pez

I am about to purchase a track prep'd 928 GT that currently runs on 17" GTS rims.

Any guide on where I can go with tyre sizes?

Any issues that the car would now run on slicks i.e. are the corners up to handling the additional loads & stresses ? Note: it runs on adjustable dampers & stiffer springs.

Thx

Mike Simard

Hoosier has a guide that includes rim widths for various tires:
https://www.hoosiertire.com/rrtire.htm
You'll want radial slicks.

17s could be hard to find, most racing tires have moved to 18.

If you're in Hong Kong you may want to look at Yokahama etc. If you use whatever is common to local racing, you can get tires from track service companies or even freebies from racers!

John Veninger

2/6 bearing issue unless the RPMs are kept under 6K, oil stays topped off and you have an accusump.

paul928s4

Any reported 2/6 bearing issues when using stock S4 rims sizes (225/50 & 245/45 R16)? Don't think I've heard of any, but I was just wondering.

mark kibort

17s vs 18s, not much difference. main question is what are the widths of the rims .If it is track prepared, then they are probably 9 to 10" min. 255 front and 275 rear would be min size I would use.
there are no oiling issues with the use of amzoil and keeping the level full.
(and not driving sweeping corners at 6000rpm. use a lower gear. )

mk

pcar928fan

Yes, a friend with a '91 GT burned up not one but TWO engines with stock sized R compound tires (I think he was running 17" GTS wheels though) AND and accusump! He then found a used GTS engine and put that in. Don't know what ever happened to him. Probably moved out of the area. Nice guy, to bad he just kind of disappeared.

paul928s4

Thanks James, that's good to know even if it is a bit concerning.

A few seasons ago I moved up to R-compounds on stock sized 16” rims for lapping days. My car doesn’t have an accusump and I haven't had any issues thus far using Mobil 1 15W50 oil (no flames please). That said, at this point 'the nut behind the wheel' is component of my lap times that is in the most dire need of improvement

pcar928fan

Paul,

I have over 10,000 track miles on my '88 S4 auto and the only problem is that I was not aware of how hard it was on transmission fluid and I am looking at a replacement (cheaper than a rebuild, but will hold on to the core should I need to rebuild at some point). I have not heard of S4's (5spds OR auto's) failing in DE mode...unfortunately I have heard of more than a few GT's having engine failure from DE's and Auto-X's...even with Accusumps.

On your car I would change your trans fluid every 6 DE weekends or so...don't do what I did and wait to long. My mechanic at the time I was DEing that car a lot would go to the track to drive and support his clients and never mentioned that I should be changing this stuff out MUCH more regularly than the manual talks about. So, just take it as a warning from someone who has been there!

paul928s4

Thanks once again James, and point well taken.

I probably didn't do my old tranny any favours by only changing the fluid every 2 years. Fortunately in March I found a low-mileage replacement unit, and I'll be sure to treat this one a lot better. Using Mobil synthetic tranny fluid and LubroMoly 75W90 diff fluid (couldn't find Mobil 1 diff fluid up here and LubroMoly came highly recommended).

mark kibort

After all we have seen with Mobil 1, you , would take the chance?? oil pressure light blinking at the track on a hot day with M1,and then back to back track days with amzoil or redline and its perfect? hmmm..... over 10 years of hard racing, NEVER missing an event, and always having perfect oil anaylsis ,showing NO issues, even though is racing hard? 5 different engines and 2 different drivers and lots of races and no issues....... If it were me, I would change it out. you might have damage now and dont even know it. I would send off a sample off to blackstone and see what it says from what you did at the track.

amzoil. no oil cooler, no accusump, no pan scraper, spacer, breather system, etc. all stock stock stock. and most of all, no problems or wear in the most extreme of conditions.

Mk

paul928s4

Hey Mark,

I have not seen an oil pressure light thus far with Mobil 1 15W50 oil. Only thing I added along those lines was a GTS pan baffle.

Due to scheduling with the family (we're big on the cottage thing), I tend to do my lapping in spring and fall only. If I was tracking the car on a hot day in July or August, I may have already encountered what you are speaking of.

That said, I have no brand loyalty and I am open to switching to something else if there are strong reasons to do so.

Giovanni

I know someone that busted their S4 LSD and a transmission gear when drag racing on slicks so be careful.

pcar928fan

Same here!! Did exactly the same thing, but in my case I already know my trans is toast...

So, Mark are you saying you like the Amsoil stuff...not sure I am hearing you! LOL!

mark kibort

I only saw it turn on and (obviously)the pressure dropped way down on turns during a hot day. on a normal day, the pressures were noticebly lower.

Try it yourself. put in redline or amzoil and see what does.

The reasons to switch in my mind is only base on what I have seen and read up about the product. If you dont see 5 bar on a 100F day, at 2500rpm, try something else.

mk

pez

car runs an accusump so hoping oil will not be an issue. We run heavy weighted oil out here as the temps & humidity are extreme.

To be honest thats my main concern - Cooiling ( oil & water) and brakes !
DO you know where I can find slotted race spec rotors that are plug & play for the GT?