Quote:
Originally Posted by msford
My placard is not much different to yours. FYI I've attached it and highlighted the section I was reading from.
I don't mind being out a few k's on my speedo but not double that amount. I'm leaning to sticking with 45 profile tyres if the effects are as severe as you estimate.
Bridgestone has offered to give me the RE050A's for $315 which will reduce to $236 per tyre after the promo. Jax have the Michelin SP3 45's for $291 per tyre with a $100 fuel card promo so that cuts it to $266 per tyre, but I haven't fully shopped around for those yet and I may find them cheaper. I wouldn't mind trying those out as I've read quite a few good reports about them.
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Well that's a very interesting placard you show.
I say that because there are two distinct tyre groups based on overall diameter;
215/55R16 = 642.9 mm dia
215/50R17 = 646.8 mm dia
235/40R18 = 645.2 mm dia
and
235/45R18 = 668.7 mm dia
235/40R19 = 670.6 mm dia
This would mean that the manufacturer would need to have two types of software constants to calculate the speed of the vehicle dependent on which of the two groups the tyres on the car fell into. Generally manufacturer's try to avoid this sort of thing because it gives them grief when the wrong software package is loaded (possible) or the wrong wheel set is fitted (probably less likely).
I endorse your feelings. Stick with the same tyre size that came on the car when bought - especially as you have some confidence that currently the indicated speed is close to the actual speed.
You might consider getting the tyre franchise to show you the two tyres side by side. A 23 mm difference in diameter ought to be easy to pick.
Cheers