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BLUE TII, you said you use that size and you don't have any problems? I know you're running a 0.7" narrower tire that's half an inch shorter than the 315 and you're otherwise stock (?), so that probably works quite a bit in your favor. I'm most surprised that you don't get any rub with half an inch more backspace in the rear. My best guess is that you don't use the same part of the suspension travel that I can get to with shorter dampers and that I have more camber.
I just finished off that set of 295/30-18 R888 on the 18x11 +45 on the RX-8.
When I went to the wider 295 R888 from the 295 Ventus TD I rolled the lip under on the fenders as a precautionary measure. Could do ST class with it as it maintained stock profile. Never had a rub on fenders and plenty of pics with car tucking wheel while turning.
Cannot quite get full steering lock- inside front rubs.
With +45 offset the rear wheel did rub the undercoat off the rear sheetmetal covering the shock when the suspension bottoms. If I was buying these wheels for an RX-8 and not my FD I would do the +43 offset (which I will do anyways fo rmy FD to get the Ultra Concave Face next wheel order).
I am running Ohlins on max low with max stock front camber available dialed in (not enough) and the rear is closer to minimum camber (happy with that).
For reference-
295/30-18 R888 Tire Rack says they are 11.8" section width and 11.2" tread width on an 18x10.5. They are quite square on 18x11
sweet! that brings the running annual "Going DSP next year" count up to a half dozen or so! The indeterminate future health of DSP is strong! Next year there will be even more "going DSP next year" soon it will be every RX-8 owner on earth who isnt Marc or Mike.
sweet! that brings the running annual "Going DSP next year" count up to a half dozen or so! The indeterminate future health of DSP is strong! Next year there will be even more "going DSP next year" soon it will be every RX-8 owner on earth who isnt Marc or Mike.
Oh you wound me sir! To the quick, I say.
Build will begin this year and it might make some locals. National level will be left to my STi
Hey guys, I've been running a half-prepped STX car for a while now but I've decided to get competitive with it... Looking at doing DSP since I'd rather spend the money on race rubber than overpriced street tires and half the interior stuff in the car is breaking anyways.
Current plans are... better brake pads, stainless lines, full poly suspension bushings, 18x10 RPF1s, 285 slicks, DIY aero, strip most of the interior out, racing seat, harness, custom single exit 2.5" exhaust with minimal muffling, and I'm sure I'm forgetting even more.
The one bridge I haven't crossed yet is doing proper suspension stuff(those things are expensive) and I'm currently running some low miles stock shocks with H-tech springs, which isn't ideal but whatevs. I'm planning on getting the progress tech sways at some point because I want to have the adjustability when upgrading as well as some adjustable end links to play nicely with it all. The next big question for me is what shock/spring combo is going to work best... which brings me to a question for you all, has anyone modeled the RX8 suspension yet?
I'm talking about roll centers, axle heights, motion ratios, weighed unsprung parts, track width, etc... I'm an engineer and like things to play by the numbers when they can and racecars is typically a place where they work out. If anyone has done this previously(or has some different software than I am using) that could save me(and us) a lot of work getting spring rates and the such properly squared away. If this hasn't been done I am doing the suspension bushings this weekend and can measure everything while I'm at it to give us something to work with...
I've read through this thread(most) and it has a wealth of knowledge already, I just want to help contribute and make this a relatively painless process for anyone looking at making the jump.
First, if your going to play in DSP you need your interior. Don't strip it out.
FCM has a worksheet with much of the info your looking for, but I don't have a link.
Ah yes, looks like the CSP Miatas play by some different rules... DSP does require an interior so it looks like all I'm pulling out are seats for some lighter ones. And thanks for the point in the right direction! I knew I had seen that info floating around before but couldn't remember where I had seen it. I will take measurements this weekend and compare them to the FCM stuff and see how they compare.
Ah yes, looks like the CSP Miatas play by some different rules... DSP does require an interior so it looks like all I'm pulling out are seats for some lighter ones. And thanks for the point in the right direction! I knew I had seen that info floating around before but couldn't remember where I had seen it. I will take measurements this weekend and compare them to the FCM stuff and see how they compare.
CSP miatas have to keep their interior too. I'm guessing you're thinking of them removing the soft top, which is allowed via the update/backdate allowance in Street Prepared (one Miata was produced with no soft top, so SP rules allow you to remove it). They can also backdate to a 1990 Miata which had a dash without airbags, for lighter weight, among various other things. You can find the full Street Prepared rules on SCCA.com.
I really want to join DSP with my RX8 next season.. the purple crack is strong.
