[chiphead]

So what is the ideal wheel width and backspace to fit about a 255/45/18 tire in the rear wheelhouse of a '67 LeMans? I'm considering going to 18" wheels to fit the C5 brakes on the AFX spindle. The issue is most 18" wheels have 4.5" of backspace, which may not be deep enough to fit most wide tires.

I really like the US Mags Bandit 109, but they only have 4.5" of backspace. Is that going to tuck a big tire (at least a 255) under a 67 GTO/Lemans with 60" axle?

[JLMounce]

You will have to get the corvette brakes on the AFX spindle and measure. You're going to end up with more front spacing than you think you'll need because of how the corvette brakes work on the AFX spindle.

Unlike stock spindle stuff, the hub flange is inset, specifically with this combination. The corvette rotors don't move the rotor face back from the hub flange, so you do also have to contend with the caliper where typically you don't. The typical cast wheels that are popular from brands like American Racing may struggle with caliper clearance as a result.

A 255 tire is best suited to an 8.5" wheel. I would think that width would be fine in a 67 LeMans, but you'll have to get it situated where it needs to be with the brakes you're going with. Buy those and get them installed, then brake out the straight edge and rulers.

The rears are going to be a little bit better to contend with, but you'll still have to work around the caliper. If you go to Tobin's site at www.kore3.com he has templates that give measurements, or that you can cut out and check with wheel manufacturers on spacing.

I can tell you definitively that the Torq Thrust II wheel does not fit around C5/C6 brakes. I've measured mine as I was originally going to do C6 brakes as well, but it's a no go.

[chiphead]

Thanks for the input. Not what I wanted to hear but oh well. That's why I asked here. Anybody using the AFX spindle can tell me what rims they used? I'm not going to do this swap and then figure out I need $3,000 in wheels.

Looks like a set of global West arms and a tall ball joint for me, boys. It's not all bad I get to keep my 15" weld prostars

[JLMounce]

Definitely one of the drawbacks of the AFX spindle. Its brake package availability precludes a lot of the popular off the shelf wheels for these cars. The US Mags Bandit may work though. I'd get the brake template from Kore3 that you were after and send it over to US Mags. They'll be able to tell you if there is going to be any caliper interference issues.

If your plan doesn't include some larger wheels, I wouldn't even bother with the control arms. I'd run the stock arms with new bushings, a tall upper ball joint, the springs and shocks of your choice and a front and rear sway bar.

Given the budget constraints, if your goal is still much improved handling, I'd take out the AFX spindle and run a stock type spindle so you can use brakes designed around it. That gets you back to being able to utilize most of the off the shelf wheel options that are cheaper. You just can't use any of the C5/C6 corvette stuff. It's either the stock type 11" discs or if you are doing a bigger brake setup, Wilwood or Baer designed for the stock spindle.

[b-man]

I used 18x9” wheels all around on my ‘64 Tempest which rides on essentially the same chassis with similar wheel well dimensions as your ‘67 I have 6.57” rear backspace and 5.5” front backspace using the AFX spindles and C6 Z06 brakes. Tires are 245/40 and 275/40-18.

I actually ended up using some O.Z. Racing Ultralegerra cast aluminum wheels that were designed for rear fitment on a BMW Z4 roadster. They’re actually pretty lightweight at 20.8 pounds and the spoke design clears the big brake calipers.

[gtospieg]

If you're keeping the stock rear drums or use Baer rear discs you need a 5.5" backspace to run 255/45/18. I'm running 255/45/17 with 5.5" back space on front and rear on my 67. Baer 12" brakes front and rear. Global west upper and lower control arms front and rear with delrin bushings.

[chiphead]

What's the chance that a set of 18" wheels/tires that fit the AFX spindle will also work with the stock GM disc brake spindle? Staying with GM drums out back. I don't want to buy front tires/wheels twice. I'm looking at the billet specialist wheels, they can do any BS and they list the caliper clearance.

https://www.billetspecialties.com/St.../item/lonestar

[JLMounce]

The AFX spindle has a track width that is very close to, if not identical to a car with a factory disc brake setup. So a wheel with a proper back spacing for an AFX spindle should not become a problem putting it on a car with a factory type disc brake.

The wheel mounting face on the AFX spindle and a stock type disc brake will be in the same place. On the AFX spindle, the caliper clearance will be less. Most calipers on the factory setup are inset of wheel pad, so there are rarely caliper clearance issues to the back of the wheel, only possibly at the wheel hoop for 14" and certain 15" wheels.

