Wheel offsets are driving me batty...

[Gwerner74]

So I'm searching for a wheel and tire combo for my 2015 RAM 2500. I've pretty much decided on the wheel and tire size I want to go with, but the offset I need is driving me a bit nuts. I know this is supposed to be simple to figure out, but for some reason I'm just not grasping it beyond that I need a zero or negative offset to get the wider stance I'm looking to achieve. I'm hoping someone smarter than I can help me out here.

What I have: 2015 RAM 2500 Big Horn sitting on the OEM 20x8 wheels and factory size 285/60R20s. No suspension mods done to the truck. This wheel/tire combo lines up great with the fender lines, but I also have the OEM "off road" fender flares installed which I love the look of, but it looks a bit ridiculous with the tires tucked so far in to the centerline compared to the flares.

What I want: Just looking to get a slightly wider tire and a wider stance to better fill out the wheel well and line up with the fender flares. I'm thinking 33 x 12.5 on an 18 x 9 wheel will get me to where I want to be. I prefer the look of more sidewall to rim which is why I landed on the 18's. I don't plan on doing a lift or level, so it seems 35's are out, but I will consider a level if needed for fitment of the 33's.

So now I'm down to the offset. How exactly do I figure out how much negative offset I need to make 33 x 12.5 look correct without sticking out past the fender flares? Thanks in advance for any help you all can give.

 

[Bigskyroadglide]

Factory wheels are + 18 offset. 10 mm is .375 inches. 25.4 is 1 inch.

All this is important

If you want your wheels to stick out another 1 inch, then it +18 - 25. Equals -7 offset. Now your not going to find -7 so you have to adjust.

0 offset is 18 or approx 3/4 of an inch 18/25.4. =.71.

So in summary, as you go down in positive and to zero then negative you stick out more. If you go up in positive from 18, they tuck under the truck more.

Since you probably will never go past factory I'd think.about it as

How much do I want to go out. Wheels usually come in +18 +12 , +6 , 0 then a bunch of minus sizes.

I use a tape measure against the hub and a yardstick against the fender to measure. It's crude but it works, then convert Inches to mm.

Hopefully this helps and makes sense. This is all 1500 related

PS, you probably could get away with a 34 inch tall tire, just stay 11.5 wide. They should not rub the upper control.arm.

Photos below red truck, 16 laramie sport 33s, on factory 20s +18 no lift 1.4 level in front.

white truck. 24 warlock 315 70 17. 34.6 x12.4. X 17. Factory 17 +18 10 mm spacer making offset +8. No lift, factory 1.4 level in front

 

[diymirage]

Backspacing made so much more sense

 

[Gwerner74]

Factory wheels are + 18 offset. 10 mm is .375 inches. 25.4 is 1 inch.

All this is important

If you want your wheels to stick out another 1 inch, then it +18 - 25. Equals -7 offset. Now your not going to find -7 so you have to adjust.

0 offset is 18 or approx 3/4 of an inch 18/25.4. =.71.

So in summary, as you go down in positive and to zero then negative you stick out more. If you go up in positive from 18, they tuck under the truck more.

Since you probably will never go past factory I'd think.about it as

How much do I want to go out. Wheels usually come in +18 +12 , +6 , 0 then a bunch of minus sizes.

I use a tape measure against the hub and a yardstick against the fender to measure. It's crude but it works, then convert Inches to mm.

Hopefully this helps and makes sense.

PS, you probably could get away with a 34 inch tall tire, just stay 11.5 wide. They should not rub the upper control.arm.

Photos below red truck, 16 laramie sport 33s, on factory 20s +18 no lift 1.4 level in front.

white truck. 24 warlock 315 70 17. 34.6 x12.4. X 17. Factory 17 +18 10 mm spacer making offset +8. No lift, factory 1.4 level in front

This is incredibly helpful, thank you!

Especially this part here, that really helps crack the code in my brain on how to figure this out.

"If you want your wheels to stick out another 1 inch, then it +18 - 25. Equals -7 offset. Now your not going to find -7 so you have to adjust."

 

[Bigskyroadglide]

Sorry missed the 2500 in your description, everything I indicated is 4th gen 1500 based. I'm never owned a 2500.

 

[Dean2]

My 2021 2500 has OEM 18" wheels, which are 18x8 with a +57 MM offset. It has OEM size Duratrac tires 275 70 18. My Laramie has the off road package on it so sits about 1" higher than the same model without that. It also has the factory flares. Those tires are 33" tall. I could easily fit 35" tall tires on the stock rims by going to 295 75 18. The increased width would make them stick out a bit further.

