Increasing Coilover Spring Rate?
 

Hello,

I have been tracking my 2001 Miata with Fortune Auto coilovers on the same race track for at least two years now. I feel I have a fairly good understanding of my car's limits as of right now, but I believe it could benefit from an increase in spring rate (particularly on the front). This last weekend I participated in Driveway Austin's first Time Attack event, and learned even more about my car's handling characteristics thanks to all of the competitive driving I did. I found under fast trail braking turns my car's rear end would get very light in this situation- to the point of me almost spinning out (oversteer) a few times Saturday. Of course, this is understandable since I am turning at 9-10/10ths of the limit while moderately braking, but I'd like to minimize the weight transfer even more so the car with be easier to drive at the limit. I currently have 8K front/ 6k rear spring rates with factory sway bars. Would bumping up the spring rates by 112lbs front and rear to 10k/8k be worthy of doing?

Thanks for the help!
https://cimg3.ibsrv.net/gimg/www.mia...46ba219ecb.jpgI actually got 3rd place, behind a Porsche 996 and S2000. Received an award for most consistent lap times of the day.

I think you would benefit more from upgrading just the fronts to 10k and leaving the rears at 6k, or go 12k front and 7k rear. But of course there are other factors like what tires you're using, how heavy your car is, and importantly you need to know if your Fortune Auto shocks can cope with the upgraded springs. I'm sure Fortune auto would be able to tell you that.

Limiting weight transfer towards the front under braking will reduce the load on your front tires. Do you want less grip available under braking and turn in? Keeping the same split in f/r springs you're gonna have the same issues.

^What Oscar said, if you keep the same front to rear spring rate balance, your car will still have similar characteristics.

Neither are good, but 10/8 would be worse than 8/6.

If you are stock sway bars, upgrading the front will help reduce oversteer, too.

Hi Nick! Just increase the front, after making sure the shock can handle it otherwise reduce the rear. Your rates are too close together. 10/6 (1.6666) gets you really close to the same ratio as the standard Xida 700/400 (1.7) and I think you rode in my car with 800/500 (1.6). Get the alignment done per 949 spec if you don't already have that, run a stock or msm rear bar and a big fat front bar, all on the 949 recommended alignment specs page.

Definitely throw a front bar at it. I was running 450/350 with RB front and stock 11mm rear and recently bumped up to 600/450. That provides pretty neutral handling and shouldn't be too lose under trail braking,but will still rotate.

Thanks everyone! (Hi Hank!)

Yes, I am willing to sacrifice some front end grip if it will result in less weight transfer. My car already has an incredible about of front end bite with my 205/50/15 Yokohama Advan AD08R tires. In this situation (which in my case, happens fairly frequently) the aggressive trail braking always results in a very hair situation that requires a very delicate balance of throttle control and smoothness. So my coilovers came with the 8k/6k setup, but I will contact Fortune Auto to see what they say about the limits of the stock valving. Upgrading the front sway bar to a RB 1.125 bar has been on my list for a while, but that will probably have to wait till I graduate college. As for the springs, does it matter what brand of spring I buy? I hear Swift is really could, but I just can't see how it would be worth twice the price of no-name coilover springs.

Hyperco and eibach's are pretty affordable and pretty good. Hypercos are apparently better, but it depends who you ask. Most people here would probably say go for Hyperco.

Hey all, one last question! I emailed Fortune Auto, and they told me I can go +3kg/mm spring rate front and rear. So I have 8k/6k now, and I could go as high as 11k/9k, but I understand you want a greater difference between the two rates. So would 11k/6k be better than 10k/6k? Again, I'm just looking for a setup that will reduce brake dive, body roll (to some extent, I know I need sway bars*), and handle reliably on a race track. Thanks!

Edit: I ask this because I was under the assumption that my coilovers (and most coilovers in general) have a +2kg/mm limit. I hadn't even considered 11kg/mm in the front.

What is the alignment and remind me what bars are in there even if you already said. I would not do the 11/6, 10/6 is a good ratio and while 11 is fine you mentioned not wanting to afford a RB bar so you probably don't want to do all 4 springs.

