If you want to change tire or wheel size on your 4Runner, READ THIS FIRST!
The Tire Fitment Guide is Below.
Thanks to
@
wfo9
for this excellent write up!
There are many factors that influence tire fitment on a vehicle.
In general, 5th gen owners want to run larger than stock AT or MT tires for additional off-road capabilities or just that rugged look .
What WILL happen when you go to a bigger size:
Before going to larger tires you should be aware that on road performance (mainly mpg and acceleration) are almost always negatively affected due to increased weight and rolling resistance. There is simply no way around this (more tire = less mpg). The difference can be minimal, but it can also be very significant depending on the particular tire and size you choose to run. Also, once you increase the diameter of the tire significantly, (> 33") re-gearing of the differentials is necessary to get the vehicle back into the proper overall gearing ratio. Larger tires decrease your overall gear ratio and can cause the vehicle to to lug out of the power band in typical road conditions. The 1grfe lacks a bit on low end tq from the start and really needs RPM to make significant power, so running the wrong gearing for your tire size can be frustrating as the motor hunts for gears and struggles to maintain speed.
It is generally accepted that the stock gearing is good up to 33" tires, after that re-gearing is highly recommended. Another factor to consider when going bigger is added stress on the drive-line. Since the 5th gen has an independent front suspension (IFS), there are several weak points to consider with the most problematic being the CV axles. Smaller tires will somewhat limit traction and stress on these components when playing in extreme off-road terrain. Going with large tires simply increases the possibility of failure via greater loads, so you need to keep that in mind when picking a tire. If you have common sense and can keep your foot from constantly jabbing the throttle in 4Lo conditions, tires > 33" can still be run without constant drive line failures on a 5th gen.
Finally, there are some other small negatives to larger tires that should be considered. Your speedometer will read lower than actual speed (although many have found going to a 33" tire actually reads correctly on the 5th gens since the speed is over reported from the factory). Your crawl speed will increase in 4LO without re-gearing.. this just relates to the change in overall gearing. Lower crawl speeds are much better for both ascending and descending difficult obstacles. The transmissions torque converter also becomes more problematic as you lower the overall gear ratio, it becomes harder to apply smooth power without flashing the converter a bit. You will see people with stock gearing and large tires lunging forward in 4Lo conditions as they try to start moving on steep terrain. Additionally, your ATRAC and other brake activated traction control mechanisms won't work quite as good as factory tire sizes (although most people don't notice any degradation with 33" tires).
The good
Now for the up side, besides just looking good, larger tires are probably the single best bang for the buck possible in terms of adding off-road capability. Not only will you get much better traction via increased contact patch (from both increased width and height), there is also a ground clearance increase and better angle of attack when rock crawling. Additionally, you can get much improved ride comfort in rough terrain when aired down properly, as the tires are a big part of your overall suspension system. In summary, don't be afraid to go up to 33" tires, but be aware there are trade offs. If you want to go larger than 33" proceed carefully and make sure to plan for all the supporting modifications.
Quick discussion of wheel diameter
The 5th gens come with two factory wheel diameters (17" on most, and 20" on the Limited). This discussion is going to focus on 17" wheels since they are the most common choice for a 5th gen built for off-road use. Most of the information here applies to any rim diameter, but 17" is really the best overall choice for several reasons (tire avilability and off-road performance). You can run any rim size you want within reason, except for 16" due to brake caliper clearance. It is technically possible to actually run 16", but it is not recommended and requires wheel spacers to get any rim to fit. 18s are not a bad choice, but you are going to pay more for tires and have fewer choices. 19s and 20s just start becoming much more of a road oriented choice and would perform and look kind of silly in a large diameter... If you want to keep 20" rims, best to stick with near stock size tires and stay below 33".
A common formula that works:
There are several factors that effect tire fitment on a vehicle, but I know many people just want to know a common formula that works and is proven for somewhat aggressive off-road use on a 5th gen, so I will outline a common setup that works first, then detail out the factors to consider when fitting larger tires for variations from that.
