USD forks, altering front geometry???

[900streetfighter]

Honestly I would call that crazy. It would be easier and for sure a lot safer taking a full alloy tube, machine a thread on to it and use that as an extension for the fork.

G.[/quote]

I would like to extend the showa legs but then preload and damping adjusters will need to be adapted + spring spaced to suit. In the 70's you could buy slugs to extend BSA/ Triumph forks for choppers and these were considered a bit dodgy back then. What you're suggesting is similar. I think my solution is safer and easier.

[JoKing]

I am looking for a Multistrada or Hypermotard fork.
They should have the correct length...

[900streetfighter]

Yes the multi and hyper are the correct length but also have more travel I think, maybe too much so the tyre might hit the rad. Not sure if 3 spoke wheels go in that type of fork either, the disc mount is different.

[paso750]

I understand that lengthening of the forks won`t do as yours are fully adjustible. It`s possible with these too but it needs some work and a lathe.

Why do you swap the forks anyway ? Are the Marzocchi not ok, can`t they match your riding style anymore or is it just for the fun of it, which I could understand. I had thought about that myself.
I had found the Paioli fork of a Laverda 750 (Zane model) to be the identical length as the P750 fork. As with all USD forks the problem is though that the fork tube diameter is 52-54mm. This requires modification of the front section of the tank or you won`t be able to fully steer. (I sold mine again)

I think my solution is safer and easier.

I do totally disagree. The geometry and physics of a bike are complex. Every bike reacts differently to changes and even changes of a few cm or 2-3° can have a huge effect. That your modification will improve the bike. I doubt it. It will probably be a placebo effect.

Very simplified, the lower triple tree is always bigger than the upper one as it carries the weight of the bike. Of course it also has a stabilizing function. The upper triple tree has more of a stabilizing function and therefore can be designed weaker.
Disregarding for a moment the fact that the fork has a dampening effect it`s a one sided lever held at 2 points, the upper and lower triple tree. The forces you put on the lower part of the fork ie under heavy breaking will transfer to them. (The fork dampening will reduce these forces. The lever shortens)
If you move the upper triple tree towards the lower triple tree there will be stronger forces to it. That`s simple physics.
If the steering angle and the fork is steeper the fork dampening will absorb less forces and pass more to the triple trees.
You now plan to weld chopped off clamps from a second triple tree to the lower side of your upper which should then hold the fork. As mentioned there will be more stress to it which brings me to the welding. There would be 2 cast alloy parts welded together. The quality of this welding cannot be compared to two steel parts welded together. (Ken, correct me if I`m wrong)
Hence chances are high that this construction may crack.
As mentioned elsewhere I`m not an engineer but if you plan things like these I`d ask one.
I can only recommend not to do it this way and if you still want to find a better way or a better matching fork.
Jm2c

G.

[samandkimberly]

Years ago I grafted a set of ZX7 forks onto a 750 Sport I was racing at the time. It was a gamble, as the forks were nearly 2" shorter but I decided to take the chance - as is the bike just did not work on the track. It helped the handling of the bike tremendously. Years later I had a chance to compare wheelbase, rake and trail to a newer 900SS; with my completely arbitrary mods they were close to identical!

There are a lot of reasons that OEMs come up with the geometry they do, and not all of them are performance related. A key reason on the Paso is probably to accommodate suspension travel - if your new front end has less than you probably don't need the space. Plus, front end geometry isn't nearly as fickle as it's made out to be - check out this interesting article on the topic by chassis expert Tony Foale:

http://www.tonyfoale.com/Articles/RakeEx/RakeEx.htm

I say try it as is. I would strongly recommend *against* welding to the triple clamps - first you're going to discover how bad some AL castings weld, then you're going to discover how useless a distorted triple clamp is. When it comes to suspension, stick to bolt on or machined parts, or welded steel.

If you just bolt together what you have, the worst case is that you're going to discover it doesn't feel right. In that case you're going to have to spend some money having someone make up a new set of triple clamps; but with those you can pretty much accommodate any geometry changes you want.

Good luck!

Sam

[ducbertus]

I agree with Samandkimberly and Paso750.
changes that radical and from the point mechnical design the "modifications" can be classified as dangerous. Welding an unknown aluminium alloy is a risky business, I wouldn't dare. If you have extended threaded caps on top of your legs you move in to the right direction. Still it will be a weak spot.

