Shorten WP43 Fork for the R80 Project

[Ras Thurlo]

Originally Posted by Airhead Wrangler

Well yeah. Definitely. Some people think airheads are supposed to have conventionals. I agree that they look better on an older bike, but I'd rather put performance and parts availability ahead of aesthetics.

I get both points of view

[Airhead Wrangler]

One more pro for conventionals is that you can use fork boots on them and thus oil seals tend to last quite a bit longer.

[ontic]

Originally Posted by Airhead Wrangler

One more pro for conventionals is that you can use fork boots on them and thus oil seals tend to last quite a bit longer.

Is that the only reason for some USD's having a tendency to blow oil seals, I thought it was something a little more inherent to the design than dust/dirt/chip damage (ie oil always sitting above seals)?

Another pro for conventionals is the ability to use fork braces.

Parts availability for our 5060's though...

[R-dubb]

Uses two interconnecting aluminium angles. Cut out most of the top flange on each.

Two holes into voids behind front of top triple, with 6mm socket heads and nuts behind. Two more bolts through front angle into oem rubber grommets on headlight shell. Then there are two bolts through the top tabs to connect the two angles in the middle, making it possible to detach. First photo in top post was too wide at the top for cables and such. This one is what it looks like now. I cut the top flanges down to 50mm wide in center and moved them very close together to keep shell tight to the clamps. Made the turn signal stalks, welded to a flat bar and bolted it to the front flange all the way across the bottom. Nothing touches, but it's close.



Bottom of shell uses a single bolt inside a spacer to a little tab and a threaded bolt hole into center of lower clamp. Pretty simple stuff.

You're all getting ahead of me. I'll post a short build thread sometime soon

[chipsdad]

used to race mountainbikes with usd forks. the aluminum ones stuck like hell. tolerances are really tight and over clamping the tubes is a major potential for issues. I know for a while the mechanics were crazy glueing the interface and doing the bolts little more then finger tight to get by. also the lack of a lowerbrace causes lots of twisting, which prevents the stansions from traveling freely. they look cool though, i'd run em.

[ontic]

Sorry for the thread drift R-dubb, just stirring the pot a little until your next post
A little bit of USD vs RSU ponderings.

Originally Posted by Airhead Wrangler

though typically USD forks are less flexy and have lower unsprung weight than comparable conventionals.

Around the net in various discussions I've read of this being challenged in many examples, and in both claims- ie some USD's have been shown to have just as much flex as the conventionals they replaced- probably less twist, but this can be remedied with a fork brace on a conventional. Where they most certainly are stiffer is up top where they are clamped... however when they flex here (as they still do) you get stiction because of the bushes, whereas conventionals when they flex, even if they do flex more, don't suffer this the same flex-stiction problem.
Also, in a crash or big front impact, rather than the conventional fork routinely bending the tubes at the bottom of the triple clamp (tubes being the easiest to replace or even straiten), the USD often bends at the sliders in the triple clamp (destroying the fork) while also often bending at the tubes where they meet the sliders, and/or might be more likely to damage the frame/headstock because of all this stiffness... If you get lucky and just slightly bend the tubes where they met the sliders, then the USD fork is still buggered and gets stiction until the tubes/lowers are replaced, whereas a conventional fork bent up top there will often keep you riding and get you home or round the other side of the world... maybe without you even realising.

The less unsprung weight claim is also often in dispute (and often less emphasised as the main advantage- stiffness is)- I've seen a few broken down weight by weight comparisons of conventional and USD forks (including clamps) of the same tube diameter, and in these cases the USD was often heavier in total, and heavier in unsprung mass- however, of the few cases that went into something approaching adequate detail, I didn't see any inclusion of oil weights within this break down (correct me if I am wrong, but USD oil is sprung weight and conventional are unsprung?- on a WP50 fork, not a small omission!).

Originally Posted by Airhead Wrangler

Unsprung weight and stiffness. USD forks are just a "better" design when you consider the forces acting on the forks.

So, advantages IMO:
'unsprung weight' depends on a case by case basis, but potentially not a huge advantage either way. (btw, it would be interesting to get some actual weights on these, I can pull apart and weight my spare WP50's when I return home in a month or so).
Stiffness yes, definitely, however if flexing when it does occur causes stiction then this needs to be weighed up against the stiffness 'advantage'- and this and all the other positives and negatives (of both kinds) speaks to the 'just a better design' claim- it depends on the details and the application.

