Wheel spacers (also called wheel spacers) are among the most popular upgrades to perfect a car’s stance and handling. By placing a spacer between the wheel hub and the rim, you reduce the effective ET value and push the wheel further out into the wheel arch. This not only gives your vehicle a muscular, wide look, but also creates essential extra clearance around shock absorbers or large brake calipers (Big Brake Kits).
Fitting spacers raises many questions: “How many mm spacer can I fit without my tyres rubbing?”, “What is the difference between push-through and bolt-on systems?” and “How do I prevent steering vibrations on the motorway?” In this technical guide the experts at Wheels 'N Customs explain step by step how to calculate the maximum spacer thickness, which thread standards you must comply with and how to drive 100% safely.
1. How Many mm Spacers Fit? Measuring the Wheel Arch
The golden rule when choosing wheel spacers is: measure accurately first, then order. Using the measurement method below you can determine within minutes how many millimetres of spacer your wheel arch allows without the tyre contacting the wing edge over speed bumps or under heavy load:
Step 1: Position the Plumb Line
Park your car on a flat, horizontal surface with the wheels pointing straight ahead. Hold a straight ruler, spirit level or plumb line perpendicular to the outer metal edge of the wing (fender).
Step 2: Measure the Distance
Using a caliper or tape measure, measure horizontally the distance between the inside of the ruler and the most protruding point of your tyre sidewall (or the rim edge for tyres fitted with 'tyre stretch').
Step 3: Safety Margin
Always deduct a safety margin of at least 3 to 5 mm from the measured distance. This compensates for dynamic suspension travel, body roll in fast corners and the elastic deformation of the tyre.
Worked example: Do you measure a free space of 18 mm between the wing and the tyre sidewall? Subtract the safety margin of 3 mm (18 - 3 = 15 mm). A wheel spacer of 15 mm per wheel (30 mm per axle) is the ideal and safe choice in this situation.
2. Difference Between System 1 (Push-Through) and System 2 (Bolt-On)
Depending on the desired thickness and your vehicle’s wheel attachment (wheel bolts or studs with wheel nuts), spacers are divided into two main constructions:
System 1: Push-through System (Through-bolt)
Common thicknesses: 3 mm up to 20 mm per wheel.
How it works: The spacer is a precision ring with holes that is placed loosely between the wheel hub and the rim. The wheel and spacer are fastened together simultaneously with extended wheel bolts that thread directly into the car’s original threads.
Shaft Length Formula:Length New Bolt = Original Shaft Length + Thickness Spacer. If your original wheel bolt has a shaft of 28 mm and you fit a 15 mm spacer, you need bolts with exactly 43 mm thread length.
System 2: Bolt-On System (Threaded-on)
Common thicknesses: 20 mm, 25 mm, 30 mm up to 40 mm+ per wheel.
Operation: The spacer is itself permanently bolted to the vehicle's original hub using the supplied special flat bolts (or nuts). The wheel is then mounted with the original factory bolts into the threaded holes of the spacer.
Crucial Point of Attention ('Wheel Pockets'): With spacers of 20 to 25 mm the original wheel studs can protrude slightly beyond the mounting face of the spacer. The back of your wheel must then have recesses (so-called 'pockets' between the bolt holes) to accommodate these protruding stud-ends without stress.
3. Thread Engagement: Minimum 6.5 to 8 Full Turns
One of the most dangerous mistakes when fitting universal or thin spacers is reusing original wheel bolts that are too short. If a bolt does not engage enough threads in the hub, the forces during acceleration or braking can pull the remaining thread out, resulting in a loose wheel.
In accordance with the official German TÜV safety standards, a wheel bolt or nut must always achieve a minimum screw-in depth. Always start the bolt by hand and count the exact number of full rotations (360° turns):
Thread Size
Thread Pitch
Minimum Number of Turns
Min. Screw-In Depth
M12 × 1.25
Fine pitch (1.25 mm)
Minimum 8.0 turns
≥ 10.0 mm
M12 × 1.50
Standard pitch (1.50 mm)
Minimum 6.5 turns
≥ 9.8 mm
M14 × 1.25
Fine pitch (BMW F\/G-series)
Minimum 9.0 turns
≥ 11.2 mm
M14 × 1.50
VAG, Mercedes, BMW, Tesla
Minimum 7.5 to 8.0 turns
≥ 12.0 mm
1\/2" UNF
American (Ford / Jeep)
Minimum 8.0 turns
≥ 11.0 mm
4. Centre Bore Height & Vibration-Free Fitting
The number one complaint with incorrectly fitted spacers is a heavily vibrating steering wheel around 100 to 130 km/h. This is almost always caused by loss of hub-centricity:
The Danger of 'Flat' Spacers (3 mm to 8 mm): The steel centre boss of your car's wheel hub typically protrudes 11 to 15 mm. If you fit a flat spacer of 8 mm without its own centre bore, only 3 to 5 mm of hub remains. Because aftermarket wheels often have an inward chamfer of 4 to 5 mm, the wheel effectively 'floats' on the studs. The bolts do not bear the load concentrically, resulting in imbalance.
Dual Centering (From 10–12 mm): Therefore, for spacers from 10 to 12 mm upwards always choose spacers with an integrated fixed centre bore. The spacer sits snugly on the vehicle hub and transfers the exact same hub diameter to the wheel's centre hole at the front face.
Check Hub Length vs Spacer Recess: Always measure the total depth of the vehicle's wheel hub. If the car hub is 14 mm long and the recess at the rear of a 12 mm spacer is only 12.5 mm deep, the spacer will not sit flush against the brake disc. This can lead to breakage or dangerous vibrations.
Free of Rust & Grease: Thoroughly clean the steel wheel hub with a wire brush before fitting. Never smear grease between the spacer and the brake disc; this contact surface must be completely dry and flat for maximum frictional resistance.
Have Wheel Spacers Professionally Fitted in Nijkerk
Unsure about the correct thickness, required bolt length or your car’s hub tolerances? In our professional workshop in Nijkerk we precisely measure your wheel arches, thoroughly clean the wheel hubs and fit certified spacers including calibrated torque retightening checks according to the strictest safety standards.
Our wheel and suspension specialists are happy to calculate the exact spacer thickness and bolt length for your car in advance.
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