I could have sworn I had seen two CSP Miatas running at one of our local events with no interior, and our old Mustang Lemons car was classed as a CSP car with nothing but bare metal in it, not even the original gauge cluster. But yes, reading the rules seems to say you can't do all those things so they will not be happening.
As far as suspension goes do a lot of you guys run the FCM setup? Are there any chock shops that will do custom valving out there that you prefer?
Local classing is always a bit like "mehh close enough" so you have things like carbon fiber hoods in STX and people with their underhood soundproofing panels missing from their engine bay and nobody gives a ****, especially if the driver sucks.
I havent seen many people on the FCM setup on here and Ive seen zero locally, but I'm on the east coast where its less common. There are plenty of STX RX8 fire sales to pick up a set of Ohlins DFV or KWV3 or something, Id just keep an eye out for one of those.
I'm a MechE also and believe me I wanted to do all the modelling and figuring stuff out for myself etc and even did some of it. but I ended up getting something that was similar to an FCM setup and paying almost as much for it. I gained a lot of knowledge along the way but if I had it to do over again Id have just bought some nice off the shelf setup.
You're coming to DSP, the world of $3500 a year tire budgets. You better be ready to invest heavily into the car from a mechanical standpoint. I have something like $5k invested in my own car at this point just in STX prep stuff, not counting the recent engine rebuild. I figure Id need at least $5k more to be passably prepped for DSP and just fast enough to lose to John V every event.
Just trying to warn you the class is tough and the costs are real. I and the rest of us im sure will be happy to sure what weve learned, just want you to have a sober view of the road ahead.
Thanks! I had found that article a while back as well and it has some good info for sure.
And in response to you Nathan, I am fully aware of what it takes... it won't be an immediate thing but I hope to have a competitive car after a season or two. There is a guy locally who runs a DSP E46 that does pretty well at national level stuff so I should be able to gauge my progress off of him hopefully, I just started sitting down looking at what it would take to get the car properly prepped for STX and realized that I don't use this car except for autocross anymore so I might as well take it a step further...
I really do hate taking people's(company's) word for things when they are trying to sell them to me. I know just enough to be dangerous when it comes to suspension math and I want to get darn close to correct the first go around if I can. Like I mentioned I hadn't dove into the suspension stuff yet because I haven't figured out the best route to go yet, I'd like something rebuildable so that I can have a shop tune them as I change things.
Current list of immediate upgrades are as follows:
Hawk HP+ Pads(going on this weekend)
Goodridge SS Brake lines(going on this weekend)
Energy Suspension Poly Bushings, all 18 of em(going on this weekend)
18x10 +38 RPF1s(here in about 2 weeks)
285 width slicks(going to run used ones for the time being due to cost and local events)
Corbeau Forza seat(within a month or so)
Takata 4 point detachable harness(only will be used at Autocross)
Spoiler/Splitter(will be made as soon as I have a free weekend)
If anything seems out of whack please let me know, and if there is anything I should be worrying about doing before these I am all ears as well.
Thanks for the links, those worksheets have a ton of relevant information in them!
My current step is finding some wide wheels for this thing... the plan was some 18x10 +38 rpf1s but I figured I'd ask here if anyone has a set of something similar or those exact wheels they would want to sell?
EDIT: Nevermind, ordered some this morning!
Last edited by roflcopter; 04-05-2016 at 06:44 AM.
Marcus Merideth is selling a set of PF01 in 18x10.5+38 with A6 already on them, I'm thinking I should just get them, sample the class and then sell if it's not for me.
Marcus Merideth is selling a set of PF01 in 18x10.5+38 with A6 already on them, I'm thinking I should just get them, sample the class and then sell if it's not for me.
DO IT!
I should have my RPF1s here this weekend, I have a set of used BFG G-Force R1 softs to throw on. I'll be rolling/pulling the fenders and figuring out how much caster I can run without scrubbing anywhere on Saturday hopefully... as well as taking measurements for aero bits. I'm getting legitimately excited now. First shake down event will be next weekend and I'll see how I like the class!
Marcus Merideth is selling a set of PF01 in 18x10.5+38 with A6 already on them, I'm thinking I should just get them, sample the class and then sell if it's not for me.
Marcus Merideth is selling a set of PF01 in 18x10.5+38 with A6 already on them, I'm thinking I should just get them, sample the class and then sell if it's not for me.
From my experience, I'd be concerned that you can't fit that wheel/tire under the fenders while keeping the car STX legal. It might just work up front, but even with maxed out rear camber, I think you'd have some trouble out back. Also, even if it clears the front fenders, it'll rub the hell out of your fender liners.