It sounds like you want to get wheels now and in the future be able to upgrade to the AFX spindle without having to change them. This should be possible if you take into account what you want to move to in the future. Even if you are not buying the brake package now, pick it out and grab the wheel fitment guide for that brake package. If the wheel you're after fits that package, it will fit the stock brake package.

Pay attention to the center bore size. When purchasing your wheels make sure the center bore is drilled to accept the larger of either the factory or AFX spindle hub register. The wheels you linked to are conical seat which means they are lug-centric and have a 3.080" center bore which is basically the largest center bore you will see. They should fit both the stock hub and AFX hub register, but you should double check that. If you decide on a different wheel, verify they are lug centric and have a center bore large enough for either the stock or AFX spindle hub register.

[Scarebird]

Originally Posted by JLMounce

Definitely one of the drawbacks of the AFX spindle. Its brake package availability precludes a lot of the popular off the shelf wheels for these cars...

One of the things I regret not doing was getting a hold of AFX and a spindle to build a more compact disc setup, a combo that would have easily fit 17" rims.

The 13" Corvette rotor and Astro caliper would have done this.

[chiphead]

I'm at the point where I need 18" wheels/tires. I've stayed with the stock spindle and disc brakes.

What's the widest tire section width that can comfortably fit in the back of a '67 GTO with 60" drum brake rear? Is it 10"?

Will 5x120mm wheels fit the 5x120.65 lug pattern?

Do you guys have a link to a how-to for determining if a wheel/tire package will fit a given wheelhouse?

[JLMounce]

You're going to have to measure. If you're going for wide, there's no way around it.

Get the car up on jackstands with the rear housing supported and the front control arms also supported so that the vehicle is "at ride height." Take the wheels off the car.

You'll need two strait edges. The rears are going to be easier to get your measurements than the fronts.

Starting in the rear, first measure the total distance between the inner wheel well and the outside quarter panel lip.
Once you have that measurement, decide how much room you want the wheel to have. Typically a half inch to the inner wall and slightly less to the fender lip will get you a "mostly" rub free experience. It may still rub as the car is traversing and undulating over depressions and gutters, typically in parking lots, but won't rub while the car is in motion (even under performance driving conditions). If you want an absolute zero rub scenario, you need a minimum of half an inch and possibly closer to 3/4's of an inch to both the inner wall and outer lip.

Subtract your needed space from the total wheel well width to determine the maximum width you can fit in the wheel well. More than likely you're going to be subtracting about an inch. So if you have a wheel well width of 11" you have 10" to work with.

This is where the car's stance, wheel and tire selection starts to become important. Wheels are measured from the inside portion of the bead seats. That means a 10" wide wheel is actually wider when taking into account the outside edges of the wheel rims. There is no standard here, but typically measured from outside edge to outside edge will be around an inch total. If the stance of your car puts the wheel itself above the fender or 1/4 panel lip, you must take into account this additional width. Likewise, if you choose a tire that is oversized on the wheel and bulges outward, you need to take this into account.

my suggestion is to pick your tires first. Decide what you want and what sizes you are going to try and stuff in the car. Then go to the specs for that tire and see what the measured width is and at what wheel size that measurement is taken on. As an example a 245 section width tire is typically put on an 8-9" wheel and is likely measured on an 8.5" wheel.

Once you know your total width measurements, now you can determine your front and backspacing and calculate your needed offset.

Take your two straight edges and lay one upright on the mounting flange of the rear drum and lay your ruler across the width of the wheel well from the lip inwards to the mounting flange. Take that measurement and subtract the amount of space you want to leave to the wheel lip. This is your front spacing.

Now do the same, measuring from the inner wall of the wheel well to the mounting flange. Again, subtract the amount of space you want to leave between the wheel and the inner wall. This is your backspacing.

It's important to note that front and backspacing is the measurement from the wheel mounting surface to the OUTSIDE edge of the bead seat (wheel rim).

Once you have your front and back spacing, you can use a calculator to determine the offset you need for a specific wheel width. I use this one from fitment industries. https://www.fitmentindustries.com/ti...et-calculators

You can now order wheels and tires for the rear based on those specs.

Moving to the front, things get challenging due to the dynamic nature of the wheel's movements, both up and down as well as in it's turning arc. Having a helper that can turn the wheel to simulate this while you measure is usually a good idea. The over all principals are the same, however.

Knowing the diameter of the wheel you are using and specifically the diameter of the hoop becomes somewhat important now. Especially on GM muscle cars. Your contact points for the wheel and tire setup become the tie-rod end first, following by the upper control arms and inner frame rails. an 18" wheel sometimes has the ability to stuff the outer tie-rod inside the hoop of the wheel. This allows you to run a lot more width. Not all hoops are the same however, and not all 18" wheel will allow this to happen. It depends on the wheel hoop diameter as well as where the tie-rod fits on the steering arm and the addition of anything like a bump-steer kit.

