The SERIOUS Wheel & Tire Thread

[Series8217]

Series,

Could you do me a huge favor and provide a measurement of the inside diameter of your 17"x7" Motegi fronts? The C5 front brakes might be too large for some 17" wheels.

Yes, I'll try to remember to do that next time I have the wheels off.

[The Dark Side of Will]

Right after I got out of college (close to 15 years ago? yikes) I bought a set of C5 Corvette wheels for a good price. They've been boxed up in my dad's shed ever since.

The rears are 18x9.5 with something like a 65mm offset. Comparing that to the front spacing of my current wheels leaves about an inch for a bolt circle adapter. I'll have to play with my Wheel-Rite and maybe order a single adapter from Skulte (or make one...), but I'll get started checking that wheel for fit and then move on to testing a 285/30-18.

This guy is trying 18x9.5-45's: http://www.fiero.com/forum/Forum2/HTML/134871.html

And is a bit worried about fitment. I have my threaded sleeves sitting on the strut clamp, so I'll have less clearance than he currently does, for the same offset.

Another guy in the thread claims he's running 18x9.5-40's with 1/4" spacer and clears coil overs.

My 16x8-25 wheels have ~76.6mm of *FRONT* spacing, which is close to as far as the wheels can stick out and tuck under the stock bodywork on compression.
An 18x9.5" wheel with 76.6mm of front spacing will have a 44mm offset. Hmm...

Oh well... I'll find out if incremental adjustment can make it work.

[The Dark Side of Will]

TireRack shows a Sumitomo HTR Z III for $142... lol. Listed as "Max Performance Summer" with a treadwear rating of 300... also lol. Will be worth it for test fitting.

[The Dark Side of Will]

I took a few to swing my Percy's WheelRite today. It measures a max of 5 1/8" of back spacing, but that wasn't enough. The '84-'87 Fiero can take about 1 3/8" more than that or 6.5" total with a rear camber of ~-1.5 degrees. This is a "bare clearance" fit and would not be appropriate for actual use... you know... with a tire.

The C5 Corvette rear wheel has an "outside" backspacing of 10 9/32 - 2.660 = 7.62" or 7 5/8 including the exterior "lip" or about 7 1/2" to the "inside" corner of the wheel, which is the part we have to worry more about.
I'll use the larger number for the sake of margin.

So the Fiero can fit 6.5" of backspacing and the Corvette wheel has 7 5/8" of backspacing, I need to make the adapter 1.125" thick. The hub circle is 5x115mm with 2.76" hub pilot (please check if you know the spec... I just measured my hub). The wheel bolt circle is 5x4.75" with a... fudge, my calipers won't fit into the Corvette wheel.

The internets say 70.6 mm (2.779").
http://www.corvetteforum.com/forums/c5- ... heels.html
http://www.corvetteforum.com/forums/c5- ... r-hub.html

[ericjon262]

anyone running a 5x4.5" wheel pattern?

[The Dark Side of Will]

I haven't heard of any currently.

I don't know enough about spline compatibility to know how to put together axles that would facilitate the swap on a Fiero.

[fieroguru]

anyone running a 5x4.5" wheel pattern?

JIms88 installed the 5 x 115mm LS4 W-body wheel bearing into the 88 rear uprights. He ended up redrilling them the to the 5 x 4.5" pattern in is LS4 install thread, but kept the fronts stock 5 x 100mm (although they could easily be drilled to match the rear).

http://www.fiero.com/forum/Forum2/HTML/125016.html
http://www.fiero.com/forum/Forum2/HTML/125877-3.html

[ericjon262]

hmmm. I think I can swing the pattern swap a little easier than that b/c I have an early car. although, I do have 88 uprights sitting in the garage and have been wanting to make some upgrades... thanks for the links.

[The Dark Side of Will]

Here's the wheel adapter which I will use to install C5 Corvette 18x9.5 rears on The Mule. It was made from a random scrapped part that my dad pulled out of the bin at the place from which he is semi retired. That's why it has the one wonky hole and the extra 6 bolt circle.



With some nuts and washers dropped into the counterbores. I've had nuts and washers on the table for a couple of months. I snagged some Dorman 610-323's tonight and will be installing shortly.

