High vs low gear count transmissions

[Scott_Milk]

Hey all,
I was just discussing with some friends earlier the benefits of having something like a 10 speed trans vs something like a 4 speed trans for on road use. It seems some people don't quite understand what having more gears mean, assuming more gears mean lower or higher rpm? Which makes no sense. While it can help get you closer to a target rpm and make it more efficient, it won't change the rpm it can run at. They also put a 10 speed in the Camaro ZL1 (top spec) which shows it's also useful for keeping the rpm in the power band when needed. Also note that lower rpm is not always better mpg, only to a point. That's why when you regear after adding all those heavy mods and bigger tires, your rpm goes up (without adding gears) and you can often get better mpg because it's not struggling to pull the weight anymore. While I can understand all this for on street, I was starting to wonder how these high gear count transmission handle off road.

I have never driven anything more than 4 gears off road so I was wondering if anyone else has. I imagine you would be shifting a lot more if you have that controll (manual or sport shifter) or if it's auto, they might be pretty good if they shift quick and smooth. But if anyone has experience with both high and low gear count transmissions for off road, I'd like to know your input.

 

[M Rose]

I have 20 gears... 5 speed transmission, 2 speed transfer case, and an auxiliary transfer case... on the street it’s five speeds, up in the hills putting down those steep gears is nice... so 20 mpg on the street running 3.75 gears and cruising at 70 mph at 2000 rpm, or crawling at .5 mph over that obstacle is nice... with the correct transmission and transfer case gear ratios, there isn’t a need to rehear the axle... yes I could have gotten similar resales by swapping to some steep 5.11 or higher gears, but top end and fuel economy will suffer.

 

[MidOH]

Depends on the manufacturer. Some just don't ''get it''. (looking at you gm square pants)

Fords 6r100g transmission in the new Super Duties had a much lower 1st gear, and slightly better overdrive than it's 5r100 predecessor. 5th and 6th gears are both overdrives. So it's easier for the truck to find the towing sweet spot with 4,5,6. Better crawling, better economy.

You might find that heavier trucks have the top 3 gears closely spaced because of towing. But when you have 7 other gears for accelerating, it's no big deal compromising the top gears for that.

Fords 10 speed is hardly any different than the 6. Should feel fine. You'll lock out the top end gears for off road. Usually 1,2,3 is plenty.

Rear end gear ratio is still key. Don't fear the gear.

 

[tjZ06]

Most of the new high-gear-count transmissions give you "the best of both worlds" as in way deeper lower gears, and way taller overdriveS (plural, as in many of them). The gear spacing is also tighter, meaning the engine can be kept in it's power or efficiency ranges better. It's really a "have your cake and eat it too" scenario, because big advances in the efficiency of conventional torque converter autos mean all of the extra gears really don't add any parasitic drive-train loss, in fact the modern 6-7-8-9-10 speed autos are more efficient overall than the 3-4-5 speed autos they replaced.

Let's take the 2021 Bronco as an example, since it's all the rage right now. The 10 Speed Automatic has ratios of 4.714:1, 2.997:1, 2.149:1, 1.769:1, 1.52:1, 1.275:1, 1.000:1 (so 7th gear is your standard 1:1 gear... in your generic Big 3 4-speed overdrive Auto the 1:1 is 3rd gear), 0.853:1, 0.689:1, and finally 0.636:1 (and FWIW, Reverse is an ultra-deep 4.885:1). Compare that to the last of the Ford Broncos, the 5th Gen that had a E4OD transmission at the end of its run, which had 4 ratios of 2.71:1, 1.54:1, 1:1, and 0.71:1 (and a relatively tall 2.18:1 Reverse).

