Cab Mount Chop: What It Fixes, and Where It Stops

September 8, 2026

The short answer: a cab mount chop trims and caps the body mount under the front firewall so a bigger tire clears at full lock and full compression. It is a Toyota problem — Tacoma, 4Runner, FJ Cruiser and the Lexus GX put the mount right where the tire wants to be. And the part nobody tells you: a chop gets you to roughly 33s, not 35s. Past that you need a cab mount relocation, which is a different job.

What actually hits

Widen the track with long travel, add a taller tire, then turn the wheel to full lock while the suspension compresses. On a Toyota the front tire runs into the body mount just behind the front wheel opening, below the firewall. It is not the fender, and it is not the frame — it is the mount itself.

Two things drive it, and lift height is not the main one:

  • Wheel offset and backspacing — the biggest factor. Pushing the wheel outward moves the tire straight at the mount. See prerunner wheels and tires before you buy either.
  • Travel — a prerunner spends real time at full compression, not just at trail speed, so a setup that clears in the driveway can still hit hard in a whoop. That is why this bites desert trucks sooner than it bites mall crawlers.

Chop versus relocation — the distinction that matters

These get used interchangeably and they are not the same thing.

  • Cab mount chop (CMC / BMC). You cut the factory mount back and weld a reinforcement plate over the opening. Cheap, well documented, and generally good for 33-inch tires.
  • Cab mount relocation (CMR / BMR). The mount is moved to a new position on the frame rather than trimmed. More work, more money, and the only real answer for 35s.

Why a chop runs out: you can only cut so far before you reach the factory bushing. That is a hard physical stop, not a matter of being braver with the cut-off wheel. Shops that do this daily report that even 34s will rub under articulation with a chop alone. If 35s are the goal, budget for a relocation from the start rather than paying to do the job twice.

Which trucks need it

This is a Toyota body-on-frame issue. Plate kits are sold for:

  • Toyota Tacoma — 2005 and up (2nd, 3rd and 4th gen)
  • Toyota 4Runner — 2003 and up (4th, 5th and 6th gen)
  • Toyota FJ Cruiser — 2007–2014
  • Lexus GX470 (2003–2009) and GX460 (2010 and up)
  • Some vendors also list the Tundra and the Prado 120/150

Building a Tacoma? Start at the Tacoma prerunner build guide; on a 4Runner, the 4Runner build guide.

What the job takes

The plates themselves are the cheap part. Total Chaos body mount chop plates are 1/8" laser-cut steel and run about $27 a pair, fitting 2005+ Tacoma, 2003+ 4Runner and 2007–2013 FJ. Offroad Elements, KP Offroad, RSG, NTK Fabworks and DRT Fabrication sell their own versions. Pricing as listed September 2026.

The work itself:

  • Cut the mount to the plate manufacturer’s marked line — follow their template, do not eyeball it.
  • Weld the reinforcement plate in. A 110V welder handles it. This is not optional trim work: you have cut into a structural body mount and the plate is what restores it.
  • Trim the inner fender liner and fold or trim the pinch seam.
  • Remove any plastic still touching the tire.
  • Paint or seal every cut edge. Bare steel behind a wheel is a rust problem waiting to happen, and this one is hidden where you will not see it start.

Figure around five hours of shop labor if you are not welding it yourself. If you do not weld, pay someone — a body mount is a bad place to learn. Our fab shop directory lists shops by region.

Cab mount chop FAQ

Will a cab mount chop let me run 35s?

No. A chop is generally good to about 33 inches. You can only cut back as far as the factory bushing, and even 34s tend to rub under articulation. For 35s you need a cab mount relocation kit, which moves the mount instead of trimming it.

Does a cab mount chop weaken the truck?

Not if it is done properly. You are cutting a structural body mount, which is exactly why the reinforcement plate gets welded in afterwards. A chop without a plate, or with a poor weld, is the version to worry about.

Do I need one if I only run a mild lift?

Possibly, because offset matters more than lift. A wheel with aggressive backspacing on a modest lift can rub sooner than a taller setup on a conservative wheel. Cycle the suspension at full lock before you cut anything.

Do Ford and Chevy prerunners need this?

Not in this form. The cab mount chop is specific to where Toyota locates the body mount on these platforms — it is one of the real costs of building a Tacoma or 4Runner that Ranger and OBS builders never pay.

More prerunner build guides

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