Tire sizes and gears. (1 Viewer)

[2ndGenToyotaFan]

There are a lot of questions about this stuff, so I'll try and clear some things up. First off, stock tire size on most of your trucks is 225/75 R 15.....

Well what does that mean? The 225 is the tread width in millimeters (About 8.86 inches), and the 75 is a ratio, that's right, it's not a measurement of anything, it's a #&%*%*$&$ ratio! Who's dumbass idea that was I don't know. And the 15 is the rim height in inches.

Back on track, 75 is really 75%, so that's 0.75 times the tread width (225 mm) equals the sidewall height, 168.75 mm. Now there are 2 sidewalls (that's 337.5 mm's total, or 13.28 inches) on the way from the ground to the top of the tire, plus the rim. So 15 inches of rim plus 13.28 of sidewalls is 28.28 inches tall.

Now to the gear part, stock gears for our "28 inch tires" (As you see they are technically not 28...) is 4.10, which means your drive shaft turns 4.1 times every time the tire makes one full turn.

The diameter, or rolling distance of our "28 inch" tire is 88.84 inches (Diameter times pi (3.14159) = circumference) Divide that by 4.1 and we travel 21.67 inches for every driveshaft rotation, and that's the number I'll be referring to, because it's directly related to your speedometer (that's the thing you're staring at...)

So now the fun stuff. I'm going to make a good picture for this.... hold on....

 

[2ndGenToyotaFan]

Ok, so here is the chart I made. As you can see the 28 inch tires with 4.10 gears have a travel of 21.67 inches per drive shaft rotation. You can cross reference tire size and gear ratio to see what your travel would be and then compare that travel to the stock figure. If it's more than stock you can be sure of less power on the road, if it's less than you'll have more power, but lower top speed.

If you want a figure of just how much difference there will be in a percent just divide the new travel by the stock 21.67. Say you want to get some 31 inch tires and stick with stock gears, you would divide 23.75 by 21.67 and get 1.095 so your speedometer and odometer will be over by just under 10% So 50 means 55, 100 is now 110 (That was a joke! )

***PLease note that tire size has little to do with the actual size of the tire once mounted on a rim, and that as a tire wears it gets shorter, so take that into consideration when reading this.***

So by the numbers the best gear tire set-ups close to stock for a truck that came with "28 inch" tires and 4.10 are:

Size/Gears

28-4.10
29-between 4.10 and 4.30
30-4.30
31-4.56
32-4.56
33-4.88
34-4.88
35-between 4.88 and 5.29
36-5.29
37-5.29
38-a little closer to 5.71 than 5.29
39-5.71
40-5.71

****If you have an auto tranny, or your truck came with a larger tire package, you will want to refigure your travel length by multiplying your tire height by 3.14159, and dividing that by your differential gear that came stock. Then you can compair your number to the chart.****

You will start to want lower than stock gearing with bigger heavier tires, but these combos are all within 3% of stock, so no exuses for speeding tickets! That's a good one!

Any more questions?

 

[Tools R Us]

Good post, a couple of points to add;

Doing the math is a good start for tire size. But if possible stretch a tape on the tires, preferably mounted on the rims. Most manufactures play loose with the numbers, with most tires being smaller than advertised.

Depending on engine, transmission, model year, stock tire size, etc there were several ratios from the factory. Your stock gearing needs to be determined before looking at an upgrade, if you have a 4 cyl auto, it may have factory 4.88's and 5.29 or 5.71 would be your only lower choices. Unfortunately the factory 4.88 housing is different and only those gears will fit, so to change ratio another set of diffs will be needed. Links to diff ID pages;

http://toyota.off-road.com/toyota/article/articleDetail.jsp?id=274535

http://home.4x4wire.com/erik/diffs/

 

[beatdown83fj60]

Yeah, I'd say that pretty much every tire I've ever ran wasn't the advertised size. I think the closest was probably my BFG AT's, and my 33x13.5 LTB's but neither of them were exactly the size written on the sidewall. Also don't forget the difference between putting that exact tire on a 15x8 or a 15x10 which afffects the final tire patch/true ride height. Im gonna lay a tape across my MTR's this weekend and see how close they got. Honestly from memory the 35" MTRs don't look a whole lot taller than my 33" LTBs were.

 

[tntoyota]

the best stuff I have, and cant down load is in the downey cat and Lc engineering cat

Awsom stuff you can see the %ages in the downey PER gear then compare to the %ages on there tire size chart EZ!


ALL Toyota diffs, gear ratio and r&p codes on one page!


LC has a RPM in 4th gear AND 5th gear/ tire size/ gear ratio, chart 30" to 44" tires and all gears available again EZ!

you can see the differences, then easaly choose up or down you can see too much to little, too EZ!