The alignment was to 949 specs, -2 front -1.8 rear. Can't remember the caster and toe, but it was whatever they recommended. I just have the stock NB sport bars on now. I think I'll just go with 10/6. It's a cheap upgrade that I think I will like. BTW, you should come to the next time attack at Driveway Austin! I'll send you a Facebook message, but it's supposed to be the first Saturday of next month. $100 entry fee, and you win prizes! The grand prize is two hours of private racing lessons by the track owner's son. I won a free kart race there.

This.

Don't buy into the Swift JDM garbage, I would not use them.

Garbage..? Swifts are excellent springs. They are priced high, so if you're looking for a bargain there are a couple other high quality options you may prefer (Eibach and Hyperco are indeed both good) but Swift springs are not remotely garbage. Garbage is the generic springs that come with a lot of coilovers that are 1.5x as heavy and have half the stroke of the good stuff.

+1. I would put Swift just above Eibach/Hyperco. Some of the benefits of those springs are lost on most people, so the price typically can't be justified, but they are most certainly not junk.

Junk was a bit strong, yes. But I've read many things about their tolerance, ie meeting the actual rating, having a greater variance than either Hyperco or Eibach.

<Trying to understand putting money into 4 springs and keeping the little stock swaybar instead of upgrading the swaybar first and then the springs later or even the front two only.

Current spring rates with RB front / 14mm rear would be pretty spot on for a dual duty setup. Could use more spring, but will still be pretty good.

IMO, current springs are too close together even with an RB front bar. With a stock rear bar, they're a mess. It's a good example of why you should buy suspension from a Miata vendor with performance chops vs. buying off-the-shelf Taiwan coilovers.

^QFT
There are so many bad spring rate coilover sets on the market.

450/350 isn't really that bad, although with the RB bar it will understeer without a rear bar to balance it out. Not saying it's ideal, but it can get the job done.

I disagree. I field calls all the time from people who have trouble with oversteer after buying coilovers with mismatched spring rates. 450/350 will never handle correctly, regardless of what sways you throw at it.

450/350 will oversteer in all situations regardless of swaybar combo, BTW.

Then I must have something really far off on my setup. I have 450/350 on koni yellow with Millen Motorsports front bar (solid 1") and stock rear, and I have issues with understeer.

(That said, I have a set of Xida sitting in a box waiting to go on.)

I wasn't going to bother following up as it's a comprised setup regardless, but with RB front / 11mm rear at 450/350 koni sports I too suffered from understeer, as stated. Saying it will oversteer in all situations is untrue. There must be another variable at play. Lack of rear travel, driving styles, etc.

Consider that Spec Miatas run 700/375 with a slightly larger rear bar, but you claim to have understeer with 450/350. By that math, SMs should push horribly, but they don't. If you two have issues with understeer, it's setup or old/bad tires.

Sounds like you guys have stock or FM alignments.

1.5 year old RE-71r, 5"f, 5.25" rear, 2/1.5camber, -0.3* toe in front, 0 rear (just how it ended up, need to fix that).

Weights are 2494 with driver

FL660 FR600
LR638 RR595.

And again, 450/350 on koni yellow with 1" solid front and stock 1990 rear.

If you can tell me why it understeers that would be great, because everything I have read says it shouldn't but it does. Could also be inexperianced driver?

Camber is maxed for the ride height. I am adding ELBJs to fix that while I put the Xidas on this winter.

Driving style. Are you pushing into the apex to scrub speed?

So you have front toe in and you wonder why the car pushes?

e: 0.3deg toe in on a 23" tire is 1/8" total front toe in. If you look up "how to make my car not rotate at all under any circumstances", you'll find "front toe in". Fix your awful alignment :)

This is the reason I posted up the specs. It is -0.3* total toe. Is that enough to over ride the mismatched spring rates? I am still learning about all this stuff and make no claims to have done anything right.

Shoot, ya ninja edited me. That answers my question though.

Yes, 1/8" front toe in is more than enough to compensate for improper spring rates. That is causing all of your problems.

Just to back up the recommendations for the smaller RB 1.125" sway bar:
Most MSM buyers prefer the RB 1.125" front sway bar despite the 1.25" being recommended by RB (I originally had the larger bar and switched to the 1.125" bar after I'd had a track day with it).
The OEM MSM rear sway bar is 14mm and is typically kept.