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The Official "RX8 in DSP" Thread

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The Official "RX8 in DSP" Thread

Old 04-01-2014, 04:52 AM
  #101  
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Originally Posted by TopGear8
Ran down in Altanta yesterday with the Racing Beat sway bar back on the rear. The car transitioned better but i'm still getting a little bit of push on corner exit..

Here's the video.



Mike Kuhn Racing Atlanta SCCA Points #3 - YouTube
Too much front rebound?

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Old 04-01-2014, 11:37 AM
  #102  
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Could be too much front rebound, After adding the stiffer rear sway I upped compression and rebound in the front. I'll take some rebound out and see how that makes the car feel Saturday.

I also had my fastest run this past weekend running 27-26 front to rear pressures in the 285 hoosiers. I might try to run the same pressure all around to see if I can get better rotation out of the car.
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Old 04-02-2014, 08:31 AM
  #103  
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Howdy,

So it's probably early days yet but...

How much "sense" do these cars make in "nationally competitive DSP trim"?

Any weak parts like wheel bearings or whatever that when you use SP allowances you start breaking but aren't allowed to fix within the ruleset?

Can you make the power you want for DSP without spending a gajillion dollars?

If history and my level of "want a change" is any guide, I'm not going to be in a CS RX-8 long term. Moving this car to STX or DSP is a strong possibility vs. getting something completely new.

Mark

(note: I'm only interested in a car that can win the Solo Nationals if driven well.)
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Old 04-04-2014, 07:36 PM
  #104  
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Hopefully the S2 manual trans will resolve that issue. Otherwise the only weak link seems to be the engine; longetivity and torque. My rebuilt motor made some decent low end torque numbers on the engine dyno (for a NA rotary engine, still no where near the typical BMW values).
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Old 04-04-2014, 07:41 PM
  #105  
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Originally Posted by TopGear8 View Post
Could be too much front rebound, After adding the stiffer rear sway I upped compression and rebound in the front. I'll take some rebound out and see how that makes the car feel Saturday.

I also had my fastest run this past weekend running 27-26 front to rear pressures in the 285 hoosiers. I might try to run the same pressure all around to see if I can get better rotation out of the car.
If its a shock transition issue you would want to increase front rebound and decrease rear bump, the counter effect is that it might increase understeer on corner entry transition.
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Old 04-13-2014, 01:20 PM
  #106  
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I auto-x my completely stock '04 automatic RX-8 when my FD RX-7 is down and I found the wheels and tires from my ASP FD fit the 8 fairly well.

18x11 +45 Forgestar F14 with 295/30-18 Z221 Ventus TD front&rear.

Wheels are just under 22lbs and cost under $1,500.

Front scrapes rim a bit on lower arm at full lock and the rear scrapes the shock/spring cover a bit on full compression with over -1 camber.

I found they are quite strong as I wrecked my FD and bent frame at ~8 degrees both sides, bent forged lower arm back 1.5" , bent spindle upright. Wheel was fine except for minor scratches- still perfect run-out amazingly!

Just putting another option out there for you DSP guys because I know from my FD that nothing past 10.5" width is easy to find in our offsets and Forgestar is available in many widths and any offset you want.

With a roll/pull on the fenders it looks like the 8 could take 18x12 +30 with 315 front and rear.
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Old 04-13-2014, 01:33 PM
  #107  
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Race tires tend to run bigger than street tires. On my RX8 a Hoosier 295/30-18 on an 18x10.5+43 rubs more than a little bit on the front ...

https://www.rx8club.com/series-i-whe...8/#post4327576



.

Last edited by TeamRX8; 04-13-2014 at 01:43 PM.
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Old 04-14-2014, 01:37 AM
  #108  
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I believe the Hankook Ventus TD Z221 were the fastest DOT-R time attack tire last year, but your point that tire widths vary by make and model is valid.

295/30-18 Hoosier A6 is 295mm section width and 274mm tread width.

295/30-18 Hankook TD is 304mm section width and 280 tread width.

On the 18x11 +45 I had zero rubbing on unmolested front fenders even with stock -0 degrees front camber and now with -1 deg front camber it is tucked 11mm in further. I was auto-x ing on stock suspension so it was healed over on the bumpstops.

