowered cars.


Gold - many production cars sit on the bumpstops in static cornering to increase wheel rates during hard turns while maintaining a softer ride for most driving conditions, but engaging the stops frequently over big displacement bumps.

In addition, many professional race teams also rely on bumpstops during static cornering to maintain a certain aero platform or to adjust the balance of the car in a given condition and modify the packer gaps 0.5-1mm at a time to fine tune the behavior of the car.

Neither would be recommended for 99.9% of the people out there unless competing at that level or doing the level of development that OEM manufacturers do. In which case there's no need to consult a forum for advice.

 

[MexiRicer]

Back from the dead. My kw v3 setip
isnt as low as I’d like. At full droop the helper spring is very very close to hitting the control arm. Has anyone run the v3 without the helper spring? Or lowered them to the point where the helper spring comes in contact with the control arm when at full stoop (on a lift)

The solution to this is simple. As you are lowering the perch and as it is approaching the control arm, grab another jack and lift the lower control arm from the lower ball joint area, slowly, as to create more clearance for the perch to be swiveled down more. Once you reach desired height, be aware the at full droop your perch collar WILL come in contact with the control arm. It will not damage anything significantly to affect safety or performance.

CLIFFNOTES for those that get lost in the above:

-Lower ride heights need stiffer spring rates to stay out of the bumpstop.
-Cutting down the bumpstop or shortening the damper body is the only way to get more suspension travel (all the examples above bottom the damper out before the spring coilbinds)
-If you want your KW V3 lower than the stock setup where the spring perch hits the upper control arm:
-----Use a shorter spring and increase spring rate at least to 457lbs. 514lbs or 571lbs (like NSX-R) would be preferable over the stock V3's 343lbs.

This is literally EXACTLY what I did. My first cup kit set up, back in 2014, utilized 65mm ID, 8kg, 5.5in swift springs on the front of my KWv3. Because the KW spring ID is 61mm, there needed to be a spring reducer at the bottom perch to compensate for the bigger ID. I was advised to use a delrin reducer that sat on top of the OE kw helper, replacing the stock yellow kw spring reducer entirely, which worked fine. Over time and after much use, the delrin reducer ended up cracking. Around this time I had gone with 16/17 wheel set up and needed more lift than what I was running at the time. I decided to hop on the bandwagon and buy a pair of Stance cups due to their lift capability (~3.5 inches vs my previous ~2in) I decided to go back to the stock yellow kw spring reducer but I had some delrin/acetal washers made to fit around it. I was told this is beneficial for the health of the pistons inside the cups, as to prevent/reduce coil binding.

After mounting everything in, I was not too comfortable with the way the Swift spring sat over the stock yellow kw spring reducer. This is okay for the struts w/o air cups but I figured it would be better to have the main spring sitting flat at all times as to prevent premature scouring along the inner walls of the air cups (I imagine slightly uneven compressed weight sliding up and down inside the cup was not a good thing). I went ahead and disassembled it again and this time went with the KW club-sport spring 8kg (rate), 140mm (height), 61mm (inner diameter). I also replaced the stock yellow kw helper spring with a 61mm ID one from Hyperco. The design allows the main spring to sit completely flat once fully compressed. Here is a picture of assembly, I do not have a picture on hand whilst fully compressed.

I know this doesn't relate entirely to OP or the question asked by [MENTION=35852]JJM4life[/MENTION] but figured I'd post this here in case it can help someone.