I was wondering if anyone here was running stock gears with 35" tires and n 302? Would that kill your top end power and keep you from staying in 5th gear. I have a 5 spd tranny. Say 65mph is as high as it will go and evan in 4th gear it still loses power going up little inclines.

 

Check your axle code. If you have the same powertrain setup I do, that's a 3.08:1 axel ratio, and YES, the huge tires will kill your top end, but more so, the already weak bottom end torque. However, I wouldn't think that badly after you got it rolling. One thing for certain, though, your clutch ain't gonna last with the fast screw in the dif and high bloatation tires.

Are we talking 4x4 or 4x2?

 

Its 4wd. I figured it would kill it some. But that bad dont seem right. The taking off isnt that bad at all. Once I get into 4th gear its like everything is cut in half.

 

Have you noticed any stumbling or missing at light throttle on level ground, or a bumpy idle? Had a tune-up lately? Checked your timing? Still, 35's are HUGE compared to the stock 255-75R15's.

 

Ya everything is working fine. Ya they are big tires but I have never had a top end loss like that before.

 

Gonna have to ask some of the other gear-heads in here, then. I've seen an awful lot of discussion about reducing gear ratios when going to fat tires, though. Gotta keep the RPM up on the 5.0. It's pretty weak at bottom end anyway. At 65 mph, it's only turning about 2000 rpm if you have the 3.08 difs with stock tires. (I don't have a tach in mine for some strange reason). With 35's, I'm guessing around 1500 or so. You're at the very bottom edge of the torque curve on that engine.

 

When I am in 4th at 65mph its at 3000RPM and its dead. I neva really paid attention to what the rpms were when I was in 5th. Evan at 3000rpms in 4th is like dead.

 

Yeah powerstang I have a 94 f-150 with 6 in lift and running 35" tires with the stock 5.0. I have the 5 speed also and 4th and 5th gear are useless. if I do use 5th it has got to be on a flat highway with not even the slightest grade in road up. at 65 i run about 2500 rpms and if I have to pass I take her all the way down to 3rd. I am in work on my motor problems now then plan on late summer to do some gear changes let me know what you come up with in the gearing area. I do some 4 wheelin but dont wana go too agressive.

 

The flat tappet 5.0's and early roller motors are very weak down low, and don't make much power up above 3500rpm either due to the cam and intake. A box stock 5.0 truck of this vintage with 3:55 gears and an auto running 28" tires will loose speed on inclines at HWY speeds. I have owned 2 of these trucks and they were both the same. The stick puts more power to the ground, but not enough to overcome the big increase in drag and the gearing disadvantage the big rubber causes. Ask anybody with a stang, almost the first thing they do is put gears in these things. These are 3500lb cars running 24-26" tires. The truck 5.0 doesn't make nearly as much power as the 5.0HO, so it has no chance at all in a big truck with these handicaps.

 

Well right at the moment I am having a HO 5.0 dropped in. It should be done Monday. My motor had 150,000 miles on it and the truck has been lifted almost its whole life. So I think that has some play with why it sucked that bad in higher rpms. I am hoping the HO 5.0 will make a differance. My bro has a dakota with the 4.7 and 35's and stock gears and it is perectly fine besides it kicks down when going up small inclines. It will still go 110mph. I will see how it runs with the new motor. I really hate to put gears cause it will cost so damn much.

 

I have a lot of experience with this...

My 95' used to have a 5.0 with the m5od, 3.55 gears, and stock tires. I did the 6" lift and at one time had the 35s on it with the stock 3.55 gears and it was horrible. To me it was unacceptable to properly move the vehicle.

The real problem is not that the tires are heavy and that they're got more rolling resistance...it's that the final drive ratio with the larger tires is much worse.

Example...

I did the calculations and found that a 35" tall tire used with a 4.30 gear ratio will be equivilant to a 3.55 and stock tires. Also, say you have a truck with stock tires and a 3.55 gear. If you keep the same tire size and you change the gears to say 4.10s, it will be the mathematical equivilant to about a 30hp gain. I chose a 4.10 gear, my other option was a 4.56 gear. I liked the gearing on the stock setup and wanted to duplicate it as much as I could so I chose the gear that was closest to it. If I wanted to sacrifice a little gas I could of gone with the 4.56s but the RPM would increase at highway speed and I didn't want that to be too high.

You've got to properly gear your axles when using larger tires. I still have my 32's and put them on occasionally, with the 4.10s. Big difference and it's not from the weight difference of the two tires...it's primarily the gearing.

Gearing makes a huge difference on the power of a vehicle. Often, these small compact cars like hondas and neons have very low (numerically high) gears. It helps in performance...

By putting a larger tire on it you affect the final drive ratio and make the final drive ratio higher (numerically lower). It becomes the eqivilant to having stock tires and say a 2.80 (not calculated, # from my head) instead of a 3.08 or 3.55.


Also, you will typically be able to run a higher top speed with a higher gear ratio over a lower gear ratio.

 

Ya I am worried about gearing it for 2 reasons. I dont want to lose more gas milage and the cost of gears is high.

 

Bumping the RPM back up may actually save you some fuel mileage. Think about it. If you're constantly holding the throttle wide open to make it move, the injectors are dumping more fuel in for the lower RPM and lower speed because all the torque is getting chewed up by wind-drag, tire drag, etc. Now, get the RPM back up, and deliver more of the torque to the wheels/tires, you'll be able to back off the throttle. I'm not real positive, but I think I've read in here somewhere that someone's mileage actually went up after going to 4.10's from 3.55's with the lift and 32" tires.

One other thing to remember. The Dakota has much better aerodynamics and is a lot smaller than the F-150, especially pre-97. I dunno yet what year model your F-150 is, but if it's pre-97, it's got the aerodynamics of an outhouse. You're pushing a very large boxy shape through the air. There goes a LOT of your HP. 97+ have better aerodynamics, but still, the competition knows if you want high speed performance, you gotta get rid of wind drag.

And, I REALLY don't think I'd want to be doing 110mph that high off the ground. Remember where your center of gravity is (above the axles). There's a lot of sidewall flex in a tire that size, meaning tread surface is lost when going around curves. One slight wobble at that speed, and more parts will be available for someone else to build a truck with. Your power loss with big mudders will seem rather insignificant to your family. You're driving a truck, not a Ferrari. The infamous Ford Rollover trick is why 97+ years also had speed limiter features built into the EEC's. My '98 Ranger would do 96 mph in 4th, or 96 mph in 5th. I could feel the timing retard and injectors cut back when I managed to get it on a steep enough hill to get it over 96 mph. I know this was true of all Ranger and Explorer models, but dunno 'bout the larger F-series. I just learned the other day that the Scootmobile (98 Ranger, 3.0V6, 5-speed, 4x2, SWB flare side) took up diving and swimming lessons, and flunked the first exam. Poor lil' Scootmobile is no more.