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Does anyone know of a formula to match rpm with axle ratio? For example, I am running a 28" tire, have a 3.08 axle and turn 2,500 rpm at 60 mph. I am wanting to figure out cruise rpm with different rear gears. I'm sure there is a simple way to do this, but I am mathematically challenged. Thanx for your help. SSuper Dave

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This is what I came up with:

28" tire @ 60 mph

4.56=3535 rpm
4.11=3210 rpm
3.73=2937 rpm
3.55=2807 rpm
3.31=2634 rpm
3.08=2468 rpm
This is with a 1:1 final drive ratio in the transmission, using an overdrive trans will give a harder launch and lower cruise speed rpm's. Philip

[This message has been edited by 64elcamino (edited 05-18-99).]
 

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Thanks, 64 El Camino, that little chart was exactly what I needed. It looks like 3.73's will be the way to go for me. SSuper Dave

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Those numbers are all too high. They look like rpm's for 65 mph.

At 60mph, 28" tire, rpms should be:

4.56 = 3285
4.11 = 2960
3.73 = 2686
3.55 = 2557
3.31 = 2384
3.08 = 2218
 

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Larry, SSuper Dave said he was turning 2500 rpm's with the 28" tire and 3.08 gears at 60 mph. I see what you are talking about as I went to www.ring-pinion.com and checked the #'s and they match yours for 60 and mine for 65.

[This message has been edited by 64elcamino (edited 05-26-99).]

[This message has been edited by 64elcamino (edited 05-26-99).]

[This message has been edited by 64elcamino (edited 05-26-99).]
 

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Whoa! Guys, I have a huge exam coming up in a week ( which is why my Chevelle is not on the road yet!), but I promise to write up a little excel program to do the calcs. It should be pretty straight up and , hopefully, Wes can include it in his section. Until then, a hand calculator works pretty good. For guys like me, I like to use "child-proof" calculations.

[This message has been edited by Gene Chas (edited 05-26-99).]
 

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As per the original question, here is the formula. It will work for anyone, just plug in all your specific numbers. This is best used/understood with a 4sp in 4th gear or 1:1 (i.e. crank turns once, drive shaft turns once.)

C = rear wheel circumfrence (2*pi*radius) or (2*pi(diameter/2))

G = Final gear reduction.


C
---------- * RPM = MPH
G * 1056

You can solve for any variable you want as long as you know the other factors. A really neat trick I've found is to set up an Xcel spread sheet and simply plug in the numbers. It lets you compare you speed vs. RPM quickly using various tire sizes and rear end ratios. I can email a sample to people who are interested.

I can walk you through the proof as to how I dervived this formula, but some people says it gives them a headache. It really was quite simple.

[This message has been edited by michael j (edited 05-26-99).] to make the formula appear correctly.

[This message has been edited by michael j (edited 05-26-99).]
 

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Thanks Gene, any help would be great I don't want to give out bad info, I have mine in excell, don't know what Randy's ring and pinion is using ,but now I have 3 different rpm's for the same set of constants.
 

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Here is some formulas I found in Jan 99 Chevy High Performance.

rpm= mph x trans ratio x rear ratio x 336
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tire diameter

mph= rpm x tire diameter
------------------------------------
trans ratio x rear ratio x 336
 

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Here is some formulas I found in Jan 99 Chevy High Performance.

rpm= mph x trans ratio x rear ratio x 336
------------------------------------
tire diameter

mph= rpm x tire diameter
------------------------------------
trans ratio x rear ratio x 336
 

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Thanks to all, SSuper Dave I was wrong use Larry's #'s. I will update my program. Philip
 

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There was a little Visual Basic program on this site that did all the calcs. Just give it 3 variables and it gave you the fourth. I DLed it but couldn't find it when I looked for it later.
 

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There have been quite a few questions regarding rpm, speed, etc., as it relates gears, transmissions, etc.

