Sherman speed

[tf15pin]

Does anyone know why the m4 shermans have a top speed of 25mph and the fireflys have a top speed of 20mph?

A lazy search (Wiki) showed that the m4's had a top speed between 25 and 30 mph and the firefly's top speed was stated as 25 mph. So the firefly might have been built on one of the slower m4 chassis but 20mph seems a little out of range.

Does anyone have a primary source that says what the firefly's top on-road and cross-country speeds were?

[SmokinLoon]

I know this inst exactly what you want, but here is the inital data.  I couldnt find the gear ratios.    Source:  http://www.tarrif.net/  (I HIGHLY recommend this site for gv data reference!!!)

I dont have a primary source handy. FYI: I just reference a few other online sources and they all give the Firefly a 25mph top sped.  However, that doesnt mean it is "official".  It could be a situation of the dreaded "copy n paste" data transfer that shouldnt have been.

M4A3

Engine Name: Ford GAA
Coolant : Water
Cylinders: V-8
Capacity: 18 Liters
Power : 450 hp @ 2600 rpm
Power / Weight Ratio : 13.92 hp per tonne
Transmission : Synchromesh
Gears : 5 Forward / 1 Reverse
 
Sherman VC "Firefly"

Engine Name: Chrysler Multibank A57
Coolant : Water
Cylinders: I-5
Capacity: 20.5 Liters
Power : 425 hp @ 2850 rpm
Power / Weight Ratio : 13 hp per tonne
Transmission : Synchromesh
Gears : 5 Forward / 1 Reverse