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Old 06-27-2010, 02:26 PM   #41
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Originally Posted by spoolin2bars View Post
if it's understeering, soften the frt. shocks a couple clicks, take a few laps see what it feels like. the softest setting that still controls the spring motion is always gonna give the most mechanical grip.
The problem is steady state. I played with them at Hallett and fixed turn-in but it was fail mid-corner.
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Old 06-27-2010, 02:33 PM   #42
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I assume you already corner balanced? You may have a bit of "wedge"(>50% weight on the LR and RF corners). It may be a simple issue that you need more -camber on the front end.

There is a shitload of variables, so I have some questions:
  • Have you verified your tire temps as measured outside/middle/inside immediately after hot lapping? You want to see slightly higher temps on the inside of the tires(especially on the fronts).
  • Do you have adjustable sway bars?
  • What shocks and spring rates are you running?

I am NO suspension guru, but I have picked a lot of minds over the years, so here are my thoughts on the subject:

If you increase the preload it will make the car sit higher and increase shock travel while static. To compensate for a higher sitting car you should then shorten the shock body(if you have adjustable body length shocks).

Preloading the springs is HUGE in the offroad and rally car world, but I am not sure how many road racers or autoxers do it. I have not experimented with it yet, but the optimal goal for every vehicle is to maximize traction, so it makes a lot of sense that the off road cars that catch a lot of air and hit tons of dips and bumps would want to use spring preloading coupled with SOFT springs to optimize the traction.

That said, people that are running FM's AFCO suspension seem to be putting down some pretty good lap times, so maybe there is something to be said for running softer springs, but having shocks with TONS of travel(coupled with spring preload to keep the static ride height).

I like the suspensions that use helper springs of decent stiffness) - this makes preloading the shocks irrelevant(unless the helper springs are not stiff enough, like under 100ft/lbs).

The results to spring preload is:
1. Less preload your suspension will have less droop and down travel.
2. More preload will add more droop and suspension down travel.

The compression/rebound damping of the shocks have TONS to do with how well they react over big bumps/dips, so spring rate + shock damping need to be taken into consideration if you are contemplating adding preload to the springs.

I played with some shocks years ago that did not have adjustable body length, but they did have adjustable ride height via spring preload. The spring rates were quite low so in order to get a decent ride height I had to add a **** TON of preload(like 15 full turns on each collar) which ended up causing the springs to coil bind under hard compression. It sucked.

On a track or autox miata I would NEVER go below 375/250 front/rear spring rates, unless you have fairly stiff helper springs on the coilovers.
No, the car is not balanced
I have uneven temps because 2.75 and 2.6* camber is not enough
sway bars are not adjustable (rb front and stock rear)
I have tein flex

I have 550/390lb springs
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Old 06-27-2010, 03:27 PM   #43
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Originally Posted by hustler View Post
The problem is steady state. I played with them at Hallett and fixed turn-in but it was fail mid-corner.
stiffen the rear, again, only a little at a time, too much and you will have oversteer. i was trying to fix that problem at h2r once and i adjusted the frt. down and it helped some but not 100%. finally i tried stiffeneing the rear shocks a little and it was just right.

when i adj. the frt. on mine it helps turn-in and steady state. just to make sure you're not creating the problem, mid corner what's happening with the throttle?

if you're slowing down too much before the corner to the point that you can add a bunch throttle mid corner, then you are creating understeer. when you give it a bunch of gas you're transferring weight off the frt. to the rear. might not be what your doing, just saying.
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Old 06-27-2010, 05:00 PM   #44
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Mid corner it will understeer even at full throttle in 3rd or so (big time understeer in 5 and 6 at Hallett. I had a bit more grip in #1 but could use a little less understeer there too. I stiffened the rear down to 4-clicks until the car started skipping over bumps and sliding that way, lol.

Right now understeer is limiting my corner entry speed. I'd like to soften the valving overall and seriously thinking I have too much weight up front.
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Old 06-27-2010, 05:03 PM   #45
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Put an adjustable bar in the back. I'm still not understanding the small/no sway bar stiff spring combo the Miata suspension guru's say works well.
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Old 06-27-2010, 05:42 PM   #46
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I agree, add an adjustable rear bar and start with the outer hole first. OR, put in stiffer rear springs. I would do the following, in this order:

1. Corner balance the car, don't preload the springs. Add more negative camber - how much depends on what temp differentials you are seeing on each corner.

still have front end understeer?

2. Add an adjustable rear bar(I would try to borrow one for a track event so you don't invest in something you may not need).

still have front end understeer?

3. Up the rear spring rate to 8k.

FWIW, I run JIC FLTA2's on the track car with the standard 9k/8k spring rates w/RB hollow front bar and NO rear bar. I am contemplating dropping the rear to 7k and adding a stock bar back in because on sweepers the sway bars would be beneficial. The rear wing helps keep the *** planted, so it is not much of an issue except when I am pushing it to the limits.

I also adjust the crossweight(~2%) depending on the track configuration - ie, Infineon is clockwise so I reduce the crossweight, but Laguna and Thill are CCW so I ADD crossweight. It noticeably helps turn in and steady state without much affect on opposite direction turn in.


I like having stiff rear springs because I like to dorifto and I like to snap oversteer the rear end using the throttle or under trail braking.
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Old 06-27-2010, 06:05 PM   #47
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This sheet will help you bigtime if you have 4 scales and need to figure out how to get the car to 50%.

