Replacing Rear Sprocket

**jonathan180iq** · 07-01-2008, 05:44 PM

To anyone who has done this,

Are there any surprises that I should know of before I switch out my rear sprocket?
Anything that you came across that isn't mentioned in the service manual?

Thanks,
Jonathan

PS:
I'm getting a 42T rear sprocket to see if it makes up for the deficiencies caused by the 16T front sprocket in the top end. I've also considered a 43T but I think that may be too close to the 15T to worth all the trouble.

Sarris · 07-01-2008, 05:55 PM

My Suzuki guru says that one tooth on the front is equal to about 4 teeth on the rear, so one rear tooth won't make alot of difference, but may help. You may want to go 2 teeth (if available) to split the diierence.

**jonathan180iq** · 07-02-2008, 09:31 AM

I was thinking that too, but the final drive ratios would end up being so close to that of the 15/41 standard combination.

15/41 - 2.73
16/41 - 2.56
16/42 - 2.63
16/43 - 2.69

If a change of .17 made that much a difference in the top end, then moving that back to .10(16/42) should be somewhere in the middle. I think that at a difference of .5(16/43) the variation from the standard 15/41 wouldn't be great enough to justify all of the extra work required with the new rear sprocket install.

Easy Rider · 07-02-2008, 10:42 AM

Quote:

Originally Posted by jonathan180iq

I think that at a difference of .5(16/43) the variation from the standard 15/41 wouldn't be great enough to justify all of the extra work required with the new rear sprocket install.

I don't think ANY small change justifies all that work.........unless you are trying to turn it into a mountain bike !!

Changing the front makes a noticeable but not drastic change. Anything less is a waste of time, IMHO.

**jonathan180iq** · 07-02-2008, 10:47 AM

We'll see.
Worst case scenario, I'm out $54.
Best case scenario, I find the PERFECT gearing combination

Easy Rider · 07-02-2008, 01:00 PM

Quote:

Originally Posted by jonathan180iq

We'll see.
Worst case scenario, I'm out $54.
Best case scenario, I find the PERFECT gearing combination

$54 and a LOT of time!

You will be adding 2 teeth total, right? One front and one back.
Are you sure the stock chain will still fit ??
If not, it would be a WHOLE different ball game.

**jonathan180iq** · 07-02-2008, 01:11 PM

No no. I already have the 16T up front.
I'll be adding two rear teeth over the factory rear sprocket.

I've thought about that. I think there is enough play in the adjustments to account for it. I need an adjustment anyway.

Like I said. We'll just hav to wait and see.

Orpheus · 07-02-2008, 03:10 PM

I've thought about this before, too(not planning on doing it, but just as a kind of thought experiment). Seems like you'd have the best of both worlds, but I might be mistaken.

If you only changed the rear sprocket to, say, a 43 tooth but left the front as a 15, would that pretty much eliminate the need for first gear (might also make it really "jumpy" on takeoff and give it a little more power uphill)? Also, would the RPMs at the top end run the risk of causing damage to the engine? I really don't know too much about this kind of thing.

**jonathan180iq** · 07-02-2008, 03:29 PM

The 15/43, as you suggested, might be over revving the engine. That gear ratio would be somewhere around 2.867, which is almost as much a difference in the high rev direction as the 16T is in the lower rev direction. I think that would rev limit the top end, instead of gear limit it. You're right. ....I'm just kind of rambling.

....

I just finished doing some math and I get the feeling that it might be a "better" overall gearing change to do the 15/40 (2.66) than the common 16T swap (2.56). It would, however, cost more money and wouldn't be as simple to install and you'd only want to do it if you haven't already done the 16T swap.

I think I've decided on the 16/42 (2.625). It's right in the middle.

Quimrider · 07-08-2008, 02:20 PM

sounds kind of interesting. let us know how the 16/42 works. I've had the back wheel off before to replace a tire. It's really not that big of a deal to take the back wheel off unless you don't have a lift or haven't made wood stands for your bike. You might even be able to get away without unhooking all the rear brake stuff, but it's just a couple xtra nuts to take off anyway. not a big deal. It is convenient how the sprocket literally falls off the wheel once the axle is taken out. I might consider going to the 15/40 if they make a 40t sprocket that fits the GZ250. That 65-70mph brick wall gets annoying on the freeway.

