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I always wondered about this, having big bars set to hard (hotchkis) limits the body roll/compression on stock suspension but it then also limits CAMBER gain, right?
my car can only get -1.1 degree of negative camber in front, so all other things being equal having softer stock bar will yield more negative camber in the corners due to the suspension being more compressed compared to the same scenario with big hotchkis bar set to hard - which limits body roll? does this sound right?
Ah, but the camber gained through compression is not as much as the camber lost due to body roll (as the body rolls, it is also tipping the tire over by the same degree). So, still a net loss when there is more compression, but less so in an RX-8 than many other cars.
However, (and this might confuse things even more) it's really the ride height that determines the amount of body roll you will get. With typically sticky tires on track you're not going to limit the total amount of body roll very much with stiffer sway bars.
Originally Posted by Nadrealista
sounds like 10/7k could be happy medium then for mostly stock car?
I believe so, yes, notwithstanding hufflepuff's recent comment about the balance being loose with stock sway bars.
Last edited by blu3dragon; 04-05-2019 at 04:50 PM.
Would your spring rate calculation apply to my car as well? What are the inputs, do sway bars play role? I have hotchkis bars on the car and I have kept the stock bars. Don't want to get something that will require me to fix issue with bars - ideally suspension would play well with bars I already have.
Also if I want custom spring rates Feal cost goes up to $1800 (only swift springs and their road race shocks), while fortune auto is $1299 with custom spring rates ($1650 with swift springs upgrade). So costs are escalating quite quickly.
Wonder if I should just get PSS for $1035 and spend money on driver mod :-)
Probably. I have the heaviest RX-8 Mazda made, weighing in at 3300 Lbs with me in it and a half tank of guess. I assume you are lighter, but my calculations are probably close enough. Keep in mind, my goal for the simulation was a full race setup, which is usually overkill for track days. 13K is the highest I would go for your application, and 10K is probably just fine. As rates go up, the potential quickness of the car can increase, but it becomes harder to drive fast. At some point, your skill level must increase with spring rates.
Generally speaking, you start with spring rates, then adjust bars for best performance. Your bars may or may not work with the new setup. Some combination probably will. You will either have to calculate the difference between stock and new spring ratios, or do some testing, or likely both. Hotchkis bars are on the stiff side of the spectrum. (My front bar is a Progress MX-5 model, which is considered medium for an RX-8. I either run the stock 16mm rear bar or a 11mm MX-5 bar I swap in under certain track conditions. And, I always have a 17mm wrench handy, so I can disconnect the rear as a quick fix, if the car is too loose.)
PSS spring rates are 6.5K / 4.5K (370 / 240). That is fine for occasional track use, and is very comfortable on the street with Bilstein dampers, but not stiff enough for any serious track use. They will limit you. (I recommend them to people who daily their cars and do a handful of track days per year.) My springs are too soft for NT01s at 8K / 5K. You won't like 6.5K.
The more I think about it, the more I think 10K is the right neighborhood for you. Maybe ask Feal to build a set with their standard springs and the dual digressive damping of their RR shocks? Swift springs are nice, but you don't need them.
Only you can address the cost considerations. I have it in my head that a serious set of track shocks always cost north of $2K, so Feal sounds like a bargain to me!
Last edited by Steve Dallas; 04-08-2019 at 09:21 AM.
mine is 2010 sport trim @ 3,064 lbs. keep in mind that I am upgrading from stock suspension with big sway bars. as is car is fun to drive - very neutral with slight touch of understeer, but I can easily get the car to rotate with throttle inputs or bar adjustment. I would like to keep original neutral/forgiving nature of RX8 which is what makes it fun at the track, lower the car to get more negative camber - better grip and longer tire life.
I do like the hotchkis bar adjustability and wonder what spring rates (10/6 or 10/7) would play better with them?
According to the specs below front can be very close to stock rx8 bar on the first setting, rear is much stiffer even on the lowest setting (390%)
Front Sway Bar :Lightweight durable and adjustable 1-5/16 in. (33mm) hollow 110% stiffer than the stock sway bar with a rate of 970 lbs/in. 150% stiffer than the stock sway bar with a rate of 1150 lbs/in. 195% stiffer than the stock sway bar with a rate of 1370 lbs/in.
Rear Sway Bar: 390% stiffer than the stock sway bar with a rate of 195 lbs/in. 470% stiffer than the stock sway bar with a rate of 250lbs/in. 580% stiffer than the stock sway bar with a rate of 340 lbs/in.
