Chain Speed & Bar Length

[UrbanLogger]

some guy at my local stihl dealer told me that a longer bar means slower chain speed so...This may sound like a stupid question, but: Does bar length affect chain speed? to me it doesn't really make sense, it only means it will take longer for a particular spot on the chain to make a full revolution, kind of like a bigger tire on a car or truck. This also makes me think, a bigger tire spinning at the same speed (rpm) as a smaller tire will travel a longer distance in the same amount of time, but will require slightly more power to do so...anyway, can someone help?

I think i'm thinking about this too hard and just confusing myself!

 

[CaseyForrest]

I dont have a PHd or anything, but I think the only thing that can slow down or speed up a chain is the diameter of the rim/spur.

Maybe he meant that a longer chain will work the saw more and slow the saw down, hence slowing the chain down???

 

[Lakeside53]

Well.... At the same RPM, the chain speed is the same.

It affects the WOT RPM, but not the "in wood" rpm all that much unless you are really over-baring a smaller saw.

 

[Chainsaw Master]

I agree chain speed can only be changed by changing sprocket size.......It takes horse power to turn the chain on a 36 inch bar. A 32 cc saw wouldn't have the power to get it up to speed out of the cut. Who's the engineer here that can figure out the mph of a chain with a 8 pin sprocket @ 14k rpms?

 

[drmiller100]

in THEORY a chain heading down the relatively straight bar doesnt' care whether it is heading down a 16 inch bar or a 48 inch bar. Once she is up to speed, the acceleration/deceleration SHOULD cancel out.

HOWEVER, racers, loggers, and most other folks all agree that the shorter the bar you run, the more "power" you will seem to have. In other words, if two guys are cutting 12 inch logs, and one has a 16 inch bar, the other a 36 inch bar, most of the pros seem to agree the 16 incher will cut substantically faster.

 

[chowdozer]

in THEORY a chain heading down the relatively straight bar doesnt' care whether it is heading down a 16 inch bar or a 48 inch bar. Once she is up to speed, the acceleration/deceleration SHOULD cancel out.

HOWEVER, racers, loggers, and most other folks all agree that the shorter the bar you run, the more "power" you will seem to have. In other words, if two guys are cutting 12 inch logs, and one has a 16 inch bar, the other a 36 inch bar, most of the pros seem to agree the 16 incher will cut substantically faster.

That's called "friction".

 

[Freakingstang]

That's called "friction".

Yes and no. Racers don't tighten their chains like the work saws...They are quite loose...


one of the big guys, said that objects will stay in motion until some outside force tries to change that.

racers run a big sprocket nose (roller nose) because it is more of a gradual turn instead of a sharp hairpin corner....just like you car, it keeps the chains speed up.

Also a longer bar has more teeth on the chain, amd more links in the chain. This adds rotational weight and takes more HP to spin it

 

[ciscoguy01]

RPM's

Ok guys, think about this now. Then you'll have the answer. My example for you, a bicycle with gears. Put down the brew and draw it, lol...

 

[ol'homey]

A longer bar means more parasitic HP loss. There is friction loss between bar rails and chain. There is also HP lost in accelerating and keeping the mass of the chain in motion. Think about how racers free up HP by using lightweight materials in all the rotating engine components like pistons, rods etc. The chain is a rotating component.
Compare the chain weights from a 16" and 32" bar and you will see there is quite a difference. Now think about the weight differences between .404, 3/8, and .325 chain on those bars. Take a look at some race chain and you'll see they have removed as much material as possible to reduce the weight of the chain.
One day somebody will replace the steel used in chains with a lightweight (titanium?) alloy and drop the weight by about half. Instant HP gain. The stock lightweight alloy chain will hang with the best steel race chains and the co that produces it will make a fortune because people will pay up for high performance chain. Are you listening Stihl, Oregon, Carlton etc. I want my cut!

 

[drmiller100]

no kidding.

sign me up for a HARD chain.

 

[chowdozer]

Yes and no. Racers don't tighten their chains like the work saws...They are quite loose...


one of the big guys, said that objects will stay in motion until some outside force tries to change that.

racers run a big sprocket nose (roller nose) because it is more of a gradual turn instead of a sharp hairpin corner....just like you car, it keeps the chains speed up.

Also a longer bar has more teeth on the chain, amd more links in the chain. This adds rotational weight and takes more HP to spin it

Are you saying you believe the power to overcome the inertia on a saw chain is greater than the friction between the saw chain and the guidebar?

 

[chowdozer]

A longer bar means more parasitic HP loss. There is friction loss between bar rails and chain. There is also HP lost in accelerating and keeping the mass of the chain in motion. Think about how racers free up HP by using lightweight materials in all the rotating engine components like pistons, rods etc. The chain is a rotating component.
Compare the chain weights from a 16" and 32" bar and you will see there is quite a difference. Now think about the weight differences between .404, 3/8, and .325 chain on those bars. Take a look at some race chain and you'll see they have removed as much material as possible to reduce the weight of the chain.
One day somebody will replace the steel used in chains with a lightweight (titanium?) alloy and drop the weight by about half. Instant HP gain. The stock lightweight alloy chain will hang with the best steel race chains and the co that produces it will make a fortune because people will pay up for high performance chain. Are you listening Stihl, Oregon, Carlton etc. I want my cut!

In addition to Ti being expensive as a raw material, it is also expensive to machine. Ti does not hold an edge well and you won't be field filing a Ti chain either. I think you would be disappointed if you could buy a Ti saw chain.

 

[musch]

Ok guys, think about this now. Then you'll have the answer. My example for you, a bicycle with gears. Put down the brew and draw it, lol...

On a bicycle, the chain doesn't change sizes.
:monkey:

 

[chowdozer]

On a bicycle, the chain doesn't change sizes.
:monkey:

That's true. But it's also true that a bicycle doesn't have a guide bar. Which chain turns more freely, a bicycle chain or a chainsaw chain? Run the chainsaw chain as loose as you'd like and it's still much more difficult to turn than a bicycle chain.

 

[Justsaws]

some guy at my local stihl dealer told me that a longer bar means slower chain speed so...This may sound like a stupid question, but: Does bar length affect chain speed? to me it doesn't really make sense, it only means it will take longer for a particular spot on the chain to make a full revolution, kind of like a bigger tire on a car or truck. This also makes me think, a bigger tire spinning at the same speed (rpm) as a smaller tire will travel a longer distance in the same amount of time, but will require slightly more power to do so...anyway, can someone help?

I think i'm thinking about this too hard and just confusing myself!

You are thinking to hard. The longer the bar the more power needed to pull the chain. Top speed could be the same(zero friction) until you load the teeth. The dealer should have told you that a longer bar means less power per cutter and could/will slow the chain down as load increases. Assessable speed is relative to workable load.

I am going outside now, I have got a Power Mac 6 carb to rebuild so I can put a 3/8 by 28" bar on it. Oak to cut and all that.

 

[fishhuntcutwood]

I dont have a PHd or anything, but I think the only thing that can slow down or speed up a chain is the diameter of the rim/spur.

Maybe he meant that a longer chain will work the saw more and slow the saw down, hence slowing the chain down???

Agreed. I was thinking the same thing.