I did a search on this and didn't come up with much.

Why are people not using 3.90 gears? Given the fact that I have 3.55 gears currently, 3.73 wouldn't be enough to spend the money on and some say 4.10 is too much. 3.90 is right in the middle, why aren't people using 3.90???

 

Great question. Any takers

 

The main reason is most people here and on other forums seem to think that the Ford Racing gears are the only good gears and the only ones that should be used. When in reality there are many great gear manurfactures.

Stick with one of the well known ones and a great installer andthe 3.90's will be fine

Richard

 

Im surprised more haven't gone this route. Some brands are better than others but it is the install that really matters. I think I am going to go the 3.90 route but its a month or two down the road. The 3.90's are slightly more expensive but oh well they sound like an ideal ratio for the S197 4.6. I will do a write up after install.

 

Good Post, also interested to hear from people who have 3.90s

 

Before deciding on rear-end gear ratio, you need to also consider how rear tire diameter will affectfinal gearing. Stock tires have a diameter of27". If you go with a short diameter tire (most 275's are 25.7"), you will increase the numerical gear ratio. A taller tire (like my 28" DR's) will reduce the numerical gear ratio. Tire diameter is a critical factor to consider before deciding on a set of gears.

 

Good point

 

I too wanted to go with 3.90s but everyone I talked to scared me off of them. Saying that Motive was the only brand who made 3.90s and their stuff was questionable. Dont know if that was really true or a good myth that got pushed out there enough that people bought it. I went from 3.31s to 3.73s so that was a good enough for me. Good luck

 

Hey, thanks for posting, I didnt even realize you could get a 3.90. Im getting ready to purchase 3.73s but may need to research 3.90s because that may be just a tad better than a 3.73. Im going to talk to hubby since he will be doing the install (he's a Ford HL tech). I dont want 4.10s so this could be good. Thanks!!!!

 

Since your husband works for Ford he will probably advise against it since FRPP does not make 3.90 only Motive does. As for me, I am not partial to either, just the gear ratio.