i have a 78 f150 4x4 with a 400m with a 2 inch suspension lift and a 3 inch body lift. it has the ford 9 inch in the rear. what is the biggest tires i could go with without changing gear rations or lifting it more. i want to go with 37x12.50 super swamper tsl. thanks in advance

 

with 37's you would need 4.56 at least and if it were me i would get 5.13's. but that 9" wontl ive long under 37's with any kind of hard throttle

-cutts-

 

Will he have enough room to turn those 37's up front? Remember, most 37" tires are closer to 36" in reality. Why won't the 9" (rear axle, I assume) last long with big tires, says the guy wanting to put 37's on his F250 rear as soon as he gets it.

 

he should be able to.... he can fit 35's with a 2" body lift and with a 3" suspension he wouldn't have any problem with 37's

9" rears are 1/2 ton axles and they wont last long under pressure with heavy meats like that. now if you drop a chunk of change into it and upgrade shafts and all ya it would be fine but by that time he could have a full float 1 ton rear. i have seen quite a few 9's implode with just 33's

-cutts-

 

Details, please......."implodes"???? Why would the rear axle fail due to tire diameter? Is it the weight of the tires when they bounce? What breaks? THNX!!!!

 

larger the diameter, the more leverage it has ont he axle shaft, and yes the heavier tires hurt it too, you can run 40's easy with that much lift, little trimming, but i woulnt run anythign more than a 37, and even then you will still grenade stuff, especially up front

 

did the oversized bolt get you home without bending your T/R, lol?

the weight of the tires and the levrage of the tires is more than enough to strip gearsets, sheer cross pins, and even take out axleshafts which when they shatter will take out everything else

bouncing is a whole different story.... you can break 1 ton axles with 33's if you do enough bouncing

-cutts-

 

so what should i go with than. would 35s be reasonable. i have 33s on now and the axles (front and rear) are stock.

 

Good info! THNX!!! I have a LONG history of filling wheelwells with max rubber and plan on 315/70 x 17's up front and 37/12.5 x 17's on the rear. The Goodyear 37's are heavier than Hell (77 lbs. and max load of 4080) and you are saying I could break stuff with these? Am I voiding my warranty with big tires?

 

The front 44 will go way before the 9" rear will. The biggest problem with the 9" rears is with the wheel bearings. granted they are one of the strongest semi float rear axles (the 35spl dana 60 and ford 10.25 semi float are stronger, as the have 35spling shafts, but the 9" 3rd member i think is stronger then the 60's as far as the gear go, but thats just me), but under fullsizes such as yours, when the tires get up past 35's you start placing a ton of load on the 2 weakest areas of the 9", the thinner axle housing (but it is mild steel, and thus easily fixxable with trusses), and the second and biggest downfall when on bigger tires is that the lateral forces (like in the rocks or hard turns) will pull the axlesrights out from the bearings, as they are press on bearings on the axles, and it doesn't take much with bigger (37's and up) tires on a stock big bearing 31 pline 9" for this to happen (i've seen this happen a couple of times), but the 31spline machined axles (which from my experience is probably what you have) are a strong axle, and i have yet to see one break with with 35's.

If you want to keep the 9" and are willing to spend some money on one you can convert it to a full float rear with 35spline axles, regear and a locker for like 1500-2g.

But if you are a very skilled welder you might be able to take a ford 10.25" rear and weld the housing ends/tubes onto a 9" center section and find a 35spline spool and have one killer axle.

 

there is always a chance of that you just have to be smart about it. think twice before doing burnouts and donuts, and the bigger you go the more you'll have to think.

i have never heard of a warranty being void b/c of bigger tires but i am sure someone somewhere has had that problem. your best bet is to get something signed by the dealer you get warranty service from stating that this size tire/wheel combo doesn't void the warranty and that you can safely use that size tire. otherwise i would stick to something close to stock size

-cutts-

 

Yeah i would check with the dealer as cutts pointed out. But if i remember right the tires won't void any warranty as long as the bigger tires aren't the cause of the problem, like you break and axleshaft when wheeling, something like that wouldn't be covered from what i've come to understand about adding mods and warranty, but if its a factory ford part then your warranty is still good.

 

mustange70, I will not have a 44 in front. I have 2WD. I find it difficult to believe I will have a 9" rear. cutts/fishman..., It does as much good to tell this guy to not do burnouts as it is to suggest I stick to tires close to stock. duh? I am buying a TOY!! Toys are to be PLAYED WITH!!!!!!!!!!!! I have 315/45 x 17's on the back of my LT4 Firehawk and upsized tires on both my F150 HarleyDavidsons and have been doing such since my 1965 Sport Fury 383 4 speed. I put 950's on the back of it in 1965.

 

lol ok, well you asked for my opinioin and through my personal experience i lent it to you. if you use it good if not... wel its your truck and money not mine. i never said not to do burnouts or donuts, i merely suggested you THINK before you act. and you're right most ppl these days are too dam stubborn to listen anyways, been there done that

have fun

BTW... i have a TOY to and it breaks all the time and i have beefed it up and have all one ton running gear.

-cutts-