Offset calculation ???

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Offset calculation ???; WTF?
Topic Started: Thu May 11, 2006 9:25 am (165 Views)
ThankYouLord	Thu May 11, 2006 9:25 am Post #1
Member Posts: 1,519 Group: Members Member #108 Joined: December 17, 2005	Ok, i'm not brilliant at maths but i will understand what's explained to me. My car should run either a 6jx15 H2, offset 49mm (ET 49) OR a 7jx15H2, offset 44mm (ET 44). Niether of which are available to me as i have new tyres waiting to go onto the car so i need to act. I do have the C class steel wheels i bought last month and they ar 6.5Jx15H2, offset 37mm (ET 37). What i need to know is what the difference will be in 'Sticky-outy-ness' in as much as i don't want them mega wide and scraping the arches. If i was running the 7x15's ET 44, with the correct 205/55/15 tyres i have bought, what would be the difference in 'sticky-outyness' if i put those tyres on 6.5x15's that run an offset of 37mm? I am ok with putting 205's on 6.5 " rims but it's the difference in width AND offset that's confusing me and it's in BOTH inches and metric - my brain is melting a bit. ANY help is much appreciated. Phil.



dave_irl	Thu May 11, 2006 9:46 am Post #2
I love offset. Posts: 8,729 Group: Admin Member #6 Joined: November 2, 2005	Using this Offset calculator, it says the 6.5J ET37 wheels will only stick out 1mm more than the 7J ET44 wheels. So if you can fit the 205/55 tyre on the 7J wheels with no rubbing, you should be fine on the 6.5's too Hope thats of help, I know calculating offsets is a pain, I was doing it for ages before I bought my wheels :lol: And they extend out roughly 54mm



rhodrimb	Thu May 11, 2006 9:58 am Post #3
Member Posts: 240 Group: Members Member #55 Joined: November 17, 2005	The distance from the face of the hub to the inner edge of the alloy will be 6.5"=165.1mm, 165.1/2 +ET44= 126.55mm 7"=177.8mm, 177.8/2 +ET37= 125.9mm The distance from the face of the hub to the outer edge of the alloy will be: 6.5"=165.1mm, 165.1/2 -ET44= 38.55mm 7"=177.8mm, 177.8/2 -ET37= 51.9mm Therefore the 6.5" alloy will stick inside the arch 0.65mm (negligable) more than 7" alloy. but the 6.5" will be sticking inside the exterior of the arch by 12.45mm (bit less than half inch) compared with the 7"alloy. It now seems obvious that with those offsets, the width of the alloy inside the arch isn't affected. therefore a 7" rim will stick out by 1/2" more than the 6.5" in relation to the bodywork. (the calcualtions just prove it) hope thats of some help Rhodri



ThankYouLord	Thu May 11, 2006 10:05 am Post #4
Member Posts: 1,519 Group: Members Member #108 Joined: December 17, 2005	That is b loody marvelous and means i can now crack on and get it all done. i knew i could count on you lot, thanks. Phil.



rhodrimb	Thu May 11, 2006 10:08 am Post #5
Member Posts: 240 Group: Members Member #55 Joined: November 17, 2005	ThankYouLord May 11 2006, 11:05 AM That is b loody marvelous and means i can now crack on and get it all done. i knew i could count on you lot, thanks. Phil. No problem mate, got 2 use my 2 maths degrees at some point in my life! :lol: :lol: :lol: Rhodri



dave_irl	Thu May 11, 2006 5:53 pm Post #6
I love offset. Posts: 8,729 Group: Admin Member #6 Joined: November 2, 2005	Soon I'll have my degree in Transport Technology that should come in handy too



Big Ben	Thu May 11, 2006 6:33 pm Post #7
Member Posts: 4,902 Group: Members Member #155 Joined: January 26, 2006	^^ Maybe you can sort out the GPS systems we have that send trucks up farm tracks and drown cars if fords! :lol: :lol: :lol: Offset is not just important for stopping the tyre from hitting the wheel arch, it also transmits the forces from the wheel directly through the centreline of the main wheel bearing. Get it wrong and you are stressing the bearing!



dave_irl	Thu May 11, 2006 9:46 pm Post #8
I love offset. Posts: 8,729 Group: Admin Member #6 Joined: November 2, 2005	Wonder how my bearings are :unsure:



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