A recent National Institute for Automotive Service Excellence (ASE) webinar discussed how to decipher tire sizes and bolt patterns, how to measure off-set and more.
Mark Lake from Summit Racing served as the hour-long webinar’s host.
Deciphering tire size
Lake said when deciphering tire size, it is best to compare the size of wheels and tires your customer’s vehicle currently has with the size of wheels and tires the customer wants to get.
He says that most everyone knows how to use measuring tape, but some techs are measuring in the wrong place on the tire.
“Where you are measuring matters,” stressed Lake. “The numbers on the sidewall of the tire confuse a lot of customers, so it is important we know what those numbers mean.”
Measuring wheel bolt pattern
There are different ways to measure four-lug, five-lug, six-lug and eight-lug wheel bolts.
“Everyone at some point in time has measured a five-lug wheel incorrectly,” said Lake.
He said that to measure five-lug wheels, a technician must measure from the middle point of one hole to the back end of the hole across from it.
“If you get the wheel bolt pattern and the tire size correct you are usually pretty good. That’s why these steps are so important.”
Backspace and offspace
Lake went through the difference between backspace and off-space in his presentation.
“Backspace is the measurement from the hub mounting surface to the back edge of the wheel,” explained Lake. “Off-set is the measured distance between the hub mounting surface and the wheel’s center line.”
He encourages techs to stick with backspace measurement in lieu of off-set measurements.
“Measuring what backspace you have now sets you up for success later,” he said.
Hub-centric vs. lug-centric
Another differentiation Lake made was between hub-centric wheels – wheels centered on the axle by the center bore of the wheel – and lug-centric wheels.
When using hub-centric wheels, it is important for the technician to choose the right hub-centric rings to “remove the gap between the vehicle hub and wheel bore.”
Lake says there are two measurements needed to determine what kind of hub ring size a tech needs – inner diameter and outer diameter.
However, most aluminum aftermarket wheels are lug-centric and these can use hub centric rings to “help center the wheel during installation. But the lug hardware is what holds the wheel in place.”
Common types of lug nuts
Lake highlighted different types of lug nuts and said that the conical seat is the most popular.
He also said it is important to measure these correctly.
TPMS
Lake also discussed direct tire pressure monitoring systems (TPMS) and indirect TPMS.
Direct TPMS measures air pressure through dedicated sensors attached to the wheel. Indirect estimates low pressure based on tire rotation speed.
If wheels don’t come with original equipment sensors, Lake said there are other ways to attach sensors to wheels.
“The outer-mount adapter and the 90-degree adapter are designed to work on two- and three-piece wheels and some forged, one-piece wheels.”
The next ASE webinar will take place on April 18 at 4 p.m. EST with the topic to be determined.
