Rim Sprockets?

[NovaMan]

So if your saw turns about 9000rpm in the cut:
7T = 63,000 DL/min
8T = 72,000 DL/min

Linear chain speed with 3/8" pitch chain (0.750" between drive links):
63,000 DL/min = 47,250 in/min = 65.625 fps = 44.74 mph
72,000 DL/min = 54,000 in/min = 75.000 fps = 51.14 mph

Does that sound right?

 

[Big Neb]

So if I wanted to get a spare 7t, would I be better to get a Stihl, Husky, Dolmar, Oregon, GB...?

Are any of them made any better than others? Better design? Better materials?

They look like they are fairly interchangeable. In fact, the 8t on my Dolmar is a Stihl.

 

[SawTroll]

So if your saw turns about 9000rpm in the cut:
7T = 63,000 DL/min
8T = 72,000 DL/min

Linear chain speed with 3/8" pitch chain (0.750" between drive links):
63,000 DL/min = 47,250 in/min = 65.625 fps = 44.74 mph
72,000 DL/min = 54,000 in/min = 75.000 fps = 51.14 mph

Does that sound right?

Yes, except that it most often will not happen that way when you cut wood.

What actually decides the cutting speed is the chain speed that you can keep in the wood, max power rpms are irrelevant,

The higher speed will create more resistanse, which means you need more torque to keep it up. However, you have already traded for less torque, so rpms will drop off faster.

At a certain level of resistanse, you will come to the point where the 8-pin actually is slower than the 7-pin, because of this.

 

[begleytree]

Yes, except that it most often will not happen that way when you cut wood.

What actually decides the cutting speed is the chain speed that you can keep in the wood, max power rpms are irrelevant,

The higher speed will create more resistanse, which means you need more torque to keep it up. However, you have already traded for less torque, so rpms will drop off faster.

At a certain level of resistanse, you will come to the point where the 8-pin actually is slower than the 7-pin, because of this.

completely agree. that (imo) is why a 460 will not pull a 3/8 9 pin. power (tq) drops off so hard that while the motor will pull the chain and gearing, it is actually a lot slower in the cut than running the correct size sprocket that keeps the rpms and tq up where the saw cuts. thats the reason I said this earlier.

and I think its more like 13% or 14% due to cutting drag, but out of the wood yup, simple math shows 15%. a high gear slows the engine easier than a low gear when under load.

 

[A100HVA]

opcorn: has anyone ever tried a 9t .325 rim on a 357xp with 21LP chain & wide tail small mount bar (ko95)oregon

i tried it with a 20" guide bar it was good for limbing softwood ,but that was about it