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 Post subject: Wheels and Tyres guide
PostPosted: Wed Apr 13, 2005 7:45 pm 
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Joined: Sat Mar 05, 2005 3:21 pm
Posts: 1249
Location: Twickenham, Surrey
one of the most commonly asked questions i am going to try and answer the best i can

the way to measure the diameter of a wheel is to measure the diameter between the inside faces of the wheel, not the exterior face you see

as tyres come in metric sizes 205/40 etc and wheels come in imperial sizes etc its best to convert the hweel size to metric as well

as 25.45 mm = 1 inch

there fore:

13" = 330.85mm
14" = 356.30mm
15" = 381.75mm
16" = 407.20mm
17" = 432.65mm
18" = 458.10mm
19" = 483.55mm

Tryes are measured in percentages

205/40 profile tyres means the contact area with the road when the wheel is perpendicular is 205mm, the side wall is 40% of this area

205 / 100 = 20.5 x 40 = 82.0mm / 2 = side wall depth in this case 41mm

The aim is to get the alloys and tyres as close to the original diameter as possible to avoid major arch work of course after going over a certain size this is not possible but the lower profile of sidewall the less you have to do IN THEORY i can turn round and say it will fit because manufacturing tolerances aren't that tight

so here we go common sizes

tyre size > sidewall depth > rolling diameter

13":
155/70 = 54.250mm = 385.100mm(15.13")
185/60 = 55.500mm = 386.350mm(15.18")

14"
185/55 = 50.875mm = 407.175mm(15.99")
195/50 = 48.750mm = 405.050mm(15.92")
195/45 = 43.875mm = 400.175mm(15.72")

15"
195/50 = 48.750mm = 430.500mm(16.91")
195/45 = 43.875mm = 425.625mm(16.72")

16"
195/45 = 43.875mm = 451.075mm(17.72")
205/40 = 41.000mm = 448.200mm(17.61")
195/40 = 39.000mm = 446.200mm(17.53")

17"
205/40 = 41.000mm = 473.650mm(18.61")

18"
215/35 = 37.625mm = 495.725mm(19.48")

19"
215/35 = 37.625mm = 521.175mm(20.48")



HTH Tony :D

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 Post subject:
PostPosted: Sun May 27, 2007 1:40 am 
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Joined: Tue Oct 24, 2006 2:15 pm
Posts: 200
Location: North West (nr manchester)
this may help as a visual to which measurement is what is only for the alloy so may help with tyre im guessing
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PostPosted: Wed May 30, 2007 9:09 am 
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Joined: Tue Dec 21, 2004 8:31 pm
Posts: 13427
Location: Birmingham (near Sutton Coldfield)
Drives: Nissan Pulsar GTi-R
Careful, people seem to have problems understanding pictures:

http://www.fiesta-si.com/forum/viewtopic.php?t=3523

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