Tire Sizing

[bvteachey]

I got a 79, 351M, a few good motor upgrades, tight tranny, 84000 original miles. Ive put about 500 miles on it lately (re-break-in) and im now looking to upgrade the suspension. I was thinking 35`s on a 4 inch lift, or possibly 33x12.50s depending on what would go better with the tranny, and gear ratios. Im gonna use it mostly on the highway as it has absolutely no rust and is being painted as we speak. What do you guys think?

 

[Bronc76]

33's would probably work better with 4" lift without fender rub. 4.10 gears would work good with 33's and will get you down the highway pretty good.

 

[Justshootme84]

Let us know what model tranny is in it, i.e C-6 auto or NP435 manual. Also the axle ratio, i.e. 3.50:1 or 3.00:1. JSM84

 

[Yoder]

i have a 79 bronco with a stock suspension and i have 33x12.5 and can fit bigger without rubbing. if this helps any

 

[bvteachey]

I got the c6 3 spd auto, with stock gears pretty sure there 350s

 

[Justshootme84]

You might be OK on the highway with 33's, but those 35's are gonna make you scream at 3000RPMs around 60 mph with the C6. A 4" lift kit or trimmed fenders would work for the 33's. I'm running 38's on the 78 Bronco with 3" cut out of the front fenders. It's hard to tell the difference from factory with a little trim or rubber weatherstrip, JSM84

http://broncozone.com/forums/index.php?showtopic=11781

 

[American Thunder]

Online tire size/RPM/speed calculator:

http://www.corral.net/tech/gearcalc.html

 

[bvteachey]

Yeah 3000rpm is just too high. What are some good ideas for different gear ratios or transmission swaps that might go well with it?

 

[Yardape]

You might be OK on the highway with 33's, but those 35's are gonna make you scream at 3000RPMs around 60 mph with the C6. A 4" lift kit or trimmed fenders would work for the 33's. I'm running 38's on the 78 Bronco with 3" cut out of the front fenders. It's hard to tell the difference from factory with a little trim or rubber weatherstrip, JSM84
http://broncozone.com/forums/index.php?showtopic=11781

Randy you confused yourself on that one. The 35's will bring the rpms down. You will probably be able to hit highway speed in lowrange. Haha, you will need closer to 4.56 gears for it to be comfortable on the highway with 35's

 

[American Thunder]

With 35" tires, and 3.50 gears, in 1:1 trans gear(3rd in a C6), the motor would be turning 1900 rpm.

 

[Justshootme84]

With the 35's and the stock 3.50 gears, C6 in drive at 60 mph (3rd) i would run about 2800-3000 rpm's on the tach. Even with 31's, I would still be around 2500 rpm's. The 4.56 gear will hel psome, but I don't think you'll get below 2000 rpms. The larger tires throw off the speedo, so that 60 mph may be actually closer to 70 mph?

 

[American Thunder]

35 inches x 3.14(pi) is 110". So every axle revolution moves the truck forward 110 inches.

If the engine is turning 2000 rpm, in direct drive (high gear) with 3.50:1 rear gears, then the axles are turning 2000 divided by 3.5, or 571 rpm.

571 revolutions per minute x 110" = 62810 inches traveled per minute. Divided by 12 is 5234 feet per minute. Divided by 5280 is .9913 miles per minute. Multiplied by 60 = 59.4 miles per hour.

Therefore, with 35" tires, 3.50 gears, 1:1 trans gear, at 2000 rpm, the vehicle is moving 59.4 mph.