Gear ratio opinions

10blacksil · June 8, 2017

I know this is an old topic but... I am planning to change wheels from my stock 20"s to newer stock Silverado wheels/tires that are 285/45R22. My current gear ratio is 3.42. Does anyone have or has anyone changed to 4.10 gears with that tire size (285/45R22)? If so, do you like it? Hate it? Recommend it? Thanks.

bgbdwlf2500 · June 9, 2017

I know this is an old topic but... I am planning to change wheels from my stock 20"s to newer stock Silverado wheels/tires that are 285/45R22. My current gear ratio is 3.42. Does anyone have or has anyone changed to 4.10 gears with that tire size (285/45R22)? If so, do you like it? Hate it? Recommend it? Thanks.

youre not going to need 4.10 gears for those tires and wheels. 4.10 gears are for drag racing, pulling or really big off road tires.

arcasey · June 12, 2017

I know this is an old topic but... I am planning to change wheels from my stock 20"s to newer stock Silverado wheels/tires that are 285/45R22. My current gear ratio is 3.42. Does anyone have or has anyone changed to 4.10 gears with that tire size (285/45R22)? If so, do you like it? Hate it? Recommend it? Thanks.

That tire size is virtually the same size as the stock tire size with 20" rims so essentially your truck will operate just as it did with the original tires, only it's going to ride a little stiffer.

10blacksil · June 12, 2017

Thanks for the replies. One of the reasons I ask is that I found a post (it's very old) by someone who switched to 3.90 gears and actually improved gas mileage... If that is true, the gears will eventually pay for themselves, at least that is what I will tell my wife. :-) And, more importantly, in the meantime it would improve acceleration and towing. I asked if the op was still around but I haven't heard anything yet. If interested, here is the post https://www.performancetrucks.net/forums/gmt-900-trucks-general-discussion-188/2010-silverado-gear-swap-results-479842/

I talked to a shop here. I'd be looking at around $1k (without also installing a tru-track posi). And based on my tire size, with 4.10 I think I would spinning around 2,000 rpm at 70mph. That doesn't sound too bad. However, given that I have a 6sp trans, I am a little concerned that 1st might be a little too quick. So 3.90 might be the sweet spot...

Nanotech Environmental · June 13, 2017

I'm sorry, I find the claims in the link (in post 19) pretty hard to believe. Pure BS.

He also happened to get a tune at the same time which could account for some improvements(if done correctly).

You don't get a big reduction in fuel usage by spinning your engine over ~30% faster. Even if you get some improvements from a bit of increased v4 activation, it's not going to make up for all the huge losses everywhere else.

10blacksil · June 13, 2017

I dunno, it sounds like after 50k miles they will have paid for themselves. Or maybe he was just trying to justify it to his wife... ;-)

Either way I agree that and a good tune will probably produce notable gains in performance but maybe not mileage.

Oh and an Air raid MIT which I believe is just as good as a CAI, if not better, because it is 1/2 the cost.

arcasey · June 13, 2017

Yea I just can't say I've known very many people who have swapped gears to a lower gearing and gained 3-4 MPGs. Most people swap gears strictly for performance. Now, with that said, his truck is lowered, but it wasn't indicated when it was lowered. You can see slight increases in MPG by lowering a vehicle and on the other side of that token you can expect to drop some when you raise a vehicle (increased air drag). Also, how was he doing his calculations? I'd be interested to see whether he was going strictly off the vehicle computer or if he was actually calculating based on the fuel ticket. Even still, I'm skeptical he gained 5+ MPGs by putting lower gears in his truck....

bgbdwlf2500 · June 15, 2017

Yea I just can't say I've known very many people who have swapped gears to a lower gearing and gained 3-4 MPGs. Most people swap gears strictly for performance. Now, with that said, his truck is lowered, but it wasn't indicated when it was lowered. You can see slight increases in MPG by lowering a vehicle and on the other side of that token you can expect to drop some when you raise a vehicle (increased air drag). Also, how was he doing his calculations? I'd be interested to see whether he was going strictly off the vehicle computer or if he was actually calculating based on the fuel ticket. Even still, I'm skeptical he gained 5+ MPGs by putting lower gears in his truck....

if you put big enough tires on a vehicle then you could gain back some mpg by changing the gears to get it closer to the factory ratio. my truck has in my opinion the dreaded 3.08 ratio. it keeps the rpms down but the truck is never in the power band so it doesn't help mpg much if at all especially on the highway.

Nanotech Environmental · June 15, 2017

if you put big enough tires on a vehicle then you could gain back some mpg by changing the gears to get it closer to the factory ratio. my truck has in my opinion the dreaded 3.08 ratio. it keeps the rpms down but the truck is never in the power band so it doesn't help mpg much if at all especially on the highway.

