Winter project: upgrading time! (R6 forks and more...)

[Bjorn]

Since I enjoy reading about all the XS650 modifications as much as the next guy, I plan on sharing some of my winter upgrade-stories here.

The list is long, but I want to start with the '00 R6 fork conversion. I have been running a Ducati rotor with calliper set-up for almost ten years now, and i'm ready for a next step. I red some people installed the R6 forks successfully, I like the look of the conventional forks and decided to go for it.

this is what the bike looked like this season

last summer I picked up these 2000 Yamaha R6 front forks:

Right now i'm trying to understand what needs to be done. It seems like there are quite a lot of variables to take into consideration (triple clamp offset, trail, fork length , steering stem dimensions, bearings you name it).

I've measured the offset difference and the original XS triple clamps are 47mm offset, and the R6 are 40mm. The R6 forks are also about 15mm shorter so i'm guessing the trail is not changing a whole lot since the two seem to counter each other (guestimate hehe). The plan is to reuse the lower R6 triple clamp and machine a new top clamp.

To be continued...

 

[arcticXS]

What exhaust systen is that? And what is the headpipe diameter?

 

[Bjorn]

Made the exhaust a few years ago. I believe the ID is around 38mm

 

[arcticXS]

S
Made it yourself! That is great! (38 ID should be 40 or 41 mm OD then)

 

[Bjorn]

I just checked, the OD is 40mm. I believe the pipes are very thin walled (1,2mm) so around 37,6ID

 

[arcticXS]

I assume both triples (stock and R6) have the fork tubes parallell with the steering stem. 7 mm less offset in the R6 triples give you around 5 mm more trail, if I got my trigonometry right. That is not a huge change, and, as you say, will to some degree be balanced out by the shorter fork.

You say the R6 forks are 15 mm shorter than the XS forks. If making a new top triple, keep in mind that a flat triple will pull the forks a bit up, compared to the stock XS top triple.

Also, the reduced offset combined with the larger diameter fork tubes may require you to modify te steering stops a little bit, to avoid the tubes hitting the tank.

And obviously, you need to check that you have clearance for front wheel and fender (mudguard) with a fully compressed fork.

And finally, you may (or may not) run into issues with the speedo drive as well. I just binned the stock clocks and bought some Daytona Velona electronic speedo and tach.

 

[Bjorn]

good thought about the flat top triple clamp. I measured that the original has about 24mm of step in it. I could do the same with the new one.

Yes there are lots of potential ''issues'' to adres. including the speedo drive. I want to keep using the original XS spoked 19'' front wheel. combined with one or maybe to brake callipers its going to be a challenge aligning everything and keeping the clearance between the spokes and callipers safe.

My first priority however is the installation of the triple clamps with forks. All the stuff below that, like axle, callipers, brake discs will sort out later.

right now i'm puzzling with the triple clamps and steering stem. I think of reusing the lower triple clamp and making a new top one. For one the original R6 is not really suitable for using a handlebar. I cant just drill holes for risers because their is not enough material. Then there is the matter of the steering stem. I know the the bearing sizes:

XS650:
top: 25x48x13
lower:30x48x12

'00 R6:
top: 30x48x12
lower: 30x48x12
source: https://www.allballsracing.com/

I need to decide whether to make a new stem or reuse the XS one. I know it's pressed and welded in. Find it hard to get my head around all the dimensions. especially the length. I like making parts, but hey...reusing saves a lot of time.

 

[FLEA]

doing the same but with 2008 r6 upside down forks so cant help you except to wish you luck , should be a good conversion

 

[arcticXS]

I guess you are planning for different (smaller diameter) discs, and using the blue spot R6 calipers?
The Ducati 320 mm disc you are currently using is unusually heavy, despite being only 4 mm thick. This is because the gold colored disc hub is steel, not aluminium. I believe there are aftermarket discs for the older Ducatis that weigh 0.5 kg less each (that is 1 pound plus lighter!)

 

[Bjorn]

I havent given the whole brake set-up a lot of attention (yet). I know that running spoked wheels with the brake callipers was tight on my original set-up. I got the two blue spot R6 callipers with the fork, might reuse them to save some money.

Interesting info about the Duc rotor! I look into that! thanks.

In the meantime ive been doing some designing of the new upper triple clamp. Some things im running into. Ive made the design with a step of 25mm. This should minimize the effect of the R6 forks being shorter. However with this stepped design, the machining becomes much harder. I haven't worked out the CAM part yet but i can tell its quite a challenge. Here are the two concepts i have now:

Both have a stepped design, i'm now looking into the bushings to fasten the handlebars. For sure i want to use a rubber mount. The original XS set-up would work, but the rubber bushings are massive. Found some smaller ducati ones i might use. Details still need to be worked out...

 

[Bjorn]

It makes me wonder how much difference a shorter fork/flat triple clamp will make on handling of the bike? I have found some spreadsheets where i can calculate the difference in Trail based on the two offsets of the triple clamps. However i cant calculate the actual trail difference when i run the shorter forks, because the rake will change but i dont know how to calculate it. Does anyone here know how to do that? And secondly, how to interpret the trail values....