For some reason, I thought you had an R3. Sport trim spring rates are 156 Lbs / 113 Lbs
Regarding sway bars, and without doing the real math... We know Mazda's spring rates typically feature a front-to-rear ratio of ~1.4. If your bars are dialed in to your liking with that ratio, you want to go with 10K / 7K to stay close to where you are now. Changing the center of gravity and adding negative camber all around will have some effect on that, but it is a decent starting point. I like more rear spring in Mazdas due to the limited bump travel in the rear anyway.
10k/7k combo with stock sways was loose
10k/7k with stock front no rear was a little loose at track, very loose at autox
Now with 255 bridgestone re71r
10k/7k with hotchkis mx5 front sway no rear is just a tad loose at autocross even with front bar full stiff . I imagine it's good for track.
I'm getting another set of fortunes, 10k/6k, valved to 12k/8k. Should have a little push at track and neutral at autocross.
More spring rate, oddly enough, reduces overall mechanical grip and makes the car more sensitive to corner balancing. I'm in favor of compliance and easy setup and easy to drive, especially with how good our camber gain is. I'm also doing more autocross and hill climb on somewhat bumpy surfaces, so compliance is helpful.
Of course stiffer springs improves transient response and may give more driver confidence on a smooth track... But plenty of really fast folks make softish setups work and win.
As for swift springs, they are lighter and more consistent. I'm racing for contingency and track records so they were worth it for me. Otherwise probably no where near as big a deal as driving well.
My latest autocross video (see sig). illustrates how fast and neutral the current setup is. Going to -3.3* front -2.9* rear camber has helped from previous seasons.
Looks like 10/7 is not optimal spring rate for fortunes if you have to run without rear say bar to achieve neutral balance, which is strange since that is close to stock spring ratio? could it be that damping in the rear is not optimized for our car?
Springs are inexpensive. Pick one or the other for the rear and swap them if needed.
Running Mazdas with little to no rear bar is very common (in everything except Spec Miata, which is its own animal). Hufflepuff and I are employing a familiar formula. The biggest rear bar I use is the stock 16mm bar. On some tracks, I prefer an 11mm MX-5 rear bar, and on other tracks, I disconnect one side and run no rear bar.
Also be aware that hufflepuff's definition of loose may be very different from yours. If he likes a tight car, neutral may be "loose" to him, for example.
I'm also running a factory rear bar with aftermarket front (I think it's the progress RX-8 one but I'd have to check). At the rear I have an NC mx-5 rear bar to swap in as adjustment to 'medium', and then disconnect for 'full soft'.
My springs are closer together than 10k/7k though.
Balance is also affected by shock body length and bump stops (or more specifically bump stop engagement), which might be different for different shocks.
Last edited by blu3dragon; 04-09-2019 at 12:31 PM.
So I just heard back from Feal and they are suggesting 16k/10k spring rate!?
yeah, some NC MX5s are running 15k front rate for the STR street tire class (180 TW) 245 tires on 9” wheels. So for a heavier chassis RX8 on the exact same suspension with DOT R tires it’s not unreasonable at all. Kind of just depends more on whether you’re a half in / half out lukewarm street car driver.
Just because you don’t hear about any RX8s running that high doesn’t mean there aren’t any who have/are ...
The 16k/10k would be in the ballpark for running no swaybars at all, front or rear.
Our setup is roughly 13.5k front, 10k rear with a stock sport front bar and no rear bar. I think the reliance on swaybars to control roll is a lie we've all been fed for too long... I do believe that the 16k/10k would produce a car that does not handle transitions or bumps very well though.
What is the rest of the suspension setup as far as bushings are concerned? Free moving spherical/delrin/roller bushings or bearings are going to influence the situation, a lot imo at those rates.
Me too on the front LCA, but it’s not quite as straightforward as the UCA. I have spherical on both ends of the shocks and roller bearings on the FSB too.
Those rates are approaching where aero considerations start influencing the equation, which I also have a dam/small splitter planned for the front and a tall/wide plate spoiler for the rear. There can be other factors too like f/r weight balance, sprung vs unsprung weights, and so on. The actual wheel/tire patch rates aren’t really that bad for competition purposes though.
