| Adding 33 inch Tires |
| This page is about how I added 33 x 12.5 -15 tires on 15 x 8 rims without a full suspension or body lift. That's right, no 4" lift, and absolutely no body lift. |
| I've been running 31" BFG mud tires with 4.56 gears for some time now. This "stock" set up works fine for light off roading, but I always intended to add bigger 32x11.5" or 33x12.5" tires for added ground clearance. At first, I considered lifting my truck the standard 4" using any one of the numerious IFS kits available. But knowing that I still needed to buy gears for the new tires made me have to seriously consider the cost factor. I began to wonder if there was another option. Certainly a body lift would be much cheaper, but I never have been a fan of body lifts. Not only do I not like the looks of B/Ls but they seem to provide no real additional clearance, except for tires and a modest gain in departure and approach angles. And the drawbacks, in my opinion, are numerious, including bumper and shifter and other mechanical alignment probems. After reading an article in a off road magazine about people cutting fenders to mount taller tires without adding a lift, I began to wonder if that was feasable on my Toyota. I certainly was weary about hacking on my truck, but I began to wonder if perhaps just a little trimming might do the trick. I had already cranked up my front torsion bars a bit and added 1.5 lift rear shackles as well as 1.5 add-a-leafs to gain a bit of clearance with my old 31s and aftermarket wheels. In doing some measurements, it appeared to me, that 33x12.5s would fit just fine with some minor modifications, in addition to my turned up torsion bars and minor rear lift. The following only applies to the '89 to '95 trucks. I'm imagine it could apply to the '86 through '88 IFS trucks as well, but because of different fender designs, I can't be sure. It would not likely apply to '85 and eariler solid axle trucks. The increased available travel of the front solid axle most likely requires a 3 or 4 inch lift to both clear 33x12.5 tires and make best use of the available articulation. For the front, the torsion bars do need to be cranked up to raise the front end, approximately 1.5 inches. For the '89 to '95 trucks with no other body or suspension lift, this generally means that the measurement between the top of the rim and bottom of the fender should be 15" to 15.5" with properly cranked up torsion bars. Aftermarket torsion bars, such as Sway-a-way's 25mm bars work great but are not absolutely necessary. The Sway-a-way bars increase the spring rate between 20 and 30 percent, which means the springs are about 20 to 30 percent stiffer than stock. This helps if the truck is equipped with a winch up front and also helps prevent the truck from bottoming out on rough roads. There are some disadvantages however, that I discuss further down. I DO NOT recommend buying or installing any of the 26mm torsion bars, such as from Rancho or Downey. They are just plain too stiff for most any application. Travel will be severely limited and ride roughness will dramaticly increase. Two additional modifications must be made to the front fenders, for the tires to fit. First, the inner plastic lining and front mudflaps must be removed, permanantly. Second, the lower rear body seam must be pounded down, if not completely flattened, and the lower rear portion of the inner front fender must be trimmed. One possible alternative to cutting the fender, is purchasing one of the many available fiberglass fenders that has a larger opening and is specificly made to clear larger tires. All Pro Off Road sells an affordable set for about $200. The amount of trimming is up to you. The tires will fit and the truck is drivable without cutting the fenders, so long as my previously mentioned mods have been made, so it will be a matter of installing the tires and then testing to see how much trimming is needed to prevent rubbing at full articulation (what little there is) and at full turn. At absolute full compression up front, which is pretty hard to achieve, there is only the slightly hint of rubbing. This could probably be solved by further pounding on the body seam. But I have not seen the need yet. For information on "cranking" or "turning" up the torsion bars check out these links: Off-Road.com Toyota torsion bar page 4X4wire.com Toyota torsion bar page For the rear, simply adding a 3" longer shackle will gain 1.5 inches of lift. This might be plenty for many, but because I carry a good deal of wieght in the bed, I also added add-a-leaf springs for another 1.5 inches of lift. At first I only experienced rubbing at full articulation which only occured during extreme circumstances. I've sinced modified the rear further by removing the rear mud flaps and inner plastic liner. I've slightly trimmed the rear fenders as well. So far, the rubbing is completely gone, but simply adding slightly more lift by adding taller springs or longer shackles would have solved the problem as well. |