I did have to roll the rear fender lip under flat as it was catching on the tire sidewall slightly with -1.5 deg camber.

I know I stumbled across a good fitment for the RX-8 when I moved these 18x11 +45 with 295 over from my FD and that is why I am posting it here to share it with RX-8 enthusiasts.

I will cross post to that thread you linked as I see that RX-8 owners are suffering from the same misguided thinking as the FD RX-7 owners and putting skinny wheels/tires with the wrong offset on their cars and calling it "aggressive".

edit- or not, because that thread is closed...
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Old 04-16-2014, 06:31 AM
  #109  
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With unrolled front fenders it was gouging rubber off the outer corner/sidewall area just driving it around in the bumpy parking lot where I store the car. Straight line is not so much an issue. When the front wheel is turned it puts the tire into contact position with the lip because its sticking out so far to the outside already in the straight ahead position.

You say your tire is wider, less camber, and on a wheel sticking out 1/4" further (probably taller too) and is no problem. Well that clearly doesn't match my own experience.

Last edited by TeamRX8; 04-16-2014 at 06:36 AM.
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Old 04-18-2014, 08:44 PM
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Are you also running max negative front camber?

I realize I am running less static negative camber, but with camber gain is it possible I have more negative camber at the point you are having clearance issues?

Perhaps it is only because I am at stock monster truck ride height that I am not having any rubbing issues up front.

Thought it rubbed the rear just fine and braking/turn in should be the highest suspension loading. Friends tell me it rolls like a ship at sea.

One point only because you mentioned wheel width-

It is wheel offset that centers the tire between the suspension on the inside and the fender arch on the outside and my offset is a tad more favorable toward the fender arch than your own.

I realize in this case my tire spec is wider negating this.

My 12" wide 18x11 wheel is the same width as my tires section width, so wheel width is not an issue with fitment.

Even if the wheel were slightly wider, it is usually not an issue to outside fender arch clearance (though could be inside to the suspension) as when the suspension compresses enough to tuck the wheel into the fender arch you are dealing with that much more camber gain compared to when it cleared the tires section width.

Anyways, what matters is actual experience- I will provide an update if/when I get some real suspension on my 8 and a proper ride height.
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Old 04-18-2014, 08:53 PM
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The Hankook Z221 is 6mm smaller diameter than the Hoosier A6 in this 295/30-18 size.
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Old 04-19-2014, 11:50 AM
  #112  
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Do you understand what DSP is (the thread topic btw)? Nobody is going to run OE shocks, ride height, and OE bump stops.

Your posts are not only irrelevant, but misleading. When and if you ever get a real competition suspension and settings with some real race rubber you will find out for yourself.



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Last edited by TeamRX8; 04-19-2014 at 11:53 AM.
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Old 04-20-2014, 08:27 PM
  #113  
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Originally Posted by TeamRX8 View Post
Do you understand what DSP is (the thread topic btw)? Nobody is going to run OE shocks, ride height, and OE bump stops.

Your posts are not only irrelevant, but misleading. When and if you ever get a real competition suspension and settings with some real race rubber you will find out for yourself.



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I'm thinking the fastest Time Attack tire is probably the wrong tire for Street Prepared Autocross classes.
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Old 04-20-2014, 09:41 PM
  #114  
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Obviously it is nowhere near as good as a Hankook RS3, so that tells you right off the bat that the only reason anyone would race on such a tire is due to some silly rules limitations
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Old 04-21-2014, 03:04 PM
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I guess I should have expected this defensive posturing as it is exactly what I encountered from the FD RX-7 guys when instead of going by the 18x10 7.5 backspace that was gospel for over a decade I dared to measure what would fit for myself.

I am not advocating anyone use the Hankook Z221 Ventus TD tire for autocross, I provided the specifications because you had dismissed it as a skinny street tire without googling its (as you still have not done).

I found that 18x11 +45 fits the RX-8 front and rear and shared it with RX-8 racers in the DSP thread as that is who the information would benefit the most.


The +45 offset with the same Hoosier A6s would provide more clearance to the outer fender arch where you say your +43 offset rubs.

