Converting my STR Miata for rallycross - It's already bent so why not!

Sooooo.... I might be able to get my hands on some free snow tires for a rallycross in two weeks. I have a 1999 Miata with hardtop and bar setup for STR autocross and was curious what all I should consider for the leap to dirt. I'm pretty terrible off-road and have already done poorly in my Dodge Intrepid and a BMW E30, so I'm not expecting miracles. I'd just like to learn without wasting my time.

What I have now:

• Some flavor of 14 or 15 in wheels and snow tires (I'm not running Rivals on 15x9s :P)
• 550 front 375 rear FatCat coilovers (I'm guessing that raising these isn't a bad idea)
• Racing Beat 1.125 in front bar; 14 mm Mazdaspeed rear bar
• Header, cat-back exhaust, CAI with ducting to behind headlight (shouldn't suck up too much dirt)
• Bent front subframe (positive camber front right; control arms replaced w/ used)
• Replacement front subframe, front control arm bushings, and motor mounts

My big questions are how high or low should the car be, should I find softer springs, and will I completely destroy my nice shocks. I remember reading that having the car near stock height actually helps prevent unexpected lifting from ruts and allows more aggression, but runs the risk of destroying the underside of my car. I'm worried my suspension will be so stiff, it won't be predictable (I should have enough travel at least). While I'm fine replacing my control arms (again), I'd rather not need a shock rebuild after this.

My minor questions relate to sway bars and alignment. I'm guessing that having them to keep the car flat is more important rallying than on autocross. I'm also guessing that toe in is better than toe out on dirt.

A lot depends on the kind of surface your local venue has. Softer and tall springs tend to be most useful to keep the wheels on the ground. I wouldn't worry about "stock height" as most rallycross cars are at stock height (mine is actually a bit lower than stock).

For sways, many people run small or no sways. There are different trains of thought on that depending on driving style. Most people agree that you definitely don't want larger sways than stock (especially if you already have stiff springs). For rallycross, suspension credo is "soft soft soft" in most cases.

For tires, the popular cheap choice is Firestone Winterforce for the non-rally-tire set. In small sizes they're like $50 each at tire rack. Narrow sizes are best, on the "right size" wheel (don't strech sidewalls!). Run high pressures like 45psi.

Take a look around dirtyimpreza forums. Yes, it's mostly subies. But there are a TON of resources there talking about what you want for rallycross that applies to all cars, not just subies. Several long sticky threads in the rallycross section you should read.

I'm hoping to convert on the cheap. That means whatever snow tires I get for free will be it (probably 195/55-15 which is "close enough"). I can definitely remove the rear sway bar and disconnect the front (or set it full soft). I autocross a lot better with both bars on the car and ride height around 4.5 in off the ground (which is probably too low for rallycross; definitely lower than stock). I'll see if I can pick up some 2.5 in ID springs that are 10 in long and 225/130ish for rates; my current ones are 7 in long and 550/375.

I'm sure Evan will post in this thread. He's the master of Miata rallycross and should have more specific/more applicable advice than I do though. e30 and Miata are very different beasts :)

Don't be so concerned about ride height you dial out all the droop travel.

irish44j wrote: I'm sure Evan will post in this thread. He's the master of Miata rallycross and should have more specific/more applicable advice than I do though. e30 and Miata are very different beasts :)

He'll be along shortly. After he replaces the engine in his, after it blew up 15 seconds into the first run at yesterday's WOR rallycross event.

Jerry wrote:

irish44j wrote: I'm sure Evan will post in this thread. He's the master of Miata rallycross and should have more specific/more applicable advice than I do though. e30 and Miata are very different beasts :)

He'll be along shortly. After he replaces the engine in his, after it blew up 15 seconds into the first run at yesterday's WOR rallycross event.

Nooooooooooo!
Seriously though, Evan has the good advice, he did just win a national championship in one of those aweful little things after all.
My advice? Put it on snows. Put it at a height that splits bump and droop. Go drive and see how it works.

Put on snow tires, find some cheap stock suspension (it's the best) and remove both sway bars. You could trophy at nationals with that setup.

Son of a bitch!
< looks outside at bone stock '99 that is sort of for sale >
< Googles local rallycross events >

SnowMongoose wrote: Son of a bitch! < looks outside at bone stock '99 that is sort of for sale > < Googles local rallycross events >

You can do it!

EvanB wrote: You can do it!

'Luckily' the only vaguely local events are... an entire state away, in Oregon.
Seems silly to have a racecar I can't race

With as many stage rallys as there are around Washington it's hard to believe there isn't any rallycross.

The hardest part is that I currently have a whopping $700 into this car...
and that includes $140 for a battery and $120 for title and plates.
(So you could say she's a good cantidate)
But yeah, none of the WA Rallycross websites seem to have been updated in several years, sad panda.

SnowMongoose wrote: The hardest part is that I currently have a whopping $700 into this car... and that includes $140 for a battery and $120 for title and plates. (So you could say she's a good cantidate) But yeah, none of the WA Rallycross websites seem to have been updated in several years, sad panda.

You can always drive to Iowa on November 9th.

So yeah: this was FRIGGIN AWESOME. Placed 15th out of 47 and improved every run by 2-5 seconds. Not bad for 225/45-15 Rivals! I really don't know why I hated my first two events.

