Thoughts on suspension set-up

Discussions relating to MX5 Tyre choice, Wheels, Brakes Suspension components and other items to keep you going around corners, stuck to the ground or stopping on a dime.

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marcellarius
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Thoughts on suspension set-up

Post by marcellarius » Sun Aug 25, 2013 5:44 pm

I'll start off with what my goals are: I want a reasonably balanced sports car which is usable as a daily driver, good on back-roads and good in gymkhana, autocross and other clubsporty sort of events -- a multi-use car.

It should:
  • be unfazed by rough roads, pot holes, speed-bumps, etc.
  • have a neutral handling balance, controllable oversteer.
  • retain the nice, factory steering geometry
I'm NOT after:
  • A slammed, stanced, hellaflush, whatever car. I want suspension travel (see above) and I don't mind if the car looks relatively standard.
  • A drift car -- drifting is fun but I'm after an all-rounder
I've currently got a set of Tein Mono-flex Winding Master Sports Spec adjustable struts. The Japanese market ones have 6kgf/mm and 5kgf/mm springs.

I've had them set up to the reference specs in the manual (even preload each side, 2mm on front, 19mm rear) , but while they've felt pretty good for street use, I haven't been happy with the set-up when pushed to the limit on the skidpad -- aside from the absurd body roll, the factory setup felt better at the limit.

It's had a bit of a tendency to unload the inside rear wheel in hard cornering/oversteer and this prevents me from putting the power down. Based on my limited video recordings of the problem, I suspected it may have been too hard into the bump stops, so I upped the preload a bit, which seemed to help the problem a bit. It seemed fine when I took it around Pukekohe.

At the gymkhana last weekend, I was pretty unhappy with the handling, but it occurred to me that the course had more left-handers than normal, and that the car handled much worse when going left than right.

This has gotten me thinking about the value in corner-balancing my car. I don't have a set of scales, and in the interests of frugality, I was contemplating whether I could estimate the corner weights and work out what I'd need to change to get the car closer to balanced.

Can anyone share their experiences/advice with this sort of thing?

Cheers.

Image

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Post by Snapfrozen » Sun Aug 25, 2013 6:52 pm

I've got minimal body roll with my Bilsteins and it is possible if your setup was second hand that the shocks have seen better days. None of them leaking?

It's a hard one as you've already got coilovers, but to get rid of bodyroll from here you'll need to spend some money

marcellarius
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Post by marcellarius » Sun Aug 25, 2013 7:23 pm

I bought the struts brand new.

I don't mind the amount of body roll the car has at the moment... I don't think it's the root cause of the handling issues.

BRM
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Post by BRM » Sun Aug 25, 2013 7:52 pm

Stiffer springs in the rear to fix that lifting of the inside front.

built4speed
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Post by built4speed » Sun Aug 25, 2013 8:02 pm

Those spring rates are way too soft imho.
I would swap the 6kg to the rear and get some 9kg for the front.
Ive always been told to never run preload, just enough tension to stop the spring rattling round. This is from guys who setup V8 touring cars etc.
Corner weighting is important, you can't setup a car off a piece of paper.
Last edited by built4speed on Sun Aug 25, 2013 9:02 pm, edited 1 time in total.

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Post by BRM » Sun Aug 25, 2013 8:46 pm

Yeah, and setting up with zero preload on the springs.
I don't understand why people preload them
all of our race cars bar one arent preloaded.

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Post by SkilletKid » Mon Aug 26, 2013 12:56 am

I'm with the school of thought that your 6kg springs are a bit too soft for performance driving. At the minimum of 8 or 7 at the front and 6 or 5 at the rear.

Are your Tein's able to be revalved? Might pay to check on that. Might save you some money compared to getting new/different coils.
If you're planning on getting new coils, do as Snapfrozen and Furai (soon to be me when they arrive) have done and get revalved Bilsteins. (Or for mad baller points with baller money get some Xidas or Ohlins =P)

Either way, revalving should get you what you're after as long as you help the guys who are doing it with some info. Along with telling them your goals and future plans for the car, other stuff to tell them are:
Corner weights; handy but in a pinch go to the dump and see if you can roll onto their scales to atleast get a gross total weight of the car in the trim that you will be running the most (so if gymkhana/track is your goal roll it on to the scales with the unnecessary stuff taken out like the spare wheel or other items in the boot/cabin. Do you run different wheels that are lighter/heavier than your road going wheels? Put them on etc.).
Motion ratios (sometimes needed, sometimes they have these already); either way they are ~0.72 front and 0.88 rear on a MX5 with the NA6/NA8 chassis and subframe.
Along with the diameter of your anti-roll bars (swaybars to some) should give them a base line to work from.

