2018-2019 Mustang Widebody Kit: How-To Install Guide

A 2018-2019 Mustang widebody kit is a bolt-on and bonded body conversion that widens the front and rear fenders so an S550 Mustang can run dramatically wider wheels and tires. Installed correctly, the Anderson Composites Type-JTP 10-piece flare set transforms a stock GT or EcoBoost into a track-stance street car, and it is one of the most requested exterior builds that rolls through our Tampa, FL shop. This step-by-step guide walks through exactly what the kit includes, the tools you need, the full install sequence, and the wheel and tire fitment that makes the whole project worth doing.

What Is a Mustang Widebody Kit?

A Mustang widebody kit is a set of replacement fenders and bolt-on fender flares that push the bodywork outward so the tires sit flush with, or slightly inside, a wider stance. On the 2018-2019 S550 Mustang, the Anderson Composites Type-JTP kit ships as a 10-piece set (part number andAC-18MUWBC): front fender flares, rear quarter flares, and the matching front and rear transition panels that blend the added width into the factory body lines. The design is patterned on GT4-style race widebody proportions, so the finished car looks purpose-built rather than tacked-on.

The core benefit is clearance. A stock 2018 Mustang GT wears 255-width front and 275-width rear tires on 9-inch and 9.5-inch wheels. A properly built Type-JTP widebody routinely clears 305-section tires out back on 11-inch to 11.5-inch wheels, which is the single biggest grip and stance upgrade you can make to an S550 short of a full aero package. The added rubber puts more of the Mustang's 460 horsepower (GT, 5.0L Coyote) or 310-330 horsepower (2.3L EcoBoost) to the ground.

Anderson Composites Type-JTP Kit: What Is in the Box

The Type-JTP kit is a hand-laid composite set, so every panel arrives in a raw, primer-ready finish that must be block-sanded, primed, and painted to match your Mustang. That is standard for a widebody conversion and it is why paint is a line item, not an afterthought. Here is the hero product that anchors the entire build.

Tools and Materials You Need

A widebody install is roughly 60 percent bodywork and 40 percent mechanical. Before you start, gather a trim removal tool set, a rivet gun with 3/16-inch aluminum rivets, panel bonding adhesive (3M 08115 or equivalent), a DA sander with 80 to 320 grit, masking supplies, and a torque wrench for the wheel and suspension hardware. You will also want a set of automotive body clips and, ideally, a lift. Plan on 20 to 40 hours of total shop time when you include prep, bonding, and paint; the mechanical mounting alone runs about 8 to 12 hours.

Because the front conversion changes the fender profile, the Type-JTP kit is designed to work with Anderson's matching Type-ST wide front fenders and Type-ST front bumper. Buy the full front set together so the panel gaps line up on the first test-fit instead of fighting mismatched OE fenders.

Step-by-Step Widebody Install

Step 1: Test-Fit Every Panel Before You Touch Paint

Dry-fit all 10 pieces before any adhesive or drilling. Mount the rear quarter flares and front pieces with masking tape and clecos, then stand back and check the gaps against the doors and bumpers. Composite panels have manufacturing variance, so you want to find and sand any high spots now. Mark mounting-hole locations with a grease pencil while everything is taped in place.

Step 2: Remove the Factory Fenders and Bumper

Pull the front bumper cover, the OE front fenders, and the wheel liners. The Type-ST front bumper explicitly requires the Anderson front fenders, so both come off together up front. In the rear, you do not remove the quarter panels; the rear flares bond and rivet directly over the factory quarters after the paint edges are scuffed.

Step 3: Mount the Wide Front Fenders and Bumper

Bolt the Type-ST wide front fenders to the factory mounting points, then hang the Type-ST front bumper with its integrated lip. Confirm the hood shut lines and the door-to-fender gap are even before you commit any hardware. This is the stage where a lift and a patient eye pay off; a 2 to 3 mm gap difference here is obvious once the car is painted.

