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OK, I'm not sure if this has been adequately addressed or not -- trust me, I've done a ton of searching on here and can't seem to find a straight answer on this.
So, I'm looking at all possible 33" to 35" tire sizes and have determined that fitting a 35" tire on a 3/1 kit is not only possible but has been done numerous times.
What I fail to comprehend is how to determine what width of tire can be accommodated without rubbing on the UCA or body mounts or plastic on the fender-wells.
The stock wheel I have is an 18"x8" with a +60 offset. I'm not sure what the backspacing is on it (though I can find out if I take one off the truck I suppose).
I assumed that having rims with a +30 or +40 offset would move the wheel out by that amount minus 1/2 the extra width of the rim. So, on a 9" wide rim, a +40 offset would move the tire out 20mm - (1/2*(9inches-8inches=25.4mm)) = 20mm - 12.7mm = 7.3mm. Of course the wheel takes up an extra 12.7mm on each side, so, 12.7-7.3=5.4mm extra on the inside and 12.7+7.3=20mm on the outside.
So does having a lesser "positive" offset (or even a small negative) offset make you more prone to rubbing on the UCA and body mounts? Or is it the other way around? I keep seeing posts where I think it is one way, only to see other posts where it clearly claims the opposite. It just seems very confusing to me. I think if there was a way to determine the precise position of these items in relation to the wheel hub, we could more easily make a conclusion as to how wide a tire with what combination rim (backspacing and offset) will fit with or without certain modifications.
If we could make that determination, maybe we can create some kind of a sticky to illustrate how to measure via wheels/tires and that way people (like me) can be a little more comfortable ordering the proper size tires.
Some of this info can be derived from those that have posted their wheel/tire measurements and observed something like 1/4" space between UCAs and body mounts, etc. I hope this wasn't too confusing... I'm just trying to narrow down what I can do without having to order and send back different sets of tires... :)
 

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I have the trail grapplers in a 35.04x13.39x18 on 18x9 KMC XD Hoss 795 with a +30 offset which is 6.18 on the backspacing. I have about 1 1/2 inches between the uca and the tire. Their was only about 1/4 clearance between the body mount and the tire and I didn't wanna take the chance of the tire getting hung up on the mount so I cut it back. The tires rubbed on the front plastic fender liner so I cut that out also. And of course I removed the mud flaps front and back and I cut my skid plate.
 

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OK, I'm not sure if this has been adequately addressed or not -- trust me, I've done a ton of searching on here and can't seem to find a straight answer on this.
So, I'm looking at all possible 33" to 35" tire sizes and have determined that fitting a 35" tire on a 3/1 kit is not only possible but has been done numerous times.
What I fail to comprehend is how to determine what width of tire can be accommodated without rubbing on the UCA or body mounts or plastic on the fender-wells.
The stock wheel I have is an 18"x8" with a +60 offset. I'm not sure what the backspacing is on it (though I can find out if I take one off the truck I suppose).
I assumed that having rims with a +30 or +40 offset would move the wheel out by that amount minus 1/2 the extra width of the rim. So, on a 9" wide rim, a +40 offset would move the tire out 20mm - (1/2*(9inches-8inches=25.4mm)) = 20mm - 12.7mm = 7.3mm. Of course the wheel takes up an extra 12.7mm on each side, so, 12.7-7.3=5.4mm extra on the inside and 12.7+7.3=20mm on the outside.
So does having a lesser "positive" offset (or even a small negative) offset make you more prone to rubbing on the UCA and body mounts? Or is it the other way around? I keep seeing posts where I think it is one way, only to see other posts where it clearly claims the opposite. It just seems very confusing to me. I think if there was a way to determine the precise position of these items in relation to the wheel hub, we could more easily make a conclusion as to how wide a tire with what combination rim (backspacing and offset) will fit with or without certain modifications.
If we could make that determination, maybe we can create some kind of a sticky to illustrate how to measure via wheels/tires and that way people (like me) can be a little more comfortable ordering the proper size tires.
Some of this info can be derived from those that have posted their wheel/tire measurements and observed something like 1/4" space between UCAs and body mounts, etc. I hope this wasn't too confusing... I'm just trying to narrow down what I can do without having to order and send back different sets of tires... :)
Going from the +60mm offset to a +40mm offset pushes the wheel mounting surface 20mm out, plus the rim is 1/2" wider. You were on the right track with your calculations but the extra wheel width is the part that you divide in 1/2. 1/4" more backspacing and 1/4" outwards. Going from a 18x8mm +60 to a 18x9 +40mm your wheel will stick out 26.35mm (20mm plus 1/4") more or roughly an inch. So I guess to answer your question the more positive the offset the more the wheel will tuck into the fender, the more negative (or less positive) you go the further out the wheel sticks. Check this link on how to figure out wheel measurements.

