31.0x10.5 R15 to ...?

I know it's some basic stuff but I've been digging through a lot off threads and still have some questions. I've got a '00 Prerunner V6. Door says 225/75R15 but I got it with 31.0x10.5's and the speedo reads true so I guess it's calibrated to the 31's. I read a couple posts saying they were factory on some of the '00s.
Anyway, it's time for new tires and I'm thinking about going down to the 225's. This is a work truck / daily driver. Most of the time I'm on the highway with nothing in it but every now and then I'm towing at the limit or hauling a lot of weight. Basically I want street tires to maximize my MPG but still plenty heavy duty enough for hauling. I'm almost never offroad. I don't really care about the look or about the speedo being a little off so I'm thinking of going back down to the 225's to get a little more acceleration and better fuel economy. The 225's are way skinner though, almost 20% (https://www.tacomaworld.com/tirecalc?tires=225-75r15-31-10.5r15) which seems pretty extreme. Should I go for something wider? Am I missing something here? What do people like for daily driving tires?

 

Oh my other question is whether there's a simple way (or anyone got a good guess) to rough calculate what increase I might get in MPG? I do like the extra lift I get from the 31.0's I live in new orleans and it floods real bad...

 

Stick with the 31's or a similar sized tire 265-75-15, you can go to tirerack dot com and they have size specs for all the tires and judge from there.

 

If you like the 31’s, just stick with them. I don’t think the mpg gained would be noticeable, if even existent. A lot of the time, when people go up in tire size, they forget to calculate the extra distance the larger tire is taking them. Larger tire=Greater tire circumference=Longer distance over same number of driveshaft revolutions

 

ALL Tacomas have the generic tire sticker that says 225/75/15, don't ask me why but they were still an option up until '02 I believe. However most that came with the larger tires (31x10.5x15 or 265/70/16) also had an additional sticker to indicate the actual tire size.

My truck still has both stickers on there.

You will "appear" to gain MPG but in reality it is just your axles spinning more than intended (as stated, larger tire = less rotation, smaller = more) based off your gearing. If you look at your door jamb and read the sticker with the VIN it will tell you codes for your gearing. that is usually the determining of the 225/75 vs 31x10.5. Most 98+ had been upgraded to the 31s and 4.10 gears while a lot of 95-97 were on 225 and 3.73(?) gears (obviously some variations depending on auto vs manual and v6 vs i4).

If your speedometer is reading correctly then stick with the tire size you have now, otherwise you will need to keep track of how fast your going, and if you calculate fuel mileage have to convert based on the smaller diameter tire.

example pic

 

my door stickers:




seems maybe they started putting the correct size in the later years?

 

I don't think you will notice anything significant in MPG, unless you went with a rock hard super skinny (Prius type) tire that wouldn't be very good for towing, hauling or handling.

If you get BIG heavy wheels and tires and do a lot of in town driving, MPG will go down. On the freeway the larger diameter means less turns per mile and lower RPM. This is all theory and depends a lot on how you drive.

Most people see a loss in MPG from larger tires because they lift the truck too. Smaller wheels will give you a bit more torque, but if you are that close on torque, perhaps you should reassess your towing needs.

In my case going from 31's to 32's with a lift. I saw about a 1-2 MPG decrease. But my wheel weight went up 20 lbs per wheel, spinning and stopping that mass takes energy. The lift made the already horrible aerodynamics even worse, then there's rolling friction of a wider tire.

Disclaimer here. I do not recommend this; This will change the handling of your vehicle and can cause tire problems. Always follow the manufacture's recommendations. With that in mind, you can "theoretically" get a bit more MPG out of any tire by increasing the PSI, but keep this well under the maximum. Less tire flex means less resistance. I've seen people run their tires at 50 PSI (max) and get better mileage and punctures too.

 

Thanks. I hadn't seen that second sticker before. Appreciate the bit about gearing as well, I'd wondering what my gearing was but wasn't sure where the info was. I've got the 4.10 too. I get that the odo/mpg gain will be inaccurate I thought that the smaller, lighter tires would give an improvement in fuel economy but seems like the consensus is it's not really or not enough to be worth it.

 

Awesome thanks this is what I was looking for. If you only lost 1-2mpg with that I'm sure whatever I gain going a size down isn't worth the hassle and like you said going really skinny isn't going to help when I'm working the truck. Guess I'll stick with the 31's.

 

So what's a good 31x10.5 for highway driving? Any strong opinions? I get that offroad guys have strong opinions but seems to me like any $150 all season tire is going to be about as good as any other

 

My 96 came with 31x 10.50s from the factory with a 2.7 engine. That was the only size I ran on it and would get 20-22 mpg. IMO BFG A/Ts were the best tires for that truck.

 

Tires are a funny topic, because it depends on what you want to do. The OEM size is the compromise of everything someone could do with their truck. If you are driving only highway, I think (me personally, just my opinion) is the larger diameter tire wold be better. But it's still personal preference and what task you need to do.

This is why size can have minimal impact on your driving experience. I had 32x11 BFG MTRs and they were great off road, but sucked on the road. But they are the exact same size as the BFG AT's that replaced them and the AT's are sooooo much better on road.

The MFGs put small diameter tires on small cars with small engines because they won't be able to effectively turn a large diameter tire. Essentially they lower the final drive ratio and make up for it with more gears.

Theoretically a larger diameter means less revs/mile and better ride. Better ride comes from the perceived bump size. A 1" bump is 1/32nd of the size of a 32" tire, versus 1/24th of a 24" tire.

Also the larger side wall allow might mean more flex and comfort. However, the larger sidewall with that comfy flex (rolling resistance) takes energy way from propelling the car and that's counter to MPG.

Personally, I always by the best tires I can, because they are quite literally the foundation of your driving experience.

 

B03a is 4.10s