I just took my first road trip with my new tires and am very dissapointed in the power of the truck. I was passing over some mountain ranges and had to go down to second gear to maintain 65mph. I am getting absolutely no power in my higher gears. Even when traveling up a gentle slope(hardly anyslope really, it seemed pretty flat to me) my truck refused to stay in overdrive, even at 65mph. I wanted to travel between 70-75mph and had to stay in third to do it, at 3000 rpms. I have a camper shell on the back, but at the most it ways 400lbs. I am really glad I wasn't towing a boat or my ski, it would have been even more discouraging than it was. I thought that with a 10 cylinder engine claiming to be 310hp stock I would have no problem rolling some bigger tires. It was a big dissapointment to say the least!!

Is this normal for all of you that have larger tires? I guess a gear change is in order, any recomendations as to what size to go to?


2001 F-250 SD V-10, ext. cab,
long bed, 4x4, 3.73, 4" pro
comp, weld rims, 35" BFG
AT, grill, cat back exhaust,
k&n intake

 

>I just took my first road trip with my new tires and am very
>dissapointed in the power of the truck. I was passing over
>some mountain ranges and had to go down to second gear to
>maintain 65mph. I am getting absolutely no power in my
>higher gears. Even when traveling up a gentle slope(hardly
>anyslope really, it seemed pretty flat to me) my truck
>refused to stay in overdrive, even at 65mph. I wanted to
>travel between 70-75mph and had to stay in third to do it,
>at 3000 rpms. I have a camper shell on the back, but at the
>most it ways 400lbs. I am really glad I wasn't towing a
>boat or my ski, it would have been even more discouraging
>than it was. I thought that with a 10 cylinder engine
>claiming to be 310hp stock I would have no problem rolling
>some bigger tires. It was a big dissapointment to say the
>least!!
>
>Is this normal for all of you that have larger tires? I
>guess a gear change is in order, any recomendations as to
>what size to go to?
>
>
>2001 F-250 SD V-10, ext. cab,
>long bed, 4x4, 3.73, 4" pro
>comp, weld rims, 35" BFG
>AT, grill, cat back exhaust,
>k&n intake


I have 4.56's in my excursion. You could go with the 4.30's from ford!
That should put you back in the stock power band before the tire change.

 

Did you have your speedometer recalibrated after the larger tires?

 

Oh the beauty of the 3.73 gears!

I had the same befuddlement with my last F250. I traded up to a F350 with the 4.30 gears. That makes all the difference in the world. I still have the stock size tires too.

I contend the 3.73 is too high a gear for this big of a truck to begin with, then add 35" tires and you have really lost pulling ability at road rmps.

I would have to switch off the OD when pulling with my last truck and still the tranny would downshift into 2nd and run around 5000 rpms. This with a 7000-8000 lb trailer going up Colorado mountain passes. It still pulled though at 45-50 mph. This with the 265x75x16 tires. I cannot begin to imagine what a nightmare it would have been with 35" tires and 3.73 gears!

The 4.30 gears are perfect for the SD V10 and stock tires. By putting 35" tires on with this grearing you will be back around a 3.73 ratio. This would probably be OK for your towing needs.

The 4.56 gears and 35" tires would be quite nice, IMHO, if you do not mind spending a lot of time at gas stations...

Dan

 

On a trip down to the beach last weekend I had two Banshees and three people in the truck with all our gear. The only time I had to shift out of over drive (manual tranny) was to pass other cars uphill doin 75mph. I think I have plenty of power for my tires. I also like to keep the rpms down around 2000 and the 3.73's are good at that.



https://www.ford-trucks.com/user_gallery/displaythumbnail.php?&photoid=4920&.jpg http://66.179.41.42/gen1/build/realgeneral.jpg

2002 F-350 SC LB 4X4 6SPD PSD. 3.73 gears. 2.5" leviling kit. Rhino lined Bed. Prodigy trailer brake controler. 35x12.5x16.5 BFG A/T. 16.5x10 ultra wheels.

 

My trucks peak values were 3300 RPM for torque and 4200 RPM for HP. Not suprising to see this kind of complaint at all. You have the "economy" gears (3.73) which are barely acceptable in the SD with either gas engine. The larger tires move your "cruise" RPMs further down away from the peak power band of the V10. You really need some lower gears- consider 4.56s.

 

I haven't recalibrated anything, I wanted to wait until I decided about the gears. Everyone told me that 3.73' would be fine with larger tires because I have the v-10. I guess maybe if I had a manual tranny I would be fine but the automatic just ain't cutting it.
4.30's or 4.56's? That sounds like a big difference. How much difference is that going to make. Going back to the stock ratio with 4.30's sounds nice but even with the stock tires it would downshift to third uphill.
I'm using a lot of gas pushing these tires already, what I really want to know is which set of gears will give me enough power to tow small trailers/boats and still get decent gas mileage on road trips without a trailer?