| The clearance between the front inner fender and the 33" tires. Note the removed, plastic insert, pounded down body seam, and cut front inner fender |
| Close up view of cut front fender. Red indicates areas that needed to be trimmed. Razor edge looks dangerious, but there's no chance of the tire hitting it. Rolling back the metal is an option, though. |
| This view shows the front tire under full suspension compression. As can be seen, the main clearance problem is the rear of the inner fender at full turn. This is where the fender must be trimmed and the body seem pounded down. |
| Lots of clearance and nothing more than the torsion bars cranked up approximately 1.5 inches and few minutes with a dremel. |
| If one is still unsure about cutting thier fenders or is still worried about having rubbing problems, a very modest 1" body lift could be added. I can certainly understand the desire not to hack one's truck up. Other options for the front do include one of the many available high clearance fiberglass fenders. |
| Horribly hacked rear fender. Needs dressing up, but it appears to have solved the rear rubbing problem. |
| This view shows full rear suspension compression. Even with 3.5" backspaced wheels, the tires tuck in nicely. The clearance problem for the rear involves the rear mudflap and part of the fender edge in front of and behind the tire. |
| 3 inch longer than stock shackles provide a total of 1.5" of lift. These shackles are from 4 wheel parts wholesalers. Combined with Procomp 1.5" add-a-leafs, the rear has a total lift of 3". My truck required a 3" lift to off set the wieght of the gear in the bed. An empty truck may only need the shackles to clear 33" tires. |
| With the rear suspension in full articulation, the rear leaf spring does go into negative arch. |
| There are some disadvantages. I personally have experienced no problems, but I include this section so that others are aware of what still could be potential problems. Cranking the torsion bars can create some potential problems. This causes the suspension to sit at or near it's maximum downtravel point almost all of the time. The tires could experience negative camber and this could cause some uneven wear, although I've yet to experience any uneven wear. The steering linkage is maintained at or near it's lowest downtravel point and that can cause increased wear on the tie rod joints and joint boots as well as wear on the idler arm. An idler arm gusset, such as from Downey, is highly recommended, as the idler arms are prone to bending when under stress. While the CV joints have little problem running at or near thier 22 degree maximum downtravel angle, the CV boots will wear out much quicker than normal, if the truck is not equipped with manual hubs. Manual hubs are highly recommended and the conversion from ADD to manual hubs is very easy, if you don't already have them. The greatest disadvantage of the IFS truck, lack of articulation, is actually worsened slightly when cranking the torsion bars. With aftermarket bars, uptravel is limited, due to the increased spring rate. Downtravel is also limited, because the suspension is already at or near it's maximum downtravel point. There are tricks to increase the downtravel, such as cutting the upper bumpstops, but the only real solution is to install different A-arms, such as from Chaos Fabrication or Advanced Toyota Suspensions which are designed to accommodate the increased travel. Additional modifications to the axles, CV joints and other components may also be required to safely exceed the factory 22 degree maximum front axle angle. If modifications are made to gain uptravel, more modifications are needed such as high clearance aftermarket fiberglass fenders or extreme fender cutting. Besides the obvious advantage of saving the time and money from not installing a full IFS kit, the center of gravity is not raised higher than necessary. While some may like the look and the additional clearance of a full 4" lift, I prefer having the advantage of increased stability on the trail during off camber situations. Since I've completed this mod, I'm more confident than ever that center of gravity is extremely important when on the trail. The last thing anyone wants is to roll their truck. And if the price I pay is slightly reduced ground clearance to keep my body panels intact, I welcome it. The clearance at the front cross member is a whopping 13.5 inches. Clearance elsewhere is also not bad, due to the larger tires and minor lift. The bottom line is, I'm pretty happy with this set up in terms of tire clearance. I am, however, completely dissappointed in the lack of articulation. But, I wouldn't experience any addition travel with a body lift or 4" IFS lift. Although, it should be noted, that some gains in compression can be made with a Rockstomper kit added to a 4" IFS lift. I used 15x8 American Racing steel rims with a 3.5" backspacing. Stock backspacing is 4.5 to 5 inches. Backspacing is measured by measuring from the back of the wheel which makes contact with the hub to the rear rim edge. This is not the same as "offset" which is another form of wheel measurement. Another size rim, including those from the factory, might have a different result than I did. Always do further research before committing to buying any tires, including 33s and/or installing a lift. As always, your results may vary. |
