how many mpg will i lose if i switch from 33"s to 35"s. i have a 400 motor 4x4 with a 4 inch lift.
Thanks,
Alex Hunt

 

Well, this might not help but..... Putting 35's on your truck could make your mpg go up, down or not change at all depending on your gearing and driving style. If you just put on the larger tires, your rear end ratio will act like a higher gear. (numerically lower) Giving you a slighly lower rpm on the freeway. If you have low gears already you mpg may increase, high gears- it may decrease because you have to give it more gas pedal to keep the same speed. If you drive conservative then you might see a positive difference or none at all. If you drive by the seat of your pants then your mpg will go down. Also you need to take into consideration where the volumetric efficiency level in your engine is compared to what your cruising speed is. (read most efficient rpm of engine vs freeway cruising rpm) IMO, I don't think you will see much difference with that small of a change. Your speedometer will however be off a little and will need to be recalibrated. (change speedo gear in transfercase). Hope this didn't confuse you too much.....

 

I cant add much to what was just said, except to add a tire chart.

<table class="maintext" align="center" border="1" cellpadding="0" cellspacing="0"> <tbody><tr> <td align="center" bgcolor="Yellow"> Better Gas Mileage </td> <td align="center" bgcolor="Lime"> Near Factory Ratio </td> <td align="center" bgcolor="Red"> More Power </td> </tr> </tbody></table>
<table class="maintext" align="center" border="0"><tbody><tr> <td>
</td> <td align="center">Gear Ratio</td> </tr> <tr> <td align="center" valign="middle">T
i
r
e