I'd emphasise a third advantage as has often been stated here and elsewhere, and I think it is the main one (when talking RSU and USD apples and apples- ie both good forks), modern USD's are modern. They are pretty much all that is being made on the top end, will be newer and will be the home of ongoing tech improvements, have more parts for longer, etc, etc.
Using the newest best forks are probably the best forks to use...

Well yeah. Definitely. Some people think airheads are supposed to have conventionals. I agree that they look better on an older bike, but I'd rather put performance and parts availability ahead of aesthetics. Shiny part up or shiny part down? That's the question.

Exactly.
However, I question the performance advantage in principle and specifically for a heavyweight bike like an airhead- well set up I don't think there would be much in it to the point it doesn't matter at all.
Even if I do expect a fine set of 4860's properly set up to (slightly?) outperform (at least in some types of use) my WP50's once they are dialed in, there are other considerations- if I blow a seal in the middle of nowhere in my country or somewhere else, I like it that I keep my oil in my fork for longer and have a much smaller chance to dump it over my caliper and rotor- and I'm prepared to accept positives and negatives and compromises along these lines because of how and where I intend to use it.

Regardless of all this, I do think it comes down to Aesthetics and Parts.
Good modern USD's win for parts and seem a more sensible option I rekon.
Aesthetically either look good to my eye but conventional look a little better for me.

At the moment I plan on keeping and using my G/S until the WP5060 and WP4354 and WP4860's forks are ALL considered too old to service, so just as long as I can stockpile enough parts for a decade or two of use it doesn't matter much to me- I'll probably have to change forks again someday (and by this time they might be making conventionals again)

[AliBaba]

Originally Posted by ontic

I'd emphasise a third advantage as has often been stated here and elsewhere, and I think it is the main one (when talking RSU and USD apples and apples- ie both good forks), modern USD's are modern. They are pretty much all that is being made on the top end, will be newer and will be the home of ongoing tech improvements, have more parts for longer, etc, etc.
Using the newest best forks are probably the best forks to use...

For me this is the most important factor.

I have two bikes (HPN & EXC400) with WP4860. Please remember that the name WP4860 is more like a family of forks. There are quite a few different WP4860 so take care if you are shopping at e-bay and remember that a lot of the forks have been used for MX/Enduro.

On my bikes stiction has never been a problem as long as the fork are aligned (take care when you mount the wheel).
The forks has approx 100mm sag so the bearings are not close to each other. You can also find that different WP4860 has different length innertubes.

When it comes to seal-failures I have not had any more problems with the USD then the RSU, but I do take care of the forks (dry them off with a dry rag when they are dirty and use some special grease for the seals).
IMHO the consequences of a seal failure on a USD is not worse then on a RSU. In fact I see the failure earlier on the USD because it doesn't have
rubber boots.

For me the negative sides is that I have to carry two more tools to be able to service the forks and I think they will be a bit stiff if I have to use ATF-oil in a third world country.

If you have a look at offroad-racing you will se that everyone use USD, and I've never heard of a single rider that has given up the Dakar rally because of a seal failure.

[R-dubb]

Originally Posted by Airhead Wrangler

Mine are particularly bad, but that's just because I bought them used on ebay and put them straight on my bike without even changing the oil. They clearly are in need of a full rebuild. That said, the other 4860s I've seen have more stiction than conventional forks, but I don't really notice much when riding them. The improvement in stiffness and overall function is so much better (on forks in good condition) that I don't really care about a bit of stiction when fully extended.

Proper setup is king. I've had lot's of WP USD forks on various bikes, probably six or seven pair. I've seen them mushy and and like a jack hammer. Always a challenge to get dialed. One of the nicest sets was a pair of 43's that started out way under-dampened on rebound. Rather than re-valving, I tried 10w oil and cranked the top clickers down to like three notches from all the way in. Worked like a dream on my heavy-ish KLX650. The thing never packed down. Go figure.

By contrast the 48's on my KTM690 are still way too harsh and stick like crazy even after being re-valved and sprung by one of the best guys in town. They are much better than before the work, but still harsh. Go figure again. The ones on my first 450exc were always excellent. Light bike = less challenge, I guess.

