Formula used- rpm x tire diameter / 336 x trans gear ratio x axle gear ratio = mph ==================================================== 1st gear at 600rpm... Bronco- ZF + 29" tire + 3.55 axle = 2.6 mph r2.6 ZF + 31.5 tire + 3.55 axle = 2.8 mph r2.8 ZF + 31.5 tire + 3.73 axle = 2.7 mph r2.7 '75 F150- T18 + 31.5 tire +3.50 axle = 2.5 mph r2.2 T18 + 31.5 tire +3.25 axle = 2.7 mph r2.3 ZF 1st = 5.72 = r5.72 T18 1st = 6.32 ~ r7.44 +.60 ---------------------------------------------------- 2nd gear at 600rpm... Bronco- ZF + 29" tire + 3.55 axle = 4.96 mph <--free Daytona's, acts too low geared everywhere else :/ ZF + 31.5 tire + 3.55 axle = 5.39 mph <--feels a little bit too tall geared from a dead stop ZF + 31.5 tire + 3.73 axle = 5.12 mph <--gonna try this with a new True-Trac :) '75 F150- T18 + 31.5 tire +3.50 axle = 5.2 mph <--feels good from a stop and crossing an intersection :) T18 + 31.5 tire +3.25 axle = 5.6 mph <--old setup, felt too tall geared here and 2nd to 3rd :/ F250 parts truck- ZF + 31.5 tire + 4.10 axle = 4.7 mph <--stock, felt way too slow but good when loaded/towing? ZF 2nd = 2.94 T18 2nd = 3.09 +.15 Mazda 1st = 3.91 Mazda 2nd = 2.24 Mazda 5 speed close ratio- Mazda + 1st + 29" + 3.55 = 3.7 mph Mazda + 1st + 30.5 + 3.55 = 3.9 mph Mazda + 2nd + 29" + 3.55 = 6.5 mph Mazda + 2nd + 30.5 + 3.55 = 6.9 mph ---------------------------------------------------- 3rd gear at 3200rpm... Bronco- ZF + 29" tire + 3.55 axle = 48 mph ZF + 31.5 tire + 3.55 axle = 53 mph ZF + 31.5 tire + 3.73 axle = 50 mph '75 F150- T18 + 31.5 tire +3.50 axle = 51 mph T18 + 31.5 tire +3.25 axle = 54 mph ZF 3rd gear = 1.61 T18 3rd gear = 1.69 +.08 3500rpm = 55 mph, T18 3rd gear + 31.5" + 3.50 4000rpm = 63 mph, T18 3rd gear + 31.5" + 3.50 4500rpm = 71 mph, T18 3rd gear + 31.5" + 3.50 ---------------------------------------------------- 4th gear at 2600 rpm... Bronco + Ford 8.8" ZF + 29" tire + 3.55 axle = 63.2 <--same as '91 F150 with E4OD, too low geared ZF + 31.5 tire + 3.55 axle = 68.7 <--needs 8t/19t speeodmeter gears ZF + 31.5 tire + 3.73 axle = 65.3 <--needs 8t/20t speeodmeter gears ZF + ~30" tire + 3.55 axle = 65.4 <--Bronco's original "stock like gearing" '75 F150 + Ford9inch T18 + 31.5 tire +3.50 axle = 69.6 <--new setup, good in town and ok on the highway :) T18 + 31.5 tire +3.25 axle = 75.0 <--old setup, good gas milage on the highway :) ZF + 31.5 tire + 4.10 axle = 59.5 <--'90 F250 speedometer gearing: tan= 19t yellow= 7t 4th = 1.0 ;) ---------------------------------------------------- Overdrive at 2600 rpm... Bronco- ZF + 29" tire + 3.55 axle = 83 mph ZF + 31.5" tire + 3.55 axle = 90 mph ZF + 31.5" tire + 3.73 axle = 86 mph ZF + 31.5" tire + 3.90 axle = 82 mph F250 parts truck- ZF + 31.5" tire + 4.10 axle = 78 mph '91-F150 /E4OD + 29" + 3.55 = 89 mph ZF 5th = 0.76 E4OD 4th = 0.71 (locked up) ==================================================== Tire sizes... 235/75-15's = 29" 7" wheel 31x10.5-15's = 30.5" 9" wheel <--like a worn out 31.5" 235/85-16's = 31.5" 7" wheel <--'75 F150 265/75-16's = 31.5" 8" wheel <--'91 Bronco 255/85-16's = 33" 8" wheel H/78-15's = 28.5"+'75 F150 <--they came new on 5+1/2" wheels and were squirrely as hell! :( pi x diameter = circumference ---------------------------------------------------- Gear ratios... 1st 2nd 3rd 4th 5th -R- T18 =========== 6.32 3.09 1.69 1.00 ==== r7.44 ZF M5OD-HD ==== 5.72 2.94 1.61 1.00 0.76 r5.24 Mazda M5OD-R2 = 3.91 2.24 1.49 1.00 0.80 r3.39 NP435 ========= 6.69 3.34 1.74 1.00 ==== r8.26 E4OD ========== 2.71 1.53 1.00 ==== 0.71 r2.18 Clark282V ===== 6.99 4.09 2.17 1.17 1.00 r5.89 NV 4500 ======= 5.61 3.04 1.67 1.00 0.73 r5.61 T19 = http://www.novak-adapt.com/images/graphics/t19_specs_gasket.gif ====================================================