 

[mith]

Any more questions?

As a matter of fact, yes.

What would be the downside of running lower gears? For example, Your chart has 4.88 as the gears closest to stock setting for 33 inch tires. If someone were to run 5.29 on their 33s, what sort of problems might they expect. I mean, aside from the speedometer reading lower than their actual speed. It wouldn't be wearing any of the drivetrain at an increased rate than the "stock" setup, right?

 

[2ndGenToyotaFan]

No problem with going with a lower (numericly higher) gear, but your speedometer would show faster than actual speed if you are "Overgeared". You would get more use out of 5th gear, but at top speed your RPM's would be a bit higher than stock.

Thanks guys, I meant to put in a disclaimer on a few points.

 

[Tools R Us]

As a matter of fact, yes.

What would be the downside of running lower gears? For example, Your chart has 4.88 as the gears closest to stock setting for 33 inch tires. If someone were to run 5.29 on their 33s, what sort of problems might they expect. I mean, aside from the speedometer reading lower than their actual speed. It wouldn't be wearing any of the drivetrain at an increased rate than the "stock" setup, right?

Anytime a lift and/or bigger tires are installed it will increase the loads, angles on drive train components, slightly increasing component wear. Bigger tires are heavier and have more rolling drag, a lift makes the truck push more air, added up it takes more power to roll down the road, so going slightly lower than "stock speedo correct" will net better driveability.

The other issue is where you drive. In Ohio's hills close to stock would probably work OK. If you live or travel to areas with mountain roads somewhat lower gears are beneficial. Think of lower gears as a longer lever arm, allowing the motor to turn the tires, move the truck with less effort.

 

[krustyroo]

Awesome info.

Krusty

 

[Devil's Slide Doug]

If you allready have serious meats on your truck just delete this, if you still got a stocker and care about my subjective thoughts on gearing it might be slightly of interest. Who has not had there truck/tire size evolve? As the original owner of a 22re 5spd truck I started with 225 r15 tires and 4.10 gears untill I upgraded to 30" followed by 31" tires. I felt a "decrease in power" every time I upsized. Next I installed factory v6 4.88 gears(with 31" tires) and the difference was quite noticable. I could now race folks from the stop light (and win). It did feel a bit buzzy on the highway however. I now have 33" tires with a mild lift and the truck feels like a slug again. Despite a gear ratio that is still lower than stock the bigger tires are just gonna take a lot more work. The funnest combo on the street was the 31" tires with 4.88's. I sure like the 33's on rougher trails though. the only reason I have not gone larger is the limitations of IFS.

 

[bkg]

Good post, a couple of points to add;

Doing the math is a good start for tire size. But if possible stretch a tape on the tires, preferably mounted on the rims. Most manufactures play loose with the numbers, with most tires being smaller than advertised.

Depending on engine, transmission, model year, stock tire size, etc there were several ratios from the factory. Your stock gearing needs to be determined before looking at an upgrade, if you have a 4 cyl auto, it may have factory 4.88's and 5.29 or 5.71 would be your only lower choices. Unfortunately the factory 4.88 housing is different and only those gears will fit, so to change ratio another set of diffs will be needed. Links to diff ID pages;

http://toyota.off-road.com/toyota/article/articleDetail.jsp?id=274535

http://home.4x4wire.com/erik/diffs/

4-cyl autos came with 4.30 gears. The only auto's that came with 4.88's from the factory were the V6 SR5 models w/ the 31 tire package.

As a matter of fact, yes.

What would be the downside of running lower gears? For example, Your chart has 4.88 as the gears closest to stock setting for 33 inch tires. If someone were to run 5.29 on their 33s, what sort of problems might they expect. I mean, aside from the speedometer reading lower than their actual speed. It wouldn't be wearing any of the drivetrain at an increased rate than the "stock" setup, right?

Run em. 4.88's w/ 32's is about as perfect a ratio as you'll find for a 22re/5-speed vehicle.

Anytime a lift and/or bigger tires are installed it will increase the loads, angles on drive train components, slightly increasing component wear. Bigger tires are heavier and have more rolling drag, a lift makes the truck push more air, added up it takes more power to roll down the road, so going slightly lower than "stock speedo correct" will net better driveability.

The other issue is where you drive. In Ohio's hills close to stock would probably work OK. If you live or travel to areas with mountain roads somewhat lower gears are beneficial. Think of lower gears as a longer lever arm, allowing the motor to turn the tires, move the truck with less effort.

Agreed. Great points that are often overlooked.