The most common formula is as follows:
- 285/70/17 AT tires (roughly a 33" tire)
- 7 to 8.5" rim with 4 to 4.875" of backspacing (a 9" rim can work but it starts to cause issues)
- Aftermarket UCAs (recommended for proper alignment, 2.5 + caster recommended, more is better)
- Pushing front fender liner forward for clearance of the plastic.
- 2-3" of suspension lift
Now the factors:
1. Tire size
2. Wheel width + offset/backspacing
3. Front wheel position (specifically how far fore or aft the wheels sit in relation to the steering pivot point.
4. Body mount and fender clearance
5. Ride height/lift
Details:
Tire size - This is pretty easy to conceptualize. Larger tires are harder to fit without rubbing. A very common size off-road tire for a 5th gen 4runner is a 33" tire. Usually in the form of 285/70/17. These can be made to fit with little or no modifications. Any tire smaller (265,-75/70/17....) should be easier to clear. Anything above a 33" tire will require more aggressive modifications in some of the other factors explained below. Also, be aware that the advertised size and measured size are not the same. There can be up to a .5" difference. In other words, the size is just a class, not the actual measured size. so do your research on each brand and model. Most tires come in metric sizes, but you can also run a tire that is advertised in inches (it is easy to convert between the two). As an example... A 285/70/17 would be 32.7x11.2 in inches. The first number (285) is the width in mm and the second (70) is the ratio of sidewall height. There are plenty of online calculators to convert and find tires offered in a given size range. I find this one very useful. Tire Size Calculator
Wheel width + offset/backspacing - Let't start with a definition of offset and backspacing. They describe the same thing, but offset is in relation the the center line of the rim and reported in mm (this number means different things depending on the rim width). Backspacing, is the same concept, but is measured in relation to the mounting surface on the vehicle and is always reported in inches. (this number tells you more directly how far the rim lip sits inboard). You can calculate one from the other easily. Backspacing = ((rim width+1)/2) + (offset in inches). The 1" is always added to the rim width because advertised rim width does not account for the lips. This video explains it well
https://www.youtube.com/watch?v=2K1lUlv9ZOA Adding a spacer decreases backspacing by its width and adds negative offset to the rims specs.
So, these wheel specs dictate where the tire sits in relation to the mounting surface (inboard, outboard, or centered). Also, wider rims will stretch a tire a little more while narrower rims will tend to keep a tire at its maximum diameter. Tires usually specify a required wheel width range. Also be aware that some tire shops will not mount a tire on a rim that does not match the specified mfg width range (this will often vary between mfgs even for the same size tire). In general, an 8 - 8.5" wide rim with 4.1 to 4.5" of Back Spacing is about ideal for a 5th gen. More width and or negative offset will result in more total track width, but this will also create more clearance trouble because of greater scrub radius as the tires are turned to full lock. Scrub radius is a common point of rubbing and is a result of the tire not turning on it's actual center-line. It scrubs the road surface and arcs as it moves from full lock in both directions. To conceptualize this, go look at the outer leading edges of your tires in relation to the wheel wells and make some full lock turns. Note the changing distances. This video explains it well.
https://www.youtube.com/watch?v=IUcZ63unEyU
Too much backspacing can also be a problem as the tire will rub on the upper control arm....
As a point of reference all 285/70/17s are specified to fit on 8" rims, Some 35s (315/70/17) specify 8 - 11", but some require a minimum of 8.5". An 8" rim is good for 35s, but you may have issues at the tire shop if the mfg requires 8.5".
