The SERIOUS Wheel & Tire Thread

[Series8217]

2000 Jetta / Mk IV GTI 15x6 (38mm offset) wheels will fit over 12" rotors with stock calipers when using West Coast Fiero's kit. There's just enough caliper clearance... around 1/8" in the rear and 3/16" up front.

These do take ball seat lug nuts. Honda lug nuts will fit Fiero studs, but I'm not sure if the ball radius is the same.

It's this wheel:


No grinding or other clearancing is required. They won't fit with Fieroguru's link drop / roll center correction brackets installed though.

Now I'm sure you're wondering "WTF? Why are you putting 15s on your car?"

I'll post some pics of them on the car this weekend.

[Series8217]

The reason for the 15s is because gravel tires are only made in 15" sizes:




Proof of concept achieved.

[The Dark Side of Will]

15's with 12" rotors is a snug fit... BMW did it on the E32 & E34 cars, but that's with a low offset wheel and a high offset rotor such that the rotor is basically in-plane with the inner lip of the wheel.

Racing slicks are WAY cheaper in 15" than bigger sizes

[ericjon262]

The reason for the 15s is because gravel tires are only made in 15" sizes:

Proof of concept achieved.

...

I have to ask... why?

[Series8217]

I have to ask... why?

I compete in SCCA RallyCross.

Racing slicks are WAY cheaper in 15" than bigger sizes

I don't have much interest in racing slicks that fit on 6" wide wheels. I can't fit very wide 15's in the wheel wells on my car; they'll run into the knuckle where the strut bolts on. The wheels need to have a larger diameter to clear the strut mounting brackets.

[The Dark Side of Will]

275/35/18 on 18x9-45mm wheels in the rear and 215/45/17 on 17x7-48mm wheels with ~10mm spacers, under extreme cornering load:


Static front camber is -3 deg with 12 degrees of caster. The rear has -2.5 deg of static camber, and fieroguru lateral link relocation brackets. You can see there is plenty of room for more front tire. However, the outside of the rear tire is rubbing on the inner face of the outer fender, and the inner shoulder is rubbing on the inner fender liner and a bit on the sheet metal. The inner sidewall also sometimes rubs on the trailing link a little bit. There is no room to go in or out with this setup.

Do you have pics of where the rubbing locations are?

Would the 285/30-18 that Terry Fair/Vorshlag likes be something that would be enough shorter to avoid some of these contact problems?

Bent trailing arms can be fabbed if that ends up being the last contact point.

[Series8217]

Do you have pics of where the rubbing locations are?

See: http://realfierotech.com/phpBB/viewtopi ... 60#p149048
It looks like that on both sides.

Tomorrow I'm converting back to my road course setup from the dirt configuration. Since I'll have the wheels off I'll try to remember to get some more pics.

Would the 285/30-18 that Terry Fair/Vorshlag likes be something that would be enough shorter to avoid some of these contact problems?

I don't know. It's shorter also 5mm wider on each side, and you have to run a wider wheel for a 285. Ultimately I think suspension travel needs to be limited further (stiffer springs). I'm still running a relatively soft setup of 1.8 Hz up front and 2.0 Hz in the rear (800#/in springs up front and 475#/in in the rear) with stock swaybars front and rear.

[The Dark Side of Will]

Do you have pics of where the rubbing locations are?

See: http://realfierotech.com/phpBB/viewtopi ... 60#p149048
It looks like that on both sides.

Tomorrow I'm converting back to my road course setup from the dirt configuration. Since I'll have the wheels off I'll try to remember to get some more pics.

Would the 285/30-18 that Terry Fair/Vorshlag likes be something that would be enough shorter to avoid some of these contact problems?

I don't know. It's shorter also 5mm wider on each side, and you have to run a wider wheel for a 285. Ultimately I think suspension travel needs to be limited further (stiffer springs). I'm still running a relatively soft setup of 1.8 Hz up front and 2.0 Hz in the rear (800#/in springs up front and 475#/in in the rear) with stock swaybars front and rear.

Is that photo behind the spring or in front?

Is there enough room for a 9.5"? I thought there was, but maybe not with -2.0 camber. I understand the camber's necessary and it would be silly to compromise camber to fit wider wheels and tires which would then be used less effectively because of the lower camber.