Starting with the wheels pointed straight, determine your frontspace dimension for the wheel.

You can't do the same backspacing measurement because the wheelhouses on GM cars are deeper than the frame rails. Your backspacing measurements need to target any suspension pieces that will be in the way, typically that tie rod end. Using yoru straight edges measure from the wheel mounting surface to the nearest suspension component and subtract your comfortable distance for clearance. Take this measurement in several different orientations of the wheel being turned. More than likely the distance will remain static to the tie-rod, but not always. That gives you your backspacing to the suspension. However you also need to check to see where that puts the wheel and tire in relation to the frame rails.

Again, with the tire you already want to run, you need the overall height on your measured wheel. Using your straight edges, turn the wheel full lock both in and out and take a measurement of your backspace at the radius of the overall tire height. You want to see how much, if any rub will occur at full lock, both right and left. Adjust your backspacing as needed depending on the amount of rub you determine may be present.

A quick note on fender rubs. The way the GM cars are designed, going to wide front wheels and tires will almost always induce some amount of rub on the inner frame rail and on the upper portion of the fender lip. These areas are typically soft and do not have sharp protruding objects. The rub that does occur almost always does so at full lock or very deep steep steering angles while coming on and off of curbs. If you're unwilling or unable to accept this amount of rub in the front, you need to drastically limit the width of the wheel and tire package, probably by a minimum of an inch and a half and about 20mm off the tire section width.

The last bit of information you need on the front is the depth of hub and dust cap from the mounting surface. Some wheels come with flat center caps, others come with shallow or deep domed center caps. The hub and spindle are going through the center bore of the wheel and you need enough mounting pad on the wheel and center cap to accommodate that.

Now you have all the dimensions you need to either select pre-manufactured wheels are certain offsets, or have a custom set built for you. If you know what your specs need to be and are finding wheels that are close, but not quite, you can use this tool to see what the difference is going to be. https://www.wheel-size.com/calc/

For the rear wheels, if you need to fudge where the offset is, err towards the wheel lip. I know this seems counter intuitive, but if you understand how the body acts on the car while it's driving it makes sense. As you make a turn the body will want to move into the turn, creating space between the 1/4 panel lip and the wheel. At the same time the body is lifting on the inside of the corner, typically pulling the 1/4 panel lip above the wheel and tire, creating more space.

The same is true in front, but you still have the dynamic action of the turning wheel to contend with. On GM cars, because the front ends are attached rigidly to the frame, there's not as much movement of the body panels in relation to the wheel and tires as there is in the back. There is still deflection in the suspension that causes some movement though.

This was lengthy, but if you want to go wide, you have to do this. There's no shortcuts.

[b-man]

I had my Moser rear axles made with the 5 on 120mm bolt pattern to fit my BMW spec wheels. Up front bought 1.063” thick custom made adapters to go from the GM 5 on 120.65mm (4.75”) to 120mm. I’m using the same wheels on all 4 corners with 6.57” backspace, including a spare wheel.

Some guys have put BMW wheels on GM cars and they do work, but the lug studs are bending inward slightly which is something I don’t like personally.

As already stated above you need to measure and measure and measure again. However I did give you a good starting point in my previous post.

[HWYSTR455]

I have the 18x9 Bandit wheels, with AFX spindles, and am running C5 brakes. The caliper clearance is close, but it works.

The distance outboard for the 18x8 is the same as the 18x9.

I am running on a 71 A-body though, not sure how much of a difference there is. I would suspect B-Man's example is a better one.

Are they Speedtech spindles or CPP?

EDIT: Looks like a touch more than an 1/8" clearance to the caliper
,

[chiphead]

Finally measured the wheelhouses. Can somebody check my math?

The driver's side wheelhouse is 11.87" wide from inner quarter panel to frame rail.
5.37" from quarter panel to brake drum
6.5" from brake drum to frame rail

So the wheel offset would need to be .565" to center the wheel in the wheelhouse.

If I use a 8" wheel, I would need a 4.5" backspace plus 13mm offset to center the wheel? So 5" of BS?
If I use a 9" wheel, I would need a 5.0" backspace plus 13mm offset to center the wheel? So 5.5" of BS?

I'd like to run a DWS 06 tire in 255/55/ZR18. 29" tall, 10.4 section width and 8.3 tread width in the rear is the biggest that will give 3/4" clearance front and back of the tire.

[JLMounce]

Your numbers jive on my end. With a 255 I'd probably opt for the 9" wheel myself. It'll keep the tire from bulging outward. This tire is probably measured on either an 8.5 or 9" wheel.

