Rallycross tire choice

I think I'm going to put together a different suspension setup so I can use my 240SX track car to run rallycross events. It will just be a set of Bilstein HD and taller softer springs so I can run the car around stock height.  Swapping the complete shock and spring assemblies out will be pretty quick. I don't have space for another car to use for rallycross so this is it.  The car is pretty light with a half cage, Cusco RS diff, and super responsive efr turbo.  I think it probably makes around 300 wheel horsepower on minimum wastegate pressure, but it is very responsive so I can easily drive it at part throttle and not utilize the full power.

My local Milwaukee scca chapter is running events at a place that has a tarmac kart track and a dirt track, so it is a mix between dirt and tarmac. What kind of tires should I run for this?  I have seen snow tires, gravel rally tires, and truck AT tires recommended for rallycross.  I would also like to do some ice / snow autocross events which would give snow tires the nod.  it seems like they would just get obliterated running on tarmac though. Does anyone run in a venue like this?

https://youtu.be/DIelzOZMH5U

The other caveat is I have Wilwood brakes with  12.2" rotors in front, so the smallest wheel I can run is a 16. I see that braid has a 16 x 7 Fullrace A that clears the big brakes on Evos and STIs so that would work. The Sparco Terra also comes in 16 x 7, unsure of brake clearance, and I already have a set on our CX5 so I'd rather not double up.  Rally tires are extremely limited in 16" sizing. There is a 205/ 55/ 16 Maxsport which would fit the car great.  Snow tire selection in reasonable sizes is excellent. I think the Geolander comes in a 215 60 16 which would probably work fine.  

Do not run softer springs.  Run stiffer.  In my experience, 200-250lb-in wheel rate is great for the front of  most cars in the 2400-2800lb range no matter what drive type, and rear rate should be 75-100% of that for a rear driver, or stock rate for a front driver.  This is assuming you keep the swaybars, if you take them off then you will need more spring, but IMO it won't handle as nice.
 

We used to run an asphalt/dirt combo course up at the SuperRallycross series that Team Illuminata was hosting/sponsoring/perpetrating.  The fastest cars were on autocross tires.  They gave up very little on the dirt and they made up lots of time on the asphalt.

(GopPro footage - $30 security camera plugged into a $25 VHS unit ziptied to the passenger seat! Tires are BFGoodrich Sport Comp2s)

Note that Euro style rallycross cars run extremely gummy slicks, even though they are running on gravel.  I remember someone actually brought a set of Colway rallycross tires to an SCCA RallyCross event, everyone was pushing their fingers INTO the rubber, it was more like a dense foam than what we normally think of as tread rubber...

Found the compilation video I was looking for.

(Bonus Knurled start-worker content at 7:12)

The neat thing about being in Michigan is that it is close to much of the population of Canada, and there are lot of Japanese imports in Canada.  There was an R32 GT-R and a Pulsar GTi-R rally car there that day.

The interesting thing about this race series (and there was a whole series) is that you were not running for time, you were racing against someone else who started opposite of you.  And you had to STOP at your start position.  So there was a lot of tire smoke and locked brakes involved.  Way loads of fun.  Wish we could do it again, but there was never enough interest.

I'm going to agree with Pete on the stiffer springs, as I raised spring rate on my SRT4 PF rallycross car to get it to respond well on the dirt and to not be bottoming out the suspension.  With the US Air site, this is even more applicable with the large tarmac sections.

For tires, I would stay the heck away from truck AT tires as the compounds are just too hard.  With the dirt sections being clay up there (correct me if I'm wrong), an autocross tire would probably do really well.

If you want to go to rally tires, there is a 17" made by Indy Sport, available through Rally.Build. It likely is not the correct tire for US Air.

If you ever want to try other venues, Iowa Region (my region) hosts an event essentially every month, year round.  Our main sites are about 4 hours from you.  There's also Stateline Rallycross that hosts events in Byron, IL, but they are not affliated with the SCCA so the rules are a bit different (no cumulative times, metal posts for course markers, etc)

In reply to FooBag :

I think I ran against you at Nationals in 2016.  200lb-in in the front of my S40, with sway bars, and the rear shocks set to full soft, was PERFECT. But the tires I had were just not good enough for the conditions.  (I bought better tires for 2017, and am forever pissed off that I wasn't able to make it in 2017, and I don't own that car anymore)   My opinion on a front driver is make the front springs stiff enough that it doesn't bottom out, leave the damping just soft enough that the tires stay in contact without stuttering, and the rear suspension should be as soft as possible so it never upsets the front.

Leon Drake also knows this, if you've seen his cars move...

You are correct, we did run against each other.  We were also on that protest committee as well.  :-/  You didn't miss much in 2017 as the event had many problems and the site didn't hold up, at all...

The SRT4 has such a crappy turning radius that we have gone quite stiff in the rear and still have the rear sway installed to get it to rotate very easily for tight corners.

PF should be interesting this year with Leon bringing a CRX Si.

In reply to FooBag :

Crappy conditions are my forte.  I was doing VERY well in PF that year until the course dried out.

IMO, tight corners are for handbrakes or entering fast enough to counter-flick it through.  But that is just me.

I ain't 'fraid of Leon.  On the other hand, I think I have my MR car "fixed" right now, so I might make another shot at being the fastest rear driver at Nationals.  Was second in 2011, third in 2012 and 2014...  (Car was fastest in 2011 and 2012, and second fastest in 2014.  But I'm MUCH faster NOW.  And I don't think I will allow Will to drive my car again, he is some kind of RWD God :( )

Knurled. said:

Do not run softer springs.  Run stiffer.  In my experience, 200-250lb-in wheel rate is great for the front of  most cars in the 2400-2800lb range no matter what drive type, and rear rate should be 75-100% of that for a rear driver, or stock rate for a front driver.  This is assuming you keep the swaybars, if you take them off then you will need more spring, but IMO it won't handle as nice.
 

