The SERIOUS Wheel & Tire Thread

Real tech discussion on design, fabrication, testing, development of custom or adapted parts for Pontiac Fieros. Not questions about the power a CAI will give.

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Re: The SERIOUS Wheel & Tire Thread

Post by The Dark Side of Will »

Series8217 wrote: Pics? Also what camber setting?
-1.5 camber
I have some pics somewhere... I'll see if I can dig them up.
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Re: The SERIOUS Wheel & Tire Thread

Post by The Dark Side of Will »

Pics with the previous set of tires:

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Re: The SERIOUS Wheel & Tire Thread

Post by Series8217 »

Based on those photos..

I would definitely consider that "sticking out past the bodywork". The sidewall looks to be almost even with the outer edge of the moulding on the door, and is past the top of the fender.

I wouldn't want to run with that clearance in a class with a "tires may not stick out past the bodywork" rule.

It looks like it needs to go in about 1/4" to 1/2" or so to fit within the confines of the fender.

It doesn't look bad from the pics, but a tire having a straighter sidewall (like a 30 or 35 aspect) won't have that rounded shoulder transitioning to the fender, and it'll be plainly obvious that it sticks out beyond the fender.
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Re: The SERIOUS Wheel & Tire Thread

Post by Series8217 »

I looked at my 17x8-48mm wheels out in the garage and they also appear to be past the top of the fender, and yet they actually look "sunk in" (too narrow). I guess the Fiero's rear fenders are weird.
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Re: The SERIOUS Wheel & Tire Thread

Post by The Dark Side of Will »

My goal with that fitment was no rubbing... I wasn't trying to meet someone's definition of "inside the bodywork".

*My* definition of "inside the fenders" is that the tire doesn't rub throughout the range of suspension motion... WITHOUT being so stiffly sprung there isn't any suspension motion.

The belt line creates a crest at the top of the fender; it makes it tough to visualize from photos, as well as allowing things to clear that don't look they should. I personally like the aesthetic.
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Re: The SERIOUS Wheel & Tire Thread

Post by Series8217 »

My 18x9-45s will be here today so I can test fit them. Tires should arrive in a few days, but the front wheels won't be here until next week.

I also ordered an Orange TPMS to go with the new shoes, so I don't have to have my current tires re-mounted to get the sensors for my Hella TPMS. I would have bought another Hella TC-400 TPMS, since they are awesome, but they're no longer available :-(. The Dill system I got for my Outback is terrible, so it looks like Orange is the only other reasonable option. I mainly use the TPMS to monitor temperature. The pressure measurement is not super accurate, so I still check everything with a gauge.
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Re: The SERIOUS Wheel & Tire Thread

Post by Series8217 »

I installed the 18x9 (+45mm offset) Motegi MR116 wheels with 275/35/18 tires on the rear today. They fit with no interference. There is adequate clearance to the spring, strut, upright, and trailing link. I have 10" springs on coilover sleeves, with the welded spring perches removed. I had tied the ebrake cable on the driver's side back close to the framerail to clear my old wheels. It still clears by at least 1/4" at normal ride height.

As far as appearance goes: They fit reasonably flush at 2.5 degrees of camber. At 1 to 1.5 it pokes out a bit at the top. They look enormous, especially since they don't have much of a lip. 17s with a slightly smaller rolling diameter probably would look better. 18s with a dished lip and/or concave spokes would look good too. Once I have the fronts I will be able to comment more on overall stance and looks.

Regarding the tires... It looks like the 275s would have a wider contact patch on a 9.5 or 10" wheel. My 18x9s have the minimum rim width for the 275/35/18 Hankook RS3. That said, the tire is still almost an inch wider than my old 255s.

I weighed the wheels before having tires mounted. They are 25.16 lbs each, with no valve stem or centercap. I think my old 17x8s were only 20 lbs. 5 lbs is a lot of weight to gain for 1" of diameter and 1" of width. Perhaps these are built for a higher load rating. The 275/35/18 Hankook RS3s are supposed to be 27 lbs each according to the specs on Tire Rack. My 255/40/17 BF Goodrich g-Force KDW 2s were also 27 lbs each. So I gained 5 lbs of unsprung weight per rear corner in exchange for almost 10% more rubber.

I don't expect the front weight to change my more than a couple pounds. The 215-45-17 RS3s are 1 lb heavier than my old tires (205-50-17 KDW 2s), and the wheels also weigh 1 lb more, even though they're the same size. I wanted to continue running 205-50-17 up front but the RS3 isn't available in that size.

Accounting for numerical tire width only, my new tire stagger will be 43.8% to the front. My old stagger was 44.5% to the front. Since I have increased diameter in the rear (from 25.0" to 25.6"), and reduced it in the front (from 25.4" to 24.6"), that should further improve stagger, since the front contact patch should be slightly smaller fore-to-aft, and the rear slightly larger.

