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There was a thread posted RE: the CX motored prototype flat tracker... with the motor mounted longitudinally and driving an "Arghhhh" chain
sorry if this is old hat, thought it might be interesting...



1979 Honda Race Team
That's one of the better write-ups I've seen. From first hand experience. I saved it in a doc form.





I didn't know that Eric Bostrom came from a dirt tracking family. That was from a link on that same site. Apparently there were several Bostroms in dirt tracking. Eric ran the 600's in the FUSA series about 10 yrs ago.
 

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What advantage is there mounting the CX500 engine in that manner? Does the chain really drive the wheel that much better, or is it due to suspension travel?



Mike
 

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What advantage is there mounting the CX500 engine in that manner? Does the chain really drive the wheel that much better, or is it due to suspension travel?



Mike


The chain is much more efficient. Each time a drive line has to "turn a corner" it loses torque. The CX is better than most shaft driven bikes -- it only has to turn 90 degrees once: at the end of the drive shaft. My Kawasaki Concours has two turns: one at the output of the tranny, and one at the end of the drive shaft.
 

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Shaft jacking may also be a reason why a chain was used rather than a shaft. Having to deal with shaft jacking while racing would make things more difficult.



Here is the definition of shaft jacking from motorcycle-glossary.com:



"Unwanted motion in the rear end of motorcycles with a shaft drive. While under acceleration, the rear suspension stiffens and the machine lifts itself. When decelerating the rear suspension is compressed, giving the opposite effect. It is considered a drawback for some traditional shaft-drive designs. Some of the modern, shaft-drive systems utilize newer technology to reduce this effect."
 

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Equally important is the fundamental engine orientation. A transverse engine will never turn in as quickly as an inline Vee layout all other things being equal. This is one of the reasons Harley has dominated flat track forever (along with the power pulse for great traction) The wider engined sportbike Inline fours also turn in slowly compared to say a Ducati or an SV 650/1000 It's a super engine layout for nimble handling it also helps in power on traction. We CX riders have all sat at the stop light blipping the throttle and felt the lateral torque reaction? It's much more effective to have the crankshaft spinning in the direction the bike is going . But hey, we ain't afraid ah no torque reaction ha ha?

Cheers, 50gary
 

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I know this will sound odd, maybe even questionable, but I kinda like that little torque twist feeling....
 

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Keeping the unsprung weight as light as possible would be another reason to go with a chain drive system on a racer. A final drive assem, especially one beefed up for racing, would add unsprung weight and adversly affect handling especially if the track is rough.

On a chain system it is also pretty easy to change the driven sprocket sizes to get different ratios for different tracks and conditions. Thats usually not easy to do on a shafty.
 

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What advantage is there mounting the CX500 engine in that manner? Does the chain really drive the wheel that much better, or is it due to suspension travel?


There is approximately a 15-20% loss of energy with a shaft drive and only about 5-10% loss with chain drive.



Equally important is the fundamental engine orientation. A transverse engine will never turn in as quickly as an inline Vee layout all other things being equal. This is one of the reasons Harley has dominated flat track forever (along with the power pulse for great traction) The wider engined sportbike Inline fours also turn in slowly compared to say a Ducati or an SV 650/1000 It's a super engine layout for nimble handling it also helps in power on traction. We CX riders have all sat at the stop light blipping the throttle and felt the lateral torque reaction? It's much more effective to have the crankshaft spinning in the direction the bike is going . But hey, we ain't afraid ah no torque reaction ha ha?

Cheers, 50gary


I am wondering where you got this information. I have never seen it before and question what you are saying. The reason Harleys win so many dirt track races is simply the rules are modified so they are about the only bike that can win. When you can only run a 500 against a 750 and have to use carb restriction besides on the 500, it more than equals things out.



I have never heard of this theory and wonder where it came from.
 

