I have an 87 f150, 300-6 four speed. It has 255/70 15 on it right now. I need a new set of tires and considering going smaller, maybe 235/75 15. Am I going to notice any performance difference between these two? Will it change the gas mileage/power? how much smaller will they look compaerd to the ones now? I like the way the 255/70 15s look and stuff, but these tires cost more and some what harder to find compared to 235/75 15? so i am trying to figure out what to do and hoping i can get some hands on expierence from the wiser.. So lets hear it..


chris

 

It depends on what your gear ratio in the rear end is. This forum helped me out maybe it would help you. My problem was i went to bigger tires and looking to get my power back. Based on my knowledge i would think it would give you more power on low end, and decrease your top speed but not by to much.

Good Luck

 

I think the difference in diameter between the two tires will be so small that you wouldn't be able to tell a difference. Handling, I couldn't say; I've always had 235/75 15's on my truck. I don't know what the 255's would do differently.

 

235/75 R15's and 255/70 R15's basically differ only in the width of the tread and aspect ratio of the sidewall height. EPNCSU2006 is correct. The final drive ration would be affected by less than 2.6%. Check Sam's Club for tires of either size in the 63.00 to 85.00 range. I run the Liberator All Terrain, made by Michelin. The 235's are more available in LT type tires based on a quick search.

 

255/70 R15's are 29.06" tall and the 235/75 R15's are 28.88" tall, so you will most likely not notice any difference at all.

 

Jumping in on this thread, I have P275-60-15's. They seem like a very small but wide tire. I have a 4x4 that sets like a 2 wheel drive. I bought it like this, they are still almost like new tires but were designed for a car and I hate them. I want a taller tire, I am thinking about going to a 235-15 myself. I think that they are a taller tire than what I have. I know the 60-70-75"s represent the heighth of the tire but is the 235 much taller than the tire I have now? The wife will not see why I am replacing the tires on the truck but they are just two small for it. Any opinions would help, I am probally going to the tire store in the morning. Thanks...Ps, how do I get my signature down in the bottom of my post for every post like others I have seen?

 

The stock tires are 235/75/R15s. The only thing you might notice is that the speedo will be more accurate.

 

I am just updating my post, I just got back from the tire store and got some 31X10.50's and compared to the P275X60's the truck is like a whole different truck, I really dont even notice a power loss (yet) and I love the new ride of the Truck. I got a good trade in on my old tires and got my Goodyear Wranglers for a price I am happy with. On the ground these tires are atleast 3-4 inches taller.
Problem is I have to go get them all muddy to make sure the wife dont notice the new rubber. ;-)

 

I have to keep my truck locked in my shop so she doesn't notice the new 38.5's an new rims along with my other new goodies , now i just have to hide my credit card statements or hell will break loose

 

I hear ya, I know exactly what you mean. I guess they have to keep us in check. lol

 

Hey Raysvan.... if I knew you were looking for Wrangler 31X10.50's I would have sold you mine. I want to get the standard size for my truck. Don't forget that you're speed o meter is going to be off now. When I'm showing 50 I'm really going about 56 or 57 according to the guy I bought my truck from.

So you got to trade your old ones in? I wanted to do that here, but they said no. I need to move to your area.

Michelle's Gottaford.

 

I live in the used tire capital I guess, there are stores everywhere that keep the used tires up front and the new out back. There is one store that has a contract with the city officials that gets to sell them their new tires for all vehicles I guess, they run adds when their tires build up, you can buy a set of used police tires there that are Michelens X police tires for under $200, probally $175.00 that look great and are even garunteed (SP) for so long.
My speed gauge has never worked in my truck so that area of the swap is not a problem. I do wish to fix that one day, for any type of reading, I have cruise control but it is electonic so it dont work either. I wonder if I just got a gear from a regular trans, would the dimensions be the same so I had no leaks? I have a 5.8 engine with a 4 speed automatic trans.
Getting back to the tires, I love these tires, if not for the lift alone I got by installing them. They look new and make the truck set like it should, I did not like the lowered look in the front of a 4x4. I really think I could have gone to a 33 as at full turn I still have plenty of room. I need to check out a friend of mine, see how his tires turn, I am just afaid I will suddenly be unhappy with my tires. come on income tax!

 

You probably know this. Make sure all your tires are the same size on a 4x4. Won't work properly otherwise. The 33's will dimensionally fit. You may experience some rubbing on the bumper and radius arm, though. Depends on the wheels, backspacing, tire width, etc.

 

Thank you for your concern. I do know about the sizes needing to be the same size, the Wrangler tires I bought are all the same size and style. I probally made my post appear like I had two sizes but I did not, I just simply went up to a taller tire.
I just got done cleaning my truck as there is a car show tonight in town and it is nice to just park and walk around all those great cars and trucks. I dont enter mine, but by the end of the evening it will be in the middle of it as the lot will fill up and I get there early. It is outdoors and free for all. They have it Saturday night but my work hours only allow me to make it there about 4 times a year.

 

Enjoy the show. Do you know the rear gearing? If not go to the tech articles and look up Ford Axle Codes. It'll tell you based on the code on your door jamb sticker. You can use the conversion formula to find the amount of speedometer error as well as the actual effective final drive ratio.