Rear Gear Ratio?

[JTautomotive]

im looking lift my 1980 k10 4 inch and put on 35 inch tires , i was wondering what rear gear ratio would be the best with a SM465 tranny. Also what speedo gears would be needed?

Thanks
-Justin

[cjlinkster]

I would go with the 3.73 gear ratio. My truck has roughly 31" tires (235/85/16), and the 3.73 seems a little too high for it. However with 35" tires, IMHO it would be spot on.

Check out the gear ratio calculators on the web, most of them allow you to enter the tire size and ratio.

[JTautomotive]

Originally Posted by cjlinkster

I would go with the 3.73 gear ratio. My truck has roughly 31" tires (238/85/16), and the 3.73 seems a little too high for it. However with 35" tires, IMHO it would be spot on.

Check out the gear ratio calculators on the web, most of them allow you to enter the tire size and ratio.

31's are equiv. to 265's. and do you know the links to the calculator?
thanks
-Justin

[cjlinkster]

Just search for one, there are every where on the web.

try this one
http://www.richmondgear.com/101032.html

[JTautomotive]

Originally Posted by cjlinkster

Just search for one, there are every where on the web.

try this one
http://www.richmondgear.com/101032.html

thank you what kind of rpms do you get on the highway with that gearing?

thanks,
-Justin

[cjlinkster]

Like I said with the 31" tires, it is a little high. My top speed is probably 70 with the engine screaming. I don't push it past 70 on the interstate. Around town, the truck is quick off the line.

35" tires would be spot on with that gearing and transmission.

[cory d]

if you dont spend allot of time on 70 mph freeways then i think 3.73 would be pretty good, and you could really pull stumps in low. i have an sm465 with 29" tires. i can start in low because of the 2.73 gears. i have yet to top it out yet, its so high its useless. i would like to swap to 3.08 or 3.42

[Desert1957]

4.10's FTW

[Benderff]

Here's the best calculator. http://www.grimmjeeper.com/gears.html

3.73 would be great, esp if you do much freeway driving. If it's just offroad, then 4.10s IMO. Not a lot of difference between the two.

Your title was "rear gear ratio" you do understand that the front and rear need to match right?

[Rubble]

It depends what your doing with the truck too,I have 35 s on my '86 with 4:10s and when it's in the mud those 35s get hard to turn in high.The 350 is around 325 hp.On the highway at 62 mph I am turnin about 2500 rpm.The 3:73 s would net a bit better mileage though.Also you will probably have some fender trimming fitting 35s on 4" lift. Mine is 4 susp,3 body & still have fronts trimmed bait, 10" wide rims.My diesel is about 6" lift on 35s with 10" rims and the tires will hit fenders when in the rough stuff.
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[spencer_41188]

i have 4.10 in my truck right now with the sm465 and the red line speed in 4th gear is 15 lol the dyno said 122 and i have 235/85r16 the perfict ratio would be 3.73 and im gana do that swop after i put the nv4500 in and thats so i can still go on the interstate with a trailer because you dont tow in o/d

i was thinking about getting the military 37" tires and 4.10 is perfict for them

when i looked these gears up i was shooting for 2000rpm @ 80mph 4th gear and i looked it up for both transmission and both tire sizes

then again this is just my 2 cents and it dont help seeing you wont 35's when i run 31's but 37's are cheap for that big of a tire only problem is its a 16.5" rim and cooker has the rims 100dollarman.com has the tires

[spencer_41188]

then again i have a 1ton and the dana60 and the 14bolt fue gears match you may have more options beeing a half ton

[mopar346]

Man you guys think different than me, a truck needs a low gear and the bigger the tire the lower the gear. By the way a high numeric gear is referred to as low and low numeric gear is referred to as high. 4.56 is a low gear, 3.08 is a high gear. To move the mass of a truck you need leverage from a low gear, as you increase your tire size you make your final drive gear higher, 35s with 56s runs out the same as 29s with 3.55s.

Here is a chart that will give you info on your RPM 1800-2200 or so is the sweet spot for mileage.

[spencer_41188]

Originally Posted by mopar346

Man you guys think different than me, a truck needs a low gear and the bigger the tire the lower the gear. By the way a high numeric gear is referred to as low and low numeric gear is referred to as high. 4.56 is a low gear, 3.08 is a high gear. To move the mass of a truck you need leverage from a low gear, as you increase your tire size you make your final drive gear higher, 35s with 56s runs out the same as 29s with 3.55s.

Here is a chart that will give you info on your RPM 1800-2200 or so is the sweet spot for mileage.

to add on that

this chart only works for a 1:1 ratio in the transmission and 1:1 in the transfer case if you dont have a transfer case dont worry for the sm465 it will be your 4th foward gear if your running an automatic weather its th350, th400, 700r4, 4l60e, or 4l80e it will be the 3rd foward gear

and the axle ratio it is a ratio like 3.73 put it over 1 (3.73/1) think of the first 3.73 number as how many times your driveshaft turns and the 2nd number 1 is how many times your tires turn the smaller the number the harder the engine works to move weight, take off is poor and you may find you idle at highway speed but when you come up to a hill the engine will start to spudder. now for high gears take off is quick and you will shift fast and when it comes to highway speed your engine screaming and gas milege will go way down

some people will put a lower gear in there axle when they have the sm465 so they can use the low as a 1st gear but when it comes to 4x4's that low is real nice to have

[mopar346]

Thank you for clarifying the 1:1 ratio Spencer. I have to point out though that you are still referring to a high numer gear as a high gear.

