OJ GTS

Hi Guys,

Sorry another wheel thread I know, but I'm on the verge of ordering some wheels from the states (I live in the UK and despite some BBS Europe contacts they've been pretty unhelpful) and would like a little reassurance that they'll fit my GTS without body contact and not cause too much in the way of nasty effects like tramlining or dodgy steering feel.

I've had a look through the various guides and wheel calculators, but just wanted another opinion before I spend a significant amount of money.

Looking at BBS RS-GT's which come in...

Rear - 18" x 10" size, 5x130 PCD, 65mm offset

Front - 18" x 8.5" size, 5x130 PCD, 56mm offset

Before anyone suggests Fiske's or the like, I've done a fair bit of research and the RS-GT is the style I like most that looks like it might be a suitable fitment.

Thanks guys

OJ

stuartph

OJ

They are good looking rims

OJ GTS

Cheers, that's a nice spec! Where are you based?

stuartph

Hi OJ

Thanks and i'm not finished yet

I'm in essex

OJ GTS

Well I bet it's quick enough already!

I'm based in Norfolk. Gradually restoring my car, possibly looking at a stroker eventually, but the cosmetics are getting sorted first!

Jerry Feather

Hi OJ:

I think you need to crunch the numbers a little. Here is how I would do that:

I have 9 inch rims on my S4 on the rear with 47 offset. I have about a half inch clearance between the tire and the edge of the wheel opening. If I put your new wheels on my car they would first take up the half inch because they are half inch wider on each of the inside and the outside. Then having much more offset, by 18 mm (about 3/4 inch), they will be moved back inside by about that much. They would end up further inside by about a quarter inch. I would probably want some quarter to half inch spacers.

Your car is about an inch wider in each of the rear wheel well areas, plus having a rolled edge to the opening which adds about another quarter inch of clearance. So, without spacers, your new wheels will end up about two inches inside the fender/ wheel opening. I think you are going to need a big spacer for the rears to fit--possibly as much as inch and a half.

The fronts on the other hand are not so far off. I have 7.5 inch rims on my front with 52 offset. I have a little less than a half inch of clearance. With 8.5 inch rims as with your new ones that takes up the half inch of clearance so I would need a little more offset to have them stay within the fenders.

With 56 mm offset you will be getting just about the right amount of extra movement inward to put them right about the maximum width for your fenders.. I think your front fenders are the same width as mine so they will fit, just barely, I think.

I think I know what this means, but then I don't care for BBS wheels anyway.

Jerry Feather

OJ GTS

Correct me if I'm wrong, but the GTS comes with 9 inch rears and a 55mm offset. Thus by your logic a 10 inch wheel with the same offset would protrude 12.5mm further out, and thus with a 65mm offset would actually protrude 2.5mm further out.

I also believe the GTS is fitted with a 20 odd mm spacer as standard, which would line up with your conclusions.

Or have I got the wrong end of the stick?

Jerry Feather

First, I cannot confirm what the GTS comes with for rear wheels. If they come with the 55 mm offset as you state and there is a 20mm spacer already there, I wonder how much clearance you have from the inner side of the wheel arch. If I am correct about how much wider the rear of the GTS car is than the S4 cars, you should have about an inch which is a little more than I would want from an appreaance standpoint.. That will be made up of the 3/4 inch clearance that I would have if my wheel arches were rolled like yours plus the 1inch extra width plus the 7mm different offset from my wheels, then minus the 20mm spacer and the half inch of new wheel width that is on the outside. And, also minus the 2.5mm you mentioned above. I still think you might want some additional spacer.

If we keep at this some more we can get down to splitting hairs, can't we.

Jerry Feather

Rob Edwards

The stock GTS rears are 17 x 9 ET55 but the factory spacer is 38mm, not 20. I just put 18x10 ET 58 on the rear with 295 Sumitomo's and they fit just fine using the stock spacer. This tire/wheel combo will also work on the rear of a GT without any rear spacer, though the inboard side is pretty close to the foreward portion of the lower control arm.

pcar928fan

Rob,

What wheel is that you put on? Is that the CIII wheel? Factory wheel?

Rob Edwards

James-

They're Cup 4's.

See here:

https://rennlist.com/forums/928-foru...-on-an-s4.html

Jerry Feather

James, if you spacers are also 38mm, I think this means that the wheels you are looking at will fit your car. Good luck.

Jerry Feather

FredR

OJ,

The most important thing you did not mention was what are you doing the upgrade for? Is it performance or cosmetic? Either way, you did not mention what tire section you wish to fit on them and that is rather critical.

