Rear wheel adjustments.

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Aphex
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Rear wheel adjustments.

Postby Aphex » Tue Sep 19, 2017 10:33 pm

So I cut my new chain a couple links too short. Good news it with the adjusters almost all the way in the chain fits and the slack is within spec.

However this is by far the shortest the wheelbase has ever been, and I'm started to notice more headshake (or maybe my recent events have made me more keen to it).

Anyways I guess my question is how short is too short for the wheel base? I believe the amount of threads showing on each adjuster bolt was 3.8mm on each side. Would a couple links (2 inches at most) make that much of a difference in how the bike handles?

My forks are just above the top triple and not quite flush so I could still push them through a little more to compensate.
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Willh
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Re: Rear wheel adjustments.

Postby Willh » Tue Sep 19, 2017 11:49 pm

Head shake is pretty normal. Suspension setup?. Run the forks flush and get a steering damper if it bothers you. I run a Scott's. A Nichols triple clamp allows you to push the forks down lower.
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Aphex
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Re: Rear wheel adjustments.

Postby Aphex » Wed Sep 20, 2017 1:04 am

Willh wrote:Head shake is pretty normal. Suspension setup?. Run the forks flush and get a steering damper if it bothers you. I run a Scott's. A Nichols triple clamp allows you to push the forks down lower.


I've got the rider sag set, however I do need to fine tune my compression and rebound.

I'd love to get a Nichols triple clamp. Just waiting for one to pop up on the used market.

I think I'm just sketched out by all the crap that has been going wrong with the bike lately, I've yet to ride the bike hard since those issues.
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Re: Rear wheel adjustments.

Postby SUPER DUKE #1 » Wed Sep 20, 2017 5:48 am

Aphex without doing anything else to the bike the next time you go for a ride take -5 to -6 clicks OFF of the FORK rebound adjuster. Free up the rebound and see if the head shake lessens or goes away. Don't change anything but the fork rebound to a 5-6 click less.......sounds dumb but try it and then make all the fun of me you want. I can take it. :wink:

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Re: Rear wheel adjustments.

Postby Aphex » Wed Sep 20, 2017 2:16 pm

SUPER DUKE #1 wrote:Aphex without doing anything else to the bike the next time you go for a ride take -5 to -6 clicks OFF of the FORK rebound adjuster. Free up the rebound and see if the head shake lessens or goes away. Don't change anything but the fork rebound to a 5-6 click less.......sounds dumb but try it and then make all the fun of me you want. I can take it. :wink:

SD#1


I'll give that a shot. I believe the rebound and compression are set up per the manual in the sport configuration.
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RichUK
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Re: Rear wheel adjustments.

Postby RichUK » Thu Sep 21, 2017 8:42 am

I soften'd mine just one click back on all settings (just for comfort) but it has also stopped 90% of the headshakes.

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Re: Rear wheel adjustments.

Postby Silverbear » Fri Sep 22, 2017 1:06 am

SUPER DUKE #1 wrote:Aphex without doing anything else to the bike the next time you go for a ride take -5 to -6 clicks OFF of the FORK rebound adjuster. Free up the rebound and see if the head shake lessens or goes away. Don't change anything but the fork rebound to a 5-6 click less.......sounds dumb but try it and then make all the fun of me you want. I can take it. :wink:

SD#1

Freeing up the rebound (making it softer)would be adding clicks.For a quicker sporty rebound,less clicks would be required.Or maybe I have misinterpreted what you mean by freeing up.Cheers

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Re: Rear wheel adjustments.

Postby PBRnr » Fri Sep 22, 2017 1:08 am

Not making any suggestions since I"m not qualified to do so, but by shortening the wheelbase via the chain tensioners, you are theoretically lowering the rear a bit and raising the front, correct?

I would guess that sag and preload would need to be looked at again front and rear after a geometry change like that...but again, not suggesting anything just musing out loud

Also, I assume you have chain slack measured when you're sitting on the bike, wheels on the ground? I've been told chain slack can look fine without the rider and be way too tight once riding it = restricted swingarm travel = bad news
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Re: Rear wheel adjustments.

