Try this one maoriand1, a bit shorter but should work...
=(IF(B2<0,4;B2+0,35;B2+1,35)*1,94/B1+17,9/B3)/2,25*B1+1,1 (for Italian excel users)
You can name cells or ranges to make formulas a bit more readable...
B1 = distance
B2 = elevation
B3 = speed
...then you can replace the cell references with the cell names.
=(IF(elevation<0.4,elevation+0.35,elevation+1.35)*1.94/distance+17.9/speed)/2.25*distance+1.1 (for UK excel users)