I see many people start off with the wrong wheel size and end up having many minor unnecessary fitment issues. I recommend looking for a vendor who specializes in supplying wheels made for Toyota trucks. You will want a 6x139.7 lug pattern with 106mm center bore and 8 - 8.5" width with 4.1 to 4.5" of backspacing. Others widths and offsets will still fit (9" rims are a popular choice), you will just may have more potential issues. Several vendors that specialize in fitting wheels on Toyota trucks stopped offering 9" rims a while back, since they typically required a body mount chop. Best bet for off-road use is to run the smallest possible width that will fit the tire. Another rule of thumb I have heard is to never run a tire diameter that is much more than double the rim diameter. You will end up with odd squishy behavior when aired down. So the max for 17" rims is about a 35" tire.
Front wheel position - There are two areas of clearance that commonly come into play when fitting a larger tire. The body mount (located behind the front wheel wells) and the front fender liner in the front of the wheel wells. In general, you want the wheels aligned as far forward as possible to allow for better caster angle and to avoid the need for a body mount chop. The front fender can be easily pushed forward and trimmed for clearance (it's just thin plastic...). .Cutting the body mount for clearance is a pretty big deal, but can be done and is necessary for anything over a 33" tire. The wheels can be pushed forward by adjusting the cam bolts on the LCAs as part of an alignment, but its not as easy as it sounds. The stock UCAs are designed for stock tires and stock ride height. So as you try to push wheels forward and add positive caster, the camber will quickly go out of spec in the positive direction. This results in the wheels not being as far forward as you might want or your camber being off. To get around this, you may need aftermarket UCAs. These come in two forms. Adjustable and non-adjustable that are statically biased towards running larger tires and a lift. There are several good solid offerings on the market that you will quickly find plenty of info on. The most flexible in terms of clearing tires and getting the wheels where you want them is the adjustable light racing UCAs. However, there are two major downsides to the LR UCAs. 1. The tech has to know how to adjust them during the alignment and most don't. 2. They are known to be less durable than many of the uniball style UCAs on the market. Some seem to have no problems and it probably comes down to how hard you are on your truck while off-roading. The natural question many will ask is can I run 33" tires with stock UCAs, The answer is, Yes, but it wont be ideal. You most likely have a lift and end up with slightly odd hwy handling as the caster will not be high enough and you may have a little trouble clearing the body mount and keeping the camber in spec. This particular area is very vehicle specific as the alignment characteristics vary on each one (that is why it is adjustable after all). Best bet is to plan on running an aftermarket UCA with a 3" lift or tires 33" or larger.
Body mount and fender clearance - Most of this was covered above in wheel position. Anything in the 33" range is most likely going to require the front fender liner to be moved forward some. This is a very easy process. You just pop out the lower screws and push it forward and create some new holes and put the screws back in. It is very thin plastic so no big deal at all. You will probably also need to trim a little bit of the plastic bumper cover in this area, but it should look very much factory original when done if you use some common sense. There should be no need to leave large holes or anything that looks out of place... The body mount is a different story, if you are running greater than 33 tires or have a wider track width from larger wheels or high negative offsets, you will need a body mount chop. This is a somewhat controversial subject, so do some research on what is involved and what this means for your truck before diving in. It is 100% required once you go over 33s and many people have done it with no problems reported. You will need some fabrication skills to do this and it is recommended to weld in a plate after the required material is removed. Once you do a body mount chop, there is also some minor cutting usually required of the pinch welds just in front of the body mount for added clearance.. There is really no going back once you do a BMC you are more or less making a commitment to a modified rig vs something that can be returned to stock with no evidence left behind. It is not required to run 33s if all the other factors are accounted for.
