I am not sure if this is the right place to post this but i have a gearing question. I already have a leveling kit and 35's but i will be lifting my truck in the next month or so and i want to regear it from my stock 3.73ls to some 4.56 and i was just wondering what the RPM difference would be and what exactly do gears do for my truck.
thanks a lot.

-Mike

 

by putting on those 35'' tires, you basically increased your axle ratio to a 3.55. in order to compensate for that and to get your truck back to stock performance, you are lowering it to a 4.56, and tires will make it an effective 4.30 or so, a step above stock. they don't make a 4.30 gear, so you got to choose either 4.10 or 4.56. 4.10's will not help performance enough to warrant the cost, so go with the 4.56's. the lift will not change your engine performance any, it is the tires that have already changed the performance. again, your rpm's will pretty close to what they were before you put the tires on, maybe slightly higher. not only will the gears help with the performance/mpg loss from the 35'' tires, they will also aid in protecting the transmission, which is put under an additional strain by the oversize tires. i hoped this helped some! let us know if you need further clarification.

 

WOW thanks a lot minimonster. That helped out a lot. The only thing im still curious about are the stock RPM's. I cant remember the RPM's at stock right now cause its been so long. Do you or anybody know?

 

What was the original tire size? Did you correct the speedo for the 35s?
If you had 255 70R16 tires and 3.73 gears and you go to 35 inch tires and 4.56:1 gears your speedo will indicate about 95% SB 105% of the actual speed. So at 100mph you will only be going 95mph.

Regards

Jean Marc Chartier

EDIT wording of actual speed sentence.

 

the stock rpms won't really matter too much... the regearing rpms will only be slightly above what it was stock. the speedometer will still be somewhat off, if you can deal w/ up to 5mph. my state doesn't even bother to pull anyone over for less than 5mph over, so i'm ok. the best thing to do would be to assess your situation, and whether you want to correct the speedometer. a dealership won't be able to help you due to the rear axle ratio reconfiguration. a chip, custom or canned is the only way to reconfigure.

 

Ok sweet thanks guys. Im not really worried about my speedo too much.

 

You will be when barney pulls you over!