FAO everyone with 18" alloys!

Post by **Mr Self Destruct** » 11 Aug 2006, 12:03

What tyres are you running?
I got a set of 8.5 x 18 Porsche cup 1's and need to put 225 40 18's on. Problem is, all the tyres I've seen only have a load index of 88 or 93, and I heard you need at least a 97 for T3's. So how critical is this (is a 93 ok?), and what's your solution?

Post by **lhd** » 11 Aug 2006, 23:09

Check the load rating......
ie, the tyres on my borbets are 670 kg per tyre which =2.68 tons
lhd.............................

Post by **busbuddy** » 12 Aug 2006, 17:14

I think most tyre places would be reluctant to put a 225 on an 8.5" rim as they would be narrower than the outer rim of the wheel but if you step up to 235 you can get a 95 load index

Post by **Mr Self Destruct** » 12 Aug 2006, 21:11

Interesting. The reason I was asking after 225's is that's what I was told the standard size is for the Audi RS2 (which is what the wheels came off). What I should be asking is, what is the standard tyre width, aspect ratio etc. for a T3, and use the tyre size calculator to find the right size!

Anyone know?

Post by **t25adict** » 13 Aug 2006, 11:49

on audis they run 225 40 18's on 8 inch rims.. not 8.5s
the audi rs4 ran 255 35 18.. on an 8.5 rim.

i was running 235 40 18 on my 8.5x18 oe. audi rs4 wheels for the fronts and 265 35 18 out back..
alot of the manufactures dont recomend stretched tyres ie. tyre walls stretched to wider than the tred width, as it rases the risk of the bead poping back if the tyre gets low on air..

idealy 225 40 is best suited to an 8 inch rim.
for a 8.5 a better tyre would be a 235 40 .

also if your are realy worried about load ratings then
one. you can in alot of makes they do "extra load" tyres rear porsche tyres are higher rated.
two. check that you rims are rated to take a good load, cheep wheels often have load ratings too and in general arnt as strong as makes such as ronal/bbs/speedline..
there is no point in fussin about higher rated tyres if the wheels are lower rated..

Post by **Mr Self Destruct** » 14 Aug 2006, 21:50

Hmm... Just read this and it made me go and recheck my wheels, definitely 8.5 x 18's, so the 235 would be better.

So, when you were running 235 40 18's, how far out was your speedo to standard? 'cos that's another consideration too!

Post by **busbuddy** » 15 Aug 2006, 11:19

check out http://www.alloywheels.com/tyrecalc.asp for your tyre size/speedo

Post by **Mr Self Destruct** » 15 Aug 2006, 15:20

I've tried a load of these sites, but they all make you put in the aspect ratio. If you don't know it, you can't compare other wheels.

Post by **busbuddy** » 15 Aug 2006, 20:55

what do you not know

Post by **t25adict** » 16 Sep 2006, 19:56

standard wheels.
185 - C - 14 (the C is 80% aspect ratio)

185 / 100 = 1.85 (1%)

1.85 x 80 = 148 (148mm hight of the side wall )

148 x2 = 296 (for both the bit that touches the road and the bit that dont)

296+ diameter of rim 14" (14x25.4mm) = 355.6 mm

296 (the tyre) + 355.6 (the rim ) = 651.6 mm your overall diameter

18" wheels 235 -40 -18
aspect ratio 40

235 / 100 = 2.35 (1%)

2.35 x 40 = 94

94 x2 = 188mm (tyre)

188+ diameter or rim 18" (18x25.4mm) =457.2

188 (tyre) + 457.2 (the rim) = 645.2 mm your overall diameter

there are other ways (im sure somone will pick at me) to work it out but thats the easy way where you get to see each bit.

so in all there is a difference of about 6 mm
which is nothin to worry about.
as between manufactures and different tyre treds you have more difference.
also there will be more deformation of a van 185 14 c than a lower profile tyre so the overall diameter changes a little..