You won't gain much back with big tires and wheels, if any. You're adding too much wind drag by raising the truck and from the tires themselves. Also, big offroad tires have higher rolling resistance & take more power to turn.

You very rarely get increased mpgs by spinning the engine faster, or keeping it 'in the powerband' as you put it. If that were the case, the Corvettes would be running at 2000+rpm on the highway. Instead, they use the low end torque to loaf along at low rpm, while getting mileage well into the 30's. In certain cases on the trucks, a bit higher rpm(key words - ' a bit') may help the engine stay in V4 more often, which can help, but the driver has to be very concious of what they're doing & the circumstances are limited as well.

You only need maybe about 50-75 hp at most to maintain speed on the highway at 65mph on flat ground & no headwinds. If you're spinning your engine at an rpm that is putting out 200 hp at those speeds in those conditions, you're wasting all that fuel that produces the extra 125-150hp that you aren't using.

Low rpm, reasonable speeds and a light foot = good mileage.

Mileage usually has more to do with driving habits/techniques than other factors. That's why hypermilers can get some pretty exceptional mpgs from normal vehicles.

bgbdwlf2500 · June 15, 2017

3beejay3, on 15 Jun 2017 - 08:45 AM, said:3beejay3, on 15 Jun 2017 - 08:45 AM, said:

You won't gain much back with big tires and wheels, if any. You're adding too much wind drag by raising the truck and from the tires themselves. Also, big offroad tires have higher rolling resistance & take more power to turn.

You very rarely get increased mpgs by spinning the engine faster, or keeping it 'in the powerband' as you put it. If that were the case, the Corvettes would be running at 2000+rpm on the highway. Instead, they use the low end torque to loaf along at low rpm, while getting mileage well into the 30's. In certain cases on the trucks, a bit higher rpm(key words - ' a bit') may help the engine stay in V4 more often, which can help, but the driver has to be very concious of what they're doing & the circumstances are limited as well.

You only need maybe about 50-75 hp at most to maintain speed on the highway at 65mph on flat ground & no headwinds. If you're spinning your engine at an rpm that is putting out 200 hp at those speeds in those conditions, you're wasting all that fuel that produces the extra 125-150hp that you aren't using.

Low rpm, reasonable speeds and a light foot = good mileage.

Mileage usually has more to do with driving habits/techniques than other factors. That's why hypermilers can get some pretty exceptional mpgs from normal vehicles.

Power band isn't the correct word because we all know they don't make full power until theyre wound way up. I'm not trying to start an argument but I will say that the "lower" gear ratios (higher numbers) can help heavy trucks gain back some mpg because the engine isn't lugging. maybe its only 1 mpg but thats better than nothing. adding weight, rolling resistance all the things you mentioned can be corrected by regearing a truck to a lower gear ratio. GM trying to improve mpg put a 3.08 gear ratio in a 5500 lb truck and on top of that in a 6 speed truck. I disabled afm due to the oil issues but with the 3.08 it never used it anyway, just not enough power to keep it rolling on 4 cylinders with that ratio. i just go back from a little road trip yesterday and on hilly ground the truck spends more time in 4th and 5th than it does in 6th with the 3.08. if someone slows me down, even just a little gas to try to regain speed causes a downshift at any speed, 65, 75 even 85. I don't run my truck hard so that has very little to do with the mpg i get which i think right now might be 17 on a highway with a few hills. for that mpg i would LOVE to be back in a truck with at least the 3.42. Pic attached is of my truck yesterday, it shows the rpm vs mph of the 3.08 gear ratio. I don't run this fast normally but traffic was running that fast so i wanted to see where the rpm was.

Nanotech Environmental · June 15, 2017

Power band isn't the correct word because we all know they don't make full power until theyre wound way up. I'm not trying to start an argument but I will say that the "lower" gear ratios (higher numbers) can help heavy trucks gain back some mpg because the engine isn't lugging. maybe its only 1 mpg but thats better than nothing. adding weight, rolling resistance all the things you mentioned can be corrected by regearing a truck to a lower gear ratio. GM trying to improve mpg put a 3.08 gear ratio in a 5500 lb truck and on top of that in a 6 speed truck. I disabled afm due to the oil issues but with the 3.08 it never used it anyway, just not enough power to keep it rolling on 4 cylinders with that ratio. i just go back from a little road trip yesterday and on hilly ground the truck spends more time in 4th and 5th than it does in 6th with the 3.08. if someone slows me down, even just a little gas to try to regain speed causes a downshift at any speed, 65, 75 even 85. I don't run my truck hard so that has very little to do with the mpg i get which i think right now might be 17 on a highway with a few hills. for that mpg i would LOVE to be back in a truck with at least the 3.42. Pic attached is of my truck yesterday, it shows the rpm vs mph of the 3.08 gear ratio. I don't run this fast normally but traffic was running that fast so i wanted to see where the rpm was.

