Wheel Specs

[Duramax_JP]

So im about to buy some new rims and tires but Im curious as to what all these different options are. Like the bolt pattern. Does that tell whther its an 8 lug or 6 lug rim? What does the second number behind the bolt pattern indicate.

I was thinkin on buying 18" kmc monsters.

They have a -12 offset, the backspace is 4.53, and the bolt pattern is 8x170.

Would these rims work for my truck with 285/60's?

Thanks


James

 

[GCncsuHD]

NO 8x170mm is the 99+ Ford lug pattern, meaning 8 lugs with 170mm center to center of two lug holes across from each other.

GM, Dodge, and 97 and older fords are all 8x6.5" or 8x165.1mm meaning 8 lugs, and 6.5" (165.1mm) across from each other.

Now then, 285/60/18 will only be about 11.2" wide and 31.5 inches tall, in other words 2.5" shorter, and about 1" narrower than your current 305/70/17s which should measure about 12.0" wide and 33.8" tall. (If it gives you an idea, I had 285/60/18 on a lowered 1500 Suburban.)

 

[Duramax_JP]

NO 8x170mm is the 99+ Ford lug pattern, meaning 8 lugs with 170mm center to center of two lug holes across from each other.

GM, Dodge, and 97 and older fords are all 8x6.5" or 8x165.1mm meaning 8 lugs, and 6.5" (165.1mm) across from each other.

Now then, 285/60/18 will only be about 11.2" wide and 31.5 inches tall, in other words 2.5" shorter, and about 1" narrower than your current 305/70/17s which should measure about 12.0" wide and 33.8" tall. (If it gives you an idea, I had 285/60/18 on a lowered 1500 Suburban.)

Thank you for enlightening me that defintely somethin I need to know.


The reason I chose such a small tire is because ill be lowering the front down to level and the back end will be dropped a couple inches. Do you think this tire size is still gonna be too small. I could jump up to some 285/65's i think which should put me at around a 32" tire.

 

[GCncsuHD]

Thank you for enlightening me that defintely somethin I need to know.


The reason I chose such a small tire is because ill be lowering the front down to level and the back end will be dropped a couple inches. Do you think this tire size is still gonna be too small. I could jump up to some 285/65's i think which should put me at around a 32" tire.

I don't think it would be that small, although I think that size would be about ideal with the front stock, and maybe the rear dropped 2" to match. But look at it this way, the stocker 245s are only 30.5" tall.

 

[Duramax_JP]

Ya I was tryin to stay with a smaller tire since I do alot of drag racing. I cant decide between the Nitto Dune Grapplers and Nitto Terra Grapplers though. Ill just have to see what I like and decide, im not in any hurry. So what was the bolt pattern I needed for my truck again? Was it 6.5? Or was that some for the older trucks

 

[GCncsuHD]

Ya I was tryin to stay with a smaller tire since I do alot of drag racing. I cant decide between the Nitto Dune Grapplers and Nitto Terra Grapplers though. Ill just have to see what I like and decide, im not in any hurry. So what was the bolt pattern I needed for my truck again? Was it 6.5? Or was that some for the older trucks

Yes, 8x6.5" (165.1mm).

 

[JoshH]

To expand on what GCncsuHD said:

Backspacing is measured from the back edge of the rim to the wheel mounting surface and is given in inches.

Offset is the distance from the center of the wheel to the wheel mounting surface and it is given in millimeters. + offset means the wheel mounting surface is closer to the front of the wheel (the part that you see). In other words, you will get more backspacing. - offset is just the opposite of positive.

Just in case you don't already know, here is how metric tire sizes work:

P285/60R18

P=passenger car. These tires are usually load range C or less. Typically not suited for our trucks. A suitable tire for our truck would have an LT in place of the P (LT=light truck).

285=the widest part of the tire in millimeters. This measurement is from sidewall to sidewall. It is almost always wider than the tread width, usually by an inch or more.

60=the tire's aspect ratio. Aspect ratio determines the sidewall height. The way you calculate that is you take the tire width (285 in our example). You then multiply that by .60 (60 is a percentage). In other words your sidewall is 60% as tall as your tire is wide. So for your particular tire, the sidewall is 171 mm tall.

R=radial. This just means you are looking at a radial tire not a bias ply.

18=rim diameter. Pretty self explanatory. This measurement is always in inches.

Sometimes all the tire size will be followed by a speed rating such as Y or Z or H or whatever the speed rating of the tire is.

