Triplex.r8

To the OP, if you still haven't had the IMS conversion done or are looking for info I can tell you that the more solid the side/front diff bushes are the less clunk you will get. Like you, I have the manual but mines in FGX form. Mine's far from stock but has the CAT600 solid side bushes and Nolathane rear. Has obvious diff whine audible through the cabin as to be expected and slight clunk when selecting 1st or reverse at a stand still but no clunk at all when changing hard through the gears. The design of the diff mounting is such that the side bushes are responsible for the rotational movement of the diff. If these mounts are solid (or close to it) there is very little movement permitted, even under high load. This means the rear mount is not left with much flexing load, therefore the bolt should never snap. On the other hand if the side mounts allow a lot rotation the rear mount will be very 'busy' and in higher power applications cannot cope and will pass the load on to the bolt eventually resulting in failure. The IMS upgrade is definitely something I've considered and is a worthy upgrade for high power, drag racing etc but I have found that with the CAT600 side bushes I do not need to go that far. But remember there is always a compromise, the less NVH the weaker, the more NVH the stronger really.

That size rear will not fit. 18" rim in that width will hit the trailing arm. +20 offset will put them well outside the guard. You need a 19" rear if going wider to clear the trailing arm

Tein Coilovers, but surprisingly no. With this high positive offset it keeps the wheel well away from the guard. Have tested it to the extremities of the suspension travel, even fully compressed against the bump stop it still has 6mm clearance to the guard

Yes, was quite costly. But Im hoping it will be worth it once I achieve the power levels Im chasing. The tyre/grip levels on these are very under-engineered for the stock power levels, not to mention 500rwkw... And no, no guard rolling required whatsoever. Even at full compression there is plenty of clearance.

As I found Jumbuck's posts from August last year the most helpful in determining my wheel specs I thought its only fair I post my findings. Hopefully this will help anyone wanting to know how wide they can go on the rear without running into guard clearance issues. I had my wheels custom made as a one off set, just like Jumbuck did. I was trying to achieve maximum possible width in tyre contact for my street setup. Rears pictured, are 19x10.5 +52 offset Tyres are: Front 245 35 19 Rear 295 30 19 Measuring across the tyre the rear is 315mm. I wouldn't advise going any wider than this. There are a few modifications to be made to accomodate this setup.. Superpro control arms (plus the addition of 2mm shims to add a fraction more clearance) Low profile bolt in upper shock mount Shortened shocks. NO guard work required. Can just make out the shims between arms and hub The shortened shocks lift the wheel slightly at full droop to avoid contacting the chassis I measured 6mm clearance to guard edit: the car is a 2015 FGX XR8. The shocks were shortened by 10mm The upper shock mount was modified by notching a square into the bolt hole to allow an internal locking bolt and the fixed nut was ground off the back to add a nylock nut for tightening Thanks again to Jumbuck

I noticed you are running 245 35 19 tyres on the front and 285 35 19 on the rear which has altered the front vs rear rolling diameter from stock. Has this caused any Traction control or ABS issues? And did you get the speedo recalibrated? Cheers

Thanks for the response. Im running Tein coilovers all round (due Shockworks not avail here in NZ), CAT600 bushes and Nolathane centre, Wavetrac LSD, 4.11 diff gears and being manual I am exposed to my fair share of NVH. Good to know M/T's quiet things down, while new at least. My FGX is actually the XR8 so slightly wider wheel from stock 19x9 et43. Not sure if theres any change to rear end vs XR6? Maybe sway bar? Out of interest did you attempt to drive it while spaced 15mm as above? Looks like it would foul the guard but I know looks can be deceiving. If I cant run the 45 offset I may be left with no option but to get custom wheels like you have done $$$$$ Thanks again for your help

Jumbuck, very interested in your findings. How do you find the M/T's on the street? Or at speed (100kmh) motorway driving? I am looking at running a similar setup on my FGX, but hoping to use a 45 offset as this gives more wheel options, and I will have custom spacers made up to move the suspension arm inwards.