Ride height - This one is a bit tricky. In general, more ride height/lift is going to increase clearance for larger tires. BUT...just because the vehicle typically rides at this height does not mean that the suspension stays there in dynamic conditions as the suspension cycles. Most people are going to run a 2-3" lift with larger tires, after all why run larger tires unless you plan to off-road where you will need better approach and departure angles in the first place. The reality is that the tires still have to clear when the suspension is fully compressed and fully extended. If you just plan to run your 5th gen on the street with large tires (often called a mall crawler), it might be possible to clear very large tires (35s) with just a suspension lift... If you actually pan to off-road it, you need to consider how the tires clear the fenders as the suspension is fully compressed. For 33" tires, there is simply nothing to mess with here as long as all the other factors above are considered. For 34" +, some changes will be required. First, the rear is probably going to require a bump stop extension of some sort (or maybe adjustable lower control arms to get the tire centered at full compression). In the front, the tire will probably rub on the washer bottle and that will need to be relocated. You will also have other fender liner rubbing issues up front, so an aftermarket style high clearance bumper is highly recommended unless you are willing to do some significant cutting of the stock bumper. Once you go over 34" and start getting into 35s the tire is going to start contacting the actual fenders at full compression. There are two ways to go from here. You could extend the bump stops or start doing actual fender modifications (think cutting and rolling) with the first step being removing the flares. Fender mods would be the best route in terms of not limiting overall performance.. .but up travel is not near as important as down travel for a trail rig, so it might be possible that you could get by with limiting up travel with bump stop extensions which can be very easily fabricated.
Another option, although very controversial is a drop bracket 6" style lift. These will clear the tires with no problems, but will also hurt off-road capability by raising the center of gravity without providing any additional suspension travel. There is also some question about the durability of these styles of lifts. I have seen them work just fine on FJs... and there are 5th gen 4 runners running around with them that actually go off-road with some success. It's not a popular choice though, and probably for good reason. I've actually seen a 2014 4 runner on 37s with this type of lift, but it was just a mall crawler.
Another slightly controversial option for more clearance, but rarely ever seen on a 5th gen is a body lift. This keeps the suspension in the same location, but just raises the body for better overall body panel clearance with the downside of raising the center of gravity slightly. This technique could be used to run 35s, but there does not seem to be body lift kits available that address all the potential issues (lines, wires, steering linkage, shifters...). A small body lift may be a more popular choice in the near future as the kinks are worked out. Here is a great post on some of the challenges of a body lift. The Build Thread of my Rocky !!! Aftermarket bumpers would need additional fab work to eliminate gaps and account for frame clearance changes.
Verification
Finally, How do you verify tire clearance for all conditions. The answer is not very easily. First you can just drive it and try things addressing them as they come up. That can take some time though and can result in a very frustrating trip to the trails when you find out your alignment is off or that you need a body mount chop. If you are real handy with a wrench and jack stands... It's not a bad idea to put your wheels and tires on without the springs (or coil overs) in place. This makes it pretty easy to cycle the suspension in various ways and verify tire clearance at all the different angles. I've also seen people use a fork lift to get the truck in various positions. It's pretty much a PITA, but the good news is you don't really need to worry about it if you stick with a formula and size that is already proven to work. If you don't pick a proven combination... you need to proceed with caution, especially on tall tires that come with a self clearance feature.
I want to run 35s What is it going to take.
Short answer, quite a few things (mostly covered above). 34s seem to be the upper limit for the 5th gen, but if you want to go there here are some things to consider.
1. Regear is pretty much mandatory 4.56 or 4.88
2. Aftermarket high clerance front bumper. No real point in 35s with a stock bumper as it will cause lots of clearance issues.
3. Body mount chop
4. UCAs
The rest depends on your goal. Ideally, start cutting up those fenders and make some clearance for full stuff. There are some shortcuts mentioned in the previous sections that can get around this (drop bracket lift, body lift, adjustable UCAs, bump stop extensions). The point is if you are going to 35s the right way you need to be ready for some serious cutting and even then you are probably going to rub the frame a little at full lock unless you go Long Travel....Another excellent option (that would avoid the fender issues) would be Solid Axle Swap, but this has not been done on a 5th gen yet and has many other challenges. Good luck and post pics. Right now there are very few 5th gens on 35s that actually go off-road. It's a big commitment to take it to that level, but should start becoming more common as the 5th gen ages and becomes more approachable to the hard core.
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