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Author Topic: C5 Vs G5  (Read 5808 times)

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Re: C5 Vs G5
« Reply #45 on: February 15, 2010, 09:46:41 PM »
I recently had a guy come up to me as I was getting ready to fire up my bike.  He said "Dude, you should get a 3 speed transmission - they're fast!"  I started to explain that gearing determines what rpm you'll be at for a given speed, but can't change your speed unless you're geared badly to begin with.  You need more power and/or less drag to go faster  He responded by starting to lecture me about his friend with a 3 speed whose bike was now "wicked fast" and that "torque is where speed comes from."  He said my 5 speed was adequate, but a 3 speed would make it scream.   ::)  I put on my goggles as he kept talking, said "nice to meet you", and rode away.  It seemed like a conversation that was going to go nowhere...   ::)

Eamon

I get the sarcasm in your story. I must also agree I am a newbie. And, If you read carefully, I am not talking of doing 100 mph on the bike, just 65, but with a lower stress on the engine, with a 20 inch sprocket.

The overdrive gear was just a theoretical question. 

Eamon

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Re: C5 Vs G5
« Reply #46 on: February 15, 2010, 10:22:32 PM »
I get the sarcasm in your story. I must also agree I am a newbie. And, If you read carefully, I am not talking of doing 100 mph on the bike, just 65, but with a lower stress on the engine, with a 20 inch sprocket.

The overdrive gear was just a theoretical question. 

Sorry, I wasn't making fun of you at all and hope you didn't think I was.  I was just relating a story  that had an extreme example.  I do think that you need to have a little bit of a power boost along with the gear change in order to have it actually result in less engine stress (like switching to a freer flowing exhaust or a carb change, etc).  Guys like Ace and Vince can say better than me, but a gearing change without added power may lower rpms, but too big a change and it might result in more heat from the motor trying to make that speed with the lower gearing.

Eamon
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http://www.sterlingloons.com

ace.cafe

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Re: C5 Vs G5
« Reply #47 on: February 15, 2010, 10:42:30 PM »
65 mph will put a big smile on my face. I have put a short exhaust. A 30 mm carb, 20 tooth sprocket and a more open air filter (undetermined yet) are next on the list.

In theroy: The Electra can go to 65 mph easily, just not recommended for cruising at the speed because of the added stress on the engine. However, with a larger gear ratio, same (not more) speed can be achieved with less stress on the engine. Thats why they have these larger sprockets to begin with.  

This theory you stated is not correct.
That theory comes under the heading of "no free lunch".

A larger sprocket actually reduces the torque-multiplier, and places more load on the engine at all speeds. The result is more load on the clutch when starting off from a stop, slower acceleration, and wider throttle openings at all road speeds to increase the engine output to make up for the reduction in torque multiplier of the gearing.
Top speed will not be higher, and may likely even be lower because of "over-gearing".
The "cruising rpm" may be a few hundred rpm lower, but the load on the engine is as high, or higher, than with the smaller sprocket, due to loss of torque multiplier in the gear train.

What you have stated here is a very common misconception. I don't fault you for it. Most people don't understand it. It stems from a lack of understanding of the load dynamics involved. Hopefully, you grasped some of what I wrote above.

However, the Electra can cruise at 65mph, but that's about its limit for long term cruising.
It already comes with an 18T sprocket, which is plenty.
It can do what you want, just barely. The larger sprocket isn't going to be "easier on the engine" despite the common misunderstanding about it.

They make larger sprockets for modified engines with higher output levels  to reach higher speeds. They are commonly used for the purpose you specify, but they do not do what people commonly think they do. They trade off a slightly lower rpm for a slightly larger throttle opening. It still takes the same hp to ride at that speed. The result is that the engine is not under any less load,  must put out at least the same output, and it isn't any easier on the engine. The slightly less friction losses from the slightly lower rpms is offset by the higher heat output from the larger throttle opening.

It might be a litte easier on the rider, because it's less buzzy at a little lower  rpm.
But the engine and the rider are two entirely different things.

