Sprocket Change - Fifth Gear Hack?

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Telesque · #1 Unread post by **Telesque** » Tue May 24, 2005 9:33 am

My VLX only has a four-speed tranny, and the engine is running along pretty well at 70. I'm wondering if a simple rear-sprocket change, maybe one tooth down, would give it much of a different feel? Would it cost me that much if I installed it myself?

Gummiente · Tue May 24, 2005 10:10 am

If you want to reduce the engine rpm's at highway speeds, you need to go one or two teeth DOWN on the rear sprocket, or one tooth UP on the front, or a combination of both. If you increase only the rear sprocket by one tooth, it will increase the engine rpm's needed to turn the wheel to go the same speed as with the stock sprocket . You'll get a bit more torque at low speeds and your stoplight launches will be quicker but you'll sacrifice top end speed. As a frame of reference, on my '86 Sporty after I increased the front sprocket by one tooth it dropped the rpm's at highway speeds by 500rpm.

Conversely, if you drop one or two teeth on the rear it will take less rpm's to move it at the same speed but you will lose some low end torque and performance. You'll find you might have to slip the clutch more than before to get going, too. And from what I remember about the VLX it needs a fair amount of clutch slippage to get going in the first place, along with some pretty wonky gear ratios that make it hard to keep the engine in the sweet spot of the powerband.

Tue May 24, 2005 10:11 am

you have a 16 tooth front sprocket and a 44 tooth rear sprocket--ratio is 2.75--to decrease engine speed you need to go up on the front or down on the rear--nobody makes anything for the front but 15 or 16 teeth so you will have to change the rear--JT Sprockets make rear sprockets in
36-37-38-40-41-43-44-45-46-47 tooth.you need to change both sprockets when doing this plus a new chain.mixing new and used chain and sprocket pieces results in much sadness.if you do the labor yourself parts is the only cost.

allawybiker · Tue May 24, 2005 11:12 am

Maybe this is a stupid question to the informed, but can such modifications be made to Shaft drive bikes?

poppygene · Tue May 24, 2005 11:25 am

allawybiker wrote:Maybe this is a stupid question to the informed, but can such modifications be made to Shaft drive bikes?

Well... I guess anything's possible, but you'd probably have to hire a mechanical engineer and the cost, well... I can't imagine. And you may not like the result, either. Changing the final drive ratio changes all the gear ratios at once.

Telesque · #6 Unread post by **Telesque** » Tue May 24, 2005 1:05 pm

Gummiente wrote:If you want to reduce the engine rpm's at highway speeds, you need to go one or two teeth DOWN on the rear sprocket, or one tooth UP on the front, or a combination of both. If you increase only the rear sprocket by one tooth, it will increase the engine rpm's needed to turn the wheel to go the same speed as with the stock sprocket .

Heehee.

I knew this, really I did.

Freudian slip, I guess. 'Up' = 'Speed'.

Between this and the chicken, I'm not sure I should be allowed to touch bikes for a while.

bigswifty · #7 Unread post by **bigswifty** » Tue May 24, 2005 1:29 pm

Maybe this is a stupid question to the informed, but can such modifications be made to Shaft drive bikes?

its a hypoid gear just like in a car. Ever hear of people putting 4.11:1 gear in their trans-ams or 5.13's wailing down the dragstrip with their nuts on fire?
same deal. You COULD chage the final drive in a shafty if the aftermarket or OEM suported it.

Telesque · #8 Unread post by **Telesque** » Tue May 24, 2005 1:30 pm

9000white wrote:you have a 16 tooth front sprocket and a 44 tooth rear sprocket--ratio is 2.75--to decrease engine speed you need to go up on the front or down on the rear--nobody makes anything for the front but 15 or 16 teeth so you will have to change the rear--JT Sprockets make rear sprockets in
36-37-38-40-41-43-44-45-46-47 tooth.you need to change both sprockets when doing this plus a new chain.mixing new and used chain and sprocket pieces results in much sadness.if you do the labor yourself parts is the only cost.

So, I'm guessing it's probably not a good idea to scour junkyards for used sprockets then?

bigswifty · #9 Unread post by **bigswifty** » Tue May 24, 2005 1:31 pm

-sorry:oops: these 2 posts were meant run together

my nighthawk is supposed to go 120 mph.
i don't want that, i'd rather have the torque multiplication and top out at 90.
she drink alot more dino juice that way though....

Telesque · #10 Unread post by **Telesque** » Tue May 24, 2005 1:42 pm

f8aw8su wrote:-sorry:oops: these 2 posts were meant run together

my nighthawk is supposed to go 120 mph.
i don't want that, i'd rather have the torque multiplication and top out at 90.
she drink alot more dino juice that way though....

Yeah. I'm always thinking about that. I mean, hey, sure, 55 MPG is a whole lot better than my car will ever get, but still.. maybe I'll get a little 250 rebel to commute with. 55 is good. 90 is better.