I have searched and read a lot on hear about the tires I intend to put on my truck...BFG AT KO 285/65/18 or 305/65/18. I have a 2006 5.4L 4x4 Supercab with 3.55 LS gears and stock 32" tires (275/65/18).

I know that the 305's will look much better but I am worried about performance. With the 285's my effective gear ratio will drop to 3.48 and with the 305's my effective gear ratio will drop to 3.38. I do not have the cash to do a gear swap for the tires and most likely won't ever do one on this truck. I would love to but the cost is too much for me to justify.

I have seen many threads saying to go with the 305s, you will be fine. Well does anyone have actual data on these tires for performance loss? Has anyone been on a dyno before and after they had these tires? I am worried about my truck being sluggish when empty and even worse losing some of my pulling capacity. Basically I am looking for data so I can convince myself which way to go. If I had 3.73's I wouldn't be so hesitant but with the 3.55's I'm nervous. I would appreciate any more available info/data on a topic that I know has already been beat to death.

Thanks!

 

So I'm guessing no one has any real data on their performance losses with these larger tires but I did some more searching around and a little bit of math and found a few things. I read somewhere that you lose ~3.5% of your torque for every inch you increase your tire diameter. I did some quick calculations and confirmed that is a pretty close number...at least for the size tires I am working with. That ~3.5% loss seems to only take into account the larger diameter and not the extra resistance from the extra width.

So if my math is correct I don't see how someone who goes from 32" stock tires to a 34" (305/65/18) does not feel a significant performance loss? I read on here that there is some loss but that it is not very noticeable. Well if you increase 2 inches in diameter then that is ~7% loss of torque plus add the extra resistance from the wider tires and lift/leveling and you have lost ~10% of your original torque with stock tires. How can that great of a loss not feel significant? Am I off here with my figuring? If so I would appreciate it if someone would chime in. That is why I was looking for actual measured data.

Thanks again.

 

Well just to throw my two cents in, just knowing about the couple trucks that I have put larger tires on in the past, your not gone to feel to much of a loss just on the average daily driving. Now if you are talking about pushing the towing limits of this truck then yea you are gone to feel it, and in that case I wouldn't do it. But I would say that most people that put the bigger tires on are not coming close to the towing capacity.

But ofcourse the rolling resistance will be greater and it will take a little more to get you up to speed which in return is seen in the city gas mileage. But being that I feel like these trucks feels like a dog most of the time, I would think about investing in a programmer...( it will correct the speedo change the shift point for the bigger tires, and give you back performance.) But if you had to think about it this much, and your not satisfied its a pretty exspensive mistake, like around 1300.

 

Thanks for the reply. I am definitely at least going with the 285s and I just need to decide whether I jump up to the 305s instead. I already have an Xcal3 with VMP Custom tunes so that would help recover some of the loss. I think gears are the only way to truly fix the problem and it is not worth it for me to go that route now. My truck is mainly a daily driver but maybe a dozen or so times a summer I tow 8000 - 10000 lb hay wagons a few miles a slow speeds. I am also concerned with it being sluggish around town with the 3.55s and 34s. Anyone else have comments on the performance loss difference between the 285's and 305's? The 305's will look so much better I'm just a little nervous with having 3.55s. If I had 3.73s I wouldn't be worrying as much.

 

You're only going up an inch from the 285's to the 305's but you will lose some performance and a little less mpg's. The truck will definitly look better with the 305's. A programmer will surely help! Your truck will have to be leveled to run the 305's also, almost forgot that part!

 

PawPaw, I see you have 34.4 inch tires. What gears are in your truck? I assume 3.73s? How does it feel around town and stuff and does it down shift a lot on the highway? Do you ever tow with them?

Like I said I have an XCal3 programmer with custom tunes. I will be installing Bilsteins all the way around (2 inch lift setting on the fronts) and an add a leaf in the rear so fitting the 305's won't be an issue. You are correct that the 305's are only 1 inch bigger than the 285's but keep in mind my stockers on there now are 32's so the 305's will be 1.6 inches bigger than stock. The 285s will be .6 inches bigger than stock. I am estimating a 6-8% loss of torque/power with the 305s and a 2-3% loss with the 285s. I just need to understand if this loss is going to be bearable for everyday driving and towing. Also another thought coming to me now is...with the 3.55 gears and the 305s will my tranny wear out a lot faster from shifting more? As it is with the stockers it will shift out of OD on the express way when I get on the gas a little.

 

Hello everybody. I have a 2005 King Ranch 4x4 with stock 275/65r18. I need to replace my tires and I like the looks of the 305's. My question is what size leveling kit do I need and is it hard to install? My wife and kids use the truck also so I dont want to go WAY BIG on the lift. Thanks everyone. Lance

 

If you are going for the 305's you will need a 2 inch lift in the front. This can be accomplished by installing a leveling kit (search "Auto Spring" or "leveling kit" on this site) or by installing new leveling shocks such as Bilstein 5100's. The leveling kit is an fairly straight forward install you can do yourself and parts will cost under $100. The shocks are tougher to install and cost a lot more...approx 300 for the front pair I think. Unless you have a spring compressor you may want to have someone else install the shocks and I've heard the labor won't be cheap. In the end the shocks will give you a better ride with more travel but the leveling kit will work just fine if you want to save money. If you do need shocks soon though getting the leveling ones is a good way to kill 2 birds with one stone. My suggestion is to search "leveling kit" and "Bilstein 5100" on this site and you will get a lot more information and opinions. Oh and the 2 inch lift in the front will just level your truck out...it won't be looking sky high though. Most of these trucks come stock with a rake (rear end higher) so that they are level when loaded. Hope that helps.

 

My truck does OK with the 3.73 gear's in town. When towing I go to level 2 with my Edge and if anything heavy I don't use OD. When accelerating the truck does real good untill 50-60 mph and then goes into a mini coma, almost like skipping a gear and I live in an area that's flat with no hills or mountains and that's with no trailer. If you go with the 305's I think another custom tune for those diameter tires will help out. Check with member's running the 305's and see what they say. Get some pics up when you get the tires on!

 

I'd go with the 2" Autospring, easy install. Get the 305x65x18's on the stock wheels then align it and you're good to go!

 

even without the level im pretty sure he can fit 305/65 on stock wheels fine. even though i have a 2000, mine fit perfect. stock suspension

 

A 305x65x18 though is a little taller, close to 34 inches and that's where the problem is. Your 305x65x17's are right at 33 inches where a 305x70x17 is close to a 34 inch and probably would rub a little without cranking the T-bars a little on your 2000.