The front inner wheel lip does rub slightly on the front lower arm at full steering lock. I avoid full lock. Street Prepared allows for two solutions to this.
1) Steering limiter
2) "Aftermarket" camber adjusting lower arms with roll center correction (this is what one should have regardless of what wheel they are using.)

The rear inner wheel lip did slightly rub the rear shock/spring cover. Once lowered and excessive camber taken out it should not rub. Street Prepated does not allow one to modify the shock/spring cover as it is inboard of the wheel mounting surface, but it is ok if the wheel/tire rubs the undercoat off the cover.

It may not be worth it to you to buy new wheels for the 1/2" width.

It may be worth it for another RX-8 DSP racer who has yet to purchase wheels to get that 1/2" advantage.

Another off the shelf solution is the newish 18x10.5 +47 Enkei PF01. It would eliminate/decrease the rub on the outer fender arch and won't rub on the inside at all.
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Old 04-22-2014, 06:30 AM
  #116  
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I think unless you are testing with a competitive autocross tire, you are likely providing misleading advice on fitment.

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Old 04-22-2014, 08:07 AM
  #117  
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It's not necessary to go on in detail demonstrating that you don't have the full picture or experience with yet. Making 11, 12, or even 13" fit is not an issue in a class where you can cut the fender out.

Did you miss my post about the custom made Bogart 17 x 10.5 +56 wheels? Did you conclude that I didn't any more check or am otherwise not knowledgable about measuring inner and outer fender well clearance then, let alone back in 2005? Do you think we don't know who Forgeline is? Do I want an autox car to be any wider than is necessary or wheel any heavier than necessary? Do I need to spit out all the near DSP specs; high spring/bar rates, high camber race alignment through custom parts, lowered, racing shock coilovers, etc. which my car has in order for you to understand that I put a used 295/30-18 on a 18x10.5+43 wheel and had more front fender interference than 2mm offset will account for? If the rules allow fender rolling/cutting, I already fit a 10.5+43 that can be easily accommodated by this rule, then instead purchased 10.5+56 custom 3-pc wheels, did you conclude that I can't possibly understand that 11" can also fit with the outer wheel lip exactly where it was with the 10.5+43 wheel? None of that is even the issue.

You're saying that 11"+45 wheel with a 295/30-18 tire fits the front with no rubbing. All I'm saying is that (on a 2005 Mazda RX8 that I drove off the dealer lot in April, 2005 with 10 miles on the odometer and has never been in an accident) I bolted on an 18x10.5+43 wheel with Hoosier 295/30-18 tire (used, new will have more rubber on it) in near DSP trim and had a significant enough interference on an unmodified front fender that it would have cut down to the corner cord carcass in only a competition run or two.

So given my personal direct experience, and now seeing you posting that the same approx. size tire on a 1/2" wider wheel that places the outer lip 10mm or so further outboard and claiming zero fender lip interference on a low camber, high ride height, limited bump travel setup using a low grip tire, can you please explain how my questioning the validity of this is being defensive? It seems to me you are standing in front of the mirror staring at your own reflection.

For the record, back in the day I ran the Hoosier 295/30-18 in the Stock class on a rules-limited 18x8+48 wheel with zero interference on the front or rear OE fenders. Everyone else here is going the 18" route. I've decided to instead pursue using the unique Hoosier 275/35-17. Using a 10.5" wheel width is questionable to some people, let alone 11". If the 275 was good enough for the 2013 DSP national champion to win with on a heavier, more powerful BMW then it might be a suitable choice, no? Professional road racers here claim that anything wider than 245 is not necessary. The 315 tire is not only significantly wider, but also taller. More than a little roll or pull will be required to get them on interference free. They won't do you any good if you can't turn the steering wheel far enough to maintain the necessary tight line that is sometimes required.


.

Last edited by TeamRX8; 04-22-2014 at 08:23 AM.
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Old 04-22-2014, 12:34 PM
  #118  
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You're saying that 11"+45 wheel with a 295/30-18 tire fits the front with no rubbing.

