Topic: Clip-Ons and front end stiffness?

[Scott S]

 I've got a little over 100 miles on the "Sweep the Floor 2" bike and it's running great. The suspension is pretty stiff, though.
 I read up on CB1100F shocks and made adjustments there (though they may always be a little stiff, as the springs have been cut. That's why my buddy gave them to me. They are the correct length for a CB550 now, though).

 The front forks are CB750. I don't have a clue what year they're from and I know different years used different fork oil amounts. It's been so long since I did them that I can't remember how much oil I used.
 Because 750 forks are longer that 550 forks, I was able to push them up through the triple and install the clip on's above the top triple. The length from the bottom triple to the axle is still stock 550 length/

 The front end seems very stiff. I'm considering letting out a little oil from each fork until I get the feel I want.
 Do Clip On bars transmit more "shock" to the rider? Even pushing down on the front end in the driveway, it seems very stiff. I'm wondering if I used too much oil for whatever year forks I have?

[flybox1]

got a pre-load spacer in there you can remove first?

[Scott S]

 Hmmm....I honestly don't remember. I guess it would be easy enough to take a cap off and see.

[Kenzo]

Cutting the springs significantly increases the spring rate. There are probably spacers installed too.

The larger the air gap makes it act like a softer progressive spring.

The heavier the fork oil the stiffer/slower the fork action.

Also fork alignment is important.

One can assume the stock CB1100F forks are sprung for a significantly heavier bike, after being cut they're not even in the ballpark of what you need. I'd start with the springs since everything else is a band-aid to try to correct the cut springs.

Cheers,
Kenzo

[Scott S]

 To clarify: The rear SHOCKS are CB1100F and the springs were cut on them to lower an 1100F. I was able to set all three adjustments to the softest settings and I think they'll be fine. If not, I'll order some replacement springs from Progressive.

 The FORKS are CB750. I don't know what year. The springs in them are stock and uncut. I'm pretty confident alignment is good. I've had problems with that in the past on other bikes and now I'm always sure to install the forks/wheel/axle, etc. correctly. I can let go of the bars at speed and it tracks straight and true with no wobble.

 I should be able to pull the fork caps one at a time without the suspension collapsing on me, right? No center stand on this bike. The frame was already de-tabbed when I got it.

[calj737]

Its been my experience that clip-ons do feel "stiffer". Often the body position has more weight on your wrists than on your hips, and that translates into stiffer.

[Scott S]

 That's what I thought, but even pushing down on the front end in the garage, it seems very stiff. I wasn't sure if I just don't have the leverage I would have with a set of handle bars or what?

[DaveBarbier]

I should be able to pull the fork caps one at a time without the suspension collapsing on me, right? No center stand on this bike. The frame was already de-tabbed when I got it.

Yes, but with the front under a little load it will be more difficult to get the cap back on. As you remove the cap, put a lot of pressure downwards so it doesn't go flying.

Regarding your first question: Maybe theoretically clipons will transfer more shock to your hands but I'm sure it's not noticeable.

On the other hand, maybe because you're body is angled down with more of your weight on the clipons it feels more rough?

[Scott S]

 Did some 750's come with spacers and some without? That's the only reason I'd remove the cap: to check for a spacer and measure the length. Whatever is in there is stock for those forks, though.
 

[Kenzo]

Doh...the 750 forks are still probably sprung a little heavy.

Most fork and I assume these will collapse when weighted if both caps removed at the same time.

Have you changed the fork oil? Setting the air gap and/or proper volume of oil very important. Overfilled can make them very harsh.

I assume there is a huge difference riding with clip-ons but in the garage with a hand full of front brake you should get a firm but smooth action through 3/4 of their travel.

Good Luck,
Kenzo

[SOHC4 Cafe Racer Fan]

The 750 forks are sprung for an additional 90 plus lbs.  You may need to go with lighter springs.

If the springs are too stiff, the front will lose traction when it goes over larger bumps.  Not so good in turns.

[Scott S]

 Well, that makes sense. If I can't get it acceptable with the oil level/weight, I'll look into springs for the forks and shocks.