I'm running 16x8-20 wheels on The Mule, which have 81.6mm of front spacing. Your wheels calculate to 69.3mm of front spacing. I don't know if you actually have room for 12 more mm of front spacing with shorter tires or not. Your 275/35-18's and my 245/50-16's calculate to the same diameter. Mine are not as sticky as yours, so I probably don't get as much body roll, even though I'm only running 325# springs. Also, your '88 suspension and link relocation bracket cause your tire to move outboard a little bit more as the suspension compresses than my early rear suspension does.

[Series8217]

That's behind the spring.

There might be enough room for an 18x9.5; I'll have to check the strut body clearance to the rim. Obviously on an '88 you'll have to deal with the ebrake cable as well as the trailing link if you're running fieroguru's camber correction brackets.

Here's a pic from yesterday:


You can see evidence of rubbing in the large area on the right, which goes through to the metal underneath the plastic liner. Also at the top left that's a hole rubbed through the plastic liner. I don't think it hit the metal there. On the other side of the car, the end of the quarter panel belt molding is also worn through, but it might have been loose.

This is the inside of the top of the fender lip, looking out from inside the wheel well:


You can see the tire rubbed through the vinyl here into the SMC base (white). Obviously if this were a metal bodied car a little bit of fender rolling would fix this.

Finally, here is the ebrake cable and trailing link worn through to the metal. Notice that I've already ziptied the trailing link closer to the frame than it normally is.

[The Dark Side of Will]

Rubbin's Racin'!

The lengths of the lateral links can be fine tuned in conjunction with the alignment to minimize tire rub. Was it FieroGuru who shortened his lateral links in order to pull the strut closer to the frame rail in order to fit a wider wheel under the fender?

The parking brake cable can be figured out, a "bent" trailing arm can be fabricated (is fabricable?), and the location behind the wheel where it rubs on metal can be "massaged" or simply carved away. (After all, that's just the trunk, right?)

[Series8217]

I can't modify the inner aspect of the metal fender and stay within production vehicle NASA TT classes.

The parking brake cable can be eliminated or ziptied out of the way. I think I have enough zipties on it that doesn't contact the wheel anymore.

[The Dark Side of Will]

I can't modify the inner aspect of the metal fender and stay within production vehicle NASA TT classes.

You and your classes... you sound like Karl Marx

The rest of us could massage that steel a little bit... if it's even necessary with the 285/30.

[Series8217]

If you're putting those tires on as part of a mission to increase lateral Gs you'll want a lot more roll stiffness anyway so you can actually use the tires. The roll stiffness will limit travel and probably prevent the rubbing in some of these spots.

[The Dark Side of Will]

I get that reduction of travel at max G will help clearance... But you're already at 475# springs and wanting to go stiffer, but I'm not sure I want to do that on a street car... so I may have to play more games with the roll center--like raising the inner AND lowering the outer pivots--or what...

[Series8217]

You might want to know that my Fiero rides better than my M3... I'm sure I can move up quite a bit on spring rates before it's too stiff for the street.


Also don't forget about swaybars; the stock rear bar seems pretty weak.

[The Dark Side of Will]

I'll get my font end converted to coil overs and probably try higher spring rates.
I need to get my Konis revalved.

[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.

[Series8217]

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.

Nice. I like those Corvette wheels because you can get them in staggered diameters too.

Is this for the Mule? Isn't there a rear bearing upgrade for '84-'87 cars that gets you the Corvette pattern? You'll want upgraded wheel bearings when you have the grip that a 285 is capable of generating.

[draven]

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.

[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.

Nice. I like those Corvette wheels because you can get them in staggered diameters too.

Is this for the Mule? Isn't there a rear bearing upgrade for '84-'87 cars that gets you the Corvette pattern? You'll want upgraded wheel bearings when you have the grip that a 285 is capable of generating.

I'll go with the W-body aluminum knuckles because of the lower tie rod boss and less unsprung weight.
Whether you think the S10 5x4.75" bearing "upgrade" "works" in the HD A-body knuckle depends on how kludgey you're willing to get with the bolt circles. Doing it right is harder than doing it the way most people do it.