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[JMW928]

Landsharkoz.com has a 928 wheel guide in pdf format that’s probably the single best document written on the subject. Very informative and worth your time reading.

The factory had a “Cup Racer” spec that utilized Cup I’s in 17x9.5 ET68 offset. That’s about as wide a fitment you can use on the front of a stock 928. The rear can accommodate up to around 11” width without extensive modifications and ET is not as critical except at the extreme widths.

Years ago over on RL, user Andrew Olsen (“AO”) created a wheel fitment calculator in Excel format. You can probably search and find it though who knows whether or not the link to the spreadsheet still works.

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[ladybug83]

These Rotiforms popped up on my Instagram. I think it’s a cool modern interpretation of the phone dials. Love the color too. Maybe someday.



But for now, I’m sticking with the satin black CIIIs. Really impressed with the comfort of the Hankook Ventus V12, quieter and softer ride than I had expected from an 18” tire

[worf]

Augment Wheels can (supposedly) make any offset you want.

Best money I ever spent on any of my 928s was going from 7.5”/9” wheels to 9”/10” and from 225/245 to 255/265.

Don’t ask me the offsets. This is 1999 FFS.

Fikses with offsets available only via 928 Specialists because D.R. indemnified Fikse against ‘doesn’t fit’ returns.

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[worf]

Do you have any recommendations to consider? Width, diameter, stance, design...it's all on the table at the moment.

Here are my recommendations:

- pick the tires first. Make sure the width, aspect ratio, and diameter you want are available. You may need to iterate. Your favorite Yokos wouldn’t work for me: no 17” 265

I had a whole bunch more recommendations and text, but fucking iOS safari ate my post when I switched to edit a photo.

TL;DR: Stay light. Stay at the OE overall diameter. Unless you’re a suspension savant.

Remove “stance” from vocabulary. Here’s ‘stance’, really great for track and A-X. Not.

[worf]

Front:
Tires - 255/35R18
Wheels - 18x9 ET67

Rear:
Tires - 285/30R18
Wheels - 18x10.5 ET40

I think those are very close to what I’ve selected for a set of 18” phone dials from Augment.

And I need to get off my ass and get my Fikses straighted. Last ‘authorized repair’ shop I spent 3 hours (round trip) lugging the wheels to blew me off after I’d made appointment on phone with owner.

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[worf]

When you have a chance, would you mind checking what the wheel and tire sizes and offsets are that you ordered? Also, are your fenders rolled?

Dude. When I wrote "Don’t ask me the offsets. This is 1999 FFS." what did you think I meant? :)

1999. That paperwork and neuron ship sailed a long time ago.

Wheel sizes are 9"x17" and 10"x17 in whatever offset D.R. specified. D.R. may remember but only Fikse knows and only if they've not thrown away those paper files.

Tires, OTOH:
255/40-17 and 265/40-17, which last time I checked, I can't find anymore. So, once my Fikses are straight I've got to do something different.

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[worf]

I meant your new augment wheels. :)

Oh. Selected isn’t the same as ordered. My todo list includes double-checking my selection off offset against the Jim Doerr-offered offsets on his never-produced wheels and against the only prototype wheel RE test fitted versus available rear spacers.

As to the other question: GT; fenders rolled at the factory, but I've got plenty of room with the 10” Fikses.

[linderpat]

I have 18" Carrera 3's on my 85 shark. My fronts are 235/18/40 mounted, no spacers. I think they are 57 mm offsets. As to the rears, 265's did not fit my car on my wheels. With 20 mm spacers and then 15mm spacers, my left side in particular rubbed the fender on the outside. Without spacers, they rubbed on the inside. I ended u[p with 255/35/18 for the rears and use 15 mm spacers. They will fit with that configuration and result in the correct factory diameter, which affects speedometer readings. One thing I think is that 18's are really too big for the car from a handling perspective. I think 17's are ideal. I plan to put 17'' Cup 1's on next spring, plus I think they are the best looking wheels anyway. I had them on my garnet 85 and really loved them.

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[maddog2020]

One thing to keep in mind with custom wheel sizes. What tires are available today will not be available 5 years from now. Pick a size of front's and rears that are on a production car. This will ensure that the tires you buy today will have a better chance of being around later. When you start getting into some oddball combo's a few years down the road you will find lots of tires in the front or the rear sizes but maybe not in both front and rear sizes.

