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Old 12-11-2018, 06:54 PM   #1 (permalink)
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Oversized front sprocket safety?

SV650SF coming soon...

Now I have to address a dilemma. The stock front sprocket is a 15T, but a 16 and UP TO 17T will fit, but the 17 is very close. Now, my question is, is that 17T unsafe? In the event of a chain failure where the chain bunches up at the front sprocket and destroys the engine cases, wouldn't a huge front sprocket prevent there even being room for the chain to bunch up to begin with?

I would much prefer the 17T to the 16T as it widens my sprocket choices and reduces chain velocity(less lube slinging).

My gearing choices right now are a 16/39 or 17/41 compared to the standard 15/45. That 17/41 will put it at 4111 RPM at 70, compared to 5113 RPM for the standard bike! That is just 6 RPM higher than what a stock SV1000S would cruise at!

I definitely won't be going into 6th gear below 25 mph with the new gearing, about time I get some tall gearing! I have been in 6th gear with my CBR 250R at 9 MPH.

Edit: Even 5th gear is too tall for 25 mph, it would be around 1650 RPM. The bare minimum RPM I want to be running is 1800.

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Old 12-11-2018, 07:12 PM   #2 (permalink)
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I would plan on not having a chain failure instead of reducing the gap to prevent chain bunching. I kinda don't think it matters how much room you make for bunching anyhow. The momentum of the chain will probably force its way anyhow.

Had a chain throw on a CB750 and it broke off the front sprocket guard, which is replaceable. Would be weird if your bike is designed to just destroy the engine case.

Regarding gearing, your plan sounds reasonable to me. I'd probably get 60 MPG on my bike if I could get some tame RPMs at reasonable speeds.
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Old 12-14-2018, 12:18 AM   #3 (permalink)
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be careful what you wish for, before my most recent bike I didn't think it was possible to have gearing too tall, so what happens is I use lower gearing local & mileage isn't what you would think, I get 42mpg, with a 96 CU IN engine, previous bike I was getting 55-57 mpg with 74 CU IN engine,

anyway I cant even get to 5th until 45-50 or so MPH, & 6th is worthless under 65, & basically I don't do but 1 small trip a year, so gearing is wrong for my driving.

I don't know your bike, but can you play with rear sprockets too? for 1 of my Harleys, I have rear sprockets from 40T to 51T & then trans from 21T-26T, plus a few engine to trans, but afraid to quote teeth, not looked at in a few years.

for a "safe" chain, look at Tsubaki, I love their nickel plated chain, non o-ring. I regularily got 18k-26k miles before having more than 1 tight spot while adjusting, never had 1 break, & I have over 500K miles on 2 wheels.
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Old 12-14-2018, 10:32 AM   #4 (permalink)
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I wouldn't say it's unsafe. Yeah, your chain will spin faster, but it does that if you go faster anyway.

I have an 18 or a 19 tooth on my little 110cc and it runs without issue.

I'd assume proper chain tension will prevent any potential bunching up.
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Old 12-14-2018, 03:57 PM   #5 (permalink)
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Quote:
Originally Posted by Stubby79 View Post
I wouldn't say it's unsafe. Yeah, your chain will spin faster, but it does that if you go faster anyway.

I have an 18 or a 19 tooth on my little 110cc and it runs without issue.

I'd assume proper chain tension will prevent any potential bunching up.
The chain will spin slower actually
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Old 12-14-2018, 04:48 PM   #6 (permalink)
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Quote:
Originally Posted by old_biker View Post
be careful what you wish for, before my most recent bike I didn't think it was possible to have gearing too tall, so what happens is I use lower gearing local & mileage isn't what you would think, I get 42mpg, with a 96 CU IN engine, previous bike I was getting 55-57 mpg with 74 CU IN engine,

anyway I cant even get to 5th until 45-50 or so MPH, & 6th is worthless under 65, & basically I don't do but 1 small trip a year, so gearing is wrong for my driving.
I much more often wish for taller gearing than shorting gearing. When you have gearing that is too tall, you are in between your optimal gearing, and it is an inconvenience. When you have shorter gearing and wish for taller gears, they will NEVER be there. You can always shift down(unless you are in 1st..), but no matter how many times I lift up on the shifter there won't be a 7th gear.

