The GM C8 Corvette TREMEC TR-9080 8-Speed DCT Transaxle (mLSD, 4.9 final drive) is an eight-speed dual-clutch transaxle.
First gear is 2.91:1 and 8th is 0.33:1. Divide one by the other and the overall spread is 8.82:1. That is a very wide spread. With eight gears to share it out, the steps in the middle can still stay civil.
8th is an overdrive at 0.33:1: the output shaft turns faster than the input shaft. Five of the eight gears are overdrives. No gear is exactly 1.00:1, so there is no direct drive.
The biggest step is 1st to 2nd, where the ratio drops 40%. The smallest is 7th to 8th at 18%. On each upshift the revs drop by the same percentage as the ratio.
It is a transaxle, so the final drive sits in the same case: 4.90:1 as listed here. The speed table uses that figure and nothing else. With a 4.90 final drive and 225/45R17 tyres, 8th at 6,000 rpm works out at 444 km/h (276 mph), and first runs out at 50 km/h (31 mph). That is how tall the gear is, not a top speed. Drag and power decide that. At 70 mph in 8th the engine turns about 1,520 rpm.
Ratios
| Gear | Ratio | Step |
|---|---|---|
| 1st | 2.91:1 | - |
| 2nd | 1.76:1 | 39.5% |
| 3rd | 1.22:1 | 30.7% |
| 4th | 0.88:1 | 27.9% |
| 5th | 0.65:1 | 26.1% |
| 6th | 0.51:1 | 21.5% |
| 7th | 0.40:1 | 21.6% |
| 8th | 0.33:1 | 17.5% |
| Final drive | 4.90:1 |