Tire diameter logic (illogic?): 31s vs. 33s and lift height

[matkal]

I've been kicking around the idea of which size tires I want to end up with, stay with 31s or go to 33s? I have 31" tires that haven't rubbed on the trails I've done so far, which are pretty much the kind of wheeling I want to do. So here's my logic for 33s; Since my 31s don't rub at stock height and 33s are only a 1" bigger radius, a 1.25" body lift or a 2" spring lift should be plenty. Yes?

Excuse my ignorance if I'm under thinking this.

 

[Jramos013]

The Recommended lift for 33” is 4” for a good articulation. In my personal experience im running 33”x10.5” with a 3” lift, However mine is a DD 90% of the time. Were i live theres constant flooding and very bad roads, thats the main reason i went with my combination. Offroading per se, i just do light trails, i don't even disconnect my sway bar links. No rocks anywhere near me, just mud pools, sand dirt roads.

 

[Fouledplugs]

I've been kicking around the idea of which size tires I want to end up with, stay with 31s or go to 33s? I have 31" tires that haven't rubbed on the trails I've done so far, which are pretty much the kind of wheeling I want to do. So here's my logic for 33s; Since my 31s don't rub at stock height and 33s are only a 1" bigger radius, a 1.25" body lift or a 2" spring lift should be plenty. Yes?

Excuse my ignorance if I'm under thinking this.

For 33 inch tires, its standard to shoot for 4 inches of lift to regain the factory suspension geometry which will provide a better ride on road and off road.

A 4 inch currie spring (or any 4 inch spring) is your best bet.

Some folks will run a 2.5 inch spring and a aluminum 1.25 inch body lift to gain the 4 inches needed to properly run 33 inch tires.

Either combination will work. Note: a SYE and adjustable links will be needed to correct the pinion angle after lifting and adding the 33 inch tires. You will also need to adress longer travel shocks and possibly brake lines and sway bar link modifications.

The suspension should be cycled to adjust bump stops to prevment the tires contacting inner fenders.

 

[taylormade73]

Width of the tire and wheel backspacing will also factor into your equation rather than just the increased radius

 

[jjvw]

As the lift height increases, the shock lengths and their travels increase. More travel means more flex which requires more clearance above the tire. Also, larger tires are usually wider, which requires less backspacing, which also requires more clearance above the tire.

 

[matkal]

I kinda thought this was the case (all previous replies) but to my shelter-in-place induced wandering mind, the math seemed logical.

 

[Apparition]

I kinda thought this was the case (all previous replies) but to my shelter-in-place induced wandering mind, the math seemed logical.

You aren’t wrong it’s just there are more variables and with increased tire size those variables may provide a different outcome.

 

[dbbd1]

For my 33's, my (almost) 4" lift came from- a 1-1/4" body lift and 2-1/2" springs/suspension.

Just an FYI.

 

[freedom_in_4low]

I kinda thought this was the case (all previous replies) but to my shelter-in-place induced wandering mind, the math seemed logical.

for high speed whoops where the tire remains roughly in the same plane as ride height, you're not totally off base.

It's just that, as @jjvw mentioned, when the tire on one side droops lower, the plane of the stuffed tire leans in at the top and in the front as it remains perpendicular to the articulating axle, and that ends up putting the tires in all sorts of places you might not predict.

Also, my 32's rubbed enough to damage the flare mounting flange with 3" of lift. I've since deleted that flange, added bump stop, and am in the process of going to a 4" lift in preparation for my next set of tires, which will be 33's.

 

[Chris]

Disregard what you think you know about tire sizes.

Measure the tires and you'll find far different sizes than what you think you are getting.

Case in point:

Both @Starrs and myself bought brand new BFG KO2 tires in 315/70R17 sizes. We both had them mounted on all 5 tires, including the spare. We both measured the spare tires mounted on the tailgate, inflated with 35 psi. Both our measurements were exactly identical, 33.3".

BFG claims in their specs that those tires measure at 34.4". In other words, those tires are an honest to goodness 1.1" smaller than the advertised size.

So don't assume you're getting a 33" tire. Some sizes run smaller, some run bigger. Cooper seems to be one that runs true to size near as I can tell.

 

[freedom_in_4low]

BFG claims in their specs that those tires measure at 34.4". In other words, those tires are an honest to goodness 1.1" smaller than the advertised size.

kinda makes you wonder if their revs/mile is correct and maybe that's how we ought to be shopping for tires.

 

[Chris]

kinda makes you wonder if their revs/mile is correct and maybe that's how we ought to be shopping for tires.

It's hard to say what size tire is what anymore. They all list specs for actual sizes, but in the case of BFG (and many others I'm sure) there measurements are grossly exaggerated.

 

[Starrs]

If you want a true 35” tire the BFG 47/12.5/17 in km3 or Ko2 will beg you a true 35.

 

[jjvw]

Disregard what you think you know about tire sizes.

Measure the tires and you'll find far different sizes than what you think you are getting.

Case in point:

Both @Starrs and myself bought brand new BFG KO2 tires in 315/70R17 sizes. We both had them mounted on all 5 tires, including the spare. We both measured the spare tires mounted on the tailgate, inflated with 35 psi. Both our measurements were exactly identical, 33.3".

BFG claims in their specs that those tires measure at 34.4". In other words, those tires are an honest to goodness 1.1" smaller than the advertised size.

So don't assume you're getting a 33" tire. Some sizes run smaller, some run bigger. Cooper seems to be one that runs true to size near as I can tell.

My new set of 35" Patagonias measure 34". A brand new MTR is actually 35".

 

[matkal]

Lot's of good info. The biggest thing holding me back from 33s or even 32s to a lesser degree is the expense of a re-gear.

 

[Chris]

My new set of 35" Patagonias measure 34". A brand new MTR is actually 35".

Goodyear as I understand it is actually pretty true to size (along with Cooper).

BFG (and apparently Milestar) are two that are definitely being overly optimistic (or flat out lying, depending on how you look at it ).

 

[jjvw]

...

BFG (and apparently Milestar) are two that are definitely being overly optimistic (or flat out lying, depending on how you look at it ).

Milestar is a very optimistic tire company.

 

[matkal]

Who among us hasn't ever exaggerated size........

 

[jjvw]

Who among us hasn't ever exaggerated size........

Charles Goodyear, apparently.

 

[Apparition]

My new set of 35" Patagonias measure 34". A brand new MTR is actually 35".

I thought your Milestars were used?