Mazdaspeed 3 Suspension Set Up

So I've been in a continual battle to fight the mind numbing understeer in this car. My set up is below, anyone have any suggestions?

Weight w/ driver ~ 3400 lbs

60/40 distribution

525 lb/in front

600 lb/in rear

Stock front sway bar (26mm)

Upgraded rear sway bar (32mm on the "stiffest" setting)

Federal 595 RS-R tires

-3 degrees front camber

-2 degrees rear camber

Zero toe all around (daily the car, can't kill tires that quickly)

So I'm pretty stuck here...The car feels pretty stiff already so I don't think going up in rear spring rate would be a viable idea since it is a daily driver. I do have a 28.6mm front sway bar sitting in my garage thinking it'll help me combat the car diving in hard banked corners but I'm hesitant to install it thinking it might just make understeer worse. I'm not trying to do anything crazy here, I just want the car to rotate well. Any advice?

My bright idea was to install that 28.6mm front bar, and get an even bigger bar for the rear. No clue how large that bigger bar is, all I know is my current bar is rated for 900 lbs/in at 1 inch of travel, where the bigger bar at its stiffest setting will do 2000 lbs/in at 1 inch of travel.

If you're lifting the inside rear tire, a stiffer rear bar won't help, as you've got 100% weight transfer already.

My suggestion, try a reverse stagger wheel and tire setup, with the wider ones up front. This is not uncommon for race cars and it's shown up from time to time on street cars straight from the factory.

Anybody know the motion ratios for the front / rear suspension on those?

MCarp22 wrote: Anybody know the motion ratios for the front / rear suspension on those?

I found them here: http://www.mazdaspeedforums.org/forum/f12/mazdaspeed-3-motion-ratios-155608/ 1.03 front .72 rear

You have waaaaaaaaaaaaaay too much front spring rate. I calculated the front natural freqency out to ~2.4Hz which is a lot higher than the rear. If you went down to a 375 in front, that would lower the front to ~2.0Hz, which would match up nicely with the 2.2Hz rear that you have now.

It'll probably improve ride quality too since the rear will now settle faster than the front.

I'll echo what MCarp22 wrote.

Also, you don't mention if your cars has been lowered and by how much.

And if lowered much, how are your front tire temperatures? If lowered much, you may have too much negative camber both front and rear.

In reply to fanfoy:

I have a modest drop of about an 1.5 inches lower than stock. Unfortunately nothing to monitor tire temps.

MCarp22 wrote: Anybody know the motion ratios for the front / rear suspension on those?

I have no clue what you're talking about, but the numbers and big words make me want to believe you . I'll look into that some more though, thanks!

A larger front bar will increase understeer. Maybe try more air pressure in the rear tires to get the back to rotate easier?

dooodstevenn wrote:

MCarp22 wrote: Anybody know the motion ratios for the front / rear suspension on those?

I have no clue what you're talking about, but the numbers and big words make me want to believe you . I'll look into that some more though, thanks!

See my next post, I found that info and more or less figured out your problem.

sergio wrote: A larger front bar will increase understeer. Maybe try more air pressure in the rear tires to get the back to rotate easier?

That's what I thought too and have tried higher pressures in the rear, I don't really know why I got this front sway bar. I think reading around on forums led me to believe it would pair well with the rear I have.

A bigger front sway bar could be good in an otherwise stock, camber-challenged car. This is not your case.

If you want real answers, you really won't have a choice but to monitor your tire temperatures. Without this information, anything will simply be an educated guess.

With that said, I would start with reducing your rear camber to -1 or even 0. You have a relatively good rear suspension geometry on the MS3, so I don't see why you would need that much camber. And it's not expensive to do.

Next would be to lower your front spring rate like MCarp22 suggested.

Work systematically with only one change at a time. Don't be tempted to just through a bunch of stuff at the car because you can get lost very easily in suspension setup and end up chasing your tail.

Could I run the upgraded front sway bar since I already have it and run a lower spring rate?

dooodstevenn wrote: Could I run the upgraded front sway bar since I already have it and run a lower spring rate?

As MCarp said get some 375/400 front springs and try them first. Then maybe you can try the front bar, but I don't think you will need it.

