Gear Ratio Calculator and Tire Size Calculator!

[Trail X]

Interesting. We don't want to get TOO specific with subforums, but you may be on to something. Let me discuss with the team.

[zpbitt]

This is great! Thanks!

[Shdwdrgn]

Hey it only took me a little over a year to notice there was a sticky about the tools. I'm special!!!

Glad every likes them. The gear ratio calc was put together when I was trying to wrap my head around just how much difference I would see when swapping between 3.42 and 4.10 gears. It was real helpful to match different tire sizes and gears on the same screen and realize that my engine wouldn't be 'screaming' going down the highway with 4.10's. I knew from you guys that 4.56's were also a common one being used, but I wanted a changeable field in case other gears were considered. The hardest part was getting it to actually calculate the colors for the power curve, rather than just hard-coding the results. Since the math is done, the table could also be expanded out to other tire sizes as well.

On the tire calc, the Tacoma site was actually the model I used for my design. I spent a lot of time trying to also plot out the swing of the tire inside a wheel-well with user-entered wheel size and offset, but I just couldn't get it to plot consistently. I still have the code if anyone wants to look, but it would probably be better to just start over.

[Bacnbit]

I used this one when looking at tires and gearing and speedo corrections befor finding you guys it has the pretty much everything. Tire comparison size, gearing per tire size etc. See what you think.
http://tire-size-conversion.com/tire-size-calculator/
If it helps great if not no big deal.

[Cody_S]

Any thoughts as to labeling dangerous zones for gear ratio/tire size combos? Like which combos should be running a transmission cooler or something?

[TBYODA]

Any thoughts as to labeling dangerous zones for gear ratio/tire size combos? Like which combos should be running a transmission cooler or something?

I have only read about not going above 32" with 3.42, there has been talk about running 33" with cooler on 3.42 between a few members and I but IMHO you should run a cooler with bypass above 31" anyways because it's cheap insurance.
I would like to know what the consensus is from the other members as what is the max tire size with each gear ratio cause it would help new members. Putting it on the chart could be helpful to every one very much.

Edit: I guess this also depends on your "mission".

[Shdwdrgn]

So, including the info that mikekey provided in the other thread, how does this look?
http://sourpuss.net/projects/vehicles/t ... arcalc.php

[Trail X]

I like it, I'd probably pull it back so that 32s and 3.42s isn't in the deep red. It's driveable. I'd put it pink. So I guess I'm saying, shift the red down a bit more.

[TBYODA]

Could you also expand the chart to include larger tires to show were the higher gear ratios starts to get pink --> red. Not that I am going there any time soon. Just think it would help those planning to re-gear in what they can do or can not do safely. Maybe also have a note that it is required to have a tranny cooler with a bypass near the pink zones.

[Shdwdrgn]

I'll leave the notations up to James if he wants to move these changes over to the site.

Red zone has been shifted some, let me know if it should slide more. I just have to change one number in the code to adjust the calculations, so its an easy change.

I increased the chart up to 40" tires so you can see the ranges... although I probably wouldn't suggest showing that much here on the site since it might give newcomers the wrong idea that they could actually build their truck that way.

[Trail X]

At first I thought 40"ers was too much, but then I remembered we had a few SAS guys that are still running the same transmission on some tires in that range, so maybe it makes sense.

I think I agree with the positioning of the red. Any other inputs on that?

[navigator]

I would agree that 3.42s and 32s would be pink.
I am running that combo right now without a cooler and have seen my temps get over 220 a couple of times either pulling my boat (in OD) or running down the interstate at 78 mph. Dropping down to 3rd pulling the boat or down to 75 on the interstate helped my temps.

I also live in flat country so guys in more hilly terrain or hotter summer temps might have more issues with temps creeping up.

[TBYODA]

I would agree that 3.42s and 32s would be pink.
I am running that combo right now without a cooler and have seen my temps get over 220 a couple of times either pulling my boat (in OD) or running down the interstate at 78 mph.

What are you waiting for to add a cooler it is very simple and cheap mod. You rather rebuild your tranny? IMHO your looking for failure.

[Trail X]

Good points Robert, but lets keep this thread on the topic of the calculators.

[Trail X]

The calculator on the ORTB page has been updated with Jeff's latest updates. Thanks again Jeff.

[N7RMK]

ok so i have 3.42 gears and run 30.5" tires. at 65mph (gps confirmed) I'm running just a hair over 1800 rpm. according to the chart i should be 1704. am i missing something here?

[Trail X]

If 65 on your speedometer matches your GPS saying 65, then your tires simply are stock diameter. Really no two ways about it.

[N7RMK]

If you look at the pic the speedo is reading 66 mph. The GPS read 65mph sustained for miles . The tach is at just a hair over 1800 also sustained for miles. So again I ask what am I missing here? 65 mph 30.56" tire hair over 1800 on tach

[Shdwdrgn]

No I think he's referring to the 100rpm difference in his tach... The numbers used for the calculations are based on what GM provided for a brand new system without any wear. You might have old transmission fluid, or slipping clutch plates, but my guess would be that your tach needle is simply inaccurate. Nothing on the dash can really be trusted. The only way to know for sure what your true RPM is would be to hook up a scanner to the ODB-II port and get the exact reading directly from the computer.

And if you really want an accurate comparison, you have to take into account that your speedo is showing 66mph (at which the chart says your tach should read 1731rpm). If your tires are completely worn down, that could make a difference of 1/2" or more, accounting for another 30rpm. Did you check your manufacture's website for the 30.5" diameter, or did you just pick that off of a general calculation for your tire size (any given size can vary by 1/2" diameter or more depending on the manufacturer and how aggressive the tires are)? Were you going up hill, down hill, or on a level surface? Was your torque converter locked? The point is, if you want to try and chase down a 100rpm discrepancy, then you need to get extremely accurate with the numbers you are using for your calculations.

[N7RMK]

Manufacture spec is 30.56 tires are maybe 5% worn. Level ground cruise control set (if that maters)