Step 4: Bond and Rivet the Rear Quarter Flares

Scuff the factory paint under the flare footprint, apply panel bonding adhesive, set the flare, and back it up with 3/16-inch rivets through the pre-marked holes. Clamp and let the adhesive cure per the manufacturer's window (typically 24 hours) before handling. The bonded-and-riveted method is stronger than tape alone and survives track heat and car-wash pressure.

Step 5: Add the Rear Valance and Aero Panels

With the flares set, finish the rear with the Anderson rear valance so the widened body flows into a proper diffuser-style lower section. This is also the moment to fit any lower aero you plan to run, because it is far easier to blend and paint everything as one job.

Step 6: Body Prep, Prime, and Paint

Block-sand every panel, seal the composite with a compatible primer, and spray in your factory color code. This is the make-or-break stage: a $4,499 flare kit looks like a $40,000 build with correct paint and like a parts-bin project without it. Unless you have a booth and spray experience, this is the part to hand to a body shop. Our Tampa shop paints Type-JTP kits on the car so the flares and factory panels share a single, seamless clear coat.

Step 7: Wheels, Tires, and Alignment

Mount your wider wheel-and-tire package, then set a corner-balanced alignment. Widening the track changes scrub radius and camber curves, so a fresh alignment is mandatory, not optional. Roll or trim the inner liners as needed to eliminate rub at full lock and full compression.

Wheel and Tire Fitment for a Widebody S550

The whole point of a widebody is the rubber it unlocks. On a Type-JTP 2018-2019 Mustang, a common aggressive setup is 11-inch front wheels with 295-section tires and 11.5-inch rear wheels with 305 to 315-section tires. Offsets in the +40 to +52 mm range keep the tire tucked under the flare rather than poking past it. Always confirm fitment with your specific ride height and suspension; lowered cars need more negative offset clearance and often a light fender roll on the inner lip.

For reference, that is a jump from the factory 275-width rear on a 2018 GT to a 305-width rear, roughly a 30 mm wider contact patch per rear corner. That extra grip is what lets the 5.0L Coyote's 420 lb-ft of torque hook up instead of lighting the tires on corner exit.

Complete the Look: Front Splitter and Aero

Once the widebody is painted, a front chin splitter sharpens the stance and adds real front-end presence. The Anderson Type-AR carbon fiber chin splitter is a bolt-on finishing piece that pairs cleanly with the wide front bumper.

2015-2017 vs 2018-2019: Which Kit Do You Need?

Anderson builds the Type-JTP flare kit for both S550 generations, and they are not interchangeable because the 2018 refresh changed the front and rear body contours. Match the kit to your model year. The table below compares the widebody components covered in this guide so you can order the right combination in one pass.

Is a Mustang Widebody Worth It? Cost, Warranty, and Street Legality

A widebody kit is worth it when your priority is maximum tire width, cornering grip, and a genuine race-car stance rather than a factory look. The Type-JTP conversion is a commitment: bonding the flares is semi-permanent, and the parts-plus-paint total on a 2018-2019 Mustang lands between roughly $9,000 and $13,000 once you include the wide fenders, bumper, valance, body labor, and a wheel-and-tire package. For that spend you get a car that clears 305 to 315-section rear tires and turns heads at every cars-and-coffee.

On warranty and legality: exterior body panels do not touch your Mustang's powertrain, so under the Magnuson-Moss Warranty Act a dealer cannot void your engine or drivetrain warranty simply because you fitted a widebody kit. The panels are street-legal in most states as long as the flares fully cover the tread of your tires, which is exactly what a correctly sized wheel-and-tire setup achieves. Because the flares bond over the factory quarters and the front conversion is bolt-on, the work is reversible up front, though the rear quarter bonding is best considered permanent. In our Tampa, FL shop we always confirm final tire coverage at ride height before the car leaves so it passes inspection and clears fender rub at full lock.

Frequently Asked Questions