15 front, 51 tooth rear sprocket? - Stromtrooper Forum : Suzuki V-Strom Motorcycle Forums
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post #1 of 23 Old 12-07-2016, 06:31 PM Thread Starter
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15 front, 51 tooth rear sprocket?

Bear with me, I'm in full mod mode. On my recent trip West I changed the stock 15/47 to a 14/47 before I left because changing a front sprocket on the road is not easy. The 14T was perfect for the trails & I never had to slip the clutch. However the 3600 mile round trip was a bit buzzy, so I came up with a plan.

Go back to a 15 tooth front, run down and buy a used rear hub and mount a 51 tooth rear on it. I can pack that easy enough and it will only take minimal tools and 20 min or so to change the rear hub when I arrive at my trail riding destination(s).

I want someone to check my calculations, but based on Gearingcommander.com, the 14/47 is almost identical in rpm(across the gear range) to the 15/51 with the 51 giving me a bit more torque.

Last, will my chain set up for 15/47 handle a 15/51?

I am asking all this because a 50+ tooth rear sprocket is not cheap and I don't want to make a costly mistake.

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post #2 of 23 Old 12-07-2016, 06:36 PM
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Originally Posted by Motor7 View Post
...Last, will my chain set up for 15/47 handle a 15/51?...
It depends. If the chain length is such that with the 15/47 the axle is pretty far back in the adjuster slot, then it will work, barely. If the axle is towards the middle, definitely not.
Assuming that you have a center stand, I'd change the front sprocket instead. Not that hard to do on the road.
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post #3 of 23 Old 12-07-2016, 07:27 PM
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If you're going through the trouble to change a sprocket out for trails, why not go with a bigger change? Your 15/47 to 15/51 is an 8.5% reduction. I'd go for a 12-15% reduction, but that will definitely need a different length chain if you do the rear sprocket.

I run 16/47 on my 2008. Not sure if the transmission gear ratios changed, but I like the taller gearing for the 75mph speed limits in Colorado, Utah, and Wyoming. I have also done some rock crawling with this ratio, with some clutching.

A front sprocket change from 16 to 14 teeth will yield a 14.3% final drive reduction, will require only one smaller part to be carried, and will not change the chain length as much. You could probably get away with not adjusting the chain at all, and just letting it ride a little loose off road, which is a good thing.

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post #4 of 23 Old 12-07-2016, 09:36 PM
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You can kind of calculate and measure if the 15/51 will still fit. It is essentially making the chain 2 segments "shorter" than the 15/47, or the axel will need to move about 1 segments forward. (Is my thinking correct?) See if you have enough room for that movement.

I did the opposite to reduce rpm's for long distance touring. 16 front and a second wheel with a larger diameter tire. Resulted in 10% drop in rpm's. I found it beneficial to have two sets of rear pads since they bed different on the brake disks. So not only changing the wheel but also the pads.

Not sure how far you would have to travel carrying that second wheel on the bike. I would think its a pita to do personally given all the other gear I take on a longer trip.

Last edited by blaustrom; 12-07-2016 at 09:40 PM.
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post #5 of 23 Old 12-08-2016, 12:26 AM
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Originally Posted by blaustrom View Post
You can kind of calculate and measure if the 15/51 will still fit. It is essentially making the chain 2 segments "shorter" than the 15/47, or the axel will need to move about 1 segments forward. (Is my thinking correct?) See if you have enough room for that movement.

Not sure how far you would have to travel carrying that second wheel on the bike. I would think its a pita to do personally given all the other gear I take on a longer trip.
Not quite. The additional teeth are all the way around the sprocket, not just the ones contacted by the chain. As the sprocket gets bigger, the circumference grows at a slower proportion for each additional tooth. The best way to explain this is that adding teeth to the countershaft sprocket will change the ratio more with less chain tension change than adding teeth to the rear sprocket to get the same amount of ratio change.

If you want to change ratio without changing chain length, the front sprocket is the way to do that.

Also, he was talking about the sprocket hub only, not a complete rim and tire.

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Last edited by Toshbar; 12-08-2016 at 12:36 AM.
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post #6 of 23 Old 12-08-2016, 12:57 AM
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If you use a clip to put your chain together, then you can put a big rear sprocket on and just add a couple lengths to the chain. About one link per two teeth. Like another poster said, made a big adjustment if you are going to mess with it. Alternatively, you can go down one in front and up two in back. That makes a pretty big change but nothing like adding, say, 10 to the back. We used to be able to buy sprocket "rings" that clamped over the existing rear sprocket for lower gearing that you could change easily without removal of the rear wheel and just adding a few links of chain. I've been thinking of that for my dirt bike/dual sport.
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post #7 of 23 Old 12-08-2016, 08:12 AM Thread Starter
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Thanks for the info and the rear sprocket being too large for the chain is what I was afraid of.

Bobby, I never heard of sprocket rings, but for big ADV bikes I always wondered why someone had not come up with an adjustable rear sprocket. Adding links is an option though.

Ok Rich, I zip my fronts off with air, so how long of an extension/breaker bar would be needed to do it roadside? Would you still tab over the washer or no?

Then again if I leave the 14T on, I can avoid those pesky speeding tickets

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post #8 of 23 Old 12-08-2016, 08:17 AM Thread Starter
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Tosh, the 12 & up do have different transmission ratios than the <2012's. The difference is noticeable when going from my K7 to the K15 & it feels smoother with more usable torque(if that makes sense).

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post #9 of 23 Old 04-01-2017, 06:52 AM
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Motor7: So what did you decide?
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post #10 of 23 Old 04-01-2017, 09:48 AM Thread Starter
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Originally Posted by spike55_bmw View Post
Motor7: So what did you decide?

Funny you should ask. Yesterday I decided to leave mid week on a ride down to NOLA, it's all pavement so my pea brain keeps repeating, "Change back to 15T or ride with the 14T????"

As for quick change overs, I have done nothing....yet. I think I will put together some kind of socket breaker bar combo and try it out here in the shop to do front sprocket only...looks like a visit to Harbor Freight is in order

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