On the rear you will invariably be looking at a 295 section I presume so that is probably not an issue but the tire will run very close to the inner side of the fender. I felt mine was slightly rubbing [285 on a ET60] but could never see where but boy did it look close- eventually I chose to run with open nuts and a 24mm spacer to be safe- assuming some distortion under load.

Your front wheel spec I do not like. People will tell you that you can fit this and you can fit that and indeed you can run with offsets like 52mm, but try the stop watch on the track and see what happens. Porsche designed our cars with a specific neutral scrub radius in mind and you need an offset of something around ET65 to ET68 to achieve this [I think the stock offset is 65mm up front]. An 8.5 inch section will permit some sort of upgrade to about a 245 section width but you will be close to or rubbing the fender, ride height, fender roll and camber depending.

I do not know the specific wheels you are considering, but I presume given they are BBS that they may be modular. If you are going this far, I suggest you get a wheel that has an offset in the region of 68mm and ensure it is either a 9 inch or preferably 9.5 inch width. Then you can run with either a 255 or 265 section up front- trust me- you will not regret this if you like to corner really hard as in track days. Note that you may need to limit steering lock with an extra spacer but then I do not have to negotiate NCP car parks!

If the upgrade is just cosmetic then I wonder why you would want to do this as the GTS wheels [both styles] are rather attractive and extremely strong. My GTS has Cup 1 wheel set [early type] and I run them with a 235 section up front and a 265 on the rear for daily driving. Works really well in my opinion. The wheel centres are painted same Cobalt blue as the car and they look terrific [original owner did that from new]. The avatar shows my big wheels- 265 up front, 285 rear [Michelin cup] and they like stick sh*t to a wet blanket, I am simply not brave enough to dislodge the front tires but they can pull well over 1G in a bend- the rears struggle to keep up with the front despite the Devek bar on full stiff.

Best wishes

Fred R

FredR

OJ,

Not withstanding what I wrote above, also be careful how you buy/who you buy from. If you are ordering through a known 928 parts source [like DR, Mark, Roger or Carl] no problem but if you are custom ordering them from a BBS agent who knows nothing about 928's remember that:
1. You must ensure the geometry of the wheel inner design clears the brake caliper- you need a sectional dimensional drawing of what they are proposing and you need to check all clearances most carefully.
2. Another potential problem is that the wheel hub may not clear the wheel bearing cover or its peripheral flange. This means that either the centre trim will not fit on the wheel or worse, the wheel itself may not mount- do not take this for granted. On my front wheels I had to remove the bearing cap to fit the wheel. Fortunately the mounting flange on the wheel was flat so I could seal the central trim with silicon RTV to stop grease from leaking. When I fit my stock wheels, I have to put the bearing covers back on because the stock wheel flange design is not flat and hence the grease compartment can not be sealed without the stock bearing covers. Easy to miss a but a real bugger if you spot this once your wheels arrive from over the pond.

Specialist 928 companies know and understand all this but wheel suppliers will invariably assume you know this and have taken it into account whe ordering their wheels. Of course, if you know they fit from other owner experience all well and good.

Regards

Fred

On my big wheels the fronts

OJ GTS

Thanks for the replies Fred and others!

The closest my GTS will get to a track is driving me the long trek there to race my 997 Cup Car, so the reasons are mostly cosmetic and I'm not really bothered about outright performance. Having said that, you say the Cups are strong, but the car has had 4 new (genuine) rears over the years because of inner rim cracking over London's crap roads, which now look like the surface of the moon since the snow in January.

I'm keen on a modular setup, because if I do bend a rim I can just whip the car down to my racing team and get them to rebuild the wheels with new parts. I know the rims aren't cheap, but they're cheaper than buying a new Cup 2 from Porsche!

Obviously I don't want to ruin the car's handling, but I'm willing to sacrifice a bit of ride quality as long as they fit without contacting under normal driving circumstances (i.e. I'll put up with the occasional scuff if I go over a big bump)

With front offset, from the stuff I've scanned, the problems with steering reputedly start below ET55 and they fitted ET60 to the Clubsport, so I'm willing to take the risk with ET56.

The rear inner clearance to the suspension worries me more, particularly when Rob says his wheels were close with a lower offset (i.e. mine will be closer to the inside). Rob, how close would you say it is, or was that without the standard spacers?

I'm not looking to go for maximum tyre width, in fact I'm quite happy to use the minimum width tyre possible without 'stretching' it, which I'm led to believe is a 255, although a 265 would be preferable. Does anyone think that is going to give me a problem?

Also Fred, when you say bearing cap, do you mean the flange that sticks out from the centre? In which case, those BBS wheels are stated as Porsche fitment with the appropriate bore centre (i.e. the hole at the centre of the wheel), is the 928 different to other Porsches in that respect?

Thanks again guys, this is all really helpful