I hope when you read the comments of other members, you reconsider your thoughts.

live wise!!

Bertus

[higgy]

The only thing I would have to say on the article by Tony Foale would be what you can get away with with 19 inch tires is far from what you can do with 17 inch wheels and most definitely dangerous when it come to 16 inch wheels.

The book he sells on his site is a must read for anyone contemplating any frame/front end mods
I read the original in 84,the same year I had the worst experience of my life as far as modifying 2 wheeled suspensions go,almost cured me permanently. JMNSH2C

[Mc tool]

I thrashed this idea to bits a while ago, it was all to hard . My plan was to see if there was enough overlap on the inner and outer tubes to allow the lenghtening of the damper rods and the fitting of spring spacers. every time i looked at lowering the whole fork assy i hit problems. Before you waste to much time have a good look at how your giong to "bearing " the SS lower clamp/spindle into the paso steering head. Tiz a great idea as ( me anyhow )am doing the 17" thing and have the whole front end of a 97 SS , and an up side down paso would be just the duck's nut's .I nearly went mad trying to figure the geometry, gain a bit here , loose it there, 17" wheel adds 1/2 an inch, bla bla bla, but it would look cool and , at the end of the day thats what counts

[paso750]

what Tony Foale did was doing all his testing with the same fork so I don`t know how comparable this is to this situation. I wonder what the results were if not only the wheels were smaller as higgy mentioned but also the fork shorter which I think would change the weight balance of the bike towards the front.

G.

http://www.wilbers.de/en/fahrwerksgeometrie.php

[higgy]

In my case G Here is what I had done to my 84 750VFR in an effort to "quickin my steering a bit"

installed a set of S&W progressive springs with a 3 inch preload spacer and went to 10w oil from 20w
New Metzlers in a track compound 18 inch rear 16 inch front
steering dampers,one on each side and lowered the tubes one inch in the trees
Incidental to these front end changes I had also installed rear sets and a Vance and Hines exhaust and lightened everything on the bike that at the time could be lightened which of course changed the distribution
on the bike " just a bit"

I was going just 40mph when the front end oscillation started

As they loaded me into the ambulance I still had the right side bar,master cylinder and half of a stainless line in my hand.

jm2c

[samandkimberly]

steering dampers,one on each side
jm2c

*two* steering dampers?

Your whole story made me laugh. I remember doing all sorts of "performance " things like that and swearing the bike was faster because it was less comfortable, stiffer, or louder.

Glad you recovered. :-)

[samandkimberly]

what Tony Foale did was doing all his testing with the same fork so I don`t know how comparable this is to this situation.
http://www.wilbers.de/en/fahrwerksgeometrie.php

My only point in posting it was to show that major changes in steering geometry do not necessarily create major changes in handling. This *may* be less true in modern sport bikes, but I would not classify our beloved Pasos as modern sport bikes.

Thanks for the article by Wilbers; very educational. But I would not agree that major suspension changes are always bad, just that they carry risk.

Sam

[higgy]

*two* steering dampers?

One mechanical,one hydralic

My only point in posting it was to show that major changes in steering geometry do not necessarily create major changes in handling.

On the other side of the same coin,seemingly well thought out changes can lead to unrecoverable events

Caution is advised FWIW

the lower the front and the quicker the steering, the easier you get front wheel wobble at high speeds and you also put more pressure on the wrists.

Not to nit pic but generally it is intermediate speeds where instability occurs and usually in transitions of front end loading.

[900streetfighter]

Thanks for your comments and links, all very interesting. I hadn't thought about the yoke distorting.
I want to(maybe) do this mod to a)improve the ride/handling, b)upgrade the forks, c)make the bike a bit trick. As I said previously Ive ridden a 907 with M1R maxton forks from a 888 that were 20mm shorter and it was fine.
I don't think the lowered front/steeper rake is a problem, the yokes I intend(ed) to use have a 4/5mm longer offset, don't know what that would do.
The parts I want to use are all spares I have so this is a cheapish mod. I'm seeing a friend at the weekend who does all kinds of mods to his bikes and is a specialist welder so I'll ask his opinion before I get in any deeper.
Cheers, Keith.

[Rhino]

Oh God you lot

Want to quicken the turn-in?

Sod altering yokes forks etc . . . . try a 16" front wheel . . .

Don't know if anyone's tried that on a Paso yet . . .