I have conflicting reports: If I change my rims/tires on my A4 from 16" to
18" does it affect the speedo/odometer readings? My tire guy says the
dealer needs to make an adjustment, but the dealer says it will have no
Seems logical that a larger diameter wheel/tire would make the apparent
mileage lower (fewer rotations to travel a given distance), but I can't find
an authoritative source. Any help?
Remember also that, if your total wheel/tire diameter changes, not only
will your speedo be off, but you will effectively be changing the
overall gearing. If your overall wheel/tire diameter increases, you
will probably have worse acceleration (with the stock tranny, anyway).
In theory, if the overall rolling circumference increases, acceleration will
suffer, but top speed increase. Unlikely to be noticeable. More significant
is the decrease in ride comfort and less resistance to aquaplaning with the
very lower profiles.
Eh? Ride comfort, sure, but I'd argue that less resistance to aquaplaning is
not truly attributable to aspect ratio.
On a given vehicle (so the performance differences are strictly due to tires)
resistance to aquaplaning is primarily a function of tread *width* and
That width is a factor in calculating aspect ratio does not somehow convey
cause to aspect ratio...
'00 s4 6spd
Well, hell's fire, boys, if we're goin' to go gettin' all
*theoretical* here, let's go all the way! The other thing that the
wide aspect tire (usually, unless you're getting the same width as the
"Postus Interruptus" ;-) notwithstanding, I believe you reiterated my point:
the size of the contact patch, not the aspect ratio, is what's in play wrt
'00 s4 6spd w/low aspect S03's, quite good in the wet...
That's *exactly* what it was. As soon as I realized I was repeating
what you'd said, I hit the "Cancel message" button. Only it said,
"Post message". Unfortunately, AFAIK, there's no 'overs' in Usenet
(no more embarrassed than usual)
When getting a larger rim, you need to get a lower profile tire, so that the
overall rim/tire combo diameter remains the same. For example, if what you
have right now is 205/55/16, then when you get your 18" rims, you'll get
225/40/18 tires in order to stay as close as possible to the OEM diameter.
This way, the difference in diameter will be so small, that you will not
affect your speedo/odo in any significant way.
You can play around wih this calculator to see what I mean:
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