Quicker Tire Question - Actual Width of 33 inch tire? For tire carrier design

[robcarync]

Hard to describe...but basically I am curious what the actual widest width is (approximately) on a 285 75 16 tire. See graphic below.

I am working on my tire carrier design...and am trying to work out the spacing from the vertical/triangular posts to the actual mating surface where the rim bolts to. Obviously that is dependent on the offset/backspace of the rim and the size of the tire. I have the stock size rim to measure off of, but I only have a 31 inch tire on it right now. Just curious how much wider a 285/75/16 tire is at the widest point?

I know how to read tire sizes etc...11.22 inches is what that works out to. Is that number just the tread width though? Does that account for sidewall to side wall at the "fattest" point? Just curious how much wider than the stock rim it would sit.

Obviously this isn't a huge difference...but I am just curious since I don't have one to test fit. I'd hate to design something then find out I left a huge gap, or that the gap is too tight.

 

[TJTJ]

Hard to describe...but basically I am curious what the actual widest width is (approximately) on a 285 75 16 tire. See graphic below.

I am working on my tire carrier design...and am trying to work out the spacing from the vertical/triangular posts to the actual mating surface where the rim bolts to. Obviously that is dependent on the offset/backspace of the rim and the size of the tire. I have the stock size rim to measure off of, but I only have a 31 inch tire on it right now. Just curious how much wider a 285/75/16 tire is at the widest point?

I know how to read tire sizes etc...11.22 inches is what that works out to. Is that number just the tread width though? Does that account for sidewall to side wall at the "fattest" point? Just curious how much wider than the stock rim it would sit.

Obviously this isn't a huge difference...but I am just curious since I don't have one to test fit. I'd hate to design something then find out I left a huge gap, or that the gap is too tight.

Section width IS the "fattest Part". The tread width is narrower than the section width.



Things to take into account:

1) A rim's NOMINAL size is about 1" LESS than its size for your purposes, so a 7" rim (As in a 16 x 7 rim) is 8" wide. (Nominal size doesn't include the flanges that hold the rubber to the rim...)

2) The BS, as you surmised makes an ENORMOUS difference in carrier clearance...as most carriers historically assume a BS of ~ 3-4", and the MORE BS, the CLOSER the rim is going to be ot the carrier/the skinnier the tire has to be, etc.

3) If you know the BS, you don't need the rim width.

4) As a 31x10.5 is about 267 mm and a 285 is, um, 285 mm, and, HALF the difference is what "sticks out farther"....That's another ~ 10 mm of carrier clearance you need.

5) If making a carrier, make it able to fit tire/rim combos LARGER than your immediate plans....this will avoid frustration down the road. Assume you MIGHT want AT LEAST a 33 x 12.5 on their...as an OPTION. Going from 10.5 to 12.5 " is a difference of ~ 2", so, another 1" of CLEARANCE per side is better than 10 mm. Then, consider the BS options...all the above assumes 5.5" of BS for all future combos. Maybe another inch or two to cover differences in section width from nominal to "fat for their size" tires and potential different BS rims, etc.

6) BS would be accounted for INCH PER INCH, not splitting the difference as with the other measurements that affect the two sides at half each....so one less inch of BS (4.5" vs 5.5") means the tire will be 1" farther from the mount.

Does all that make sense?

 

[robcarync]

Great info as always. I didn't realize tread width was different from section width - for some reason I forgot that detail. Ideally I'd like it to be capable of 33x12.5 so I'll plan on that. Thanks tjtj!

 

[TJTJ]

Great info as always. I didn't realize tread width was different from section width - for some reason I forgot that detail. Ideally I'd like it to be capable of 33x12.5 so I'll plan on that. Thanks tjtj!

np


Its not a perfect measurement...the nominal tire sizes vary a lot, and, the tread width to section width ratios are all over the map.

For example, a 33x12.5/15 BFG AT ko has a NARROWER TREAD width than a 305/70/16 BFG AT ko, even though technically, 305 mm is only 12" not 12.5".

The 305 might be taller too, etc...as the 305's are typically 33" on the nose and the 33x12.5's tend to be ~ 32.5 - 33" etc.


As section width does nothing for you in of itself....its the TREAD that is giving you flotation/traction, etc...you don't care about the section width as much as tread width for performance...but for CLEARANCE, the section width does matter, as its what sticks out the farthest.

