Well tell me if I am right? If my speedo is off that much wouldnt I notice a difference at other speeds also? I dont know much about how the speedo works.

 

well, what they're talking about, is the faster you go, the more inaccurate the speedometer can be.
But at slower (legal) speeds, it would be close to the real speed.
It gradually will be off by a few more mph the faster you go.

 

If you want a better idea of your speed, use the tacho instead. It’s not perfect either, but it’ll be a lot closer to reality at high speed than the speedo will.

Find the gear and diff ratios for your car, and measure the rolling radius of the rear wheels in millimetres (measure between the ground and the wheel centreline, don’t measure the width and halve it!), then use this formula:

(rpm x radius) ÷ (gear ratio x diff ratio x 4244) = speed in mph

For speed in km/h, replace 4244 with 2653.

So for a Turbo in 5th (0.762:1 gear, 4.1:1 diff) @ 4000rpm with stock 300mm radius tyres:

(4000 x 300) ÷ (0.762 x 4.1 x 4244) = 90.5 mph

For gz91rx7, redline in 4th:

(7000 x 300) ÷ (1.0 x 4.1 x 4244) = 120.7 mph

 

If you really want to know how accurate your speed is find one of those things that the police set up that tells you your speed. I went by one at 70 on my speedo, and the sign said 63.

 

I believe series 4 and series 5 TURBO II manual transmissions are geared the same. They are the same transmissions. Gearing is the same.

Anyone want to argue that?

Cuz if not, then how in the hell is a Series 5 have a higher MPH @ 7K than a Series 4 MPH @ 7K???? That would make no sense if the gearing is the same, regardless of Horspower b/c it wouldn't matter.

That's like saying a 2 1/2 inch exhaust outflows a mirrored 2 1/2 inch exhaust. lol.

Duh!

 

Well, almost ALL RWD trannies have a 1:1 4th gear - there are a couple exceptions, but as a general rule, if you pull the stick back to go into 4th then 4th gear is 1:1. So the trannys are the same in that respect