The best way to increase cruising speed, or reduce the stress on the engine at the cruising speeds is to reduce the load the bike must overcome to maintain that speed.
And that is done by improving aerodynamics, to reduce wind drag, which is the largest factor of load that the engine must use its power to overcome at those kinds of road speeds.
If you do that, then you truly do have less load, and can then use a taller gear without increasing the stress of the engine, because there's less load to overcome, and the bike can accomplish that at a lower engine rpm more easily, thus you don't need to increase the throttle opening any bigger, and you can use that taller gear to get lower rpms at the same throttle opening as before or maybe even less, because you've cut the load by improving your aerodynamics.

If you want the math, here it is.
(Torque x rpm)/5252 = horsepower.
Lower your rpm, less hp.
.
It takes a certain amount of hp to overcome the resistance loads at speed.
If you lower rpm, you lower hp.
How do you increase the hp back to overcome the load to do that speed?
Increase torque by opening the throttle more.
That's the answer.
« Last Edit: February 16, 2010, 01:36:23 AM by ace.cafe »

jayprashanth

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Re: C5 Vs G5
« Reply #48 on: February 16, 2010, 07:04:18 AM »
Terrific explanation there, Ace.

Cheers,

Jay

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Re: C5 Vs G5
« Reply #49 on: February 18, 2010, 06:52:05 PM »
The best way to increase cruising speed, or reduce the stress on the engine at the cruising speeds is to reduce the load the bike must overcome to maintain that speed.
And that is done by improving aerodynamics, to reduce wind drag, which is the largest factor of load that the engine must use its power to overcome at those kinds of road speeds.
If you do that, then you truly do have less load, and can then use a taller gear without increasing the stress of the engine, because there's less load to overcome, and the bike can accomplish that at a lower engine rpm more easily, thus you don't need to increase the throttle opening any bigger, and you can use that taller gear to get lower rpms at the same throttle opening as before or maybe even less, because you've cut the load by improving your aerodynamics.


On a low calorie diet and back to the gym. Reduce weight = Less stress on engine; Better shape = Less drag .

 ;)

Ice

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Re: C5 Vs G5
« Reply #50 on: February 20, 2010, 04:41:53 AM »
Perhaps one of our resident math wizards can prove or disprove this old time wives tale,,

"Every seven pounds you shave of the bike and rider combo is equal to a one HP increase."
I can break it better,,,,at night, in the rain, on the trail,, 20 miles from nowhere.

REA #136

"TIMEX", the '06 Iron Barrel Military that takes me everywhere I want to go... and some places I shouldn't.

motomataya

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Re: C5 Vs G5
« Reply #51 on: February 20, 2010, 03:50:08 PM »
It seems to me to be to complex to put a number on. Weight is a detriment on take off, acceleration and hills. Top speed and cruising speed are more about aerodynamics. Of course if you big person your heavy and punch a big hole.

ace.cafe

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Re: C5 Vs G5
« Reply #52 on: February 20, 2010, 04:15:14 PM »
Perhaps one of our resident math wizards can prove or disprove this old time wives tale,,

"Every seven pounds you shave of the bike and rider combo is equal to a one HP increase."

This result would be based on a simple power to weight formula.

Let's look at the UCE for example.
The basic bike is about 400 pounds, and let's say we have a 200 pound rider.
That's 600 pounds.
At our latest dyno rating of the UCE, it had about 21 hp at the rear wheel.
That makes this combo have 28.57 pounds for every hp.
You'd need to drop 28.57 pounds off, to gain the equivalent of 1hp on this bike/rider combo.

If you had a fast bike that had 7 pounds for every hp, then if you dropped 7 pounds off, it would equate to about 1 hp. Such a combo might be a 400 pound bike and 230 pound rider, yielding 630 pounds total, and having rwhp of 90hp.
7 pounds for each hp in that case, and the "old wives tale" calculation would hold in that case.
So, it's all related to the power to weight ratio of the bike.

Now, as motomataya mentions above, there are other factors regarding what effects this power to weight situation will have. And he correctly points out that it is most effective in acceleration and hills, but has  less effects on top speeds because of aerodynamics taking a substantial part in the loads at higher speeds.
« Last Edit: February 20, 2010, 04:21:55 PM by ace.cafe »

Ice

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Re: C5 Vs G5
« Reply #53 on: February 20, 2010, 04:56:07 PM »
Thank you gentleman.
I can break it better,,,,at night, in the rain, on the trail,, 20 miles from nowhere.

REA #136

"TIMEX", the '06 Iron Barrel Military that takes me everywhere I want to go... and some places I shouldn't.