There are 5 measurements/dimensions that drive our tire sizing, and this article will walk you thru how we measure for tires.

Remember – If you need a tire we don’t currently offer – you can use this guide to capture measurements for us – and we can make the tire you need!

Accurate measurements help us ensure proper fit and allow us to closely match the original tires. When we make for a new tire – we measure in hundreths of millimeters (0.00) and round to the tenths of millimeters (0.0). We check each dimension at least twice (the old adage – “measure twice…”) and take the average. 6-inch digital calipers that read in millimeter are the best way to measure. If you don’t have some – you can find them for $10-$15 on Amazon (free shipping), and for slightly more at Harbor Freight in a pinch.

It’s difficult to accurately measure wheels and tires on most cars (unless they are open wheel – like Formula 1 cars), so we generally recommend removing the body of the slot car to make measuring easier.

The 5 Measurements

Tire Diameter

Outside Diameter of Tire when mounted on the wheel – this provides the overal ride height and chassis clearance off the track. It’s critical to have the calipers only touch the tires and not squeeze or pinch the tire to give a false, smaller reading.

Tire Width

Here we’re measuring the width of the tire from sidewall-to-sidewall – being careful (again) not to squeeze the softer, rubber material (leading to a smaller reading).

Wheel Diameter

Here we’re measuring diameter of the wheel where at the outside sidewall and the inside sidewall. On the vast majority of slot cars – the diameter will be the same on the inside and outside. However, there are some cars where the inside of the wheel (where the inside sidewall of the tire touches the wheel) is a smaller diameter than the outside. Carrera’s Evolution/D132 McLaren 720S GT3 is one example of this – as you can see in the photos below.

Rib Width

Here we’re measuring how wide the center rib is on the wheel. If this were an “air gap” wheel (like NSR) – then we would measure the air gap ridges from edge-to-edge, and measure the width of one ridge so we can calculate how much to fill-in with Tire.

Rib Diameter
(to calculate Rib Height)

Here we’re measuring the diameter of the wheel on the rib (or rib edges for “air gap” wheels). Using this measurement and the Wheel Diameter – we can calculate how tall the Rib is – so we now how tall to make the rib void in the tire.