I've been playing with a calculator to figure rpm at a given speed, trying to figure what rearend gear I want BEFORE i buy one. I'm hoping maybe some one could check this see if I've missed something or made a mistake. Thanks for any help. Speed 70 mph Tire 26.5 in. Trans gear ratio .5:1 Rear gear 3.70 RPM 1642 If I change rear gear to 4.0 I get 1776 rpm Does this sound right??
I've got 215/70s or something like that and they're right around 26" measured. Your math works, though. If I had a .5 OD gear, I'd get 4.30s or something, but that's me.
You are correct [ within a decimal point ] with your maths. looking at the ratios you're using a T56 6speed with a 0.5 O/D 6th. Here's something to scare all you fellow "H.A.M.Bers"....... a math lesson MPH x 336 x Overall Ratio divided by Tire Diameter [ inches ] = RPM or RPM x Tire Diameter divided by Overall Ratio divided by 336 = MPH or RPM x Tire Diameter divided by MPH divided by 336 = Overall Ratio simple with a calculator [even if truancy was the best subject at skool]
Go to this site www.et-studios.com/motorsports/gears/gears.html put in information as to tire size, ****** ratios
Thanks guys. It is indeed a T56, the tire dia. is pretty close to what stated, and I'm leaning towards a 4.11 gear, which would give 1823 rpm at 70mph
there are several site on the internet that will calculate what you need.That .5-1 final drive sounds tall.Are ya sure about those#'s? R~R
Another check I like to do is look at the overall gear ratio in 1st gear. Many of the newer transmissions start to get a "gear bound" feel and do not want to come out of 1st if that number gets too high - say like over 11. Most Tremecs don't like to shift much above 6500 RPM. It looks like most T56s with the .5 OD have a 2.66 1st gear, so your 4.11s look OK. However if you happen to have a T56 with a 3.27 1st gear - not so much. Make sure you look at the transmission tag and look up the gear chart based on the model number. The T56s come in a bunch of configurations.
<TABLE cellSpacing=1 cellPadding=1 width=505 border=0><TBODY><TR><TD align=middle width=92 bgColor=#cccccc rowSpan=2>TREMEC Part Number </TD><TD align=middle width=59 bgColor=#cccccc rowSpan=2>Weight (lbs) </TD><TD align=middle width=63 bgColor=#cccccc rowSpan=2>Torque Cap. (lbs-ft) </TD><TD align=middle width=59 bgColor=#cccccc rowSpan=2>GVW (lbs) </TD><TD vAlign=center align=middle width=182 bgColor=#cccccc colSpan=7>Gear Ratio Chart </TD></TR><TR><TD vAlign=center align=middle bgColor=#cccccc>1st </TD><TD vAlign=center align=middle bgColor=#cccccc>2nd </TD><TD vAlign=center align=middle bgColor=#cccccc>3rd </TD><TD vAlign=center align=middle bgColor=#cccccc>4th </TD><TD vAlign=center align=middle bgColor=#cccccc>5th </TD><TD vAlign=center align=middle bgColor=#cccccc>6th </TD><TD vAlign=center align=middle bgColor=#cccccc>Rev </TD></TR><TR><TD align=middle bgColor=#ffffcc>1386-000-003 </TD><TD align=middle bgColor=#ffffcc>129 </TD><TD align=middle bgColor=#ffffcc>330 </TD><TD align=middle bgColor=#ffffcc>3,460 </TD><TD align=middle bgColor=#ffffcc>2.66 </TD><TD align=middle bgColor=#ffffcc>1.78 </TD><TD align=middle bgColor=#ffffcc>1.3 </TD><TD align=middle bgColor=#ffffcc>1.00 </TD><TD align=middle bgColor=#ffffcc>0.74 </TD><TD align=middle bgColor=#ffffcc>0.5 </TD><TD align=middle bgColor=#ffffcc>2.9 </TD></TR><TR><TD align=middle bgColor=#cccccc>1386-000-006 </TD><TD align=middle bgColor=#cccccc>129 </TD><TD align=middle bgColor=#cccccc>350 </TD><TD align=middle bgColor=#cccccc>3,327 </TD><TD align=middle bgColor=#cccccc>3.36 </TD><TD align=middle bgColor=#cccccc>2.07 </TD><TD align=middle bgColor=#cccccc>1.35 </TD><TD align=middle bgColor=#cccccc>1.00 </TD><TD align=middle bgColor=#cccccc>0.8 </TD><TD align=middle bgColor=#cccccc>0.62 </TD><TD align=middle bgColor=#cccccc>3.28 </TD></TR><TR><TD align=middle bgColor=#ffffcc>1386-000-007 </TD><TD align=middle bgColor=#ffffcc>129 </TD><TD align=middle bgColor=#ffffcc>350 </TD><TD align=middle bgColor=#ffffcc>3,327 </TD><TD align=middle bgColor=#ffffcc>2.97 </TD><TD align=middle bgColor=#ffffcc>2.07 </TD><TD align=middle bgColor=#ffffcc>1.43 </TD><TD align=middle bgColor=#ffffcc>1.00 </TD><TD align=middle bgColor=#ffffcc>0.8 </TD><TD align=middle bgColor=#ffffcc>0.62 </TD><TD align=middle bgColor=#ffffcc>3.28 </TD></TR><TR><TD align=middle bgColor=#cccccc>1386-000-011 </TD><TD align=middle bgColor=#cccccc>115-129 </TD><TD align=middle bgColor=#cccccc>450 </TD><TD align=middle bgColor=#cccccc>3,327 </TD><TD align=middle bgColor=#cccccc>2.97 </TD><TD align=middle bgColor=#cccccc>2.07 </TD><TD align=middle bgColor=#cccccc>1.43 </TD><TD align=middle bgColor=#cccccc>1.00 </TD><TD align=middle bgColor=#cccccc>0.8 </TD><TD align=middle bgColor=#cccccc>0.62 </TD><TD align=middle bgColor=#cccccc>3.28 </TD></TR><TR><TD align=middle bgColor=#ffffcc>1386-000-012 </TD><TD align=middle bgColor=#ffffcc>115-129 </TD><TD align=middle bgColor=#ffffcc>450 </TD><TD align=middle bgColor=#ffffcc>3,260 </TD><TD align=middle bgColor=#ffffcc>2.97 </TD><TD align=middle bgColor=#ffffcc>2.07 </TD><TD align=middle bgColor=#ffffcc>1.43 </TD><TD align=middle bgColor=#ffffcc>1.00 </TD><TD align=middle bgColor=#ffffcc>0.8 </TD><TD align=middle bgColor=#ffffcc>0.62 </TD><TD align=middle bgColor=#ffffcc>3.28 </TD></TR><TR><TD align=middle bgColor=#cccccc>1386-000-016 </TD><TD align=middle bgColor=#cccccc>115-129 </TD><TD align=middle bgColor=#cccccc>450 </TD><TD align=middle bgColor=#cccccc>3,327 </TD><TD align=middle bgColor=#cccccc>2.66 </TD><TD align=middle bgColor=#cccccc>1.78 </TD><TD align=middle bgColor=#cccccc>1.3 </TD><TD align=middle bgColor=#cccccc>1.00 </TD><TD align=middle bgColor=#cccccc>0.74 </TD><TD align=middle bgColor=#cccccc>0.5 </TD><TD align=middle bgColor=#cccccc>2.9 </TD></TR><TR><TD align=middle bgColor=#ffffcc>1386-000-017 </TD><TD align=middle bgColor=#ffffcc>115-129 </TD><TD align=middle bgColor=#ffffcc>450 </TD><TD align=middle bgColor=#ffffcc>3,327 </TD><TD align=middle bgColor=#ffffcc>2.66 </TD><TD align=middle bgColor=#ffffcc>1.78 </TD><TD align=middle bgColor=#ffffcc>1.3 </TD><TD align=middle bgColor=#ffffcc>1.00 </TD><TD align=middle bgColor=#ffffcc>0.74 </TD><TD align=middle bgColor=#ffffcc>0.5 </TD><TD align=middle bgColor=#ffffcc>2.9 </TD></TR><TR><TD align=middle bgColor=#cccccc>1386-000-018 </TD><TD align=middle bgColor=#cccccc>115-129 </TD><TD align=middle bgColor=#cccccc>450 </TD><TD align=middle bgColor=#cccccc>3,460 </TD><TD align=middle bgColor=#cccccc>2.66 </TD><TD align=middle bgColor=#cccccc>1.78 </TD><TD align=middle bgColor=#cccccc>1.3 </TD><TD align=middle bgColor=#cccccc>1.00 </TD><TD align=middle bgColor=#cccccc>0.74 </TD><TD align=middle bgColor=#cccccc>0.5 </TD><TD align=middle bgColor=#cccccc>2.9 </TD></TR><TR><TD align=middle bgColor=#ffffcc>1386-000-019 </TD><TD align=middle bgColor=#ffffcc>115 </TD><TD align=middle bgColor=#ffffcc>390 </TD><TD align=middle bgColor=#ffffcc>3,223 </TD><TD align=middle bgColor=#ffffcc>2.66 </TD><TD align=middle bgColor=#ffffcc>1.78 </TD><TD align=middle bgColor=#ffffcc>1.3 </TD><TD align=middle bgColor=#ffffcc>1.00 </TD><TD align=middle bgColor=#ffffcc>0.74 </TD><TD align=middle bgColor=#ffffcc>0.5 </TD><TD align=middle bgColor=#ffffcc>2.9 </TD></TR><TR><TD align=middle bgColor=#cccccc>1386-000-020 </TD><TD align=middle bgColor=#cccccc>115-129 </TD><TD align=middle bgColor=#cccccc>450 </TD><TD align=middle bgColor=#cccccc>3,327 </TD><TD align=middle bgColor=#cccccc>2.66 </TD><TD align=middle bgColor=#cccccc>1.78 </TD><TD align=middle bgColor=#cccccc>1.3 </TD><TD align=middle bgColor=#cccccc>1.00 </TD><TD align=middle bgColor=#cccccc>0.74 </TD><TD align=middle bgColor=#cccccc>0.5 </TD><TD align=middle bgColor=#cccccc>2.9 </TD></TR><TR><TD align=middle bgColor=#ffffcc>1386-000-021 </TD><TD align=middle bgColor=#ffffcc>115-129 </TD><TD align=middle bgColor=#ffffcc>450 </TD><TD align=middle bgColor=#ffffcc>3,968 </TD><TD align=middle bgColor=#ffffcc>2.66 </TD><TD align=middle bgColor=#ffffcc>1.78 </TD><TD align=middle bgColor=#ffffcc>1.3 </TD><TD align=middle bgColor=#ffffcc>1.00 </TD><TD align=middle bgColor=#ffffcc>0.79 </TD><TD align=middle bgColor=#ffffcc>0.63 </TD><TD align=middle bgColor=#ffffcc>2.9 </TD></TR><TR><TD align=middle bgColor=#cccccc>1386-000-022 </TD><TD align=middle bgColor=#cccccc>138 </TD><TD align=middle bgColor=#cccccc>350 </TD><TD align=middle bgColor=#cccccc>3,400 </TD><TD align=middle bgColor=#cccccc>2.66 </TD><TD align=middle bgColor=#cccccc>1.78 </TD><TD align=middle bgColor=#cccccc>1.3 </TD><TD align=middle bgColor=#cccccc>1.00 </TD><TD align=middle bgColor=#cccccc>0.74 </TD><TD align=middle bgColor=#cccccc>0.5 </TD><TD align=middle bgColor=#cccccc>2.9 </TD></TR><TR><TD align=middle bgColor=#ffffcc>1386-000-023 </TD><TD align=middle bgColor=#ffffcc>119 </TD><TD align=middle bgColor=#ffffcc>375 </TD><TD align=middle bgColor=#ffffcc>3,223 </TD><TD align=middle bgColor=#ffffcc>2.66 </TD><TD align=middle bgColor=#ffffcc>1.78 </TD><TD align=middle bgColor=#ffffcc>1.3 </TD><TD align=middle bgColor=#ffffcc>1.00 </TD><TD align=middle bgColor=#ffffcc>0.74 </TD><TD align=middle bgColor=#ffffcc>0.5 </TD><TD align=middle bgColor=#ffffcc>2.9 </TD></TR><TR><TD align=middle bgColor=#cccccc>1386-000-024 </TD><TD align=middle bgColor=#cccccc>119 </TD><TD align=middle bgColor=#cccccc>375 </TD><TD align=middle bgColor=#cccccc>3,223 </TD><TD align=middle bgColor=#cccccc>2.66 </TD><TD align=middle bgColor=#cccccc>1.78 </TD><TD align=middle bgColor=#cccccc>1.3 </TD><TD align=middle bgColor=#cccccc>1.00 </TD><TD align=middle bgColor=#cccccc>0.74 </TD><TD align=middle bgColor=#cccccc>0.5 </TD><TD align=middle bgColor=#cccccc>2.9 </TD></TR><TR><TD align=middle bgColor=#ffffcc>1386-000-025 </TD><TD align=middle bgColor=#ffffcc>115 </TD><TD align=middle bgColor=#ffffcc>385 </TD><TD align=middle bgColor=#ffffcc>3,400 </TD><TD align=middle bgColor=#ffffcc>2.97 </TD><TD align=middle bgColor=#ffffcc>2.07 </TD><TD align=middle bgColor=#ffffcc>1.43 </TD><TD align=middle bgColor=#ffffcc>1.00 </TD><TD align=middle bgColor=#ffffcc>0.84 </TD><TD align=middle bgColor=#ffffcc>0.56 </TD><TD align=middle bgColor=#ffffcc>2.9 </TD></TR><TR><TD align=middle bgColor=#cccccc>TNET1077 </TD><TD align=middle bgColor=#cccccc>115-129 </TD><TD align=middle