[The Dark Side of Will]

hmmm. I think I can swing the pattern swap a little easier than that b/c I have an early car. although, I do have 88 uprights sitting in the garage and have been wanting to make some upgrades... thanks for the links.

I'm sure you've read about the A-body large pattern hub carrier swap. It bolts in, uses the Fiero ball joints and the outer CV's plug right onto the Fiero manual transmission axles. They also have vented 10.5" brakes with giant iron single piston calipers. The down sides are that you lose the partking brake and gain 13# of unsprung weight (!) per side. I have this on The Mule and that's how I'm running the 16x8 Grand Prix wheels on the rear.

If you're *REALLY* serious, then you can use the U-body minivan (Dustbuster!) hub carriers. I have not used those, but I've been told that they take larger ball joints than the Fiero units, but these ball joints still bolt into the Fiero control arms. The bolt circle is still 5x115, but the hub bearings themselves and the splined shanks of the CV joints are larger than the A-body units. The CV joints still plug right into the Fiero manual transmission axles. Brakes are up to 11", likewise with big iron calipers. I don't know the weight gain, but it's likely over 15# per side.

[ericjon262]

hmmm. I think I can swing the pattern swap a little easier than that b/c I have an early car. although, I do have 88 uprights sitting in the garage and have been wanting to make some upgrades... thanks for the links.

I'm sure you've read about the A-body large pattern hub carrier swap. It bolts in, uses the Fiero ball joints and the outer CV's plug right onto the Fiero manual transmission axles. They also have vented 10.5" brakes with giant iron single piston calipers. The down sides are that you lose the partking brake and gain 13# of unsprung weight (!) per side. I have this on The Mule and that's how I'm running the 16x8 Grand Prix wheels on the rear.

If you're *REALLY* serious, then you can use the U-body minivan (Dustbuster!) hub carriers. I have not used those, but I've been told that they take larger ball joints than the Fiero units, but these ball joints still bolt into the Fiero control arms. The bolt circle is still 5x115, but the hub bearings themselves and the splined shanks of the CV joints are larger than the A-body units. The CV joints still plug right into the Fiero manual transmission axles. Brakes are up to 11", likewise with big iron calipers. I don't know the weight gain, but it's likely over 15# per side.

not really interested in that huge of a weight increase, and I've also since acquired an 88 rear cradle, so that's gonna happen too. right now, I'm trying to find options to swap to a wheel pattern that offers more wheel options or adapting the C5 parking brake to mt stock '88 uprights. at the same time too, I'm trying to find an outer CV that can take a little more abuse...

[The Dark Side of Will]

I can get ASTs for half that price that will handle a 800 lb/in spring.. Koni 2817s (your $1200 struts I assume) are nice but not necessary for a 600-800 lb/in wheel rate. A Koni 8611 is only $350 per corner and I can easily fabricate a housing for it if it doesn't fit in the stock Fiero housing. I understand that they can be revalved to handle around 800 lb/in, but its close to the limit. Anything above that and a 2817 would be necessary. I will talk to my Koni rebuilder and see what they say. Bilstein has universal motorsports struts now but I haven't found a dealer yet. I'd like to check out their offerings since they're usually owner-rebuildable. I need a better excuse than simple curiosity for building my own shock dyno anyway..

I was looking to refresh my memory on your spring rates before I order new springs, and came across this quote. We need to have a discussion about building Fiero-specific wide-tire strut housings. For example, like Bilstein did for their inverted struts. Have you stumbled across a common shock "form factor" which multiple manufacturers use which would be suited to that job?

By "wide tire" I mean using a taco clamp that pushes the strut 3/4" or so further from the knuckle, making room for wider wheels.

[pmbrunelle]

I decided to dust off an old Drag DR-31 17x9 ET+38 wheel I purchased for fitment purposes:
http://www.fiero.com/forum/Forum2/HTML/138710.html
It appeared to fit OK.

Of course, since I bought the Drag wheel in 2016, and the manufacturer is a shitty company without a stable product offering, I missed the boat to buy three matching wheels...

Now that I have a sort-of-working powertrain, I can pay attention to wheels/tires again. Nowadays, I'm leaning towards Enkei RPF1 wheels (seems to be a stable product).

