ok i have a little misunderstanding about gear ratios. ive got 3.55 gears, now the higher the number the more turns of the drive shaft it takes to turn the wheel one full turn correct? there fore the higher the number the lower the gears? so could i go with 3.73's and correct a little bit of the difference in the speedo with the tires on there being bigger than the original tire size?

 

that 'bout sums it up

 

That sums it up and NO!!!

You don't change your gear ratio to fix your speedo. You change the gear on your speedo to match your gear ratio...or best fix yet, buy yourself a gps for your car, it will tell you how fast you are going and then learn to adjust...much easier and much cheaper.

You change your gear ratio for more power w/big tires, or the other way thinking that you'll gain enough economy to pay for the the change (you usually don't).

I'm not sure that Ford makes a 3.73 and there is very little dif between it and 3.55.

 

The difference between 55's and 73's arent worth the cost of the swap. I did the swap years ago on a mustang. But me and another guy swapped rear ends, so cost was only couple hours of time. I did notice a difference but woulda been PISSED if, I woulda bought gears, and paid to have them installed.

 

well i am having to replace the rear anyway, but i went ahead and ordered the 55's just because thats what came on my truck. I wasnt saying i was going to i was just making sure all these years of thinking the higher the number the lower the gears i was correct. But ford does make 3.73's they put them on some of the 150's if im not mistaken.

 

What size tires do you have and what sort of trans? (Is it an overdrive?)

3.55 and 3.73 are good ratios for power and economy w/31" tires, W/O OD. But, they are on the tall side for use w/OD, and 31" tires...w/shorter tires and a lighter truck.

There is much that hasn't been provided...what sort of truck and which motor. But, if you have an OD trans...lets just say, that the big three have tried to lower engine rpm so much, in order to increase economy that they have made trucks and all cars dogs. So, you are moving in the right direction.

 

89 5.0 aod 265/75/16, my speedo is off 9.2 percent due to the bigger tires, they are to big for a 2wd, that is why it lugs so much.

 

Well, that is a start. That would be about a 5% change. W/those tires, I don't expect that you use OD very much.

4.11 would be a better ratio.

 

well when i travel over about 50 i usually do. but other than that i drop it down to D. its funny how it shifts into OD even when im going 35...