Player0

Hi all,

Now that the car has more than 400RWHP, I suspect that the 245/45R16s are a bit under qualified. I currently have early offset, fuchs 8 & 9, phone dial 7 & 8.

This is a dedicated HPDE car so I'll be running ultra high performance summers or entry level R tires. Things I can get the best bang for the buck for, good endurance, minimal care and feeding. I might end up with Hoosiers at some point but not this year.

The selection of 16" tires is slim pickings. 17" tires are okay but the best selection seems to be at 18".

For **** and pickles I mounted the spare set of OZ Ultraleggera Cayman S rims I have in 255/35R18 and 285/35R18. Offsets are 53 front and 40 rear. They actually fit even without spacers! But I ordered a set of hub centric spacers to move them out anyway.

FWIW, I have a full race suspension and am using Turbo S spindles.

Questions:

1.) I've searched everywhere and I cannot find the 1986 944 Turbo's scrub radius. I know it's positive and switched to negative offset in 87 with the ABS introduction. But I can't actually find what the scrub radius *is*, so I can't compute how much different offsets are impacting it. I want to make sure I avoid accidentally choosing a 0 scrub radius and getting 'squirm'.

2.) Hub centric spacers will not *fit* over the dust caps on the front spindles. I reckon they'll be fine on the rear. I have run 5mm spacers in the front (the 8" fuchs require this to clear the S4 brake calipers) that aren't hub centric. But I'm thinking I need at least a 20mm spacer for the cayman wheels. I just installed 80mm studs but as this is a track car, this isn't giving me a warm vibe. Is running such a wide non-hub centric spacer on the front of a track car a very stupid idea?

3.) I could also remove the dust cap and/or put a cap on the spacer itself. This would kind of suck if I have to change tires at the track because it's just another step. I would like to keep using the 16" wheels I have as track spares but primary on the 18". If I put a cap on the spacer, does all the grease tend to ooze out between the hub and the spacer? Especially once it gets liquidy hot?

4.) is there a dust cap for these hubs that do not have lips that extend past the hub center?

Long term I want to order a custom set of forged 18" wheels for this car which will eliminate the spacers, but I'm trying to save some funds this year and recycle the cayman rims if I can. Plus, I'm not sure how I'll like the feel of the 18s or if the rest of the car will survive the added wheel weight. So I'd kind of like to trial out this fitment before committing the funds.

Auto_Werks 3.6

The 275/45/16 Hoosier R7 is made for a 9" wheel according to Tire Rack's site. I'd start there, and run them on your fuchs instead of spending a bunch of money on wheels. If you want a 200 treadwear tire, you're basically right that you should look at 18" wheels.

https://www.tirerack.com/tires/tires...R6R7&tab=Sizes

Player0

Yeah I may on occasion mount the Hoosiers on the 16" rims. But I don't have the budget to run those all season long. And I'd still need to buy a second set of rims because with Hoosiers you gotta bring spares. And rains. I'd like to figure out the 18" situation.

Auto_Werks 3.6

I'm not saying you're wrong about needing a set of rains... but the pricing on the R7 in that big 16" size is cheap compared to the big street tires in 18" sizes. When I saw the price I was jealous that I can't put tires on my GT3 for that cheap. And yes there's some valid argument about how long a hoosier will last, but in reality longevity is kind of out the window with the super street tires too.

FrenchToast

18" has a very good, maybe the best, selection for wheels and tires. But, that doesn't mean they are the best choice for the car.

The shorter sidewall on an 18" tires is going to transmit more force into the wheel and the suspension.

How are you running Turbo S spindles on early offset? Nevertheless, I don't know what kind of extra loads a spacer is going to have. Turbo S spindles are probably undersized if you're running that much power, especially with wider front tires or any downforce. The 968 TRS was probably the outer, outer limit of what those parts were designed for; and I'm sure Porsche Motorsport had a pretty aggressive service and inspection interval. And that was with tire technology from 25 years ago.

If you are running wider tires and downforce, you should probably meet with a suspension engineer and develop a service interval to crack test the hubs and spindles. Wider, newer tire technology and downforce likely exceeds what the parts were designed for.

Additionally, with 400hp and wider tires, your S4 calipers probably are soon to be or are already overpowered.

Yes, the bearing grease will leak out if it isn't fully sealed. To remove the lip you'd need to make custom caps. Due to the nature of their construction, I think if you shave the lip significantly they would fall into two pieces.

Player0

Yeah, I'm planning to UV dye test the spindles at least yearly. But you could well be right, it could be way too much for these stock parts. I do see some people claiming to run 18" wheels at the track here but was hoping to see more recent accounting of that.

The S4 calipers aren't yet overpowered but to replace them would take 17" rims. The weight difference between a 17 and 18" rim is not enormous. It's possible the S4s would be overpowered with heavier wheels however. I'd welcome less brake lock up since I don't have ABS.

I have camber plates which allows the spindles to work with early offset and maintain the kingpin angle, which would be greater on a late offset car. I don't take credit for knowing how this works, I just did this several years ago when setting up the car from Rennlist advice.

I can convert to late offset simply by switching to the late offset control arms in the front. But doing the rear would be more involved with the trailing arms but I don't think it would buy me much.