07-01-2008, 05:44 PM	#1
jonathan180iq Super Moderator Join Date: Jan 2007 Location: Dalton, GA Posts: 3,996	Replacing Rear Sprocket To anyone who has done this, Are there any surprises that I should know of before I switch out my rear sprocket? Anything that you came across that isn't mentioned in the service manual? Thanks, Jonathan PS: I'm getting a 42T rear sprocket to see if it makes up for the deficiencies caused by the 16T front sprocket in the top end. I've also considered a 43T but I think that may be too close to the 15T to worth all the trouble. Login or Register to Remove Ads
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07-01-2008, 05:55 PM	#2
Sarris Senior Member Join Date: May 2007 Location: New Port Richey, Florida USA Posts: 1,348	Rear My Suzuki guru says that one tooth on the front is equal to about 4 teeth on the rear, so one rear tooth won't make alot of difference, but may help. You may want to go 2 teeth (if available) to split the diierence. __________________ Prudent riders live longer than moron riders.
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07-02-2008, 09:31 AM	#3
jonathan180iq Super Moderator Join Date: Jan 2007 Location: Dalton, GA Posts: 3,996	I was thinking that too, but the final drive ratios would end up being so close to that of the 15/41 standard combination. 15/41 - 2.73 16/41 - 2.56 16/42 - 2.63 16/43 - 2.69 If a change of .17 made that much a difference in the top end, then moving that back to .10(16/42) should be somewhere in the middle. I think that at a difference of .5(16/43) the variation from the standard 15/41 wouldn't be great enough to justify all of the extra work required with the new rear sprocket install. Login or Register to Remove Ads
	0

07-02-2008, 10:47 AM	#5
jonathan180iq Super Moderator Join Date: Jan 2007 Location: Dalton, GA Posts: 3,996	We'll see. Worst case scenario, I'm out $54. Best case scenario, I find the PERFECT gearing combination Login or Register to Remove Ads
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07-02-2008, 01:11 PM	#7
jonathan180iq Super Moderator Join Date: Jan 2007 Location: Dalton, GA Posts: 3,996	No no. I already have the 16T up front. I'll be adding two rear teeth over the factory rear sprocket. I've thought about that. I think there is enough play in the adjustments to account for it. I need an adjustment anyway. Like I said. We'll just hav to wait and see.
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07-02-2008, 03:10 PM	#8
Orpheus Senior Member Join Date: Feb 2008 Location: Arizona, Tempe Posts: 174	I've thought about this before, too(not planning on doing it, but just as a kind of thought experiment). Seems like you'd have the best of both worlds, but I might be mistaken. If you only changed the rear sprocket to, say, a 43 tooth but left the front as a 15, would that pretty much eliminate the need for first gear (might also make it really "jumpy" on takeoff and give it a little more power uphill)? Also, would the RPMs at the top end run the risk of causing damage to the engine? I really don't know too much about this kind of thing.
	0

07-02-2008, 03:29 PM	#9
jonathan180iq Super Moderator Join Date: Jan 2007 Location: Dalton, GA Posts: 3,996	The 15/43, as you suggested, might be over revving the engine. That gear ratio would be somewhere around 2.867, which is almost as much a difference in the high rev direction as the 16T is in the lower rev direction. I think that would rev limit the top end, instead of gear limit it. You're right. ....I'm just kind of rambling. .... I just finished doing some math and I get the feeling that it might be a "better" overall gearing change to do the 15/40 (2.66) than the common 16T swap (2.56). It would, however, cost more money and wouldn't be as simple to install and you'd only want to do it if you haven't already done the 16T swap. I think I've decided on the 16/42 (2.625). It's right in the middle.
	0

07-08-2008, 02:20 PM	#10
Quimrider Senior Member Join Date: Jun 2007 Location: Toledo, OH Posts: 198	sounds kind of interesting. let us know how the 16/42 works. I've had the back wheel off before to replace a tire. It's really not that big of a deal to take the back wheel off unless you don't have a lift or haven't made wood stands for your bike. You might even be able to get away without unhooking all the rear brake stuff, but it's just a couple xtra nuts to take off anyway. not a big deal. It is convenient how the sprocket literally falls off the wheel once the axle is taken out. I might consider going to the 15/40 if they make a 40t sprocket that fits the GZ250. That 65-70mph brick wall gets annoying on the freeway.
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