Opinions on gear ratio?

[RecklessWOT]

RPM = MPH x Gear Ratio x 336 divided by tire diameter. Run that equation for every single scenario you can think of in relation to tire diameter and gear ratio, and make a spread sheet if you need to, but at least write down each result, and then mull over the numbers to figure out what will work for your specific setup. Nobody will be running the exact same thing as you are, and only you have to live with your decision.

Huh, I never knew that. So with the 700r4 I believe the super tall OD is 30%, 25%? With this equation, at 80mph in D at 1:1 that puts me at 3714 RPM if I go with the 4.56s. In OD that drops me down to 2600 RPM if it's 30% (which is actually pretty good) and 2786 if it's 25% (which really isn't even that bad either considering I'm going 80mph in a big ass truck). Works for me. Obviously I will drop my speeds if towing heavy trailers like the 3/4 ton I seem to pretend it is, but for normal daily use 4.56s actually sound perfect to be honest.

 

[DoubleDingo]

Huh, I never knew that. So with the 700r4 I believe the super tall OD is 30%, 25%? With this equation, at 80mph in D at 1:1 that puts me at 3714 RPM if I go with the 4.56s. In OD that drops me down to 2600 RPM if it's 30% (which is actually pretty good) and 2786 if it's 25% (which really isn't even that bad either considering I'm going 80mph in a big ass truck). Works for me. Obviously I will drop my speeds if towing heavy trailers like the 3/4 ton I seem to pretend it is, but for normal daily use 4.56s actually sound perfect to be honest.

You got it. And if you have a speedometer that is iffy, you can figure out various speeds that you'll drive around town, but you need a tach for that work. 2,600 at 80 is good, but you need to calculate a more realistic speed. 80 mph is not what you'll drive all of the time, so you want it to be a good rpm at say 65, but I just checked and 65 is 2,100. Not too bad as long as you have the torque to keep things rolling. If not, 3,000 rpms in D will keep you going no problem.

 

[RecklessWOT]

2,600 at 80 is good, but you need to calculate a more realistic speed. 80 mph is not what you'll drive all of the time.

Hah, unless I'm driving around town, yeah 80 is completely realistic for me, I rarely go 65. If I'm not going 80 chances are I'm going faster (unless I'm stuck in traffic).


But I know what you mean. Yeah at lower speeds this thing isn't exactly a torque monster, though considering the fact I'm switching from 3.73s it looks like 4.56 will be a HUGE improvement in any scenario. I have already been driving it this way long enough, I just wanted to make sure that 4.56 wasn't too SHORT of a gear for me. That whole 65mph thing you mentioned is exactly what I'm trying to avoid. I got a couple friends with 1 tons that are basically maxed out at 70mph on the highway, I would never want to end up in that situation. Driving that slow makes me lose my mind (lol - see username)

 

[DoubleDingo]

I used to drive like that.

 

[RecklessWOT]

Hah, I have chilled out a LOT now that I'm older (I know I'm still "young" and some of you are legit old dudes, but I'm married and have a kid and am not some crazy 20 year old anymore that's all I meant). I'm not screeching the tires around corners and doing burnouts at every traffic light like I used to. But when I've got somewhere to be I'm not exactly wasting any time getting there either, I'm very high strung and impatient. If I'm on the highway and there is open space in front of me damnit I'm using it I don't care what some sign says. An open lane means cover as much ground as you can while you have the chance. I'm not weaving thru traffic and risking lives or anything, but I'm most certainly not farting around either...

 

[Jrgunn5150]

It's not as simple as just tossing a 2.73 gear in and idling around at 100 mph though.

Gears that are too tall increase load on the engine, and the transmission. They cause the transmission to hunt, and shift up and downshift needlessly. If I can't hold 60 mph on a two lane without the converter locking and unlocking constantly, and the thing downshifting two gears, screaming rpm, slamming back up a gear every time I hit a bug, my gears are too tall.

With 33's on my 4.10 truck, it's borderline too tall for me and I really don't care for how it tows compared to when it was stock with 245's. And I can easily cruise at 80-85 mph down the freeway still.

 

[4WDKC]

Huh, I never knew that. So with the 700r4 I believe the super tall OD is 30%, 25%? With this equation, at 80mph in D at 1:1 that puts me at 3714 RPM if I go with the 4.56s. In OD that drops me down to 2600 RPM if it's 30% (which is actually pretty good) and 2786 if it's 25% (which really isn't even that bad either considering I'm going 80mph in a big ass truck). Works for me. Obviously I will drop my speeds if towing heavy trailers like the 3/4 ton I seem to pretend it is, but for normal daily use 4.56s actually sound perfect to be honest.

Od ratio on 700 r4 is .7:1 and you need to keep in mind the rpm band of your engine tooling around at 3k rpm wont give you an option to down shift and pass someone with these tbi trucks.

