Author Topic: Switch to 48 tooth rear sprocket  (Read 2391 times)

coarsegoldkid

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Switch to 48 tooth rear sprocket
« on: February 14, 2014, 10:48:38 am »
I thought to try out a 48t rear sprocket.  That's three teeth larger than stock.  In stock trim I have proper chain slack with the shorter surface of the adjuster up against the stop.  So with the larger sprocket I suspect it won't even go on.  So the question is how much longer should I make the chain.  Certainly not more than three links.  Is there a rule of thumb for such swaps.  This could all be avoided with a one tooth smaller countershaft sprocket and be easier.  However I understand that a smaller countershaft sprocket induces increased stress on the chain.

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Endo

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Re: Switch to 48 tooth rear sprocket
« Reply #1 on: February 14, 2014, 11:16:17 am »
Larger sprocket in back? Do you find the 690 too tall in gearing? After changing my pipe I've been contemplating going to a smaller rear sprocket to regain a bit more top end & freeway speed. I thought the 6spd tranny & stock trim had plenty of power (even a bit too much at times) for decent trail riding. Just curious to hear your opinion & thoughts. & don't know of any "rules of thumb" (even though I'm sure there is one)  to answer your question. I usually start over w/ a new chain & install it w/the wheel on and eyeball where to shorten the link. Not a big fan of adding new links to a worn chain, unless its an emergency. But that's just me.

coarsegoldkid

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Re: Switch to 48 tooth rear sprocket
« Reply #2 on: February 14, 2014, 12:41:32 pm »
My stock chain and sprockets have only 5000 miles.  I would expect to go three times that with proper lubrication before changing the drive.  A link or two riveted on should not present any issues with this used chain/sprocket combo.  With 10K miles maybe I'd do a complete new driveline. 

I don't really need top end speed.  Lower gearing by three teeth larger on the rear or one tooth smaller on the front will only tach a few hundred more rpm for any given speed.  The 690 has plenty rpm to play. I'm of the opinion that the lower gearing will lower the crawling speed for downhill terrain when off throttle.  Currently the bike doesn't go slow enough at idle for sufficient engine braking in first gear.  The thought just occured to me that perhaps the slipper clutch has something to do with that.  Having said that I realize I could benefit from more experience riding hills either up or down.

I await responses from all experienced dirt riders.  Bye the way I have 48 years of pavement experience and the last 35 or so on machines with driveshafts.  Dirt not so much.

Endo

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Re: Switch to 48 tooth rear sprocket
« Reply #3 on: February 15, 2014, 01:28:01 pm »
Well I am by now means the worlds best rider (be it street or dirt) but I find using to engine breaking going downhill especially on anything even remotely technical to be a bit herky jerky and more cumbersome than helpful. I prefer to descend in neutral or occasionally pull in the clutch & rely on my brakes to negotiate most downhills. All engine breaking or trying to go too slow usually does is cause me to get off balance or lose too much momentum & crash. Most fast guys I know say to look ahead and embrace momentum to roll over or through things & when in doubt throttle out. But thats just my two cents when dirt riding.

Tmblwd

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Re: Switch to 48 tooth rear sprocket
« Reply #4 on: April 11, 2014, 01:52:11 pm »
I've been reading that the 48 drops the speed in first gear at 1k rpm from 5mph to 4mph something i would be interested in also, i feel it would help in the tight stuff. i thought i might gain enough slack after a couple of chain adjustments?
 i'm interested to hear how it works out.

coarsegoldkid

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Re: Switch to 48 tooth rear sprocket
« Reply #5 on: April 11, 2014, 05:59:11 pm »
On my bike I would need at least two links longer I think.  Certainly the stock chain length is too short.  I gave it half a try, chain too short, I put it all back to stock to go ride.  So when I have a down time I'll look more closely into it.

SDMF_Reaps

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Re: Switch to 48 tooth rear sprocket
« Reply #6 on: April 11, 2014, 06:34:14 pm »
I haven't looked at my bike this closely but I know that you can flip the axle blocks.  You should check it out, it may be enough to keep your current chain.

Dogfarm

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Re: Switch to 48 tooth rear sprocket
« Reply #7 on: April 21, 2014, 05:43:43 pm »
I was looking at my gearing on the 690. Compared to my WR250R the 690 seems too tall. I did gear it down from stock to give it more pep. I like to go real slow in the technical stuff.

I checked and the PO put 48 rear on the back already. Is there any harm in going down a tooth in front? Since 3 in the back is equal to one in the front, I don't see why coarsegold couldn't just go down in the front 1 tooth and keep the same chain too.
2009 KTM 690r
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coarsegoldkid

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Re: Switch to 48 tooth rear sprocket
« Reply #8 on: April 21, 2014, 06:56:20 pm »
I could and save money in the process.  The wisdom over the years is that a smaller countershaft sprocket will hasten the wear the chain due to the smaller radius or something like that.  Maybe it's not a big deal.  Anyway I have the 48 sitting on the shelf because the chain needs to be longer.  I should have explored this beforehand.  The chain is now got 6500 miles on it.  Probably at half life.  I just might bold in a smaller one as you say.

mcrider

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Re: Switch to 48 tooth rear sprocket
« Reply #9 on: April 22, 2014, 04:13:18 pm »
Different brands of chain have different pin diameters. If the added link pin is to small it will cause slackie movement; to large and it will bind.  Mic both; they MUST be exact same size.
« Last Edit: April 23, 2014, 04:06:09 pm by mcrider »
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Adanista

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Re: Switch to 48 tooth rear sprocket
« Reply #10 on: July 13, 2014, 01:15:27 am »
Engine braking, downhill, off trail is a no no from all I've learned.

Rusty Shovel

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Re: Switch to 48 tooth rear sprocket
« Reply #11 on: July 17, 2014, 09:43:03 am »
The 690's gearing is an odd duck; too tall in 1st and too short in 6th.  I currently do plenty of freeway jaunts, so I'll stick with stock.  Once I stop using the bike as a commuter, I'll probably get a higher toothed sprocket out back.

The one saving grace (on the 2014 at least) is the smooth throttle.  I can run at very low idle without the snatchiness I'd expect from a big thumper.  Still, the slowest I can idle along without clutch is about 8-9 miles an hour.  I'd prefer 5-6.
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truck11

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Re: Switch to 48 tooth rear sprocket
« Reply #12 on: July 18, 2014, 07:05:58 am »
I dropped 1 tooth up front and changed the map setting to 'crazy' (ok , sport mode) and get better engine braking now.  I put the mapping back when on the road so it's not too herky jerky.
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