switched to 3:90 Diff and speedometer is off
#1
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I switched to a 3:90 diff for my 01 turbo Miata 5 speed and the speedometer seems to be off. It seems that I am going faster than the speedometer indicates.
Does anyone know a fix?
Is there a formula to figure out how fast I am actually going?
Thank you,
Greg
Does anyone know a fix?
Is there a formula to figure out how fast I am actually going?
Thank you,
Greg
#11
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If your speedo is spot-on then you are de facto calculating the number of tire rotations per mile accurately. Your odometer is likewise reading correctly. And if one was off, both would be off by the same measure.
#12
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*Pretty sure I've got this right, but I've been wrong before*
#14
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I really like the new diff. 1st gear is much more usable and the car revs lower on the highways. I did the swap primarily for the track. I will be going to VIR on 7/2, which will be my first time with this turbo Miata. I can't wait to see how it does.
My last turbo Miata, a silver 1991, caught on fire on the track at VIR last december. I'm hoping for a bit better results this time around!
I'm looking for a higher top on the back straight at VIR. With my 1991 turbo Miata, I was redlining around 122 or so in 5th. I want more!![](https://www.miataturbo.net/images/smilies/smile.gif)
I see we have something in common other than Miatas. I own Pool Cues and Billiard Supplies at Discount Prices.
Are you going to the BCA? If so, let me know. Perhaps we can meet for a drink.
Greg Savoie
My last turbo Miata, a silver 1991, caught on fire on the track at VIR last december. I'm hoping for a bit better results this time around!
I'm looking for a higher top on the back straight at VIR. With my 1991 turbo Miata, I was redlining around 122 or so in 5th. I want more!
![](https://www.miataturbo.net/images/smilies/smile.gif)
I see we have something in common other than Miatas. I own Pool Cues and Billiard Supplies at Discount Prices.
Are you going to the BCA? If so, let me know. Perhaps we can meet for a drink.
Greg Savoie
#20
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Speedos in Miatas are long noted for reading high, this is easily checked instantaneously via GPS. What's more difficult is the odometer, which is best checked over a longer distance to expose minute error that presents itself on a larger scale over longer distances, and may not be obvious using mile markers on the freeway.