Stick with the 18x9 in the front and the `8x10 in the rear. the extra half inch isn't anything that you will notices but will drastically limit your tire choices down the road. Most car manufacturers don't do half sizes. make it easier for yourself down the road.

When I had my current fikse wheels made in 2007 the tire choices were endless. now I have 2 choices and neither of them are available in the winter or early spring.

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[worf]

One thing I think is that 18's are really too big for the car from a handling perspective.

Factory 18" (and bigger) wheel sets for the later cars are heavy. I weighed my wife's 11.5x20" 991 rear summer wheel last week and it was ~58 pounds. The front <whatever>-x20" was ~51 pounds IIRC.

It's all about keeping unsprung weight as close as possible to what the factory suspension "wants." The wider tire is, itself, likely - if not definitely - going to be heavier that an OE-sized tire, thus making it more important to get a light wheel.

That's actually one of the open questions I have for augment: weight of various offerings. You can get forged magnesium which is nicely light. On the other hand, probably not a great idea for a street car that might see potholes. They ain't exactly cheap either.

Now, you can run a heavy wheel on a 928 but not with the stock dampers. You'd need custom valving for the dampers if not stronger springs too. I used to have a client that was a suspension idiot savant who could drive anything, come back and say "You need x% more/less bump and y% more/less rebound" and damn if he wasn't right every time. His 928 was *set up* and had some big-assed 18" wheels.

If you want to experiment you can order (maybe still order) Bilsteins (from them directly) with "Leguia 928" valving that might just work better with heavy wheels.

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[worf]

Am I missing something?

Nope. Not a thing.

Just make sure to double-check once you think everything’s ‘set’ and that the order’s in at Fiske.

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[worf]

You mean by some other method besides asking 928 Specialists for the status?

That’s what I mean. With “2020” going on I just assume that a larger-than-usual percentage of things will not be perfect. Since I get many orders from the big three and, additionally, deal with many other service providers I can tell you that the general error rate throughout the supply chain is higher than usual. Key folks here and there get distracted. Following-up early is risk mitigation.

For example: a part I ordered - not from our Big 3 - that I need tomorrow is now either not shipped or has been misrouted after arriving in my state. Had I checked the status the day after I ordered I might have been able to mitigate the risk of the first case.

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[maddog2020]

Tires are designed to fit on a range of rim widths, not just one specific width. They do specify what rim width the section width specification is accurate for, but that doesn't mean it's the only rim that the tire performs well on.

I don't think this is news to anyone on this forum. Different tire sizes overlapwheel sizes. The point that I'm making is that not every tire goes from a 195 to a 345. There are gaps in sizes for a reason. Tread models are designed for specific car models or classes. I went with 18x9 and 18x12, because there were tons of tires in the 265/35 18, and also in the 335/30 18. Nobody makes a 325/30/18. Now there are only 2 street legal options. I don't like the stretched look where the tread is more narrow than the wheel. I'm on my 3rd set of custom wheels on the 928, and 2nd set of Fikse's. You might want to wait on your order, as Fikse is coming out with some new finishes. The current technipolish is a fragile finish and if it is marred or srcatched, you have to get a new center as it can't be re'cleared because getting off the clear will change the surface. not to mention what ever gouged of the clear coat damaged the wheel center.

just trying to help out. Because tire models are seasonal, and some sizes are only made one production run per year, and if you have a blow out or failure you have to wait until they are available to get a matching tire. I've had all this stuff happen, and I'm OCD about my wheels and tires.

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[Mrmerlin]

Rob Edwards has 17 inch phone dials custom made you might want to check them out

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[maddog2020]

measure the backspacing, and what rim halves are what. You will find that the Fikse wheels stick out some in the front. I have the FM 10's and they stick out on the front. They always have. Measure from inside the bead to inside the bead as well as from the seal where the halves meet to the outer bead surface. I'd be interested in seeing your build sheet. Should be a fikse doc that shows what the measured bits are.