2001 F-250 SD V-10 ext.
cab, long bed, 4x4, 3.73, 4"
pro comp, weld rims, 35"
BFG AT, grill, cat back
exhaust, k&n intake

 

We used to have a '97 Expedition with 4.6L engine and 3.55 gears. I put 33" BFG ATs on it and got the same bogging/down-shifting that you are experiencing. Had 4.10 gears installed and the highway economy went up from 16 to 20 MPG. Those are real world calculated numbers- not any kind of trip computer stuff. With the 4.10s, the SUV would stay in OD on hills that previously caused a down-shift. My guess is that staying in OD over the course of a trip was causing lower RPMs than down-shifting to 3rd for half of the trip.

 

[updated:LAST EDITED ON 12-Jun-02 AT 04:49 PM (EST)]When I went from the stock tires to the 255/85's the truck was very doggy until I recalibrated the speedometer. Then it ran much better. I don't think it would solve your problem, but it might help it. I didn't notice much difference going from the 255/85's to the 315/75's.

Keep us informed if you decide to change gears. I'm thinking of doing the same thing one of these days since I've went to the 35" tires. The truck is still acceptable with the 3.73 gears but I can tell it would be better with lower gears. I'd also like to put a decent limited slip in the rear as well. I'm leaning towards 4.30 gears but 4.56 sounds interesting, too.

Also, the speedometer only needs to be recalibrated when the tire size changes. Gear changes don't affect the speedometer.

 

I used to run 33" tires on a Navajo with 4.56's, the mileage was the same or better than stock and it could cruise up hills in OD no problem. If I were to run 35" tires on any vehicle the minimum ratio I would use would be 4.56's. The rpm difference won't be much more than the 4.30's and the truck won't be as prone to search for gears so the mileage shouldn't be too different. Having a big powerfull motor helps turn big tires with small gears but you will work it with an auto tranny. If you go with the 4.56's I bet you will not be dissapointed at all. As an added benefit you will save your brakes as the deep gearing lets the engine slow it for you. In OD over Vail pass I could let it cruise down and it would never go over 70, which was plenty fast for the curves in a lifted truck!

Though I'm a newbie to the Super Duty my hobby is rock crawlers where the proper gear selection in your T-Case and diffs either makes or breaks (literally) the truck.

 

In discussing the gearing, don't we take into account the overall gearing and not just the differential gear ratio. Now a lower differential gear ratio (higher numerical), will provide more torque not only because the engine will run at a higher RPM, but the physically larger ring gear, will provide more 'leverage', then a smaller gear. But if we just take into account the gearing (overall gearing, not just the differential), wouldn't say a 4.30 differential with the transmission in overdrive (say .78, I'm guess on ratios because I don't have access to the specs right now), be close to a 3.73 differential with the transmission in 3rd (1.0).

4.30x.78 = 3.35 effective ratio
3.73x1.0 = 3.73 effective ratio

So in effect if you want to "lower" your differential ratio for heavy loads/towing, why not just lower the transmission one 'gear'? It seems that with the higher differential gear (3.73), you are in effect having a higher overdrive, with the ability to select lower gearing when it is needed for towing, heavy loads, etc, without the penalty of higher RPM, and hence less fuel mileage, and increased wear, when you do not need the added RPM/torque of a lower gear(4.30). In effect doesn't a 4.30 gear negates the overdrive in your transmission?

I have 3.73s with 35" tires, and at a cruse speed of 65mph, I'm running right around 1750 rpm, which seems 'sweet' for gas mileage. Once I go over 2000 rpm, mileage drops off by about 20% (14.6mpg @ 1750rpm, 12mpg @ 2000rpm). If I need to get up in the torque band for towing, it is just a matter of down shifting (if necessary), and I can control the rpm range I am in.

I'd say for a lot everyday towing / heavy loads / campers, the 4.10/4.30 would be the way to go since you would be needing them, but in my case were 97% of the time, in is just me in my F-250, I sure don't need the added torque, and appreciate the better gas mileage ($1.81 for regular gas here), and the less wear on the engine. Towing (7000lbs load), is fine other the steep hills, then I just down shift for the miles that it is need.

Just my 2 cent (maybe not even worth that), and I'd sure value other's input on this gearing idea.

Mark Peterson
'02 F250 CC, SB, V10

 

Unimog,

WHERE IN "SAM HILL" DO YOU LIVE THAT UNLEADED IS $1.81 PER GALLON?????

I just filled up, in NE Minnesota at 1.29/ gallon

 

>I just filled up, in NE Minnesota at 1.29/ gallon


That almost makes me want to move to Minnesota! I'm paying around $1.80 a gallon for 92 octane.

Wait... I just imagined winters in Minnesota :-X23 Chicago is bad enough!

 

[updated:LAST EDITED ON 14-Jun-02 AT 10:24 AM (EST)]Hey dog, do you drive that thing in the snow??

 

>Hey dog, do you drive that thing in the snow??

I don't mind driving it in the snow... But I try not to when the roads are slushy and full of SALT.