It's easy to see how the 10 speed has advantages across the board, on or off road. Starting with 1st gear, we're looking at 4.714:1 in the 10 speed vs. 2.71:1 in the 4 speed. The way "deeper" or "lower" (aka numerically higher) 1st gear in the 10 speed will make the vehicle much more peppy off the line, much better for slow-speed off-roading, and much better for towing as well. Think of it this way, assuming the same size tire, the old 5th Gen Bronco with a 2.71:1 1st gear would need 6.49:1 axle gear ratios to have an equivalent overall 1st gear ratio (in high range) to the 6th gen with its 4.714:1 1st gear and the tallest, most mild axle gears that will be offered of 3.73:1. If the 5th gen with it's 2.71:1 1st wants to equal the overall 1st gear ratio of a 6th gen equipped with the 4.7:1 axle gearing (and still having its 4.71:1 1st gear in the trans) it would need a 8:17:1 axle ratio. Now, let's ignore the fact that you can't get 6.49, much less 8.17 gears for a Ford 8.8" axle and look at the other end of the spectrum. If the 5th gen was on 33"s and had that 6.49:1 axle gear ratio but only the 0.71:1 overdrive of it's 4 speed, it'd turn 3k rpm at 65... with our theoretical 8.17s it jumps to 3839 RPM at 65. The 6th gen, even with the deepest 4.70 gears would only turn 1978 RPM at 65 MPH on 33"s, with the 3.73s it'd be only 1570.

So, you see the 10 speed gives a much, much deeper overall ratio for getting moving - but also a much taller ratio for cruising. Then, on top of that it has many more splits in between. For example, let's keep the 33"s but go back to a reasonable 3.73 rear end in the 5th Gen. The RPM jump at 65 MPH with the 4 Speed when knocking it out of OD would be 716 RPM (from 1753 RPM in OD, to 2469 in 3rd). In the 6th gen when going form the tallest gear (.636 10th) to the next-tallest (.689:1 9th) is only 131 RPM (from 1570 in 10th to 1701 in 9th). To be frank, that's almost a ridiculously small drop and I doubt the trans would do much actual 7-8-9-10 or 10-9-8-7 shifting in order. Instead, it has a whole host of ratios to choose from and can find the gear that's most ideal for a given scenario, so you might find it downshifts from 10th to 8th and skips 9 as you go up a slight grade, that type of thing.

-TJ

 

[Billiebob]

I have never driven anything more than 4 gears off road so I was wondering if anyone else has. I imagine you would be shifting a lot more

no, shift early, hold longer, skip a gear

more gears give closer ratios or, add an extra overdrive gear, or as on the new Bronco add a deep reduction granny low
remember old Ford 4speeds in F250s, you always started in 2nd gear. 1st was only used when heavily loaded
that 4speed was technically a 3speed. just like the Broncos 7speed is technically a 6speed
even my Rubi I mostly start in 2nd gear

 

[Billiebob]

They also put a 10 speed in the Camaro ZL1 (top spec) which shows it's also useful for keeping the rpm in the power band

This is a newer engine phenomenum. In the 1960s engines made good torque under 1K rpm and strong horsepower from 2K rpm thru 5K rpm. For years the Chevy 2 speed automatic was the only automatic in Corvettes. Todays engines burn cleaner and with better gas mileage by running in a real narrow rpm band hence the 10 speed transmissions.

If you look at marine engines or fire truck engines they make way more horse power because they are built to run under a constant load.... pumping water, they don't need to shift gears the load is constant so they can be tuned for more power. Which is what automotive engineers are trying to do, narrow the rpm range with many gears and make mega HP.

That is also why the clutch is almost gone. Humans cannot be trusted to manage gear selection like a computer controlled automatic transmission. Letting us pick the gear means poorer gas mileage and excessive pollution so the clutch is gone from pickup trucks. The hold outs will be the off roaders like the Wrangler and the new Bronco.

 

[rtexpeditions]

Interesting discussion. Single range transmissions with more gears particularly in European 4wd's is becoming more common. The VW Amarok, we get in Australia, has a single range 8 speed DSG/Auto transmission with wide-spaced gears whilst only the rare manual transmission models had a High/Low transfer case. A lot of people consider the auto better offroad.

The extreme case of an offroad single range gearbox would have to be Mercedes Unimogs with 8-speed manual gearbox, no reverse gear either, they just reverse the whole direction in the transfer case. Onroad you start in 3rd or 4th gear. Forget Highway speed in 8th though.

 

[tjZ06]

This is a newer engine phenomenum. In the 1960s engines made good torque under 1K rpm and strong horsepower from 2K rpm thru 5K rpm. For years the Chevy 2 speed automatic was the only automatic in Corvettes. Todays engines burn cleaner and with better gas mileage by running in a real narrow rpm band hence the 10 speed transmissions.

