majik16106 Posted September 22, 2003 Share Posted September 22, 2003 I knwo how mm of offset work, but im a little confused on how back space is measured, i know if I have an 8 inch wheel with 4 inches of back space, im at zero offset, and I know at 10 i need 5inches of backspace to be at a zero offset. MY question is i guess, if i have the 8 inch wheel at 4 inches of backspace, and I move to 5 inches of back space, is the wheel coming in to the suspension or going out away from the car giving me more lip ? Quote Link to comment Share on other sites More sharing options...
blueovalz Posted September 22, 2003 Share Posted September 22, 2003 Backspacing is how far inboard the inner rim is positioned when the wheel is attached to the hub. This is measured from the wheel mounting surface (where it touches, or is attached to the hub) backward to the edge of the rim. A straightedge placed across the backside rim edge will allow you to measure this distance from the wheel's mounting surface, out to the edge of the rim. The more backspacing (the larger this measurement), the deeper the wheel is placed inboard toward the strut. If two wheels, of same width but different backspacing are compared, then the wheel with more back spacing (hence, more offset) will stick out less on the "lip" side, and will be closer to the suspension. Quote Link to comment Share on other sites More sharing options...
Guest greimann Posted September 22, 2003 Share Posted September 22, 2003 Here is a diagram about how backspace is measured. Chcek out this link for a chart that tabulates the relationship between backspace, offset and width. http://www.mindspring.com/~lfry/wheel.htm Quote Link to comment Share on other sites More sharing options...
majik16106 Posted September 22, 2003 Author Share Posted September 22, 2003 ok awesome, i knew it was measured from the center out, but i didnt know which direction out. Thanks, that helps, I might've ordered my wheels backwards.. Here is what I know, with a zg flare you can fit a 10 inch wide wheel on the back with 5 inch backspace So here is my Math: the wheel I want is 9.5 wide for the rear, so i should be able to put it on with 4.5 inches of back space and it should come out just as far. So Then If i extend the flare an extra inch, the size of the IMSA flare Ill be running (according to MSa one inch bigger than the ZG) I could run the 9.5 at 3.5 inches of backspace, but the company has a minimum back space of 3.75, which should stay far away from the suspension, be almost out to the flare, allow me to run a 275/35/17 rear tire and give me almost 6 inches of "lip" provided the spokes are even with the mounting point, which these wheels are. And for the front ill just use an 8 inch wide wheel with liek a 235 or 245 and give it some negative offset as well. Quote Link to comment Share on other sites More sharing options...
Dan Juday Posted September 23, 2003 Share Posted September 23, 2003 Here's a little piece of advice from someone who has been down the road you're going. Before you order those expensive non-refundable custom wheels do the home work. Buy your flares and tires first. Mount up one front and one rear (if you are planning on different size front and rear) on a cheap/borrowed wheel of the same width as you plan to use (need not be the right offset or bolt pattern). Bolt it up (pop out 3 studs if the bolt pattern is off) and take lots of measurements. This worked very well for me. You can design exactly where you want your tires to end up. Still I was paranoid. So I ordered my rims with 1/8" more backspacing for a fudge factor. You can always add spacers to bring it out but if they stick out too far you're stuck. Remember when you're measuring that you must allow for suspension travel. Good luck! Quote Link to comment Share on other sites More sharing options...
Guest Z-rific Posted September 23, 2003 Share Posted September 23, 2003 This may help a little. I have 15x8's all the way around with 3.5" backspacing. On the fronts are 225/60/15's and the backs are 265/50/15's. My flares are of unknown origin, but give me about 2" extra front and 3" in back. I have Tokico shocks/springs on front, which supposedly lower the car 1". My front tires rub the front wheel well at original sheetmetal, which must be cut back about 2" to clear. (With tire turned most way). Close to rubbing at back of tire, but not quite. A 225/50/15 would be a better choice for me. I haven't put new shocks/springs on rear, but it sits close to the 265's at the top of the wheel well. So 265's with 3.5" backspacing on stock are okay. I haven't tried with a full tank of gas, which I fear will cause rubbing on bumps. From all that I have read and seen, 4" backspacing would work fine for any wheel, as long as you have flares large enough to accomodate and cut original wheelwell sheetmetal enough. 4.5" backspacing and more starts scaring me a little. Clearance to the strut assembly also depends on how much wider the tire is than the rim. A 275 on a 8" wheel obviously causes more problems than a 225. I agree with above post. If you do have too much backspacing, you could always get a high quality spacer and fix the problem. Also, research available tire sizes before any purchase, as some sizes are getting harder to find. Quote Link to comment Share on other sites More sharing options...
majik16106 Posted September 24, 2003 Author Share Posted September 24, 2003 You running a much higher sidewall than ill be running, i plan on running a 275/35 or 40 on a 17, i know people with zg flares that run a 10 inch wide wheel with 5 inches of back space and 18's so i may just use the 9.5 at just under 4.75 back spacing, like a 4.25 or 4, in stead of hoping for the 3.75 to work, and in the front ill use an 8 inch wheel with say... 3.75 as well. According to another source, people have run a 12 inch wide wheel on these flares in the back.. barely but its been done, so there is lots of space to push them out.... Quote Link to comment Share on other sites More sharing options...
Guest Z-rific Posted September 24, 2003 Share Posted September 24, 2003 Sure, you can go with a 10" wheel. Or even bigger. You can use a 20" wheel so long as your backspace stays below 4.5 or 5". I would check with the guys with the ZG flares and make sure they have not converted to coil-overs to get a 5" backspace to work. I think it works with some and not with others. Like I stated earlier, I think it also depends on how much wider the tire is than the wheel it's going on. An 8" wheel may be fine with a 225 and 5" backspacing, but not with a 275. Also, your sidewalls will be shorter, but remember your wheel is also 2" taller. I'm using 15's. But I don't think height will be as much an issue for you as finding the range of backspace/wheel size/tire size to get you off the spring perch and inside the flare. When it comes to wheels, I try not to deal with offset measurements at all. Measurements tend to be inconsistent in the wheel and tire businesses anyway. So I try to find backspace only and deal with that measurement. The good news is, if you're wheel hits the spring perch, you can always go to coil-overs or wheel spacers (bolt on variety). If the tire sticks out too far, you can modify the flares. They are fiberglass, right? Quote Link to comment Share on other sites More sharing options...
gramercyjam Posted September 24, 2003 Share Posted September 24, 2003 FWIW - I run 16X10's on 16X10 3 piece wheels with 5" backspace and .5" rear spacers, .6" spacers in the front, 3" studs and coilovers on a 240. There is not enough clearance for the coil over springs or seats to extend below the top of the wheel. The wheel rubs on the springs or seats unless you move the perch high enough so the springs and seat stop above the top of the rim. The 3" studs are barely long enough with my wheels and spacers. Front tires fit in the stock fenders without fender rub with just a rolled lip. Rear tires require some rolling and flaring. The car is lowered so I have about 3.5" of ground clearance at the rocker pinch welds. YMMV. --John B Quote Link to comment Share on other sites More sharing options...
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