 

[4RUNNY]

Awesome write up. 33's and 4.10 with a 3.0 just don't mix on mountain highways, but in low gear the set up can still perform moderately.

 

[G8tor]

I have a 94 x-cab with the 3VZE / Auto / 4.88 setup on 33x12.5-15 BFG MTR's and it performs well both on and off the highway. Once I do my SAS, I will switch to 529's and 37's.

When I was getting my Detroit installed, the guy who did it forgot about the 4.88 third being different and had to put 4.30's in for about a week. The difference was obvious to me on the freeway. I didn't have the torque or the top end with 4.30's. Seemed like I was always driving in passing gear because 5th just couldn't keep up.

 

[pappy]

This is a good back to basics post.

Run em. 4.88's w/ 32's is about as perfect a ratio as you'll find for a 22re/5-speed vehicle.

Well, I'm not going to agree. I ran 32" tires forever with my 4.10 gears. Ya, it sucked, but I did it and didn't have any problems.

Fast forward 12 years, and I installed 4.56 gears. Much better with the 32s, which I still run on the street (until bald). The 4.56 gears are good with my 33" MT/KMs too. With a low-than-stock transfer case this is a great combo. Lower rpms on the freeway, combined with the lower gears needed for off-road.

I ran 4.88 with 33" MT/R on my xcab and the freeway rpms were way too high. I really didn't like it. I don't consider 3200rpm acceptable on the freeway.

What it comes down to is personal preference and how well your engine handles the gears. With a lower-than-stock transfer case you can run a higher diff gear (numerically smaller) to keep the engine from screaming on the highway, and still have plenty of gear for the rocks. With a stronger engine you can also get away with higher diff gears. FJ60s came with 3.70s. Guys with 33" tires frequently regear to 4.11. If we used Jerod's table for the FJ60 and installed 4.88 in the diffs the engines would be living at redline on the freeway.

The table Jerod posted is a great starting point, but there are other factors that need to be considered.

 

[2ndGenToyotaFan]

Well that table is really for the 22RE/5 Speed combo... but the math can be worked out for any other vehicle or engine trans set up...

 

[Hilux]

. I don't consider 3200rpm acceptable on the freeway.

Hate to dis-agree with you, but, depends on the engine. A 3Vz with an auto tranny will fall on its face if it's not turning high rpms on the freeway...god I hate to say that...(good motor, but lousy highway mpg)

THIS is exactly what gets a lot of ppl in trouble. They THINK it's a Chevy motor that can tool around at 1,500 rpms at 70mph...

Not gonna happen with most pre-mericanized Toyota's (V-8's, aluminum block & alum head), that includes the 1fZ IMO.

Not boat motors, motorcycle motors...they need to spin...

Also can be seen on torque curves.

 

[GRM]

I ran 4.88 with 33" MT/R on my xcab and the freeway rpms were way too high. I really didn't like it. I don't consider 3200rpm acceptable on the freeway.

I run 5.29's and 35's, and run 3200 on the highway. Its high, but acceptable. It makes driving the hills much nicer. I normally run it between 3000-3600.

Also note, that if you run a bias ply tire, your rpm's will be slightly lower than with radials, due to a slightly higher rolling radius.

Now talking about re-gearing, who is familiar with changing out speedometer gears, as my truck reads 80 mph when Im really doing around 73.

 

[pappy]

Well that table is really for the 22RE/5 Speed combo... but the math can be worked out for any other vehicle or engine trans set up...

I realize that, which is why I said:

What it comes down to is personal preference and how well your engine handles the gears.

The table Jerod posted is a great starting point, but there are other factors that need to be considered.

I run 5.29's and 35's, and run 3200 on the highway. Its high, but acceptable. It makes driving the hills much nicer. I normally run it between 3000-3600.

I agree that sometimes higher rpms are necessary. But, that is what I have a transmission for. I can cruise all day in 5th on the flat ground. But, I guarantee you when I make the climb to Flagstaff from Phoenix I'm down a gear or two. I just don't find it necessary or desirable to run those 3000+ rpms all the time.

 

[GRM]

I agree that sometimes higher rpms are necessary. But, that is what I have a transmission for. I can cruise all day in 5th on the flat ground. But, I guarantee you when I make the climb to Flagstaff from Phoenix I'm down a gear or two. I just don't find it necessary or desirable to run those 3000+ rpms all the time.

I also don't find it desirable to go slower than 70 mph, which is why I run my truck at 3000-3200 down the highway.

Compared to my old 4runner with 4.10's and 35's, and it didn't have the torque to hold 5th gear and drove at 3200 rpm's anyway.

 

[WristPin]

so what gears do i need to run my 52" michlens?