If you look at marine engines or fire truck engines they make way more horse power because they are built to run under a constant load.... pumping water, they don't need to shift gears the load is constant so they can be tuned for more power. Which is what automotive engineers are trying to do, narrow the rpm range with many gears and make mega HP.

That is also why the clutch is almost gone. Humans cannot be trusted to manage gear selection like a computer controlled automatic transmission. Letting us pick the gear means poorer gas mileage and excessive pollution so the clutch is gone from pickup trucks. The hold outs will be the off roaders like the Wrangler and the new Bronco.

Personally, I think the whole "old engines had so much torque" but newer engines don't have torque is largely a misconception. Yes, the Powerglide 2-speed was the only auto-trans available in the 'vette for some time, in fact the first 2.5 model years of 'vettes ONLY had the 2-speed Powerglide auto. However, I'd contend that was more out of necessity than engineers thinking the 2-speed was ideally suited to the Corvette or it's engines (just a 6 cylinder in the first two years, then the original small block V8 later in the 3rd model year... when a 3-speed stick also became available). The '54 'vette made a whopping 155/223 HP/TQ. Sure, at a quick glance that looks "torquey" but by modern standards, it's not that the engine had a lot of torque... it's just that it had no horsepower. ;)

For comparison, let's look at that 2.3L EcoBoost that is the base engine in the Bronco. It's rated at 270/310 HP and TQ. While it's the baby, 2.3L base engine it out-torques the old-school engine by nearly 100 lbs-ft. Furthermore, its peak torque is only at 3000 RPM, just 600 RPM higher than the old Blue Flame I6's peak of 2400 RPM. However, the 2.3L makes it's peak HP out at 5500 RPM and carries power well to ~6k. So it has a 3k+ RPM power-band. The Blue Flame makes its peak HP at just 4200 RPM and is all done by 4500 tops, giving it more like a 2k power-band.

In the end, if you asked me to pick between an old Blue Flame or the new EcoBoost to pair to a 2-speed PowerGlide, I'd take the EcoBoost. The fact is, modern small displacement boosted motors make broader torque curves and have great low end torque and response. Sure, everything gets better for the "old school" when you start talking V8s... but you name an old V8 that was paired to a 'Glide or say a 3-speed TH300/400 and I promises you they didn't pick 2 or 3 speeds because it was optimal, just because that's what they've had. Heck, I'm a V8 guy... I've had something like 7 different LS-powered vehicles, a couple LT1 cars (as in the mid-late '90s Gen 2 small block LT1, not the original '70-72 LT1 everyone forgets about, and not the current direct-injected LT1), 4 different Hemi vehicles (three 5.7s, and a currently a 6.2 SC'ed Trackhawk) and picked my WJ partially because it's a V8. I just prefer V8s... but something like the 2.7L TT V6 in the Bronco is a "better" motor in every way than my 4.7 HO. With any of my V8s I'd take a 10-speed if I could just snap my fingers and make it happen. Heck, our Trackhawk makes 707/645 HP/TQ and part of what makes it so silly-fast (for an SUV) is the 8-speed auto.

Let's take another example, the tried-and-true Jeep 4.0L that is well known for being very "torquey." Ask anybody if they should buy a 4.0L Jeep and right after they finish saying how it's the most reliable motor ever, they'll praise it for being a "torque monster" that is well suited to Jeepin'. Now, I don't agree the 4.0L is a great motor, and well suited to Jeepin' in the lighter XJs and T/LJs. Still, let's look at the numbers. At it's very best ('01-06) it made 190/235 HP/TQ. I wouldn't call that a TON of torque, personally... I'd just say that it doesn't make much HP. It also has a pretty narrow peak power range, with torque peaking at 3200 and HP peaking at 4600. Anybody w/ a 4.0 knows they don't like to spin much more than 5k, though the torque even down at 2k is pretty good. Still, if anything something like the 4.0L would benefit a TON from tighter gear spacing and more overall ratios to keep it in that 3200-4600 sweet-spot when doing work. I mean, when you talk WJs with people they often poo-poo the 4.7 first on reliability (and they're not entirely wrong there... I had a super clean, well taken care of/maintenanced example that still dropped valve seats before 110k miles) but next saying the 4.0L is a "torquey" motor and better for the WJ. That's odd, with the HO like mine makes 265/330 HP/TQ... nearly 100 lbs-ft more torque, yet the 4.0L is the one known as the "torquey" motor. HP peaked at 5100 RPM and torque at just 3600 RPM. So the torque peak is only 400 RPM higher, but at the same RPM as the 4.0L's peak it's still making way more torque than the 4.0L.

