going square how did you like it?

boosted180

yes, that's exactly what I was concerned about also. I didn't want an inch lower b/c of the lower sidewall. thanks for the info.

boosted180

I'm not going from 19" to 18" to go faster (necessarily). I wanted to save some weight, and save some money and just wanted to experiment and see. My main concern was having something that will work on both street and track (which I don't go to that much anymore).

If I can go faster, that'll be a bonus, but that's not the main reason why I'm doing this. In fact, I don't track nearly as much as I used to, so I'm not that obsessed about time anymore.

PharmDZ

Didn't mean to really say an inch lower overall, but even the .4 inches would be brutal to me right now at my ride height. I need me a new driveway lol

boosted180

Yeah, I realize that it would only be half the calculated 1" difference since the wheel is mounted in the center. But even half an inch is way too much for me. In fact, I called Eibach today to ask if it's common for their springs to sag. When I first put them on 5 years ago, I was able to make it in and out of my driveway just fine. Now the front of the car scrapes, even if I'm very careful. And it looks lower also.

But I'm surprised that you went for 305 35 19 to 285 35 18 and you saw almost no difference in overall diameter/ height?? or did you mean 285 35 19 and 305 35 18, which would make more sense b/c the added width would add to the sidewall height a little and negate some of the change to a smaller wheel.

For my fronts, should I go with a 255 40 18 or a 245 45 18? (rears will be 275 40 18). The general rule of thumb is that when you go up or down 1" in wheel diameter, you compensate for that by adding or subtracting 5 to the sidewall number. But the width would affect the overall diameter also, so I was thinking I can stick with the 40 sidewall if I increase the width to 255 instead of the stock 245? And this will give me almost the same overall diameter?

BGTV8

So I have been running Enkei PF01 in 18 x 9.5 ET35 (Subaru fitment) with 25mm spacer at the rear and 12mm spacer at the front fitted with integral hub-centric locating rings to suit the Enkei bore-size of 75mm.

I have progressively reduced the rear bar stiffness from Whiteline to full soft and am now about to go back to a std rear bar and may even try without a rear bar sometime in the near future.

I have run 265/35R18 Yokohama A048 R-Specs (Nitto NT01 in 275/35R18 earlier but could not get replacements until very recently) and most recently ran the A048 with a 4:08:1 rear diff ratio and the car simply keeps getting quicker.

I am now carrying nearly 4 degrees of (negative) camber on the front and the car continues to point and take a set with power without darting or over-steering on throttle application BUT I do have to be very smooth on turn-in and going to WOT - too abrupt and you need to have your game-face on to catch the rear.

The more I stiffen the front and soften the rear with bars on the A048, the better it turns, the more mid-corner it carries and the quicker the car gets.

I am running a lot more rear rebound and front bump than in the past so weight transfer onto the front under brakes is slowed down a bit or the rear brakes can get a bit chirpy (I am still running OEM ABS but have disabled the yaw sensor to avoid the ABS controller getting its knickers in a twist and trying to pitch me off the circuit).

I'm running Kw V3 dampers and when I have recovered from purchasing my sequential box (was a 5-figure investment that I've still not shared with SWMBO) will invest in Penske shocks (I bought a pair for the front of my historic race car and they are a superb piece of kit) as the next upgrade. I already have a selection of 2.25" ID springs from 400lb/in to 1200 lb/in in 100lb increments so I don;t think I'll need more springs .. if so, they can be had locally from our motorsport spring winder (King Springs).

Whilst I can appreciate that some of the hi-power cars on the forum can exploit a lot of tyre, I'm still pretty happy with my (relatively) narrow width as I certainly don;t mind drifting the car at high-speed - the only thing I demand is balance and predictability at the limit.

My last dyno run netted 208Kwatw which is a lot less than some reported figures for NA cars here, but I am happy that all the killer-wasps are under the load pedal and can be called up when needed.

In terms of ride height, I run little tyres to gain a CoG benefit without extreme suspension arm angles of lowering the car on the coil-over. I get to keep near standard amounts of bump and droop which means I can avoid the camber gain in bump that comes from being 50mm lower on the coil-overs - it also gave me a gearing benefit and I find that with the 645mm diameter 265/35R18 tyre, my 4.08:1 FD, that I get to use 6th a lot more than I used to (previously I'd hold 5th to Vmax at the faster circuits we use) although last year at our quickest track, I was running out of rev's in 5th because the setup was getting me onto the straight faster and I had to use 6th. With the 4:08:1 FD, I'm now pulling 6500-6600rpm into T1 at PI GP circuit and need 6th uphill at the back straight at Sandown and this is as much about the setup getting me onto straights faster as well as the gearing benefits of little tyres and low FD ratio.

My bottom line is that square has been very good for me on the track, but I continue to make changes and have never gone back to my initial setup (because the OEM shocks are long gone).

The key is having 2 sets of wheels, but since you are not tracking, maybe not important.

I run 245/45R18 on the front on 8.5 x 18 and 275/40R18 on the rear on 9.5 x 18 RAYS Gram Lights for DD duty

Picking 245/45R18 or 255/40R18 is simple - I would not go 255/40 because the OD is ~661mm and the OD on the 275/40R18 is 677mm which is near as dammit the same as 245/45R18. The difference is 15mm and that might just about be enough to confuse the ABS calibration - others might offer e definitive response but I have always stayed with 5mm OD for my tyres.

I realise you're not tracking so much, so take my comments with a grain of salt, but I see your choices being driven as much my how low the car is as much as anything else.

245/45R18 on an 8.5 wide wheel with 275/40R18 rear on a 9.5 wide tyre is a match but 255/40R18 is not a good match unless you so the same front and rear.

Rusty

You get that tranny installed yet?

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BGTV8

Is going into the race car first. Dog-Box with straight cut gears in a daily driver can be a PITA.

2015 is about acquiring HR head conversion bits and Grand-Am spec rods and 14.5:1 pistons and then building a hi-comp Grand Am spec motor for E85. When the engine is built and goes into the car, so will the trans (I have an H-pattern Holinger available to go back into the race car). For the Z34, I'll need to go Motec or Haltech to run the engine and that means the car comes off the road, loses 350kg, gets a cage and I go Modern Sports Car racing with the Z34 instead of historic racing.