Is there a reason you are wanting a 29" tire? You should verify you have enough room at the leading and trailing edges of the fenders and 1/4 panels for that tall of a wheel/tire setup. You may also want to estimate how much compression travel you have before you hit the inner wheel houses.

On 18" wheels I still typically recommend a 26" overall tire diameter for most of these cars, unless you really just need a bit more sidewall, then I'd go to a 27" tire. At 19" on the wheel I step up to a 27" tire to keep some sidewall on the tire. This typically puts you in corvette sizing where tires are easy to come by.

The 255/45/18 would be my recommended tire size for this car. You won't quite get 3/4's of an inch on both sides, but you'll still have enough room that I don't believe you'll have any rubbing issues.

[b-man]

I once tried to switch from 10x28” slicks to 9x29” (15x8.5” wheels) on my ‘64 GTO bracket car. A total no-go, just way too tall.

Just to get the 10x28” slick on there I had to hammer the rear inside corner of the inner fender where it meets the trunk pan for clearance. Nothing too crazy but hammering was a must.

I’d forget about wanting a 29” tire unless you’re planning on cutting and welding to make them fit.

I’m running a 275/40-18 on a 9” wheel that’s 26.7” tall on my Tempest, it’s a good fit. I’m running 6.57” backspace, keep in mind I’m running a later 8.5” rear that’s 1/2” wider per side and rear Z06 disc brakes that widen the track a little more as well.

For an 8” wheel I’d have to agree that a 27” tall 255/45-18 would be ideal.

[Tim Corcoran]

Oh no, 18" wheels on a GTO??? Yikes

[b-man]

Kinda want 19” wheels now instead of the 18” ones but I’m good.

[chiphead]

Originally Posted by JLMounce

Your numbers jive on my end. With a 255 I'd probably opt for the 9" wheel myself. It'll keep the tire from bulging outward. This tire is probably measured on either an 8.5 or 9" wheel.

Is there a reason you are wanting a 29" tire? You should verify you have enough room at the leading and trailing edges of the fenders and 1/4 panels for that tall of a wheel/tire setup. You may also want to estimate how much compression travel you have before you hit the inner wheel houses.

On 18" wheels I still typically recommend a 26" overall tire diameter for most of these cars, unless you really just need a bit more sidewall, then I'd go to a 27" tire. At 19" on the wheel I step up to a 27" tire to keep some sidewall on the tire. This typically puts you in corvette sizing where tires are easy to come by.

The 255/45/18 would be my recommended tire size for this car. You won't quite get 3/4's of an inch on both sides, but you'll still have enough room that I don't believe you'll have any rubbing issues.

That's what I'm trying to do, keep some sidewall on the tire. I could run the 255/45ZR/18, that's a 27" tire that's 10" wide, so it would give me plenty of space.

About the wheels. Would a 9" wheel with 5.25" BS fit? The bandit US mags have the right "look" and are 18". But they are only avail 8" by 4.5"BS and 9" by 5.3" BS. Would a staggered set up fit the car? 9" wheels in the back and 8" wheels in the front? I'd only use a 225-235 tire in the front. It's better than the wheelbarrow tires in the front now.

What other 18" wheels have a vintage look and 5.5" BS?

[JLMounce]

Moving the wheel outward towards the wheel lip, generally works a bit better than the reverse. If you think about what is happening to the body and suspension when cornering, moving the wheel out doesn't post as big of a problem as moving the wheel in. Imagine you are turning hard left. The body on the car will tend to want to move out and away from the outboard wheel of the turn, while also pivoting downward. Although the body is getting closer to the wheel on the inboard side of the turn, the body is also pivoting up and away from the tire.

There is a point where it's too much though, you do still have to have some space between the tire and the wheel well lip. But in your case, the move from a 5.5" BS to a 5.3" BS shouldn't be an issue.

On an 18" wheel, a 27" tall tire will have around a 4.5" sidewall. Compared to the 29" tall combo that will have around a 5.5" tall sidewall. Honestly if you want 5.5" of sidewall, I wouldn't be looking at 18" wheels anyway. I'd put a 15" wheel on there. You're getting the same sidewall size by doing that, and you're in a 26" tall sizing which the car was more designed to handle. As b-man has already shown, increasing the tire height starts to require modifications to the wheel houses, or you need to jack the rear end up in the air to add clearance.

A 28" tall tire would split the gap here and give you about a 5" sidewall. That would be a 255/50/18 size.

I've included a pic of my wife's previous Chevelle. This is an 18" wheel with a 27" tall tire; 275/40/18. Everyone's taste is different, but I felt like this was still a good amount of tire.