Now I'm going down the rabbit hole of the negative spacer even after buying Fikse wheels. Glad to see you got your wheels. I emailed DR last week to see if he had any records on mine, and I guess since I live within 25 miles of Roger, I'm now non gratis.

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[maddog2020]

Measuring the backspace and all dimensions is one of the first things that I did. I did not receive what I ordered.

I'm going to leave it at that until I can get a little more clarity on whether or not the situation will be rectified.

For your wheels, you can send Fikse your serial numbers and they can tell you the specifications that the wheels were built to.

no, they can't. dealers may tell you that but I've spoken to the current owners as well as past owners, and that info wasn't transferred with the sale. Jim Fikse went bankrupt. Kodiak wheels purchased the designs about 1.5 years after Fikse went dark. Then it was sold to the current owners, who don't even have some of the center cap designs. Center caps came in 3 flavors. Flat which where about 1/4 inch thick and concave on the back which won't work with the 928 front wheel bearing dust caps. (those are what is on your wheels) Then there were the medium dust caps that worked fairly well, for the 928 dust caps but the current owners can't make because they don't have the cad drawings for them. These were about 3/8ths of an inch tall and actually looked nice. Then there are the tall ones that are about 1 1/4 inch tall. I call these the dolly parton versions because they are huge. If you buy them now, yes the current owners have your specs, but if it gets sold again who knows. I love my fikse wheels but they are not for everyone, and to keep them you will have to have some thick skin if they get sold again.

In looking at your pics of the fronts, I'm betting you got 7's and 2's which puts the wheel center too far inboard. I have 8's and 1's which is the shallowest they can go, and they still don't fit correctly. on the 17's they made wheel centers that were thinner but not sure why they can't with the 18's.

[Scott at Team Harco]

The wheels have arrived:

 

image.png

Nice looking wheels. Looks like a lot of offset. Too much?

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[worf]

I emailed DR last week to see if he had any records on mine, and I guess since I live within 25 miles of Roger, I'm now non gratis.

Did you send email to "928specialists at gmail dot com" or some other ancient address?

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[maddog2020]

My old 17" fikse wheels had 1/4" thick spacers screwed to the back side where the wheel bolts to the hub/rotor. I took them off because they stuck out further than I like. My 18's didn't come with the screwed on spacers. Looking back now I wish I had taken more measurements and pictures of the 17's. I'm worried that your fronts may stick out further than mine do.

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[Scott at Team Harco]

So the real question is: how do they fit?

[maddog2020]

for the fronts the outer lip is a 1" and the inner barrel is an 8" back spacing is 7 1/8th which would be a 54 backspacing.

make sure you are measuring the backspacing from the bead surface. where you would see the 9" measurement.

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[maddog2020]

if you are going from outer lip for backspacing you better calculate 9.5 width instead of 9.

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[maddog2020]

I measured my wheels and outer lip to outer lip is 9.5, You can't use 9 inches to calculate your offset, as your wheel size ,and then measure backspacing from the outer lip when lip to lip is 9.5.

you'll figure it out mount the tires and get it on the ground. you can't tell squat with the suspension hanging.

try arguing with the wheels and tires at that point. I'm not posting on this thread again as you are the wheel god and know what you are doing and can forsee the future.

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[Scott at Team Harco]

Offset is the dimension between the center of the rim to the hub-mating face of the wheel. The center of the rim is easy to measure on the side that the tire likes to live on. Finding that same centerline on the inboard side of the wheel is more difficult.

Rim width is measured from one bead seat to the other. Not from the outward extremities of the rim.

This all comes down to how well the wheel fits on the vehicle. If you have the wrong offset, you will have issues. Too much offset and the wheel will sit inboard too much and may actually create interference. This is not good. Sometimes, spacers can be used to correct this. Not enough offset and the wheels extend outward too much. This usually causes a non-optimal force (moment) on the wheel bearing.

For what it's worth - backspace - is a dumbed-down method of measuring offset. It is never used in the wheel manufacturing industry. It is only used as a method for approximating offset for those that don't understand how to work through this properly.

I'd like to see photos of these wheels trial fitted on the car. You will be well advised to do this before having the tires mounted. Best of luck.

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[Scott at Team Harco]

What's your degree in?

How long were you a wheel and tire engineer?