to each his own - but in my experience - I love the chrome-clad 20's - look great and VERY easy to take care of


and - IMPORTANT - if you swap the tires out on the one that has them - you will get hit with a $1200.00 trade-in DEDUCT when and if you trade the car in

 

Unless I'm wrong the 3.73's should get better gas mileage; less rpm's at highway speeds. The takeaway is if you're drag racing less "out the hole" oomph. Either way, I don't think there's a world of difference between the two. My '94 Mustang GT had 3.27 gears and I know some people that went to 4.25's. Lots of oomph with that range difference, but it's a screamer on the interstate.

If I've got this backwards, let me know.

 

Subscribed. I know nothing about gearing. I would like to get some of your takes on gearing vs wheelsize vs acceleration, and advantages or disadvantages in top and bottom end.

 

The final gearing will be the same with each combo. However, future plans will determine what you want to do. If gas mileage is a concern, get the 3.73. If you want to get out of the hole quicker, get the 3.92.

 

not really, the stock 235/55-18 and the 245/45-20 are only 1.8% different in size. there is a 5.1% difference between the 3.73 and the 3.92

overall, you will see a 3.3 % lower gear ratio if you have the 20s and 3.92s. i would get the 20's and sell off the rims. that way you still have 20" tires to use on other rims.

 

I am pretty sure the overall diameter of the wheels+tires is about the same between the 18's & the 20's. I went with the 3.92 gears on my RT and 6th gear is still great on the interstate even while speeding.

 

The 3.92s are tall gears. I can actually take off in 2nd gear no problem. Maybe even 3rd although I've never tried it.

My R/T had the track pack and 20" wheels.

The 3.73s with the 18s should be about the same. 3.73s with 20s will lower the over all gearing, but I don't think that'd necessarily be a bad thing.

With my 20s in 6th on the highway I'm turning about 1800 RPMs at 80MPH.

If you want to do some calculating to help go to the following site and punch in the numbers to see what RPM you'll be at with a given speed:

http://www.f-body.org/gears/

6 speed gearing is:

1st: 2.97
2nd: 2.10
3rd: 1.46
4th: 1.00
5th: 0.74
6th: 0.50

 

Wow, thanks for that link Speedy. If I'm reading this properly there is hardly any difference at all. And to me it looks like the 3.73's with the 18's are slightly better than the other combos. I will post all the ones I ran. FYI, I used the gearing ratio you provided as I am looking at a 6-speed. I used 5700 as redline and used stock tire sizes listed by Dodge as reference points.

Note: Number readouts are in MPH

3.73's with 235/55/18 tires
RPM 1st Gear 2nd Gear 3rd Gear 4th Gear 5th Gear 6th Gear
500 4 5 8 11 15 22
600 5 6 9 13 18 27
700 5 7 11 16 21 31
800 6 9 12 18 24 36
900 7 10 14 20 27 40
1000 8 11 15 22 30 45
1100 8 12 17 25 33 49
1200 9 13 18 27 36 54
1300 10 14 20 29 39 58
1400 11 15 22 31 43 63
1500 11 16 23 34 46 67
1600 12 17 25 36 49 72
1700 13 18 26 38 52 76
1800 14 19 28 40 55 81
1900 14 20 29 43 58 85
2000 15 21 31 45 61 90
2100 16 22 32 47 64 94
2200 17 24 34 49 67 99
2300 17 25 35 52 70 103
2400 18 26 37 54 73 108
2500 19 27 38 56 76 112
2600 20 28 40 58 79 117
2700 20 29 42 61 82 121
2800 21 30 43 63 85 126
2900 22 31 45 65 88 130
3000 23 32 46 67 91 135
3100 23 33 48 70 94 139
3200 24 34 49 72 97 144
3300 25 35 51 74 100 148
3400 26 36 52 76 103 153
3500 26 37 54 79 106 157
3600 27 39 55 81 109 162
3700 28 40 57 83 112 166
3800 29 41 58 85 115 171
3900 30 42 60 88 118 175
4000 30 43 62 90 121 180
4100 31 44 63 92 125 184
4200 32 45 65 94 128 189
4300 33 46 66 97 131 193
4400 33 47 68 99 134 198
4500 34 48 69 101 137 202
4600 35 49 71 103 140 207
4700 36 50 72 106 143 211
4800 36 51 74 108 146 216
4900 37 52 75 110 149 220
5000 38 54 77 112 152 225
5100 39 55 79 115 155 229
5200 39 56 80 117 158 234
5300 40 57 82 119 161 238
5400 41 58 83 121 164 243
5500 42 59 85 124 167 247
5600 42 60 86 126 170 252
5700 43 61 88 128 173 256

