2nd Gen Non-Engine/Transmission gear ratio question

[boilermkr]

I have 3:54 with 305's now and I go down the road at 70 mph at 2000 rpm. I was thinking of going to 4:10 does anyone know what this will do to my mph at 2000 rpm's?. I realize that my speedo is allready off because my truck came with 265's I'm just trying to find out how much it will change

 

[B KIRK]

Try this chart. It should get you close.



Brad

 

[fmj]

boilermkr, if your satisfied with the rpm and the 3:55s then here is a formula that will tell you the gear ratio to go to with the new tires and keep approximately the same rpms.

new tire size/stock tire size=%ratio change x orig gear ratio=new
gear ratio

You can use this or Brads chart. Remember if you use the chart that is for a 1:1 ratio. For overdrive it will be about 15 to 20% less and autos will be higher due to converter slippage.

 

[onestackdram]

Well I can tell you that 4:10's with 255's on a 1 ton @ 2000 rpms' will equal roughly 58-62 mph's and thats it. Be prepared for serious loss of MPG's.



On a side note, 4:10's are only good if you tow A LOT, I mean A LOT. Other wise stay with the 3:54's and when you do tow they can handle it very well. JMHO



Russell

 

[dlange]

I had 3. 55s with 35's. When I switched to 4. 10s I went back to a 3. 55 ratio with the 35's.

 

[fmj]

You guys must be running some tall gears using 3. 55s with 35s. I agree with onestack that 255s and 4:10s run some high rpms. I think they are about 29"tall. My 265s are 30" tall, an with the 3:55s I tack about 2400 in 3rd at 60, and 1800 in O/D doing about 70. That works for me towing and empty respectively. I like towing at 60 and no faster, blowouts above that are scary for an old man. So if you had a 30 tall tire stock and went to a 35 with 3:55s heres the math.

35/30 = 1. 166 x 3. 55 = 4. 14

So if you are satisfied with the rpms and stock tires with 3:55s and are going to a new 35" tire, then 4. 10s are about right to keep the same rpm as you origionally had, assuming you had the same size tire as me. Shorter or taller tires, refigure. Running too low rpms (high gears) while towing, works the engine too much. Running too low of gears, like onestack said kiss off milage. Personal choice, but I think you should keep the rpms no lower than 1800 at highway speeds (whatever that is) and no higher than 2500 towing. My $ . 02 worth.

 

[bmoeller]

here's a calculator-



http://dodgeram.org/tech/specs/axle/rpm_vs_mph.htm

 

[fmj]

Ya gotta love this site. Bmoeller, thats a great link.

 

[PWeber]

4. 10's suck. My 1 ton auto shifts out of first gear within about 1. 5 sec. after starting out. The engine constantly gets right up to the governor and then says "now what?" when driving it.

 

[onestackdram]

Hey Phil,



On a side note, how did that bumper come out?



Russell

 

[JBlock]

Expanded the Table for Dodge OD. ,69

HI



I took the table and copied in to Excell and added overdrive for . 69 ratio. Email for the spread sheet. Lost all the pretty color and formatting copying into the TDR file.









Gear Rato

Tire OD Ratio 0. 69



Diamater 3. 55 3. 73 4. 11

29 1845 1938 2136

30 1783 1873 2064

31 1726 1813 1998

32 1672 1757 1935

33 1621 1704 1877

34 1573 1653 1822

35 1528 1606 1770

36 1486 1561 1720

37 1446 1519 1674

38 1408 1479 1630

39 1372 1441 1588

40 1938 1406 1548

41 1305 1371 1510

42 1274 1339 1475

43 1244 1307 1440

44 1216 1277





I not sure how to attach the spread sheet itself



JOe