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      01-09-2013, 10:39 AM   #1
Porschefile
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How to calculate track width from offsets?

I am going to do my own alignments using string for toe and digital calipers for measurement. I stumbled upon a pretty nifty spreadsheet that runs the geometry calculations for you if you have the necessary input values. The problem is the track width is different now than stock since I have aftermarket wheels.

Does anyone know how to calculate the new track width with offset and wheel width? Stock track width is 1540mm F/R.

Thanks in advance, and I'll try and post a DIY alignment thread if it works.
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      01-09-2013, 01:10 PM   #2
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Track width is measured from wheel centerline to wheel centerline.

I would calculate the new and old wheel front spacing, subtract the old front spacing from the new front spacing, and then add two times the delta front spacing to the orig track width (TW):

New TW = Old TW + 2*Delta Front Spacing
= Old TW + 2*[(new wheel width-old wheel width)/2 -
(new offset - old offset)/25.4]

This assumes TW is in inches, wheel width is in inches, and offset is in mm (offset is usually listed in mm).
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      01-09-2013, 01:15 PM   #3
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Quote:
Originally Posted by M3SQRD View Post
Track width is measured from wheel centerline to wheel centerline.

I would calculate the new and old wheel front spacing, subtract the old front spacing from the new front spacing, and then add two times the delta front spacing to the orig track width (TW):

New TW = Old TW + 2*Delta Front Spacing
= Old TW + 2*[(new wheel width-old wheel width)/2 -
(new offset - old offset)/25.4]

This assumes TW is in inches, wheel width is in inches, and offset is in mm (offset is usually listed in mm).
Thanks. Old wheels were the stock 19", 8.5" front 9.5" rear. I'm not sure what the offset is though.

New are Forgestar 19x11 et33 and 19x9 et 25 I think. I need to double check the offsets.
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      01-09-2013, 03:04 PM   #4
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Quote:
Originally Posted by Porschefile View Post
Thanks. Old wheels were the stock 19", 8.5" front 9.5" rear. I'm not sure what the offset is though.

New are Forgestar 19x11 et33 and 19x9 et 25 I think. I need to double check the offsets.
Stock 220M's are 19x8.5et29 and 19x9.5et23.

Based on my calculations your new track widths are:
F: 61.4"
R: 61.3"

Last edited by M3SQRD; 01-09-2013 at 03:11 PM.
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      01-09-2013, 04:00 PM   #5
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Quote:
Originally Posted by M3SQRD View Post
Stock 220M's are 19x8.5et29 and 19x9.5et23.

Based on my calculations your new track widths are:
F: 61.4"
R: 61.3"
Thanks!
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      01-09-2013, 10:59 PM   #6
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Good info guys. Love learning new shit would suggest moving this to the suspension/brakes/chassis as think it would get more exposure. Nonetheless, good work.
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