I have a 2003 Limited 4x4 with the 6.8L. I occationally tow a 29 foot TT that ranges between 6300 to 7700 based on loading. What are all of your thoughts? The 285s look cool but are there downsides?

 

Higher gear ratio, more chance of overheating your tranny and blowing a seal on the freeway, less power, snowchains won't fit if you use them, etc.

 

Do you spend much time on the highway towing your TT? If so what cruising speed do you like? 285s will decrease your rpms a few hundred on the highway so you have less effective torque at a given speed. For example, I am at exactly 2000 rpm at 70mph with my 285s. 265s probably put you at 2200 or so (somebody correct me please). So if you like to cruise at 70mph and 2200 towing your TT but you want to stay at 2200 rpm so you're not in and out of overdrive you may have to speed up to 75.

In my opinion, changes in rpm at highway speeds is the only downside in going from 265s to 285s, if it is a downside and not a plus in your situation. The loss in power is pretty negligible with a diesel or the V10 and small change in diameter. The biggest issue is deciding what rpm you like to cruise at and whether or not you can afford to (speed limits, safety, etc.) add 5mph to maintain that rpm.

 

I agree, the tranny is designed to maintain the best shifting pattern which you would upset by going to a larger diameter tire, not to mention less power at take-off and wear on the tranny from constant shifting and unlocking the clutch in the converter constantly. I wouldn't do it just because it fills the wheel well a little more.

 

Check the weight of the new versus old, could add more unsprung weight which will lower your mpg.... by all means though be sure not to drop down on load range....

dangerous and white knuckle when Discount tire put the wrong tires on mine !!!

 

Ive run 285's on my X since it was nearly new. and I have had no problems with 287,000 miles with over heating. I have had to replace my water pump twice but I dont see any connection to the tires. Almost all the miles on this truck are without towing but our boat was over 5k. and again no problem.

 

The overheating thing is probably not a big factor but if your conditions are such that you tow and are on the verge of overheating the tranny why add to the chance of it? The engine and tranny will definetly have to work harder to a degree and to just fill a wheel well a little more why chance it? Trailers and low gears go together, not higher gearing.

 

Sorry. Disagree. Weight of tires (rotating mass) will not appreciably change mpg. Diameter changes mpg. It is the change in effective gear ratio that makes the difference in fuel economy. You could recover almost all of the loss in mpg if you changed the differential(s) back to same original overall gear ratio--but that is way too expensive to be worth it.

 

I agree with Forest about the mpg. The extra rolling mass is harder to get moving but lets you coast longer because there is more. These can actually be considered benefits. Many people add flywheel weights to dirt bikes to make them more manageable - same concept.

Ex10, I'm not trying to start an argument, but my Ex too has had 285s on it since almost new. I really think the difference in strain on the tranny and drivetrain caused by 285s is so negligible it is similar to carrying an extra few hundred pounds, or a few people, in the vehicle, if that. The power loss is really minimal, it's just the rpms changing at different speeds. The transmission doesn't necessarily shift in and out of overdrive solely because of the slightly larger tires. One just needs remember his or her cruising speed needs to increase slightly to keep the rpms the same as with smaller tires. This can be a good thing or a bad thing if you don't want to increase your favorite cruising rpm. 285s won't make the tranny hunt for the right gear or work any harder unless you drive right around a shift point slowing and accelerating, just like with 265s, only you'll be doing 3 to 5 mph more.

 

I know it's not a lot of difference but there is a difference so why make it any worse? I also disagree with the first part of the post; the extra mass is almost nothing (if it is even there) compared to the total weight of the vehicle and help in coasting is negligible also and doesn't outweigh the 90% of the time you are dragging the extra weight around and the flywheel effect doesn't apply here at all unless you crash into some heavy brush and want the momemtum to carry you through it which would be rediculous also. No offense but I think you need to brush up on your physics. You are trying to give credit to a larger tire but there is no credit due other than it fills the wheel well a little more. Ford designed it to work with the 265 and any larger diameter is going in the wrong direction. Also, the WEIGHT of the 285 tire has almost no effect on anything here.

 

The outside temperature also doesn't make much of a difference but would anyone planning on moving to a warmer climate really choose not to because of the effect on their drivetrain? No. I just think you're acting like the negative effects of 285s are much larger than they are. I'm not going to argue about physics or imply as to your education level but I will point out that you saying my claims are negligible has no more weight than me saying your claims are negligible. Increased rolling mass helps when hitting hills and staying in a higher gear. The effects are more obvious and best shown with flywheel weights on off road motorcycles. Lastly, I think the negative effects of 285s are best documented by those that have run 265s and 285s.

To quote Forrest Gump, "That's all I have to say about that."

 

There isn't much difference in the 2 sizes other than the larger size is going in the negative direction for towing purposes which is why they make an optional lower differential gear. As for the flywheel effect, the reason for any flywheel is merely to maintain a smooth transistion to the next revolution and has zero effect when is comes to wheels on vehicles. An engine with no flywheel would be very choppy and could easily reverse itself under idling conditions. Wheels that are spinning down a hill are merely going along for the ride and aren't generating any energy whatsoever but if they weighed about 100 times as much they would help with the next uphill movement for about 100 yards +-.

 

I think 285's actually increased my fuel mileage by dropping my rpm into the sweet spot at road speed. I had no issues with 285's at all.....other than hitting a chunk of something in the road and getting a blow out.....in the freezing rain.....at 9:00 PM.....changing it in a mudhole beside the road.....yep you are right ..285's suck !

 

nj, that would bias me too !!! (git it - bias in a tire thread )

Wow - will try one last time....

my reference to weight is valid in that if you are changing,
weight is something to consider too !
If heavier is better, I wonder why F1 drivers don't get heavier tires for their racers?!?

weight is weight and unprung weight is the worst kind - I would expect you motox's to really understand that... if u put more weight on a bike, it's to smooth out power impulses certainly not for more responsiveness...

the same size tire from different mfg's can be much different weights...

so take your time and go to tirerack.com where they have all the specs you should consider... treadwear, traction, speed rating, load range, etc....

good luck... and apologies for this threads direction to your simple question....
(but even this is nicer than the Audi forums I have visited - they are real 'arrogant incompetents' there )

 

Are you sure about that? I've read in several places including this site that the Excursion was actually designed to work with 285. I know for a fact that my speedometer is spot on now with 285s.