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Check my ET calculations

 
Old 12-17-2018, 09:39 PM
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Gus
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Default Check my ET calculations

Ok, possibly getting some custom wheels made. I need to calculate the desired ET front and rear. Using sample I watched on Utube I came up with these numbers.
Front
Current ET is 50, to confirm I measured depth of wheel to floor at 234mm. Divided this in half 116mm. Then added the spacers I use to the back side of wheel center and measured this at 156mm . So taking 116 from 156 leaves an ET of 40 for the new wheels. More simpler way is - current ET=50, using a 10mm spacer - so 50-10=40mm ET.
Did dame for rear - Current ET = 65. Height was 285, half is 142.5. Difference was 206 less 142 gave me 64mm - close enough.
with 30mm spacer this changes to176mm. So 176 - 142 leaves 34mm. So new rear wheel ET should be 35mm. Simple way 65 ET - 30mm leaves 35mm - so all checks.
??? Doesn’t it???.
Now have to decide if I am going to increase wheel width from 8 to 9 in front and how this will affect ET. Same for rear from 10 to 12 and how this will change ET. In both cases I do not want to move wheel further inward as am testing limits now.
Thanks for feedback.
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Old 12-17-2018, 10:16 PM
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LPMM
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I used this calcualtor to figure out my new ETs when I went with different wheel widths
https://www.1010tires.com/Tools/Wheel-Offset-Calculator
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Old 12-18-2018, 08:04 AM
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I use this calculator. It includes additional info with a slightly more informative graphic.
https://www.willtheyfit.com/
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Old 12-18-2018, 10:01 AM
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Bill Verburg
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Originally Posted by Gus View Post
Ok, possibly getting some custom wheels made. I need to calculate the desired ET front and rear. Using sample I watched on Utube I came up with these numbers.
Front
Current ET is 50, to confirm I measured depth of wheel to floor at 234mm. Divided this in half 116mm. Then added the spacers I use to the back side of wheel center and measured this at 156mm . So taking 116 from 156 leaves an ET of 40 for the new wheels. More simpler way is - current ET=50, using a 10mm spacer - so 50-10=40mm ET.
Did dame for rear - Current ET = 65. Height was 285, half is 142.5. Difference was 206 less 142 gave me 64mm - close enough.
with 30mm spacer this changes to176mm. So 176 - 142 leaves 34mm. So new rear wheel ET should be 35mm. Simple way 65 ET - 30mm leaves 35mm - so all checks.
??? Doesn’t it???.
Now have to decide if I am going to increase wheel width from 8 to 9 in front and how this will affect ET. Same for rear from 10 to 12 and how this will change ET. In both cases I do not want to move wheel further inward as am testing limits now.
Thanks for feedback.
your calc are correct, measuring is tricky

I've never seen 9 or 11 let alone 12 on a n/b 964

here are some examples
This beautiful car built by Dan Jacobs uses 8ET52 245/35 & 10ET65 w/ 21mm spacers 275/35 all 18

This is a friends 8.5ET40 245/35 & 10ET45 275/35 all 18


others
8.5 ET55, 10 ET65 w/ 15mm spacer for ET50

8Et40 225/40 & 10ET56 265/35 all 18

8ET50 & 10ET44 225/40 & 10 ET44 (65-21) 265/35 all 18

8.5ET48 235/40 & 10ET51 275/35 all 18

8.5ET45 235/40 & 10ET50 265/35 all 18

8.5ET51 245/40 & 10ET44 275/40 all 17

8.5ET58 225/40 & 10ET51 265/35 all 18 also 9.5ET48 265/35

factory Carrera Cup 8ET52 235/45 & 9.5ET47 275/40 all 17 or 8x18ET52 235/40 & 9.5ET47 265/35 all 188



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