Just got this car 3 weeks ago & I thought my Speedo was off. So today I drove by one of those stationary signs that tells you your speed and it said I was doing 32 & my Speedo said I was doing about 40ish. It's an 88 Vert with stock wheels and tires (new 205/60/15) . I did a lot of searching on this site and it basically said that there should be no reason why the speedo is wrong unless you change your gears or different tire size (that's not the issue either). What else could it possibly be? Anythign I can check or adjust? Cars got 69K original miles - got it off of a rich guy who was the original owner so I know he didn't do any rear end mods to it.

any help would be great.

 

The wrong tranny or rear end will result in the speedo being off. So if either was replaced with coupe ones, you could have problems.

Most speedo shops have adapter gears that can be made to properlly calibrate the speedo.

And Mazda's spec on the speed says at maximum it canbe up to +5 MPH at 60 mph and still be within spec.

 

Ive had "sticky" ones before....

My 86 beater actually does this.........if I make a pull from say 80km/hr, I will feel a rise in speed, look down and Im doing 80....80...82.....then it shoots up to about 110..........doesn't go smoothly up and down in conjuction with the car, but Ive never had an inaccuracy problem.

Doesn't sound to be too far off though to me........interesting to know about Mazda's considered spec's for the range on the speedo though......

 

Yeah it can be .5 MPH off low at 60 (displaying 59.5) but display up to 5 MPH high (display 65 at 60 MPH).

Pretty common to read high.

My verts speedo is off progressivly and at 100 MPH it is actually displaying 110, but at 50 mph it is only off by 2 mph (displaying 52 mph).

 

I'll have to see if I can get some history on the car to see if either the tranny or the rear end has been replaced. If not that, I'll have to find a speedo shop in the area to see if anything can be done about it. My guess is that this is a progressive problem and that it's off by some %, but haven't tested it any faster than ~40mph so far. Just seems drastic that it's off by almost 3% ie: doing 33, shows up as ~40mph. So maybe the car has less miles on it than thought????

 

It could just be RX-7 folklore but I hear the speedometer is routinely optimistic in these cars by +10 MPH or more.

Like I said, I can't be sure of the validity of such a statement.

iSP33D-for-J3SUS

 

Mine is also progressively off.
At lower speeds it appears to be fairly accurate.
Around 50mph it starts to get questionable (maybe 5mph off).
Above 60 it can be between 5 and 15 mph optimistic.
At 135 on the speedometer, my handheld gps said about 115mph.

 

I did the same thing in my '88 SE yesterday - drove by radar speed indicator sign - my speedo was about 40 or so & the radar said 35. I have been driving by this particular radar sign several times lately and my speed was always slower by at least 5 mph. So I would say either the radar sign is out of whack(could be) or that my speedo is fast by about 5 mph @ 35 mph. I guess it might help me avoid speeding tickets.... I did get a ticket for 94 mph in a 55 zone once & I thought I was doing about 100. My ride is bone stock on rims & driveline and my Dad bought it new so nothing has been modified to affect my speedo & I'm on new tires... I'll check the radar sign again 'cause it's on the way to the beach & I go there almost everyday.

Ramses666

 

progessively=wheel or differential changed from stock...
always the same amount above or blew, realign your speedo needle, i thought mine was off for a long time, but it just needed moving a wee-bit.

 

How do I realign my speedo needle? Easy or hard?

 

My speedo is off as well, but I have a TII tranny and different size wheels so its to be expected.