I bolted on an 18x10.5+43 wheel with Hoosier 295/30-18 tire (used, new will have more rubber on it) in near DSP trim and had a significant enough interference


For the record, back in the day I ran the Hoosier 295/30-18 in the Stock class on a rules-limited 18x8+48 wheel with zero interference on the front or rear OE fenders.

From your own experience you understand the perfect auto-x offset for the RX-8 seems to lie somewhere between +43 and +48 (depending on camber) to fit the widest tire possible.

It seems to me you just misunderstand the role of wheel width on tire fitment or I misunderstand where the tire was rubbing on your fender with your 18x10.5 +43.

If your tire on the 18x10.5 +43 was rubbing on the fender at the sidewall between the bead seat and about halfway up the sidewall on the tire you are correct that the 18x11 +45 would make your rubbing worse.

If your tire was rubbing where I imagine it would be the outer tread block "shoulder" to about halfway down the sidewall than the 18x11 +45 would decrease your interference by virtue of the higher offset centering the tire more inboard toward the suspension.

Here is a great site that has helped me visualize different offsets and wheel/tire widths. Note the visual representation to the right of screen.

Online Wheel and Tyre Fitment Calculator. Offset, Tyre Stretch and Speedo Error | Will They Fit

I've decided to instead pursue using the unique Hoosier 275/35-17.

Sounds like a worthy experiment to try to get the wheel/tire weight down and a shorter overall height.

Even on the 275/35-17 Hoosier recommends up to a 11" wide wheel in that size so there may be some small benefit to wider than 10.5". The smaller diameter 17" wheel would have more interference with the front lower arm on full steering lock though.

The FD RX-7 guys use the 285/30-18 Hoosier as it is shorter than the 295 and the tread width is exactly the same.

At least one is experimenting with the 275/35-15 Hoosier which barely clears the FD brakes with certain wheels.

This 275/35-15 should also fit on an RX-8 that was swapped down to base model 16" wheel brakes (DSP legal).
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Old 04-22-2014, 11:40 PM
  #119  
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I never said that. Are you even paying attention?

Originally Posted by TeamRX8 View Post
Received the Bogart 17x10.5 +56 wheels this week


Last edited by TeamRX8; 04-22-2014 at 11:42 PM.
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Old 04-23-2014, 12:12 PM
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The 17x10.5 +56 is 5mm closer to the inside (suspension) than the 18x11 +45.

Inside was the area where my wheel set up rubbed.

A 5-10mm spacer should do the trick for you.

I am not slamming your choice in wheel/offset.

Its easier to add spacers to decrease backspace and get the ideal offset than send your wheels back in to increase the backspace to get more offset.

You might not have rubbing in back lowered with rear camber taken out as the Bogarts probably have thinner material at the inside wheel lip than the 18x11 +45 Forgestars I had on. It will be really close here.

I don't see how you can avoid rubbing on the stock front lower arm near full steering lock as the 17" diameter wheel will have more issue here than the larger 18" diameter wheel.
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Old 04-23-2014, 11:51 PM
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Actually, looking at the proportions of your wheel- are you sure you didn't order 17x10.5 with 7.5" back space?
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Old 05-04-2014, 10:58 AM
  #122  
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Back to topic, congrats to Zelse for finishing 3rd in DSP and fastest RX8 overall at the NJ Tour today after finally resolving some issues.

Finally able to get back to working on my own car now ...


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Old 05-05-2014, 07:19 AM
  #123  
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Both of those RX-8s are pretty impressive. I knew they would handle but I did not expect the straight line speed they had. Nice driving guys.
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Old 05-20-2014, 12:51 PM
  #124  
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Making some progress and feeling the itch to get moving on this now. Probably still 2 or 3 months out from completion.










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Attached Thumbnails The Official "RX8 in DSP" Thread-clutch-installed.jpg   The Official "RX8 in DSP" Thread-engine-s2trans.jpg  

Last edited by TeamRX8; 05-21-2014 at 12:21 AM.
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Old 05-20-2014, 08:36 PM
  #125  
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Word of caution; from what I am seeing, many aftermarket radiators are not meeting the minimum OE core width and length dimensions as required by the SP allowances.

the S1 radiator core dimensions are now added in post #1


.

Last edited by TeamRX8; 05-22-2014 at 10:48 PM.
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