Preload is generally avoided by most and you're better off getting better bump stops. I do know of a few V8 touring car teams who run a fair amount of preload on their coilovers. But they run some weird German brand ones that aren't Bilstein or Koni in a spec/controlled series so we can almost ignore that.

If you think/know that you are crashing on to the bump stops excessively in corners it might be that you're running too much rebound damping. But until you have a camera sitting in the bumper facing your shocks it will be hard to tell.

And I agree with built4speed; if you're concerned about handling then corner weighting is important (atleast if you want to be competitive). I have yet to see one of the race cars at work be sent out the door of the workshop (some times pit box) without being corner weighted.

In any case, here is the "Handling Cheat Sheet" (ie Quick Fixes) from Keith Tanner from Flyin' Miata:

UNDERSTEER:

Corner Entry/Transition
Increase front shock compression damping
Decrease rear shock rebound damping

Mid-corner/Steady State Cornering
Stiffen rear swaybar
Soften front swaybar
Increase rear spring rate
Decrease front spring rate
Raise rear ride height
Lower front ride height
Increase front camber
Decrease Front toe-in
Increase rear toe-in (careful with this one)

Corner Exit/Transition
Increase front shock rebound
Increase rear shock rebound

OVERSTEER:

Corner Entry/Transition
Decrease front shock compression damping
Increase rear shock rebound damping

Mid-corner/Steady State Cornering
Soften rear swaybar
Stiffen front swaybar
Decrease rear spring rate
Increase front spring rate
Lower rear ride height
Raise front ride height
Increase rear camber
Increase front toe-in
Decrease rear toe-in

Corner Exit/Transition
Decrease front shock rebound
Decrease rear shock rebound
"Yes, you got that, 16 years of [MX5] ownership and you too can become the Obi-wan Kenobi of not giving a s**t." - Moti

marcellarius
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Post by marcellarius » Mon Aug 26, 2013 1:25 am

Racelign can revalve, but I don't believe that harder springs would be beneficial unless I was racing the car seriously. The springs are still fairly firm for road use.

Regarding preload: I don't see the problem. They are constant rate springs and unless you're getting coil bind, it's changing the ride height and where in the damper stroke the car sits. If I ran just enough preload to keep the springs captive, it would be hitting the bump stops hard. And Tein's spec is to have the rears quite preloaded.

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Post by SkilletKid » Mon Aug 26, 2013 1:40 am

marcellarius wrote:Racelign can revalve, but I don't believe that harder springs would be beneficial unless I was racing the car seriously. The springs are still fairly firm for road use.
Fair enough, but even with stiff(er) springs the right valving should keep them fairly comfortable.
marcellarius wrote:Regarding preload: I don't see the problem. They are constant rate springs and unless you're getting coil bind, it's changing the ride height and where in the damper stroke the car sits. If I ran just enough preload to keep the springs captive, it would be hitting the bump stops hard. And Tein's spec is to have the rears quite preloaded.
If the manufacturer's spec sheet instructs you to preload then do so. I was more making that comment on how you increased it from the factory setting. Speaking of which were you getting coil bind since you upped the preload?
"Yes, you got that, 16 years of [MX5] ownership and you too can become the Obi-wan Kenobi of not giving a s**t." - Moti

marcellarius
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Post by marcellarius » Mon Aug 26, 2013 2:21 am

I don't think so, but putting the go pro in the bumper could be interesting to see what's going on.

I reviewed some videos I took last weekend, and it definitely seems to be asymmetric, which makes me think that balancing the corner weights could help solve it.

BRM
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Post by BRM » Tue Aug 27, 2013 3:03 pm

So much science for gymkhana

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Post by SkilletKid » Tue Aug 27, 2013 3:25 pm

BRM wrote:So much science for gymkhana
Lol just a matter of time before someone starts suggesting doing front roll couple calculations =P
"Yes, you got that, 16 years of [MX5] ownership and you too can become the Obi-wan Kenobi of not giving a s**t." - Moti

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Post by BRM » Tue Aug 27, 2013 3:30 pm

Haha yup!

