Gearing, speed, and the like - Yamaha Raptor Forum
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post #1 of 147 (permalink) Old 11-08-2006, 08:17 PM Thread Starter
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Gearing, speed, and the like

Gearing and speed are always common topics on any orv powersport board. In an effort to answer some broad questions I offer this post.

Stock Top Speed:

There are a lot of answers out there, but most are in the range of 68-77 on a flat patch of good ground. FME it's in the low 70's. Anyone claiming 80+ is either modified, going down a huge hill with a tail wind, or blowing smoke. Anything lower than 65 either has modifications (shorter gearing/smaller tires) or there's something wrong with it.

For most of us 70 is more than fast enough. At those speeds and higher the tires, twitchy handling and wind resistance start making things significantly less safe. If you're one of these people it's a good idea to shorten up the gearing to accellerate faster.

If you have a reason to go faster or a need to lower the rpms in top gear for a cruising speed then it's time to look into taller gearing.



Sprocket Sizes:

The 660 accepts front sprockets of 12-15 teeth with the oem shroud, 16 tooth will work without it. The rear sprockets can be sized from 39 teeth on up, with your ground clearance most likely being the limiting factor. Anything smaller than 39 and the chain will start to ride on the sprocket hub mounts instead of the sprocket.

For an idea on what sprockets do to top speed on a stock bike, I offer these calculators. In stock trim the 660 revs somewhere in the 7k-8k rpm range, but more on that in a minute.

Sprocket/Top Speed Calcuators
http://home.earthlink.net/~gellett/raptor02.htm
http://www.jandjcreativedesign.com/sprocket.php (Thanks to SandSquid for all his work on this one)



Higher Revs:
This is all keeping in mind that your bike is stock, meaning that it can only rev so high and only has enough hp to pull a certain gearing. But when you can rev higher the bike will go faster.

You'll notice in pipe comparison dynos that most aftermarket pipes not only increase the hp but also increase the peak rpm. Many of the modifications that you add to your machine will have a similar effect, including when you free up air intake. This also means that your top speed will increase, assuming as we will that you're not limited by wind resistance. So if you were able to go 70mph stock adding more hp might make that same bike go 75mph now. The more hp and higher revs you can get out of the bike, the faster the bike will go on that gearing.

But this also has an impact on gearing. If you only need to go as fast as you did stock and you modified the bike to reach higher rpms and therefore a higher top speed then you can change your gearing to keep that stock speed and get there faster at the same time.

The following numbers are for explanation purposes only. For instance, say your bike does 75 stock. You do some mods, now your bike goes 80. We all know that lower gearing (higher ratios) means less top speed, but we also know that it means increased accelleration. If you go from 13/40 down to 12/40 on your modified bike you'll have the benefit of greater accelleration and because your bike can rev higher than it did stock you can maintain the 75mph top end at the same time.

My 660 is a good example for me. Stock it did somewhere in the low 70's. I've made some modifications and now running 12/42 gearing and 20" tires my bike has the ability to rev high enough to exceed 78mph. My top speed hasn't gone up all that much, but with the shorter gearing I'm able to reach the original top speed significantly faster that I did when it was stock. And honestly it's still a little too fast on top so the 44 tooth is ready to go on for next year.


I've explained, at least in part, this topic as best as I understand it. If there are any discrepancies or questions please let me know. Hopefully it's able to clear some things up.
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post #2 of 147 (permalink) Old 11-08-2006, 08:43 PM
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Re: Gearing, speed, and the like

great write up maddog thanks should stick this btw

~~~~~~~~~~~~~~~~~~~
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mild self polish
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stock gearing
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~~~~~~~
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post #3 of 147 (permalink) Old 11-08-2006, 11:22 PM
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Re: Gearing, speed, and the like

gOOD THREAD
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post #4 of 147 (permalink) Old 11-08-2006, 11:27 PM
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Re: Gearing, speed, and the like

good thread man

I've also noticed that stock I ran around 72-73 mph, but after putting a 12 tooth and a pipe/jetting I'm actually faster than stock by a few mph..I actually gained 2mph at the dragstrip with a pipe and 12 tooth.

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post #5 of 147 (permalink) Old 11-09-2006, 01:14 PM
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Re: Gearing, speed, and the like

Awesome write-up Mike.

-Eric<br /><br />2006 Yamaha Raptor 700 - Big gun evo exhaust , Prodesign filter, Dobeck Controller , Trail Tech Vapor , YFZ450 Tires , Pro Tapers , Powermadd Handguards, 15t, YFZ450 shocks, Maiers grill and tank piece, Full skids, AC rear grab bar &amp; Nerfs, PIAA&#039;s&nbsp;ect...<br /><br />Also have a Raptor 660 and a 400EX
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post #6 of 147 (permalink) Old 11-09-2006, 09:46 PM
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Re: Gearing, speed, and the like

So given a stock 660, anyone know if it actually reaches max rpm in top gear or if load/resistance is the limiting factor. I guess weight is a big factor, so assume a 180lb person.

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post #7 of 147 (permalink) Old 11-09-2006, 09:48 PM Thread Starter
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Re: Gearing, speed, and the like

Quote:
Originally Posted by gobeer net
So given a stock 660, anyone know if it actually reaches max rpm in top gear or if load/resistance is the limiting factor. I guess weight is a big factor, so assume a 180lb person.
Re-read the initial post, somewhere in the 7k-8k rpm range. Limiting factors include hp, airflow, and cam profile. Wind resistance plays a part as does weight but they aren't going to make dramatic differences for top speed on a stock bike.

Thanks guys, hope the post helps some people out.

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post #8 of 147 (permalink) Old 11-10-2006, 08:13 PM
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Re: Gearing, speed, and the like

i weigh 230, when mine was stock i could hit the limiter in fifth.

can the raptor motor handle going 1000rpm over stock without handgrenading? I still run the stock cdi and still like the fact that my motor is reliable.
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post #9 of 147 (permalink) Old 11-11-2006, 09:50 AM Thread Starter
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Re: Gearing, speed, and the like

Quote:
Originally Posted by danos660r
i weigh 230, when mine was stock i could hit the limiter in fifth.

can the raptor motor handle going 1000rpm over stock without handgrenading? I still run the stock cdi and still like the fact that my motor is reliable.
What kind of conditions were you in when you hit the limiter and what was the gearing setup? I ask because it's extremely unusual on a stock bike because of the mechanical and physical restrictions to hit it in lower gears, let alone top gear.

Can it handle it, yes but it won't last nearly as long as it should and I'd start looking for an oem rod through the cases. The long and short of it is if you're hitting the limiter you need to shift faster not raise the limiter. The engine is well past peak hp output if you've reached 9k rpm and adding the ability to rev higher can actually slow you down if you spend too much time in each gear.

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post #10 of 147 (permalink) Old 11-13-2006, 12:23 AM
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Re: Gearing, speed, and the like

This may sound like a dumb question, but as you increase the torque output of the motor, won't you actually accellerate faster with taller gearing? What I guess I'm really asking is does traction become a limiter with the shorter gears - more wheelspin and less forward movement? I have been wondering this exact thing a lot lately, as I have now had my @$$ handed to me by two different DS650's, one bone stock and the other piped but not jetted/filtered. I run 12/41 gearing and have been beat on both my 20" paddles and my 22" dirt tires. Any input?

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