Frame rail spacing and frame rail diameter
When purchasing a motor mount it is critical that you know what the frame rail spacing and frame rail diameter of your chassis is.  Here’s a quick primer to get you up to speed.

Frame rail spacing
There are essentially three different frame rail spacings: International, American and CRG.  The International spacing is 92mm center to center.  The American spacing is 2 7/8″ (73.025mm) and the CRG spacing is 90mm.  Of course it’s never quite as simple as it could be, right?  Not all American made frames use American spacing.  In fact, very few do.  The vast majority of frames produced today use International spacing whether they are made in the U.S. or elsewhere.  The exception being any kart produced by CRG which will have a frame rail spacing of 90mm.  The point here is that if you have any doubt, measure!  It’s easiest to measure from the outside of one frame rail to the inside of the other.

Frame rail diameter
Just to make things a bit more complicated, you also need to know your frame rail diameter.  For European karts this will be 28, 30 or 32mm.  For an American manufactured kart it will probably be 1 1/8″ (28.575mm) or 1 1/4″ (31.75mm) unless they are using European tubing.

Motor mount clamps
The main reason you need to know these measurements is to insure you get the correct motor mount clamps.  An incorrectly sized clamp will either not hold the mount as securely as possible or even worse, damage the frame rails.  Some mounts (primarily 4-cycle) will offer clamps in either International or American spacing and will be universal in terms of frame rail diameter.  Most however, will offer precisely sized clamps in one of the following: 28/92, 30/92, 32/92, 28/90, 30/90 or 32/90.  The first number is the frame rail diameter and the second is the frame rail spacing. Below is a table that lists some of the more popular chassis brands and their frame rail spacing.  If you have any questions, just give us a call at 801-972-4631.

Frame rail spacingBrands
92mmTony Kart, Kosmic, Alonso, Exprit, Birel, Ricciardo, Intrepid, Top Kart, Arrow, PCR, Margay
90mmCRG, GP, Maranello, Zanardi, LH (Lewis Hamilton), DR (Danilo Rossi)