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I saw you out there briefly Mike but you were between runs and I didn't want to break your vibe or anything. Great job on the 3rd place finish, DSP is a tough class. I was rooting for my fellow DC brethren and former RX-8 guy John V to win but after he coned away the whole first day I was pulling for you :-)
Next year I'll find time to say hello, or maybe I'll see you in NC sometime.
has anyone tried just running 245's on 9" wheels? I'm curious about diminishing returns on tire width.
So the old Rick Ruth R-comp multiplier was 0.975 which is basically the difference from STX to DSP: 831/855=.972 so close enough-ish so I do understand that the new class of street tire is closer in performance now but it seems like I should be able to just install same size Hoosiers on my STX car and PAX similarly, and the rest of the SP allowances will just serve to make me more competitive in class.
got a little side tracked there. Anyway, I'm wanting to challenge the notion that "you just need to stuff as much rubber under there as possible" and I guess the only way to do that properly would be to test on the same car some 245/45/17 A7's on 9" wheels on the same car as some 285/30/18 on some 10" wheels and see what the difference is.
Such a test is too rich for my blood, but anyone have any experience/anecdotal evidence?
Some past road racers claim 245 on 9" is more than enough, but they typically don't see the same level of tire loading delta that an autox vehicle does. I had the same thought myself at one time, but the wider is better philosophy has basically proven out in the SP autox category. The exception is that at some point you can't go wider without also going taller (larger OD), which combined with also increased wheel weight to fit them properly has a greater impact on a low torque application. The 275/40-17 and 285/35-18 option maintains the 245 OD. The 295/35-17 and 295/30-18 option starts pushing the envelope, 315+ is not likely to be beneficial without a power adder like FI, more rotors, etc.
I have a pallet stacked full of slightly used 245 RR slicks sitting in controlled storage that I plan on use with 9" wheels for local stuff just to save on Hoo$ier cost$
I think in general a comparatively narrower tire will be optimal for road racing than for autocross, due to the differences in percentage of time spent cornering, where the extra grip helps vs. going straight, where the extra drag hurts.
Brian Goodwin's been quoted as saying that his testing showed that 275's were faster on tighter road courses, whereas a 255 was faster on faster tracks.
Alright so I talked to John V about 17x10 vs 18x10 some, he seems to think I'll end up on the 18's eventually anyway, so I might as well just get those from the outset(plus this means I'll have the option to screw around locally on the low run 285/30/18's that he doesn't want anymore heheh)
I'm looking at what's available out there, I found Forgestars to be well recommended.
Options from them are (EDIT:found weights)
F14 18x10+42 20.3#
CF5 18x10+50 21.0#
the weights are quoted from a distributer, and I saw guys weighing sets on scales and have +/- a few tenths from this value http://www.americanmuscle.com/glossb...8x10-0512.html
I've seen comments on offset from Team, but am not clear on if it's a scrub radius issue or a fitment issue. the 42 seems pretty close to the +38 RPF1 that gets poo poo'd on here so I'm thinking once I have weights and prices(edit: non issue, price is the same for both) I'll have to determine if the 8mm of offset is a 'gotta have' or a 'nice to have'
If you guys have looked into this yourselves Id love to hear your thoughts.
EDIT:: Ok so I looked around on the forum some more and found some good threads on the issue, I think I just need to go with the +50 (which suck cause the F14 looks like sex)
Last edited by Nathan Atkins; 11-09-2015 at 03:20 PM.
Reason: added weights, searched and found shit, who knew?
I've seen comments on offset from Team, but am not clear on if it's a scrub radius issue or a fitment issue. the 42 seems pretty close to the +38 RPF1 that gets poo poo'd on here...
Where did this happen? I've been running those RPF1's with 285/30/18 BFG R-1S's and they work just fine. There is evidence of rub in places that a higher offset would still have it, but for autocross, they function perfectly well. The only real hit that I took was losing a bit of steer at full lock so it's harder to get around paddock and it's a not as easy to catch GIGANTIC slides or to drift. When I got my wheels, I considered the 18x10 D-force and Forgestar options from Vorshlag, but I didn't really want to buy from them and I like how the Enkeis look better anyway so I took a gamble on it (also based on the fact that I think Mike ran 18x9 +20-something wheels on his at some point) and it worked out with just rolling the fender lips. You can see a picture of it on the first page of the thread.
