Tuesday, December 14, 2010

How Much Horsepower Does a Motorcycle Need?

Of course it's fun to go out once in a while on a motorcycle with a huge amount of horsepower. But sometimes it's also fun to have just enough power to get you down the road. Ever thought of how Santa decided on eight reindeer? I'm sure he could have had as many as he wanted, and we all know he is hauling some serious a**. But he decided eight was enough. I guess he didn't have any other Santa's out there trying to one-up him on number of reindeer for the Christmas Eve toy run. And every reindeer over eight is just an extra mouth to feed.

With a motorcycle, I think that anything over 50 horses is going to be too many to use fully. On bikes over 130 hp, I'm guessing you would never use full throttle in the lifetime of the bike.

I have had some bikes that were clearly more powerful than they needed to be, and some that were just adequate. The bikes that were just adequate required a lot more concentration to ride. You had to think about wind, and hills. To pass a car or truck safely with a smaller bike often required using a whole bag of tricks.

I think between 10 and fifty would be just the number of horses. My Honda CD175 has 15 horsepower. My old Yamaha DS7 (a two stroke) had 25 hp. Mary Ann's Burgman has 32 horsepower. My Honda Silverwing 500cc had 50 hp. My Vulcan 900 also has about 50. On the other hand, most modern 600cc sportbikes have about 100 hp. Honda's new Shadow 750RS has 42 hp.

The Honda 175, with 15 hp, can do an indicated 75 mph, with the engine screaming on a flat road with no headwind, and me ducked down out of the air stream. And that may be less measured with a radar. It also takes quite a while to get there. I need a long unobstructed run, like the Bonneville Salt Flats. At 75 mph I feel the engine's pain. But I think the engine is comfortable driving at 50 mph all day. Well actually, how would I know what the engine feels, as I don't have nerve endings inside the engine. I should say the engine "seems" to be happy at 50 mph, in that it vibrates less, uses less gas per mile, it can accelerate more easily from that speed if it needs to. Also the chain does not get hot and dry, or stretch so that it need tightening at lower speeds. With 15 hp I have gone on the freeway, but it feels scary, and I think it would feel even more scary to someone who was not used to small bikes. I have not tried the CD175 on high speed roads in the mountains, and I suspect it would not be too good for that task. Also you don't overtake trucks or cars without a paid up life insurance policy.

My Yamaha 250, with 25 hp, had more than enough power except when going through the mountains two up, where I needed to gear down at times to maintain 100 kph up the hills. When I rode that bike on the freeway, I tried to stick to the slow lanes. Otherwise it was much like a car, in that you could easily keep up with traffic and even pass some cars at times, with the same passing zones you would use in a normal car.

One thing you soon realize with a low powered bike, is that your main disadvantage on the road is at high speed, not in low speed acceleration. In town, a 15 hp bike is enough to dust off most car traffic. That's because bikes are lighter than cars. But out on the highway, wind resistance is the big factor, and even a small bike has almost as much wind resistance as some smaller cars.

The 1982 Honda Silver Wing 500cc had about the same power as the Vulcan 900. The Vulcan has a big enough engine, that the designers can sacrifice horsepower to have a lot of torque at low rpm. The Silver Wing was a higher revving engine. I believe the Silver Wing was faster, as it was lighter. But with either bike I had no trouble keeping up with, or even staying ahead of, average traffic on the freeway. I also have no trouble going up mountains grades. I suspect 50 horsepower is about all you really need to go almost anywhere the road goes.

I noticed at the motorcycle show that the 250cc class is reviving. At first I was thinking that this might be a bit small, and why not do a 350cc bike? Here are the claimed horsepower ratings: Honda CBR250R = 26 hp, Hyosung 250 = 28 hp, Ninja 250 = 32 hp. Suzuki is being very secretive about the horsepower of the TU250, but I have seen estimates on the Internet from 16 to 20 hp. One thing most people agree on is that it is not as powerful as the other 250's out there.

When you are looking at the 250 class, you will need to consider horsepower. Big bikes have so many horses you will never need them all. You could probably pull the plug out of a few cylinders without noticing a loss of power. But with a small bike, you are probably going to use every horse, and more than once. So make sure you have enough before you buy.

Finally, if you are deciding on which 250 to buy, I advise you to not waste your time looking at torque figures The amount of torque these small bikes make will not amount to a hill of beans anyway. With 250 cc, you need to rev the engines and change gears if you need to get out of your own way. And that's the fun of it, too.

Picture: I photoshopped a bigger exhaust onto a Boss Hoss motorcycle (they have about 500 hp), to illustrate the concept of "more power than you actually need"


  1. Having grown up in the Sixties when the hot bikes were 500 and 650 cc twins pumping out anywhere between 40 and 55 HP, much more than 50 HP seemed like an awful lot.

    In fact, back in those simpler times, the most common machines were standards like Honda's CB350, which made a modest 35 HP, but which most of us were more than happy to take on long tours.

    In fact, we used to sneer at the Harley riders, whose big Panhead 'Seven-Fours' may (nominally) have produced 55 HP, but which wasted most of it shoving around a 700 pound monster (almost twice the weight of those CB350s!)

    The TU250 is apparently rated at just under 20 HP which, on a 320 pound bike, may seem limiting. However, the power-to-weight ratio is practically identical to those classic one-lunger 'Brit bikes' of the Sixties, such as the Royal Enfield Bullet (at 22 HP for 370 pounds).

    How much horsepower does a motorcycle need? How long is a piece of string?   ;-)

  2. My interest in low-powered bikes is because with diesel engines, they get crazy heavy, crazy bulky, and crazy expensive the higher you go. Right now I'm looking at a Kubota D722 to stuff in something like a mid-sized frame. the engine is about 390 lbs and puts out about 16hp naturally aspirated.

  3. Today 250cc is getting even more power. The new ninja 250 packs a modest 39 hp. Guess i should get one.