 

[shiftpro]

Hah, I have chilled out a LOT now that I'm older (I know I'm still "young" and some of you are legit old dudes, but I'm married and have a kid and am not some crazy 20 year old anymore that's all I meant). I'm not screeching the tires around corners and doing burnouts at every traffic light like I used to. But when I've got somewhere to be I'm not exactly wasting any time getting there either, I'm very high strung and impatient. If I'm on the highway and there is open space in front of me damnit I'm using it I don't care what some sign says. An open lane means cover as much ground as you can while you have the chance. I'm not weaving thru traffic and risking lives or anything, but I'm most certainly not farting around either...

Same here, but I am actually 'older' @ 59. 31 is NOT older (you lucky guy).
What has really slowed me down is the last 15 years I haven't had anything fast enough to get out of it's own way.
Most of the highways in BC are 90Ks (sorry for the metric... about 55 mph). I feel this is already really slow and when I have to deal with someone driving under the limit I tent to umm, tailgate a bit. Or the tourists from another great province that has only straight roads, they hit the brakes and basically 'walk' their vehicles through the curves. Then when there is the odd straight section with enough room to pass, those fuckers boot it and I can't pass. It's easier this summer as I'm driving Big Blue with a 454.

Even with my gutless 305 3/4 ton 4x4, I still estimate my driving time be simply counting an hour for each 100 kilometers (60 miles).
I will surpass the speed limit where I can mountain driving. My 305 does better at 120Ks anyway, keeping it on the pipe.


Back in '80 or '81 I drove from Estevan Sask to Grand Forks BC, just a tad under 1000 miles in 11 hours! I have to admit I was driving a Ford... '73 Thunderbird with a 460. It was difficult to keep it under 80 mph. I left my folks farm at 10 pm and flew through two prairie provinces averaging 100 mph. I had to carry a gas can as I knew there was a stretch with no open gas stations between Swift Currect Sask and Lethbridge Alta. By the time I made it to Lethbridge it was early dawn, and after filling up and heading out of town I could see the mountains on the horizon and that just woke me up and I pushed my foot a little deeper into the carb!

 

[shiftpro]

My project one ton crew cab will be running 4.88s with a 4l80 and 35" tires. And a 496 up front twisting the shafts.
If I find it a little too revy I'll just step up on tire size.

 

[Jrgunn5150]

My project one ton crew cab will be running 4.88s with a 4l80 and 35" tires. And a 496 up front twisting the shafts.
If I find it a little too revy I'll just step up on tire size.

That's probably a good gear, my 496 would really like 4.56's with the 33's.

 

[Rusty Nail]

If you got 4.88s, you TOW that sumbitch to the strip then!
4.88s are for drag racin, silly wabbits.

 

[K588]

I have a 90 V1500 suburban with 33" tires and 4.10's, 700R4 , 350 . I bought it that way from the PO, it runs great, better than any of these trucks I've driven with 3.08 or 3.73 gears in them. If I was the one swapping the gears I wouldn't hesitate for a second to put a least 4.56 in it with an OD trans.
Plans changed on another project and I have a set of 1 tons with 4.88's that will probably end up in this truck in the next year or so.
In my GM world none of these 700R4 trucks would have left the factory with anything higher than a 4.10.
My brother has the same truck as me with 4.56 gears and 34" tires . He daily drives it and has a tendency to drive it like he stole it, hes never once complained about the gears being to low.
The ones above who said swap in a 14B SF 6 lug rear at the same time are giving good advice.

Just my .02

 

[Shorty81]

496/sm465/208, 31" tires, 3.73. 2500 @ 65. I have low range to pull wagons, creep around woods. Perfect for me.

 

[RecklessWOT]

Yeah I ended up buying 4.56s a few weeks ago, now the trouble is finding someone to put them in.

I do all my own work, but properly shimming a differential is just about the one and only thing I'm not about to do myself. Well, I guess I would be more likely to do that than take apart an automatic transmission (tried it once and no thanks ever again) but seriously that's about it. It's so weird though, none of the shops anywhere near here want to touch it, not even the custom 4x4 shops.

I called a good 20 different shops that specialize in trucks, drag cars, driveshafts, transmissions, etc. They all say the same **** "oh we used to have an old guy who did that kind of stuff but he retired/moved/can't do it anymore, you know gears are pretty tricky". Hah, no **** that's why I'm offering to pay someone else to do it. Even the places that were recommended to me by other shops all still turned me away. I was able to find ONE transmission shop who said they'll do it but gave me a rough estimate of over a grand.

**** that. I got a buddy down in CT who will do it, he's got a shop he runs on the side and he's real old school like, used to build Trans Ams and GTOs back in the early 80s (still got a couple of toys and a few piles of parts laying around). I KNOW he's played around with quite a few rear ends over the years, I was just hoping I wouldn't have to drive it 3 hours to drop it off. Not sure when I'll have time to do that.

 

[shiftpro]

If you got 4.88s, you TOW that sumbitch to the strip then!
4.88s are for drag racin, silly wabbits.

No Ruster it's a perfect ratio for overdrive and 35s. Or 5.11s and go to 37s.
I still want my truck a little revy, not lugging in overdrive. Heavy truck, mountain driving...