Prep: raised the car by lifting the existing 7x550 front springs and putting 10x300s in the rear. Disconnected sway bars. Didn't bother with an alignment since the subframe is bent still.

EvanB wrote: With as many stage rallys as there are around Washington it's hard to believe there isn't any rallycross.

Doesn't Steve Warren/Warren Rallysport run a bunch of rallycross events in Washingtong/Orgeon area?

kylini wrote: So yeah: this was FRIGGIN AWESOME. Placed 15th out of 47 and improved every run by 2-5 seconds. Not bad for 225/45-15 Rivals! I really don't know why I hated my first two events. Prep: raised the car by lifting the existing 7x550 front springs and putting 10x300s in the rear. Disconnected sway bars. Didn't bother with an alignment since the subframe is bent still.

man, with a course that smooth, you could probably just run a race suspension lowered, lol. I would kill to run on a course that looks that comfortably smooth :)

irish44j wrote: man, with a course that smooth, you could probably just run a race suspension lowered, lol. I would kill to run on a course that looks that comfortably smooth :)

There was a bump or three that were hard. As in, I'm glad my hardtop was bolted on the sides because the top latches popped off hard.

Course was 2 minutes long though! We had quite a few Nebraskans and a very fast car or two from Kansas and they were all thrilled. This was the site last year:

I'm really going to have to convert this into a builds/projects thread! Can a modmin move this?

So, DMVR has announced the next event is December 7th but we're still deciding if we want to go to Indianola (dirt/grass) or try Newton (gravel). Either way, I have some work to do to my car!

Before the first event, I learned that 12 in springs do, in fact, fit on Miata coilovers.

However, they don't clear the rear drive shaft without more compression (which I couldn't add before the event). Oops! I jacked up the front spring perches (7 in 550 lb/in) and put my "front" springs in the rear (10 in 300 lb/in) for the first event. For the second, I'm going to move the 10 in 300 lb/in to the front and put 10 in 175 lb/in in the back. Hopefully the fronts will take 10s better than the rear took 12s!

Other than that, I'm going to add thrust bearings to all my springs and I got an actual coilover wrench. Apparently, channel locks and a pipe wrench aren't good for aluminum.

Finally, here's a pic with the GRM sticker taken by Steve Wickersheim.

Wow, that's stiff.

I'm considering going back to stock 1.6 springs next year to try out. I need an engine first though.

Winter tires are finally on the car. 195/55-15 General Altimax Arctics. I'm not sure if rally tires would fit on 15s but I really can't complain about the price of these. Plus, our earliest rallycross is always in November and is usually below freezing.

Both front and rears have 10 in springs now: 300/175. Front is a few threads from bottom and is at about 6 inches pinchweld to ground. Rear is threaded up half way and is about 6.3 in to ground. If I launch seriously hard into my condo's parking lot (it can bottom out my boss' Boxster), I lightly hit the bump stops in the rear (not metal on metal; score!). I reconnected the front sway bar to help with the squishy sidewalls. It seems to handle nicely on the ice and gravel twisties around here in bumfudge Iowa.

So, I had some fun over winter and finally fixed the subframe this spring. After an autocross or two, it's time for another RallyCross! We're rocking a field near Ames, IA that's supposedly smooth (good!) but rain is expected (bad!). Time to test those snow tires!

I got the car ready today. 400 lb/in front; 225 lb/in rear. Front sway only. Squishy General Altimax Arctic tires.

kylini wrote: So, I had some fun over winter and finally fixed the subframe this spring. After an autocross or two, it's time for another RallyCross! We're rocking a field near Ames, IA that's supposedly smooth (good!) but rain is expected (bad!). Time to test those snow tires! I got the car ready today. 400 lb/in front; 225 lb/in rear. Front sway only. Squishy General Altimax Arctic tires.

what are the "actual" converted rates for those springs, out of curiosity? (e.g. what is the motion ratio for Miata suspension front and rear?).

I run 250# (actual, strut) front and 350# (with a .6 motion ratio, so equivalent to 225# rear) on the e30, which is about 10% heavier than a Miata (2200ish).

First, I haven't looked into actually calculating anything yet. It probably would be smart!

Second, according to Shaikh at FCM, a 2000 Miata would have motion ratios of 0.686 / 0.721 (F/R). If I'm understanding the calculation, that'd give me adjusted values of 274 / 162. The calculation didn't seem to care about height, just offset which I'm "normal" with my C1Ms.

I guessed the rates based on a touch of trial and error. 700 / 400 is popular for STR autocross (and works great on my car with a rear sway bar) so I gave 300 / 175 a go. 175 in the rear had coilbind issues so I needed something stiffer, so I switched to 300 / 225. This handled pretty darn well on ice but I wanted to try getting back to that 7/4 ratio, so 400 / 225 it is for tomorrow!

It's pretty snappy and neutral in the local skid pads (traffic circles) and isn't upset when I "skip" the turn (they have a lip for trucks to drag their trailer; handy for simulating a half-car upset at speed). I am deliberately raked back (rear is lower than the front slightly) because the front already has enough snappiness from the sway bar to turn in sharply. We'll see if it works off-road! If not, I've been getting a collection of springs from Craigslist to test.

Bad: I'm terrible at driving in the wet. Absolutely terrible.

Good: My codriver isn't and kept up with the pack. He requested rear sway bar next time to help rotate. If that doesn't do the job fully, we'll soften the front back to 300 lb/in.

Ugly: See pics.