OK getting myself confused- TYRE SIZES?

[Mikeyas]

Hey all

Picking up new rims soon in 16". Looking for some assistance regarding tyre size. Went to tyre power and was quoted for some 205/50 tyres.
Tyre guy said this would be the closest fitting tyre to the rolling diameter.

was using this calculator:
(http://www.miata.net/garage/tirecalc.html)
and tried the stock size of 185/65/R14 to
205/50R16. Sizes look about the same, but speed is calculated at 0.26% to slow and when speedo says 100kmh i am going to go 102.6kmh. When trying 205/45/R16 the speeds go negative such as 0.9% too fast and when speedo says 100kmh id be travelling at 99.1kmh..

Getting confused at size now. Also looking at lowering the car, does this come in as a contributing factor?

need help!!

[quangsta]

with the speedo being read at the hubs, in ur case, when travelling on 205/50 you have a larger rolling diameter therefore should be going a tad faster then you would be on 205/45.

included is a simple explanation on what the tyre details mean...

for example

205 / 50 R 16 82 H

205 - Section width in millimeters
50 - Aspect Ratio (50% of 205), if it was a 60 here it would be 60% of 205
R - Radial Construction
16 - Rim Diameter in inches
82 - Load index
H - Speed Rating