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Old 03-06-2013, 09:15 PM   #31
Phreaky Phil
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Joined: Mar 2006
Location: NEW ZEALAND
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Question

Quote:
Originally Posted by ontic View Post
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.



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!).




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...




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)
I was speraking with Gary Emig of Emig Racing about clamps and offsets for my DR as I would like more stability on sand tracks and his opinion is USD's are the go. He reckons there is to much flex at the wheel with any RSU forks and the front wheel goes where it wants in the sand. He reckons they change all the XR650R's to USD. They have a USD clamp kit for DR650s. I quized him on the conventionals being smoother, he says they have no problems with the Showa's they use.
Hmmmm
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Old 03-06-2013, 11:27 PM   #32
Prutser
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Quote:
Originally Posted by Phreaky Phil View Post
I was speraking with Gary Emig of Emig Racing about clamps and offsets for my DR as I would like more stability on sand tracks and his opinion is USD's are the go. He reckons there is to much flex at the wheel with any RSU forks and the front wheel goes where it wants in the sand. He reckons they change all the XR650R's to USD. They have a USD clamp kit for DR650s. I quized him on the conventionals being smoother, he says they have no problems with the Showa's they use.
Hmmmm
He is right about the showa's. They are smooth when setup correct.
But they still try to bend in a place where the two tubes suppose to slide over each other...
Not all the RSU forks are better than all the usd's

Last week I spoke to some people with two ktm's one with a WP50 the other with a new ish WP48usd.
The one with the usd had trouble with the handling. It always wanted to run to the outside of a corner, felt firm and still bottomed when braking hard or jumping.
The bike with the RSU WP50 had no problems with stiction or handling. It was smooth and if you pushed on the seat the whole bike would go down like it should.
The bike with the USD would NOT go down on the front when the owner got on the seat exept for when you would give it a good push. But than the fork would stay low thats what you see with most of those wp usd's even after some tuning they stick.
They told me they were planning to do a fork transplant to go from RSU WP50 to USD because everybody told them that would be better.......

My girlfriend's G650xcountry just had a forktransplant from the stock 45mm to 45mm shiver. Which is waaaay smoother and a huge improvement compared to the sticky stock forks. Both the forks are the same brand.
That fork is good enough now and almost without stiction. So it is posible to get some usd's set up right. With some brands or types its just harder or you wil never reach a satisfying result. Still they can be better than the stock forks in some ways.
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