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Curious about fender rolling, tire downsizing, wheel spacers or the differences between racing and street wheels? We provide the details.

Quick Tips for Using a Fender Roller

Many metal vehicles include a pronounced inner lip within the fender that reinforces the panel and supports the arch. This edge can create a risky contact point for tire sidewalls on lowered cars fitted with wide rubber. Rolling that sharp lip provides a simple method to eliminate a potential issue.

Fender rollers are reasonably priced today. Eastwood and similar suppliers offer units for roughly one hundred dollars, while rental options remain available from various sources for about forty dollars weekly plus shipping. Their availability does not prevent serious errors if used incorrectly. Follow these guidelines when operating a fender roller:

Problems can develop quickly, so proceed with small adjustments. When rolling lips, advance the main screw about a quarter turn per pass. Multiple minor adjustments are safer than fewer large ones that might crease the metal.
Fender openings rarely form perfect circles. The roller, centered on the hub, follows a circular path and may apply uneven pressure across the panel. Before committing to full rolling, test tension across the full motion range after initial contact.
Apply heat to assist the process. A heat gun warms both paint and metal, reducing the chance of cracks or other damage. Avoid excessive temperatures that could blister the finish, but moderate warmth simplifies the task.
Account for opposing forces. As pressure is applied upward on the lip, the fender pushes downward on the suspension. This movement helps with irregular shapes, yet suspension travel limits can cause sudden tension shifts between adjustments.

Chonckers: Why Did We Downsize Our M3 Tires?

The ideal tire setup sometimes calls for smaller sizes rather than larger ones. Although many track their BMW M3 models on 18-inch wheels, our 2004 example moved to 17-inch sizes to cut running expenses.

Compare costs for the Falken Azenis RT615K+ track tire: the 265/35R18 size lists at 203 dollars each, while the 255/40R17 version costs 166 dollars.

Does the change reduce contact patch? Roughly 0.3 inch per corner, yet the setup still exceeds the original 225/45R18 fronts and 255/40R18 rears for noncompetitive track use.

The final step involved fitting 17-inch Falkens on our M3 using Apex Race Parts 17x9.5-inch square setups designed for E46 M3 track cars. This arrangement simplifies rotation, aided by a 12mm spacer to position the rear wheels correctly inside the fenders.

We selected Apex flow-formed ARC-8 wheels. Each weighs under 17 pounds, includes knurled beads, generous socket clearance and big-brake compatibility. They also satisfy the paper test with BimmerWorld spacers. Priced at 319 dollars each, replacements are available at half price if damaged.

Does this cost much performance on track days? We prioritize balance and lower consumable expenses over marginal gains. The added sidewall also delivers the popular chonky appearance.

-David S. Wallens

Spaced Out: How the Simple Paper Test Can Prevent a Major Failure When Running Wheel Spacers

Wheel spacers appear frequently in our projects and even on factory BMW M4 GT4 race cars. No universal standard exists. Many include a centering snout similar to the hub, yet nothing guarantees compatibility between different spacer and wheel combinations.

Proper fit matters because an incorrect chamfer engagement can leave a gap between spacer and wheel. The outcome may include broken studs and further complications.

The BimmerWorld team suggests the paper test to verify seating. Perform it with the wheel and spacer off the vehicle.

Step 1: Insert a sheet of paper at the spacer-wheel interface using notebook or copy paper.
Step 2: Press firmly on the spacer at a point 90 to 180 degrees from the paper location.
Step 3: While maintaining pressure, pull the paper. If it slides free, a gap exists and seating requires correction.

What Makes a Race Wheel?

Although no official motorsport certification applies, certain features distinguish competition-ready wheels beyond low weight. These details often increase cost.

Recessed spokes reduce damage risk during side impacts.
Knurled beads limit tire slip on the rim under high lateral loads.
Generous lug clearance accommodates impact sockets and speeds tire changes.
Off-the-shelf or custom designs? Custom options add expense.
Centering rings may slow pit stops.
Big-brake clearance is essential without needing larger rims.
Avoid sharp edges that hinder quick tire swaps.
Light weight matters, yet load rating and curb-impact strength are critical.
Lip support must withstand track stresses.