So to find the height and width of your tire take the width in millimeters (285) and convert it to inches (divide by 25.4). You should get 11.2". This is the width of your tire. Now take the sidewall height (171) and multiply it by 2 (because you have sidewall on both sides of the wheel). Now convert that number (342 in this case) to inches (divide by 25.4 again). You should have come up with 13.5". Now add the rim diameter (18"), and you will see that your tire height is 31.5".

I hope that helps.

 

[Duramax_JP]

Yes, 8x6.5" (165.1mm).

Alright thanks.

To expand on what GCncsuHD said:

Backspacing is measured from the back edge of the rim to the wheel mounting surface and is given in inches.

Offset is the distance from the center of the wheel to the wheel mounting surface and it is given in millimeters. + offset means the wheel mounting surface is closer to the front of the wheel (the part that you see). In other words, you will get more backspacing. - offset is just the opposite of positive.

Just in case you don't already know, here is how metric tire sizes work:

P285/60R18

P=passenger car. These tires are usually load range C or less. Typically not suited for our trucks. A suitable tire for our truck would have an LT in place of the P (LT=light truck).

285=the widest part of the tire in millimeters. This measurement is from sidewall to sidewall. It is almost always wider than the tread width, usually by an inch or more.

60=the tire's aspect ratio. Aspect ratio determines the sidewall height. The way you calculate that is you take the tire width (285 in our example). You then multiply that by .60 (60 is a percentage). In other words your sidewall is 60% as tall as your tire is wide. So for your particular tire, the sidewall is 171 mm tall.

R=radial. This just means you are looking at a radial tire not a bias ply.

18=rim diameter. Pretty self explanatory. This measurement is always in inches.

Sometimes all the tire size will be followed by a speed rating such as Y or Z or H or whatever the speed rating of the tire is.

So to find the height and width of your tire take the width in millimeters (285) and convert it to inches (divide by 25.4). You should get 11.2". This is the width of your tire. Now take the sidewall height (171) and multiply it by 2 (because you have sidewall on both sides of the wheel). Now convert that number (342 in this case) to inches (divide by 25.4 again). You should have come up with 13.5". Now add the rim diameter (18"), and you will see that your tire height is 31.5".

I hope that helps.

Thanks Josh. I knew the whole metric measurement system pretty well. But the backspacing and offset part is good info and is very helpful. So judging by what you said my offset and backspaing are pretty good with those rims if I want them to be sticking out of the fenders a little or in line" with the fenders? Or are they gonna be tucked up in the fender wells. I like them sticking out a little more so thats why I was lookin at the neg offset

 

[JoshH]

That wheel has over a quarter inch less backspacing than the stock wheels are more than likely 2.5 or more inches wider, so just with the wheel alone, the width of the truck will be almost 6 inches wider than stock.

 

[Duramax_JP]

That wheel has over a quarter inch less backspacing than the stock wheels are more than likely 2.5 or more inches wider, so just with the wheel alone, the width of the truck will be almost 6 inches wider than stock.

So am I lookin at wheels that stock out like way too far out of the wheel wells or just like an inch. An inch would be perfect IMO

 

[whitetrash21]

So am I lookin at wheels that stock out like way too far out of the wheel wells or just like an inch. An inch would be perfect IMO

these are approx an inch.... only 16" wheel though
http://www.duramaxdiesels.com/forum/album.php?albumid=92&pictureid=933

 

[GCncsuHD]

So am I lookin at wheels that stock out like way too far out of the wheel wells or just like an inch. An inch would be perfect IMO

Depends on the width of the wheel, but guessing 18x9 (using the offset and backspacing you gave) they will just stick out probably about an inch, and about flush in the rear as the rear is narrower than the front.

And Josh's info is good on the offset, backspacing, and tire size, I just didn't feel like going that in depth last night. But to extend on the backspacing/offset thing, there is one mistake alot of people make when converting one to the other if only one value is given to them, and thats not taking into consideration the "lip" of the wheel. So lets say since your wheel has an -12mm offset /25.4 that is 0.472mm offset, so take your wheel width of 9" (bead surface to bead surface, the width that is advertised with the wheel), and add the thickness of the bead area, (a good guess is around .5" for each side, actual measurement could be less or could be more depending on the wheel) and that gives you a total rim width of 10", so you divide that by 2 to get the center line of 5", and add the offset of -.473", which gives you 4.527" Backspacing.