Driving Speed Fuel Economy Comparison Calculator

The measurement being modeled

Compare fuel use over the same distance at two measured or modeled cruising economies — the comparison is meaningful only after its reference case is fixed.

Traffic, wind, temperature, and elevation should be similar between scenarios — that condition defines when additional fuel at speed b is comparable with another result.

When the vehicle decision also requires you to compare E85 volume with gasoline using an entered energy-content ratio, calculate it independently with the E85 Gasoline Energy Equivalence.

Turning the inputs into a result

Fuel economy at speed A. Observed or estimated economy at the first cruising speed — for this measurement, use a stable operating point and document any tire, gearing, grade, or wind condition that affects it.

Document Fuel economy at speed B as observed or estimated economy at the second cruising speed — this means you should use a stable operating point and document any tire, gearing, grade, or wind condition that affects it.

The Comparison distance entry represents distance traveled in each scenario — before calculating, measure from the stated reference points and note whether the vehicle or component is loaded.

In “fuel difference = distance ÷ MPG B − distance ÷ MPG A,” the printed units define how each term is interpreted.

No term beyond fuel economy at speed a, fuel economy at speed b, and comparison distance is introduced in “fuel difference = distance ÷ MPG B − distance ÷ MPG A.”

Using the supporting measurement

Additional fuel at speed B answers “Compare fuel use over the same distance at two measured or modeled cruising economies.” The additional displays, Economy change, Fuel at speed A, and Fuel at speed B, are a different view of the same entered measurements.

This calculator uses the entered MPG values rather than predicting them from speed alone — when that condition changes, compare separate calculator runs instead of blending the inputs.

Because traffic, wind, temperature, and elevation should be similar between scenarios, a disagreement between additional fuel at speed b and an outside reference should trigger a review of fuel economy at speed a and comparison distance.

A field-check procedure

Prepare both comparison cases before changing the vehicle and write down the single condition intended to differ — this workflow must also account for the fact that traffic, wind, temperature, and elevation should be similar between scenarios.

• Record Fuel economy at speed A as observed or estimated economy at the first cruising speed — use a stable operating point and document any tire, gearing, grade, or wind condition that affects it.
• Record Fuel economy at speed B as observed or estimated economy at the second cruising speed — use a stable operating point and document any tire, gearing, grade, or wind condition that affects it.
• Record Comparison distance as distance traveled in each scenario — measure from the stated reference points and note whether the vehicle or component is loaded.

Operating conditions outside the formula

A change in comparison distance is not isolated if another vehicle condition changed between the two cases — for comparison distance, the page specifically expects distance traveled in each scenario.

Build another useful comparison to compare annual fuel volume using gasoline and diesel economy estimates with the Diesel vs Gasoline Efficiency.

Before using this result