This is my problem tryin to find the perfect tire size for my 1991 ford 150 4x4 with 3.55 rear end and 351 stock motor . The purpose of this truck is dailydriver slash hunting  fishing mostly. Gotta tow and drive long highway miles need the towing and some off road torque plus good highway milage some tall order boys and girls but i think im askin the right people                                                  thanks     Slip

I don't know from experience but I know that Ford's automatic tranny's first gear is around 2.40:1. Considering that, and if you want good torque with your 3.55:1 rear gears (while in 2wd or 4 Hi) you'll probably want tires between 30-31 inches tall. That'll give you a first gear comparable to a basic rear-drive car like a Town Car or Crown Vic. My mom's Town Car has a 2.45:1 first gear and 3.08:1 rear gears on a tire around 26.8" tall. Though that is not even close to "drag" gearing it still not slow, gives decent torque from the 4.6L V8 and still cruises nicely. If you went up to 33 inch tall tires, I reckon it'll really hurt torque when the t-case is not in low.  

Continued... If your not towing very heavy stuff and only need real strong torque sometimes, (so you'd use 4wd Lo) 33's wouldn't be all that bad if you need a much larger tire. If you probably don't, I'd look at 30's, 31's and maybe 32's.

Thanks aircraft sounds  like good advice to me thaks for your time

i agree with aircraftmechanic. 33's are a good size for that gearing. i have a bronco with 302 auto and 33's. goes good offroad and on highway. i would recomend a/t tires because they will last longer on pavement.  good luck.  

That's cool if you think 33's work well greengate. I however intended to say that I think 31's would be around the perfect size, if our buddy would like a first gear like a Town Car or Crown Vic. (I realized my second message was a little hard to follow) 30's would also be good for a little more torque. 32's would be almost as good (torque-wise) as 31's. I only recommend 33's if our friend needs a real big tire like to keep from sinking in goo when 31's won't do. This is because I think it'll suck quite a bit of power...

But greengate could be right. He says he's got a 302 auto and says 33's work fine...  But I don't know what kind of gearing he's running...

allot of chevys ran 3.08 gears and 285/75-15 tires that are around 28" tall and they are good for the hwy not for towing or wheeling just good gas milage.  this is almost like running 33" with 3.55 so at most would be 33's i would go with a little less like 31's myself or the motor will really be lugging in overdrive and still may with 31's this is assuming you don't have a four speed w/no overdrive and a low 1st which i might try 33's or 35's but would not pull well or have good power in 4th.  

Thanks for the time and the info  

Check Randy's ring and pinion web site, they have a gear/tire size selector that can help you figure out engine RPM v/s tire size v/s gear ratio, if you know your tranny gears you can plug those in also. 

http://www.randysringandpinion.net/calculators/calculatorsind.html

my bronco is running 33s with 3.50 gears. i've had no problems of any kind due to tires. they pull good and offroad good, as long as you have clearence. my bronco has cut fenders.  

Im running some 31X10.50r15 michelin ltx m/s tires right now on my bronco stock, with the 351w and 3.55 gears.  they are the best road tire out i think right now.  they also do good on the beach and in the mud, but if you do a ton of offroading and ride down the road just go with some bfg all terrains  

Hey ronny! When you said a lot of chevys ran 3.08 gears with 285/75R16 tires and said they're 28" tall I got confused. Did you mean some people "put" 285/75R16's on trucks with these gears or was that a typo? (because the 285's are about 33" tall) I know that chevy used 235/75R15 and 235/75R16's on basic trucks. These are about 29-30" tall. Did you mean when using the stock tires with 3.08 gears made them suck for towing or 'wheeling?  

I had a 76 chevy with 3.07(maybe3.08) gears and ran 33's with an sm465 4 speed with granny low. But tha was with built 327 small block.

3.55s will proably work OK, but if you tow alot or really want better low end power, 3.73 or 4.10 would help.