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BGTV8 · 02-03-2015, 04:39 AM

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.

02-03-2015, 04:39 AM	#65 (permalink)
BGTV8 A True Z Fanatic Join Date: Dec 2009 Location: 03350 Australia Posts: 1,514 Drives: 09 Nissan 370Z M6 Rep Power: 39974	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.