front sprocket change S4RT

[booger]

I just bought a 45T quickchange rear & 520 kit with a new 15T front sprocket. This S4RT has a different front sprocket setup than my S2R, instead of the retainer plate with the two bolts it's got a 32mm nut and bent washer. So how can I lock the assembly for removal/final torque? The nut takes 186Nm torque. Just wondering how to keep that front sprocket still. Also is it a bad thing to use an impact to get the nut off? Thanks

[Duck-Stew]

Impact is how I roll.

[greenmonster]

+1 on impact off.

[booger]

OK great, it's not reverse threaded or anything is it? And how do you guys lock the output to torque it?

[Duck-Stew]

Standard thread.

Put the chain on, have someone hold the rear brake while you torque it.

[booger]

OK thanks. I thought I needed a flywheel lock tool or some such. 186Nm is a lot of torque.

[stopintime]

Standard thread.

Put the chain on, have someone hold the rear brake while you torque it.

Does the rear brake work? 

[Speeddog]

Have an assistant hold the bike with the rear wheel up against any handy immovable object.

[booger]

Sprocket Center has notified me that they have no 45T sprockets in stock, and won't get any for 3 months. I went with the 46T rear. Same ratio as a 14/43 (3.07) which I hope isn't going to be too much. I was kind of hoping to be more subtle about it but I'll give the 46T a try. One concern is the sprocket teeth getting a little too close to the bend in the swingarm. Right now with the stock setup the sprocket teeth have about an inch clear of the swingarm. I wonder how much increase in sprocket diameter will result from the addition of 3 more teeth?

Is anyone else running a 46T rear on a S*R bike?

[stopintime]

Pitch is 15.875 mm

15.875 x 43 = circumference 1

15.875 x 46 = circumference 2

Find the two r's


I'll be back in ten minutes to check your answer.

[ducpainter]

Pitch is 15.875 mm

15.875 x 43 = circumference 1

15.875 x 46 = circumference 2

Find the two r's


I'll be back in ten minutes to check your answer.

Time's up.

[booger]

 

~683 mm for the 43T & 730.25 for the 46T. So convert that to diameter (d= C/3.14) and we get ~218mm for the 43T and ~233 for the 46T. So it's 15mm larger in diameter than the stock sprocket. Divide that by half, 7.5mm. So 25.4mm is an inch, minus 7.5mm - roughly 18mm from the tips of the sprocket teeth to the paint job on the swingarm. A little less than 3/4". Doing all this math for the 45T we get ~21mm or a little over 3/4" clear.

Is the 46T clearance going to be a problem by chance? Like at full honk will the cush drives distort bringing the sprocket teeth into dangerous proximity to the swingarm?

Is my math even correct? 

[stopintime]

..........

Is my math even correct?  

Sorry - lost track of time.

I'm no math wizzard, but I think I'm better than you   Let's see .....

683
730

2 pi r = 683
2 pi r = 730

r = 683/6.18
r = 730/6.18

r 1 is 110mm
r 2 is 118mm

EDIT: Oh make the beast with two backs - I lost your 7.5  We're equal 


the difference is 8 mm and if everything else stays the same (it doesn't), that's how much closer the teeth will be to the swingarm. Measure. Add a couple of mm to allow for a twisting sprocket.

Not done yet.... how long is the new (?) chain? Even if it's the same number of links, it'll be shorter (not yet stretched). That, on it's own, positions the sprocket closer to the swingarm. How much? Next week's home work. Plus the larger front sprocket....


in the golden years of forums, this thread would be on fire. Mm or inches... 14 or 15 even if off topic...  and even the fact that the math is not accurate - because the distance between pins is not at the circumference - it's sightly inboard (even if the differene, which is the point, is close enough for this exercise)

[booger]

Yeah I think my math is about right. 46T is not going to let me sleep at night. I'm going to go with a 44T instead. It will be super subtle, nigh unnoticeable- but the poly cush drives and the lighter setup could make up for it.