How Superior Is Rear Engine To Front Engine?

[nicholastanguma]

A long time ago on ADVrider I started a discussion about whether a horizontal single or a vertical single provided the best handling characteristics for a road racing bike. As can be expected, viewpoints were mixed, but the most standout point was that no manufacturer has used a horizontal engine configuration in professional racing for several decades now, all having opted for vertical (or a bit forward slanted). This seems to clearly indicate the ultra low center of gravity provided by a horizontal design, while great for the street, doesn't actually make for the best handling road racing machine.

In thinking back to that discussion, I'm now wondering how it applies to automotive road racing. It was in the 50s that rear mid-rear engine design started gaining traction in various formula racing series, and by the 60s those had become the de facto designs for everyone from shadetree Formula Vee racers to big budget teams in IndyCar and Formula 1.

Clearly a rear or mid-rear engine design provides the best handling for road racing, apparently even over a mid-front engine design.

Here's the question, then:

If you pitted a 900cc, 80hp, rear engine twin cylinder open wheel racer against a 1000cc, 100hp, front engine twin cylinder open wheel racer --and both cars were otherwise identically equipped and piloted by equally skilled drivers-- which car would likely be winner the most times out of ten?

[perfesser]

in answer to the motorcycle part of your question, the biggest reasons horizontal engines are not used in roadracing is the effect such a design has on wheelbase. the long engine requires a more raked steeing head which slows handling and extends the wheelbase. if one modifies the frame design to move the steering head forward to regain a quick steering head angle (say 22*-25*), this also extends the wheelbase and adds frame mass.

a related issue with the long horizontal engine is it shifts the center of gravity back towards the rear wheel. modern racebikes are forward weight biased to increase the braking power of the front tire.

[xxdabroxx]

What does the weight distribution of the two look like? I think that is what it would come down to.

[PackardV8]

One factor is driver seating position and thus driver feel. Two cars with equal weight distribution, the front-mid-engine will feel completely different to the driver than the rear-mid-engine.

The position of the driver's inner ear with respect to the center of mass/pressure/axis-of-rotation is a very real factor.

Fifty years ago, I started racing a four seat car which had the driver's seat back vertical and close to the steering wheel. The first thing I did was replace the OEM seat with an adjustable seat which allowed this tall guy to straighten out his legs and arms. Changing the seat also moved my head down and back; it effectively became a different car.

[plovett]

I don't know much about racing, but regarding the two open wheel cars, it would seem that the type of track would make the difference. The front engine car from your example has a better power to weight ratio, but poorer handling? So more and longer straights would favor it?

paul

[frnkeore]

The front engined car, will have a higher CG and/or a weight bias, to one side or the other. Good for oval tracks but, not road racing.

The rear engined car should have a less drive train, HP lose, too.

[frnkeore]

To address your question, more directly, it is very hard to over come a 20 HP disadvantage, especially in a low HP, open wheel car. You state :
--and both cars were otherwise identically equipped and piloted by equally skilled drivers-- That does not cover weight. The rear engine car will weigh less. Less weight = more cornering power. Even if the weight has to be the same, you can ballast the needed weight lower, in the car and where it will be of more advantage for corner weight.

Less frontal area will also be a rear engine advantage. With that small of engine, 20 HP is a BIG advantage (25%) and VERY hard to over come on a faster track but, with all the rear engine advantages the 80 HP car could do it on a tighter track with it's improved cornering force.

Last, acceleration is a product of HP per lb and if there isn't a weight limit, you could equal the 100 HP acceleration if you can get the same HP per lb.

With no weight limit, I would go rear engine. Same weight and faster course, I would go with the 100 HP, front engine.

[nicholastanguma]

To address your question, more directly, it is very hard to over come a 20 HP disadvantage, especially in a low HP, open wheel car. You state :
--and both cars were otherwise identically equipped and piloted by equally skilled drivers-- That does not cover weight. The rear engine car will weigh less. Less weight = more cornering power. Even if the weight has to be the same, you can ballast the needed weight lower, in the car and where it will be of more advantage for corner weight.

Less frontal area will also be a rear engine advantage. With that small of engine, 20 HP is a BIG advantage (25%) and VERY hard to over come on a faster track but, with all the rear engine advantages the 80 HP car could do it on a tighter track with it's improved cornering force.

Last, acceleration is a product of HP per lb and if there isn't a weight limit, you could equal the 100 HP acceleration if you can get the same HP per lb.

With no weight limit, I would go rear engine. Same weight and faster course, I would go with the 100 HP, front engine.

Very helpful, thank you!