Some tires have a rounder shoulder profile, and some are squared. The squared ones put all the lug edges on the ground as part of the normal contact patch, whereas the rounded ones have the edge lugs receeded up a bit so they don't hit the ground unless you're heeled over more or in deeper stuff, etc.

For a carrier, the rounder shoulders fit easier, as the lugs don't stick out to the sides as far.

This is also why you might see two people arguing about how one trimmed ABC and the other guy said he didn't have to....and one might have an AT and the other an MT, or, a square vs rounded shoulder. One guy's lugs are playing the wells like a baseball card in the spokes of a bike, and the other guy's lugs clear and don't make any card noises at all, etc. One guy's 33x12.5 might be 32" in diameter and the other guy's might be 33" in diameter, and so forth.

 

[rokdaddy]

Not sure if this will help but here are the measurements on my BFG AT KO's on 8" wide wheels. Tires are "E" load range @ ~40psi on the front axle of a ~6500lb rig.

Tread width:


Section width (alignment isn't great in the pic but I used a straight edge to line things up before taking the pic):


Tire info:



Hope this is useful.



-Rok

 

[robcarync]

Awesome info rokdaddy!!!! Exactly what I was curious about. That gives me empirical data to go off of.

 

[rokdaddy]

No problem, sir. I was sitting in the garage when I read your post and I already had the calipers out so it was a quick and easy check. FWIW, I really like this size (of BFG AT's) on an 80% highway/ 20% trail rig. A bit less drag than the standard 33 x 12.5 that I was running before this set.

Looking forward to seeing how your tire carrier turns out.


-Rok

 

[C3po]

Here's the one Ricel and I built.

The tire mounting plate is welded to an inner tube that slides the tire in and out. With a bolt to lock it in place. I left it adjustable to carrying a 35".

 

[robcarync]

I also had a similar idea to make it adjustable. Still deciding on the right balance between function and cost...obviously cheaper to just have a fixed tube, but it would be nice to not have a huge gap between the tube and smaller spare tire for now.

Where did you get the tire mount plate? I have been looking for one with holes already drilled in it. You just pressed in the lug studs?

Edit: I see COMP4x4 on there...I used them for a few different kinds of recovery points! Good guys to work with! Didn't think to check them out again...good find!!!!

 

[C3po]

I used comp4x4 for every part. They have a really good hinges with greasable bearings, very smooth to open and shut, itll be a huge benefit after a couple new england winters.

If you dont want to make an adjustable mount (which you should), you could always have someone hold the tire while you make a few tacks.

If I did it again, I'd make the swingarm lock open. In nose down situations, I fight to get stuff out the back which holding on the swingarm open.

 

[robcarync]

I only have a 265.70.16 spare tire right now, hence the thread asking for actual width of a 285...I don't have actual tire to build around, so wanted to make sure I left enough room. The adjustable mount seems to be the way to go...50 bucks for the mount, sleeve, and plate isn't too bad. For 60 bucks you can get the tube already welded and the studs and lug nuts, so that isn't a bad deal at all, I don't think. Lots of options for bushings I see...so I will have to look into them!

One question if you can...could you take a photo of the adjustment/set screw used to lock in the carrier position? It is a little confusing because on the website it mentioned having to weld a nut on the inside of the tube to complete the vertical stop?

 

[C3po]

Top Bolt holds the extension in place. The hole was predilled and tapped.

Ill weld an additional bolt or nut in the cut out later.

The cable and bike lock just helps to deter the theives.

 

[robcarync]

Well...this is technically the wheel and tire section...but a tire carrier conversation has already started, so I figured I'd continue here instead of making a new thread:

Someone with a tire carrier, can you post a photo of the swing arm completely open ~180*, and post a measurement similar to the attached photo below?

Basically, I am working on my design for a half width swing arm, but of course you have to make sure the tire is far enough out that it not only clears the hatch, but doesn't hit the plastic corners or the tail light. I am designing for a 34" tire (just to ensure a half inch or so of gaps here and there if I bump up to 33s)...Based on the 3D model I have developed, the tire swings out wide enough to clear the hatch, but I didn't take into account the location of the corners and tail light to see if the tire can actually swing out enough.

So...what is your approximate length of the swing arm from the edge of the bumper/pivot to the center of the tire? Does your arm open 180*?



PS: My brother is borrowing my Xterra currently, so I can't take the measurement directly off the truck...so thought I would ask for some actual measurements that are known to work. Any help would be appreciated...