We're throwing science at my racekor,
But not for gymkhana/drift miata.

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Post by chris » Tue Aug 27, 2013 3:45 pm

With your suspension, I don't feel the spring rates are to soft, especially for gymkhana which (at the moment) is where I see you most weekends versus the track.

Do you have adjustable dampers? If so they are always a great place to start playing with different setups.

As a temporary solution you could try stiffen the actual body of the car by using a metal bar between the seatbelt towers..
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marcellarius
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Post by marcellarius » Tue Aug 27, 2013 3:46 pm

I don't really see the point in spending significant money making a car handle objectively worse than it did from the factory...

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Post by marcellarius » Tue Aug 27, 2013 3:59 pm

NA8C, so a bit more braced than the early NA6s. They already have a bar between the seatbelt towers, as well as bracing on the rear subframe. I'd like to get something like the FM butterfly brace to cut down on flexing though

The car felt pretty good (although slow) when I took it to Pukekohe a couple of months ago, but I can't attend many track days and compete in anything much beyond autocross without getting homologated roll protection and a lower seat, so that's pretty high on my priority list.

I've played with damper settings a bit, but I haven't tried setting the left/right sides differently. It doesn't feel like a winning solution.

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Post by chris » Tue Aug 27, 2013 4:13 pm

When's the next Gymkhana/skidpad day?
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Post by SkilletKid » Tue Aug 27, 2013 4:14 pm

Setting damper settings differently left to right is not recommended unless you have shock dyno curves to work from to match them side to side.

The settings you can change from left to right (aside from ride height in your case) are tyre pressures; taking note of lap times and how the car felt after each run is probably the most cost effective way to do things.
Can also take note of both cold (before a run) and hot (immediately after you finish a run) tyre pressures if you have a gauge handy.
If you have some spare cash, a needle type tyre pyrometer is the way to go in terms of determining the best tyre pressures to use but I don't think many of us have those.

Edit: Since it's primarily a gymkhana/autocross car I doubt you will be getting the tyre temps up high enough to affect pressures so ignore that line about getting the pressures before and after runs.
Last edited by SkilletKid on Tue Aug 27, 2013 4:19 pm, edited 1 time in total.
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Post by BRM » Tue Aug 27, 2013 4:18 pm

^^i do!

Chris - when ever we organize one

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Post by SkilletKid » Tue Aug 27, 2013 4:20 pm

BRM wrote:^^i do!
shhh lol. I'm getting one soon =P
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Post by chris » Tue Aug 27, 2013 4:33 pm

BRM wrote:Chris - when ever we organize one
Gymkhana day or skid day though?
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marcellarius
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Post by marcellarius » Tue Aug 27, 2013 4:52 pm

Yeah, tyre pressures are such an effective way of changing the feel of the car. I've found that ~28psi is pretty good at reducing NVH on crap roads (maybe Mazda were onto something...) but I run 32-40 for gymkhana depending on conditions. A good tyre pressure gauge is invaluable :)

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Post by Furai » Tue Aug 27, 2013 5:00 pm

Sounds like you need more travel in the rear. Tried raising it slightly or maybe go shorter bumpstops or extended tophats?

Look at your height and read this.
http://fatcatmotorsports.com/FCM_app_gu ... #Bumpstops

My best combo was Bilsteins with 8/6kg springs and valving to suit those springs. Rode better than stock and did well at gymkhana, only went stiffer because mines a drift car and I need better control.

The key to the rear though is travel and thats why I went extended tophats not keepers.

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Post by BRM » Tue Aug 27, 2013 5:00 pm

chris wrote:
BRM wrote:Chris - when ever we organize one
Gymkhana day or skid day though?
Gymkhana's gay. Skid day, so we can try drift and niki can show us how to drift an Ace

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Post by marcellarius » Tue Aug 27, 2013 5:01 pm

I'd be keen-as-beans for an actually difficult gymkhana day. I find the unstructured skid/drift days terribly boring... a minute of aimlessly skidding around and the next 20 minutes sitting in a queue being serenaded by tortured tyres and the drone of SR20s. ;)

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