Gears to MPH conversion

[Makdaddymac]

hey all, got some 3.73's in with a t-5 swap....

so i did have 2.73's with a aod speedo tooth(it works in the t-5 dispite what some say) i know its off but i dont know how bad.....
can anyone convert some mph for me....
basically a (white)aod tranny gear/tooth with 3.73's........doesnt seem to off but idk and want to be safe

so what RPM = what MPH

or what MPH = what real mph....

also have the 80mph speedo if that matters

 

[5.0Torx]

there are plenty of gear calculators online that you can fiddle with to your hearts content.

another way to do it is to drive an indicated 60 mph (set the cc) and get a stopwatch to time how long it actually takes to cover a mile (which is marked on the highway). if it takes 70 seconds to cover a mile, you do 70/60 = 1.16666666666. take the number of teeth currently on your speedo gear and multiply it by 1.166666666666666 to get the number of teeth you should have. More than likely youll get some crazy fraction (like 24.345698743 teeth) in which case youll have to round up or round down (in this case, 24 would be better than 25).

just my 2 cents

 

[Makdaddymac]

ok quick question,

what is my tire diameter roughly i have the turbines with 16/45/255....
also transmission ratio and transcase?? ratio???

 

[5.0Torx]

lol, again, most of this is available online, but ill be a nice guy and help you out

The best way to check tire diameter, actually, is to go out and measure it yourself. Different manufacturers have different definiteions for what a milimeter is, it seems. One guys 275 is anothers 285. In an ideal world, though, a 255/45/16 is 25.035" in diameter. Standard 225/55/16 tires are 25.7", so youre a little shorter than stock.

You say you have turbines....arent those 15"??? I dont know, my car had ponies when i got it.

Just going off of memory here, i beleive for a T5
1st - 3.35:1
2 - 1.99
3 - 1.33
4 - 1
5 - .675

with those gears, those tires, and 3.73s you go
1st gear - 5.96 mph per 1000 rpm
2nd - 10.03
3rd - 15.01
4th - 19.97
5th - 29.58

with those tires, thsoe gears, and 2.73s, the numbers change to
1st gear - 8.14 mph per 1000 rpm
2nd - 13.71
3rd - 20.51
4th - 27.28
5th - 40.42

so if you want to know what speed youre going in fifth at 2500 rpm, you multiply by (2500/1000) which equals 2.5. so with the 2.73s at 2500 rpm youre going about 100 mph. the 3.73s would put you at about 75.

Hope this helps

(and get a gear calculator! lol)

 

[5.0Torx]

you can also manipulate the gear ratios any way you want.

for example, just working within your 3.73 vs 2.73 scenario.

2.73 / 3.73 = .73xxxxx

(2.73/3.73) * 8.14 = 5.96

the 8.14 is the speed in first at 1000 rpm with 2.73s. by using our 73% multiplier, we got the 5.96 mph at 1000 rpm with 3.73s!

so now you can play with 3.08, 3.27, 3.55, 4.88 all you want. yippeeee!

 

[habiv]

This calculator is much easier

Ford Mustang: Mustang Tech: Calculators & Decoders: RPM Calculator