For the rear, they come in a 17x9 ET+45 version. This will bring the wheel closer to the strut, so this brings clearance concerns. The worst case for strut clearance is with the maximum amount of negative camber.

In this initial evaluation, I am assuming that the Enkei wheel will be exactly like the Drag wheel, only shifted 7 mm closer to the strut.

IMG_5559.JPG (522.23 KiB) Viewed 4293 times

On the Drag wheel, I was able to fit a 14.4 mm socket in the strut-to-wheel gap (worst-case camber). Therefore, I would have a (14.4 mm - 7 mm = 7.4 mm) gap with the Enkei, which should be enough.

IMG_5560.JPG (495.5 KiB) Viewed 4293 times

IMG_5562.JPG (614.44 KiB) Viewed 4293 times

However, I would not be comfortable sliding a threaded sleeve over the shock body; that would reduce the clearance too much for my taste. So I may want to either use a stock-style spring perch, or install the threaded sleeve on the weld of the perch.

I guess that I should be wary of tires that have "rim protectors".

I am a bit hesitant to go with Enkei RPF1, because the 16x7 for the front has an offset of 35 mm. I'd probably rather have 50 mm or so, especially as I may want to space out the front wheels with a brake modification.

Since I am broke, I am also considering custom steel wheels; they might be a way to get the sizes I want at a price I can afford.

[The Dark Side of Will]

Well Huh... I thought I had put more info into this thread, but I guess not.

An early C5 Corvette rear at 18x9.5-61 will fit with a 25mm spacer/adapter. This means that a 17x9.5-36 (61-25=36) should fit without a spacer.

By "fit" I mean it will clear the strut at maximum camber and, if you assemble the suspension without the spring, then jack the wheel up until the strut has metal-to-metal contact with the bell washer underneath the strut top mount, the tire will just tuck just inside the fender. That's a 285/30 on the 18x9.5.... you can do the tire size math.

QA1 now makes "long travel" springs. I replaced my 325x12 old school standard springs with 325x10 LT springs and was able to raise the spring perch enough to be helpful with tire clearance. I also recommend seating the threaded sleeve on the spring perch weld, as you mentioned.

A long series of posts on my misadventures figuring all this out starts here: https://realfierotech.com/viewtopic.php ... 08#p152208

As far as the Enkei's go, tossing a 3-6mm spacer into the mix shouldn't be a problem.
Check out these guys for adapters that make sense: https://www.motorsport-tech.com/
Especially if the Enkei's have a larger hub pilot bore than the Fiero hub pilot journal, making hub-centric spacers won't be a problem. Their prices aren't bad either.

Check out Dorman 610-323 if you need a longer lug stud.

[pmbrunelle]

I remembered reading about your adventures with your dad's aluminium piece, I just didn't think to dig back and think to use your tire as a "working envelope" for my situation. It is a valid envelope for the tread and sides of the tire. Good to remind me of that.

For the inboard lip area of a 17" wheel, I don't consider your envelope (from the 18" wheel) to be applicable, due to the kingpin angle of the strut.

In my day job it is an objective to reduce parts count and assembly difficulty for the factory, so I carry this mindset to my Fiero project. I know that wheel spacers can be functional, but they go against my design-for-manufacturing objectives.

I found some wheels that almost fit the bill. Enkei PF05:
https://enkei.com/shop/wheels/racing/pf05/
16x7 ET+48 5x100
17x9 ET+40 5x100

I cannot say I really love the style, but I suppose they could grow on me. Looks like they would have enough room to install bigger brakes when the time comes.

The main problem with PF05s right now is that they are on backorder from Enkei. I have signed up to be notified by email when they become available again.

[The Dark Side of Will]

For the inboard lip area of a 17" wheel, I don't consider your envelope (from the 18" wheel) to be applicable, due to the kingpin angle of the strut.

So my finger would squeeze between the inner lip of the wheel and the threaded sleeve I have in place for my coil overs. I didn't try using a socket to measure it, but that's maybe 10mm. Welding on a perch for the threaded sleeve in order to lift the bottom of the sleeve so as to improve wheel & tire clearance would give 3-4 more mm of distance to the strut. I wouldn't have suggested downsizing to 17 if I didn't think that would work. I do get your concern regarding the angle of the strut though. That's what can let '88's run wider wheels than '84-'87 cars.