bgColor=#cccccc>415 </TD><TD align=middle bgColor=#cccccc>3,260 </TD><TD align=middle bgColor=#cccccc>2.97 </TD><TD align=middle bgColor=#cccccc>1.78 </TD><TD align=middle bgColor=#cccccc>1.3 </TD><TD align=middle bgColor=#cccccc>1.00 </TD><TD align=middle bgColor=#cccccc>0.74 </TD><TD align=middle bgColor=#cccccc>0.5 </TD><TD align=middle bgColor=#cccccc>2.9 </TD></TR><TR><TD align=middle bgColor=#ffffcc>TNET1247 </TD><TD align=middle bgColor=#ffffcc>108 </TD><TD align=middle bgColor=#ffffcc>450 </TD><TD align=middle bgColor=#ffffcc>3,460 </TD><TD align=middle bgColor=#ffffcc>2.66 </TD><TD align=middle bgColor=#ffffcc>1.78 </TD><TD align=middle bgColor=#ffffcc>1.3 </TD><TD align=middle bgColor=#ffffcc>1.00 </TD><TD align=middle bgColor=#ffffcc>0.74 </TD><TD align=middle bgColor=#ffffcc>0.5 </TD><TD align=middle bgColor=#ffffcc>2.9 </TD></TR><TR><TD align=middle bgColor=#cccccc>TUET1576 </TD><TD align=middle bgColor=#cccccc>115 </TD><TD align=middle bgColor=#cccccc>415 </TD><TD align=middle bgColor=#cccccc>3,968 </TD><TD align=middle bgColor=#cccccc>2.66 </TD><TD align=middle bgColor=#cccccc>1.78 </TD><TD align=middle bgColor=#cccccc>1.3 </TD><TD align=middle bgColor=#cccccc>1.00 </TD><TD align=middle bgColor=#cccccc>0.79 </TD><TD align=middle bgColor=#cccccc>0.63 </TD><TD align=middle bgColor=#cccccc>2.9 </TD></TR><TR><TD align=middle bgColor=#ffffcc>TUET1660 </TD><TD align=middle bgColor=#ffffcc>137 </TD><TD align=middle bgColor=#ffffcc>350 </TD><TD align=middle bgColor=#ffffcc>3,400 </TD><TD align=middle bgColor=#ffffcc>2.66 </TD><TD align=middle bgColor=#ffffcc>1.78 </TD><TD align=middle bgColor=#ffffcc>1.3 </TD><TD align=middle bgColor=#ffffcc>1.00 </TD><TD align=middle bgColor=#ffffcc>0.74 </TD><TD align=middle bgColor=#ffffcc>0.5 </TD><TD align=middle bgColor=#ffffcc>2.9 </TD></TR><TR><TD align=middle bgColor=#cccccc>TUET1694 </TD><TD align=middle bgColor=#cccccc>115-129 </TD><TD align=middle bgColor=#cccccc>450 </TD><TD align=middle bgColor=#cccccc>3,260 </TD><TD align=middle bgColor=#cccccc>2.66 </TD><TD align=middle bgColor=#cccccc>1.78 </TD><TD align=middle bgColor=#cccccc>1.3 </TD><TD align=middle bgColor=#cccccc>1.00 </TD><TD align=middle bgColor=#cccccc>0.79 </TD><TD align=middle bgColor=#cccccc>0.63 </TD><TD align=middle bgColor=#cccccc>2.9 </TD></TR><TR><TD align=middle bgColor=#ffffcc>TUET1806 </TD><TD align=middle bgColor=#ffffcc>115-129 </TD><TD align=middle bgColor=#ffffcc>550 </TD><TD align=middle bgColor=#ffffcc>3,460 </TD><TD align=middle bgColor=#ffffcc>2.66 </TD><TD align=middle bgColor=#ffffcc>1.78 </TD><TD align=middle bgColor=#ffffcc>1.3 </TD><TD align=middle bgColor=#ffffcc>1.00 </TD><TD align=middle bgColor=#ffffcc>0.74 </TD><TD align=middle bgColor=#ffffcc>0.5 </TD><TD align=middle bgColor=#ffffcc>2.9 </TD></TR><TR><TD align=middle bgColor=#cccccc>TUET1259 </TD><TD align=middle bgColor=#cccccc>115-129 </TD><TD align=middle bgColor=#cccccc>450 </TD><TD align=middle bgColor=#cccccc>3,260 </TD><TD align=middle bgColor=#cccccc>2.97 </TD><TD align=middle bgColor=#cccccc>2.07 </TD><TD align=middle bgColor=#cccccc>1.43 </TD><TD align=middle bgColor=#cccccc>1.00 </TD><TD align=middle bgColor=#cccccc>0.8 </TD><TD align=middle bgColor=#cccccc>0.62 </TD><TD align=middle bgColor=#cccccc>3.28 </TD></TR><TR><TD align=middle bgColor=#ffffcc>TUET1260 </TD><TD align=middle bgColor=#ffffcc>115-129 </TD><TD align=middle bgColor=#ffffcc>450 </TD><TD align=middle