Anyway... my point is any/all motors can benefit from the extra gears (if managed properly). Older stuff didn't have 2-3 (or even 4 and 5) speed Autos because they were "best", they had them because they were what existed at the time...

-TJ

 

[Boostpowered]

It all depends on what your trying to do.

 

[Smileyshaun]

With a manual going up a steep hill If you have ever had to choose between being almost redlined or lugging the heck out of the motor and stalling you’ll be thankful for more gears ..... or a second transfer case .

 

[Billiebob]

A lot of people consider the auto better offroad.

The auto is better for everything.

But the manual is bullet proof where as an auto can and does die way too often.
And the repair bill is often more than new tires.

I've never had a stranded issue with a clutch but of 6 autos I've had, 3 of them needed a deck truck.

 

[Scott_Milk]

A lot of people consider the auto better offroad.

The auto is better for everything.

But the manual is bullet proof where as an auto can and does die way too often.
And the repair bill is often more than new tires.

I've never had a stranded issue with a clutch but of 6 autos I've had, 3 of them needed a deck truck.

I agree the auto is better in most cases and the manual is more reliable, but that's not the conversation I was hoping to have with this thread. I already know all that.

Interesting discussion above however. While I had seen the higher overdrive gears for these higher count trans, I hadn't thought about it also starting in a lower ratio. I guess if you start low enough (say 5:1) you almost wouldn't really need a high/low in the transfer case, assuming you still got torque from the engine low enough. But a torque converter would help with that in an auto. Makes sense why these higher count trans are always auto.

 

[tjZ06]

It all depends on what your trying to do.

What is the scenario where "what you are trying to do" means less gears is better?

 

[tjZ06]

The auto is better for everything.

But the manual is bullet proof where as an auto can and does die way too often.
And the repair bill is often more than new tires.

I've never had a stranded issue with a clutch but of 6 autos I've had, 3 of them needed a deck truck.

I *mostly* agree, but in inexperienced hands a manual does have one huge liability: the clutch. Modern auto are much, much, much better than older stuff and with proper cooling are pretty "bulletproof" themselves. It sounds like you might have had a lot of Fords or RAM/Dodge stuff from a decade or more ago, or perhaps GMs with the 4L60Es? Even in the most modern sticks a bad driver trying to off-road it can fry a clutch and ruin your day. Granted, I have to assume the select-few people still buying manual transmissions in off-road oriented vehicles know what they are doing... but you never know.

-TJ

 

[Smileyshaun]

A big reason older rigs had a granny first is not only to help taking off with a load but it was hard to drive slow with a carb motor , with fuel injection you can lug a motor and it will happily go along ( to a point ) and not over fuel or stall out as easy . A carb motor is much happier with some rpm to help draw that fuel into the motor .

 

[Smileyshaun]

The best thing about a 4l60e is its dirt cheap to have rebuilt lol You know quantity helps to lower prices.

 

[Smileyshaun]

Also auto trans get a bad rap because it’s actually frightening how many people don’t understand that there is a filter inside there and that the fluid needs to be changed regularly.

 

[Downs]

Also auto trans get a bad rap because it’s actually frightening how many people don’t understand that there is a filter inside there and that the fluid needs to be changed regularly.

I'm glad my AW4 has a drain plug lol.

 

[Boostpowered]

What is the scenario where "what you are trying to do" means less gears is better?

Off the top of my head, drag racing, mud bogging, rock crawling, competitive hill climbing. you wont find 10 speed trans there buddy. Transmissions with 4+ gears or overdrive are better suited for going highway speeds while hauling stuff or if your worried about gas mileage. If you have a ton of power and you want it fast and now a 3 speed th400 is the way to go.

 

[MidOH]

Driver: ''My dear transmission, it is now time to partake in the 2-3 gear shift.''


4l60e: ''NONE, SHALL PASS.''