WHEEL AND TIRE TECH 101

Get a bet­ter un­der­stand­ing of the wheels on your car

Street Rodder - - 2018 Ultimate Wheel & Tire Guide -

Off­set is the lo­ca­tion of the flat mount­ing sur­face of a wheel rel­a­tive to the wheel’s cen­ter­line. Neg­a­tive off­set means that the mount­ing sur­face is to­ward the cen­ter of the car, pos­i­tive off­set means that it’s to­ward the out­side of the car, or the wheel is “pulled in” to­ward the cen­ter. Off­set af­fects many things other than just whether the wheel has the ap­pear­ance of “stick­ing out” past the fen­der. The wrong off­set can cause rub­bing prob­lems when the sus­pen­sion is com­pressed or the wheel is turned. Off­set af­fects the steer­ing ge- om­e­try’s scrub ra­dius, pos­si­bly lead­ing to prob­lems with torque steer or self-cen­ter­ing char­ac­ter­is­tics.

Off­set also af­fects the sus­pen­sion’s mo­tion ra­tio, which di­rectly de­ter­mines the ef­fec­tive spring and damper rates. Po­ten­tially, in a very heav­ily loaded ve­hi­cle, or with ex­treme changes in off­sets, wheel bear­ing life can be af­fected, but this is more often talked about by truck peo­ple than by small car en­thu­si­asts. It’s very, very im­por­tant that the proper off­set wheels be used.

While not di­rectly a mat­ter of off­set, brake caliper clear­ance is a related is­sue. If you have or plan to have big brakes on your car, be sure that your wheels, or the wheels that you’re go­ing to use will fit over the calipers. Spac­ers are avail­able to solve the prob­lem if they don’t, but it’s best to get a wheel with enough dish to meet your off­set specs and still fit your brakes. Con­sult­ing the wheel and brake man­u­fac­tur­ers ahead of time is wise. Many af­ter­mar­ket brake com­pa­nies even have tem­plates of their brakes avail­able that you can eas­ily check against any wheel.

NEG­A­TIVE OFF­SETZERO OFF­SETPOS­I­TIVE OFF­SET

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