Zip Corvette: Offset and Backspacing (Link in Body)

During my research on new wheel/tire packages for my 76 Corvette, I came across some good info regarding offset and backspacing.

Zip Corvette

“Wheel back Spacing is very simple and is often confused with the offset. To determine a wheel’s offset you must first find the wheels back space. The back space can be measured in inches but should be converted to millimeters before proceeding to find the offset. To find the back space place a straight edge across the rear of the wheel and measure to the mount pad. The distance equals the wheels back space, which in this case is 6.75″. Multiply the back space by 25.4 to convert the back space to mm (6.75″ x 25.4mm = 171mm).

Wheel offset is the distance between the centerline of the wheel to the wheel mount pad. It is measured in millimeters and the outcome can result in a zero, positive or negative measurement. To have a zero offset, the wheel mount pad must be even with the centerline of the wheel. A positive offset means that the mount pad is shifted past the centerline towards the face of the wheel, while a negative offset means the mount pad is shifted past the centerline towards the rear, or the brake side of the wheel. To determine the offset of a wheel you must first measure the overall width of the wheel. Lets say the wheel measurements are 18″ x 9.5″. Now convert the width to millimeters by multiplying the width by 25.4mm (9.5″ x 25.4mm = 241mm). Next divide the wheel width by 2 to determine the wheels centerline (241mm/2 = 121mm). With the centerline and back spacing of the wheel determined and converted to millimeters simply subtract the centerline from the back spacing for the offset (171mm – 121mm = +50mm).”

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COPO Camaro

Before the marketing department created a COPO model it was the “Central Office Purchase Order” by which a few dealerships, notably Yenko and Gibb, ordered options not normally available for the Camaro. The Camaro of the 60s could not exceed a 400ci engine unless the COPO loophole was exploited.

Anyone that tells you that no COPO Camaro ever had a VIN nor were they street legal doesn’t know the history.

“Unlike the model built in 1969, the later versions of the COPO are not street legal.”

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Listen Slick…

Those are not my high-beams.

I’m sorry that my YJ sits as high as it does. I also apologize that your 1985 Cavalier RS sits that low.

At this point, all I can say is that you are lucky I haven’t done my HID conversion yet. And before you ask, yes my lamps are adjusted properly given the height of the vehicle and the width of the headlight mounts.

Letting me pass you was commendable but passing me later (and getting behind a vehicle that just turned on to the road) served about as much purpose as you flipping me off and slamming on your brakes. It is, at this time, I would like to inform you that the Jeep is armored, front to rear, with 3/16″ steel… minimum. My bumpers are heavier.

Since any vehicle with head lamps more than 18″ off the ground will continue to cause you discomfort, I can only suggest the following items;

1. Learn to flip your rearview mirror. Maybe this article, “How does a car’s rearview mirror work when it’s in the glare-resistant setting?” will help.
2. Failing to accomplish driving tip #1, I would suggest tinting your rear window. It will look cool on your Chevy and is perfectly legal.

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Accessory Relay/Fuse Box

Trying to keep the wiring rat’s nest to a minimum, I created a Fuse and Relay box.

Parts list:
1 Project box a la Radioshack
1 Power distribution block
1 Fuse holder
4 Appropriately sized relays
4 Appropriately sized fuses
Various wires and connectors

I started by bridging the power distribution block followed by mounting it to the side of the box. The 4 fuse block was mounted to the lid.

I then drilled two holes in the lid for power access to the relays the box will contain.

After putting it all together, it successfully kept the wiring to the relays (4 wires per) from spreading all over the engine compartment.

Specific instructions would depend upon the type of box, fuse block etc you get.

All the pics, of this build, start on this page of the gallery.

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Stereo Hookup

Recently I had a slight battery drain issue which I narrowed down to the stereo install. Apparently there was power applied all the time, regardless of ignition switch position. Even with the unit off, there was a significant draw.

I did some digging and found a wiring diagram for the unit.

Brown, phone mute. (unused)
Yellow, 15A fused, memory backup lead. (needs power all the time)
Yellow, 3A fused, bus power. (needs power all the time)
Red, power. (needs power when ignition is on position)
Blue/White, amp turn on. (not used at this time, but will in future)
Black, ground.
Orange/White, illumination. (connect to light switch?)
Blue, auto antenna. (LOL, on a YJ? unused)

So now I have to figure out where all this is SUPPOSED to go in the wiring harness.

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Electrical Accessories

A laundry list of items to be installed.

XRC8 Winch
~400W Inverter (40A)
2x 100W SRS Lights (20A)
12V Air Compressor, OBA (30A)
12V Power Port (20A)

In theory, I’d like to have a power distribution point under the hood and in the cabin area provided the items connected don’t draw too much amperage. Clean wiring is the name of the game.

Everything that can will have a relay connected to an illuminated switch to indicate power is applied and system is active. All items will be fused as well.

The winch remote plug-in will be mounted in the switch panel.

The first order of business is to estimate what the max draw of each of these items.

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Winter Planning

Since it’s too cold out to actually do any work, it’s time to make plans for the future.

I need to work on multiple systems on my YJ. Recovery, electrical, suspension and a seeping leak etc.

Luke over at Frontier 4×4, is currently designing a front bumper to house the Smittybilt XRC8 I will be buying soon.

Move hi-lift to rollbars or hood.

I will be putting LED replacement dash lights in. Half the bulbs I have are burnt out.
Get gauges working or replaced.
Alternator upgrade for winch use.
Install dash speakers.
Install 12Vdc air compressor.
Wire in XRC8 winch.

I have a small leak at the transmission cooler that needs corrected.

Finally trim u-bolts.
Install bump stops.

Adjust E-brake

I’ll add more as I think of it.

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