 

We used to run an asphalt/dirt combo course up at the SuperRallycross series that Team Illuminata was hosting/sponsoring/perpetrating.  The fastest cars were on autocross tires.  They gave up very little on the dirt and they made up lots of time on the asphalt.

 

Thanks for the input.  That's around what I was thinking for spring rates.  I meant softer then what's on the car now for road course R comp usage.  I think they're around 500/400.  Stock spring are really soft, around 120 lbs/in IIRC.  Motion ratio is pretty close to 1.  I can try it with the sways hooked up if that will help it drive better.  They're not massive.  

I have a set of wheels with Hankook RS3s, could give these a try.  

In reply to turtl631 :

Do it!  You will be much happy.  And since you have an S14, I assume that you can pitch it sideways like some sort of drifter god when necessary, so you won't need to resort to chassis set-up compromises like the rest of us need when it comes to making the car go where we want it to go,\.

The car is set up pretty neutral, but it rotates nicely especially at lower speeds where the wing isn't doing much. There will be a little weirdness raising the car because it has roll center correction with drop spindles but for just getting out there and having fun, I'm sure it'll be fine. Goal here is to enjoy the car and events, not assemble a winning purpose built rallycross car.

You'll have fun. I just did my first event in my BRZ and was one of the slowest cars there but had so much fun. I was running Altimax Arctic snow tires but the whole course was dirt.

I'm no RX expert...far from it.  But have shopped tirelessly (pun intended) for appropriate tire for my Porsche 911 "safari" build. Leh Keen runs BFG MO2 A/T TIRES in 215x65x16 on his builds with lifted suspension.  I considered that but major downside was that tire is HEAVY...35 LBS.  Besides I wanted to run 15 diameter wheel. I considered geolanders but they, too, we're heavy and not very agreesive tread. 

geolanders AT

I ended up with General Grabber A/T in 205x75x15 and onl y 25 lbs.

Compared to 255x40x17 used on street.  24.8 vs 27" height.  I think smallest in 16 is a 225x60x16.

Paul Eddleston, teamilluminata on here, is RX ING a 911, BUT is building an Audi RX car similar in size to your car.  He runs true rally tires in 195x60x 16 or 195x65x16.

He's a really nice guy and I think he would be happy to discuss by phone your options as I think he has gone down this road experimenting with snow tires.

I considered snow tires due to size availability and tread patter, but living in deep south and my plans to use both on and off road may use of snow tires a no starter.

All this rambling and I could have just said "Better call Paul."

AT truck tires have lugs but what they do not have is good rubber compound.  On dirt, like asphalt, slicks with good rubber compound will be better than hard rubber of any tread design.

Interesting, I thought having chunky lugs was more important on dirt.  That's just intuition though, no facts. 

So at this point the plan is Evo 8/9 Bilstein HDs with 240SX strut mount brackets welded on, coilover sleeves with springs around 300 front and 250 rear, sways attached, and my 17x9.5 wheels with 255/40/15 Hankook RS3.  It's tempting to just try it with the current suspension but the springs are closer to twice those rates, it's fairly low, and it sounds like Konis don't handle rallycross great.  Too many things to fail.  

I guess I'll just cross post the link to Nissanroadracing about this.  The most current discussion starts with post 8.  Any further thoughts on springs from the guys who do this currently? The dual spring idea is intriguing.

http://nissanroadracing.com/forum/universal-discussion/general-chat/6334-ice-autox-rallyx-etc-car-build

The Grabber A/T2 isn't a terrible rallycross tire.  Compound is a bit hard, but I've seen a good driver on A/T2s be right at the pointy end of the field with the good drivers on rally tires or snows.  

How much rubber compound vs tread pattern matters will really depend on the dirt.  The looser or muddier it is, the more tread will matter.  As it gets more packed, compound will start to matter more.  

Paul does not run 16s rally tires only come up to 15"

VERY RARELY you will find a 16" to this day it doesn't make sense because everything comes with 20" wheels these days...  usually if they are 16" Its a re-tread as well. 

I'll try my summer tires.  I may end up getting a set of stock spindles and smaller brakes for the front, and could then run 15s which opens up the options.  Could do this with snows for the winter events.  My front spindles are drop spindles for roll center correction which may make it difficult to achieve reasonably high ride height.  If I put together a separate set of spindles with brakes and strut assemblies attached, I could swap out with just 3 fasteners up top for the camber plates, 1 for tie rod, 1 for lower control arm ball joint, and then brake line.  Would just need to set toe to reasonably align.  

If the course is more than 20% tarmac and the dirt and gravel sections are dense hardpack, definitely run the best autocross tire that you can find in the size. Honestly, on hardpack they're often a faster option than snow tires anyways, it's not until you get into mud and wet clay where snows pay dividends. 

Yeah we sometimes run dirt oval tracks and on dry days an autocross tire or all season is just as fast (or faster) than a gravel tire.

In reply to fidelity101 :

Not last weekend at Oak Shade    The dust was intense, I think the best tire choice would have been an industrial vacuum cleaner mounted to the front bumper.

(I said I wouldn't but I did. Also, funny trivia, the last time I posted a rallycross video of me in my AWD car, Burke was riding along.  That's Burke's daughter, he asked if she could ride along and I never turn down ride alongs.  Also, that car launching at the start of the video is Burke, he has an Evo X now.  Much nicer than that Civic...)

I still wouldn't want to run a gravel tire, as they'd get shredded after like four runs.