FWIW- I drove a '17 crew 4x4 with 5.3 and a 3.08 recently on a 300 mile trip with about 800lbs or so in it. The terrain was somewhat hilly and driving conditions we're pretty bad(lots of rain and idiot drivers). I never felt the engine was lugging at any time. The truck had good power and acceleration. With the 6 speed, downshifts are much reduced compared to the 4 speed in my truck. I could keep it under 2k rpm much easier than my own truck. Most of the 'downshifts' were just the TC unlocking when a bit more rpm was needed. Once I was out of headwinds, v4 came on quite a bit. Fuel mileage was quite good on the trip compared to what my 06 would have got.

arcasey · June 15, 2017

Okay, there are RARE occasions that adding larger tires and re-gearing would increase the MPG of a vehicle over the previous configuration but it would only be because the new gearing is closer to the new optimal gearing after the tire size increase. What I mean by that is that the optimal gearing is the rear differential gearing that can be coupled with the transmission gearing to give you the maximum travel speed at an engine speed closest to the most efficient engine speed. It's a complex curve that is ever changing. So, while there are outliers, let's not stir up too much false hope because as a general rule adding larger tires and then re-gearing for them is not going to net an increase in fuel economy. The added weight and rolling resistance alone requires more total work to be done in order to accomplish the same task as before.

Now I'm not saying that re-gearing a stock truck will not net an increase in fuel mileage because I've driven a 6-speed with a 3.08 rear end and I did not like it at all and could definitely see where a different gear ratio might have improved it. The biggest issue that I see when these types of discussions come up is that people are referencing someone else's data, that wasn't captured in a controlled environment. They don't have other data to compare it to because each data set was captured in a completely different environment. Why do you think testing done by scientist are done in controlled environments? If they are testing multiple variables against another then how can they ever be sure that one had an affect on the other? It's all relative based on the actual instance in which the data was captured and then presented on these forums.

sdeeter19555 · June 15, 2017

I put 35s on a 2500 Dodge Cummins with 4.10s (that had factory 245s) and went from a high of 20mpg (hand calculated) to just under 25mpg (hand calculated, measured distance, not from odometer). I was a traveling a measured mile and registering about 0.8 miles on the odometer! I was registering about 80 miles in a 100 mile trip. That was a nice combination until the tires all went out of round and I dropped to 265s.

A lot of folks forget to recalibrate the speedo/odometer to account for the larger tires...they are actually traveling further than they think they are based on the odometer.

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bgbdwlf2500 · June 15, 2017

FWIW- I drove a '17 crew 4x4 with 5.3 and a 3.08 recently on a 300 mile trip with about 800lbs or so in it. The terrain was somewhat hilly and driving conditions we're pretty bad(lots of rain and idiot drivers). I never felt the engine was lugging at any time. The truck had good power and acceleration. With the 6 speed, downshifts are much reduced compared to the 4 speed in my truck. I could keep it under 2k rpm much easier than my own truck. Most of the 'downshifts' were just the TC unlocking when a bit more rpm was needed. Once I was out of headwinds, v4 came on quite a bit. Fuel mileage was quite good on the trip compared to what my 06 would have got.

my opinion is a downshift means the engine is lugging so it drops a gear to compensate for it and bring the rpms up. I don't know if the new trucks have more power but mine is a 2010 with 118k. when I had my 500 hp 1000 ftlb duramax diesel I would have loved for that truck to have the 3.08 ratio. it got 22 mpg with 3.73s and would never downshift because it had the power, which kind of goes back to your corvette comment. big power doesn't mean crappy mpg, if you keep your foot out of it and let it cruise mpg will be pretty good.

arcasey · June 15, 2017

I put 35s on a 2500 Dodge Cummins with 4.10s (that had factory 245s) and went from a high of 20mpg (hand calculated) to just under 25mpg (hand calculated, measured distance, not from odometer). I was a traveling a measured mile and registering about 0.8 miles on the odometer! I was registering about 80 miles in a 100 mile trip. That was a nice combination until the tires all went out of round and I dropped to 265s.

A lot of folks forget to recalibrate the speedo/odometer to account for the larger tires...they are actually traveling further than they think they are based on the odometer.

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I can believe that. To a degree, larger tires on a diesel truck don't have as much negative effect because they have inherently more torque than a gas truck so they can over come the larger tires easier. So you can see where I was going with the previous post. Every situation is different and because one person gets one result doesn't mean someone else will, even with the same setup. And yes, that speedometer/odometer recalculation is something that gets over looked a lot.