Question..... Speedo accuracy OE & ring pinion change, new calibration needed


HOOKED ON GT

GT Owner
Oct 26, 2006
468
Orlando & Australia
In the midst of 3:90 change and wondering about the current speedo and what we know about its accuracy and how "off" mine will look after the new final drive gets plonked in.
I think GT's read too slow at low "gated community" speeds but maybe pretty accurate at high (at the track) speed?

Stuart
 

DakotaGT

GT Owner
Mark II Lifetime
Dec 9, 2012
1,694
Sioux Falls, South Dakota
You can change this pretty easily with a handheld tuner, typically an SCT tuner (see link below)

 

HOOKED ON GT

GT Owner
Oct 26, 2006
468
Orlando & Australia
I think Torrie can do it?
 

HOOKED ON GT

GT Owner
Oct 26, 2006
468
Orlando & Australia
Hers a cool calculator www.blocklayer.com/rpm-gear.aspx
 

HOOKED ON GT

GT Owner
Oct 26, 2006
468
Orlando & Australia
Jason Heffner did the reinstall of the trans and did the adjustment on the 3:90 and Bridgestones speed calibration and now Id say that my speedo shows say 60mph and my phones "speedo" shows about 63-64mph.
I better make sure I remember this (assuming the phones accurate) as most cars read the other way.
 

Nafod

GT Owner
Mark IV Lifetime
The old fashion way.. Mile marker and stop watch. or your local police neighborhood radar(your driving to fast).
Phone GPS can be close, but then , who makes the phone, how old is it, how many satellites does it see.
I use a new iPad for various utilities, one being worldwide charts and approach plates in a aircraft that cruises at altitude (30k's) and for long periods(2-16 hrs). Most of the time the gps isn't accurate enough to display known location on the iPad. Just depends.
Gear ratios/ final drive/ rear tire measurement and RPM. But you would need an accurate RPM, and my guess is the speedo in the GT with known issues is not that accurate.
I say the dyno setup should be fairly accurate. Jason I'm sure has a dialed in dyno.