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Kenny Roberts proved that the Harleys can be beat with a Yamaha 4 cylinder water cooled 2 cycle in a dirt track frame - but it wasn't easy. The bike had twice the horsepower of the Harley and was difficult to get traction. I was at this race and the crowd went absolutely nuts when Kenny passed the Harleys on the last straight and crossed the finish line. Kenny was interviewed and said that Yamaha could not pay him enough money to ride the bike again. The bike was later banned from dirt track racing. Kenny was just about unbeatable riding the road racer version of the same bike.

http://www.youtube.com/watch?v=8k8hJWKIVNs

A childhood friend of mine was a Yamaha dealer and we raced the TZ750 at Daytona in 1977. We could not compete with the factory teams and finished 40th out of 80.

The bike was unbeaten in the local WERA race circuit for 2 years. He sold the bike to a youngster who raced it until he dropped it in a turn and put a hairline crack in the engine case. A friend of his said he could Heliarc it not knowing the cases were magnesium. The thing went up like a railroad flare and all that was left of the engine was the crank.

It was a hell of a machine. Billrod
 

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There is approximately a 15-20% loss of energy with a shaft drive and only about 5-10% loss with chain drive.







I am wondering where you got this information. I have never seen it before and question what you are saying. The reason Harleys win so many dirt track races is simply the rules are modified so they are about the only bike that can win. When you can only run a 500 against a 750 and have to use carb restriction besides on the 500, it more than equals things out.



I have never heard of this theory and wonder where it came from.


It's not a theory at all it's simple physics. If you have ever seen a tight rope walker on the high wire they often carry a very long pole held transversely to move the weight further out from their center of gravity this slow down the movement a great deal for easier balance. A much greater polar moment of inertia. For quick turning one would move the weight closer to the center of gravity, this could be represented by a figure skater doing a spin. Even though they are losing total energy they can increase their rate of spin by drawing their arms tight to the chest, they still weigh the same but the mass is very much closer to the center of axis allowing quicker turn rate. Motorcycles with single cylinder or V motors on the centerline axis will turn in easier than a twin, triple or four cylinders (all other things being equal) this is especially true when the motors are spinning.

KR could beat virtually anyone regardless of the bike, they don't call him King Kenny for nothing.

Cheers, 50gary
 

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It's not a theory at all it's simple physics. If you have ever seen a tight rope walker on the high wire they often carry a very long pole held transversely to move the weight further out from their center of gravity this slow down the movement a great deal for easier balance. A much greater polar moment of inertia. For quick turning one would move the weight closer to the center of gravity, this could be represented by a figure skater doing a spin. Even though they are losing total energy they can increase their rate of spin by drawing their arms tight to the chest, they still weigh the same but the mass is very much closer to the center of axis allowing quicker turn rate. Motorcycles with single cylinder or V motors on the centerline axis will turn in easier than a twin, triple or four cylinders (all other things being equal) this is especially true when the motors are spinning.

KR could beat virtually anyone regardless of the bike, they don't call him King Kenny for nothing.

Cheers, 50gary
Show me some articles to back up what you are saying.
 

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Dave from Wisconsin, the principle is the same regardless of what body or mass the laws of physics are applied to be it a motorcycle engine a figure skater or whatever you may choose to debate about. that's why it's called a "law of physics" If you need validation from a higher authority just call Race Tech Suspensions or some such place that does professional suspension design and setups. I also realize many people do not care for Harley Davidson.

For a very good technical read find the book "How and Why - Motorcycle Design and Technology" by Gaetano Cocco He's an engineer for Aprilla I highly recommend the book.

Cheers, 50gary
 

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One of the members of our current administration (I don’t remember who) was questioning a member of the scientific community. I wish I could remember the situation (I am 71 and memory is not as good as it was). The politician asked a “why can’t we do that” type of question and the scientist stated because it would violate the laws of physics. The politician said “we need to see about rewriting that law to make it more useful.”

Just think - if he rewrites the laws of physics our twisted twins will have a better chance against the Harleys.

This must have been the same guy that said we should re-train the 200,000 plus cattle crossing guards in this country. These folk are not only allowed to breed but write our laws.
 
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