need help with gear choices
03-05-2009, 08:51 AM
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Default Want to know the Effect of Changing Gear Ratios? Look Here First!
Stock Gear Ratios:
M6: 3.42
A4 Standard: 2.73 (GU2 code on the door sticker)
A4 Performance Axel: 3.23 (GU5 code on the door sticker)
WS6 and SS models came with 3.23s.
Your A4 did not come with 3.42s.
If your sticker is gone you tell which gears you have by your highway rpms:
3.23s @ 2000 rpm = 67 mph; 2.73s @ 2000 rpm = 80 mph
3.15s were available in A4 Vettes
The attached file has the mph & rpm for the most popular gear ratios for F-bodies:
M6:
3.73
3.90 (requires aftermarket rear)
4.10
A4:
3.42
3.73
4.10
The mph assume a stock 245/50/16 F-body tire. Those on 17" wheels will find this pretty close since your tires are a narrower aspect ratio. If you run ET Streets, they are generally larger than stock tires. Depending upon which tire you select, you can add 2% - 5% to the mph numbers to estimate your rpm for a given trap speed.
A stock A4's converter is unlocked at WOT. Therefore when you cross the line your rpms will be higher than shown in the chart. While the amount slip will vary by converter, you should figure an extra 5 - 8% above the rpm shown in chart when looking at the high rpm numbers where you are likely to be at WOT.
If you want to play further with tire sizes and gear ratios go here:
http://www.f-body.org/gears/
Additional Info for A4's:
Swapping from 3.23s to 3.42s is a waste of money. There is barely enough gain to justify the cost of a bottle of gear oil and additive, no less buying the gears. If you have 3.23s your next move is to 3.73s.
If you don't have a high stall torque converter, you really should look at that first. The big gains come from a converter, not from gears. You'll be amazed what a 3000 stall converter will do to the launch of a 2.73 geared car. Look in the automatic transmission forum for more info on them.
Stock Gear Ratios:
M6: 3.42
A4 Standard: 2.73 (GU2 code on the door sticker)
A4 Performance Axel: 3.23 (GU5 code on the door sticker)
WS6 and SS models came with 3.23s.
Your A4 did not come with 3.42s.
If your sticker is gone you tell which gears you have by your highway rpms:
3.23s @ 2000 rpm = 67 mph; 2.73s @ 2000 rpm = 80 mph
3.15s were available in A4 Vettes
The attached file has the mph & rpm for the most popular gear ratios for F-bodies:
M6:
3.73
3.90 (requires aftermarket rear)
4.10
A4:
3.42
3.73
4.10
The mph assume a stock 245/50/16 F-body tire. Those on 17" wheels will find this pretty close since your tires are a narrower aspect ratio. If you run ET Streets, they are generally larger than stock tires. Depending upon which tire you select, you can add 2% - 5% to the mph numbers to estimate your rpm for a given trap speed.
A stock A4's converter is unlocked at WOT. Therefore when you cross the line your rpms will be higher than shown in the chart. While the amount slip will vary by converter, you should figure an extra 5 - 8% above the rpm shown in chart when looking at the high rpm numbers where you are likely to be at WOT.
If you want to play further with tire sizes and gear ratios go here:
http://www.f-body.org/gears/
Additional Info for A4's:
Swapping from 3.23s to 3.42s is a waste of money. There is barely enough gain to justify the cost of a bottle of gear oil and additive, no less buying the gears. If you have 3.23s your next move is to 3.73s.
If you don't have a high stall torque converter, you really should look at that first. The big gains come from a converter, not from gears. You'll be amazed what a 3000 stall converter will do to the launch of a 2.73 geared car. Look in the automatic transmission forum for more info on them.