For anyone reading through at a later date I will cover what all I had to do to get them to fit nicely. Specs are 285/30R18 BFG Gforce R1 S on 18x10" +38 RPF1s all around. Definitely had to do a decent bit of fender rolling and pulling to keep them from making contact at the top, the rears don't look like they will clear the suspension cover thingy in the back but they do as you lower the car down.
In the rear I had to pull the plastic fender liner out(it could have stayed but I was rubbing through it quickly at the top) and cut the plastic tab where the bumper mounts as well as bend the metal part of the fender where it mounts. This was not completely necessary but it was making a teensy bit of contact there and I'd rather get it out of the way now. I will need to come up with an alternate method for affixing the corners of the bumper now, maybe those ricetastic rubber band things.
The front seemed to fit fine with the fender liners out and the fenders pulled/rolled, after doing a little driving I realized that they were in fact hitting that pinch weld behind the wheel. To fix this we ended up dialing in more caster and that seemed to solve the problem, I now have about 1/4" clearance there with the car sitting on level ground and the wheel turned where it is the closest.
This process has left me with a few questions... we picked up alignment equipment so we can tweak things ourselves now and after getting everything to clear the settings I ended up with seem a bit suspect. As the car sits now(and how it will be run at next weekends event I think) are as follows:
Front
Camber: -2.6 degrees
Caster: +8 degrees
Toe: 0.02" total out(was aiming for zero and figured that was close enough for now)
Rear:
Camber: -1.9 degrees
Toe: 0.00"
From previous posts I figured I would need LESS caster up front to fix the issue with the pinch weld not more, but that made the issue worse and I ended up cranking it up to make it all clear. I would like to run a bit less but got tired of tweaking it yesterday. I was surprised with the amount of front camber my car could get with that amount of caster as well, maybe I am measuring things slightly wrong or have my turn angles incorrect for the caster... anyone have some input on that?
As if this post wasn't long enough, here are some pictures of the process and end results:
Did my first event in DSP last weekend, I think it went pretty well. The car is a lot quicker with the bushings/brakes/wheels/tires but it definitely highlighted some issues that will need addressing before the car can be properly fast.
First issue, I need more suspension(I knew this going in). The spring rates are no where near high enough and I'll need shocks to match. The relatively stock setup I had been running just can't handle the forces I'm throwing through it, in the slaloms I could essentially drive the car through the turns faster than the weight could transfer. This ended with me plowing a cone due to the car just refusing to turn at one point. In the corners it wasn't as bad since the weight transfer happens slower. I want to do things properly and have been looking at both the FCM and Ohlin setups available and plan to do that sometime towards the beginning of next season. On that note, is there any stop-gap measure I could take that wouldn't set me back a whole lot but at least make the car a bit more competitive in the mean time? Just doing springs on the stock shocks? Single adjustable shocks with the rebound cranked way up? Please let me know if you have any ideas.
Second issue, I need to do more fender pulling. The front was rubbing pretty bad on full compression. Easy fix.
Now for the good stuff, the alignment seems pretty good. A tad understeer-y in the slow stuff but oversteering slightly in the fast stuff and I took tire temps after a few runs and it seemed I have almost enough camber, which means trying to slot things or find acceptable control arm replacements can be put on the back burner.
I definitely need more seat time with the new setup, the margin of error has become a lot smaller and the intricacies of the car have changed quite a bit. I should have aero sorted out in a week or three and I have another event this Saturday to try and learn the car a bit more.
On that note, is there any stop-gap measure I could take that wouldn't set me back a whole lot but at least make the car a bit more competitive in the mean time? Just doing springs on the stock shocks? Single adjustable shocks with the rebound cranked way up? Please let me know if you have any ideas.
Not to be too self-promoting, but I'll be selling my old coilovers pretty soon for cheap. They're just Koni Yellows that I made adapters for and modified a bit to accept 2.5" ID coilover springs plus sphericals in the lower mounts of the rears. They worked great for me in STX trim, and I found that my car worked really well with just a set of R compounds slapped on to run DSP with no suspension changes from STX trim. Feel free to send me a PM if you're interested.
My opinion on the two options that you've suggested is that neither one will really be worthwhile because you really need more spring for that much tire and more spring will necessitate more damping.
Also, I'm surprised that you had tire rub that can be fixed with more fender pulling. Where is it rubbing? I have the exact same tires on the exact same wheels and they fit inside the fenders with just a roll.
Last edited by Kennetht638; 04-20-2016 at 01:10 PM.
02-26-2016, 08:21 AM