This is what i know:

Original set-up:
(Total fork length: 770mm+25mm stepped XS triple clamp)
Wheel radius: 328mm
Rake: 27° (source: internet)
offset: 47mm
calculated trail: 114mm

R6 :
(total fork length 755mm)
wheel radius: 328mm
rake: ?
offset 40mm
calculated trail:?

A flat triple clamp design would make everything a bit easier.

 

[Bjorn]

Dont know if this makes sense but here is what i found:

XS650 original: 114mm trail

R6 with stepped top yoke: 124mm trail

R6 flat top yoke: 128mm trail

Some feedback is appreciated

 

[gggGary]

Using YZF600 forks, blue spots will not work with a spoked wheel dammit. however.... Calipers from the Big yamaha ventures are bolt on, they have only outside pistons not inner pistons so offer more wheel clearance. The YZF legs were extra long cuz the "clip ons" attached above the top triple.
This project has a long way to go but eyeball says fork will work even with the 17" wheel, which I'm using, but will go with a taller tire.

 

[arcticXS]

Using YZF600 forks, blue spots will not work with a spoked wheel dammit. however.... Calipers from the Big yamaha ventures are bolt on, they have only outside pistons not inner pistons so offer more wheel clearance. The YZF legs were extra long cuz the "clip ons" attached above the top triple.
This project has a long way to go but eyeball says fork will work even with the 17" wheel, which I'm using, but will go with a taller tire.

What if you shave a off a little bit of material in these 3 locations:
-Inside of caliper, where the spokes hit
-Outside of caliper mounting lugs
-Inside of fork slider lugs
For the 2 latter modifications, you'll need to space out the disc the same amount.
Personally, I dislike floating calipers/ calipers with pistons on one side only.......(That's why my stock -77 calipers, master and discs are at the bottom of a cardboard box...)

 

[Bewarethemoon]

Using YZF600 forks, blue spots will not work with a spoked wheel dammit. however.... Calipers from the Big yamaha ventures are bolt on, they have only outside pistons not inner pistons so offer more wheel clearance. The YZF legs were extra long cuz the "clip ons" attached above the top triple.
This project has a long way to go but eyeball says fork will work even with the 17" wheel, which I'm using, but will go with a taller tire.
View attachment 157203

She’s looking great Gary!

 

[gggGary]

What if you shave a off a little bit of material in these 3 locations:
-Inside of caliper, where the spokes hit
-Outside of caliper mounting lugs
-Inside of fork slider lugs
For the 2 latter modifications, you'll need to space out the disc the same amount.
Personally, I dislike floating calipers/ calipers with pistons on one side only.......(That's why my stock -77 calipers, master and discs are at the bottom of a cardboard box...)

A quick look said it was just too much to gain. I've toyed around with machining a set of wider triples which might be less work...
Hear what you say on the "slide mount" calipers. But there's a set of SV650 forks "spoke wheel ready" in the shed and I even have cartridge emulators for them but do like the external adjustments on the YZF forks.

 

[Bewarethemoon]

I was just re-looking over your build Gary and I thought “hang on a moment, those forks don’t look like mine” and then I re-read your post stating they’re off a YZF600R.

Any idea how they differ from YZF R6 forks???

 

[gggGary]

I was just re-looking over your build Gary and I thought “hang on a moment, those forks don’t look like mine” and then I re-read your post stating they’re off a YZF600R.

Any idea how they differ from YZF R6 forks???

Here's some numbers from the 2005 YZF forks as I have them set in pic above. (fully extended)
Axle CL to top of tubes 806mm
Axle to bottom of frame neck 559mm (Stock 35mm forks 552mm)
tubes C to C 200mm
offset about 32mm
Blue dot caliper inside to inside 43mm
I have also been chewing on SOME sort of handlebar damping.

 

[Grimly]

I found this site useful to see if my substution of GS1000 forks on my 850 would alter anything. The 1000s are 19mm shorter.
https://www.rbracing-rsr.com/rakeandtrail.html
According to the calculator, there's no difference, but there definitely is - the steering sharpened up just a little bit, which compensated nicely for the extra weight of the fairing. When I had a go at roughly working it out with paper, I could see that there is slight reduction in trail, but that is ok, as the lardy old GS probably had too much anyway.

 

[LEGEND_10]

Using YZF600 forks, blue spots will not work with a spoked wheel dammit. however.... Calipers from the Big yamaha ventures are bolt on, they have only outside pistons not inner pistons so offer more wheel clearance. The YZF legs were extra long cuz the "clip ons" attached above the top triple.
This project has a long way to go but eyeball says fork will work even with the 17" wheel, which I'm using, but will go with a taller tire.
View attachment 157203

Looks like you already have some mag wheels but here is a picture of Blue dot calipers installed with the r6 forks with a spoked wheel. The mounting lugs on the calipers need to be milled down and a little on the inner side of the calipers taken off. Then obviously some pretty thick spacers for the rotors were needed.