whit
Apr 23rd, 04, 11:15 AM
I'm just starting a full frame-off resto on my '66 and wondering about new wheels. I'm thinking 15-7's up front and 15-9's in the rear. But what the heck is "backspacing?"
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1966_L78 Apr 23rd, 04, 12:34 PM Whit... "Backspacing" is the distance from the extreme external portion of the wheel lip to the wheel mounting surface, all measured on the 'inside" of the wheel (the part facing the car). Lay a wheel "face" down on the floor and lay a straightedge across the wheel (not the tire though, so its easiest to measure a bare wheel). Measuring from the mounting surface (where the wheel and axle/brakes meet) to that straightedge will calculate the backspacing... More backspacing will cause the wheel/tire to be further into the wheelwell... Less backspacing will cause the wheels to stick out more... Also be aware that with most wheels, the rim "width" is measured between the rim beads (where the tire actually seats)... This is usually 1-inch narrower than the overall width... So a 7-inch wide wheel is actually 8-inches wide overall. A few questions for you to ponder that will affect wheel choices: Do you have a wheel style of choice? a tire size in mind? Do you want the maximum sized tire or just something fairly wide? Do you have the stock 1966 rearend? are you planning on running disc brakes? Aftermarket or GM discs? Why the 15X9s in back? Do you have a specific rim thats available in that size only? personal choice? what tire size? I run 15X8 rims in back... The rear tire is a 295/50/15, which is about the maximum tire without modifying the outer body lip... Any wider than 15X8 rims will likely cause interference with the lower shock mount on the rear axle, unless modifications are made there too... with a 15X9, you should look for between 5.25 and 5.5 inches of backspacing to center the wheel within the wheelwell (to maximize the tire size). whit Apr 27th, 04, 1:08 PM Thanks Tony - lots of good info here. I'll be running a 12-bolt posi rear, 3:23. Probably an M20 or M21 4-speed. Jonathan Apr 29th, 04, 9:05 AM Here's a good diagram I found a while back showing what the wheel terms mean... http://web.njit.edu/~jjj8778/Chevelle/whlterms.gif | ||