And since we're on the subject, does anybody know of any decent higher-offset 18x12's (I'm also maybe open to 11's)? I'm considering going the Forgestar semi-custom route or getting some reproduction Corvette C6Z rears and bolt pattern adapters. The Rota P45 18x12 +20 may be ok because it puts the inside about where an 18x10+45 would be and that's probably only a few millimeters from the maximum amount that I can push inward, but I'd rather start tighter and add spacers than to start with known extra clearance and have nothing I can do about it.
Last edited by Kennetht638; 11-09-2015 at 04:35 PM.
And since we're on the subject, does anybody know of any decent higher-offset 18x12's (I'm also maybe open to 11's)? I'm considering going the Forgestar semi-custom route or getting some reproduction Corvette C6Z rears and bolt pattern adapters. The Rota P45 18x12 +20 may be ok because it puts the inside about where an 18x10+45 would be and that's probably only a few millimeters from the maximum amount that I can push inward, but I'd rather start tighter and add spacers than to start with known extra clearance and have nothing I can do about it.
Since we're in the same boat, the only thing I've been able to find are the following:
Forgestars F14 (same issue with Vorshlag, but the price and weight is hard to beat) (~22lbs) +37 [ie. custom]
SSR Professor SP1 (~22.9) +37
SSR Professor MS1
SSR Professor MS3
RAYS Volk Racing TE37SL (~19.7lbs) +37
Each of the SSR / RAYS are between $700 and $850 per wheel. The Forgestars are around $350 per wheel, though. I think Evasive Motorsports has them for that price, which is the same as every other place (I think American Muscle might have something similar, but haven't looked around closely). Finding used Forgestars for a reasonable price is pretty easy, but everyone is running staggered stuff and stuff that has an offset that's too low.
When my car is "done", I'll probably grab a set of RAYS because by that point, it'll all be incremental gains. I'll be starting out with a set of Forgestars later this year, I think. They do look pretty great:
Now, with that being said, there's nothing like the classic Volk look on a JDM car:
Since we're in the same boat, the only thing I've been able to find are the following:
Forgestars F14 (same issue with Vorshlag, but the price and weight is hard to beat) (~22lbs) +37 [ie. custom]
SSR Professor SP1 (~22.9) +37
SSR Professor MS1
SSR Professor MS3
RAYS Volk Racing TE37SL (~19.7lbs) +37
Each of the SSR / RAYS are between $700 and $850 per wheel. The Forgestars are around $350 per wheel, though. I think Evasive Motorsports has them for that price, which is the same as every other place (I think American Muscle might have something similar, but haven't looked around closely). Finding used Forgestars for a reasonable price is pretty easy, but everyone is running staggered stuff and stuff that has an offset that's too low.
When my car is "done", I'll probably grab a set of RAYS because by that point, it'll all be incremental gains. I'll be starting out with a set of Forgestars later this year, I think. They do look pretty great:
Now, with that being said, there's nothing like the classic Volk look on a JDM car:
BTW, XXR 531 18x11s look to be reasonably priced, heavy and a spacerable offset (+20).
BTW, XXR 531 18x11s look to be reasonably priced, heavy and a spacerable offset (+20).
Yeah, the XXR's were my first thought because they're so ridiculously cheap, but on the presumption that an 18x10 +50 will fit, you'll get the narrowest car with ~7.5" backspace, which works out to 18x11 +38 or 18x12 +25. The XXR's would make your car nearly 1.5" wider than it needs to be which I'd rather not do, though it will still be 0.6"narrower than I'm planning to be with 12's. I may just cheap out and get the Rotas and sacrifice 10mm. I'm gonna pull off the brake rotors to check clearances on the Enkeis at ~+44 to see if it even makes sense to go much higher offset than +20 on the 12's.
Originally Posted by dannobre
How do you expect to get 18x11 +20 to fit for an autocross setup with proper camber??
Since we're in the DSP thread, you would obviously just remove anything that gets in the way.
