azn akira

yes but the rmagic car aslo has the fuel tank in the passanger seat area. plus it has about 150hp more than the amemiya

pan speed runs (or ran, my mag is kinda old) 16/16 kg spring rates

the pan speed car just got beat by the top fuel s2000 on the tsukuba time attack. not really relevant to anything, but interesting

eoph

So the RX-7 no longer holds fastest RWD in Tsukuba anymore?

azn akira

thats correct. its the fastest rwd car around tsukuba is now the top fuel s2000

sevensix

iTrader: (1)

if its the same top fuel s2000.. the thing has 871 hp.. and cf body panels, maybe all the panels?

DRAGON_PERFORMANCE

Dont think so, panspeed hold the record with there new wide arch car dont they?

Daniel Gardh

Pan Speed - Tsukuba 55.603
R Magic - Tsukuba 55.7
Top Fuel/Zero-1000 S2000 - Tsukuba 55:350

eoph

Maybe if the rx7 cars put some wider tires on the car rather than 255's? Or is there some regulation with tire sizing?

azn akira

the top fuel runs 265's i believe, so they could go bigger

thetech

iTrader: (1)

Slightly on a tangent, but I do find it fascinating that all the Japanese tuners use such small tires. Even on some of the highest hp racecars over there they use (by american standards) ridiculously narrow tires.

azn akira

i've also found that interesting why 255 seems to be the largest tire used on the fd. i use 255 on my car, but then again i am still using the stock turbos

azn akira

http://www.maxrev.net/index.php?location=revspeed.htm

thats a good article talking about the 07 tsukuba time attack (the one were pan speed set the previous record). it has some good info on some of the time attack cars and really good pics

Black91n/a

Well there's more to grip than tire size, and there's more to speed than grip. As you go wider it's harder to keep the full tire in contact with the pavement (camber sensitivity) and those wide tires will be causing more drag, slowing them down on the straights, presuming they can get traction.

eoph

I was gonna get some 285 tires for my car after I do a widebody. So should I forget about that idea and just look at more suspension setups?

eoph

Can anyone give more incites on tire sizing?

sleeepyhead

Wider is better, even if a wider tire is more camber sensitive, a track record setting car on 255s probably has the tire flat as can be throughout its suspension travel anyway. More tire equals more grip at some cost to drag, weight, and slip angle. Lower slip angle at a certain g load is faster anyway because of the drag caused by high slip angles. These cars should have enough power to negate the drag, plus with the huge wings, the tires' drag is basically irrelevant. The only flaw, imo, is weight and the fact the whole suspension has to be adjusted to suit the new characteristics.

Btw, the fastest stock class autox rx8s use 285s

Black91n/a

That'a not entirely true, I believe thenationals winning RX-8 was actually on some 245 V710's. I know that on Miatas, with stockish power 205's are generally faster than 225's on the track, so sometimes wider isn't better. The tradeoff is that you get more corner speed, but you loose some acceleration and top end speed on the straights. Depending on the track this can help or hinder.

Only testing will tell if one's faster than the other, and I'm sure they wouldn't be using 255's unless they were faster for them, but that's not to say that they'll be faster for you. Wider is usually more fun though, and unless it's a competition it doesn't really matter that much anyway.

Daniel Gardh

sleepyhead: So you think that Panspeed say "oh no, we have to reallign the suspension now that we have wider tires so we better not do that" when they have done all the things to their car already. Don't forget how much driving they actually do and have done with the FD's in Japan.

eoph

Has anyone here actually gone back to skinnier tires?

eoph

I have a theory that mabe they limit rim size? Since i am sure there are restrictions, or we would see people bringing the supergt cars out...........

Black91n/a

In autocross where wheel size is limited people put 285/30/18's on 18x8's, 225/45/15's on 15x6's and stuff like that. In Prod and GT racing with the SCCA where they limit rim size they run cantilever slicks that are over 10" wide on a 7" wheel.

That's probably not it, unless it's a rim and tire size limit.

eoph

I meant because they are limited by rim size, they have found the optimum to be what they are?

gracer7-rx7

iTrader: (16)

Since we are on the topic of race suspensions, I wanted to ask about people's experiences with sway bars and why they chose their sway bar setup.