944crazy

Easy way to get a basic idea on the scrub radius is to turn the steering back and forth with the car on the ground (ideally on dirt or dusty concrete or similar) and then roll the car forward a little. You'll be able to see concentric circular marks on the tyres, and the centre of those marks is the axis of rotation. Where that axis is in relation to the centreline of the tyre will tell you wether you have positive, zero or negative scrub radius.

GPA951s

FWIW, I am running 17's (88 Turbo-S) If you are running the Turbo-s spindles, I wouldn't worry about them as much as I would the Ball Joint. With stock type tires, I never worried about A-Arms /ball joints.. They just cant generate the G force.. They slide too much.. I have been running Toyo 888R's. They are a decent track tire and for the money.. you really cant beat them. Sure you will be slower than Hoosiers but you need to determine if Shaving a little bit of time is worth an extra $400 a set? This year I am actually Racing, so I will be on Either Hoosiers or Hankooks. I will STILL Run the Toyos at DE's
Once you start going faster and having longer runs.. You will find that the Grease cap will pop off the front of your car.. The heat builds and even with a tiny bit of moisture they pop off and end up somewhere on the track.. You can put a setscrew in them OR Drill a Tiny hole in them to vent... This didn't happen to me until I was Really Driving the car Hard...

And By the way, The Track Records for MANY Tracks here on the East coast is held by a guy who runs 15" Rims...

Player0

Yeah I like the 888s. They're a solid tire though I've been getting faster times on RE-71 and S4s for some reason on the other cars. So a little more about my suspension, I have the lindsey steel lower control arms, the racer edge hubs, and escort cup struts. Spherical mounts all around.

The grease cap thing is super annoying. I have set screws in the hubs now that hold them on solid. I've never lost one out of the wheel though, but I do bring spares!

Awesome tip for the scrub radius dust thing. That's super helpful.

I've been searching and searching, trying to find any evidence of suspension failures caused by 17 or 18 wheels and I'm not seeing much. Porsche recommends not using 18s for anything old in a non-specific way but don't have an issue 17s on the 944.

I'd reckon my stiff suspension or heavy springs would be harder on the suspension than a couple extra pounds of unsprung mass. But I am still worried enough about the unknown that I may not run them

JustinL

I've tracked and raced on 18s. They are a bit big and heavy, but that's never been the part of the car that's let me down. My 18s are forged 18X10 and running RA-1 tires or sumitomo HTR zIII street tires. We also ran some tanks of 18X8 Fuchs replicas with RE-11R tires for endurance racing on a n/a 944. They slow the car down, but we never had trouble over 12 hours or whatever they were on the car for. We try to keep it off the curbs (except for Brock). For the rear I'm very confident that 18s won't cause anything to fall apart... in the front though I worry about the castor block and the ball joints. My fastest laps are on 16X9 clubsports with hankooks on the race car, but 16s don't fit over the big reds on my 951S street car. For that car, 17s are the best performing, but again the tire selection is dwindling. Also this is a good excuse to spam the board with some car pics!

Player0

Thanks Justin, awesome cars.

Do you run the stock castor block? I have the elephant racing control arm monoballs and hopefully they're an upgrade.

The lindsey control arms still have a 17mm pin. I was thinking maybe I should move to a 19mm pin. But then I'm weakening the spindle by boring it out.

JustinL

On the Yellow #144 and the 951 I have Charlie arms (with 19mm pins) and High Strung arms (with 17mm pins). The ball joints are a wear item, so you have to keep an eye on them and be prepared to replace them. The castor blocks are all spherical bearings now on those cars. On the n/a we ran with champcar, we were restricted to stock components, but now that that series is done in Canada, I think our team will move to some more sturdy arms and components. We did upgrade the castor blocks to the 968 style on that car too though.

I haven't seen many pictures of broken spindles. Where do they normally fail? And was it a fatigue fail, or impact?

Player0

My understanding is that it's the smaller pre-1987 spindles that have cracked. And I've heard of hubs cracking too but I don't recall the details.

I might upgrade to 19mm ball joints. I looked in to what sizes are used on other cars and 17mm seems a bit small.

My only concern with the 19mm pins is reaming out the spindle which I assume would make it weaker. With your 19mm pin arms, did you braze extra material on to the spindles to account for the material loss?

And just to be clear, you're worried about failures with the upgraded castor blocks?

JustinL

It's been a long time since I was under the #144 (engine fire), but I don't think the spindles are built up at all. It was the previous owner of the car who did the suspension build, but I think they were just machined out. Interestingly High Strung doesn't even make 19mm pin control arms and they seem to hold up pretty well. That car also has forged Racers Edge hubs so I'm happy about that. I think the M030 hubs are also a bit stronger.

As far as the castor blocks, the only reason I think about that one is because of the bulletin from Porsche saying that you need the 968 style caster blocks to go to 17s, so I would assume that it's even more important with 18s. I'd only be worried about the old style castor blocks.

GPA951s

I Saw one of the high strung44 A arm snap at Watkins Glen last year... I ended up going with the Fabcar arms, They ARE heavy but they are strong as hell and have one beefy ball joint. (No Drilling as well) .. My Friend hit the wall at Road Atlanta and bent the frame of his car, wrecked a rim, The castor block bolts were bent, and Even BENT the fabcar ball joint, But it never broke... The A arms were straight! Unfortunately I don't think Charlie Arms OR fabcar arms are in production anymore.