3.73's with 245/45/20 tires
RPM 1st Gear 2nd Gear 3rd Gear 4th Gear 5th Gear 6th Gear
500 4 5 8 11 15 23
600 5 7 9 14 19 27
700 5 8 11 16 22 32
800 6 9 13 18 25 37
900 7 10 14 21 28 41
1000 8 11 16 23 31 46
1100 8 12 17 25 34 50
1200 9 13 19 27 37 55
1300 10 14 20 30 40 59
1400 11 15 22 32 43 64
1500 12 16 24 34 46 69
1600 12 17 25 37 49 73
1700 13 19 27 39 53 78
1800 14 20 28 41 56 82
1900 15 21 30 43 59 87
2000 15 22 31 46 62 92
2100 16 23 33 48 65 96
2200 17 24 34 50 68 101
2300 18 25 36 53 71 105
2400 18 26 38 55 74 110
2500 19 27 39 57 77 114
2600 20 28 41 59 80 119
2700 21 29 42 62 83 124
2800 22 31 44 64 87 128
2900 22 32 45 66 90 133
3000 23 33 47 69 93 137
3100 24 34 49 71 96 142
3200 25 35 50 73 99 146
3300 25 36 52 75 102 151
3400 26 37 53 78 105 156
3500 27 38 55 80 108 160
3600 28 39 56 82 111 165
3700 28 40 58 85 114 169
3800 29 41 60 87 117 174
3900 30 42 61 89 121 178
4000 31 44 63 92 124 183
4100 32 45 64 94 127 188
4200 32 46 66 96 130 192
4300 33 47 67 98 133 197
4400 34 48 69 101 136 201
4500 35 49 71 103 139 206
4600 35 50 72 105 142 210
4700 36 51 74 108 145 215
4800 37 52 75 110 148 220
4900 38 53 77 112 151 224
5000 39 54 78 114 155 229
5100 39 56 80 117 158 233
5200 40 57 81 119 161 238
5300 41 58 83 121 164 242
5400 42 59 85 124 167 247
5500 42 60 86 126 170 252
5600 43 61 88 128 173 256
5700 44 62 89 130 176 261

3.92's with 235/55/18 tires
PM 1st Gear 2nd Gear 3rd Gear 4th Gear 5th Gear 6th Gear
500 4 5 7 11 14 21
600 4 6 9 13 17 26
700 5 7 10 15 20 30
800 6 8 12 17 23 34
900 6 9 13 19 26 38
1000 7 10 15 21 29 43
1100 8 11 16 24 32 47
1200 9 12 18 26 35 51
1300 9 13 19 28 38 56
1400 10 14 21 30 40 60
1500 11 15 22 32 43 64
1600 12 16 23 34 46 68
1700 12 17 25 36 49 73
1800 13 18 26 38 52 77
1900 14 19 28 41 55 81
2000 14 20 29 43 58 86
2100 15 21 31 45 61 90
2200 16 22 32 47 64 94
2300 17 23 34 49 66 98
2400 17 24 35 51 69 103
2500 18 25 37 53 72 107
2600 19 26 38 56 75 111
2700 19 27 40 58 78 115
2800 20 29 41 60 81 120
2900 21 30 42 62 84 124
3000 22 31 44 64 87 128
3100 22 32 45 66 90 133
3200 23 33 47 68 92 137
3300 24 34 48 71 95 141
3400 24 35 50 73 98 145
3500 25 36 51 75 101 150
3600 26 37 53 77 104 154
3700 27 38 54 79 107 158
3800 27 39 56 81 110 163
3900 28 40 57 83 113 167
4000 29 41 59 86 116 171
4100 30 42 60 88 118 175
4200 30 43 62 90 121 180
4300 31 44 63 92 124 184
4400 32 45 64 94 127 188
4500 32 46 66 96 130 192
4600 33 47 67 98 133 197
4700 34 48 69 101 136 201
4800 35 49 70 103 139 205
4900 35 50 72 105 142 210
5000 36 51 73 107 144 214
5100 37 52 75 109 147 218
5200 37 53 76 111 150 222
5300 38 54 78 113 153 227
5400 39 55 79 115 156 231
5500 40 56 81 118 159 235
5600 40 57 82 120 162 240
5700 41 58 83 122 165 244

