Gear Ratios

[gerald28]

Hello All,

I have an 06 YZ450F and am looking to add 2 teeth to my rear sprocket. Someone said I should go to a 14/55 instead of a 13/51. Both have almost identical final drive rations 3.929 vs 3.923, respectively.

Ok gear whizzes, my question is how does changing the front sprocket effect the ride of the bike, assuming the final drive is identical (ie. 14/56 and 13/52). Besides need a longer chain:) Why would 14/55 be better than 13/51?

Thanks

Gerald28

06 YZ250 #28

06 YZ450F #29

[grayracer513]

It would be better because:

>The chain bends less around larger sprockets, and use a little less power because of it.

> Larger sprockets wear more slowly (a 15 should last 7% longer than a 14, just because each tooth engages the chain 7% less often)

> The chain has more clearance against the swing arm.

It would be worse because everything is bigger and heavier.

Of all of this, the improvement you would notice most is likely the longer sprocket life.

[aford541]

You will have to modify the chain guide if you go over 51T.

The stock yz450 has a 13/49, I run a 13/51, you'll be ok with that!

[PK]

If you change one tooth on the front sprocket, it's like changing almost 4 on the rear, depending which way you go. I would just go get the 51 tooth sprocket and call it good, the difference you'll notice on the bike is too small to tell for mere mortals.

Something else your friend didn't tell you is that if you add that many teeth (1 up front & 6 in the back), you'll have to buy a new chain because it will be too short.

[gbalias]

i have an XLS file that calculates gear ratios/top speed, etc. is there a way for me to upload it for everyone to use? otherwise, post your email and ill send it to ya. its great for calculating top speed, total ratio, etc.

[grayracer513]

I've made one of those as well. It's pretty simple actually, and it's useful for comparison, but not for calculating true top speed. The "paper" speed that you calculate in that way assumes that you have the power to reach a particular RPM in high gear, and that the tire won't slip. The first assumption is often invalid, and the second one always is.

Still fun to do, though, and like I said, it makes it much easier to compare the effect of gearing changes.

[Zique]

How much heavier do you suppose the larger sprocket set-up would be?

[grayracer513]

I'll guess 5 ounces or less, including the extra chain

[jimi-neutron]

The Renthal web page has a complete gear ratio chart. Great to reference. Very convenient once printed out.

[bigblock450]

Have done both,

Increased one tooth up front

unimpressive and engine not near as happy.

Replaced with stock pinion

increased rear to 51t

The engine is happy and rips

no doubt the way to go.

[gerald28]

Awesome, thanks!

[Baron Von Beard]

Good luck finding a 55 tooth rear sprocket and getting it to fit. I ran a 14/53 setup on my CRF and it definitely helped turning due to the shortened wheelbase but was a pain to modify the chain guide. Go with a 50 or 51 rear with the 13 front. It will work great and won't be nearly as much hassle.

[grayracer513]

Go with a 50 or 51 rear with the 13 front. It will work great and won't be nearly as much hassle.

One does have to stay within what's practical.

And welcome back. ? How are you feeling?

[Baron Von Beard]

One does have to stay within what's practical.

And welcome back. ? How are you feeling?

Getting better every day. I'm hoping to be back on the scooter in a month or so. We'll see though.

Thanks.

Oh, congrats on turning Mod, how's it working out for you? Pain in the ass, ain't it?

[grayracer513]

Pain in the ass, ain't it? ?

A little. But it's been pretty quiet around here recently, too.