My FD is running Koni sport adjustables, H&R street springs and an Eibach front sway bar with the stock rear 93 bar. Long story but I had to switch out my Eibach rear bar due to a problem with the bushing.

I was at Horse Thief Mile recently and while I was there I had the opportunity to screw around on their skid pad. I found that with this setup, my car understeered a lot. It was very difficult to get the rear out or even just keep the cornering attitude balanced.

I see a lot of people running the large Tripoint bar up front with the stock rear bar. Don't you guys see a lot of understeer with that setup?

Thanks.

Black91n/a

That'll be entirely dependant on the spring rates being run. If you've got stiffer rears then you don't need as much bar to have the same balance. Also, as you go stiffer, the influence of the bar goes down (less roll = less deflection = less force).

2MCHPWR

iTrader: (2)

werd up did you make any adjustments while on the skid pad to address the understeer? what tires? what air pressure front and back? what alignment settings? what shock settings front and rear? If you had understeer, you could have softened up the front shocks and you could have lowered the air in the front tires in an effort to get it to the style you want. Or leave it alone and live with the understeer because it is safe on road course.

For the last 2 seasons of AX/RR, I had progressive rate springs (approx 412 lbs front, 288 rear) and KYB/mazdaspeed shocks. It was very compliant and soft. Easy to drive. But lots of body roll with sticky tires (only 245's up front, 275 rear v710):


Over winter, I got JRZ triple adjustables with 900 lbs front/ 650 rear springs (16kg front/12 rear is about what they convert to I think). The national winners in SCCA run slightly higher so I wasn't really concerned they were too stiff. Feels great on street.
Switched to bigger front tires (more grip) and ran 285/30 v710's all around on 18x9.5's +50mm.
Yesterday was first event of year for me. I got a real experienced friend to co-drive with me and after a few adjustments to low speed bump (set it to softest setting, 1 of 6) the car felt amazing. Supremely balanced when I did loose traction. Less body roll even though grip increased. No rubbing at all:


The car reacts a lot quicker but even on a pretty cold 45 degree day, tire temps didn't go over 100 with 2 drivers, the stick was amazing. Still using suspension techniques 1.25 solid front sway bar. I will put tripoint bar on for tomorrows event and put it to the 2nd softest setting to start out with.

Tire pressures were 29 hot front, 25 rear. Rear grip was pretty good. I had thoughts of removing rear sway bar, but now I will leave it on because of how well it felt. I put new hawk HP+'s pads and new fluid and the braking was awesome.

My co-driver, set FTD with a 44.1 and I came in 3rd with a 44.5 (missing 2nd by .008 seconds from an EVO that made that up at the starting line only). 3rd out of 105 cars ain't bad for my first event of the year.
I did have axle hop at the start so I know I was leaving time on the table at the launch; 30 aspect ratio can't take a shock. Maybe in the warmer weather it'll hook up better. That issue was just at the starting line. On a warmer day, I will adjust the slow speed bump up from softest to up 1 or 2 clicks (out of 6).

gracer7-rx7

iTrader: (16)

My setup is not final as I'm waiting for a fix to my rear sway bar bushing but this is what I was running at HSM...

My Koni shocks were set full stiff front and half a turn from full stiff rear.
Air pressures were 31 Front and 29 Rear set cold.
Tires are Kumho MX 255/40/17 all around.
Front camber was around -1.5 front and about -1.2 rear.
Caster at 6 degrees.
Front toe maybe .04 or .06 toe in. Rear toe should be at 0.
I had just done rear diff bushings and a new gas tank and I think the alignment might have changed slightly.

I didn't get to the skid pad until late in the day and didn't do much in terms of adjusting through the day other than playing with shock stiffness. I was mostly out for fun and testing the various changes I made to the cooling system and brakes and making sure the car was reliable. It was.


Looking at the spring rates that some people run with the Tripoint bar, it doesn't seem like the rear spring rates people use are all that much higher from a percentage standpoint to balance the car against the size of the front bar. Hence my question.


Its not worth commenting on my setup right now as it will be changing shortly. I guess I'm more interested in understanding how much spring you need to balance the large TP bar or if people are indeed running the car with more understeer.