Postby Aphex » Sun Sep 24, 2017 1:04 am

PBRnr wrote:Not making any suggestions since I"m not qualified to do so, but by shortening the wheelbase via the chain tensioners, you are theoretically lowering the rear a bit and raising the front, correct?

I would guess that sag and preload would need to be looked at again front and rear after a geometry change like that...but again, not suggesting anything just musing out loud

Also, I assume you have chain slack measured when you're sitting on the bike, wheels on the ground? I've been told chain slack can look fine without the rider and be way too tight once riding it = restricted swingarm travel = bad news


I measure the chain slack while the bike is on the side stand, however I do make sure to check in multiple spots and adjust it at the tightest part of the chain. Should I also be doing it while on the bike?
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Re: Rear wheel adjustments.

Postby nampus » Sun Sep 24, 2017 4:26 pm

Why not just adjust according to the manual?
7 mm of slack between the chain and swingarm when pushing the chain up with the bike on the sidestand. Has always worked fine for me.

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Re: Rear wheel adjustments.

Postby Aphex » Sun Sep 24, 2017 11:51 pm

That's exactly what I do. :D
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Re: Rear wheel adjustments.

Postby PBRnr » Mon Sep 25, 2017 5:25 am

can't argue with the official KTM recommendation since I have no data to refute it...gotta ask "is the suggestion for 7mm of chain slack based on research focusing on bike performance? on longevity of parts? both?"

Chain tension (like suspension setup) is set while the bike is static, but does the measurement technique take into consideration the dynamic application? Heavier riders, greater need for shock/swingarm travel will be part of the equation. If there's wiggle room in suspension settings and tyre pressures why not in chain tension?

If chain tension is set via the owner's manual and seems taut (whatever that means in mm slack) when the rider sits on it, the suggested 7mm of chain travel may limit swingarm travel, shock performance, and traction is all I'm thinking. Take it with a grain of salt :)
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Re: Rear wheel adjustments.

Postby SUPER DUKE #1 » Mon Sep 25, 2017 5:54 am

PBRnr wrote:can't argue with the official KTM recommendation since I have no data to refute it...gotta ask "is the suggestion for 7mm of chain slack based on research focusing on bike performance? on longevity of parts? both?"

Chain tension (like suspension setup) is set while the bike is static, but does the measurement technique take into consideration the dynamic application? Heavier riders, greater need for shock/swingarm travel will be part of the equation. If there's wiggle room in suspension settings and tyre pressures why not in chain tension?

If chain tension is set via the owner's manual and seems taut (whatever that means in mm slack) when the rider sits on it, the suggested 7mm of chain travel may limit swingarm travel, shock performance, and traction is all I'm thinking. Take it with a grain of salt :)


It's really all based on the position of the rear sprocket when it is at the farthest away from the drive sprocket, this is where the chain will be the tightest on the top and bottom. That position is generally when the drive sprocket, the swingarm pivot (i.e., swingarm axle) and the rear wheel axle are in a perfect straight line. There are a couple of ways to get those three points into a straight line. This one is time consuming but if you are working on the bike and happen to have the shock removed then a small jack or blocks of wood and the bike on a center stand or crate you can put those three points into a straight line. Then check or adjust the chain tension to 13mm to 17mm at the center point of the swingarm (between the swingarm pivot axle and the rear wheel axle. The other method is to use a ratchet type tie down strap to pull the rear subframe down or actually pulling the rear swingarm up :? Using a long straight edge to align the three points check and adjust the chain to the 13mm - 17mm and note some kind or reference point on the swingarm and undo the strap or re-mount the shock and check what you have for slack on the side stand......most likely it will be the 7mm that KTM has determined :wink:

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Re: Rear wheel adjustments.

Postby Scotty » Mon Sep 25, 2017 12:05 pm

Hopefully I'm reading what you've written correctly SD#1, but if the chain slack is set to 13-17mm with both sprockets and the swingarm pivot aligned, it'll be loose like a bit of old knicker elastic with the bike in its normal attitude, a lot more than 7mm of slack in that position.
Where did the 13-17mm value come from? Apologies if it's been lifted directly from some KTM service literature, though I've seen differing torque values for the same fastener between the owners' handbook and the main workshop manual, so anything's possible :roll:
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