tire to gear to speedo questions...

Feb 16, 2010
ok here's my deal....

87 limited regal had 2.41 rear gear with 200c trans and 195/75R14 oem rims and tires

87 limited with 3.42 rear with 200r4 trans with 205/60/R15 on 15" TR rims

now i know the 205/60's are way too small. i'm getting new tires but need a few questions answered first

215/65/15 (26" diameter) stock TR tire size
205/60/15 (24.68" diameter) on car now

215/65 to 205/60 Diameter Difference is 5.08% and tire calculator says speedo
difference is 5.337% too fast which is 63.2 mph compared to 60 mph
but here's the deal my speedo is far more off than that..
my speedo is 10 mph too fast.

did it get farther out of wack with the rear gear change ? or is the vss the problem ? i read somewhere online that since the rear gear is different the whole thing will have to be calculated again with trans gear, rear gear and tire sizes....but i figured this problem has been fixed by someone here by now....
i'm gonna put 235/60's on the rear and leave the 205's on the front
but i'm pretty sure the speedo will still be off even though gnttype.org say the 235/60's are the stock equivalent because its way farther off now than it should be....sorry if i made anyones head hurt with this ....lol