Will these tires rub?

[dward]

I found a set of Big Horn wheels on CL for a great price but tires are about gone.
I would like to go with the new Nitto Ridge Grappler 295/70/18 for a little more width and 4080 lb load rating.
They are 34.29” tall and 11.77” wide which is a little over 1” taller and less than 1” wider than the stock Firestone Transforce 275/70/18 at 33.19” tall and 10.98” wide.
My buddy put the 33/12.5/18 on his LB and they like look great but only have 3300 lb rating.
I don’t want to have to lift the truck or use a leveling kit.
Im thinking I should be ok and not have any rubbing or clearance issues.
Anyone running a similar size on a stock truck?
Also, the 275 or 285 / 70 has the lower load rating also unless I go with a 75 and that increases the height to 35”.
Thanks.
“

 

[EDankievitch]

They will be close. I have the same size on my 2013 What I found was the tires rubbed on the controll arms at full hard over. You have the 3 link front end my 13 has the older 5 link system. I think you'll have more clearance than I had. What I did do to stop the rubbind was to drill and tap the steering stops on the knuckles for a 1/4-20 x 1/2" long bolt. the thickness of the head of the bolt was all that was needed to keep my tires from hitting the controll arms and I don't notice any loss of how tight I can turn. I do have a 2" leveling kit on my truck but these tires will clear the fenders with out it. On the stock wheels. Hope this helps.

 

[Jim W]

On my 2008 truck I am using LT 285/70R 17 Nitto Dura Grappler tires on Mickey Thompson Side Bitter II rims. I have no rubbing issues at all, with no lift on the truck , but I did discuss with the tire supplier to pick the right size rims for my truck. I think they are Zero outset.

 

[cerberusiam]

Offset means nothing, dependent on rim width, back spacing is the important number. Measure back space on both sets and see if they are comparable. The 6.5" back space on newer rims will cause some tires to run that never did. A 295 tire on stock 3rd gen rims did not rub, but, with the extra backspace of the newer rims it might. Have to test fit tires and rims to see if it is acceptable.

 

[AEdelheit]

Offset means nothing, dependent on rim width, back spacing is the important number. Measure back space on both sets and see if they are comparable. The 6.5" back space on newer rims will cause some tires to run that never did. A 295 tire on stock 3rd gen rims did not rub, but, with the extra backspace of the newer rims it might. Have to test fit tires and rims to see if it is acceptable.

Actually Offset is the only number that matters as it does not change at all with rim width and dictates where the tire will rub. Back spacing changes with width and is very misleading. The 4 link trucks use a +44mm off set where the radius arm trucks are +57mm, Ideal offset for tire clearance is +20mm for clearance between the radius arm and fender. The Offset is usually listed on the back of the wheel.

 

[cerberusiam]

Actually Offset is the only number that matters as it does not change at all with rim width and dictates where the tire will rub. Back spacing changes with width and is very misleading. The 4 link trucks use a +44mm off set where the radius arm trucks are +57mm, Ideal offset for tire clearance is +20mm for clearance between the radius arm and fender. The Offset is usually listed on the back of the wheel.

Other way around. Offset is the distance from the mounting face to center of the wheel, it will be based on rim width and construction. Back spacing is absolute, it has no dependencies. 6" of back space is the same whether the rim is 8, 10, or 12 inches wide IF the wheels are built to fit correctly. Without knowing rim width one cannot assess suitability of the wheel. With known backspacing potential for rub and amount of poke can be estimated and adjusted to fit correctly.

 

[AEdelheit]

Other way around. Offset is the distance from the mounting face to center of the wheel, it will be based on rim width and construction. Back spacing is absolute, it has no dependencies. 6" of back space is the same whether the rim is 8, 10, or 12 inches wide IF the wheels are built to fit correctly. Without knowing rim width one cannot assess suitability of the wheel. With known backspacing potential for rub and amount of poke can be estimated and adjusted to fit correctly.

