What gears should I get? 4.56 or 4.30?

[Chuck6669]

I just put a 8" lift on my truck with 37" Toyos. Which gear ratio would get me back to the stock rpm range? Right now at about 70 mph I am running somewhere around 1700 rpm. How many rpm's would I be running at with the 4.56 at 70 mph? And how many rpm's will I be running at with the 4.30 gears?

[Chuck6669]

Anybody??

[layson]

What do you do with the truck? How do you like the combo you are at right now?

I have 4.30's for 40's. It is great for me, for what I do with the truck. Joe on here, CSIPSD has 4.30's with 37's and he hates it. It is great for towing. Most recommend 4.10's for 37's, but that to me isn't worth the cost for such a slight change.

If I have time tomorrow I will throw them in my excel sheet and see what RPM you want to be at...

[Chuck6669]

Originally Posted by layson

What do you do with the truck? How do you like the combo you are at right now?

I have 4.30's for 40's. It is great for me, for what I do with the truck. Joe on here, CSIPSD has 4.30's with 37's and he hates it. It is great for towing. Most recommend 4.10's for 37's, but that to me isn't worth the cost for such a slight change.

If I have time tomorrow I will throw them in my excel sheet and see what RPM you want to be at...

I do some towing with my fifth wheel camper and a horse trailer.
I was looking at a rpm calculator and at 70 mph, 37" tires, 4.56 gears and .71 final drive the calculated rpm is about 2060.
With 4.30 gears it comes out to 1942 rpm which is close to the calculated 1960 rpm with stock size tires.

However it seems like actual real time rpm is slightly greater than a conversion chart.

Using a mph calculator: at 2000rpm, 4.30 gears, 37" tires and .71 final drive it comes out to 72 mph. Using the same formula with 4.56 gears it comes out to 68 mph.

I am hoping as many people that read this will chime in and share their experience with their setup after lifting their truck and going with bigger tires. Thanks guys and look forward to everybodys experiences.

Also Layson if your excel shows different results PLEASE let me know. I really dont want to be under geared or over geared either.

[Fall Guy]

I havent messed with the gears in my 7.3. My mud truck 84 Chevy K30 I used to have 4.88's w/ 40's. Worked great, but totally different scenario. From looking at different setups it looks like a popular combo is the 4.30's & 38-40" tires

[layson]

Here is mine, 4.30's and 40's...

[Chuck6669]

Wow! it looks I definitely should not get the the 4.56 gears I almost bought a set from a guy on Ebay. He was saying his truck seemed pretty wound up going down the interstate.

For the guys that have 37" inch tires what gear ratio did you change to?

Seems like I should be getting the 4.30's and no more. What do you guys think?

[layson]

Yep, shoot a pm to CSIPSD. He has 4.30's and 37's. I think a guy named oregonstroker has 4.56's with his 37's or 38's...

[belz]

According to the calculator i used with a OEM size of 265/75/16 (I think thats what comes on the truck) when comparing to a 37" tire, if you run 4.30 gears u get an effective ratio of 3.68 with the stock tire and if u run a 4.56 u get an effective ration of 3.90. And it says you will be looking at a difference of about 291 rpms up or down depending on the 4.30 or 4.56. Either way I would not do a 4.10.

I run a 4.56

[Chuck6669]

Originally Posted by belz

4.30 will put u slightly under stock tires and 3.73. 4.56 will put u slightly over. I run 4.56 and I am very happy. Lots of power on takeoff and runs 80 easilly on the hwy.


Sent from my portable forum surfing device.

Actually the reason I was even considering 4.56 gears was because the guy that did some body repairs on my truck has 38's on his truck and he was saying he liked the setup and it put him pretty much right back at stock rpm.

Just doing a comparison between Toyo M/T's, the 37's should run about 68 mph with 4.56 and the 38's, actual size is 37.7, should run 69 mph at 2000 rpm.

The same setup with 4.30 gears, using a mph calculator from angelfire.com.
37" tires should run about 72 mph and the 38's 73 mph.

Just to complicate things a little more using the same calculator, 40" tires at 2000 rpm with 4.30 gears should run about 78 mph and with 4.56 gears it comes out to 74 mph.

But the reason I started this thread was to get as much info from you guys, from your real experiences after you modded your trucks and not exactly from some rpm and mph calculator. I guess with the calculator it will get us close to our goals but ultimately it boils down to what we are willing to sacrifice regarding mph vs rpm.

But lets here a few more testimonials with your current or previous setups, hopefully this thread will help other people decide which gears they should choose after they they lift their truck up and put bigger tires on. I will try to insert the link from where I was getting all the data for mph and rpm calculations. MPH Calculator Woody's Fairlane Site

Thanks every body I appreciate everyones help.