I expect that going from the BFG KDW 2s to Hankook RS3s will be a much more significant improvement than the marginal stagger increase, and I couldn't have done the upgrade to RS3s without losing some front to rear balance if I kept my 17x7 and 17x8 wheels. The only option would have been 215-45-17 and 255-40-17 which is 45.7% front. In addition, the 17x8 is actually smaller than the minimum rim width range for a 255-40-17, so the contact patch was likely smaller than intended (though perhaps more tolerant of the horrible camber curve).
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Re: The SERIOUS Wheel & Tire Thread

Post by Series8217 »

Got the fronts mounted and put them on the car today. Everything fits fine. Front wheel gap is a bit larger than before since the front diameter is smaller, and there's a lot more rake since the rears are bigger AND the fronts are shorter. Appearance-wise, needs more lowering. But I'm going to the leave the ride height as-is, in the interest of not messing with the suspension geometry.

My driver's side inner CV started leaking grease; looks like it may have been hitting the forward lateral link inner mount. I need to adjust the mounting position of the drivetrain before I can drive it more. There's an autocross coming up at the end of January so that will likely be the next time I do some testing.

I'll post pics sometime this week.
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Re: The SERIOUS Wheel & Tire Thread

Post by Series8217 »

Motegi MR116 17x7-48mm and 18x9-45mm with 215/45/17 and 275/35/18 Hankook RS3:

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The 17x7-48mm Motegi MR116 with a 215/45/17 Hankook RS3 weighs 42.6 lbs.
The 18x9-45mm Motegi MR116 with a 275/35/18 Hankook RS3 weighs ??? lbs. (I made a measurement but I can't find it. I'll edit it in when I find it. Should be about 50 lbs).

Slightly lighter wheels with the correct width and offsets would have been ~$200/$300 each (instead of ~$130/$160 each) with a 8-12 weeks lead time. Team Dynamics Pro Race 1.2 would have been my other choice. Their 17x7 is 3 lbs lighter. However their 18x9 is still 24 lbs like the MR116. There seems to be a big jump in weight going from 17s to 18s.

For reference, my old wheels were 17x7-42mm Raze R74 with 205-50-17 BFG KDW2s at 40 lbs and 17x8-48mm Raze R74 with 255-40-17 at 44 lbs. So I did add some unsprung weight on each corner and almost 20 lbs overall. Not ideal, but probably inevitable without spending a lot more than I want to on this car.
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Re: The SERIOUS Wheel & Tire Thread

Post by The Dark Side of Will »

Nice setup.
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Re: The SERIOUS Wheel & Tire Thread

Post by AkursedX »

I just thought I would mention this since I own a '11 WRX. The '11+ WRX's use a 5x100 pattern and with the wider bodywork over the older models, many manufacturers are making 9.5" wheels for it. You can find many 18x9.5 wheels with ~40mm offset (Giver or take a few mm either way) pretty easily on the Subie boards. Also, the BRZ and FRS use a 5x100 pattern so I see wide wheels in the 5x100 pattern being quite popular and more readily available.

I just recently purchased a set of Black 17x9 et45 RPF1's for my WRX and I would have killed for this option when I had my Fiero. The weren't even that expensive (I got them locally at Oakos for under $250 a piece).

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Re: The SERIOUS Wheel & Tire Thread

Post by The Dark Side of Will »

Awesome.
18x9.5-40 won't fit the rear of an '88 without mods, though, will they?

I've been wondering what the most common offset of 18x8 is for the front of The Mule.
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Re: The SERIOUS Wheel & Tire Thread

Post by Series8217 »

AkursedX wrote: I just recently purchased a set of Black 17x9 et45 RPF1's for my WRX and I would have killed for this option when I had my Fiero. The weren't even that expensive (I got them locally at Oakos for under $250 a piece).
Yeah, there are now tons of options at the ~$250/wheel price point for wide 5x100 wheels in offsets suitable for a Fiero.
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Re: The SERIOUS Wheel & Tire Thread

Post by Series8217 »

I had my wheels at the shop to get the tires flipped and needed to set my car down on the ground, so I stuck my old rear wheels/tires on the front to see if they would fit.

17x8-48mm with a 255-40-17 fits on the front of the '88 with room to spare. I turned it lock to lock and don't see any interference.

Now to find some 6-spoke 18x10.5-40 wheels for the rear so I can run 315-30-18 back there with 255-40-17 (or 245-40-17) up front......
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Re: The SERIOUS Wheel & Tire Thread

Post by Series8217 »

I just talked to Fred Goeske, the wheeladapters.com guy.

Depending on what the back of the wheel looks like, it may be possible for him to make me an 20mm-thick adapter from 5x4.75" (Corvette) to 5x100mm (Fiero). That is a very thin adapter. I think the reason the back of the wheel matters is because he could use the extra room for the hub stud nuts to stick out past the face of the adapter.

Various track-oriented rims for the Corvette are available in 18x10.5 with a 65mm offset, such as the TSW Interlagos. With a 20mm adapter that puts them at 45 mm effective offset --- exactly what I have in the rear right now with an 18x9. Clearance to suspension components will be tight (my e-brake cable rubs on the inside, and there is ~1/4" to the trailing link) but I could always space it out a bit if I have to, or modify the suspension link. Without spacers, it will poke an extra 18mm. It will look fine, especially since 17x8-45mm up front will be poking out a tiny bit anyway.

