Omega Owners Forum
Omega Help Area => Omega General Help => Topic started by: Lesopc on 21 July 2010, 01:03:27
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Me again, bet you are all bored silly by now?
Would the Ronal alloy wheels i mentioned earlier (R44 in size 7.0x17" and the R39 in size 8.0x18") fit straight onto a miggy or would i need to make some adjustments?
Also would there be any effect on speedo reading?
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speedo reading depends on the tyre size.
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speedo reading depends on the tyre size.
225x45x18
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Be aware that you need to make sure the stud pattern and offset are compatible too.
Kevin
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Be aware that you need to make sure the stud pattern and offset are compatible too.
Kevin
Already ahead of you on this one.
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Be aware that you need to make sure the stud pattern and offset are compatible too.
Kevin
Already ahead of you on this one.
Just making sure. :y
kevin
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Standard sizes are 205/65 15 and 225/55 16 for Elite. Working it out, that means Elite has 1% bigger diameter so the speedo would be that amount different between standard and elite - not sure if Vx would have bothered gearing the elite speedos differently to compensate for this.
Your suggested 225/45 18 would be slightly bigger still - 0.9% bigger than Elite or 1.8% bigger than standard. Could also consider 225/40 18 which would be a little smaller than the standard sizes - 1.6% smaller than standard (so actually closer to standard than the 45's would be), but 2.6% smaller than Elite size.
Wouldn't you want something fatter, though, for your racer replica/lotus tribute?:) 245/40 18 would be spot on Elite size. I think the Lotus Carlton even has 265 on the rear!
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Standard sizes are 205/65 15 and 225/55 16 for Elite. Working it out, that means Elite has 1% bigger diameter so the speedo would be that amount different between standard and elite - not sure if Vx would have bothered gearing the elite speedos differently to compensate for this.
Your suggested 225/45 18 would be slightly bigger still - 0.9% bigger than Elite or 1.8% bigger than standard. Could also consider 225/40 18 which would be a little smaller than the standard sizes - 1.6% smaller than standard (so actually closer to standard than the 45's would be), but 2.6% smaller than Elite size.
Wouldn't you want something fatter, though, for your racer replica/lotus tribute?:) 245/40 18 would be spot on Elite size. I think the Lotus Carlton even has 265 on the rear!
Yeah, still a lot of homework to do on this.
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225/45 x 18 are quite big (diameter)
compared to 205/65 x 15, there's 6.1% difference
compared to 225/55 x 16, there's 5.1 % difference
these figures are very large, so I wouldn't advise fitting these - you may not even get front tyre to strut clearance on these.
for reference,
205/65 x 15 = 817 wrpm
225/55 x 16 = 811 wrpm
225/45 x 18 = 770 wrpm
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Maths error somewhere there, 2woody. Unless I made one - but that's imposible :). 225/45 would be a good choice for 18's to replace the standard wheels - see my calcs above.
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Yeah, the miata.net tyre calculator comes out with different numbers: http://www.miata.net/garage/tirecalc.html
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using these tyre calculators and trying to do it with geometry causes WRONG results.
the automotive industry uses wheel revs per mile, which is a measured property of a tyre, taking into account the static sag in the laden radius and the forward motion slip.
it's a property that can only be measured and not calculated.
you need to get the figures from a tyre company - as I did. Check out bridgestonetyre website for example.
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Maths error somewhere there, 2woody. Unless I made one - but that's imposible :). 225/45 would be a good choice for 18's to replace the standard wheels - see my calcs above.
just out of interest - how have you done this ? - have you used (225mm x 45%) + (225mm x 45%) + 18inch
have just been back to work out the error.
205/65 x 15 calculated wheel revs per mile = 791. Actual wheel revs per mile = 817
225/55 x 16 calculated wheel revs per mile = 783. Actual wheel revs per mile = 811
245/45 x 18 calculated wheel revs per mile = 776. Actual wheel revs per mile = 770
you're right in that the difference between, say 205/65 x 15 and 225/55 x 16 is 1% in diameter just considering the tyre on the floor on its own, but adding wheel weight and slip gives a different answer. Precisely why the industry uses wrpm.
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Oh - you've done it properly!:) I just worked out diameters and am surprised the 18" is so much further away from the 15" and 16" when worked out 'properly' than when worked out the simplified way! What info did you use out if interest - couldn't find anything on the bridgestone site? I guess it's due to the increased rigidity of the 18" wheel/tyre? Interesting.
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oddly enough, I've never really considered this,I suppose that the narrower sidewall flexes less and therefore causes less tyre slip.
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I would have thought it'd have less to do with slip, which should surely stay pretty much the same, and more to do with the fact that the extra sidewall flex of the higher profile tyre would significantly reduce the laden rolling radius, wheras the 18" with low profile tyre would stay much closer to it's calculated unladen rolling radius.
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there'll be an element of both, but the slip is my favourite
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seat of the pants, so not rearlly relevant, but i have 245 40 18 (8j ET38 if that helps)with sc3's on the rear which have just replaced linglongs of the same size, thank god.
The ride is noticeably more compliant as you would expect, but the point is i would swear the gearing feels a little less tall than with the linlongs which did feel taller or higher than stock, which the previous figures would prove.
Wish i had meaured the rear ride hight now as the sc3's seem to sit lower for the same size, or done those sat nav measurments woody spoke to me about via pm... or i've imagined it, which is indeed entirely possible.
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it's possible.
tyres can differ forom make to make, especially in their sidewall construction, and to add tio the argument, the geometry of the sidewall can fool you into thinking it sits differently (optical illusion).
furthermore, different manufacturer's tyres of the same nominal size will have different wrpm.
the cheaper tyres will doubtless have softer rubber, that's how they get the grip without the technology