Questions about gearing for solely dirt riding

[J4Fun]

I’ll bet the 15t sprocket will hit the sweet spot for what the OP was asking! The rest of the story should be called “The Driver and the Driven” and their relationship.

[red2003]

Originally Posted by Thumper

Not exactly what he is asking, and changing the gearing WILL help him.

His 2nd and 3rd gears are too tall for his riding conditions. The engine isn't revving high enough to be in the more powerful part of the powerband under those conditions. He wants a little more torque under those conditions. Increasing the rpm by 11% WILL give him more REAL POWER, ACTUAL TORQUE difference in those gears under those conditions, because the engine will be running at a higher rpm. This assumes that he won't change his choices and start running in 3rd and 4th under those conditions!

The real difference will be that he has more gears to select from that keep the engine higher in the rpm range that produces more power. 1st is too low geared, and 2nd/3rd are geared too tall for what he needs. That 11% change will help in the gravel/sand.

Well, we don't know that is the case. Thats why I asked what rpm he is running now. If he is too low in the rpm range in 2nd and 3rd, then use 1st and 2nd in those situations. Thats what gears are for. He's a new rider and probably read that changing gears will give him more power. Well,as you are aware, it will not.

[red2003]

[QUOTE=Megadan;409536]Gearing does change the amount of torque at the rear wheel. That's what gear ratios do, divide rpm and multiply torque. Horsepower doesn't change because it is a function of rpm and torque. Changing gear ratios just alters the relationship between those two on their side of the equation.[/QUOTES

Sure, but we don't know that gearing is the issue here as we don't have information about the rpm he is hitting where he is looking for "more power". If he is currently turning 8000 rpm at 25mph, raising the gear ratio is going to move him even MORE out of the peak torque band. It sounds like the OP is looking for an easy answer to give his bike "more power", and gearing isn't that answer.

[Thumper]

I guess OP will find out. He will have more torque in the conditions he describes. I guess that is what he wants.

[ProDigit]

Originally Posted by Thumper

OP can drop two teeth on the front sprocket for a 11% gearing change, and probably won't even need to remove a link. Adding two teeth on the rear would drop rpm 2/50 = about 4%. He probably won't need a new chain with the larger new rear sprocket, but removing a link would be the opposite... Dropping 1 tooth on the front sprocket would give OP a 5% drop in speed at same rpm, with the same/similar gearing advantage to adding two teeth on the rear sprocket.

Front sprockets are less expensive, and OP wants to explore this gearing change. It may be the opposite of what you would do, but it is a low cost option/test. I was amused at your suggestion to use an ethernet cable to rewire a harness in another thread. Talk about opposite...Now that is a bold and fascinating proposal! Clearly you have novel ideas for motorcycle maintenance and repair. I recently wired up an isolated lighting system on my KTM. I used spools of 12, 14 gauge wire and brass end connectors with insulation. I guess I went a little more boring and "conventional".

I meant 2t down on the front sprocket, not rear (because I usually think in terms of going up on the front and down on the rear).
but yeah, 2-3 down on the front, and 3-4 up on the rear cause you to have nearly the same chain length setting on the adjusters.

An ethernet cable can handle blinkers and data/sensor wires just fine, provided they are LED lights. Might even run a tail light.
I wouldn't use it for break or headlights, unless you plan on using multiple wires. I think each wire handles about 1 amp, equals about 12W. The LED blinkers are about 5W, or half the maximum capacity of the wire.

You can also reuse some of the wires on the harness. Like the ground wire.
The ground wire on the blinkers and tail light are all the same. If you disconnect the ground wire on the tail light or blinkers, and disconnect it at the other end as well, it'll free up a wire on the harness for other purposes.

The tail and blinker lights can easily be grounded to the body of the bike, or to another ground point.
I'd rather do this, than replace an entire wire harness, for a few faulty wires.

[ProDigit]

Originally Posted by Megadan

I never said HP rating changed, nor is anybody talking about at the engine... So your reply is confusing. We are strictly talking about sprockets, so the engine isn't even a factor here since this is about gear reduction between the counter shaft of the transmission and the rear wheel.

Gears do not affect horsepower. Period. Sorry, but you are wrong.

Torque does affect acceleration, nobody argued that. Again, not sure what your argument is here exactly.

Horsepower is the result of calculating an equation involving both torque and RPM. It's a measure of energy from Force over distance and time. That's it. Torque is the measured force. The Distance and Time is the Revolutions per minute of the rear wheel (in this instance). Since the gear ratios multiply AND divide said force and the rpm by the same ratio, the resultant horsepower figure remains unchanged.

This is algebra 101 stuff and I won't argue this further. I am correct on this. If you want to argue more, go hit up google and do some more studying. I have little time for know-it-all arguments.

