I definitely need some expert advice on this topic and will probably also consult with my local auto dealer. I'd like to go a "little" bit larger on tire size than what I have now, which is just slightly larger than stock. However, I don't want to go too big...or may even consider not doing it at all if I get the feeling that I'm putting too much strain on my TV. I'm already pushing the limits of my TT/TV combo, so I need to be careful.
I want to go from a 285/65 R18 to a 305/65 R18. New tire will be approx .8" wider and 1.2" taller. Something to note though is I currently have a Load Range E tire; I don't think I need that. I plan to keep a LT tire but go with a lighter load range, so maybe some of the weight/resistance will wash itself out.
How can I determine if it's okay for me to upgrade my tire size w/out killing my truck while towing????
2012 Keystone Bullet 286QBS
2006 Ford F150 5.4 V8
Not a good idea. You might be happy with the looks, and lack of power when not towing, but add on that big trailer and i'm pretty sure you will not be a happy camper. Just my opinion speaking from similar experience. It will really cut down your power, and driving pleasure.
The 1.2" change in diam will effectively change you axel ratio from say a 3.73 to a 3.55, 342 to a 3.2, 4.10 to a 3.95........Someone will probably do some math and come up a bit different.....but close from a typing/discussion stand point.
What also will kill you as noted, the extra wt of the tire. Not sure the ration in auto's, but for bicycles, if you removed 1oz off the rim, sproket or equal moving part, from a human power standpoint it was like taking 1 or 2 lbs off the frame or other non moving part. So potentially adding 5-10 lbs per tire, could be like adding 500-1000 lbs of wt to the rig! Hence why a lot of folks will go to aluminum rims so off set the heavier tire with a lighter rim so the tire wt is the same or lighter in some cases.
I went from a 245-75-16 on previous two rigs to 265-75-16 tires, similar upsize, but also included a 7.5" aluminum rim. For the most part I did not notice the difference. As the overall wt was about the same, so really only have the effective ratio change. One was a TBI 454 with 235/385 motor/th400 3 sp auto, the other a 6.5td 185/385 w NV4500. The latter due to the 50hp less noticed it a bit more, but having the 5sp manual more than made up for the taller tires. IMHO the taller tires on this rig made the gears in the trans more usable for "MY" useage even tho I was slightly taller in my overall ratio's.
The how good/bad it is, can depend upon multiple items as pointed out.
05 Chev CC D/A LS Dooley
92 Navistar dump truck, 7.3L 7 sp, 4.33 gears with a Detroit no spin
00 Chev C2500, V5700, 4L80E, 4.10, base truck, no options!
92 Red-e-haul 12K equipment trailer
3 Single axle utility trailers
but for bicycles, if you removed 1oz off the rim, sproket or equal moving part, from a human power standpoint it was like taking 1 or 2 lbs off the frame or other non moving part. So potentially adding 5-10 lbs per tire, could be like adding 500-1000 lbs of wt to the rig! Hence why a lot of folks will go to aluminum rims so off set the heavier tire with a lighter rim so the tire wt is the same or lighter in some cases.
The ratio is actually for every ounce taken off the wheel or tire it equals two ounces on the frame. It is all about rolling inerita and it does not apply to constant speeds only accelleration. The slightly heavier tires on the truck would only be an issue during accelleration and not constant speeds. However, why do it? For towing it is all about power, not looking cool.
* This post was
edited 04/12/12 09:26am by jmtandem *
'05 Dodge Cummins 4x4 dually 3500 white quadcab auto long bed.
'09 299bhs Tango.
Assuming your stock tire size had a diameter of 31.5", and you already have 285's, which are 33", and now you want to go 1.2" larger than that, so 34.2", that is a almost a 3" overall increase beyond the stick tire diameter.
This is all with a high revving 5.4 gas engine, in a truck with a factory stock axle ratio of likely no more than 3.73. This is not a good recipe for towing a heavy trailer that is, as you have already stated, pushing the limits of your truck. You've already added a power tuner to get the most extra oomph out of that little rev happy motor. Now you want to further tax it with even taller tires. Not good.
Your transmission is going to have to work harder too, because of the higher effective axle ratio due to the larger diameter tires causing less torque multiplication after the transmission.
Your brakes are already doing more than they should, trying to overcome the increased rolling radius of the tires, and their additional weight, as well as a hitch weight that is likely near or above the rear axle rating of the 1/2-ton truck. Your braking performance is going to be less than it is now. That is a backwards direction from where a performance minded person would want to go.
On top of that, you want to go from a nice, stiff side wall E range tire, to a softer side wall D or C range tire. This is not good for your truck's handling, especially with the heavy hitch weight bearing down on the truck.
Overall, I would say your plan is quite flawed and shows a lack of understanding of how all the components of truck operate and the stresses they are under carrying and pulling a near-limit or possibly over-limit load.
I don't recommend it. I would stay right where you are on the tires, or go back to stock, if the stock tires can carry the weight. I would not up size the tires.
listen to SCDR,never steered me wrong
What size tire was stock?
I have the stock 275-65-18 and the Ford manual says to deduct 500lbs from the tow rating.
Forum members are trying to give good advice,at least you could reply
2006 F150 4wd 7200gvw,Lt275-65-18,Scan Guage,Garmin,flowmaster,load levelers,Firestone work rites, sat radio 50s on 5
2013 Bronco 800