What I like about the current fender coverage is on gravel and mud, it keeps more off the paint. The further out they stick, the more the paint gets beat up.

 

[mtnrider]

Factory wheels are + 18 offset. 10 mm is .375 inches. 25.4 is 1 inch.

That is Not correct, Factory 2500/3500 wheels are +57.


OP, for best fitment without sticking out out too far you want a 9" wide wheel with a +18 offset, that is the sweet spot for fitment on a 2500.

Here is all the fitment data you need..

2014-2022 RAM 2500 TIRE AND WHEEL FITMENT

Choose the right wheel and tire combo for fender clearance, especially with 0-3 inch lifts. Learn why our setup works best for durability and performance. #WheelandTireCombo #ThurenFabrication #TruckMods

www.thurenfabrication.com

.
.

 

[Dean2]

That is Not correct, Factory 2500/3500 wheels are +57.


OP, for best fitment without sticking out out too far you want a 9" wide wheel with a +18 offset, that is the sweet spot for fitment on a 2500.

Here is all the fitment data you need..

2014-2022 RAM 2500 TIRE AND WHEEL FITMENT

Choose the right wheel and tire combo for fender clearance, especially with 0-3 inch lifts. Learn why our setup works best for durability and performance. #WheelandTireCombo #ThurenFabrication #TruckMods

www.thurenfabrication.com

.
.

From what I have looked up, there appears to be a very wide range of claimed offsets. From +18 to +57 on the 18" wheels. Only way to know what you are starting with for sure would be to measure your existing rims. I have not physically done that on mine, so my claim of a +18 offset is based on published data. Could easily be +57 if the other data turns or to be correct. However, +18 to +57 is only 29 mm difference and given 1" is 25.4 mm, that is only 1.14 inches.

Either way, my OEM rims put the OEM tires in the right spot and they would for the bigger 295 75 18 size too.

 

[mtnrider]

From what I have looked up, there appears to be a very wide range of claimed offsets. From +18 to +57 on the 18" wheels. Only way to know what you are starting with for sure would be to measure your existing rims. I have not physically done that on mine, so my claim of a +18 offset is based on published data. Could easily be +57 if the other data turns or to be correct. However, +18 to +57 is only 29 mm difference and given 1" is 25.4 mm, that is only 1.14 inches.

Either way, my OEM rims put the OEM tires in the right spot and they would for the bigger 295 75 18 size too.

Nope, there is no +18 factory option, they are +57 (except the PW). And factory is a 8" wide, but don't quote me on that one. It's not a 9" I know that

.

 

[Dean2]

Nope, there is no +18 factory option, they are +57 (except the PW).

.

Good to know. Thanks. changed my original post so it isn't misleading.

 

[Gwerner74]

Nope, there is no +18 factory option, they are +57 (except the PW). And factory is a 8" wide, but don't quote me on that one. It's not a 9" I know that

.

Thank you to everyone for your help!

I can confirm that the factory 20" wheels are 8" wide on the 2500 Big Horn according to my build sheet.

 

[Gwerner74]

That is Not correct, Factory 2500/3500 wheels are +57.


OP, for best fitment without sticking out out too far you want a 9" wide wheel with a +18 offset, that is the sweet spot for fitment on a 2500.

Here is all the fitment data you need..

2014-2022 RAM 2500 TIRE AND WHEEL FITMENT

Choose the right wheel and tire combo for fender clearance, especially with 0-3 inch lifts. Learn why our setup works best for durability and performance. #WheelandTireCombo #ThurenFabrication #TruckMods

www.thurenfabrication.com

.
.

This is perfect, thank you. Now I just need to decide if I want to level or not, and if I should go 33s or 35s.

 

[mtnrider]

This is perfect, thank you. Now I just need to decide if I want to level or not, and if I should go 33s or 35s.

35's look better, I think 33's will look small? I see you have a hemi so the impact on performance and mpg will be greater with the 35's. You can get away with 35's and no level but it does look better with one in my opinion.

.

 

[Bigskyroadglide]

35's look better, I think 33's will look small? I see you have a hemi so the impact on performance and mpg will be greater with the 35's. You can get away with 35's and no level but it does look better with one in my opinion.

.you could look into 315s. A 315 is a very close approximation to a 35-inch tire, with the metric size typically measuring slightly smaller in diameter when mounted.

 

[Dean2]

One thing most people miss is that leveling a pickup reduces gas mileage a lot. Becuase it is often done with bigger tires and other changes, those usually get blamed. However, we started leveling 1500s with.no other changes when adding rear air bags for handling weight in the box. We saw 2 to 4 mpg drops on highway mileage. If we removed the front dam you saw double that. I don't level them any more unless there is a real good reason.