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Hi

I've got 1983 CB400T. Wondering if anyone had experimented with different front and/or rear sprocket sizes to improve top end speed and how far is too far in terms of affecting rideability.

Thanks in advance, Dan.
 

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Welcome to the forum, Dan. Great to see another 400 series here. Got any pics of it?
I changed my front to a 17 and left the stock rear 35 and like the revs on the highway being lower.
 

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I've used 17/34 which dropped the rpm significantly at freeway speeds while keeping the engine in the power band area. It was slower on acceleration but not enough to be concerned with.
 

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Gearing it taller won't necessarily give you more top end speed. It depends on horsepower and aerodynamics, which determine if the bike can pull redline in top gear with any given sprocket combination. Taller gearing can make the highway a more pleasant place, though.
 

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Gearing it taller won't necessarily give you more top end speed. It depends on horsepower and aerodynamics, which determine if the bike can pull redline in top gear with any given sprocket combination. Taller gearing can make the highway a more pleasant place, though.
yes, that's the only reason why I upped my front......much better on highway. It doesn't crave for another gear so much.
 

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Air resistance increases the faster you travel through it. Bernoulli states (somewhat condensed) that drag increases by the square of velocity.
Therefore to increase speed more power is required. or more streamlining (reducing the resistance to moving through the air)
 

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Yeah, I have a 17 front and 36 rear on my CL 350, and even when I had a somewhat-streamlined fairing on it years ago, it wouldn't hit the 10,500 rpm redline in 5th gear. It would peg the speedometer, though...:D

 

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Air resistance increases the faster you travel through it. Bernoulli states (somewhat condensed) that drag increases by the square of velocity.
Therefore to increase speed more power is required. or more streamlining (reducing the resistance to moving through the air)
Power increased by the cube too. 2x the speed is 4x the drag and requires 8x the HP.

An Early ford Taurus requires about 15Hp to do 55 MPH. To do 110 MPH requires about 120 HP (at the wheels). 220 MPH requires 960 HP....If you notice, most 200+ MPH cares have 800-1000 HP, a little less if they are really aerodynamic.

Motorcycles, even faired ones, are not very aerodynamic at all....Cars are much better, but there frontal surface is lot greater. If bikes were as aerodynamic as a modern car, even a 250 could hit the ton easily.
 

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A ton? 2,000 mph? That'd have to be really aerodynamic, lol.

BtW, nice explanation of HP vs. top speed. Years ago I read specs like that but with no explanation and I didn't understand why vehicles needed so much horsepower if those small amounts were enough to do the (then) maximum legal speed limit. But thinking about it now... That Taurus might only require 15HP to maintain 55mph, but probably takes much more to actually reach it in a reasonable amount of time/distance (say, the length of the onramp leading to that 55mph highway, lol?).

Regards,
 

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MDM : ton is slang for 100mph
 
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Hi, I am amazed at your bike which is very well finished. Can I ask a couple of questions about it? Did you replace the comstar wheels? If so what with? Also I have the opposite gearing question...what is needed to make a 400 superdream pull away quicker and where on earth would you buy those sprockets in the UK?

I am looking for a 400 Honda custom as a project so your work is very relevant....and also very well done.
 

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A ton? 2,000 mph? That'd have to be really aerodynamic, lol.

BtW, nice explanation of HP vs. top speed. Years ago I read specs like that but with no explanation and I didn't understand why vehicles needed so much horsepower if those small amounts were enough to do the (then) maximum legal speed limit. But thinking about it now... That Taurus might only require 15HP to maintain 55mph, but probably takes much more to actually reach it in a reasonable amount of time/distance (say, the length of the onramp leading to that 55mph highway, lol?).

Regards,
Taurus/15Hp to maintain 55mph....Acceleration is another story. Back then, the Taurus came with either a 2.5L 4 Cyl. at 88HP, or a 3.0L at 140 HP. I had the 2.5L (company car). You drove that with the gas pedal floored all the time....The V6 (had a later Sable with it) was adequate.

Back when I was in engineering class, we looked at HP requirements, energy efficiency...The Taurus was the model we used to determine the highest MPG that car could get if the engine was 100% efficient. About 65 MPG if you care. That would require all the available energy from the fuel, and no heat from the radiator or exhaust. Most engines are in the 30-35% efficiency range, even today. If you take 35% of of that MPG max number, you get about 20MPG...which is what the car really had.....

There are other factors, but the fastest way to increase MPG is to reduce frontal area and have better Cd (Coefficient of drag). Modern engines are still at the 35% range, but have generally smaller frontal cross sections and much more aerodynamic.
 
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