Disclaimer: This article is simply an informational resource to give you an idea of what is required to tub a vehicle for over sized tires before deciding to attempt it yourself. Coastal Offroad nor myself are responsible for any problems you encounter while tubbing or as a result of tubbing your own vehicle.
What You’ll need:
Any given suspension needs up and down travel to function properly. This allows your tires to move up and out of the way when they hit a bump, or drop down into dips and potholes. A stock 3rd generation 4runner has approximately 8” of wheel travel from max extension/droop to full bottom out on the bumpstops. When at static ride height, let’s say it sits right in the middle of its 8” of suspension travel, giving it 4” of up travel and 4” of down travel as shown below. The wheel positions at max compression and extension are shown in grey and the wheel position at static ride height is shown in black.
This travel range give the tires a comfortable suspension range to follow both bumps and dips in the terrain. Then, a 3” suspension lift is installed, moving the static ride height position 3” downwards in its 8” of total suspension range, as shown below:
Starting the Clearance Process
With those pieces removed, it’s time to remove the windshield washer system from the front of the passenger side wheel well. The washer reservoir must be replaced with a smaller unit and moved up into the engine bay. I don’t cover this relocation in this article, but there are other resources out there as well as complete relocation kits that can be purchased. Below is a picture of the wheel well space created by relocating the washer reservoir.
It is also necessary to relocate the vacuum system canister located at the front of the driver side wheel well. Luckily, I found that it could be simply moved further into the corner of the wheel well without any tire interference or the need to extend the vacuum line. I simply unbolted the bracket, bent the bracket arms slightly, and push the canister as far into the top corner of this space as possible. I then reinstalled the canister using an existing hole in the wheel well and an additional nut and bolt. Easy!
It’s finally time to make your first cuts! The basic procedure here is simple. Jack up the suspension to full compression and then turn the steering full lock to full lock. Anything that the tire touches gets cut out. With the strut removed, you may now easily jack up the suspension to full compression to mimic a full bottom out scenario. To do this, place your floor jack underneath your lower control arm – the closer to the tire the better. Now, jack up the lower control arm just until the jack begins to lift the entire vehicle. It’s possible that even with your tires pointing straight ahead, your tire will hit the firewall before you reach full compression. That is ok. Mark out where the tire is contacting the firewall. Lower your jack back down a few inches so that the tire is no longer rubbing the firewall. Turn your vehicle on and turn the steering one way and the other. Hop out and recheck where the tires are rubbing the firewall while turning. Do this a couple times at various jack heights to give yourself a good idea of the arc that the tires take when steering. This will give you a better understanding of the extent of how much cutting you will need to do.
Once you have a good idea, remove the tire and start cutting! I used a combination of a 5” angle grinder with cutting wheels and a smaller pneumatic grinder with a 3” cutting wheel on it. Every so often, reinstall the tire, jack it up and turn the steering lock to lock again to reassess where more material needs to be removed. While cutting, be extra careful that none of the electrical wires or components have shifted and have fallen back down into harm’s way. I can assure you that I will not be writing a how-to article on how to re-wire your 4runner so you’re on your own for that one. Below is the final amount of cutting required for the driver’s side:
Creating the Firewall Tub
Before tacking your piece of sheet metal in place, double check that your damp towel is still in place behind your firewall to catch any sparks or excessive heat from damaging your interior. Now, take your sheet metal patch and lay it over the opening. To achieve a nice contour that maximizes tire clearance, I started by tacking the top edge to the firewall and then hammering the sheet metal into the opening. I then repeated this process of tacking and then hammering until the whole piece of sheet was contoured and tacked to the firewall. If you are using multiple pieces of sheet metal, repeat this process until the whole opening is filled. The driver’s side looked like this:
Then, finish off all sheet metal edges with weld beads. Take your time and use many short passes with the welder. Depending on your welder and amount of sheet metal welding experience, you may only be able to weld for a couple seconds at a time before burning through the firewall. So be patient and take your time. Once fully welded, move to the other wheel well and repeat this process. After tubbing, my passenger side looked like this:
Now it’s time to seal your firewall against corrosion and any water leakage into the interior. I use polyurethane sealant as it provides excellent adhesion to the firewall, dries slightly flexible to prevent chipping, and is paintable. To seal my firewall, I placed a generous bead on all welded seams as well as on the backside of the tub in the interior for extra peace of mind.
I followed this up with a few coats of primer and then a rubberized undercoating that will absorb road debris spray rather than chipping off. Below are some views of the finished driver side tub:
And the passenger side:
Trimming your Outer Fenders
How did I measure out a clean cut? I simply plotted points all around the fender opening by measuring 1.25” from the fender edge and marking the point with a permanent marker. I marked a point every couple inches around the fender and then connected the points with a straight edge, as shown below.
Once marked out, I used a small pneumatic air tool with a 3” cutting wheel to carefully cut the new fender profile. Once you are finished your cut, place the fender loosely back in place on the vehicle and ensure that you cut enough off by jacking the tire back up to full compression and turning it lock to lock. Trim more off the fenders if necessary. Before finishing off the edge, my final cut looked like this:
Once both fenders are cut to their final profile, be sure to paint the exposed metal edge to prevent corrosion. I then finished the edge with some black automotive edge trimming. The adhesive on the product I purchased wasn’t the best, so I added some super glue to the fender lip and pressed the edge trimming firmly in place. This creates a clean, factory looking fender edge and also protects the edge from rock chips and the resulting corrosion. I will go as far as to say that I think my cut fender profile looks better than the original factory lines!
You are now pretty much finished clearancing your 4Runner for 35’s! Reinstall your fenders, front struts/coil overs, and wheels, being sure to tighten everything to their specified torque values.
Move to the interior and put all of the wiring you have displaced back into position. Replace the carpet in its correct spot. Depending on the shape of your tub profile, your interior kick panels may or may not require trimming to fit properly. For me, I was able to reinstall my passenger side kick panel cut-free, but my drivers side panel did require some trimming to get back in place. Even still, my dead pedal is about half the size that it used to be but like anything, you will get used to it. At the end of the day, it’s a small price to pay for fully functional 35’s! Here is a view of my passenger side foot well:
Here are some photos of the finished fender and firewall profiles with the tires reinstalled. As you can see, my cut line smoothly follows the factory fender line until the bottom corner, where it tapers to a slightly more substantial cut. The drivers side: