is there a simple way to determine brake horsepower

[Alpo]

I'm reading a story. The kid has just got a 200cc Yamaha 2-stroke. He is happy, because Texas law says he can have up to a 250cc bike at his age. Wonderful. That Makes Sense.

 

Back when I was 15, and getting my restricted driver's license, with a restricted license you could ride a motorcycle with up to five brake horsepower.

 

Since there's no way in the world that my father would have allowed me to have a motorcycle, I never really paid any attention to that, except for wondering what the hell five brake horsepower meant.

 

Since it was only five, I assumed it meant a small engine. But is there some sort of conversion table, where you can say, "yes, this 225cc street bike meets their spec for five brake horsepower or less", or would you have to get the specifications for whatever motorcycle you wished to ride and verify that it's engine only produced that much?

[LawMan Mark, SASS #57095L]

The difference between hp and bhp is that the hp is a unit of measurement of the power of the entire system and does not include frictional losses, whereas the bhp is the amount of the power output by the engine and includes frictional losses.

 

I found this on the web...

[Imis Twohofon,SASS # 46646]

In Colorado, 55 years ago, when I started riding it was based on Manufacturers Advertised HP. That meant that somewhere around 75 - 110 cc was the cutoff. Oh, how I wanted that Yamaha 110 cc twin.

 

Imis

[Alpo]

3 hours ago, LawMan Mark, SASS #57095L said:

I found this on the web...

I found that also, but that didn't really answer my question.

 

There I am, as a 15-year-old boy, wanting to get a motorcycle to ride to school using my restricted driver's license.

 

Is there something somewhere somehow that would let me know which bike had five brake horsepower or less, so I could legally ride it.

[Alpo]

1 hour ago, Imis Twohofon,SASS # 46646 said:

In Colorado, 55 years ago, when I started riding it was based on Manufacturers Advertised HP. That meant that somewhere around 75 - 110 cc was the cutoff. Oh, how I wanted that Yamaha 110 cc twin.

 

Imis

So you're saying that if I wanted that neat 250 Zusucki, I go down to the rice burner shop and get the brochure for the 250, and somewhere in the advertising it would say "4.6 brake horsepower"? And I would be good to go, but if the brochure said it had 5.2 brake horsepower I was SOL?

[Ozark Huckleberry]

1 minute ago, Alpo said:

So you're saying that if I wanted that neat 250 Zusucki, I go down to the rice burner shop and get the brochure for the 250, and somewhere in the advertising it would say "4.6 brake horsepower"? And I would be good to go, but if the brochure said it had 5.2 brake horsepower I was SOL?

That’s likely what law enforcement would base it on, anyway. 
 

It’s not as if the state would haul every small bike in to throw them on a dynamometer and get a list of what passed the cutoff. 

[Sgt. C.J. Sabre, SASS #46770]

I think that just about any motorcycle will have more than 5 hp. You can get a chainsaw with more than 5 hp. That type of law allows one to ride a moped without a license, as they are specifically advertised as less than 5 hp.

[Larsen E. Pettifogger, SASS #32933]

is there a simple way to determine brake horsepower

 

 

No.

[El Chapo]

There is no simple way to determine "brake horsepower"  but it is simple to determine if something has 5 or more.  I had a 105cc 2 stroke that was something like 27 horsepower--so it should be obvious based on that, that 200 cc motorcycle is not close to 5 horsepower and likely has at least 8 times that number.

[Still hand Bill]

Brake hp, would be called brake, because that was the type of dynamometer used to get your hp reading.  Originally they would simply be some sort of brake with a long arm attached.  By measuring the force on the arm you can determine the torque and if you know the rpm, you can calculate hp.  Torque x rpm/5252.  With torque in ftlbs.  
 

now most hp readings are taken using inertial or eddy current dynos.  Water brakes are not used much anymore.  
 

5 hp would be a pretty small engine. Probably 50cc or so.  An 80cc chainsaw will make more than 5 hp.  A liquid cooled 80 cc dirt bike is 15+ hp. 

[LawMan Mark, SASS #57095L]

4 hours ago, Alpo said:

I found that also, but that didn't really answer my question.

 

There I am, as a 15-year-old boy, wanting to get a motorcycle to ride to school using my restricted driver's license.

 

Is there something somewhere somehow that would let me know which bike had five brake horsepower or less, so I could legally ride it.

1. BHP = (Torque × RPM )/5252,where torque is lb -ft and n = revolution per min

[Sgt. C.J. Sabre, SASS #46770]

7 hours ago, LawMan Mark, SASS #57095L said:

1. BHP = (Torque × RPM )/5252,where torque is lb -ft and n = revolution per min

You're telling a 15 year old boy wanting a motorcycle to do MATH?!?!?

[sassnetguy50]

2 hours ago, Sgt. C.J. Sabre, SASS #46770 said:

You're telling a 15 year old boy wanting a motorcycle to do MATH?!?!?

A small price to pay for such a freedom.  There is a good chance he'll have to do math for the premix.  What was the last street legal Yamaha 200 2t?

[Pulp, SASS#28319]

And supposedly larger engines could be restricted with carburetor mods.  A friend had a Honda 150 that was supposedly restricted to 5 hp.  But since it would run 60 with two aboard I don’t think it was restricted.

[J.D. Daily]

You can't trust mfg's specifications.  GM for years understated engine power for owners insurance cost purposes.  Also, each mfg. has their own "Standard Conditions".   Some correct dyno measured power to zero pumping losses (combustion air piping, air cleaner or flame arrestor and exhaust piping & silencer).  If you are talking about heavy duty engines there is an ISO standard for engine rating.  Automobile & motor cycle ratings are equivalent to ISO "Fuel Stop Power"  Basically "Wide Open Throttle" or "Balls to the Wall".

[sassnetguy50]

We have all assumed this was a gasoline bike.  Did the book say it was a gasoline engine @Alpo?

 

A naturally aspirated 200cc diesel could easily be below 5hp for a low revving, fuel efficient bike.  Maybe he was excited to get over 200mpg.

[WOLFY]

hp = engine output

bhp= hp measured at the wheel

[Alpo]

6 hours ago, sassnetguy50 said:

We have all assumed this was a gasoline bike.  Did the book say it was a gasoline engine @Alpo?

 

A naturally aspirated 200cc diesel could easily be below 5hp for a low revving, fuel efficient bike.  Maybe he was excited to get over 200mpg.

Did they make diesel 2 strokes?

 

Regardless, it's a gasoline bike.

 

>"It's a 1976 Yamaha RD 200. They were a great little two-stroke bike, air cooled with twin exhausts. Six speed. It had a front drum brake, but I converted it to a disk brake."<

[Dungannon Gunner]

On 8/12/2021 at 11:09 AM, Sgt. C.J. Sabre, SASS #46770 said:

I think that just about any motorcycle will have more than 5 hp. You can get a chainsaw with more than 5 hp. That type of law allows one to ride a moped without a license, as they are specifically advertised as less than 5 hp.

Sorta off original subject however just an FYI, back in the day with parents permission many states allowed those between 14 and 16 to take an MC test and receive a license for Motorcycles with less than 5HP. My 90cc Kawasaki was rated at 4.99 hp and that baby would do 55 on a good down hill road. Mopeds also had pedals and depending upon terrain required the occasional pedal power.. Back in those days anyone calling our Motorcycles 'Mopeds was a call for trouble. we did not allow Mopeds in our MC gang. Our MC gang consisted of 4 guys, me on the 90cc, 2 on Honda 50cc and 1 on something homemade. 

[sassnetguy50]

48 minutes ago, Alpo said:

Did they make diesel 2 strokes?

 

Regardless, it's a gasoline bike.

 

>"It's a 1976 Yamaha RD 200. They were a great little two-stroke bike, air cooled with twin exhausts. Six speed. It had a front drum brake, but I converted it to a disk brake."<

Yes, they did and still do make 2T diesels.  I don't know if Yamaha made one for a bike.  Most diesel bikes are sold overseas.

 

Ah, it is a fictional book.  The RD200 put out about 20hp.

[Alpo]

32 minutes ago, sassnetguy50 said:

Ah, it is a fictional book. 

Well, yeah. I kinda thought this would make it obvious.

 

On 8/12/2021 at 3:03 AM, Alpo said:

I'm reading a story

 

[WOLFY]

I remember (and still see) many laws referring to displacement as opposed to horsepower.  I had a YL1 Yamaha as a kid.

That 100cc 2t twin was so fun.

[Sedalia Dave]

 

 

 

 

 

[Wallaby Jack, SASS #44062]

5 hours ago, WOLFY said:

I remember (and still see) many laws referring to displacement as opposed to horsepower.  I had a YL1 Yamaha as a kid.

That 100cc 2t twin was so fun.

 

 even back in '76 they should have spelled their name right ..... (left to right, not right to left) .......   

[Alpo]

But the Japanese write right to left.

 

And all these years us stupid gaijin have been mispronouncing A-ha-may.

[WOLFY]

13 hours ago, Wallaby Jack, SASS #44062 said:

 

 even back in '76 they should have spelled their name right ..... (left to right, not right to left) .......   

I think those were 60’s era rides, if my memory swerves.  

(i didn’t even notice that picture was flipped)