https://www.rsracing.com/tech-wheel.html
 

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i have 35x12.50x18 trail grapplers with a +12 off set,with a 4" kit,i had to trim the body mount,and alot of trimming on the bumper,and i still rub,doesnt matter to much,my tubed bumpers should be done soon.
 

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Discussion Starter #5
Thanks for posts guys! My question isn't so much about how to calculate the offset or backspacing or even the relationship of that with the original wheels (regular or TRD). I'm more concerned with finding a way to calculate or measure the distances between the items that may rub (i.e. body mounts, UCAs, skid plate, plastic trim in fender well, etc.) and the wheel hub. That way, for example, if somebody says that they are going to put in a 35" wheel that is 12.8" wide on a rim with a 6.5" backspace and a +12mm offset, we can say something to the effect that "the wheel/tire combo will fit with a 3/1 lift, but you'll need to cut part of the plastic off the front fender well, trim/bend the skid plate a 1/2" and remove the mud flaps" or we could say something like "it will fit, but you'll be 1/4" from the UCA with that combination... if your rims had a +X offset instead, you would be a good 3/4" away from the UCA" or something to that effect.
My goal for this is to come up with a formula for being able to tell what possible issues will be present with certain wheel/tire combinations so a lot of these types of issues can be avoided before ordering the tires/wheels or having to try on lots of different sets.
I'll probably need to figure a way to the truck up on the lift, but also get more input into the common types of "modifications" required to make a tire/wheel combo fit. So far, to start off with, the most common things I've seen that need to be altered are:
  • front plastic trim in fender-well
  • rear-plastic trim in fender-well or mud flap
  • body-mount cutting/grinding and re-welding
  • bending the skid plate
As I understand it, I haven't seen examples of somebody modifying the UCA to accommodate the wheel/tire combo, but if somebody has and would like to chime in on how to do it or whether it was even worth doing, I'd be all for adding that to the list. Also, there are probably other things that I'm missing from the list, but I would certainly like to grow it as much as possible.
 

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Discussion Starter #6
I gotta give this a bump...
Trying to see if there is some mathematical way to make a determination about whether or not a certain size tire/wheel combination will fit with/without lifts. All help is appreciated!

P.S. - I've seen the numerous threads on wheels/tires including the infamous 35" tire on 3" lift. I'm trying to find out myself whether a 325/60r20 will fit on a 3" lift with a +40mm offset (don't know what the backspace is, but will determine that when I receive the rims) but not sure since it is literally a 35.4" tire. But more importantly, if there is a way to devise what items need to be considered for clearance/rubbing issues and if it could be measured in such a way as to help determine what tires/wheels would work, that would be even better! (Probably save a lot of multiple tire/wheel posts)
 

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as good as it sounds, to have a formula for all tundras, this is probably not possible. Keep in mind not all trucks are created equal. If you go to the dealer and measure the clearances, you'll see a difference between RCSB, DC, and Crewmax. Also, there will be some variance between like makes of 4x4 and 4x2, and probably even between identical vehicles. Throw in weight differences between engine choices and you'll get a whole different set of data according to some on this forum. Finally - look at manufacturers tire sizes and a 325/60r20 by BFG is different than the same size by nitto, etc. Good luck.
 

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Discussion Starter #8
Yeah, maybe it was too ambitious of a goal, but I know it could have certainly helped a lot of people. It is just frustrating having to go through this trial-and-error-type method... but I guess that is what its looking to be...
 

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yea - I know we're only talking fractions of an inch here and there, but each fraction of an inch causes an effect somewhere else. so many possible combinations and slight differences.
 
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