Sprockets and chains

jojofuller

jojofuller

I'm sure the answer to this is "it is in the manual"(I'm looking for one.), but none the less...

I have to change the front sprocket and chain on my 2003 Suzuki RM125. My investigation has led me to stock specs on the front as a 12 spoke and the rear as a 49 with a 114 link chain. My bike has an 11 spoke sprocket on it. It also has 3 broken teeth on it. The rear sprocket is a 51. According to a calculator I found online, the current set up produces an approximate 17% torque curve and an opposite -17% top speed difference when compared to the stock set up. I think that this may be the reason for the broken teeth...too much torque. Or could be sloppy chain. (Opinions?)


So I am going to replace with a 12 spoke sprocket and will leave the rear 51. If I install this set up, the calculator indicates I will have an approximate 9.5% torque curve and opposite top speed. The calculator also says I will need a 116 link chain. Does all of that sound right?
 
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hondacr500af

hondacr500af

Having a smaller sprocket causes pinching in the chain. The radias is small and it will cause the chain to wrap tightly around the sprockets. Eventually something has to give. Whether it's the chain or the sprockets. The 12/51 combo is a good choice for a 125. SideWinder chain and sprockets is a good place to start. :smirk:
 
jojofuller

jojofuller

hondacr500af:
Having a smaller sprocket causes pinching in the chain. The radias is small and it will cause the chain to wrap tightly around the sprockets. Eventually something has to give. Whether it's the chain or the sprockets. The 12/51 combo is a good choice for a 125. SideWinder chain and sprockets is a good place to start. :smirk:[/QUOTE

What about that suggested chain length of 116 link? Does that sound right?
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hondacr500af

hondacr500af

That chain length might be a little short. I'm thinking more like 118 would be a safe place to start. You can always remove a link if it's to long.
 
SRAD97750

SRAD97750

Moderator
Staff member
I don't think the power of a 125 could damage a new steel sprocket. I have run 12 tooth fronts on my 130+HP sportbikes 10K miles without issue. (520 chain conversion)
I imagine the chain and sprockets were well worn and broke due to age, or a rock could have possibly jammed it. Either way, the size of the sprocket is not what caused the teeth to break.

Changing the 'final drive' is a great way to fine tune the way your bike performs. Trial and error is the only way to find what YOU like.
-BIG DAN:thumb:
 
hondacr500af

hondacr500af

You are right about the power of the 125 being so much less than say a 250. But, I beleive that because of the higher revs the 125 pulls, is a factor in the broken teeth. Plus it could have been caused by a rock. I thought he said the 11 tooth had the broken teeth though. :noidea:
Your chain on your street rocket is most likely a 530 or 630 chain size. Which is a bit stonger than a 428. What size is the 125 chain anyway? :noidea:
 
jojofuller

jojofuller

hondacr500af:
You are right about the power of the 125 being so much less than say a 250. But, I beleive that because of the higher revs the 125 pulls, is a factor in the broken teeth. Plus it could have been caused by a rock. I thought he said the 11 tooth had the broken teeth though. :noidea:
Your chain on your street rocket is most likely a 530 or 630 chain size. Which is a bit stonger than a 428. What size is the 125 chain anyway? :noidea:
Click to expand...


An 11 tooth is currently on the bike with 3 broken teeth. It is a 520 chain. I am replacing with 12 tooth.
 
SRAD97750

SRAD97750

Moderator
Staff member
hondacr500af:
Your chain on your street rocket is most likely a 530 or 630 chain size. Which is a bit stonger than a 428. What size is the 125 chain anyway? :noidea:
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520 on a 125-500cc dirtbike
My streetbikes ALL get the 520 conversion for less rotating weight and sprocket availability. Common modification.
I'm pretty sure at 14K rpm and 145mph, with an additional 100hp, that sprocket is seeing alot more forces than a 125 or any dirtbike could ever produce.
-BIG DAN:thumb:
 
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O

ossagp

Two rollers should do it. Somewhere I have the longwinded formula for figuring that. It is in Audel's and any bearing shop can give you a card with things like that on there. I like to have enough chain that I can get to within about 3/8 inches of max adjustment travel. for the riding I do it works well. if you ride more tight stuff you may not like it as well as I do. it is easy to go shorter though once you tried it stretched out a little. Please know that it makes both ends seem just slightly softer. going shorter or longer on your wheel base via the swingarm is the only thing i know that will change both ends of the spring requirements at the same time.
 
hondacr500af

hondacr500af

I used to own a 1987 Suzuki GSXR 1100. That was the fastest I have ever rode. the bike was worked a little bit with porting, bigger cams and Vance&Hines Advanced kit. Oh SuperTrap exhaust. I was a bit crazy with the throttle. Never lost a race with it. Drag Race. I sold it before I was killed or I killed someone else. I did not respect the power and speed of the bike. I grew up. I would love to buy a GSXR 1000. But, you know.
 
O

ossagp

Well I was thinking about one that has a 'sail' on it. Seriously, I have a goldwing in Taft that I have yet to actually touch. an 82 aspencade with all of 6500 miles on it. from what i can tell, absolutely no modifications other than and updated casette deck. i believe it has sat since 1996. I want to come down and use it, and not spend all my time working on it instead of vacationing. you up for doing that this spring? carb clean, cam belts, water pump, and gosh knows I think it needs the master cylinders and calipers gone through. I also have some newer wheels to swap onto it. I am sure I would take a good 4 days on it. 40 hours wouldnt seem out of the question.
 
SRAD97750

SRAD97750

Moderator
Staff member
ossagp:
...you up for doing that this spring? carb clean, cam belts, water pump, and gosh knows I think it needs the master cylinders and calipers gone through. I also have some newer wheels to swap onto it. I am sure I would take a good 4 days on it. 40 hours wouldnt seem out of the question.
Click to expand...
I am willing and able to do most anything motorcycle related! PM an exact list of things you want done and I'll provide a quote to you. -BIG DAN:thumb:
 
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