Nope, I literally deal with this every day. As you said Offset is the distance from the mounting face to center of the wheel which is what matters when it comes to tire rub, realistically wheel width has very little to do with tire rub as the width where the bead mounts doesn't have much effect on section width of the tire which is where the rub is. Lets say you a trying to stick with 4.5" back spacing, if you go from a 7" to 12" wide wheel that will drastically change the fitment of the wheel and tire and tire rub, if you stick with 0 offset a 7" wide wheel will fit pretty much the same as a 12" wide in terms of rub an clearance.

I agree the way you measure back spacing does not change with width but how the tire will fit and rub drastically changes changes with width when using backspacing where it does not when using offset.

 

[cerberusiam]

if you stick with 0 offset a 7" wide wheel will fit pretty much the same as a 12" wide in terms of rub an clearance.

Lets do the math on that. A 7" rim with 0 offset has 3.5" for back space and 3.5 inches of front space. A 12" rim with 0 offset has 6" of backspace and 6" of front space. If you have 2" of backspace needed to fit tire size X you have over extended the back space by .5" and it will run on the control arm at full lock. The offset has to change to maintain back space to stop rubbing on control arm.
This is completely ignoring front space and clearance to fender which is dependent on suspension height and body design.

The Dodge Rams are heavily back spaced so when adding a taller wider tire you have to decrease that back space to stop inside rubbing. It is whole easier to visualize and articulate "I need a 5.75 backspace wheel to fit X tire" than to try to calculate the offset depending on rim width and height. A 295/70 tire on a 17" rim has different requirements than a 297/70 on a 20" rim.


Measuring back space does not change, it is what it is. Offset and wheel width determine what it will be.

 

[AEdelheit]

Lets do the math on that. A 7" rim with 0 offset has 3.5" for back space and 3.5 inches of front space. A 12" rim with 0 offset has 6" of backspace and 6" of front space. If you have 2" of backspace needed to fit tire size X you have over extended the back space by .5" and it will run on the control arm at full lock. The offset has to change to maintain back space to stop rubbing on control arm.
This is completely ignoring front space and clearance to fender which is dependent on suspension height and body design.

The Dodge Rams are heavily back spaced so when adding a taller wider tire you have to decrease that back space to stop inside rubbing. It is whole easier to visualize and articulate "I need a 5.75 backspace wheel to fit X tire" than to try to calculate the offset depending on rim width and height. A 295/70 tire on a 17" rim has different requirements than a 297/70 on a 20" rim.


Measuring back space does not change, it is what it is. Offset and wheel width determine what it will be.

Again deal with this every single day and Offset is a far more reliable method. Only looking at backspacing is great if you dont care about the fender being torn off when you turn but most people do so ignoring half the wheel is really not ideal. You cant move a tire away from the control arm for more clearance without looking at how it will impact the fender and that is very difficult to do with backspacing, very simple with offset. A 295/70 tire will need the same offset regardless if wheel diameter as wheel diameter does not effect rub. A 8" wide wheel would need a different backspacing then a 10" wide wheel however they would need the same offset regardless of wheel diameter.

 

[MRoberts]

From the Thuren Fabrication site:

Measuring wheels using offset, and the advantage to using this method.




Wheel offset is the best way to spec and measure wheels. This gives you the exact placement of the tire tread, no matter how wide the wheel is. A 6" wide wheel with +18mm offset, and a 12" wide wheel with +18mm offset, both put the tire tread in the same place. The definition of offset is referencing the mounting flange placement where the wheel bolts to the axle, in relation to the centerline of the wheel where the tire mounts between the beads, and then how far the main wheel is offset in or out from the mounting flange. For example, +18mm offset would move the whole wheel where the tire mounts, inward 18mm from center, towards the engine. So, + offset numbers move the wheel inward from center, and - offset is moving the wheel outward from centerline. Higher + offset number keeps the truck more narrow in width, and closer to zero or negative offset, makes the truck wider.









Backspace measuring, and the problems with it.