In my day job it is an objective to reduce parts count and assembly difficulty for the factory, so I carry this mindset to my Fiero project. I know that wheel spacers can be functional, but they go against my design-for-manufacturing objectives.

I found some wheels that almost fit the bill. Enkei PF05:
https://enkei.com/shop/wheels/racing/pf05/
16x7 ET+48 5x100
17x9 ET+40 5x100

I cannot say I really love the style, but I suppose they could grow on me. Looks like they would have enough room to install bigger brakes when the time comes.

The main problem with PF05s right now is that they are on backorder from Enkei. I have signed up to be notified by email when they become available again.

I happen to like that particular 5 spoke style

If you don't like spacers, you can always go to ForgeStar and have them cut you a set of wheels with custom offsets.

[pmbrunelle]

I superimposed pictures of the Enkei PF05s (on a grey Mitsubishi) onto a white bumperpad (like mine) Fiero pic I found online.

Fiero with PF05.jpg (800.64 KiB) Viewed 4244 times

Hmmm...

(not an mspaint.exe /photoshop expert)

[Honest Don]

I decided to dust off an old Drag DR-31 17x9 ET+38 wheel I purchased for fitment purposes:
http://www.fiero.com/forum/Forum2/HTML/138710.html
It appeared to fit OK.

Of course, since I bought the Drag wheel in 2016, and the manufacturer is a shitty company without a stable product offering, I missed the boat to buy three matching wheels...

Shame you can’t get more. We coulda been twinsies!

I’m probably not any help, mine are 3rd hand bought from a guy with a cavalier, who bought them from a guy with a neon I think.

17x9 and while they fit, the offset could be a little better. I had to massage the rear kyb spring perch a little to fit a 235/45-17. You would probably clear easier with the coilovers?

[pmbrunelle]

Heh, Fiero and Fiero is close enough already.

I'm preferring the 40 mm offset (vs. 30 or less) at the moment so the wheels don't stick out too much. That's according to my criterion of a police officer looking casually at the car, and then hopefully thinking it doesn't look modified. Well actually for myself too, I want my Fiero to look mostly stock.

This (fuzzy) criterion places the outside of the wheel more inboard than Will's (pretty clear-cut) objective of avoiding contact with bodywork.

********************************************************************************

Not always, but in a multi-aspect problem, I like to tackle aspects which are more constrained at first.

So I begin by focusing on getting the outside of the wheel where the car won't look too modified.

I have three possible solutions in my for spring perches, so that is a flexible aspect of the build. Therefore, I transfer difficulty from the outside wheel position over to the spring perch puzzle.

Once the wheel is where I want it, I shall have the mental bandwidth to deal with the spring perches.

I just need enough foresight to avoid painting myself into a corner.

********************************************************************************

I asked iRace Auto Sports in Ontario if they could order me one 17x9 ET+40 5x100 Enkei PF05 wheel, with a possibility of returning the wheel if it doesn't fit. I proposed to bring my strut assembly to the store, where I would be able to decide if I would take the wheel or not. I was willing to be refunded only half the selling cost, in order to compensate for their troubles if the deal doesn't work out.

I told them that I was 80% confident that the Enkei wheel would work out for me.

Anyway, from the risk evaluation (20 minutes of google) on their side, the risk was too high that the wheel wouldn't fit, and therefore they weren't willing to work with me.

As I purchased a $700 clutch from them this summer, I was expecting better service, but whatever, I guess I won't be vendor-loyal then...

[The Dark Side of Will]

This (fuzzy) criterion places the outside of the wheel more inboard than Will's (pretty clear-cut) objective of avoiding contact with bodywork.

I asked iRace Auto Sports in Ontario if they could order me one 17x9 ET+40 5x100 Enkei PF05 wheel, with a possibility of returning the wheel if it doesn't fit.

You are correct in thinking that the fitment I mentioned is rather obvious. It does protrude out from under the stock fender lip at ride height.

This means that a 17x9.5-36 (61-25=36) should fit without a spacer.

So if you want to cut 1/2" off the outside lip while keeping the inner edge where I have it, the resulting 9" wheel would have a 42mm offset. Anything from 40mm to 45mm would probably be good, with 45 biasing a little more toward your "stealth" criterion.