Gearing issue

[G-Bek]

So i just got new sprockets for the tard and want to keep the same ratio. I was running 16/42 but couldn't get them so i ended up with a 15/45. now i've confused myself as to whether this is the same or have i gone the wrong way on the front?

[Dark Shadow]

It depends on what you were looking for!

what you will have from your change is better response but lower top speed (higher revs at same pace)

check this
Gearing Commander: Motorcycle Speed, RPM, Chain & Sprockets Calculator

Select your bike from the drop downs then make your changes to the Final Drive data in the Current & Custom to see the effects of proposed changes against the stock detail on top row

[Viper]

hmmm that's strange ... says my top speed is 265.7 ... I know that ain't right.

nice site though for sorting out ratios.

[BigTim]

Nah, you've gone the wrong way. 17/45 will be closer to 16/42 than the 15T front.
You've just geared it down for more lower end, at the expense of top speed.

[filbert]

Mental calculation tells me you should have gone 15/39 or 17/45 to get a close match and +1 for what dark shadow said, it's roughly equal to 6 extra teeth on the rear so its going to be quicker getting moving but lower top speed by around 20% or more, all mental calculation so I'm prepared to be wrong

[Dark Shadow]

hmmm that's strange ... says my top speed is 265.7 ... I know that ain't right.

nice site though for sorting out ratios.

There is further info (disclaimer) about the data which may explain what you were expecting to find
-----------------------

The Max. RPM in the Gearing Commander database is the RPM when reaching the top of the power curve (Max power @ x RPM) stated by either manufacturer (when available), bike reviews, published Dyno-runs or other sources when available. It is not the Red-Line or Rev-limiter RPM ! But since you can change the value of this field as well, you can enter the RPM you think your bike is making ....


BTW: It also does not mean the calculator is off when it shows a top-speed higher then you've ever seen on the bike or the dyno...

[Viper]

ah yep ...

[Dark Shadow]

If you ever want to check what sprocket combination you need to be comparable to another when changing either the front or the rear, just divide the rear by the front and check your ratio

example: your preferable choice was 16/42, 42 Div by 16 = 2.625 meaning your front will spin 2.625 times for 1 revolution of the rear
if you slapped a 15 on the front and wanted to match up to original ratio you'd need the rear to be a 39 giving you a ratio of 2.6 (a 40 would give you 2.66)

[agrid]

Gearing commander is your friend but make sure you put in the correct year because the LC4 primary ratios changed in '03. I found this is a spreadseet I used to use.


rear procket front sprocket ratio
45.000 17.000 2.65
42.000 16.000 2.63

primary ratio
2002 Supermoto 81.000 30.000 2.70
2003 Supermoto 79.000 31.000 2.55

[I Fancy Holidays]

Mental calculation tells me you should have gone 15/39 or 17/45 to get a close match and +1 for what dark shadow said, it's roughly equal to 6 extra teeth on the rear so its going to be quicker getting moving but lower top speed by around 20% or more, all mental calculation so I'm prepared to be wrong

This sounds right. Be careful with small rear sprockets on motards, my 38 rear chewed up the chain guide/slider really quick.

[agrid]

I used to switch between a 42 and 45 on my SM with only a little chain adjustment.

[G-Bek]

Aha good for wheelies then! Yeah I thought that was the case. I'll just get a 17t front, after I give it a run n see how she goes.

While we're on the topic, do u reckon I'll get another run from the same chain? I always change them together on my dirt bikes but a birdie says I can get 2 runs on the tar..

[filbert]

i thought it was the other way round, with steel sprockets you can sometimes wear out a chain and still have enough life in the sprockets to have another shot, but i guess it's possible if you have alloy sprockets that wore out before the chain you could give it a go just make sure the chain is in spec for stretch (measurement of set number of pins under tension) and keep it well lubed and you might pull it off without a hitch.

[smeghead]

^^WFS plus no frozen links.

Use a W or X ring chain & a good chain lube regular like.