LOL....figured. unless you have access to some nice fender flares I didn't know about 😊
Well, you can fender flare anything But like Ken said, this makes a REALLY wide car and we all know that's one of the banes of Solo. I kept trying to find a reason to use them b/c they are so damn cheap, but just looks to be a pipe dream. Honestly, the Forgestars are a good deal for what they are (being the cheapest of the usable 18x11s) and none of them are terrible considering how much you see RAYS / SSRs going for in the "used" market.
One more wheel option that I didn't know existed until now is this (semi-custom?) Enkei PF01 18x10.5 +47. It doesn't show up on Enkei's website for some reason but I'd feel pretty good about running 285's on these with a roll.
I was recommending that size on RX7club for an off the shelf FD wheel after seeing them on Mustangs, but the FD people were telling me it was a limited run and they couldn't get them.
---------
Sorry I don't have an exact weight on my Forgestar F14 18x11 +45 that I am running on my RX-8 with 295s, but it was 21lbs and some oz (told under 22lbs) when I weighed them at a postal center (no valvestem, no center cap, no weights).
I imagine weight will vary as that is a big wheel with a lot of surface area and they are powdercoated wherever Forgestar can get them done in my experience.
A true racer would order them raw for maximum weight savings and anodize or passivate them (cheap cheap).
They now offer 18x11 +43 F14 in Super Deep Concave, so I will go with that on my next set for some extra BLANG. And in Gold, because I am no true racer.
I am running 295 R888 on them now and they are nice and wide, square tires with an awesome sidewall. OFC the grip sucks compared to even the Ventus TD...
To my understanding, more tire is almost always better, within reason. I'm still new to RX-8's, but in the world of Miatas running CSP, they've found that the more Hoosier they can stuff under there the better. They are maxed out at 275's in the 15" size, and the cars only weigh ~2,000lbs and are significantly less powerful at ~140whp. An RX-8 making around stock power of ~190whp at stock weight of 2700 is the same power to weight ratio, but I imagine in DSP trim the RX-8 should be making into the 200's for WHP and getting the weight down a little more to result in a better power to weight than a CSP miata.
That tells me that the RX-8 could benefit from more than a 275 based on the better power to weight ratio (more ability to lug around a heavier tire) and the heavier curb weight (so even more capable of heating the tires up). I'm actually surprised you guys are only running 295's. Can you not fit more than that?
Has anyone built a DSP legal RX8 engine to the max of the rules yet? What kind of power did it make?
I'm actually surprised you guys are only running 295's. Can you not fit more than that?
295 is the max width without making the track wider than the original fenders (making the car wider) and also the max on stock profile fenders (if you wanted to be able to go back to Street Touring.
RX-8 has over fenders available or fenders could be pulled to fit any width wheel/tire made
The SSM FD RX-7s do pretty well and most those are running overfenders and 315/335s (they are limited to ~25" tall tire up front).
RX-8 is a better platform than the RX-7 and able to fit 26" tall tires in any width, but no one has developed the chassis the way the FD guys do.
Sadly the RX-8 doesn't seem to inspire the same passion as the FD.
Ok, I did some tire/wheel fitup work over the last week or so and the situation isn't as good as I would have liked but I haven't seen much info shared publicly so here's what I got. Maybe others have tried this already and have some insights. I have available to test fit:
285/30/18 BFG R1-S on 18x10 +38 (7" backspace)
315/30/18 Hoosier A7 on 18x10.5 +30 (6.93" backspace)
Here's the width difference between them:
The 285's on 10's fit with a roll as I posted on the first page of this thread. It actually fit in the front without rolling the fenders when I did a clearance check, but a full opposite lock slide by my co-driver put a cut in the tire, so I ended up rolling the fronts too. Also, full lock is limited by the tire hitting the control arm and not by the steering rack so (non-autocross) parking lot maneuvers are a little tougher. I have evidence of rub in a few places on the inner fender: At the top right next to the shock mount, in the back on the pinch weld that sticks forward into the wheel well (behind the fender liner), two small spots inboard of that pinch weld, the front of the fender liner that attaches to the fascia and on the LCA as I already noted. So not a lot of room, especially considering that I want to add an inch of wheel and more than an inch of tire.
