E30 Zone

how much do e30 speedos overread as standard?

just wondering as i know going to 50 profile increases the reading by 3.4% over origional overread.

depends on your wheel/tyre size but mine over-reads by 10%

Mine has a bit bigger winter tyre atm but still it shows 60kmh when I'm going 54.

i was assuming 10% as the 10mm ish of diameter change with wear has to be accounted for. 10% seems to be the norm with most cars.

i expect the winter tyers you have wont be large enough difference to make a big change to the speedo going from 205/55/15 to 205/50/15 is only 3.4% faster on the speedo. (3.4mph less actual at indicated 100.)
might get mine down to slarkraceengineering and get them to give it a dyno run and speedo check on there dyno.