Voices

When 147kW loses to 135kW. Toyota 86 vs BMW 220i

How come a light, powerful car is no faster than a heavier, weaker competitor?

The Toyota 86 automatic weights 1278kg and has a motor good for 147kW.  It does the 0-100 sprint in 7.6 seconds, which is the same time as the BMW 220i convertible (review here).  But the BMW manages only 135kW and weighs 1530kg.
 
Here’s the figures, and within that table is the answer:
 
 Toyota 86BMW 220iDifference
Length424044325%
Width177517740%
Height132014137%
Weight1278153020%
    
Power147135-8%
Torque20527032%
Gears6 auto8 auto2
    
Max speed 2nd95km/h80km/h15km/h
Power/weight8.79.59%
Torque/weight6.24.7-24%
    
0-1008.17.6-6%
 
The BMW pegs back its power to weight disadvantage in three ways.  First, it has a quick-shifting automatic, far quicker than the 86’s.  It also has eight gears, which is crucial.  Both cars need two gearchanges to make 100km/h, but the 86’s is at 95km/h.  The BMW’s is at 80km/h. The BMW’s narrow gear ratio means its engine can be in its best power band pretty much all the time.
 
The third and most important BMW advantage is a wide power band.  Peak power is maintained from 5000 to 6250rpm, quite a wide powerband.  When you change from second to third at the 6500rpm redline you drop 2000rpm to 4500, so you’re only 500rpm off maximum power.
 
The 86’s peak power is 7000rpm, and it is peaky, so below 7000 the power drops off dramatically.  And when you change from the 7500rpm redline the revs drop 2300 to about 5200rpm…which is way more than 500rpm off peak power, so the car wouldn’t be developing 147kW at 5200rpm, and probably not even 135kW.
 
So that’s how it’s done.  No great mystery – quicker shifting gears, more gear ratios, and and engine which produces nearly the same power but over greater rev range.
 
Yet the 86 feels no slower, because it’s lower, the engine has more of an abrupt punch compared to the BMW’s linear power delivery, and towards redline the 86 is deliberately racous, whereas the BMW is more understated.
 
Just goes to show that looking at power figures has never been, and never will be a reliable indicator of performance.
 
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Robert Pepper

Robert Pepper