D
i
a
m
e
t
e
r
</td> <td> <table class="maintext" valign="CENTER" align="center" bgcolor="Silver" border="1"> <tbody><tr bgcolor="Aqua"> <td>
</td> <td>
</td> <td>3.31</td> <td>3.42</td> <td>3.55</td> <td>3.73</td> <td>3.91</td> <td>4.11</td> <td>4.27</td> <td>4.56</td> <td>4.88</td> <td>5.13</td> <td>5.29</td> <td>5.38</td> <td>5.71</td> <td>6.17</td> <td>7.17</td> </tr> <tr></tr> <tr> <td bgcolor="Aqua">27"</td> <td>
</td> <td bgcolor="Yellow">2677</td> <td>2766</td> <td bgcolor="Lime">2872</td> <td>3017</td> <td bgcolor="Red">3163</td> <td>3325</td> <td>3454</td> <td>3689</td> <td>3947</td> <td>4150</td> <td>4279</td> <td>4352</td> <td>4619</td> <td>4991</td> <td>5800</td> </tr> <tr> <td bgcolor="Aqua">28"</td> <td>
</td> <td>2582</td> <td bgcolor="Yellow">2668</td> <td>2769</td> <td bgcolor="Lime">2909</td> <td>3050</td> <td bgcolor="Red">3206</td> <td>3331</td> <td>3557</td> <td>3806</td> <td>4001</td> <td>4126</td> <td>4196</td> <td>4454</td> <td>4813</td> <td>5593</td> </tr> <tr> <td bgcolor="Aqua">29"</td> <td>
</td> <td>2493</td> <td>2576</td> <td bgcolor="Yellow">2674</td> <td>2809</td> <td bgcolor="Lime">2945</td> <td>3095</td> <td bgcolor="Red">3216</td> <td>3434</td> <td>3675</td> <td>3863</td> <td>3984</td> <td>4052</td> <td>4300</td> <td>4647</td> <td>5400</td> </tr> <tr> <td bgcolor="Aqua">30"</td> <td>
</td> <td>2410</td> <td>2490</td> <td bgcolor="Yellow">2584</td> <td>2715</td> <td bgcolor="Lime">2846</td> <td>2992</td> <td bgcolor="Red">3109</td> <td>3320</td> <td>3553</td> <td>3735</td> <td>3851</td> <td>3917</td> <td>4157</td> <td>4492</td> <td>5220</td> </tr> <tr> <td bgcolor="Aqua">31"</td> <td>
</td> <td>2332</td> <td>2409</td> <td>2501</td> <td bgcolor="Yellow">2628</td> <td>2755</td> <td bgcolor="Lime">2896</td> <td>3008</td> <td bgcolor="Red">3213</td> <td>3838</td> <td>3614</td> <td>3727</td> <td>3790</td> <td>4023</td> <td>4347</td> <td>5051</td> </tr> <tr> <td bgcolor="Aqua">32"</td> <td>
</td> <td>2259</td> <td>2334</td> <td>2423</td> <td bgcolor="Yellow">2546</td> <td>2696</td> <td bgcolor="Lime">2805</td> <td>2914</td> <td bgcolor="Red">3112</td> <td>3331</td> <td>3501</td> <td>3610</td> <td>3672</td> <td>3897</td> <td>4211</td> <td>4894</td> </tr> <tr> <td bgcolor="Aqua">33"</td> <td>
</td> <td>2191</td> <td>2263</td> <td>2349</td> <td>2469</td> <td bgcolor="Yellow">2588</td> <td>2720</td> <td bgcolor="Lime">2826</td> <td>3018</td> <td bgcolor="Red">3230</td> <td>3395</td> <td>3501</td> <td>3561</td> <td>3779</td> <td>4093</td> <td>4745</td> </tr> <tr> <td bgcolor="Aqua">34"</td> <td>
</td> <td>2126</td> <td>2197</td> <td>2280</td> <td>2396</td> <td>2512</td> <td bgcolor="Yellow">2640</td> <td>2743</td> <td bgcolor="Lime">2929</td> <td>3135</td> <td bgcolor="Red">3295</td> <td>3398</td> <td>3456</td> <td>3668</td> <td>3963</td> <td>4606</td> </tr> <tr> <td bgcolor="Aqua">35"</td> <td>
</td> <td>2065</td> <td>2134</td> <td>2215</td> <td>2328</td> <td>2440</td> <td bgcolor="Yellow">2565</td> <td>2664</td> <td bgcolor="Lime">2845</td> <td>3045</td> <td bgcolor="Red">3201</td> <td>3301</td> <td>3357</td> <td>3563</td> <td>3850</td> <td>4474</td> </tr> <tr> <td bgcolor="Aqua">36"</td> <td>
</td> <td>2008</td> <td>2075</td> <td>2154</td> <td>2263</td> <td>2372</td> <td>2493</td> <td bgcolor="Yellow">2590</td> <td>2766</td> <td bgcolor="Lime">2961</td> <td>3112</td> <td bgcolor="Red">3209</td> <td>3264</td> <td>3464</td> <td>3743</td> <td>4350</td> </tr> <tr> <td bgcolor="Aqua">37"</td> <td>
</td> <td>1954</td> <td>2019</td> <td>2095</td> <td>2203</td> <td>2308</td> <td>2426</td> <td bgcolor="Yellow">2520</td> <td>2692</td> <td bgcolor="Lime">2881</td> <td>3028</td> <td bgcolor="Red">3123</td> <td>3176</td> <td>3370</td> <td>3642</td> <td>4243</td> </tr> <tr> <td bgcolor="Aqua">38"</td> <td>
</td> <td>1902</td> <td>1966</td> <td>2040</td> <td>2144</td> <td>2247</td> <td>2362</td> <td>2454</td> <td bgcolor="Yellow">2621</td> <td>2805</td> <td bgcolor="Lime">2948</td> <td>3040</td> <td bgcolor="Red">3092</td> <td>3282</td> <td>3546</td> <td>4121</td> </tr> <tr> <td bgcolor="Aqua">39"</td> <td>
</td> <td>1854</td> <td>1915</td> <td>1988</td> <td>2089</td> <td>2190</td> <td>2302</td> <td>2391</td> <td bgcolor="Yellow">2554</td> <td>2733</td> <td bgcolor="Lime">2873</td> <td>2962</td> <td bgcolor="Red">3013</td> <td>3198</td> <td>3455</td> <td>4015</td> </tr> <tr> <td bgcolor="Aqua">40"</td> <td>
</td> <td>1807</td> <td>1867</td> <td>1938</td> <td>2037</td> <td>2135</td> <td>2244</td> <td>2331</td> <td>2490</td> <td bgcolor="Yellow">2664</td> <td>2801</td> <td bgcolor="Lime">2888</td> <td>2937</td> <td bgcolor="Red">3118</td> <td>3369</td> <td>3915</td> </tr> <tr> <td bgcolor="Aqua">41"</td> <td>
</td> <td>1763</td> <td>1822</td> <td>1891</td> <td>1987</td> <td>2083</td> <td>2189</td> <td>2275</td> <td>2429</td> <td bgcolor="Yellow">2599</td> <td>2733</td> <td bgcolor="Lime">2818</td> <td>2866</td> <td bgcolor="Red">3042</td> <td>3287</td> <td>3819</td> </tr> <tr> <td bgcolor="Aqua">42"</td> <td>
</td> <td>1721</td> <td>1778</td> <td>1846</td> <td>1940</td> <td>2033</td> <td>2137</td> <td>2220</td> <td>2371</td> <td>2538</td> <td bgcolor="Yellow">2668</td> <td>2751</td> <td bgcolor="Lime">2798</td> <td>2969</td> <td bgcolor="Red">3208</td> <td>3728</td> </tr> <tr> <td bgcolor="Aqua">43"</td> <td>
</td> <td>1681</td> <td>1737</td> <td>1803</td> <td>1894</td> <td>1986</td> <td>2087</td> <td>2169</td> <td>2316</td> <td>2479</td> <td bgcolor="Yellow">2606</td> <td>2687</td> <td bgcolor="Lime">2733</td> <td>2900</td> <td bgcolor="Red">3134</td> <td>3642</td> </tr> <tr> <td bgcolor="Aqua">44"</td> <td>
</td> <td>1643</td> <td>1698</td> <td>1762</td> <td>1851</td> <td>1941</td> <td>2040</td> <td>2119</td> <td>2263</td> <td>2422</td> <td>2546</td> <td bgcolor="Yellow">2626</td> <td>2670</td> <td bgcolor="Lime">2834</td> <td>3063</td> <td bgcolor="Red">3559</td></tr></tbody></table></td></tr></tbody></table>

 

Masterbeavis, what speed is the rpm's in that chart calculated for? 60, 65 mph?

 

The above table can be used to get a rough idea on gear ratios. The colors represent ideal RPM's at highway speeds (65). For highway cruising and best fuel economy stay towards the yellow (2600 rpm), around town daily driving is color coded green (2800 rpm), and for better towing power or just more 4-low power use the ratios near the red (3100 rpm). These calculations are assuming a manual transmission with a 1:1 ratio. If you drive an automatic your RPMs will be slightly higher, and the opposite is true if you have overdrive (your RPMs will be slightly lower).

 

i have some maxxis 35's on my '78, without changing any gears. it had a 351m in it and i swapped it out for a mildly built 400. and it also had some 33's before i swapped it out for some 35's. i really didnt notice any difference, i dont tow much either.