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I don't know your bike, but can you play with rear sprockets too? for 1 of my Harleys, I have rear sprockets from 40T to 51T & then trans from 21T-26T, plus a few engine to trans, but afraid to quote teeth, not looked at in a few years.

for a "safe" chain, look at Tsubaki, I love their nickel plated chain, non o-ring. I regularily got 18k-26k miles before having more than 1 tight spot while adjusting, never had 1 break, & I have over 500K miles on 2 wheels.
18-26K on a non o-ring chain??? Did you have an auto oiler? Yes I can play around with sprockets. Ideally I get it right the first time so I don't have to adjust the number of chain links.
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Old 12-15-2018, 02:23 AM   #7 (permalink)
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a larger front sprocket is less likely to break the chain do to reduced tension
on the chain. Chain speed goes up vs RPM but angular momentum goes down at the contract point.
the individual links bend less and cause less vibration problems as well
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Old 12-15-2018, 10:54 AM   #8 (permalink)
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Quote:
Originally Posted by Daschicken View Post
I much more often wish for taller gearing than shorting gearing. When you have gearing that is too tall, you are in between your optimal gearing, and it is an inconvenience. When you have shorter gearing and wish for taller gears, they will NEVER be there. You can always shift down(unless you are in 1st..), but no matter how many times I lift up on the shifter there won't be a 7th gear.



18-26K on a non o-ring chain??? Did you have an auto oiler? Yes I can play around with sprockets. Ideally I get it right the first time so I don't have to adjust the number of chain links.
ok, my bike is stock geared, but it is a lightweight bike, but too tall! only one I ever had like this, & first is even too fast, my driveway is 1/4 mile up washboard mountain side, & its slip clutch to control speed, and when its been raining, really scary. & I been riding motorcycles since I was 16, so very experienced.

as for the mileage out of the chain, I was a lubrication geek, every 200-500 miles, on road trips usually every gas stop, or every other gas stop, depending how far I took tank down. I have used Tsubaki nickel plated enough to praise them, where most chains are lucky to get 10 to12k out of them, growing up I worked at an independent "club" bike repair shop for over a decade, & I never saw but 1 get better mileage, stock chains, in a fully enclosed chain guard, that was oil bath, so chain was 100% lubricated all the time, google Harley FLT enclosed chain guard, late 1970's to early 1980's was original equipment on FLT bikes but was a PITA to put tires on.

my current bike has belt drive, I still prefer chain, & my old bike had 6 gallon tanks & after tweaking it got 57mpg, so could push gas stops close to 300 miles, but usually filled up closer to 175-225 miles
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Old 12-15-2018, 12:26 PM   #9 (permalink)
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Quote:
Originally Posted by Daschicken View Post
The chain will spin slower actually
Umm...no.

If you have a 16 tooth sprocket and the output "shaft" it's attached to is spinning at 200rpm, the chain is moving 3200 links per minute. (16x200)

If you have an 18 tooth sprocket spinning at 200rpm, the chain is moving 3600 links per minute. (18x200)

You will, however, be spinning the engine at a slower RPM for the same speed, which is probably what you're thinking.
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Old 12-15-2018, 07:00 PM   #10 (permalink)
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Quote:
Originally Posted by Stubby79 View Post
Umm...no.

If you have a 16 tooth sprocket and the output "shaft" it's attached to is spinning at 200rpm, the chain is moving 3200 links per minute. (16x200)

If you have an 18 tooth sprocket spinning at 200rpm, the chain is moving 3600 links per minute. (18x200)

You will, however, be spinning the engine at a slower RPM for the same speed, which is probably what you're thinking.
I probably don't know what i'm talking about. Either way, the larger sprocket allows for a more gradual turn around, slinging less lube.

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Best trip in V6: 52.0
Best tank in V6: 46.0
Best tank in CBR: 61.3
Best tank in VFR: 57.1
Best tank in SV: 74.9

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You can lead a fashion-conscious horse to unusual-looking water...

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