The HPN/WP 38mm variation on my old PD were downright horrible. Not sticky but flexed like mad and were way too soft. Never really set-up correctly because I bought the bike with them installed, parts were weird, and I didn't want to mess about and break stuff.

The other huge variable is weight balance and rear shock. If the bike isn't centered, no amount a fiddling will result in a stable situation. Front too high, forget about it. Sometimes that's tough to figure out, specially if the rear shock is too soft, or under dampened. The rear squats or pogos, and it feels like the fork is out of whack. Many times, not so. The forces are translating. I'm no expert but even good hardware sucks if it's not well dialed.

I just don't think you can properly judge a fork until every effort has been made to get it right! Certainly don't assume that because a buddy can't get his sorted that it is the fork's fault. It's hard to know, what the potential is. That's my 2 cents. The 43's going on this new bike will be made right even if I have to redo them five times.

[Prutser]

Originally Posted by R-dubb

.

The other huge variable is weight balance and rear shock. .

Does this mean you are going to use progressive front prings too ?
(to get it balanced)

[Ras Thurlo]

Originally Posted by Prutser

Does this mean you are going to use progressive front prings too ?
(to get it balanced)

Pls explain comment

is it because the softer initial springing allows a bike to find its own balance more readily?

btw- I had assumed that progressive springs are not good for off road use, because you quickly get to the firmer end of the compression, leaving you with stiff suspension with little travel. Is this right?

[Prutser]

Originally Posted by Ras Thurlo

Pls explain comment

is it because the softer initial springing allows a bike to find its own balance more readily?

btw- I had assumed that progressive springs are not good for off road use, because you quickly get to the firmer end of the compression, leaving you with stiff suspension with little travel. Is this right?

I just asked because I noticed the progressive spring that is mounted on his YSS shock.

[R-dubb]

Originally Posted by Prutser

I just asked because I noticed the progressive spring that is mounted on his YSS shock.

That's a work in progress

Yee ole airhead is full of compromise... as in, normal dirt bike logic need not apply.

[Prutser]

Originally Posted by R-dubb

That's a work in progress

What spring number did they use R-dubb ?

[Beemerboff]

Good post Ontic - covers up pretty much what I know of the relative merits of USD against RWU forks.

And R-dubb, nice to see some recognition being given to front to rear balance, at last.
Most suspension set up guides dont even mention it, but when you get anywhere close to the sweet spot that is mainly what you are setting.

Any rear shock that is not perpendicular to the radius of the swinging arm will have a progressive action, and the more laid down the more progressive - simple high school mechanics.
KTM recently returned to laid down shocks in lieu of linkages, and given that they were one of the innovators with USD forks maybe we will see them going back to RWUs as well!

I think the uneven windings on springs has more to do with the harmonics of the spring, that is, the inherent resonances. Does next to nothing for progressiveness on evry set I have measured.
Even some valve springs come that way now, but this is a complex subject I have no experience with.

I have found that using the best synthetic fork oil I can find reduces stiction on my G/S forks, and my local KTM specialist sells nothing else.
But I dont want to turn this into a "199 things you can put in your forks other than fork oil which dont work" thread.

[R-dubb]

Originally Posted by Prutser

What spring number did they use R-dubb ?

As you may know EPM is the US dealer for Hyperpro. Klaus originally sent me a single rate spring with the YSS. It was too soft, resulting in excess sag, and preload was exhausted. Rather than going to a stiffer spring he offered the Hyperpro in a size which matches my needs.

I've always used single rate springs and was reluctant at first. I once had a progressive spring on my Ohlins (1150 GS) and swapped it out because the going in rate was too soft, but the bike jacked too high when enough preload was applied to eliminate the wallow.

Here I am giving it another go. Fingers crossed. Since this bike is a work in progress with the height adjustment and WP fork (I still can't test anything cause it ain't done), I decided to give the progressive another look. For the record, this bike will not be entertaining any rock gardens. I wan't a super smooth namby-pamby dual sport that I better not fucking crash. Too much work and way too pretty. A cush, but hearty traveler.

The spring is: Hyperpro 1381 designed for a KTM 690 SMC. (SP-KT06-SSB002). If you have a way to decepher an equivilent single rate spring, I'd love to know how it plays.