anybody have some evidence of how "optimistic" the 996 speedo is? or has anybody verified against another car?
i have my doubts...

 

GPS verified on my 03 C4S is 3 MPH slower than whats on my speedo

 

Also GPS verified - mine is about 7% fast.

 

3 different gps tests and mine is about 3-5miles faster than the gps.

 

Same here!

 

this iss all great news to read. my car doesn't feel as fast as the speedo suggests.

what would you suggest i do to test accuracy? what gps or other product can i buy/borrow to help me test the accuracy just one time?

 

Mine reads about 1 mph higher than the actual speed for every 15 mph, i.e. at an indicated 60 mph, I am actually only doing 56 mph.

 

mine is dead on.

 

it really depends on the tire profile you have...makes a diff on the top end. You can check speed diff here: http://www.miata.net/garage/tirecalc.html

 

How does this apply I wonder to those speeds into the 3 digit range?
Coming off racing sportbikes and some street machines, the speedo was near accurate until you reached higher speeds. The indicated and actual were off by a lot in some cases.
Say for example that I wanted to locate an isolated area to go play. What would the actual speed be if the indicated was on the other side of 145? Not that I would but if I could.

 

Mine is usually 3-4m.p.h. higher than actual. I asked my service advisor about it and he told me there is a kilometer/mile conversion decrepancy which makes it out of whack, apparently very common and nothing they can do about it. I think it's a royal p.i.t.a. to "mind convert" how fast I'm actually going.

 

you guys need to ask the question if they're running stock wheels/tires or aftermarket

 

Mine is bone stock....

 

bone stock wheels/tires, diff, and tranny.

 

4000 rpm in 6th gear is 174 km/h with F225/R265 18" (winter) and F225/R295 18" (summer) tires