What gears are factory and what should I run ?

[swathdiver]

Does that also include having the 22x14 wheels as well ?

No, it's the diameter of the tire that affects the rpms. Take note, that every pound in rotational mass that you add to your truck is the same as adding 8.4 pounds to the body or payload.

For example, my white Sierra's original tires and wheels weighed 73 pounds each. Then added 35 inch tires which weigh 81.5 pounds each and the wheels happened to be 5 pounds less than the stock ones. So that wheel and tire assembly is 111.5 pounds. Subtract the two and you can see that we've added 38.5 pounds per wheel of rotational mass! Times four that's 154 pounds added to the weight of the truck but it has the net effect of adding 1,294 pounds of rotational mass to the truck. So even with 3.73s and the 6.2 motor she still only turns 15s in the quarter mile when she should have been a second faster. Regearing helps.

 

[swathdiver]

GM under-gears nearly everything they make - trying to satisfy CAFE MpG tests and avoid fines.4.10 would DEFINITELY be better - city MpG would improve, enough to overcome the highway MpG penalty, at least for me.If 4.10 is 'more equivalent' to GM's OE gearing, then 4.56 would be better.

Better has to be defined. The engine would turn more rpms but at less load. Gas mileage around town might be the same or better but highway mileage may suffer. Then there's the potential for exhaust resonance due to the higher rpms if the system was modified.

Our 6-speeds with 3.42s have deeper gearing than the 4-speed guys with 4.10s:



The 10-speeds now make our 6-speeds look antiquated!

 

[Marky Dissod]

GM under-gears nearly everything they make - trying to satisfy CAFE MpG tests and avoid fines.

... been told that 3.73 wasn’t enough for 32" tires.

4.10 would DEFINITELY be better - city MpG would improve, enough to overcome the highway MpG penalty, at least for me.

... So if you compare the before and after, you guys were correct and I was wrong about 4.56 being more equal, 4.10 would be more equivalent while running 37s!

If 4.10 is 'more equivalent' to GM's OE gearing, then 4.56 would be better.

Better has to be defined.

Indeed.
1: GM under-gears their vehicles off the showroom floor (especially their V8 vehicles) as per above.
Despite the superior initial gearing of the 6L80E, 8L90E, and the FGM 10L/R90, those last gears are STILL under-geared, because the CAFE tests misrepresent how normal Americans cruise on the highway in real life.

2: As per your previous post ...

... every pound in rotational mass that you add to your truck is the same as adding 8.4 pounds to the body or payload.

If GM already under-gears their trucks & SUVs, and then someone adds 1,300lb of rotational payload ...

4.56'd be better than 4.10, even with a 6L80E. I'd not even suggest or consider 4.30 instead of 4.56.

Driven a few Caprice PPVs - 6L80E, 2.92 axle, under-geared as per GM's usual.
I personally know a guy who went with 3.45 axle in his PPV (same wheels & tires by the way).
Highway MpG unchanged despite disabling V4mode permanently, city MpG improved.

 

[swathdiver]

...because the CAFE tests misrepresent how normal Americans cruise on the highway in real life.

Can you elaborate on this, I don't quite understand what you mean. Around here most folks are doing 80 on the highway and a higher ratio would seemingly offer better mpgs.

GM offered the 3.08s for those interested in fuel economy and 3.42s for those wanting to tow. Then for the pickups, they even offered 3.73s for even better towing prowess.

 

[OR VietVet]

Can you elaborate on this, I don't quite understand what you mean. Around here most folks are doing 80 on the highway and a higher ratio would seemingly offer better mpgs.

GM offered the 3.08s for those interested in fuel economy and 3.42s for those wanting to tow. Then for the pickups, they even offered 3.73s for even better towing prowess.

I am curious about that too.

 

[Marky Dissod]

CAFE = Corporate Average Fuel Economy
GM - not just Chevy or GMC or Buick or Cadillac, but GM - has representatives of all the vehicles it sells in any given year tested for the 'city' and 'highway' fuel economy scores you see on a new vehicle's Monroney sticker.

The tests are based on 'drive cycles' that were not accurately representative of how normal drivers drove in the 'city' or on the 'highway' in 1975 (after the 1973 OAPEC Oil Embargo), and are even less representative of 'city' or 'highway' driving today, despite adjusting the scores downward.

Although individual vehicles do not have to meet these standards, the entire fleet sold as an aggregate does.

A car company can adjust its CAFE MpG aggregate score by:
selling more tiny schidtboxes / incentivizing customers by adjusting prices for Chevy Sparks
creating 4.3L V6s, 4.8L V8s, downsizing 5.7L V8s to 5.3L, etc
creating technological advancements such as EGR, variable valve timing & lift, V4mode, stopstart, etc.
under-gearing vehicles larger vehicles with larger engines
creating the L3B / L2R TurboMax 4 cylinder engine

 

[OR VietVet]

Oh, I know they average it every year for the gov. I also know they try to make 'em lighter each year and more aerodynamic and all to get the mpg up. I was just confused how the gearing you spoke of would arrive at the point of helping with that.

 

[Marky Dissod]

Oh, I know they average it every year for the gov.
I also know they try to make 'em lighter each year and more aerodynamic and all to get the mpg up.
I was just confused how the gearing you spoke of would arrive at the point of helping with that.

Normal people usually calculate MpG to two places (xx MpG).
CAFE tests calculate MpG to four places (xx.xx MpG) for each vehicle, AND all vehicles sold by a company yearly.

So, to improve GM's CAFE in the mid-'90s, for example:
Caprice & RoadMaster wagons, and Fleetwoods, had 2.56 or 2.93 instead of 3.08 or 3.23
Which allowed only so many Caprices to be 9C1 or WX3 with 3.08, and very few Fleetwoods to be V4P with 3.42
(V4P Fleetwoods just barely limbo'd under the gas-guzzler threshold by 0.9MpG)

To us, the MpG difference between one 3.73 vs one 4.10 Tahoe or Suburban may be meaningless.
To GM, that difference gets multiplied by each vehicle sold, which is why many are slightly under-geared
(and a few woefully so).

Long story short:
The gov't incentivizes car companies to slightly under-gear heavier vehicles with larger engines.

 

[Jonpen]

So I went with the 4.56 gears and I guess we will see how it goes

 

[Jonpen]

Thank all you guys for the advice and info