18" wheels/tires for 1970 GTO

[GTO Freak]

Hello..new member, lots of questions. Building on my intro thread...

I have a 1970 GTO that is currently under restoration. Looking to upgrade the wheels/tires to 18" US Mags Ramblers (front 18x8, 4.5BS, +1mm offset / rear: 18x9.5, 5.25BS, +1mm offset) with Nitto 555 G2 tires. Going to use a 2" drop spindle that supposedly widens the track 3/8" each side.

Wondering what the max tire width on the front and rear I can run that won't rub without modification taking into account the additional 3/8" widened track. Was planning on 245/45/18 on front (before I realized I'd lose 3/8") and 275/40/18 on the rear to keep the sidewall height and diameters similar. Will this work without rubbing? If so, can I go any wider on the front or rear without rubbing?

FWIW...I'm probably going to pick up the BMR tubular upper and lower controls arms, UMI standard springs in front and 2" lower in rear with Bilstein B6 shocks. On a budget...the restoration has been $$$. 2" drop spindles are coming in a Right Stuff Big Brake package 4 wheel disc conversion...https://www.getdiscbrakes.com/afxdc51ds

176411

Thoughts??

[andrewb70]

I replied to you first thread, but I am sure others will chime in.

Andrew

[GTO Freak]

Hey Andrew...saw your build thread, quite impressive.

You're running 255/40/18s in the front...right? What width rim, backspacing and offset...if you remember?

So paranoid about the 245/45/18s rubbing the front with the extra 3/8"...want to do it once correctly. I think I could probably fit 285s in the rear with the BS on the Ramblers.

[Wacker7977]

Each car is a little different but you should be able to stuff 305s in the rear of the 70-72 GTOs as they are a little wider than the 68-69 which usually fit 295s. I had 245/45 18s in the front of my 72 Lemans.

As for the suspension I'd steer away from the drop shackles. Now if you have time give Mark a call at Savitske Classic and Customs. He will help you get a great suspension for your budget and goals. He will talk front to back and spend at least an hour discussing it. I'm running one of his kits with SPC upper and lowers up front with SPC springs. Currie control arms out back with SPC springs and double adjustable shocks all around.

Here's a picture of my old Lemans for reference. 176412

[GTO Freak]

Thx for the info...was contemplating 285s on the rear.

Curious...why steer clear of the drop spindles?

I was told that keeping the stock steering geometry and spring length would provide a little less harsh ride while still allowing for a lower stance and improved cornering...on a budget. I can get the complete Right Stuff 4 wheel big brake disc conversion package (slotted rotors, twin piston calipers, master cylinder/booster, stainless lines, etc) with drop spindles, BMR upper/lower tubular control arms, Bilstein shocks, UMI springs (stock front/2" lower rear) for @ $2900 -3100. I'm guessing similar with SPC components would be significantly more?

The restoration is soaking me, so having to sacrifice some of my suspension wishes for now.

Always willing to learn...thx.

[Wacker7977]

A lot of drop spindles dont fix any of the issues and can actually lead to slower steering due to needing longer steering arms. They give the desired drop but dont fix any of the bump steer and mostly resemble the old school option of a b body spindle swap.

[andrewb70]

The Speedtech spindles and control arms are the best solution for A-bodies.

Andrew

[Wacker7977]

That's true I want those spindles really bad but budget drop spindles arent doing anything and he would be better off with drop springs and control arms that actually fix geometrical issues.

[andrewb70]

That's true I want those spindles really bad but budget drop spindles arent doing anything and he would be better off with drop springs and control arms that actually fix geometrical issues.

I would agree with that.

Andrew

[cdrod]

As I understand it, the biggest problem with the GM A-body front suspension is the poor camber curve as the suspension moves up and down. The factory suspension causes positive camber as the suspension compresses (in bump) which the AFX spindles correct. An alternative approach is to install "tall" upper ball joints and a pair of SPC tubular upper arms. The SPC arms are about $400 and the tall ball joints are available from Howe Racing and ProForge at reasonable prices. The SPC arms will also allow more caster without huge shim packs for a better alignment specs.
Rodney

[GTO Freak]

So...I spoke with the builder about nixing the 2" drop spindles and he recommended the BMR package below (with 2" lowering springs) as a cost-effective alternative using the stock spindles. Since the GTO already has 1 1/8" front/rear sway bars, might nix those and the rear control arms, since this won't be a full-on autocrosser, just better steering/cornering than stock and dropped 2". That puts the front upper/lower control arms, front/rear 2" lowering springs and Bilstein shocks @ $1100. Full package is $2100.

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Has anyone used this kit and/or can comment on the approach, given my budget/goals?

[Bad66gto]

X2 on the drop spindles, don't do it. The BMR kit you picked should do well for a nice sport suspension. On my '66 GTO I'm running BMR upper/lower arms with tall joints & standard spindles, Hotchkis drop springs front & rear, Hotchkis boxed rear arms with adjustable uppers. Bilsteins front & rear. The car handles great, corners flat and has a fairly plush ride. Your going to want the adjustable uppers to correct pinion angle after dropping the rear.

[GTO Freak]

X2 on the drop spindles, don't do it. The BMR kit you picked should do well for a nice sport suspension. On my '66 GTO I'm running BMR upper/lower arms with tall joints & standard spindles, Hotchkis drop springs front & rear, Hotchkis boxed rear arms with adjustable uppers. Bilsteins front & rear. The car handles great, corners flat and has a fairly plush ride. Your going to want the adjustable uppers to correct pinion angle after dropping the rear.

Did not think about the difference in pinion angle with 2" lowering in the rear. The kit has non-adjustable rear upper control arms...guess I need to replace with one of their on-car adjustable versions. Looks like they have 5 versions with 3 variations here (https://www.bmrsuspension.com/?page=products&vehicleid=14&maincatid=43&catid=99) (poly bushings, spherical bearings and rod ends) for 68-72 A-bodies...not sure which is necessary for my application. Sorry guys...new to this end of things.

[andrewb70]

Also be aware that when A-bodies are lowered in the rear it causes driveline issues that cannot be corrected with adjustable rear upper control arms.

Andrew

[GTO Freak]

Also be aware that when A-bodies are lowered in the rear it causes driveline issues that cannot be corrected with adjustable rear upper control arms.

Andrew

Okay...what method would correct the driveline/pinion angle changes with a 2" lowering spring? Not looking for a raked look. :eek:

[cdrod]

Also be aware that when A-bodies are lowered in the rear it causes driveline issues that cannot be corrected with adjustable rear upper control arms.

Andrew

Marc at SC&C told me that a 1" drop in the rear was the most you ever do without screwing up the handling.

[andrewb70]

Okay...what method would correct the driveline/pinion angle changes with a 2" lowering spring? Not looking for a raked look. :eek:

You can either raise the back of the transmission, but that will be limited by the floor pan, or you can get a CV driveshaft, like I use in my GTO and my Cougar. Obviously, you can also modify the transmission tunnel.

Andrew