Wheel Guru Assistance

[MCAT069]

I have a 2004 2500 8.1 4L85E 4x4 Suburban with stock 245/75R16 tires. My cousin has blown the engine on his truck and has given me a set of 18 inch rims that have a +18 offset. The tires on the new rim set are LT285/65R18 which I believe is just under 33 inches.
1.) What would I have to do to use these rims and tires without any rubbing issues?
2.) If I put a bigger tire on, will I need different gears as well? The suburban currently has 3.73 from the factory

 

[Fless]

This might be helpful, you can compare two different sizes here:
https://tiresize.com/comparison/

 

[06JET]

Your gears are fine with those tires. With that motor you shouldn't need anything but a gas station pretty often. Nice!!!

 

[adriver]

Unless those new wheels are heavy look at me chrome wheels, they will make a small difference but nothing you would need new gears for. They will hurt your acceleration slightly, and mileage by probably 1-2mpg, but you should notice an improvement in handling.


Not sure what wheels you currently have, but you need to know what the width is and offset. It will say ET ** but not sure where on whatever wheel you have, it should be visible on the inside of the wheel.
Your new tires are 2.1" taller (which is 1.05" higher per side closest to the top of the fender well, and will sit your truck 1.05" higher off the ground). So height should be fine.
Your new tires are 1.6" Wider. So you have .8" closer in towards the fender IF your new wheels are the same width with the same adjusted offset. The 18" wheels are probably wider.

Once you know your current wheel width and offset, you could use it to figure out your centerline, or just use some simple math to figure out the difference.

Example if your current wheel is 16 x 7 with a zero offset, and new wheel is 18 x 8.5, (1.5" wider = .75" width difference on each side/from centerline on both). 25.4 mm = 1 inch.
25.4 x .75 (wheel width) = 19.05 mm/ +19 ET would push the centerline out farther to get your new wheel's edge the same distance from the wheel well. Then
25.4 mm x .8 (tire width) = 20.32 mm, then another 20 ET would push the wheel out another 20mm to put the tire the same distance away from the side of the fender.

So for every inch wider the new wheels are, your wheel lip/edge is 12.6mm closer to the wheel well (assuming zero/same offset from centerline). & We know the new tires are ET 1.6" / 40mm wider / 20.32 mm wider on each side (closer towards the wheel well when we have the same centerline).
Then if you really want to know, you will need to go check at full steering wheel lock and see how much room you have (front of one side, back of the other).

 

[MCAT069]

Thank you all for your replies. The wheels I have now are oem 16 inch. I believe the factory offset is +28mm and the backspace is 5.60. The new rims are xd82089080718 with +18 offset and 5.71 backspace. I'm not too worried about acceleration, it's a 3/4 ton suburban "quick" is not what she was designed for. 8.1 and MPG are only seen together in jokes so no problem there either. Aside from not fitting, I was really only worried about needing to re-gear

 

[adriver]

I don't think that's right. If they were 16" with a 5.6" backspace, and a 28mm offset, that means your offset is 1.1".
5.6" - 1.1" = 4.5" centerline. Which means they would be 16 x 9" factory wheels. That could be, but I would expect a factory 16" to be 16 x 7-8" probably 16 x 7 or 7.5".


The only wheels I have the size for off hand are the avalanche wheels I put on my Silverado from a 02-06 Avalanche. They are opt N89 17 x 7.5 with an offset of -31.

 

[adriver]

https://www.roadreadywheels.com/products/1999-2010-16x6-5-chevrolet-suburban-2500-aluminum-wheel-rim?msclkid=66938a13b23f17b2d86ed1c3dece8494&utm_source=bing&utm_medium=cpc&utm_campaign=BPA - Items - Chevrolet&utm_term=4582627028882084&utm_content=BPA Item - Chevrolet|Suburban 2500|100-125|C:60

If this is it they are 16 x 6.5" with a 28mm offset




I had to reread and doublecheck. I forgot when you give a wheel's size, you are saying it for the size of where the tire mounts. When you figure out backspacing you need to add 1" to account for the outside of 1 lip to the inside of the other.


If these are them, these would be 16 x 6.5, but when you figure out backspacing you have to figure it out as 16 x 7.5". (7.5" / 2) = 3.75" + 28mm offset/ 1.1" = 4.85" of backspace on what I think are your current wheels. Your new wheels would have 5.71" (-4.85" = .86"of backspacing) + .8" wider on your tires. Your new tires edge would sit about 1.6"" deeper into the wheel well.


If they were too close, you can always just add a spacer. I'm heading off, or I'd double check, but I think to get the geometry as close to as it is with your factory wheels, you would ideally want to add a 10mm spacer. Its definitely not required, and I would only bother with it if you need the extra clearance for the tires.

 

[MCAT069]

These are my oem wheels. The specs I posted earlier are the ones I got from call Discount Tire. I am in no way knowledgeable with regards to backspacing and offset which is why I asked for assistance. The specifications on the rims that were gifted to me are from the manufacturer website. That being said, in theory, the gifted set should fit and I do not need to re-gear, correct?

 

[adriver]

No, you won't need to regear, but you will notice a slight loss in acceleration. I see those OEM wheels weigh in at 25lbs, and the new wheels are 33 lbs (first and only weight I saw that I'm going off). Then a larger tire is going to be several pounds more. You're going from roughly 50 lbs per corner to roughly 65 lbs.