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ontic 07-12-2013 02:40 AM

KTM front wheel hubs- help please
I am trying to build a 19" front wheel and am trying to figure out what hub I have.

This front wheel will be for a WP50mm extreme (WP5060) front end (on a bmw airhead).

I have a 21" wheel that came with my front end, it has a 17mm axle.

I bought a bare ktm hub that was sold as being for a 17mm axle for a bike of the same vintage (that the forks came from), but today when changing the bearings in the 21" wheel and comparing the hubs side by side there are some important differences.

To go with these descriptions below there will be photos.

The 21" hub takes two different sized bearings- a 35mm OD 10mm deep bearing on the rotor side and a 40mm OD 12mm deep bearing on the other side. On the rotor side once the bearing is in there is space for a 35mm OD oil seal in the same bore. On the other side once the bearing is in there is a larger bore for a 52mm oil seal.

The bare hub I have takes two 35mm OD bearings the same size, and at 10mm deep there is no room for oil seals on top. The bearings are also further apart so will require a longer spacer between them. The spoke holes on this hub (from one side to the other) are also a little bit further apart/wider (approx 4mm).

some photos,
the old hub on the 21" wheel
rotor side

other side

the new bare hub I have.
Rotor side

other side


1. With this bearing set-up does anyone know what bike/year/range this hub would be from?

2. Is the 35mm OD 10mm deep bearing the right one for this hub? If so, is this hub meant to have a oil/hub/shaft seal on top? How?

3. Depending on what hub this is, what year etc, can anyone tell me if this is a Japanese or European spoke pattern? (my 21" wheel is Japanese). (I don't know how to tell with a bare hub what pattern it is).

I have a Jap pattern 36H Excel 19X1.85 rim ready to go and am trying to figure out what spokes to use to try to lace these together. Not sure if an off the shelf set of spokes will work or if I need to get some custom spokes.

Today, pulling out the bearings on the old wheel to check out the internal spacer, I was in a friends machine shop ready to start machining the internal and external spacers... then with the bearings out we figured out the hubs are different.:1drink

Machining up spacers will be no problem. Figuring out a way to get seals on as well was looking a lot more complicated. My bearing guy told me I could run these double sealed Nachi bearings I've bought without a seal/cover, as they are already very well sealed, and if required just replace them sooner....? This 19" wheel will be for a set of road oriented dual purpose tyres, for general road riding and commuting and touring... dirt riding and dirt oriented touring will be done on the knobby 21" set of wheels.

If there are any other measurements or photos or anything else required, let me know, I am trying not to make this post too long:lol3


johnno950 07-12-2013 03:05 AM

Looks like a honda hub,early xr/xl600 style bike?

ontic 07-12-2013 03:12 AM

I'm pretty sure it is a KTM hub (I don't think the seller was that wrong:D), the KTM rotor bolts up perfectly...

here is a different shot of the hub,

ontic 07-12-2013 04:32 AM

Never trust the memory,
the old listing has disappeared from ebay and I can't find it in google cache, but the item heading in the old emails from when I won the item are:

"KTM LC4 620 640 Radnabe Nabe Vorderrad (front wheel hub) 17mm ,20 mm 660 690 Duke"

17mm and 20mm and fitting all those models (with no year listed...):D

I am not sure what information was in the item description itself...

Anyway, with the smaller bearings it fits the 17mm axle no problem. The rotor bolts up and the correct offset for the caliper should be easy enough to figure out with wheel/axle spacers.

By eye the spoke holes between the two hubs appear to line up perfectly so I am hoping it is a japanese pattern.

If I could find out what hub it is, I am hoping I might be able to figure out what spokes to order, rather than handing it over to a wheel builder (which I can't afford at the moment),


Foot dragger 07-12-2013 06:54 AM

Spoke angle can vary and the right rim needs to go with the right hub.
There are different spoke patterns for different wheels. Cross-3 is common where 3 spokes cross each other,but you need the right rim for that hub or things wont go well.

ontic 07-12-2013 09:36 AM

Thanks for the posts,

Foot Dragger, as far as basic spoke pattern goes, I've relied pretty heavily on this post by Woody,

My 21" wheel has that exact Japanese pattern.

I have closely looked at both my new Excel 19" rim and the bare KTM hub I am trying to lace together.
Both hub and rim seem to have this exact same Japanese' pattern as well. It looks like I could easily replicate the lacing from the 21" to the 19" wheel so long as I had the correct spokes.
If I am right in this observation, whether the actual angles of the holes line up perfectly would depend on the diameter of the hub (where the spokes start) this rim was intended for (a rear hub)...

After playing around with it, it doesn't look too bad to me- might be spot on or not far off.

From measuring spokes, it looks like the 21" wheel has spokes around 235mm and for the 19" wheel/hub I would want then around 205mm.
approx measurements of
holes in hub = 5.1mm
holes in rim = 8.7mm

Googling around brings up tons of spoke sets but hasn't helped much trying to figure out how long these spokes actually are...

I'm done for the night.

ontic 07-14-2013 12:04 AM

I'll try another bump with another question.

At the point where the spokes go through the hub can anyone tell me how the diameter of a KTM rear hub compares to the front? From googling images they often look the same?

I think I found reference of the rear spokes for some 19" KTM wheels being 205mm long, thus am thinking of trying a set of spokes intended for a KTM rear 19" wheel. Bulldog stainless spokes are looking good at this point.

I'm hoping to hear back from some emails to spoke suppliers trying to confirm the lengths...

My fallback at this point will be buying a set of spokes for 21" and shortening and re-threading them.

any advice appreciated,

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