Where did you go for the JRZs?

I bought a car a few months ago just because it had them so that I can remove them and then I sold the car. yeah I have issues.

Engine.
Power: 490ps
Boost: 1.2 kg/cm2
Port: Side Port
Plug: NGK 11
Fuel Pump: Bosch
Injector: 1000cc x4
Computer; MOTEC
Regulator: Sard
Turbine: HKS T04Z
Boost Controller: Blitz D-SBC
Wastegate: HKS GT2
AirCleaner: Original
Intercooler: Blitz V-Mount
Radiator: Original 3 turn Aluminium
Oil Cooler: Original Twin
Piping: in 70mm out 80mm
Exhaust Mainfold: Original 50mm
Front pipe Original 80mm
Drive Line
Transmision: Hewland 6 speed sequential
Clutch: OS giken Clutch
Flywheel: OS giken flyweel
LSD: OS giken 2 way
Final: 4.1 final drive
Suspension
Damper: Ohlins PCV
Spring: S.W.I.F.T (front 16kg / rear 18kg)
Bush: Full Pillow Bushing
Arm: Original One Off Design
Footwork
Brake Rotor: PFC
Brake Pad: PFC
Brake Calliper: Brembo
Wheel: RAYS Volk Racing Wheel CE28 (10.5x18 ET+18) 30mm Spacer
Tyres: 265/35/18 Direzza 03G
Interior
Seat: Bride
Seat Belt: Sabelt Harness
Steering Wheel: Juran GT
Roll Cage: Original 13Pt
Meter: Motec
Fuel cell: Original
Dash and Console: Original Dry Carbon
Exterior
Front Bumper: Pan Speed GT2004
Fender: Pan Speed GT2007
Bonnet: Pan Speed GT2000
Side Step: Pan Speed GT2007
Door: Pan Speed Carbon
Rear Gate: Pan Speed Carbon
Rear Fender: Pan Speed Original Over Fender
Wing: Pan Speed Original
Diffuser: Pan Speed Original
Lights: RE-Amemiya Sleek lights (modified)
Mirror: Pan Speed.

These are specs for Pan Speeds tsukuba time attack vehicle. It seems they do use a very wide rim, 18x10.5, but they like to fit skinnier tires on it than wat most ppl here would fit(285).

That's interesting, but I don't know how well any of that translates to our cars. I don't see an average RX7 with 265's and heavier 18 lb. rear to 16 lb. springs handling worh a crap.

It could be that those springs are necessary given a massive chassis-mounted rear wing & functional diffuser. Could also be that with significant downforce that they feel that the gain in less rolling resistence or drag from 265's vs. 285's works out in their favor.

I think you'd need to replicate their ENTIRE car (and drive on their tracks) though for the coilovers or springs, or tire sizes specifically to be relevant.

Another thing to look at is that they at least use spacers to take advantage of the widebody. So maybe its possible the gain from that was more than increasing the tire size? I don't have the experience to say what an increase in tire width does compared to things like compound and wheel base.

Sounds more like theres a tire size limit. Why the hell would you put a widebody on a car to use 265's?

But some cars use 255 rather than 265 tires. It wouldn't be manufacturer measurement based either, since most cars use a048, but some use 255 while others use 265. I can still see some gains from the widebody by positioning the tires farther apart. Dunno how much though.

There are other advantages to a widebody such as longer suspension arms for better control of the dynamic alignment, wider track for less weight transfer and more grip and such. There is a price to be paid in aero drag, but if they're able to use narrower tires which will have less rolling resistance then maybe they cancel each other out for no net effect?

Also, because of the custom suspension, it will act differently than a normal FD with those spring rates because it's probably got much different motion ratios now.

On the side. All the record holding FD's in Japan seems to have changed their suspension geometry. What do they change? Where do you buy some of these parts?

In order to change suspension geometry, you'd need to modify the pick-up points (requiring welding and fab, no bolt-on), or lengthen the A-arms, which at the rear would require custom drve shafts. I doubt any of that stuff is a part you could just buy.