With a 17x8 front and 18x10.5 rear, I can run 245/40/17 up front and 315/30/18 in the rear. The BFG Rival and Hoosier A6 are available in that fitment.

If the front of my car ever gets heavier (bigger brakes, radiator, aero or something else) I can move up to a 255/40/17 with no other changes.

Total cost for BFGs, wheels, and adapters $2k. Or Hoosier A6s for Time Trials or Solo Street Modified would be $328 more.

Probably going to need some stiffer springs though, to keep body motion down with the higher cornering forces. 800 lb/in in the rear would need something like a 1900 lb/in spring in the front to keep the frequencies close with the crappy motion ratio of the A-arm suspension. I don't know if Koni reds can be revalved to be reliable with that kind of spring rate. I'll have to do some research to see what's sensible...
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Re: The SERIOUS Wheel & Tire Thread

Post by The Dark Side of Will »

315/30 sounds a bit wide for a 10.5 wheel... Do the tire MFG's recommend that?

The total system cost goes up sharply. To handle spring rates like that, you'll need to go straight to a race damper. I would not expect that a street-based unit could satisfy you in that performance envelope.

Koni Motorsport has "universal struts", which are basically just an aluminum damper with a steel sleeve on the bottom. You weld whatever bottom securing mechanism your strut uses to that sleeve and race. They're about $1200 each.

And once you upgrade to spring rates like that, you get into difficult questions, like how your wheel rates compare to that of the "fifth spring".

What's your wheel bearing life going to be like with tires that wide and sticky?

At that point, save yourself frustration and buy a race car.
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Re: The SERIOUS Wheel & Tire Thread

Post by Series8217 »

The Dark Side of Will wrote:315/30 sounds a bit wide for a 10.5 wheel... Do the tire MFG's recommend that?
BFG lists the rim width range for the 315/30/18 Rival as 10.5 to 11.5 inches. The Hoosier A6 in the same size needs a width of 11-12".
The total system cost goes up sharply. To handle spring rates like that, you'll need to go straight to a race damper. I would not expect that a street-based unit could satisfy you in that performance envelope.

Koni Motorsport has "universal struts", which are basically just an aluminum damper with a steel sleeve on the bottom. You weld whatever bottom securing mechanism your strut uses to that sleeve and race. They're about $1200 each.
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..

For a natural frequency of 2.2 Hz up front and 2.5 Hz in the rear, the required spring rates are 1100 lb/in (front) and 813 lb/in (rear). These go down a lot if the car gets lighter or if the tires are stiffer -- I'm assuming 2000 lb/in here. More unsprung weight (which is gonna happen with bigger brakes and wheels) also decreases the required spring rate. So it may be around 1000 up front and 750 in the rear. Not impossible for an 8611 in the rear.

The front is an unknown, I think it will require some shock tower and LCA modifications to fit something that will handle those rates.

I don't really expect to have double the cornering capacity; maybe 20% more... but the spring rates above would be the ideal.
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Re: The SERIOUS Wheel & Tire Thread

Post by Shaun41178(2) »

How much will unsprung weight increase with the corvette rims over your current rims?
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Re: The SERIOUS Wheel & Tire Thread

Post by Series8217 »

Shaun41178(2) wrote:How much will unsprung weight increase with the corvette rims over your current rims?
Actually they will be lighter...

Motegi MR116 18x9 - 23 lbs (current rear)
TSW Interlagos 18x10.5 - 21.05 lbs (new rear)

Motegi MR116 17x7 - 20 lbs (current front)
TSW Interlagos 17x8 - 17.1 lbs (new front)

Hankook RS3 275/35/18 - 30 lbs (current rear)
BF Goodrich Rival 315/30/18 - 29 lbs (new rear)
Hoosier A6 315/30/18 - 27 lbs (alternate new rear, need 11" wide wheel though)

Hankook RS3 215/45/17 - 22 lbs (current front)
BF Goodrich Rival 245/40/17 - 24 lbs (new front)
Hoosier A6 245/40/17 - 21 lbs (alternate new front)

So with the Rivals I would drop 3 lbs per rear, and 4 lbs per front. More if I do the A6, minus the weight of the wider rear wheel required for the A6 vs the Rival.

The adapters will add a bit of weight back to the rear.


I would expect to add some weight with bigger brake rotors and calipers, though that could be offset with aluminum hats.
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Re: The SERIOUS Wheel & Tire Thread

Post by The Dark Side of Will »

Series8217 wrote: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.

The front is an unknown, I think it will require some shock tower and LCA modifications to fit something that will handle those rates.
Does AST have universal struts? I see they have apps for Porsche and Subaru.

A universal inverted strut would be ideal for the Fiero, as it would BOTH reduce unsprung weight AND give slightly more wheel clearance. I've maintained for a long time that a 10" wheel on the rear of a Fiero is workable, but an 11" would definitely be badass.

I was browsing the WCF site recently to see what things they have and found this: http://www.westcoastfiero.com/suspensio ... hocks.html

Looks viable, unlike some of the other things they do.
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