As a computer scientist I have written quite a few and there are plenty out there on the web but here is one for the 700R4 transmission.

The program is written in Microsoft Quick Basic which is normally included with Microsoft operating systems. Its name is 700R4.BAS

The thing I like about it is it puts the information in a file called 700R4.dat when you run it. Open the file in Note Pad and print it out. You can see the rpm at any speed in any gear. It doesn't make real good sense to look at 1st gear rpm at 200 mph but the computer will calculate it. What is informative is to examine "normal" shift points in each gear and the rpm at 55 to 65 mph. Then one can examine speed at maximum rpm shift points for racing too.

You can edit the file and change the tire size, rear end gear ratio, etc. You can rename the file while in edit to 200R4 and then put in the transmission ratios for the 200R4. Or copy it into a file called T350, delete the lines for 4th gear, put in the T350 ratios and you have a program to calculate T350 information.

I must have a dozen of these for various transmissions, calculating tire diameter, etc.

PRINT "Input the starting speed"
INPUT SS
PRINT "Input the ending speed"
INPUT ES
TIREDIA = 27.99213
PIE = 3.14159
TIRECIR = PIE * TIREDIA
ISM = 63360
RR = 3.73
GEAR1 = 3.06
GEAR2 = 1.62
GEAR3 = 1!
GEAR4 = .7
OPEN "O", #1, "700R4.DAT"
PRINT #1, TAB(30); "GM 700R4 four speed OD"
PRINT #1, " "
PRINT #1, TAB(10); "With"; GEAR1; "first"; GEAR2; "second"; GEAR3; "third"; GEAR4; "fourth"
PRINT #1, " "
PRINT #1, TAB(10); "Using a"; RR; " rear end ratio and "; TIREDIA; "inch rear tires."
PRINT #1, " "
FOR I = SS TO ES
RPM1 = (ISM / TIRECIR) * RR * GEAR1 * (I / 60)
RPM2 = (ISM / TIRECIR) * RR * GEAR2 * (I / 60)
RPM3 = (ISM / TIRECIR) * RR * GEAR3 * (I / 60)
RPM4 = (ISM / TIRECIR) * RR * GEAR4 * (I / 60)
RPM5 = (ISM / TIRECIR) * RR * GEAR5 * (I / 60)
RPM6 = (ISM / TIRECIR) * RR * GEAR6 * (I / 60)
PRINT #1, I; RPM1; RPM2; RPM3; RPM4
NEXT I


Hope this helps someone as this site has been a great source of information for me.

John
 

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SSuper Dave,

Assume you are running a Turbo 350 transmission using a 28 inch tire and a 3.08 rear end.

The T-350 has a 2.52 first, a 1.52 second and a 1.00 third.

The rmp will look like the following from 10 mph all the way to 200 mph.

This is just in case you don't want to muck around with running computer programs, rather you just want an answer to your question.