I have seen fabricated upper front A-arms (I think Rishie sells them) that are heim jointed and adjustable for camber, but unless you can't get the static setting you want with the stock lower arm, I don't see the point—and their bound to be less durable.

Unless you're building a race car, AND have a very specific need in mind as far as revised geometry, the FD doesn't need revised geometry. Don't bother.

I read something interesting on the miata.net forum the other day. Apparently someone building an Evo for time tirals found that 265's were faster than 295's, untill the 265's overheated after a few laps. That works well for time trials, not so much for road racing. This is one big reason that wider is generally better for road race cars and track cars, as the wider tires, while they may take longer to heat up, are going to be faster over the course of the whole session than a narrower one, which will be more prone to overheating.

Keep that in mind when looking at the Japanese "time attack" cars, they're going for the one fastest possible lap, basically a qualifying winning setup, not necessarily a race winning setup.

Wouldn't it be logical that they would go for the one fast lap in the 285's or bigger after they warm it up with a few laps? Or changing to a softer/harder compound instead to deal with the heat?

It's all just a tradeoff of grip and rolling resistance. Getting around the corners 5% faster is a major step backwards if it costs you 5% on the straights, because let's face it, well over half the time you're going more or less straight (very track dependant, but I'd be surprised if any track even gets close to 50% time in the corners).

For most of us it's pretty much irrelevant though, as a setup that's prone to overheating requires you to slow down, which isn't fun for recreational lapping, or it gets you passed in road racing.

That's true. I just want my car to remain cool so i can get the most out of lapping days :)

Well, if they're using DOT tires, there aren't a ton of compounds to go through... it's not like a SCCA slick where you've got 3-5 compounds to choose from in a single tire.

Black91n/a makes a great point about heat—I've noticed the same with lower profile tires

265/35 used in time attacks in Japan might be just the right compromise of grip, quick heat up, rolling resistence, without need to go more than one hot lap... with the setup they use, track, driver, etc.

If you're looking for a good track day setup, I'd look less at Japanese race cars, and more at what experienced track day goers in the States are using. Typically, that's stock wheels with 245/45, next step up is 17x9" w/ 255/40, then a 17x9.5 or 10" w/ 275/40, and finally an 18x10" w/ 285/30. Depending on power levels, budget, etc., those are probably the best bet.

I'm pretty sure they do get a fair bit of choice about compounds, because I've read in the past that you can get some super soft "Time attack" compounds from some of the Japanese tires, like the A048, which is available in several compounds over here, as are Hankook offerings and maybe others.

Back to the Miata, was it as you guessed, the owner said it was time shortened on the straight?

I'm not sure if anyone who tested it has specifically stated it that way, but that'll be the reason, yes. That's only for basically stock powered ones though, apparently above about 130whp 225/45/15's become faster than 205/50/15's, at least with RA-1's and tires like that, with Hoosiers or something like that the crossover might be higher or lower, and then there's the issues of weight, track layout (how much is straight vs turns) and so on.

Because with wider tires, I would assume they have a faster exit speed, which would cancel out the roll resistance?

More grip will help get you onto the straights faster, but if you can't accelerate as well because of increased rolling resistance and increased rotational inertia then you may end up being slower on the straights as a whole. The longer the straight, the more this matters. Basically with more power you're better able to overcome this and the wider rubber allows you to put the power down sooner or more aggressively out of the corners, giving you a better launch onto the straight and helping you to be faster overall where narrower tires would be spinning.

The ONLY way to be sure for you and your car at any individual track is to test the different setups back to back, but then you get into other issues such as each different tire requiring a slightly different setup for it to be maximized.

But what at what speed does the aero become effective?

These guys find aero help during AutoX speeds:

http://www.7parts.com/cars.html

I would say that aero can be a effective at a variety of speeds, depending on how it's developed.

Hey, does this look like it'll help a lot with the geometry, given u give the right adjustment?
http://www.rhdjapan.com/jdm-low/Ikey...D3S-RX-7-51487

I dunno how in theory this helps though. In theory, don't we want more roll with the double wishbone suspension, so we don't have to dial in so much static negative camber?