JamesWilson
Yoda
Offline
I recently took my Rochdale Olympic for an extended drive and used my SatNav.
I noticed that the speedometer would read ~80 MPH while the SatNav only showed a speed of ~68 MPH. I'm pretty sure the SatNav is correct.
The Rocjdale is a kit car made up of components from varius sources and I really want to reconcile the Speedometer with the true speed.
The car has a 1275 BMC A engine with a 4-speed MG Midget transmission. I believe the differential is a 3.7:1 but cannot be sure of that.
I propose driving it at top gear (a 1:1 ratio through the gearbox) and note the RPM, the Speedometer indicated speed and the true speed from the SatNav.
There's a formula somewhere for determining speed given engine RPM, tire size and gearing, etc. Can anyone direct me to it? I reckon I cna use that to determine what differential is in the car.
But how then do I fix the Speedometer? I don't want to change out any drive gears in the gearbox... Swaping the guage itself would be do-able. But I recal having seen a gizmo that allows a up- or down- gearing that could be fit to the drive cable. Can anyone direct me to those or a vendor?
TIA
James
I noticed that the speedometer would read ~80 MPH while the SatNav only showed a speed of ~68 MPH. I'm pretty sure the SatNav is correct.
The Rocjdale is a kit car made up of components from varius sources and I really want to reconcile the Speedometer with the true speed.
The car has a 1275 BMC A engine with a 4-speed MG Midget transmission. I believe the differential is a 3.7:1 but cannot be sure of that.
I propose driving it at top gear (a 1:1 ratio through the gearbox) and note the RPM, the Speedometer indicated speed and the true speed from the SatNav.
There's a formula somewhere for determining speed given engine RPM, tire size and gearing, etc. Can anyone direct me to it? I reckon I cna use that to determine what differential is in the car.
But how then do I fix the Speedometer? I don't want to change out any drive gears in the gearbox... Swaping the guage itself would be do-able. But I recal having seen a gizmo that allows a up- or down- gearing that could be fit to the drive cable. Can anyone direct me to those or a vendor?
TIA
James