Biggest tire for lifted trailblazer and wheel spacers question

HARDTRAILZ

Moderator
You also need to take into account that the envoy and TB fenders are not exactly the same and require different trimming. Also you can take two trucks with identical stats and they need different trimming. Been proven many times over the years. There were many spring rates and the alignment adjustments and general wear of other parts or tweaking of the truck overall that affect things. There is no exact science so the trimming was left out other than noting. You may be better to delve into that knowledge of exact setup on the forum where the chart was built. Not all of those offroad guys are on here, in fact i would say a small percentage at this point.

I just bought what I wanted and cut to fit back when there were no 3 and 3 lift options...actually had to cut with hacksaw to leave the show grounds of the All truck Nationals when I got my first pro comp setup.

If you are trying to get precise, this may help... https://www.wheel-size.com/calc/ its what i use on my car and to get a feeling for sizes and changes of certain setups.
 

paul2005tb

Well-Known Member
Westucky, Can you please give me your opinion of the following plan:

Rims = 16x7 ,0 offset
Adapters =1.5in thick (so 2in of backspace)
tires =32.7/11/16

As I calculate it this is going to just barely clear the aft/back side of my front fenders.

From your experience with your vehicle can you tell me what you would expect with this tire/wheel/adapter set up ?
 
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paul2005tb

Well-Known Member
..There is no exact science so the trimming was left out other than noting. You may be better to delve into that knowledge of exact setup on the forum where the chart was built. ..

I just bought what I wanted and cut to fit back when there were no 3 and 3 lift options...actually had to cut with hacksaw to leave the show grounds of the All truck Nationals when I got my first pro comp setup.

If you are trying to get precise, this may help... https://www.wheel-size.com/calc/ its what i use on my car and to get a feeling for sizes and changes of certain setups.
Wow, that ... https://www.wheel-size.com/calc/ is a fantastic tool!. .if only it could give me the side view so I could see the rear side fender interference.
 
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HARDTRAILZ

Moderator
Rims = 16x7 ,0 offset
Adapters =1.5in thick (so 2in of backspace)
I am confused by your numbers. A zero offset 7 inch wide wheel is 4 inch backspace typically. the adapters at 1.5 would push the wheel out and you get 5.5 backspacing.
 

paul2005tb

Well-Known Member
Wait,
1) I used 3.5in backspace for a 7in wide rim with 0 offset, ok I missed a 1/2 in of rim lip.

2) 1.5in adapter would indeed push the wheel out. I viewed that as cutting into backspace since the mounting surface of the hub is now 1.5in more (less the .5in I missed) inward relative to the inside rim (3.5-1.5=2)suspect I am not obeying convention.

What I see as the key is the diagonal distance between the steering pivot point and the far outside corner of the tire. For a 32.7inX10.5 diameter tire I calculate this diagonal to be approximately 18in.

At 18in with my 3+3 lift and adapters my wheel well should just barely accommodate a 32.7x11 tire. No metal cutting at all.
 

HARDTRAILZ

Moderator
1. Correct. It is not exact, due to material thickness but common practice is 4.

2. You are increasing backspace as you push the wheel out, so 4 plus 1.5 is 5.5 the effective backspace.
 

paul2005tb

Well-Known Member
Ok, understood, so I have at most 8 inches from the outside tread to the steering pivot point/knuckle with the spacers.

Now: diag=sqrt(8^2 + (32.7/2)^2)=18.2in

With the 3+3 I have more than that much space in my wheel well from the center of the hub. With only the 3in suspension lift and the spacers I would not clear that rear corner of the fender. But with the 3in body lift I think that I can clear that rear of front wheel well with 285/70/17 or 285/75/16 (32.7x10.5) without cutting metal.
 
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HARDTRAILZ

Moderator
You should be find with 285s and stock wheels. What wheels are you going to run? 7 wide is a bit thin for 285 width tires and may lead to poor wear when the tread pattern crowns a bit.
 

paul2005tb

Well-Known Member
My stock wheels are listed as 17x7.


Are they really that narrow . Id like to go with the 285/70/17
If I have to go up to 17x8 then I have to buy the 6-5.5 adapters.

As much as I would prefer 16in rims, I dont want to buy16in rims and then have no use for them 30 years (and 300k miles) from now when my faithful trailblazer gives up the ghost! All of the brake calipers on late model Silverados and Tahoes (my likely replacement for the trailblazer 30 years from now!!) are too big for 16s.
 
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HARDTRAILZ

Moderator
You can get by with the 7 wide. If you were buying new wheels I certainly would look to an 8 but in your case I think the stock is best option with all the variables.
 

paul2005tb

Well-Known Member
Thanks HardTrailz. I made some measurements. As I measure the distance to my upper control arm ball joint, I will have about 1/8in of space between the control arm and a 285/70/17 on my stock 17x7 alloy rims, (I have the MarkMC spacers). I will have about a 1/8in clearance between the 285/70 tire and the back side of wheel well fender (this is where the 3in body lift serves me well).

If the tires are wider than expected and they hit the upper control arm I will just get out the grinder and grind it down so the tire clears.
 

paul2005tb

Well-Known Member
Just installed the 285/70/17s on the rear wheels. They list at 32.7in diameter. I measured the tread width and they are at least 1in less than 285mm(11.2inches). But still it is a huge improvement.. The truck now rides like im on a cloud, what a difference, exactly what I hoped for.

My only regret is that I didnt do this sooner. I will install the fronts as soon as I get the time. This has taken more time for me due to the fact that before I mount the new tires, I have been cleaning and painting the rims. Ill try to get pictures up.

1) 3in suspension lift, 3in body lift. If I could slice a hockey puck into two 1/2in slices and increase my body lift to 3.5in I would.
2) Still need to install an adjustable panhard bar because I can see the right rear tire sticks out at least an inch more than the left side.
 

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