There really isn’t a simple answer to this question. It could be 33s, 35s, or something as big as 49s (yes, there’s an FJ out there rolling on 49s as we speak). Tire size greatly depends on what you’re doing with the FJ, supporting mods, and budget. Obviously the bigger the tire the more expensive it’s going to be. 33s and 35s are the most common in the FJ world but more and more people seem to be pressing their luck with 37s lately – including myself! Beyond those sizes a solid axle swap is recommended to fit all that meat under an FJ.
What do I have to do to fit 33s (285/70/17 ) on my FJ?
I’d say 33s (our case 285/70/17s) are probably the most common tire upgrade among FJC owners since you really don’t have to do much to make them work. In fact, you could install these on a bone stock rig with very minimal rubbing, if any, depending on the specific tire, wheel, and front-end alignment.
I should note that a true 33 inch off-road tire will measure around 33″ in diameter and 12.5″ wide. Attempting to run these tires on stock wheels and stock suspension won’t work without wheel spacers due to the offset and backspacing of the factory FJ wheels. They’ll end up making contact with the upper control arm (“UCA”) and likely won’t allow you to mount the wheel to the hub. If you go with the wheel spacer route I would recommend 1.25″ Spidertrax spacers. I’ve been personally running these spacers for about 8 years now without a problem. They’ve seen 33s, 35s, and now 37s. Now that you’ve spaced the wheels out more you run into issues with rubbing on the mud flaps and body mounts. Mud flaps are an easy fix – take them off! The body mount isn’t quite as easy. I’ll touch base on that next.
Some of the most common supporting mods for fitting 285/70/17s are typically a 2-3 inch lift and/or a body mount chop (“BMC”) as mentioned above. What’s a body mount chop you ask.. If you look behind your front mud flaps you’ll see a rounded piece of metal protruding into the the wheel wells from just below the firewall. These are your “body mounts”. In order to keep them from rubbing on the tires you will need to “chop” or cut them back a bit. We’ll get more into details on the BMC at a later date.
What do I have to do to fit 35s (315/70/17) on my FJ?
35s will need a decent amount of work to properly fit your FJ without rubbing. In addition to what was mentioned above for the 33s you’re going to need aftermarket UCAs, a more aggressive BMC, a cutting tool for plastic, a BFH (Big Fuggin’ Hammer), extend rear bump stops, body lift, alignment, and possibly a regear. Yes, I said “possibly a regear”. While it is recommended, I can’t say it’s absolutely needed.
Let’s start by explaining what needs to be done to fit 35s without rubbing before I get into the gearing part of it.
- Aggressive BMC – you’ll have to cut the body mount back as far as you can to prevent rubbing at full lock.
- Cut and/or remove plastic – there’s going to be plastic on the firewall side of the wheel well that needs to be trimmed and likely some parts of the OEM fender flares. If you still have a stock bumper, you’ll probably have to do some trimming of the lower part of the bumper and front plastic part of the wheel well.
- Start hammering – pinch welds in the wheel wells (front and back) and some of the raised spots on the firewall in the front wheel wells that stick out a bit. A good alternative to beating up the firewall is a body lift. A 1 inch body lift should be just enough to get the firewall out of the way at full tuck and full steering lock
- Extended bump stops – there are several companies out there that make bump stop spacers so the rear wheel doesn’t rub the inside of the wheel well when fully tucked.
- Aftermarket Upper Control Arms – the idea here is to increase the caster a couple of degrees which will move the tire away from the firewall and body mount. Some of them have 2-3 degrees built into them while others will allow you to adjust the caster and camber.
- Alignment – after installing the aftermarket UCAs you’re going to need an alignment.
- Gearing – as stated above, I definitely recommend regearing if you have the funds and means to do so but it isn’t always needed. You’ll get better mileage, retain factory power, and still be able to use cruise control. If you live in the mountains or an area with a lot of hills you’re definitely going to want to regear. Otherwise your transmission will constantly be searching for gears and the power loss will drive you insane.
For FJs with 35s that are being daily driven I typically recommend a 4.56 : 1 gear ratio. If it’s more of a weekend warrior, I’d suggest 4.88s. If you have an 8″ rear diff you can go up to a 5.29 : 1 gear ratio. Click here for gearing options.
Tire size note – 315/70/17s are very close in size to a typical 35″ x 12.5″ off-road tire. Depending on the manufacturer they will measure out to be about 34.5″ x 12.4″
An FJ Cruiser on 37s and IFS you say!?
Yes, you read that correctly! Some guys (including myself) are running 37s. While it’s not something I’d typically recommend doing it’s certainly possible.
I’m not going to go too far into depth with this but everything you did to fit 35s you’ll have to do again to fit 37s – and then some. Instead of a Body Mount CHOP you’re likely going to need a body mount RELOCATION. You’ll also have to do some cutting and welding in the wheel wells to make everything fit without rubbing when fully tucked. I’m not sure regearing is an option at this point. I couldn’t even imagine trying to turn these monsters on the stock 3.73 gears. I’d go with 4.56 : 1 at the very minimum but would highly recommend 4.88s or even 5.29s. I regeared to 4.88 when I had my 35s but kind of wish I had 5.29s now.
If you’re not into cutting, hammering, welding, and regearing I wouldn’t recommend 37s.
40 inch tires and beyond!
Going over 37s is ill-advised unless you have a lot of time and money on your hands. While there are still a couple of guys out there that insist on running 40s on IFS, most will do a solid axle swap (“SAS”) and rip out all the IFS – which is basically where I’m at this point. We’ll be running 42″ Pitbull Rockers on a Dana Super 60 up front and Sterling 10.5 in the rear. Stay tuned for some build posts of that project during the winter months!
Last but not least I should mention that your style of wheeling should be taken into consideration as well when it comes to tires. If you’re a pedal to the metal kind of guy that likes to bounce their rig over obstacles with speed I’d stick with a smaller tire. The larger the tire, the more rotational mass, the more you’re going to break…
Hopefully I covered enough to help you choose the biggest tire for your FJ, but if I didn’t, drop us a comment below or send us an email and I’ll get back to you as soon as possible.