tire sizing questions for a truck
 

Before I ask, yes I have done some reading/searching. Still have questions

The stock tire size for my 01 2wd s10 is 205/75/15. Everything I've looked at was talking more about cars than trucks. So my question is, would running a 205/70/15(5% shorter sidewall) be a benefit or not?

Your speedo will be out by that much. And you'll be revving that much higher, therefore wasting that much more gas. If you went the other way, you might have some FE gains.

Your cheapest bet is to pump the tires up a good % over recommended, within the max pressure printed on the sidewall of your tires. But you'll probably gain the most by switching to a Low Rolling Resistance tire, if they make them for trucks in your size.

Don't put smaller tires on anything unless you are going to also lower the drive axle ratio.
When the first gen prius came out they advertised that it had smaller tires for better fuel economy ever since then people were convinced that putting smaller tires on their vehicle would help them too.. But the transmission gearing in the prius was designed around this smaller tire.

Smaller wheels often help, the craze for 20, then 22, then 24" wheels was terrible for performance in almost all aspects, economy, acceleration, ride, braking. Maybe handling could be benefited but probably not because they would losen up the rest of the suspension so the ride wouldn't kill you. Usually a low profile tire with a big diameter wheel will weigh more than a high profile tire and small diameter wheel that has the same overall outside diameter.
Smaller overall could help but as pointed out will raise rpm at equal speed. Smaller would lower the truck and reduce frontal aera. Some 2wd guys will run the smaller tire on just the front lowering the front end. Overall that wouldn't change the frontal aera and a lower airdam would have the same effect.
Overall I doubt the difference in a 205/75 vs a 205/70 would even be detectible. It looks like the 70 series less per tire and has low rolling resistance versions available which could be noticible.

i definitely will be lowering my axle gear ratio. my truck is currently 4.10 gears with drum brakes. i plan on going down to a 3.73 or 3.42 ratio and disc brakes using a rear axle from a blazer/jimmy. direct bolt in, lower ratio, better braking. win win. thanks guys

Does this matter?

When the S10 was designed, it shared more parts from the cars of the time than the trucks... It's basically the GM G-body with the largest trunk.

very true lol. never even considered that. although i did think last night that the stock tire size is the exact same size as whats stock on my grandpa's '05 buick century, so my truck falls more into the car category.

I would move up to a 225 or 235 section width. The more air a tire can hold the less the tire will deform.

First, read my webpages on the subject:

Barry's Tire Tech - Fuel Economy and Rolling Resistance

Barry's Tire Tech - Fuel Economy and Rolling Resistance2

Short version: Tire sizing plays a small role in rolling resistance. Better to spend time in the selection process (meaning make and model of tire).

As a general rule, larger tires are better for RR than smaller tires - BUT - see the statement above. Also, there are other tire properties where going larger is an advantage.

In your case, it is a bad idea to go from a 75 series to a 70 series. That's going smaller.

a wider section width would mean that much more rubber touching the road. more surface area means more friction and more material to push. correct me if im wrong, but i would need to have a really good LRR tire set to max pressure just to break even compared to the same parameters for a 205 tire