An Unholy Union III: WP 4860 USD Forks on an Airhead

[Airhead Wrangler]

Originally Posted by Airhead Wrangler

Anybody know of a good quality regular old ROUND brake rotor for KTM dirt models? Ideally, something larger than OEM KTM and floating.

Looks like brembo makes just what I'm looking for, but of course it costs $100 more than all the other oversize rotors on the market.

[One Less Harley]

Get them to knock off the $100 Brembo buttons.

Thanks for the fork reply.

[Houseoffubar]

Originally Posted by one less harley

get them to knock off the $100 brembo buttons.

Thanks for the fork reply.

+1

[bgoodsoil]

+2

[jimbee]

+3 thx

this thread moves fast

[Airhead Wrangler]

Originally Posted by One Less Harley

Get them to knock off the $100 Brembo buttons.

Thanks for the fork reply.

Ha! I actually found exactly that. QTM uses the same exact brembo rotor on their own carrier - no blingy brembo buttons - and guess what - it's $100 cheaper.



In defense of the brembo one, it DOES include a set of brake pads.

QTM also sells this one which is a bit more... um... Judaic?

[Houseoffubar]

Ask, and ye shall receive!

[AntonLargiader]

Originally Posted by espressodrinker

SWould it be possible to take the cartridge out of one of these modern forks and then fit them inside the standard R100 forks? Similar to the hugely expensive HPN cartridge that isn't available any more?
Seems to me to be an easy upgrade without the pain of all the extra machining mods - although you don't gain any extra suspension stroke.

I asked around on that issue about a year ago and didn't get much:

http://www.advrider.com/forums/showt...2#post13103892

For me, the 225mm stroke is OK, 250 max. I just want better performance.

[Airhead Wrangler]

Originally Posted by AntonLargiader

I just want better performance.

I think the biggest thing hurting the performance of the stock GS forks is the 20 pounds of wheel and front brake at the bottom of them. The wheel itself is 13 pounds, the rotor 4, and the caliper almost 3. I'd bet a lighter front wheel setup would improve things drastically, but as long as you're going that far it'd be easier to just do the whole front end.

[espressodrinker]

Originally Posted by AntonLargiader

I asked around on that issue about a year ago and didn't get much:

http://www.advrider.com/forums/showt...2#post13103892

For me, the 225mm stroke is OK, 250 max. I just want better performance.

I also like the idea of keeping the existing steering geometry - not that I really know if it's optimal. I can only assume that the infamous HPN cartridge inserts are actually standard parts from somewhere that they probably just tweaked a bit?

[AliBaba]

Originally Posted by espressodrinker

I can only assume that the infamous HPN cartridge inserts are actually standard parts from somewhere that they probably just tweaked a bit?

The HPN cartridge inserts have nothing to do with HPN.
The inserts was available from BMW but different German tuners also had them in stock (I bought mine from Q-tech when they where NLA at BMW). HPN had a lot in stock, probably because they use them for their model HPN-Basis.
------

The original front rim is heavy but it's also very solid. I used one for 180.000 kms without problems and no maintenance. On my KTM I change wheel-bearings at least every year and the rims get dented pretty easy. The wheel-axle is hollow and I wouldn't used it for a GS.

Another issue is the KTM mastercylinder, the reservoir is small so guess what happens when the pads wear out... But all this can be fixed, and I'm not sure if the issues I mention is valid for all KTM-parts.

4860 comes in a lot of variations (springs, shims, preload, number of bearings etc) and it would normally require a bit of fiddling to get them to work properly. But they are great shocks and parts and knowledge is widely available.
The increased steering-radius is an issue but personally I think an upgrade to a WP4860 with 220-250mm stroke is an interesting upgrade for a bike with standard frame.

[Airhead Wrangler]

Care to tell us more about the 4860 setup you have on your HPN? You use the HPN setup with wider leg spacing and the R100GS front wheel, right? Do you happen to know what stem to leg offset the HPN triple clamps use and what exactly the leg spacing is? Any hints for spring weight and valving? How much travel on yours? Detailed pics wouldn't hurt.

[Stagehand]

[AliBaba]

Originally Posted by Airhead Wrangler

You use the HPN setup with wider leg spacing and the R100GS front wheel, right?

My HPN-setup is built to fit standard brake and wheel (they also have other options). I use a standard hub with a Behr-rim (not TL) and 4mm spokes.

Originally Posted by Airhead Wrangler

Do you happen to know what stem to leg offset the HPN triple clamps use and what exactly the leg spacing is?

I don't have any proper tools handy so this is a bit rough:
Leg spacing = 210mm (std =190mm)
Stem to leg offset = 25mm (std = 38mm)

Originally Posted by Airhead Wrangler

Any hints for spring weight and valving? How much travel on yours?

The travel on mine is 300mm.
My springs are a bit stiff. I use weight 5 oil with an airgap of 100mm, with a softer spring I think 105-110 mm airgap would be correct.
Valving is difficult... Mine is pretty good but I know a suspension-tuner who has made a great setup for KTM950SE and I will talk to him next year when I change the springs.
If you buy a used forks a lot of them have been revalved, and it's hard to know what you get. The WP4860 on my EXC is revalved and it's extremely nice, but it's far to soft for the BMW.

Originally Posted by Airhead Wrangler

Detailed pics wouldn't hurt.

A mix of old pictures:


Building:


Old and new:


Lubed:


Overview:


Distance:

[Airhead Wrangler]

Originally Posted by AliBaba

I use a standard hub with a Behr-rim (not TL) and 4mm spokes.
Leg spacing = 210mm (std =190mm)
Stem to leg offset = 25mm (std = 38mm)
The travel on mine is 300mm.
My springs are a bit stiff. I use weight 5 oil with an airgap of 100mm, with a softer spring I think 105-110 mm airgap would be correct.

YES!! Thanks. That's some really good info. I was surprised that the offset was as small as 25mm. Everyone so far has told me that HPN used roughly the same offset as BMW, but looking at your photos it's obviously not even close. Any idea what your spring rate is??