If you say gears adjust torque, then gears also adjust HP.
Gears have everything to do with harvesting max torque or HP out of an engine, and have absolutely everything to do with this topic.

I don't see anything I've written out of line with the conversation. Just merely responding to an incorrect assumption on your part.
You think everything is math,but your math ain't mathing, if you agree that gears change torque without changing HP.

The formulas you're using aren't applicable to gearing, but just to engine testing. Once you add gearing to the equation, engine output and HP ratios change. It's just a fact.

[XLsior]

Oh boy, its going to be one of those...


We are not changing the crank and rod inside the engine to implicate the known engine out put.


Or changing the internal gearing at the output shaft...


The HP an torque of the engine is what it is.


Changing sprockets, wheel diameters, overall weight and chain type/length will merely shift the output dynamics.

[ProDigit]

Originally Posted by XLsior

Oh boy, its going to be one of those...


We are not changing the crank and rod inside the engine to implicate the known engine out put.


Or changing the internal gearing at the output shaft...


The HP an torque of the engine is what it is.


Changing sprockets, wheel diameters, overall weight and chain type/length will merely shift the output dynamics.

Changing gearing changes the load on the engine.
Engine ratings are done at a fixed load, and thus the rating of any dyno is fixed.
Increase the load, increases the efficiency, and thus also the HP output.

Try reading a dyno in 4th gear, and in 6th gear. You'll understand what I'm talking about about.

[bogieboy]

Originally Posted by XLsior

Oh boy, its going to be one of those...


We are not changing the crank and rod inside the engine to implicate the known engine out put.


Or changing the internal gearing at the output shaft...


The HP an torque of the engine is what it is.


Changing sprockets, wheel diameters, overall weight and chain type/length will merely shift the output dynamics.

And shifting the output dynamics changes the percieved torque in any given gear, which is what the OP is looking to do... we know the science behind what you are trying to say, but we also know real world factors make changing the final drive a viable option to get the powerband where we want it.... which is exactly what the OP was asking about...

Take a drag car, if you put a 2.22:1 gear in the rear end, its not going to accelerate (percieved torque) near as fast as a 4.60:1, or a 5.72:1 rear end. Has the engine output changed? Nope... has the acceleration changed, causing a percieved torque shift, absolutely...

[flopsweat]

I remember something like this coming up with a seemingly simple question I asked in my first days here. After getting very confused with what I was reading, I looked around this forum and realized... Megadan is probably right.

[buzz]

So true flopsweat

[Thumper]

And as described in posts #6, #8, #13, and especially #15.
Torque. Gear reduction provides TORQUE. It effectively increases power output by reducing the rpm of the engine through gears.

This is exactly what OP is asking about. The engine is spinning at MUCH higher rpm than the rear wheel which results in multiplication of power. So he can power through gravel and sand.

I have a planetary 6x gear reduction unit bolted to the direct digital drive with a variable speed controller on my chile roaster. It multiplies the output and provides low speed control. If I put a sprocket on the thing, it would drag a 1000 pound motorcycle into the air. Without that gear reduction, the stepper motor wouldn't have enough juice.

This is exactly the same thing that reducing the gear ration using sprockets does.

[Thumper]

Here is the stepper motor without the planetary gear reducer.



The gear reduction box increases the power output of the stepper motor. As Megadan mentioned, this is simple math.

[red2003]

Originally Posted by Thumper

Here is the stepper motor without the planetary gear reducer.



The gear reduction box increases the power output of the stepper motor. As Megadan mentioned, this is simple math.

Yes, it is simple math. But, the math you are leaving out is the resulting rpm. In your example, yes your drum has more torque, but at a sacrifice to its resulting rpm. Yes raising the gear ratio results in increased torque, but at a reduced speed. You cannot get more torque and not lose something on the other side of the equation. So, the OP stated he wanted more torque in 2nd and 3rd gears for his typical speed of 25 mph. Well, he can accomplish that by dropping from 3rd to 2nd and 2nd to 1st when more torque is needed. That's why bikes have transmissions. If he was running out of torque at the lowest possible gear, or rpm at the highest possible gear, THEN gearing would be beneficial.

Equally important is the fact that your stepper motor is, well a motor. Electric motors have constant torque at all rpm. Engines do not, so using this as an example of the "simple math" involved here is not applicable.

[Thumper]

Originally Posted by red2003

Yes, it is simple math. But, the math you are leaving out is the resulting rpm. In your example, yes your drum has more torque, but at a sacrifice to its resulting rpm.
...
...
...
Equally important is the fact that your stepper motor is, well a motor. Electric motors have constant torque at all rpm. Engines do not, so using this as an example of the "simple math" involved here is not applicable.

Yes, having lower gearing on 2nd and 3rd will give OP more choices with higher rpm at the same speed that he wants to go to power through the sand/gravel more easily. Hence the additional torque with lower gearing.
This is exactly what he wants.