Backspacing is a terrible confusing way to spec a wheel. Not sure why wheel manufacturers ever started this. If you put a wheel down on a bench, outside of wheel facing up, and then measure from the table up to the mount flange, this is the wheels backspacing measurement. Notice it's from the table? So, this measurement also includes the thickness of the tire bead mounting lip. I have seen wheels vary +/- .5" easy in lip thickness, so here is one part of the backspacing gamble. Then, this is only referencing the backside of the wheel! If you have an 8" wheel with 5" backspacing, and a 10" wheel with the same 5" backspacing spec, the tire placement is WAY different comparing the two. Backspacing is tough to nail down, so be VERY careful with this.

 

[cerberusiam]

Only looking at backspacing is great if you dont care about the fender being torn off when you turn but most people do so ignoring half the wheel is really not ideal.

Ridiculous. Backspace defines the other half of the rim width, rim is sized to the tire we want to run anyway.

Dodge rams have plenty of room in the fender well unless you mess up the position by trying to use offset as a determining factor.

very simple with offset.

Not unless you know rim width. As demonstrated and verified by Thuren offset is dependent on rim width to position tire in the wheel well. The math is simple, spatial relationship easy to understand.

wheel diameter does not effect rub.

Please demonstrate the physics of this.

they would need the same offset regardless of wheel diameter.

No. Demonstrating the previous will invalidate that statement.

 

[AEdelheit]

Ridiculous. Backspace defines the other half of the rim width, rim is sized to the tire we want to run anyway.

Dodge rams have plenty of room in the fender well unless you mess up the position by trying to use offset as a determining factor.



Not unless you know rim width. As demonstrated and verified by Thuren offset is dependent on rim width to position tire in the wheel well. The math is simple, spatial relationship easy to understand.





Please demonstrate the physics of this.




No. Demonstrating the previous will invalidate that statement.

Hahahahaa oh man you remind me of a high school kid just rambling on trying to defend there stance. I know you are very knowledgeable about these trucks in general but I dont think tire and wheel fitment is your strong point. I deal with it on these trucks every day fitting 37"+ tires and always use offset for accuracy and simplicity as there is little room for error.

You seem to only be worried about the back half the tire , back spacing does not in any way define the other half of the wheel. If you go into a shop and say you need a 4" BS wheel the fitment would very greatly from a 7.5" wide wheel to a 10" wide wheel but unless you know the wheel width in advance you wont know how it will actually fit on the truck. If you use Offset it takes the entire wheel into account and as I said before though you likely laughed at it the actual rim width does not have a drastic effect on the section width of the tread where rub occurs so I am looking at where the center line of the wheel is compared to the hub as that will dictate clearance around the tire.

In terms of wheel diameter have you ever measured the tread width of a 17" vs 20" tire of the same rated height and width? I have, its the same where rub occurs and requires the same offset for clearance from a 7.5" wide to 10" wide wheel. With offset +18mm is ideal, Now if we were using backspacing that would go from 4.96" on a 7.5" wheel to 6.21" on a 10" wide wheel so far more variables and room for error.

The fender wells are decent size on these trucks but it doesn't take much to start hitting the rear of the inner fender with aftermarket wheel and larger tires so you have to look at where the inside and outside of the tire will be.

 

[Jim W]

O.K. I am sorry I ever mention offset in my post. Although when I was made a designer at where I worked, my first job was tires and rims on wheel skidders. That is were I informed about offset and back spacing from the Tire and Rim Association using their text book. Although this a was in the early 70's so, maybe this has changed. Offset was what we always used in designing the rim and tire fitment for these tractors.

 

[AEdelheit]

O.K. I am sorry I ever mention offset in my post. Although when I was made a designer at where I worked, my first job was tires and rims on wheel skidders. That is were I informed about offset and back spacing from the Tire and Rim Association using their text book. Although this a was in the early 70's so, maybe this has changed. Offset was what we always used in designing the rim and tire fitment for these tractors.

Well it did derail the thread and I apologize for that I do enjoy a good debate from time to time. Offset is still used in most off highway applications.