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Author Topic: 640 sprocket swap  (Read 736 times)

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Offline djembe

640 sprocket swap
« on: October 02, 2015, 11:03:35 am »
Firstly a thousand apologies if this should be in Trade-Forum, it seems to fit better here.

Have brand new unused 15-42 counter-" + sprocket & EK 116L chain, KTM OEM parts bought direct from RAD

However after doing a trip on the 640 running stock 16-42, I realize my mistake with buying the above. Highway cruising no good. Need to bring down RPM in 5th.

I'm ideally looking for 16 or 17 CS & 40 rear, but open to what's available, new or used.

Anyone wanna swap?
 

Offline Ruff

Re: 640 sprocket swap
« Reply #1 on: October 02, 2015, 03:47:03 pm »
Check out this site,  http://www.gearingcommander.com/  ,it helps you to calculate what different gear ratios do on your bike.

I'm running 16-38 on my bike and it works well on the highway. It does want a higher ratio for off road though. 16-38 and 17-40 are similar ratio's, but just make sure if a 17 CS actually fits on your bike. Which 640 do you have?
 

Offline djembe

Re:
« Reply #2 on: October 02, 2015, 03:52:32 pm »
Thanks have already played around with ratios on that site, very useful.

Yep 17 requires sprocket casing to be ground down or catches teeth.

640ADV 2007

So how do you find off road running 16 38?

I'm sure it's less than ideal but is it workable as a compromise?


Sent from my SM-G900F using Tapatalk
 

Offline evansv

Re: 640 sprocket swap
« Reply #3 on: October 02, 2015, 04:19:04 pm »
I'm running 16 - 40, standard on the SXC.

Great off road so far & not too shabby on the black stuff.
DT 125, GSX 750 ES, XJ 900, KX 125, YZ 250, WR 200, RMX 250 (280 kit), FZ-6, 2006, DT 125 LC (rear ended by Fortuner - written off), DT200R (current), KTM 625 SXC (current)
 

Offline Ruff

Re: 640 sprocket swap
« Reply #4 on: October 02, 2015, 04:35:07 pm »
I currently use a 40 tooth rear on a different set of wheels for offroading so I don't know.  Previously I took a 42 and a 45 off road as well, but that was with a different chain length. It obviously depends on what you do off road, but the 16-42 worked the best for me off road. The first gear is low enough for almost any sprocket ratio but I feel the difference in the higher gears 'cause I like to steer with the rear wheel. With the 42 looong corner drifts are butter smooth and happens naturally whereas with the 40 I need to focus on when the rear wheel breaks loose. The 45 was unnecessarily high, but I got it for free.

That's my subjective opinion and it's small differences obviously. My bike is a 625sxc with ADV  tank and fairing.
 

Offline Ruff

Re: 640 sprocket swap
« Reply #5 on: October 02, 2015, 04:41:46 pm »
I don't get why they never put a 6th gear on the LC4 engine. It has the power for it. Apparently the 690 has an even narrower gear range even with 6 gears. Don't get it. Maybe they sell more of the big bikes by deliberately making the small DS's uncomfortable on the highway.
 

Offline evansv

Re: 640 sprocket swap
« Reply #6 on: October 02, 2015, 04:58:26 pm »
I've got the 18L KTM tank from a Duke II. I'm a feather weight, so drifting the rear is my natural cornering action on the dirt, especially when meerkatting :thumleft:
DT 125, GSX 750 ES, XJ 900, KX 125, YZ 250, WR 200, RMX 250 (280 kit), FZ-6, 2006, DT 125 LC (rear ended by Fortuner - written off), DT200R (current), KTM 625 SXC (current)
 

Offline djembe

Re:
« Reply #7 on: October 04, 2015, 08:13:20 am »
Thanks for the feedback guys,
Good informative reading.
Going to try 17 40 or 16 38.

Still stuck with brand new 15 42 sprocket and chain  set 😕

Let's see if RAD take returns...

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Offline Ruff

Re: 640 sprocket swap
« Reply #8 on: October 04, 2015, 09:23:09 am »
According to the calculator, the change in sprocket distance is less than 1mm if you go from 15-42 to 17-40. So maybe you can keep the chain and just exchange the sprockets?
 

Offline djembe

Re: 640 sprocket swap
« Reply #9 on: October 10, 2015, 08:49:47 pm »
According to the calculator, the change in sprocket distance is less than 1mm if you go from 15-42 to 17-40. So maybe you can keep the chain and just exchange the sprockets?

Done just that.
The great guys at KTM CPT swopped me 15/42 for 16/38 and I paid in the difference of R110.