Turbo-Hydro 350

With 2.52 First, 1.56 Second and 1 third

Using a 3.08 rear end ratio and 28 inch rear tires

10 931.7677 576.8086 369.7491
11 1024.944 634.4894 406.724
12 1118.121 692.1703 443.6989
13 1211.298 749.8511 480.6738
14 1304.475 807.532 517.6487
15 1397.652 865.2128 554.6236
16 1490.828 922.8937 591.5985
17 1584.005 980.5744 628.5735
18 1677.182 1038.255 665.5483
19 1770.359 1095.936 702.5232
20 1863.535 1153.617 739.4982
21 1956.712 1211.298 776.473
22 2049.889 1268.979 813.448
23 2143.066 1326.66 850.4229
24 2236.243 1384.341 887.3978
25 2329.419 1442.021 924.3726
26 2422.596 1499.702 961.3476
27 2515.773 1557.383 998.3224
28 2608.95 1615.064 1035.297
29 2702.126 1672.745 1072.272
30 2795.303 1730.426 1109.247
31 2888.48 1788.106 1146.222
32 2981.657 1845.787 1183.197
33 3074.833 1903.468 1220.172
34 3168.01 1961.149 1257.147
35 3261.187 2018.83 1294.122
36 3354.364 2076.511 1331.097
37 3447.54 2134.192 1368.072
38 3540.717 2191.872 1405.046
39 3633.894 2249.553 1442.021
40 3727.071 2307.234 1478.996
41 3820.247 2364.915 1515.971
42 3913.424 2422.596 1552.946
43 4006.601 2480.276 1589.921
44 4099.778 2537.958 1626.896
45 4192.955 2595.638 1663.871
46 4286.131 2653.319 1700.846
47 4379.308 2711 1737.821
48 4472.485 2768.681 1774.796
49 4565.662 2826.362 1811.77
50 4658.838 2884.043 1848.745
51 4752.015 2941.724 1885.72
52 4845.192 2999.404 1922.695
53 4938.369 3057.085 1959.67
54 5031.546 3114.766 1996.645
55 5124.722 3172.447 2033.62
56 5217.899 3230.128 2070.595
57 5311.076 3287.809 2107.57
58 5404.253 3345.489 2144.545
59 5497.429 3403.17 2181.52
60 5590.606 3460.851 2218.495
61 5683.783 3518.532 2255.469
62 5776.96 3576.213 2292.444
63 5870.136 3633.894 2329.419
64 5963.314 3691.575 2366.394
65 6056.49 3749.255 2403.369
66 6149.667 3806.936 2440.344
67 6242.844 3864.617 2477.319
68 6336.02 3922.298 2514.294
69 6429.197 3979.979 2551.269
70 6522.374 4037.66 2588.244
71 6615.55 4095.34 2625.218
72 6708.728 4153.022 2662.193
73 6801.905 4210.702 2699.168
74 6895.081 4268.383 2736.143
75 6988.258 4326.064 2773.118
76 7081.434 4383.745 2810.093
77 7174.611 4441.426 2847.068
78 7267.788 4499.107 2884.043
79 7360.965 4556.788 2921.018
80 7454.142 4614.469 2957.993
81 7547.319 4672.149 2994.968
82 7640.495 4729.83 3031.943
83 7733.672 4787.511 3068.917
84 7826.848 4845.192 3105.892
85 7920.025 4902.872 3142.867
86 8013.202 4960.553 3179.842
87 8106.379 5018.235 3216.817
88 8199.556 5075.915 3253.792
89 8292.733 5133.596 3290.767
90 8385.91 5191.277 3327.742
91 8479.086 5248.958 3364.716
92 8572.262 5306.638 3401.692
93 8665.439 5364.319 3438.666
94 8758.616 5422 3475.641
95 8851.793 5479.681 3512.616
96 8944.97 5537.362 3549.591
97 9038.146 5595.043 3586.566
98 9131.323 5652.724 3623.541
99 9224.5 5710.405 3660.516
100 9317.676 5768.085 3697.491
101 9410.854 5825.766 3734.465
102 9504.03 5883.447 3771.441
103 9597.207 5941.128 3808.416
104 9690.384 5998.809 3845.391
105 9783.561 6056.49 3882.365
106 9876.738 6114.17 3919.34
107 9969.914 6171.851 3956.315
108 10063.09 6229.532 3993.29
109 10156.27 6287.213 4030.265
110 10249.44 6344.894 4067.24
111 10342.62 6402.575 4104.215
112 10435.8 6460.256 4141.19
113 10528.98 6517.936 4178.165
114 10622.15 6575.617 4215.139
115 10715.33 6633.298 4252.115
116 10808.51 6690.979 4289.089
117 10901.68 6748.66 4326.064
