Suspension Upgrade - moving forward after the build

[clem]

Well, I went and shifted gears on this whole extravaganza. After I went back and remeasured some of the existing geometry I realized that the current front end does not have the appropriate amount of offset. It currently has 30mm which give me +4 on trail. I don't want to state exactly how much because someone is liable to ask me if I am trying to build a Honda shadow clone. I ordered a set of EX250 forks(37mm) to match up to the rear end. These are smaller than the current ZX6(41mm). I don't have the exact amount of offset on the EX front end but figured it to be about 50mm by calculating the listed rake and trail numbers. I am going to see if I can position the forks to get close to 27 deg. rake which should put me closer to the 3.5ish stock trail for the YDS7. The EX250 is about 30 or so pounds heavier than my bike so lighter springs may be needed but since most 250 Ninja riders complain that the front is too soft for that bike in stock form it may work fine. They sell aftermarket preload adjusters for those forks and of course emulators will be needed to fine tune the front end.
I removed the GSXR shock and replaced it with a stock EX250 shock until I can have the GSXR shock re-valved and re-sprung. Hopefully I'll get it all back together soon.

One question that I have is concerning the height of the top of the steering tube. I have seen some people add a spacer on the top of the upper bearing race to make up for the longer stem in the EX triples. By doing this would that raise that measurement or does it still need to be tallied from the actual top of the neck? I may just press in another DS7 stem but wanted to see if this was a viable option. Thanks

 

[xb33bsa]

Well, I went and shifted gears on this whole extravaganza. After I went back and remeasured some of the existing geometry I realized that the current front end does not have the appropriate amount of offset. It currently has 30mm which give me +4 on trail. I don't want to state exactly how much because someone is liable to ask me if I am trying to build a Honda shadow clone. I ordered a set of EX250 forks(37mm) to match up to the rear end. These are smaller than the current ZX6(41mm). I don't have the exact amount of offset on the EX front end but figured it to be about 50mm by calculating the listed rake and trail numbers. I am going to see if I can position the forks to get close to 27 deg. rake which should put me closer to the 3.5ish stock trail for the YDS7. The EX250 is about 30 or so pounds heavier than my bike so lighter springs may be needed but since most 250 Ninja riders complain that the front is too soft for that bike in stock form it may work fine. They sell aftermarket preload adjusters for those forks and of course emulators will be needed to fine tune the front end.
I removed the GSXR shock and replaced it with a stock EX250 shock until I can have the GSXR shock re-valved and re-sprung. Hopefully I'll get it all back together soon.

One question that I have is concerning the height of the top of the steering tube. I have seen some people add a spacer on the top of the upper bearing race to make up for the longer stem in the EX triples. By doing this would that raise that measurement or does it still need to be tallied from the actual top of the neck? I may just press in another DS7 stem but wanted to see if this was a viable option. Thanks

right on clem get after it
the bottom yoke and how far from the front axle it is would be one point of reference you could to use

what happens up top does not effect the height unless adding the spacer forces you to slide the forks up higher to breed
the top yokeholes
kinda got a mind block going eh ?

 

[irk miller]

Some may argue the appropriateness of it, but to install an RM front end on an XL frame I cut out the top of the steering tube from the RM, machined it to set in the top of the XL tube and seat at the same level of the original XL race. Then welded it all in place. So my lower bearing utilizes the Honda sized race and the upper is RM, plus it extended my steering tube enough to fit the RM stem. Had I not had an RM frame to cut up, I would've machined a spacer just the same. The geometry would've changed had it been done on the bottom of the tube, but not at the top.

 

[sav0r]

My experience is that most bikes tend to be a little undersprung from the factory. This is especially true with older bikes. And even more so when you consider that most nuts who are willing to go through this much shit to make a bike fast are going to ride harder than 90% of the population. I guess what I am getting at is that you shouldn't sweat the spring rate of those forks, they will probably be spot on. I generally like to achieve my minumum sag numbers (plus maybe 5%) with the least amount of preload as possible. This means you end up with the stiffest spring that still achieves the right sag. My current suspension for example provides 25% sag with zero preload. As a result you get the most bump resistance possible on a straight rate spring, your bike will have the most platform stability you can achieve outside of dampening, and means you can get away with as little dampening as possible should you need to do so.

As for the stem, I used a spacer on mine for a few months until I had fully satisfied with all of the parts. At that point I cut down the stem. Easy.

 

[clem]

I think the spacer on top is what I'll do for now, I can always add threads later if needed to bring the top clamp down. Anybody up for a set of ZX6 forks with triples and clip ons?

Sent from my SAMSUNG-SM-G920A using DO THE TON mobile app

 

[sav0r]

I cut a plug on the lathe and sectioned out the middle of the stem, then welded it back together with the plug in the middle. No threading required. Took less than an hour.

 

[canyoncarver]

Anybody up for a set of ZX6 forks with triples and clip ons?

Seriously? Pm'd.

 

[clem]

I've have been wanting to update this for a week but just got the chance so here I go.
It took a couple of weeks to pull all of the parts for a new EX250 front end together. As you may know I already had the EX250 wheels and brakes set up on the bike with the ZX6 front end. Anyway, I did as suggested and cut the EX250 stem down, turned a plug and re-welded the stem back together to fit the DS7 neck. I took the bike out on a 465 mile trip through Arkansas with the new setup and immediately felt a difference in the steering/handling characteristics of the bike. I never got a chance to ride the stock setup since the bike was trashed when I got it so I can't compare what I have now to the stock bike.
The bike now turns in and settles through the corners well whereas before once you were into the corner it would want to push the front end straight. The springs feel good for the bike weight although I can see where stiffer compression would tighten up the underbraking and turn in feel. One of the fork seals gave up on me during our trip and the bike still outperformed the previous setup. This was an expensive lesson that I learned here and I hope that someone else considering doing a swap accounts for all of the variables to actually improve the bike.
The rake sits at 27 deg under the current ride height now with a trail of 3.5xx". I think that now being at the point of having the complete STOCK EX250 suspension on the bike I can attempt to fine tune it through valving upgrades and so on.
Through this exercise I can clearly state that a bike with 70's geometry will not handle well with the newer sport bike front or rear ends unless you can find something with a setup that is near identical to what came off of the bike. If a guy throws a GSXR600 USD fork and triples on and old CB and says that it improves the handling he either doesn't know how to ride a motorcycle or he doesn't want to admit that he screwed up.

 

[sav0r]

A big problem with modern forks upgrades, outside of simply managng spring rate, geometry, and damping properties of the forks themselves, is that a system of springs is only as good as the softest spring. So you better start improving swingarms, frames, bias ply tires, and the list goes on if you expect to gain much. And if you look through the evolution of technological advance a lot of these items developed hand in hand. As a result supplanting modern technology doesn't directly result in improvement, not without significant study anyways.