"now for high gears take off is quick and you will shift fast and when it comes to highway speed your engine screaming and gas milege will go way down"------these are characteristics of a low gear (high numeric, 4.10, 4.56, 4.88)

"some people will put a lower gear in there axle when they have the sm465 so they can use the low as a 1st gear but when it comes to 4x4's that low is real nice to have"---------- I believe you mean a high gear (low numeric, 2.73, 3.08, 3.42)

Not nitpicking, just trying to avoid confusing people that don't know gear ratios.

[spencer_41188]

lol its funny how 2 things can mean the same but not ... im just gana turn the microwave off and quit nuking it and say you know what i mean

but i have a web site .... all you need is your tire size, axle ratio(of your choice and make shure they make it for both axles if its 4wd), your red line rpm, and your transmission gear ratios(if you wont put 1 in the 1st gear space) this will tell you how fast you will go at what rpm but best of all it will tell you what rpm you will be running at 80mph (my truck got 3500rpm@81mph with 235/85r16 tires, 4.10 axle ratio, 6000 red line, and 1 in 1st gear space) http://www.f-body.org/gears/

if you wana know how fast you can go in each gear just fill out the 1st-6th gear ratios real nice if your thinking about a o/d trans

[JTautomotive]

Originally Posted by Benderff

Here's the best calculator. http://www.grimmjeeper.com/gears.html

3.73 would be great, esp if you do much freeway driving. If it's just offroad, then 4.10s IMO. Not a lot of difference between the two.

Your title was "rear gear ratio" you do understand that the front and rear need to match right?

yes i do know i need to swap both, thanks for the link and i think i will be going with a 3.73 since i will be doing quite a bit of freeway driving and offroading. Thanks everyone for all the input
-Justin

[mopar346]

3.73 will not move 35s very well, you'll probably take off fine with the 465 but you will lose a lot of speed on hills.

[JTautomotive]

so which gear ratio? 3.73 4.10 or 4.56?

[clinebarger]

4:10's....You NEED mechanical leverege to move big tires.

I also call Numerically high gears "Lower gears" or "Low geared". This is a teminology thing. I think just about everyone calls 1st gear in a transmission "Low Gear" even though its the highest numerical gear??

[JTautomotive]

Originally Posted by clinebarger

4:10's....You NEED mechanical leverege to move big tires.

I also call Numerically high gears "Lower gears" or "Low geared". This is a teminology thing. I think just about everyone calls 1st gear in a transmission "Low Gear" even though its the highest numerical gear??

Thank you very much
-Justin

[Ski-me]

Although I have the 700r4.....I am currently running 35" tires with 3.73 gears and 6,000 ft elevation. The blazer does a "decent job" but it certainly is not winning any races. At freeway speeds with a slight uphill climb, it works pretty hard and does downshift to maintain the speed. Maybe numerically it looks good on paper but when you throw in a much larger rolling mass (tires) + added wind resistance, the 3.73's might be a bit high.

I'd probably go 4.10's but I don't know how your tranny effects the end result compared to mine.

Right now I have a 14 SF axle that will eventually be 4.10's sitting in the garage waiting to be installed.....

[JTautomotive]

Originally Posted by Ski-me

Although I have the 700r4.....I am currently running 35" tires with 3.73 gears and 6,000 ft elevation. The blazer does a "decent job" but it certainly is not winning any races. At freeway speeds with a slight uphill climb, it works pretty hard and does downshift to maintain the speed. Maybe numerically it looks good on paper but when you throw in a much larger rolling mass (tires) + added wind resistance, the 3.73's might be a bit high.

I'd probably go 4.10's but I don't know how your tranny effects the end result compared to mine.

Right now I have a 14 SF axle that will eventually be 4.10's sitting in the garage waiting to be installed.....

im thinking that im gonna try and pick up a 3/4 ton set dana 44 14 bolt with 4.10s already in them. figured since axles will be out to do lift might as well swap them and have the gears plus stronger axles

[sqzbox]

Originally Posted by JTautomotive

im thinking that im gonna try and pick up a 3/4 ton set dana 44 14 bolt with 4.10s already in them. figured since axles will be out to do lift might as well swap them and have the gears plus stronger axles

Be careful and be sure to check the lug nut count for 8 lugs. their not cheap to buy, used or new and the drums are hard to find for 8 lugs. I have a 76 4x4
with 8 lugs look for 6 lugs.

[russgt]

Originally Posted by JTautomotive

im thinking that im gonna try and pick up a 3/4 ton set dana 44 14 bolt with 4.10s already in them. figured since axles will be out to do lift might as well swap them and have the gears plus stronger axles

Thats a good plan. I went this route and scored a set for $150. They are plentiful and sometimes the frame they are attached is included for free.