Mine is pretty neutral at 27/32 bars on full stiff, i.don't remember what my spring rate is though. Static 2* camber all 4 corners. Probably 2.5 lower than stock

sergio wrote: Maybe try more air pressure in the rear tires to get the back to rotate easier?

If you get a looser rear end with more tire pressure, you're slightly sabotaging rear grip. It works well for adjusting the handling balance but it would be better to fix it with a spring or roll bar change while keeping the rear tires set for maximum grip.

mndsm wrote: Mine is pretty neutral at 27/32 bars on full stiff, i.don't remember what my spring rate is though. Static 2* camber all 4 corners. Probably 2.5 lower than stock

If you ever find those rates it would be super helpful!

GameboyRMH wrote:

sergio wrote: Maybe try more air pressure in the rear tires to get the back to rotate easier?

If you get a looser rear end with more tire pressure, you're slightly sabotaging rear grip. It works well for adjusting the handling balance but it would be better to fix it with a spring or roll bar change while keeping the rear tires set for maximum grip.

I was discussing this with a few other friends as well that air pressure as well as reducing camber in the rear to get the car to rotate would give up max grip to make up for handling characteristics. Not really sure where to go, but seems like the above advice of lower rates would be my first step.

Assuming the front end is maximized for best grip, then reducing the rear grip below maximum will help get the car better balanced and should lead to faster times. One has to look at it from a whole car perspective, not just one end of the car at a time.

That said, I'd be focused on increasing front grip to better match the rear, be it through alignment, suspension, or wheel and tire changes.

RX8driver wrote: If you're lifting the inside rear tire, a stiffer rear bar won't help, as you've got 100% weight transfer already.

If you're lifting an inside rear tire, increasing front stiffness will increase front grip. Lowering the rear relative to the front will also help.

I hate to say it but it's probably driver problem. If a front drive car understeers, it means you're not attacking hard enough entering a corner.

dooodstevenn wrote:

mndsm wrote: Mine is pretty neutral at 27/32 bars on full stiff, i.don't remember what my spring rate is though. Static 2* camber all 4 corners. Probably 2.5 lower than stock

If you ever find those rates it would be super helpful!

H&r coilovers. I know that much. berkeley if I know what I did with the paperwork. Turns in like a demon, none of that spooky snap oversteer they like either.

I would visit the manufacturers that actually race your car. People like racing beat put a lot of R&D into ACTUAL WORKING AND REAL WORLD TESTED suspension components. That's huge. You can't beat time and race tested components. Because, let's face it, at some point, somewhere, is a guy with the perfect Miata spring rate. And when that rate is known, 90% of Miata people will learn of it and use it (provided the same variables are present for their repsective chassis, such as weight) you can work out all sorts of calculations. In the end, you'll end up in the same ballpark as the company that figured it out a long time ago. And you will probably end up buy from them anyways, because no one else will sell a coilover setup that way.

mndsm wrote:

dooodstevenn wrote:

mndsm wrote: Mine is pretty neutral at 27/32 bars on full stiff, i.don't remember what my spring rate is though. Static 2* camber all 4 corners. Probably 2.5 lower than stock

If you ever find those rates it would be super helpful!

H&r coilovers. I know that much. berkeley if I know what I did with the paperwork. Turns in like a demon, none of that spooky snap oversteer they like either.

I don't think H&R publishes their spring rates.

If you have a tape measure and a micrometer, you can find the spring rates fairly easily.

You need way more spring rate for serious auto-x with such a heavy car.

I'm running 550/450 on a 2300lb Mazda2 with .97/.96 motion ratios. That works out to 2.4/2.9hz rates IIRC. Will be running 700/600 more than likely within a year or so with no front bar based on some other Mazda2 national competitors.

Ride frequencies be damned, you need to keep the contact patches happy.

And I daily it 100mi/day. A second set of less harsh all season tires helps greatly.

Edit: also raise the car up some if possible. Your roll centers drop way faster than COG when lowering causing even higher rates to be necessary to keep body roll from hurting camber during turns. Make sure you aren't hitting the bumpstops when turning hard/in... That will spike the true rate way high and cause understeer. I actually run my rear slightly higher than front(rake) about 3/4in, made a huge difference in loosening the rear up some, more predictably than using high rear pressures to compensate.

All this talk about motion ratios and rates (in Hz) has left me even more confused.