bgColor=#ffffcc>3,260 </TD><TD align=middle bgColor=#ffffcc>2.97 </TD><TD align=middle bgColor=#ffffcc>2.07 </TD><TD align=middle bgColor=#ffffcc>1.43 </TD><TD align=middle bgColor=#ffffcc>1.00 </TD><TD align=middle bgColor=#ffffcc>0.8 </TD><TD align=middle bgColor=#ffffcc>0.62 </TD><TD align=middle bgColor=#ffffcc>3.28 </TD></TR><TR><TD align=middle bgColor=#cccccc>TUET1452 </TD><TD align=middle bgColor=#cccccc>115 </TD><TD align=middle bgColor=#cccccc>385 </TD><TD align=middle bgColor=#cccccc>3,223 </TD><TD align=middle bgColor=#cccccc>2.66 </TD><TD align=middle bgColor=#cccccc>1.78 </TD><TD align=middle bgColor=#cccccc>1.3 </TD><TD align=middle bgColor=#cccccc>1.00 </TD><TD align=middle bgColor=#cccccc>0.74 </TD><TD align=middle bgColor=#cccccc>0.54 </TD><TD align=middle bgColor=#cccccc>2.9 </TD></TR><TR><TD align=middle bgColor=#ffffcc>TUET1453 </TD><TD align=middle bgColor=#ffffcc>115 </TD><TD align=middle bgColor=#ffffcc>385 </TD><TD align=middle bgColor=#ffffcc>3,223 </TD><TD align=middle bgColor=#ffffcc>2.66 </TD><TD align=middle bgColor=#ffffcc>1.78 </TD><TD align=middle bgColor=#ffffcc>1.3 </TD><TD align=middle bgColor=#ffffcc>1.00 </TD><TD align=middle bgColor=#ffffcc>0.74 </TD><TD align=middle bgColor=#ffffcc>0.5 </TD><TD align=middle bgColor=#ffffcc>2. </TD></TR></TBODY></TABLE>
Don't over look the torque range in which your engine runs, and don't figure on good gas milage just because of the low rpm at 70 mph. If your engine torque is to low in overdrive, your foot will be deep into the throttle just to keep up with traffic. Wind drag is terrible at 70 mph, so figure that in as well. Gear it so the engine runs in its sweet spot, not the lowest rpm you can get. Joe
Here is a cool speed calculator I like - you can change the ****** grear ratio to match you overdrive if you wish http://vexer.com/automotive-tools/speed-rpm-calculator
I don't seem to have a tag, but I know I have a .5 6th gear, and from your chart it looks like all .5 6ths have 2.66 1st. So that sounds good too. Can you explain overall gear ratio for me?
Not sure what you mean by sweet spot, I ***ume where torque and hp are highest, which is usually quite high in the rpm range. I wouldn't think thats where I want to be for highway travelling. Rather that a low RPM would be the ticket, remember I can always gear down, but at 70 things seem to flow along smoothly without any need for drastic acceleration. Just sifting along like
Overall gear ratio = trans ratio x rear axle ratio. So if you do have a 2.66:1 first trans gear and run a 4.11 rear gear, in first gear your overall ratio is 2.66 x 4.11 = 10.93. Use that in a gear calculator and you can figure RPM and MPH in 1st gear. Work one out for all trans gears and you can get a feel of how driveable it might be at average RPMs based on the torque band of the engine and not just max RPMs.
You don't want it buzzing along at peak torque, but you also don't want it bogging down while trying to run at highway speeds. A friend of mine has a .68 OD T-5 in his '66 Mustang along with a 2.73 rear end. He has a 306 with a 224/232* cam with 112 lsa, not a wimp but not radical either. In that car, even with 25" tall tires, fifth gear is completely useless. At 75mph it will buck and sputter until you put it back into fourth. Find an RPM where your car is comfortable and reacts well to tip-in throttle. That RPM is what you should gear toward.
The Jalopy Journal
