Sprockets

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MakeCarsStandSTill · Fri Oct 06, 2006 9:05 am

What gearing do you guys have?,, I was told to bring it up easier and still have some speed go -1/+1 ? any thoughts?

xsyamahadg · Fri Oct 06, 2006 9:55 am

If you are talking about sprockets, generally speaking, up 1 tooth on the front is equal to 2 teeth down on the back. Going down one tooth on the back as a rule will drop your RPM by about 300 RPM at speed. Usually going down 1 or 2 teeth on the back will only modestly reduce your off the line performance. Be careful about going up 1 tooth on the front, you want to make sure the chain and sprocket doesn't come close enough to any castings to take a divit out during chain rotation.

bcarlson · #3 Unread post by **bcarlson** » Fri Oct 06, 2006 2:52 pm

What are you looking to accomplish? Dropping your ratio will increase the bike's top speed and decrease its acceleration. This generally makes the bike less street friendly. Increasing the ratio will of course have the opposite effect; greater acceleration and less top speed. Since you cannot use the top speed on a bike anywhere legally, I'm assuming you want to make the bike more streetable. There are some good ratio calculators online that will show you the effects of your sprocket changes (I also have one I made in Excel).

Personally, I just dropped a tooth on my bike (15 to 14 in front) and it was dollar for dollar the most significant improvement I could have made. True I lost probably 10mph, but who cares. Every gear is quicker and the bike is easier to take off from a stop. On my bike, the smaller front was easily done without replacing the chain; slack was taken up with tensioner. A rear sprocket would require removal of the rear wheel and possibly a new chain if the tensioner does not have enough travel.

Sorry if this is all elementary, but its all I know.

VermilionX · Fri Oct 06, 2006 2:55 pm

the common thing people do is -1 on the front.

some guys like to do -1/+2 but you lose way too much top speed and your bike will be revving so high even at not so high speeds.

if im gonna do something... i'll go w/ the -1 only.

camthepyro · Fri Oct 06, 2006 3:30 pm

bcarlson Posted: Fri Oct 06, 2006 6:52 pm Post subject:

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What are you looking to accomplish? Dropping your ratio will increase the bike's top speed and decrease its acceleration. This generally makes the bike less street friendly. Increasing the ratio will of course have the opposite effect; greater acceleration and less top speed. Since you cannot use the top speed on a bike anywhere legally, I'm assuming you want to make the bike more streetable. There are some good ratio calculators online that will show you the effects of your sprocket changes (I also have one I made in Excel).

Personally, I just dropped a tooth on my bike (15 to 14 in front) and it was dollar for dollar the most significant improvement I could have made. True I lost probably 10mph, but who cares. Every gear is quicker and the bike is easier to take off from a stop. On my bike, the smaller front was easily done without replacing the chain; slack was taken up with tensioner. A rear sprocket would require removal of the rear wheel and possibly a new chain if the tensioner does not have enough travel.

How much does this help acceleration. Say your bike does 0-60 in 4 sec. and has a top speed of 120mph. How much more acceleration could you get by taking the top speed down to 100mph?

bcarlson · #6 Unread post by **bcarlson** » Sat Oct 07, 2006 8:47 am

I don't think there's a hard and fast formula to use to make this calculation (drop 20 mph and gain how much time off 0-60). But, my top speed dropped by 7.05% which in your example equates to about 0.282s reduction in 0-60. This is of course assuming a direct relationship between top speed and acceleration which I'm sure is not the case. I'd look more for 0.1 to 0.15 seconds. But this is all strictly just a WAG.

J.R. Bob Dobbs · Sat Oct 07, 2006 4:20 pm

On my CB750 I did -1front and +1rear, a 10% gear reduction. Made a big improvement in acceleration and driveability. Actually increased fuel mileage (!) Dropped top speed to 120mph (redline), but I've never gone that fast. The bike would probably not hit redline in top gear stock, but probably would now.

On my ZRX1100, I did -1 front, a 6% gear reduction. God I love this bike

Rev limiter should kick in around 145mph, but as I said earlier, I don't go that fast.

The rear sprocket is alot more work than the front and costs a little more too, but you can fine-tune your changes better with the rear.

You can get a new front sprocket for around $30. Best modification IMO unless you're concerned about top speed more than acceleration.

camthepyro · Sat Oct 07, 2006 5:06 pm

I'd be more concerned with acceleration. I don't ever plan on going more than 100mph, but I love to accelerate quickly.

VermilionX · Sat Oct 07, 2006 5:10 pm

camthepyro wrote:I don't ever plan on going more than 100mph

uh huh... yeah... i believe you.

spinner · #10 Unread post by **spinner** » Sun Oct 08, 2006 7:42 am

I just went -1 front on my bike and bought a speedohealer to recalibrate my speedometer. With that set up on my particular bike, my true speed is equal to my rpm/100 while in top gear. So since I redline at 16000, my theoretical top speed is now 160mph as opposed to 167ish before the switch. After the swap I took it on a nice flat road. I got it up to 130, and sure enough the tach was at 13000rpm (I do not look at my tach at that speed, I set the shift indicator at 13k).