Just bolting on the 10.5's and 315's (dampers are off so I can cycle the suspension):
These aren't very close to fitting under the fenders at all. Which was 100% expected. The +30 offset is obviously too low, but a 12" with the same backspace would stick out a lot more, so it still works as an indicator for me. However, turning the front wheel reveals that the tire hits the pinch weld on the back of the wheel well (just as Zelse warned me about), and it's not just a rub. I actually can't turn the wheel past that point, which is about 270 degrees of steering wheel rotation. So I guess 12's are out of the question.
Next thing to try is removing the brake rotor to get another 7mm of offset. The 315 still doesn't tuck under the fender in the front, but it's very close. It hits the corner marker pretty bad with some steer though, so pulling the fender would require pulling the fascia outwards quite a bit.
However, it still hits some very structural sheetmetal at about 450 degrees of steer when the wheel is at 12" from hub center to fender. It also looks like there's still some room to the inside.
The 10" wheel with 285 allows me to steer until nearly full lock, and runs out of vertical travel maybe a quarter inch higher.
In the back, it's also pretty close to tucking into the fender, but would definitely require a pull.
In the rear, outboard space is pretty much unlimited, but widening the back of an autocross car kinda sucks, so I'm not considering stagger just yet. However, this is a good opportunity to see what the max backspace I can run is. The 285 on the 10 with no brake rotor effectively has a 7.27" backspace, and that looks like the maximum to me (not the most excellent photo, but all the black stuff on the left is wheel, and the thing on the right is where the shock top hat goes in. Also at 12" from hub center to fender):
So in conclusion, I'm probably going to order some Forgestars in 18x11 +45 and play with spacers to optimize offset. I'm also going to have to limit steering a little bit (which would likely put the turning radius in line with the Corvette I was driving last year) and maybe even raise my ride height ~0.5" but hopefully not that much.
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.
That's my oversized post about tire fitment, so hopefully it helps somebody. I'd also love to hear any input from anybody who has tried and succeeded or failed in this department before I spend a bunch of money. I'm going to take a few more measurements tonight, but I'll need to order pretty soon if I'm going to have this stuff ready to go for this season!
Last edited by Kennetht638; 01-05-2016 at 09:36 AM.
So on the front, is it only making contact in the back of the fender? Could you play with caster settings to make it fit? Also, considering you can get 270 degrees of steering wheel turn, are you considering just adding a steering limiter?
That's awesome that you can fit a 315 in the rear so easily.
So on the front, is it only making contact in the back of the fender? Could you play with caster settings to make it fit? Also, considering you can get 270 degrees of steering wheel turn, are you considering just adding a steering limiter?
That's awesome that you can fit a 315 in the rear so easily.
Tamra
Both the narrow and wide tires rub the fender liner in the front of the front wheel well too but there's no metal behind it, and the wider tire rubs the fascia but that can be moved too. I'm already at minimum caster so I can't gain any more with the factory adjusters, but I'm going to play with moving the UCA forward a little bit to see if that does enough to matter. Otherwise, yeah I'm just going to put some steering stops in to keep it from going to full lock.
Alright, Rotards. Who is coming out to do some ProSolos this year? Marc? Mark? Mike?
We're down at least one driver in DSP for 2016 and it would be great to have a full class at the east coast events and not constantly get bumped. Out of the whole RX-8 DSP community I've only seen Marc come out to a Pro. What's the deal?
Alright, Rotards. Who is coming out to do some ProSolos this year? Marc? Mark? Mike?
We're down at least one driver in DSP for 2016 and it would be great to have a full class at the east coast events and not constantly get bumped. Out of the whole RX-8 DSP community I've only seen Marc come out to a Pro. What's the deal?
09-14-2015, 08:08 PM
But like Ken said, this makes a REALLY wide car and we all know that's one of the banes of Solo. I kept trying to find a reason to use them b/c they are so damn cheap, but just looks to be a pipe dream. Honestly, the Forgestars are a good deal for what they are (being the cheapest of the usable 18x11s) and none of them are terrible considering how much you see RAYS / SSRs going for in the "used" market.
