Right now I have 4.88's with 35's. Starts are sketchy and I can use 5 gear, not enough power to maintain unless it's on flat ground. I'm going to 5.29's or 5.71's and 38's or 40's.

 

I wouldn't get 4.56's if i was you, i don't see them making any real difference with 35's. Personally i run 35's with 4.88's. With 4.88's you will have very good acceleration in 1st - 3rd gears (you'll notice a huge difference starting off in 1st) but top speed isn't great, you won't be winning any races. I do have to shift between 4th an 5th but that doesn't bug me, an there is one long steep grade around here where i have to shift into 3rd, but thats still doin like 50mph. Still i can cruise at 70 if i want, but i usaully keep it at 60-65 just to save gas. I wouldn't run 5.29's because i prefer to get my low gearing in the transfer case and keep my axle gearing as close to stock as possible.

 

I disagree. The pre-figured tables maybe. The equations are just that, mathematical equations. There are variables and constants. Speed and engine torque are constant. The tire size and gearing can be varied. The equation allows you to determine the appropriate gear change for the tire size change that has or will be made. (or vice versa - gears for existing tires or tires for existing gears)

Ex.
Stock Toyota 65mph x 4.10 x 336 / 29 = 3087

Altered Toyota 65mph x 4.88 x 336 / 35 = 3045

Or 65mph x 5.29 x 336 / 35 = 3300

So which is closer to stock as designed by the Toyota engineers? It has nothing to do with V8 or I4 or V6 or any of that. Now those examples I have given are based on the equation in the link I posted earlier. From what I can gather that is the figure for 4th gear in a 5 speed transmission. I base that on info found in this link from Randy's Ring and Pinion.
http://www.ringpinion.com/Calc_RPM.aspx
The above results coincide exactly with the 4th gear results in the calculator found there. Unfortunately the 5th gear #s will be off because Randy's assumes a 0.80 5th gear and (at least for me with a W56 the figure is actually 0.85) Also note that the Randy's site shows recommended RPMs for a 4 cylinder engine in the 2200-3200 rpm range so...

I'd like to see this statement backed up with some documentation.

I'll go along with that. Pretty much true of any engine.

As requested by the OP, please keep it on the subject at hand. He is trying to solve a problem, not just accept the status quo or give up.


To the OP, it looks like you got the info you needed from 4crawler in a concise and straightforward manner. The rest of it is just opinions, mine included, and you will have to sift through them and decide which you agree with and why. If you decide to buck the trend of the majority, good for you, but expect a certain amount of backlash for doing so. Again, good luck and let us know what you do and how it works out for you.

 

Ok, so I crunched some numbers today and had an epiphany after I noticed similarities between my truck and what "theAuthority" had said about his on post #21 . I am going to risk exposing myself as a DB but will do so in hopes of helping someone else.

I am now very confident that I have 4.88 gears in my truck. I was assuming my gears were stock since the truck is undergeared but now I suspect that the person (kid) I bought the truck from upgraded from 33" to 35" without changing the drivetrain.

I will be looking to swap my tires for some 33s asap and will likely get some 31 or 32" tires for towing and 4.7 gears in the transfer case for wheeling.

Id like to thank everyone who posted in the thread, you helped me realize what I think is the best options for my truck

 

How did you determine this? Just curious.

 

i used this equation knowing that my truck odo read about 16% different (less) than the odo on my gps

.84x=4.10

x = what gears I have in my truck
.84 = 100%-16%
4.10 is the stock gears that my truck odo is calibrated to


solve for x
x=4.10/.84
x=4.880952....
YAY math class!

 

Jack it up and count the rotations to be sure. One full rotation of the tire will equal your gear ratio in turns of the drive line (4.88 turns). If you are locked it's easy. If you are open, leave one rear tire on the ground and do the same, but rotate the tire two full turns. Good luck.

Chock your tires and put the tranny in neutral with the parking brake off.

 

will do, thanks

 

Did Toyota engineers design for this 100hp engine to have 35's on it? No the did not you have the extra rotational weight, and extra width of the tire all causing drag on the drivetrain......

I'd also like to know how you have 4.88's?, jack it up and rotate and see how many rotations it takes.

 

You can't use how far off your speedometer is to determine your axle ratio, the speedometers are always off (even from the factory) and you don't know where it started. For example, my 4Runner's stock tire size is around 30", and I'm running 33" tires now. That's a tire size increase of 10%, but my speedometer only reads 3% slow, because it read incorrectly from the factory.

If you're too lazy to jack up your truck, you can record your RPM's at 60mph (on your GPS) in 4th gear (we will assume your tach is reading correctly). Using this number you can calculate your axle ratio since you know (approximately) your tire diameter, you can calculate the number of tire rotations per minute at 60mph, and the 4th gear ratio is 1:1. For example, if your tires are exactly 35" in diameter, and you have 4.88's, you should be around 2812 rpm at 60mph in 4th. If you have 4.56's, 2628rpm. If you have 4.10's, 2363rpm. For reference, 5.29's would be 3048rpm.

 

I didn't use the speedo. I used the odometer difference after a full tank (over 230 miles). I am confident my math is correct but I am not lazy, I will jack up my rig today

 

Haha, the odometer uses the same input as the speedometer (it's just a summation over time of the speedometer). Using one is the same as using the other.

The only way to get an accurate measurement is my method which assumes the tachometer and GPS are accurate (probably a good assumption), or jacking up the vehicle and measuring the ratio directly. Keep in mind that you'll want to spin the wheel several times and watch how many times the driveshaft rotates, the higher the number of times you spin the wheel the more acurate your measurment will be (around 10 times is probably best, where the driveshaft should rotate around 41-48 times depending on your gear ratio).

 

my FSM says the speedo is within factory specs while being up to like 5mph off...

 

Yep, speedo and odo can read differently, odo is most "accurate" in that is is 100% gear driven off the cable and simply counts revolutions. Of course it can be off with gearing/tire size mismatches, since it in effect counts drive shaft revolutions and not tire revs. The speedo is more prone to being off as it relies on a spinning magnet and a spring (in a mechanical speedo) to register a speed. On my '85 with 4.88 gears, I find the odometer is within 1% error with 33" tires but the speedo is off, have to drive nearly 70 on the speedo to go 65 MPH. But with 35s, the speedo is almost dead on and the odo is off (due to the larger tire diameter).

 

This is what I have found with my 35/5.29 combo. Speedo 70mph - Actual 65mph (per a gps unit) I lose about 1 mile for every 20 travelled on the odo.

 

OK, now I am officially confused. I rotated the tire twice and the driveshaft moved just over 4 times. Is this odd that I can drive around even on the steepest hills in Seattle in first gear with the truck undergeared so much. Albeit its not fun to do but i can do it

 

Spin it 10 times and watch the driveshaft, it will give you an accurate estimate of the ratio. Twice isn't really enough, but it sounds like you definitely don't have 4.88's, maybe 4.10's.

Keep in mind, were both tires spinning, or was one stationary? That will throw a factor of 2 in your result. So say you spin the tire twice and the driveshaft spins 4 times, if both tires were spinnning together the d-shaft would have spun 8 times.

 

Several ways to determine differential gear ratio:
- http://www.4crawler.com/4x4/4R_TechI...oDetermination

 

Sounds like you have a 4.10 then. Toyota's have low first gearing traditionally.

 

One tire was still on the ground, I will have to wait for my roommate to get home to rotate the tire that much