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alansimon
05-25-2005, 03:06 PM
In the past, I tried some Panasport wheels, I forget the width. I found all the problems with interference that others experienced. After I resolved these problems, the steering still did not feel "right". I then took the tires (215/70-15 Michelins...closest revs per mile)and had them mounted on the stock wheels. The steering felt normal. Here are my questions: What is the standard TR6 6J X 15 offset (What does the "J" mean)?Have any of the membership found that maintaining the standard wheel offset is preferable to changing it when going to alloy wheels? Which wheels have you folks been successful with? Is there a wheel supplier that Forum members have dealt with that give discounts?

I apologize if this has been discussed before, but several site searches did not turn up anything.

Thank you.

Rick O.
05-26-2005, 11:13 AM
The stock TR6 steel wheels are 5 1/2" x 15 with 4 holes on a 4 1/2" circle (pitch circle diameter - PCD) with 3 1/2" backspacing. Offset is calculated by subtracting half of the rim's overall width from the backspacing. Backspacing is the distance from rim edge to the flat surface where the wheel mounts on the hub (lay a straight edge on the edge of the rim flange and measure from the straight edge to the flat mounting surface). Overall width is the distance from the outside of the rim to the other and is greater than the rim width by the thickness of the bead. The rim width (5 1/2 inches on a 5 1/2" x 15 wheel) should never be used on any wheel measurement because the bead width is variable from wheel to wheel and can be from 1/2 to 1 inch. You can not measure this dimension with the tire on the rim, so don't use it. Some offsets are wrong because rim width was used in the calculation. To answer your offset question, someone will have to provide a measurement of the wheel's overall width.

A positive offset is going to place the mounting surface further away from the wheel's centerline or inboard flange, moving the wheel further inboard when mounted. Becasue of this, you have to be careful you don't specify too much offset as the wheel will foul suspension components or the wing edge. Conversely, a negative offset will be on the opposite side of the centerline and closer to the inboard flange. Negative offset wheels appear to stick out really far when mounted. Zero offset wheels will lie right on the centerline. The lower the offset number, the further out the wheel is going to mount.

I have a set of Revolution 5-spoke sport wheels that are 6.0x15, ET rim, 4 x 4.5 PCD, 73.1 mm backspacing, and 8 mm offset. With 205/70 profile tires, the front tires rub the wing edge when turning at full lock.

Hope this is helpful.

alansimon
05-26-2005, 11:29 AM
Rick O,

Thank you for your well written and understood description of offset, which is very helpful.

Alan

Any other wheel experiences out there from other members?