| Click on picture for detailed diagram of common wheel measurements |
| The following ideas were of Joe Micciche Joe's Homepage While I'm not able to increase compression travel with the current set-up, I was able to increase downtravel by about 1". This is accomplished by cutting the upper A-arm bumpstops down to about 1/4". You can also purchase aftermarket bumpstops from Downey and other manufactures, which I have since done. (See picture below) To aid in the ability of the suspension to downtravel to it's maximum point, I added about 1/2 inch of spacer between the tops of the front shocks and the shock mounts, effectively lowering the shocks 1/2 and given them 1/2 longer travel. This translates to about 1" or more vertical downtravel from the suspension. |
| One issue facing those of us with 33x12.5-15 tires is where to store the spare tire. While those with open differentials can get away with using a smaller diameter tire, those with lockers and limited slips cannot. Running different diameter tires can and likely will damage the locker, limited slip and/or differential. Even with open diffs, running different sized tires in 4 wheel drive is not recommended at all. Therefore, a full sized spare tire is a requirement. Some just throw it in the bed. Others, such as 4Runner owner's, can mount them on the rear tire mount. While mounting a 33x12.5 tire under the bed in the stock spare tire location is possible in at least some Toyota truck models, including mine, it does cause some clearance problems. The issue is that the tire is so wide, that on trucks with minimal lifts, the tire hangs down too far. The departure angle is drasticly affected. The solution, is to install a 33x9.5-15 tire. I found that this size fit perfectly under the bed in the stock spare location. When using a 15x8 wheel as I did, the tire actually sat up about 1/2 inch higher than my previous 31x10.5-15 spare on a 15x6 wheel. It should be noted that one advantage of the 31x9.5-15 tire is that it can be mounted on the stock spare wheel, whether the wheel is 15x6 or 15x7. The 33x9.5-15 tire can be mounted and safely driven on with the other three 33x12.5-15 tires. In addition, one can safely continue to 4 wheel out of the area and to civilization. I discovered this first hand, when I was not only forced to drive off road with my 33x9.5 spare, but was also forced to drive over 90 miles on the highway. I found that on the highway, I couldn't even tell the difference. Off road, however, the skinner tire did provide less traction than the other tires in extreme mud, but otherwise performed well. If you do decide to purchase a 33x9.5-15 spare tire, be sure to at least remove and attempt to hang one of your 33x12.5 tire under your bed first. Some models may not accept the 33" tire. Mine did, but it was close. I have heard reports that at least some other models will accept them as well. |
| This is a 33x9.5-15 BFG Mud Terrain tire mounted on a 15x8 rim being used as a spare. The tire may appear in the pictures to hang low, but it's actually 1/2 inch higher than the previous 31x10.5-15 spare tire mounted on a stock 15x6 rim. Mounting the 33x9.5-15 tire on a narrower rim, such as a stock 15X6 or 15X7 might gain even further clearance. As you can see, the 33" tire fits perfectly fine. However, I doubt that a taller would fit. A 33x12.5-15 spare would fit, but it hangs several inches lower. |
| When switching to larger tires, often times regearing is neglected. While I'll could include formulas and figures that show why not regearing is bad, I suffice to say, that whatever you do, REGEAR!! By retaining the stock gears, you lose power, fuel mileage and low speed crawl. Drivability factors that apply both on and off road. In my opinion, if you can't afford to regear, then don't bother with taller tires, unless your only in it for the looks. For more information on Toyota gearing, check out my gears page: Brian's Gear Page |
| I later installed an entirely different IFS system and then replaced that with a solid front axle. But this set up has always been one of my favorites. If I could afford more than one truck, I would likely set up a second truck just like this, as a daily driver and light off roader. For the complete article on my "new to me" WCOR IFS that I later installed kit go HERE. For my article on installing a solid front axle, go HERE. |
| To view more pictures of my IFS in action, click HERE . |
| NOTE: I've since installed an entirely new IFS suspension with new A-arms and axles, and then later swapped in a solid front axle. For the A-arm kit click HERE. For info on the solid front axle, click HERE. |
Why
How
Disadvantages
Advantages
Wheels and Backspacing
Increasing IFS travel
Spare Tire Options
Gearing
Final Thoughts