Most people seem more attuned to street car tuning and there are some fairly successful people who advocate similar wheel rates for upper performance street tire competition (180-200 TW). Hoohoos should be fine imo given that everything else is done properly to back it up. I did agree with the quoted Feal statement that people using lower rates aren’t taking full advantage of what a high grip tire is actually capable of, but I get that some may be willing to compromise for whatever their reason(s) may be.
The rest of the pivot points will get address as time/money happens, unsprung weight is down a lot due to rotors and the full aluminum shocks, they have sphericals top and bottom except for the rear tops (still need to modify the hats). But the car works and I'd rather be competing than tweaking for the time being.
With that said, my car with those rates also has a splitter/dam up front and a class limits plate spoiler out back, and 285 Hoosiers. It's provided for a very balanced car with no surprises, it handles bumps/jumps/etc VERY well. I'm also running a very non-toe-aggressive alignment, mostly for tire life purposes but the car still turns in great.
I wouldn’t agree with no FSB, but think the rear rate needs to be even higher with a rear wing/spoiler and also depending on some other factors. Would probably use a tender rather than zero helper too. Reality always defines the final result though.
So doing some research for a different topic/thread, for MCS double adjustable NC MX5 shocks the offered spring setup for dual-purpose cars is 700#/475# (12.5k/8.5k) and the offered race car spring package is 900#/600# (16k/11k). That chassis is 350-400 lbs lighter, but as always, the shock valving plays into how well it may grip in transitions and bumps.
So doing some research for a different topic/thread, for MCS double adjustable NC MX5 shocks the offered spring setup for dual-purpose cars is 700#/475# (12.5k/8.5k) and the offered race car spring package is 900#/600# (16k/11k). That chassis is 350-400 lbs lighter, but as always, the shock valving plays into how well it may grip in transitions and bumps.
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I had 850 / 650 on my car with the mazdacomp medium front splined bar and a stock rear, and it felt unnecessarily stiff all around. I'm at 750 / 500 now but haven't run the car since swapping. We'll see where I end up, I suspect my car is a little lighter than most.
Yeah, but you’re coming out of a bimmer with struts, everything seems too stiff compared to that
Compared to softer spring setups that stiff springs need a lot less compression valving and a lot more rebound valving. If the shocks aren’t tuned for that it likely won’t go well. It also will be more sensitive to excessive/incorrect inputs.
well I ordered a set of Feal 441+ in Feb this year. I finally put them on the car this last weekend. Haven't taken them to the track at all yet but will be signing up for an event soon. So far I've figured out they made the rear shocks wrong and it can't go low enough in the rear currently. They have informed me that I have to send in the rear shocks and have the stroke shortened and shorter springs installed.
Despite the ride height limitations in the rear they ride really well so far. I can't wait to put them to the test with some real tires soon. I'm going to send them back in a day or so when I have time to swap back to my old setup and I'll report after getting some track time in.
No they’re just doing it wrong selling an NC Miata setup for the RX8. It needs taller rear shock mounts so a longer body and stroke will fit while also allowing the proper ride height clearance
these are just general numbers, the true numbers require a lot more detailed calculation, it just emphasizes the general point
NC MX5 wheelbase: 91.8”
NC MX5 rear track: 58.9”
cross-angle distance from front to rear wheel: 109.1”
RX8 wheelbase: 106.4”
RX8 rear track: 59.3”
cross-angle distance from front to rear wheel: 121.8
106.4/91.8 = 1.16
for the same degree of true front/rear pitch the RX8 rear wheel will travel 16% more than the NC
121.8/109.1 = 1.12
for the same degree of opposing front/rear cross pitch the RX8 rear wheel will travel 12% more than the NC
considering the RX8 is 500 - 600 lbs heavier than an NC it generally needs a longer length and stroke rear shock just as they designed it between the two; RX8 rear shock hat is approx. 2” taller than the NC rear hat. So, 1” longer body + 1” longer stroke gets you that two inches, but also allows one more inch of stroke clearance (2” taller hat, 1” longer body). The longer shaft then also allows more extension in forward pitch so the rear wheel doesn’t come off the ground, or in the case of a short race spring/zero helper spring combo let the combo unload/load abruptly.
Any updates on how the Feals and Fortune Autos are? I'm trying to make that decision between them. It seems like the Feals have more of an upgrade path but the rears being straight from the NC without a longer stroke is a bit concerning. Cheaper rebuilds as well since online they quote 400 for all 4 corners while fortune is charging 600. Seems like they both have good history though.
04-05-2019, 04:48 PM