3.92's with 245/45/20 tires
RPM 1st Gear 2nd Gear 3rd Gear 4th Gear 5th Gear 6th Gear
500 4 5 7 11 15 22
600 4 6 9 13 18 26
700 5 7 10 15 21 30
800 6 8 12 17 24 35
900 7 9 13 20 26 39
1000 7 10 15 22 29 44
1100 8 11 16 24 32 48
1200 9 12 18 26 35 52
1300 10 13 19 28 38 57
1400 10 15 21 30 41 61
1500 11 16 22 33 44 65
1600 12 17 24 35 47 70
1700 12 18 25 37 50 74
1800 13 19 27 39 53 78
1900 14 20 28 41 56 83
2000 15 21 30 44 59 87
2100 15 22 31 46 62 91
2200 16 23 33 48 65 96
2300 17 24 34 50 68 100
2400 18 25 36 52 71 104
2500 18 26 37 54 74 109
2600 19 27 39 57 76 113
2700 20 28 40 59 79 118
2800 21 29 42 61 82 122
2900 21 30 43 63 85 126
3000 22 31 45 65 88 131
3100 23 32 46 67 91 135
3200 23 33 48 70 94 139
3300 24 34 49 72 97 144
3400 25 35 51 74 100 148
3500 26 36 52 76 103 152
3600 26 37 54 78 106 157
3700 27 38 55 81 109 161
3800 28 39 57 83 112 165
3900 29 40 58 85 115 170
4000 29 41 60 87 118 174
4100 30 42 61 89 121 178
4200 31 44 63 91 124 183
4300 32 45 64 94 126 187
4400 32 46 66 96 129 192
4500 33 47 67 98 132 196
4600 34 48 69 100 135 200
4700 34 49 70 102 138 205
4800 35 50 72 104 141 209
4900 36 51 73 107 144 213
5000 37 52 75 109 147 218
5100 37 53 76 111 150 222
5200 38 54 78 113 153 226
5300 39 55 79 115 156 231
5400 40 56 81 118 159 235
5500 40 57 82 120 162 239
5600 41 58 83 122 165 244
5700 42 59 85 124 168 248

 

Let me throw you a twist. My SRT8 came with 3.92 gears and now has 4.56. I love the car with steeper 4.56 gears. The 6th gear is so high on these cars that it is rarely used. After driving my 4.56 setup, I could never consider the 3.73 gears. The 3.92 will serve you well. I used to get 21+ MPG with 3.92 gears if I could keep my foot out of it. Problem was it was so damn fun to drive, I always had it going hard.

Drive it like you stole it and never stop grinning, you will love the car!

 

4.56 gears, nice! If I kept my 6 speed I was going to go that route. However, everyone told me they were not available. Did you put them in the stock rear?

 

I have them in the Paramount 8.8" Ford setup. I wanted to do a 9" Ford, but that was not available last year when I made the change.

Let me know when your 392 arrives. I will be up at MAM in the spring to get some road course track time, I had a blast there my last trip up in September.

 

I have them in the Paramount 8.8" Ford setup. I wanted to do a 9" Ford, but that was not available last year when I made the change.

Let me know when your 392 arrives. I will be up at MAM in the spring to get some road course track time, I had a blast there my last trip up in September.

Figured you had to do some type of swap. Thanks.

Were you at MAM with the Viper group?

 

I went up for one of the MAM Fast Friday sessions. It is basically an open track day for the road course. I made four 30 minute sessions before I broke a sway bar link in the early afternoon. I only had two other cars on the track with me at most during the morning. Mid-afternoon a few Corvettes showed up, seemed to be all related to the same dealership. I was broke then, so I packed up and limped home. It was a 5 hour drive, but I had a huge grin on my face and 1/8" less rubber on the tires, so it was a good drive home.

 

09 Plym
I'm having my 09 Auto changed now from the 306 to the 391/392 that should put me pretty close to where you are with the 6 speed and 456 gears. What kind of RPMs are you running at 70 or 80 MPH.

 

Here's a good link to tire swap gear ratio calculators. Just remember to convert the tires to inches first.

Tyres1.com Tires, Wheels, Suspension - Calculators

 

Heck I'd go with the 3.92's. I have a feeling they stuck the 3.92's on the 20" cars due to weight of the wheels, but I could be wrong.
I vote the 3.92's

 

Heck I'd go with the 3.92's. I have a feeling they stuck the 3.92's on the 20" cars due to weight of the wheels, but I could be wrong.
I vote the 3.92's

I know it has been posted here before but how much do the 20's weigh?