No, it's just a matter of the overall diameter of the wheel and tire.
If you think you might be getting blown or sucked than you should get the FRPP 3.73s.
I have CS67 20” rims with 275/35 tires on the back and a manual transmission. I went with the 4.10 gear because it made better sense for my setup but I almost went with the 4.30 gears. Here is why I went the way I did:
- I like to run my car at the track and on the street (not street racing).
- I wanted to maximize my trap speed and rpm with the gear at the ¼ mile while running my street tire and maintain a drivable car (although I will get a second set of rims with DR in the future).
- I am currently putting on a standard V-3 Vortech supercharger (best bang for the buck); it is a centrifugal type and should not affect the low end as much as the other blower types; this should put me at ~110-115 mph through the trap.
Here is the math:
3.73 gears with 275/35 (27.6”) tire, speed at 6000 rpm in each gear
1st – 39 mph
2nd – 66 mph
3rd – 100 mph
4th – 132 mph
This gear puts me going through the trap in four gear between 4950-5250 rpm. This will leave me short shifting into fourth gear right before the trap, giving up some usable HP. With the supercharger, I will be running the car deep into the red zone in third gear to hit my mph (6600 rpm for 110 mph). This leaves no room for growth without changing something (gear or tire size).
3.90 gears with 275/35 (27.6”) tire, speed at 6000 rpm in each gear
1st – 37 mph
2nd – 63 mph
3rd – 96 mph
4th – 126 mph
This gear requires a shift into four gear and leaves me in the same situation as a 3.73 gear does.
4.10 gears with 275/35 (27.6”) tire, speed at 6000 rpm in each gear
1st – 35 mph
2nd – 60 mph
3rd – 91 mph
4th – 120 mph
This gear is a compromise but allows for growth. This will put me through the trap in 4th at between 5500-5800 rpm. This gear was my best option for drivability on the street, the track, and overall flexibility. With this gear, I can optimize my performance with a 26.5” tire.
4.30 gears with 275/35 (27.6”) tire, speed at 6000 rpm in each gear
1st – 34 mph
2nd – 57 mph
3rd – 87 mph
4th – 114 mph
This gear optimizes my setup but is not as common as the 4.10 gear setup. This will put me through the trap in fourth at between 5750-6000 rpm. This is actually the gear I almost went with because it would have dialed in the trap rpms and mph. When it comes right down to it though, if I chose to go to a shorter tire (26.5”), this will be too much gear. This would be a perfect fit for a 28.5” tire. The 4.10 was my compromise.
Here is the information for the 305/35 (28.4”) tires and manual transmission. You can make the call:
3.73 gears with 305/35 (28.4”) tire, speed at 6000 rpm in each gear
1st – 40 mph
2nd – 68 mph
3rd – 103 mph
4th – 136 mph
3.90 gears with 305/35 (28.4”) tire, speed at 6000 rpm in each gear
1st – 38 mph
2nd – 65 mph
3rd – 98 mph
4th – 130 mph
4.10 gears with 305/35 (28.4”) tire, speed at 6000 rpm in each gear
1st – 37 mph
2nd – 62 mph
3rd – 94 mph
4th – 124 mph
4.30 gears with 305/35 (28.4”) tire, speed at 6000 rpm in each gear
1st – 35 mph
2nd – 59 mph
3rd – 89 mph
4th – 118 mph
I hope this is helpful.