Put in the current weights and it will tell you how much you need to add/remove to each corner.
Attached Files
File Type: xls Corner Balance.xls (100.5 KB, 113 views)
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Old 06-27-2010, 06:22 PM   #48
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I had the RB rear bar but it was wayyyyyyyyyyyy to much rear bar. Last time I had too much oversteer everyone told me to switch to the smaller sway bar, lol. I have camber maxed with ride height, which is really low to the point of tucking the tire a bit in the front.

Most of the fast Miatas in Cali run the same springs and sway bar set-up that I'm on. I think I have too much weight in the front with all the turbo crap.

I wonder if zero bracing in the rear (1.6 car) is part of the problem?
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Old 06-27-2010, 10:48 PM   #49
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Too much weight on the frt? No, all of us have turbo's. from what you're describing, it sounds like your driving. you need wags to take a ride with you. If you were going fast enough mid corner, you wouldn't be anywhere near full throttle until track out point or close to it. Like I said, when you give it gas you're transferring weight to the rear which is taking weight OFF your front end. to regain traction you must lift off the throttle which puts MORE weight to the frt. Same thing Aero would be doing, adding weight to your tires through the downforce generated. (Or reduction of lift)

Last edited by spoolin2bars; 06-27-2010 at 11:06 PM.
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Old 06-27-2010, 10:51 PM   #50
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Too much weight...maybe you need moar hole saw?
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Old 06-28-2010, 03:35 AM   #51
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A few thoughts from watching the discussion...

If the front is understeering, fix the front, don't make the rear grip less to fix the issue (which is what stiffening the rear springs/rear bar will effectively do).

If you're serious about going fast the first thing you'll do is get corner balanced and then retest... you honestly can't get a usable baseline until you do this.

If you continue to have a steady state understeer problem, check tire temps across the tread immediately after you come off the track from hot laps... you MUST have someone else do this in the hot pits just as you come to a stop or the results are skewed. A contact pyrometer is the correct tool, IR temp gauges aren't terribly accurate for this.

My guess is you need more front camber, if you need more than you can get now buy offset bushings.
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Old 06-28-2010, 10:03 AM   #52
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I guess I'll balance the car and go from there. If it were any other track, I'd entertain the possibility that its driver error, but I have not had this problem in my car previously nor when driving John's car at that track. Turn 1, 5, and 6 are throttle steer corners there where the faster I enter, the more curbing I grab and more throttle I put down to rotate the car. I'm not going full throttle in either corner, but I'm grabbing a lot of loud pedal there.

When I had the big bar in the rear I had fear/scary oversteer.
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Old 06-28-2010, 12:39 PM   #53
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Quote:
Originally Posted by hustler View Post
When I had the big bar in the rear I had fear/scary oversteer.
That is why I kept lowering the spring rate in the back end. When I bought the car, it had 500/375 springs in it. It now has a more spec miata ratio of 430/220 with the rear bar on full stiff. Again, no real track experience, just auto-x and off ramp testing.
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Old 06-28-2010, 03:50 PM   #54
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Originally Posted by chpmnsws6 View Post
That is why I kept lowering the spring rate in the back end. When I bought the car, it had 500/375 springs in it. It now has a more spec miata ratio of 430/220 with the rear bar on full stiff. Again, no real track experience, just auto-x and off ramp testing.
...and softer rear spring means less weight in the front on the loud pedal. If anything I should go stiffer on the spring and remove the sway bar.
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Old 06-28-2010, 10:36 PM   #55
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Ah ha, that is why they suggest ditching the bar and going to a stiffer spring.
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Old 06-29-2010, 01:08 PM   #56
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yeah, he doesn't have the oversteer anymore, now it's understeering.
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Old 07-01-2010, 11:16 PM   #57
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Old 07-02-2010, 09:15 PM   #58
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I think increasing the rear spring rate is the way to go to reduce acceleration over-steer and not affect steady state cornering as much by jacking with sway-bars.

So apparently I can increase spring rate by increasing pre-load independently from ride height. I'm going to do this in the rear because right now the body and spring perches are sammitched together. I'll have to increase preload by raising the spring perch, then lower the body to compensate.

I kind of wish I didn't have adjustable body length because it adds another variable to the mix. What are everyone's thoughts on lowering the bodies all the way down and only adjusting preload for height adjustment?
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Old 07-02-2010, 11:32 PM   #59
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Ok time to dispel this whole "preload" myth....

Unless you have the spring cranked up so far that you've maxed its travel (and therefore have zero droop travel), you aren't "preloading" the spring, all you're doing is holding up more of the cars weight.

What body length adjustable coilovers (like Flexes) are able to do is to adjust bump/droop travel at a variety of ride heights which is something normal coilovers can't. The tradeoffs are more complexity as you noted, and more unsprung weight.

IMHO, if you know what height you want and order your coilovers accordingly there's no advantage to body length adjustables. I've yet to see a purpose built road racing car use a body length adjustable shock, up to/including F1 cars.

To answer your original question, no... you need to buy the correct rate spring, install them and reset your corner weights/alignment.
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Old 07-03-2010, 12:18 AM   #60
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Thanks...it really sucks that each time I change something I have to pay $300 for a new alignment so I want to make sure I get everything right before I **** with it. I don't really know what spring rate I have in the rear because the swift springs part number is a sticker and its gone.

I wish i had money for JRZ or Xida.
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