Jherriott

I currently have -3 degrees. How much more can I go before tires wear/spin too easy? I have some rubbing on passenger side that I'd like to remedy.

Rear wheels are 11x18 turbo twists with 295/30/18s

mark kibort

you should do some gentle wood baseball bat rolling 3 degrees is a little too much. 2 should be max race/DE setting. whats the offset or backspacing of the wheels? sounds like they are near 7" backspacing.

Jherriott

Hey Mark,

The rears are 45mm offset. No spacers. The fenders have been rolled and pulled as far as they are going to go before paint gets boned!

I should have taken pics on the offending side... Like most cars the drive-train is not perfectly centered in the chassis. The passenger side is uber tight.

FredR

Jason,

What prompted you to run with -3 degrees on the rear wheels- was this an attempt to make them fit? ? As Mark suggests that is too much even for a track car IMHO.

Your front wheels look stock items rubber wise so unless you have something up front to nail the front end such camber on the rear is just a waste of time cornering wise. Even if you had something significant up front I would suggest the maximum camber for the rear would be about minus 1.5 degrees.

My rears are currently set at close to minus 2 degrees and they struggle to grip away from the lights so presumably yours must be like a bar of soap all things being equal [our tarmac over here is not so grippy as it is blown at higher temperatures in a bitumen plant to survive the heat].

At the moment I cannot set my rear camber any lower than this and I presume this is because the dog bone bushes have sagged more in our heat [not to mention cornering loads! ].

Your basic problem I would politely suggest is that with wheels that size you need a rear offset of ET60 [like mine] on the S4 to successfully mount a 295 section. Yours would work on a GTS that has about 17mm extra width available due to the flared arches.

Needless to say the clearance issue is only going to get worse if you reduce the camber to where it really needs to be.

You appear to have the typical aftermarket wheel problem with the inadequate offsets of wheels that were simply not designed for the 928. Let me guess- you have front wheels that are 8 inch with an offset of about 52mm running a 225 section [maybe 235]? Do they tramline quite badly? The 928 front suspension is designed for a neutral scrub radius of about minus 13mm if my memory serves me correctly- I suspect your front wheels have probably eliminated most if not all of this.

I dare say the side clearance may vary a little side to side but I think we are talking a couple of mm either way - not more- remember this is a Porsche built chassis- not GM.

Apologies that I cannot offer you anything a bit more positive. Remember some tyres are wider than others size for size and could consider reducing the section width to a 285 but that may not a good idea on an 11 inch rim width.

Sounds as though you are running wheels designed for a 911. There are off-take wheel sets that fit better from the likes of the Panamera [I think] but we do see this type of problem posted quite regularly -usually more a problem on the front wheels.

Trust the above helpful even if it is not what you want to hear. Rubbing tires is not an acceptable option.

Regards

Fred

Jherriott

Hey Fred.

My fronts are 245/35/18s on 8 inch rims. They have 50mm offset and I know I am in the trouble zone as far as scrub radius. The steering is good, they don't grab undulations... but I haven't had a sudden blow-out at high speed yet :P

So I guess I'll have to attempt more pulling of fenders at this point, or just live with it. Eventually I'll get some rims that are made with proper offsets. For now they were a cheap option to get the car looking sweeter. The only time they rub are when I have a full tank and 2 guys in the car and you hit one of those slow swooping dips on the highway. Hard quick bumps don't seem to do it.

Thanks very much for all the advice!

Jase.

FredR

Jason,

They most certainly look nice-indeed perfect in my opinion as I love the reverse spoke design, they look up to date & very "Porsche". The trouble with rubbing on the fender is that they tend to rub just when you do not want them to - i.e. in extreme [there goes my no claims bonus] conditions and that is no time to find out whether you are in trouble [or hopefully not]. In an extreme condition if you get a hard rub at speed no one can tell you whether the tyre will withstand the event- as long as you understand this and can live with the risk fair enough.

A 245 section up front is quite a nice size but the problem is it will also give you quite a fair amount of lateral grip and thus expand the envelope of potential for contact.

Must say I would very be very surprised if a 245 on a 8 inch ET50 wheel did not rub the fender even with rolling but YMMV. Presumably you have checked to ensure that width/combo profile is within the acceptable size range for your rim- at best it must be a bit tight.

I also noted from your photo you have the problem fitting the wheel centre trim. If the wheel mating face flange is flat all the way round you can leave the hub grease cap off and use the centre trim with some silicon RTV to seal it from weeping grease- ask me how I know!

Rgds

Fred

Regards

Fred

Jherriott

Hey Fred,

I also heard that some people tap the grease cap with a hammer of sorts until it is "flatter" in profile allowing the wheel cap to fit. Does this sound correct?

Jase.

FredR

Jason,

My primary problem was the base circle of the cap would not engage the hub flange of the wheel. I considered machining this but spotted I could fit the cap and seal it to achieve the same result. If I wanted to switch back to my stock GTS wheels then I had to re-seal the area as the GTS wheel did not have continuity on the hub face.

I also studied the geometry of the grease cap to see whether it could be "flattened off" to increase the available clearance to fit the cap. I concluded some improvement may be possible but at quite some effort that I considered not worth going for.

I have seen your type of wheel have the same problem on several other 928's but i have not come across anyone who solved it. I wondered if it may be possible to fabricate something from aluminium that had a raised cap and attached to the wheel- not perfect but way better than what you have at the moment [cosmetically speaking].

Rgds

Fred

mark kibort

those looked rolled nice, but i could give you another .5" with the baseball bat and no duck bill. that doesnt look anwhere near 3 degrees

Jherriott

You have a good eye Mark! That photo is at 1.5 degrees. I will put them back to that and give the fenders another tug. Here is a pic of the offending side from last year still at 1.5 degrees, but you can't get your finger in there... (The actress said to the bishop!)



Can you buy GTS fenders still? :/

Jase.

FredR

Mark surely has a good eye- not only does he roll the fenders with his baseball bat he does the alignment with it as well!!

Louie Ott used to do a GRE flare for the 928 [performance928.com]- no idea if he can still get them- big job though.

Rgds

Fred

Jherriott

Hey Fred,

I dunno. Those Ott fenders are not my thing. Especially around the fuel filler!

Jase.

FredR

Jason,

Those fenders are not for everyone and are designed for very wide rubber [as in about 335].

If you are running 3 degrees and you are getting a rub then sad to say I think you are out of options assuming the rear is rolled to the extent possible. The wheel flanges most likely will not have enough meat on them to machine anything of significance off them.

My wheels are 9.5 inch ET68 [front] and 10 inch ET60 [rear]. I can play around with the configuration by fitting different half section widths but the spec is so ideal the only thing I could ever conceive doing would be on the rear if I ever wanted to fit anything wider than a 295 or whatever a 10 inch rim can safely handle.

I see new wheels in your future!

regards

Fred

dr bob

To the front wheel bearing cap issue:

I ended up doing a little bit of hacksaw and file surgery to the caps on my S4, after new wheels caused the issue you are experiencing. Caps came off, and I made a line at 6mm from the inner edge with a Sharpie felt marker. Then careful work with the hacksaw on the bench trimmed that off. File the edges smooth, and clean out the filings and all. I tapped the cap on until it was against the end of the spindle, then made another mark on the lip of the cap. Then tapped the cap back out a little so it wouldn't rub a hole inside the cap.

I had looked at the option of using the GTS bearing caps, which have a flatter profile than the ones on the S4. They were a little too spendy for this new, no used readily available, and the method I used ended up working fine.