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Fork Axle offset

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This is not a suspension topic but since suspension and geometry are interdependent I thought I could post here.

 

Does any one know what was KTM's WP fork Axle offset in 2014 which is 2mm less in 2015?

What fork Axle offset do yamaha kYB sss have?

what about the new TAC, do they use the same offset?

 

Is there an accurate way to measure this?

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15 must be 33mm as they changed by 2mm

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Yamaha KYB SSS. Different flavours for different years.

 

12+ 250F = 54 upper OD, 32mm lugs
10+ 450F = 54 upper OD, 32mm lugs
08 - 11 250F = 56 upper OD, 32mm lugs
08 - 09 450F = 56 upper OD. 32mm lugs
06 - 08 All = 56 upper OD, 35mm lugs
12+ WR450F = 56 upper OD, 35mm lugs

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Are you guys sure about the YZ/KYB axle lugs?  30mm center-to-center is the most often mentioned measurement (which doesn't mean that its right!).  However, you can eyeball the difference between a WP/KTM and a KYB/YZ and tell that it's more than 3 mm and both are certainly not  35 mm.  I have tried to measure YZ SSS fork lug offset and have never been confident in my measurements due to keeping all the measurements on the same centerline.  If you have measured these offsets please tell me how you did it!

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You ask, you get! What I did when working out offsets for my KYB conversion on my Beta:

Do it this way, measure the following carefully with a good caliper (example dimensions are from my KYBs):

Dim A = dia of the lower thin wall part of the foot, should be 33mm

Dim B = height of the small casting rib(on some fork lugs) on the rear of same foot section, approx .25mm

Dim C = axel bore. easy at 25mm

Dim D = the distance from the inner ID surface of the axel bore to the top of the small rib on the rear of the foot, approx 36.5mm

The idea is to get good numbers on easy to measure surfaces and calculate the tough one to actually measure accurately.

Offset is the distance from fork tube center to axel center, so we use the dia of the foot and axel to calc them, and reference with D minus the rib height. The KYB is much easier due to the smooth casting, but same principle applies.

Offset = D-B-A/2+C/2

=36.5-.25-33/2+25/2 = 32.25mm

Jakobi has posted correct numbers, we have both done conversions and have this down. Offset has a profound effect on handling and will make or break a conversion. In my case I corrected a -3mm lug offset difference with +3mm clamps.

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What difference is the axle to fork center if you don't know the fork center to steering stem center?

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It's NOT the same !

Axle offset feels different as clamp offset.

 

 

How so? An example that comes to mind that I have first hand experience with is on one of KTM's big dualsport bikes, the 690. The earlier years used the same axle offset as every other KTM offroad bike (35mm) with 22-24mm adjustable triple clamps. The problem was that because of the trellis frames, they only got 69* of steering sweep before the fork tubes hit the frame, so in 2012 they switched to 32mm triple clamps with 25mm axle offset. They ended up with exactly the same trail, and made no other geometry changes but now have a full 80* of steering sweep (like a normal dirtbike.) So unless you are suggesting that one could actually feel the theoretical reduced stiction of the setup with less fork lug offset, I just don't see where the difference in feel would be?

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It's NOT the same !

Axle offset feels different as clamp offset.

Absolutely correct!!!

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There will be friction differences ,you want less offset at the axle so the fork pushes in a straight line upwards

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I understand that part of the theory, but why then don't MX bikes come from the factory with the axle directly inline with the fork (like a road bike) along with triples with much more offset to compensate? I've seen only a few of the factory SM bikes delivered this way and they had open cartridge forks. Is it just an internal packaging issue that would make things more complicated with a closed cartridge setup, or maybe it would require a longer overall length to maintain the same travel?

 

I'm not trying to play devil's advocate. I am genuinely interested as I am hoping to use a greater offset triple along with an E-axle (or maybe even different fork lugs???) to gain steering sweep while maintaining my current (or VERY close to it) trail exactly like I mentioned in my previous post but with CC forks.

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Yes they can not package the forks with the axle below the fork

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Ok whats the best way to compensate then? For example i was loking at fooling around and putting my set of 2007 yz250f forks on my 2013 kx450f. The upper triple would have to be bored out as the yz forks are bigger diameter but im concerned the axle offset is going to be alot different.

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I think I'd you use the showa off the kxf 250 it's a straight bolt in with no offset changes

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I want to but i have a set of SsS with loke $1200 into them so want to try

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There is a post somewhere saying the axle offsets of most modern forks ,doubt the search will work how ever

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