QA1 Suspenssion 335 tire?

[keefro]

I've searched the forums but have not found very good results.

The pictures below are of my 1971 GMC with stock 12 bolt rear end, QA1 coilovers front and rear with a 4/6" drop. I'll have some custom 20" wheels made and am trying to decide on tire size. The 335/25R20 installed on the wheel fitment tool is off my Z06. I'll run a taller 35 sidewall at a 29" diameter and the tubbed inner fenders (wood bed makes it easier).

The speedway motors tool says I can run a 20x12.5 with 7.75 backspace and +25 offset (1").

Math:
(12.5" wheel + 1") / 2 = 6.75
7.75 - 6.75 = +1" or +25

Has anyone gone this wide?
12.5" wheels?
+25 offset?

[CC69Rat]

If you measure from the inside of one brake backing plate over to the other side in the same place. Is it 57" or 55.5"? I'm betting 57".

I usually run 20x10, 6" backspace on the 55.5" axle. At 4/6 or 5/7 static it will clear 295/45 no problem. 295/40 if that's your preference.

Of course this would change if you have the wider rear axle. (Late 69, on up )

My only thought would be the outboard rear coilover mount, I'd be really cautious there .. but I feel like it would work (?)

I'm considering the same setup on my 67 to be honest.. curious to see how it plays out.

[keefro]

Thanks for the response. I'm new to these years and forgot about the difference in track width with the disc brakes. My 71 was originally a leaf spring rear end that I converted to track arms with coilovers.

When I measured base plate to base plate, it measured just over 57".

The wheel fitment tool allowed me to check the clearance on the Coilover. It was just over 1" away with the 7.75 backspacing.

I think what confused me was people talking about the 6" backspacing and me not considering the difference in axle width.

I may end up doing 8" backspacing and run a spacer to give me some optionality on tire width.

[keefro]

Well, I've been searching high and low and the widest off-the-shelf rims I can find are 10-11". I was at SEMA last week and talked to every wheel vendor there. Lot's of $5k options at any size and offset, but that's not in the budget for what I'm building - a daily driver.

I'll post pictures of the build as it sits next week.

[ullose272]

Originally Posted by keefro

Well, I've been searching high and low and the widest off-the-shelf rims I can find are 10-11". I was at SEMA last week and talked to every wheel vendor there. Lot's of $5k options at any size and offset, but that's not in the budget for what I'm building - a daily driver.

I'll post pictures of the build as it sits next week.

i was in the same boat, ended up getting 20x10 ridlers using 315/35r20

[keefro]

Thanks. What do you run on the front?

[ullose272]

20x8.5 and 255/40r20

i dont have them on the truck yet just a quick test fit

[keefro]

Well, I searched all over and the only thing offered over 10" were custom wheels. Most starting at $1k+ each. Talked to several manufacturers and just couldn't justify $4-5k in wheels for this build.

So, I went with the US Mag CTen wheels. Specs below.

Front: 20x8.5" - BS 5.03" - Nitto NT555 G2 255/45R20
Rear: 20x10" - BS 5.54" - Nitto NT555 G2 295/40R20

They look good on the truck and I'm happy with the fitment. I'm going for the red and chrome grill so the wheels match up nicely.

With the QA1 front suspension and Wilwood Pro 2.5" dropped spindles, it has a good 1" of clearance at full lock. In the rear, It has at least 2" to the coil overs.

[Jason Banks]

I had the exact same wheel and tire combo. When I still had drum brakes on the back, I cut a 1/4 thick wheel spacer for the rear to bring them out just a bit more. I looked amazing.

[keefro]

Thanks, Jason.

I haven't had the fleetside bed on yet with these wheels. But it's a '71 with a wider rear end. I have some spacers available if I need to move it out. I may do the same in the front as they are a little narrow for my liking. I went with the 8.5" vs 9" so the backs had the deeper dish look.

[biketopia]

What is the backspacing on them?

[keefro]

I updated the post to include the backspacing.

Front: 20x8.5" - BS 5.03" - Nitto NT555 G2 255/45R20
Rear: 20x10" - BS 5.54" - Nitto NT555 G2 295/40R20