i know questions like this have been asked on here a million times, but i cant find anything directly relating to what i need. Everyone asks with 35inch tires if they should run 4.10 or 4.56. I basically do 100% hwy driving. Right now my truck has 285/75/16 (1997 f150 4x4, 4r70w, 3.55, 4.6L) and i might upgrade to 315/75/16 as i have purchased a 6 inch lift. What i was wondering is if it is still going to be hard on the tranny with the 4.10s and 35s? I tow very little, 2 atvs at most once or twice a year. The 3.55 with the 285/75/16 i have now would actually be less power then the 4.10s with the 35s? any imput would be great, thanks. And i realize i would have lots more get up and go with the 4.56, i am more concerned about not rebuilding my tranny.

 

With a 4.6 and 35's you should get 4.56's.

 

I just remember after reading your post I had a 84 Ranger lifted with a 2.8 V-6 and 36"'s.
I had the same issue but a much less power and a 5 speed. I replaced the rears with 4:56's or 4:88's and the truck drove absolutly fine with those tires no lack of power. great gas milage considering what all was done with the truck.
It comes down to this your 285/75/16 are basically 33" tall and with that 3.55 gearing you have now your basically ******* your gas milage and your not hitting your trucks full power potential. Now putting the 35" on there with a 4:56 is gonna put in the butter zone right about were the truck should be. If i'm right I dont think your going to need to recalculate the speedo because changing the gearing and tires will balance it out evenly.

 

i realize i will have a lot more get up and go with the 4.56, but i am doing 100% highway miles pretty much, i drive 5 hours each way to work and back 2 times every 2 weeks, my issue is that i dont want to be reving at 2300 or 2400 on the highway getting 13mpg. right now at 70mph i rev at about 2050 rpm, which is about what i assume 4.10 with 35s would rev at. I really dont want to have to slow down so i can keep the rpms at a reasonable number.

 

4.56 all the way. on the highway i get 18+ mpg with 4.56 and 35"s and thats with my rpms at 75 around 2800 and 80 at around 3000

 

You will push the rpm's down with the 35's making the engine lug in overdrive more causing it to shift into third more. More shifting = more heat = sooner breakdown.

Adrianspeeder

 

^^^

http://www.miata.net/garage/tirecalc.html

http://www.ajdesigner.com/phpgear/ge...gear_ratio.php

MGD

 

how do you get 18mpg at 2800rpm, ive never seen 18 stock, let alone if i was reving that high, and thats what i dont want, i dont need an engine with 160000miles on it to be reving at 2800 rpm on the highway for 5 hours all the time. is that what your f150 revs at at 70mph on the hwy with 4.56 and 35s?

 

That's only because I have a manual an the OD gear is higher than in the auto trans trucks. The rpms would come down if I went to 37"s. And idk exactly how to explain the Mpgs but on the highway for trips I get 18 when cruising and but it gets lower when I put more load on it for hills etc but still doesn't struggle hardly at all and no where near as bad as it did with the 3.08's. Motor has only about 50k on it

 

Changing gear ratios will not change the speedometer.

Adrianspeeder

 

on 97-98's it does

 

I agree 35's made my show a percent slower than i was really going. When i put the 4.88's in it made it show a percent faster than i was going. Changed the speedo gear, now its dead on with a 23tooth gtear

If you want over all mileage and your an easy driver i say 4.56's.

 

i decided to go with 4.56s and ordered them monday, should be here at the end of the week, hopefully i wont be dissapointed, does anyone have the rpms on the hwy at 70mph with 35s, 4.56, 4.6L with the 4r70w, 4x4?

 

yes it does, a lot more than tires do. when i had my 38s my speedometer was about 8 off at 70, when i picked up my truck from getting my 4.88s installed i got on the highway and when i was going about 70 my speedo said i was doing 90+. my programmer fixed all of this though.

it was funny i had the speed volume on and all of the sudden my radio turned up really loud and i didn't know why until i looked down at the speedo and it said i was going 95.

 

that happened to me when i picked mine up from getting the 4.56 on 35"s it said about 90 at 65 haha