trans shift points
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Elder User
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trans shift points
Hi,
...what controls the transmission shift points? Is it rpm's or mph?
I am wanting to add taller tires (35) and change the gear ratio (5.13) for compensation, including adding a Gear Vendors unit. ...effectively making my truck a 6 speed with the benefit of better around town drivability.
...what controls the transmission shift points? Is it rpm's or mph?
I am wanting to add taller tires (35) and change the gear ratio (5.13) for compensation, including adding a Gear Vendors unit. ...effectively making my truck a 6 speed with the benefit of better around town drivability.
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Joined: Jun 2007
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From: Corvallis, OR
5.13s will be VERY LOW with 35s. I just got 4.30s to install and with 35s the end ratio is still 5% lower than stock. With 5.13s and 35s you'll be 26% lower than stock. With 4.30s I'll be turning about 2016 rpms at 65mph, thats only 50-100 rpms above nominal for best fuel economy. I don't usually run higher than 65 because power required to overcome wind resistance goes up with the cube (3rd power) of velocity.
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With the Gear Vendor unit, I will be turning 1,917 rpm's at 70mph, which is lower than stock. With stock tires and 3.73's, I turn 2,096 rpm at 70.
Mark, does it shift at a specific speed, or does it look for a leveling off of aceleration to shift?
Thanks for your reply.
Mark, does it shift at a specific speed, or does it look for a leveling off of aceleration to shift?
Thanks for your reply.
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What specific problems might you see with my scenario?
Will it work okay?
I was trying to emulate a stock truck w/factory 4.30 gears, which would actually necessitate 4.88 gears. However, I was wanting to gear higher to try to increase around town fuel economy, which is why I am thinking the 5.13 ratio.
35's, 5.13 gears, Gear Vendor overdrive unit (.55) The G.V. will only be used as a 6th gear (OD)...it will not be used to under/over shift between gears.
Will it work okay?
I was trying to emulate a stock truck w/factory 4.30 gears, which would actually necessitate 4.88 gears. However, I was wanting to gear higher to try to increase around town fuel economy, which is why I am thinking the 5.13 ratio.
35's, 5.13 gears, Gear Vendor overdrive unit (.55) The G.V. will only be used as a 6th gear (OD)...it will not be used to under/over shift between gears.
Lead Driver
Joined: Jun 2007
Posts: 6,757
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From: Corvallis, OR
With the cost of a gear vendor unit, wouldn't just going with 4.30s be a happy medium? You'd get near ideal highway rpms and get better in-town fuel economy as well. Unless you do a ton of in-town driving it will take a long time for it to pay itself off.
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I'm guessing the ecu would look at map, rpm and throttle position interpolating the three to work back to engine load and use that for the shift points. So it should auto adj to different tire sizes, diff ratios (kinda) - just as if you had a tail or head wind...
just my 2c.
JT
just my 2c.
JT
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Thanks, datsun....
I do a lot of town driving, and some highway...probably around 24,000 in town per year and maybe 6,000 highway.
4.30's would be okay, but I would not get any extra multiplication for stop/go with the bigger tires over stock, and my highway miles would surely suffer.
I am not too concerned about the pay off. I figure it will take about 2 1/2 years to break even, and after that I will be saving money. I can even transfer the unit over to a new truck, and save even more.
I do a lot of town driving, and some highway...probably around 24,000 in town per year and maybe 6,000 highway.
4.30's would be okay, but I would not get any extra multiplication for stop/go with the bigger tires over stock, and my highway miles would surely suffer.
I am not too concerned about the pay off. I figure it will take about 2 1/2 years to break even, and after that I will be saving money. I can even transfer the unit over to a new truck, and save even more.
Lead Driver
Joined: Jun 2007
Posts: 6,757
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From: Corvallis, OR
With 4.30s your highway miles are only going to suffer if you get it over 65mph a lot. 35s with 4.30s will put you a hair over 2000 rpms which is where you should get the best mileage because the engine is most efficient there.
I did a lot of reading before choosing 4.30s over 4.10s for gearing with 35s. With stock tires people are seeing better fuel economy with 4.10s over 3.73s because the rpms are in a better range, if they are too low you have to give it more fuel for the amount of power that is produced. I'm seeing this right now with 35s and 3.73s, at 65mph I'm only turning a little over 1700rpms and it has to kick down a gear whenever I hit a decent hill unloaded.
I did a lot of reading before choosing 4.30s over 4.10s for gearing with 35s. With stock tires people are seeing better fuel economy with 4.10s over 3.73s because the rpms are in a better range, if they are too low you have to give it more fuel for the amount of power that is produced. I'm seeing this right now with 35s and 3.73s, at 65mph I'm only turning a little over 1700rpms and it has to kick down a gear whenever I hit a decent hill unloaded.