118 10994.86 6806.341 4363.039
119 11088.04 6864.022 4400.014
120 11181.21 6921.702 4436.989
121 11274.39 6979.383 4473.964
122 11367.57 7037.064 4510.939
123 11460.74 7094.745 4547.913
124 11553.92 7152.426 4584.888
125 11647.1 7210.106 4621.864
126 11740.27 7267.787 4658.838
127 11833.45 7325.468 4695.813
128 11926.63 7383.15 4732.788
129 12019.8 7440.83 4769.763
130 12112.98 7498.511 4806.738
131 12206.16 7556.192 4843.713
132 12299.33 7613.873 4880.688
133 12392.51 7671.553 4917.663
134 12485.69 7729.234 4954.638
135 12578.86 7786.915 4991.613
136 12672.04 7844.596 5028.588
137 12765.22 7902.277 5065.562
138 12858.39 7959.957 5102.537
139 12951.57 8017.638 5139.512
140 13044.75 8075.319 5176.487
141 13137.92 8133 5213.462
142 13231.1 8190.681 5250.437
143 13324.28 8248.363 5287.412
144 13417.46 8306.043 5324.387
145 13510.63 8363.724 5361.362
146 13603.81 8421.404 5398.337
147 13696.99 8479.085 5435.312
148 13790.16 8536.766 5472.286
149 13883.34 8594.448 5509.261
150 13976.52 8652.128 5546.236
151 14069.69 8709.809 5583.211
152 14162.87 8767.489 5620.186
153 14256.05 8825.17 5657.161
154 14349.22 8882.851 5694.136
155 14442.4 8940.531 5731.111
156 14535.58 8998.213 5768.085
157 14628.75 9055.894 5805.06
158 14721.93 9113.575 5842.035
159 14815.11 9171.256 5879.011
160 14908.28 9228.936 5915.986
161 15001.46 9286.618 5952.96
162 15094.64 9344.298 5989.935
163 15187.81 9401.979 6026.91
164 15280.99 9459.659 6063.885
165 15374.17 9517.341 6100.86
166 15467.34 9575.021 6137.835
167 15560.52 9632.702 6174.809
168 15653.7 9690.383 6211.784
169 15746.87 9748.064 6248.759
170 15840.05 9805.744 6285.734
171 15933.23 9863.425 6322.709
172 16026.4 9921.106 6359.684
173 16119.58 9978.787 6396.659
174 16212.76 10036.47 6433.634
175 16305.94 10094.15 6470.609
176 16399.11 10151.83 6507.584
177 16492.29 10209.51 6544.559
178 16585.47 10267.19 6581.533
179 16678.64 10324.87 6618.509
180 16771.82 10382.55 6655.484
181 16864.99 10440.23 6692.458
182 16958.17 10497.92 6729.433
183 17051.35 10555.6 6766.408
184 17144.52 10613.28 6803.383
185 17237.7 10670.96 6840.358
186 17330.88 10728.64 6877.333
187 17424.06 10786.32 6914.307
188 17517.23 10844 6951.283
189 17610.41 10901.68 6988.258
190 17703.59 10959.36 7025.233
191 17796.76 11017.04 7062.207
192 17889.94 11074.72 7099.182
193 17983.12 11132.4 7136.157
194 18076.29 11190.09 7173.132
195 18169.47 11247.77 7210.107
196 18262.65 11305.45 7247.082
197 18355.82 11363.13 7284.057
198 18449 11420.81 7321.032
199 18542.18 11478.49 7358.007
200 18635.35 11536.17 7394.981

You can see that column three (3) lists 2033.62 rpm in 3rd gear at 55 mph for this rear end and tire configuration.

If you consider 6400 rmp a good racing rpm shift point then:

6429 is 69 mph in 1st gear
6402 is 111 in 2nd gear
6433 is 174 in 3rd gear

Hope this helps you out.

John
 

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Double Whoa! You guys are way more high-speed or high Mhz, than I'll ever be. Holy Moly! I'm not gonna put together an excel routine 'cause you all have got it licked already. Al, what's the tech end of puting one of these programs on the site (preferably one with a single output so as to not lock things up here).
You dudes are blowin' me away! Rage on!


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