Hi everybody,


2011 F250 with Toyo AT2 285/75r18 on stock rims,3.73 gears.Planning a road trip with a 6500-7000lbs travel trailer and some 1200lbs of stuff in the bed.


Should I consider down sizing the tires,or just forget about 6th gear(maybe 5th sometimes ) ? I am not talking about grades.



Thanks,


Jo

 

That's only a little more than half of what it's rated to tow, so even with the bigger tires I can't imagine the truck will have any problems.

 

It's really going to depend on road conditions, if it's windy and you are heading into it you will end up in a lower gear but if it's behind you 6th gear and let it cruise.

Last week I was going north on 183 in OK and KS into a very stiff north wind so no 6th or 5th gear but 3200 rpm in 4th was no problem. I'm running 4.30 gears not 3.73 so your rpm will be different but I'm also pulling a wide body tall 5th wheel that comes in at the 16K range.

Don't worry about it it will do just fine

Denny

 

Just by curiosity, what tire size on your truck ? Mine are just a bit under 35 inch.


Thanks


Jo


Jo

 

Mine are the standard 245/75/17 that come with a DRW, I think they are 32" if I remember right.

Denny

 

Since I recently got my trailer,I only pulled it from dealer to home.And that drive felt quite a bit loaded.


To make a comparison,I checked tire rev/mile and this is what I came with:


285/75r18 = 592 rev/mile
245/75r17 = 655 rev/mile


At 60 mph the 285/75r18 spins at 592 rpm
At 60 mph the 245/75r17 spins at 655 rpm


In my case : 592 rmp through a 3.73 axle on 6th gear (0.67:1 ratio) gives me a theorical 1480 rpm engine speed at 60 mph.


In your case : 655 rpm through a 4.30 axle on 6th gear (0.67:1 ratio) gives me a theorical 1890 rpm engine speed at 60 mph.


If I drop from 6th to 5th (0.86:1), the engine should be running at 1900 rpm at 60 mph.


On 4th (1.15:1), the engine should be revving at 2540 rpm at 60 mph.


Am I wrong saying that if I keep my 285/75r18 , I should forget about using the 6th ?


Thanks for your advices.


Jo

 

Yes 95% of the time you will not be able to hold 6th, when you first start pulling give it a chance to adjust to the load and for you to get used to the way it pulls. I came from a 2000 with a V10 4 speed that I had for 13 years and it took me a while to figure it out. Just play with it trying different gears until you find out what works the best for your setup. When I really need the power I found that keeping it between 3000 to 4500 works the best, I use the manual mode and change gears to keep it in that range.

Denny

 

Will driving in 5th and 4th for a long period will affect the transmission?


Are the 5th and 4th gears desinged for this ?




Jo

 

It will have no affect at all, remember 5th and 6th are both overdrives.

Denny

 

No worries!!!! All the negativity that the folks have told me about my set up.... They were 100% wrong. Then again I did carry about 200 gallons of water and about 2000 lb's in cargo.
37's 8" lift....

 

Since you're towing on basically flat land, I would just put it in Drive, engage Tow/Haul, and let her buck. You can lock out 6th if you really want to, but just let the engine and trans do what it's designed to do.

A non-event imho.

 

Doesn't tow/haul lock out 6th automatically? I don't think mine has ever gone into 6th in tow/haul.

 

It will still shift into 6th but the TH tends to hold the gears longer so unless you back out of the throttle it may not shift into 6th.

After you have been towing and the computer has adjusted to the load the shift points will change close to what the TH uses but it will shift instead of holding gears. I use TH when coming into towns because of the transmission braking and I like the way it shifts in traffic but most of the time on the highway I use drive. You will also get better fuel mileage when not using TH on the highway.

Denny

 

Good to know, thanks!