[Scott S]

It handles fine on smooth roads, but big dips or a road with frost heaves and it gets too jumpy.

 I could only push down through about a third of their travel, when it should be closer to 3/4.
  I used my graduated cylinder and a syringe to remove 12cc from the drain hole of each fork. That seems to have helped in the "grab the brake and push down" test. I'll ride it again later on and see if it actually did anything, though it did give me more travel....about 1/2 way now.

[flybox1]

Stock springs do not come with spacers, and yes, do one at a time or you'll have your front on the floor 
I switched to progressives.  Without the spacers, its REALLY soft...like bottom out soft under hard braking.
With the spacers, its about perfect.   I prefer ATF(7w) over fork oil(15w)

[Scott S]

 I have access to a set of Progressive fork springs but my buddy took them out because he said they were too STIFF!
 If I install them without spacers, they're actually softer?

 I used 10W fork oil.

[Lostboy Steve]

Stock springs do not come with spacers, and yes, do one at a time or you'll have your front on the floor 
I switched to progressives.  Without the spacers, its REALLY soft...like bottom out soft under hard braking.
With the spacers, its about perfect.   I prefer ATF(7w) over fork oil(15w)

I found the same to be true for mine.

[BomberMann650]

1/3 of travel....not alignment related?

[Scott S]

 I had an XS650 once that the forks were binding because on an alignment issue. This is not like that...they're just stiff. Very firm forks.
 I'm willing to listen to suggestions, though. But I installed forks, tightened top triple, installed wheel, axle and fender and just left everything finger tight/snug. Pushed up and down on forks to align lowers/axle. Then tightened lower triple, axle nut, fork end caps and then fender.
 I'm not saying it's NOT an alignment issue, but I don't *think* it is.

[seanbarney41]

pretty sure 750 springs are gonna have too high of a rate for a 550...as mentioned earlier we are talking about a 90lb difference.  Maybe more.  The stf2 bike looks to be considerably lighter than a stock 550.

I had a similar problem after swapping a gl1000 fork onto my 750.  The stock gl springs had much too high a spring rate.  I just emailed Race Tech, bought the recommended parts(new springs, emulators, and adapters)and asked for set up instructions.  The set up provided has got my front end to be very good...a few tweeks and it will be ideal.

[Stev-o]

I switched to progressives.  Without the spacers, its REALLY soft...like bottom out soft under hard braking.
With the spacers, its about perfect.   I prefer ATF(7w) over fork oil(15w)

From what I've read, The Progressive springs come with the spacer for the K7-8 bikes, their forks are a little longer than the early models.

I have Progressives w/no spacer and ATF and is good for me.

[scottly]

The K7/K8 lower legs are longer than the earlier 750s. From the axle centerline to the top, the early ones are about 12.5", and the late are about 14".
I noticed the same symptoms with the K7 front end on my bike, after adding the recommended amount of ATF. Since my bike is a lot lighter than a stock K7, I figured the springs were too stiff, and, if I recall correctly, there were no spacers. I think the earlier 750s did have spacers? I tried some 550 springs (thanks David!), but it didn't really help. I finally drained some ATF, and got a much better fork action. With the front wheel off the ground, I checked the fluid level with a dip-stick from the top of the forks with the springs installed, and the level was something like 16"? It might be a little low, but Bot's Dots don't hurt my hands anymore.

[Rookster]

It looks like you have a the K2-K6 type fork.  There should not be a spacer with the stock setup.  There is a washer between the fork cap and the spring only.  With the Progressive springs you will need to use a preload spacer.  The Progressives come with a 1-1/4" preload spacer.  I used a 1" spacer instead with Progressive springs and ended up with 29.3 mm fork sag.  To get a basic setting I would check the sag with what you have and then go from there.  Fork sag should be close to 30mm for a street bike.  If the stock spring is too stiff then there is no fix other than to replace with a softer spring.  The Progressives should allow you some tuning by shortening up or eliminating the preload spacer.

Scott

[PeWe]

Progressive springs in my CB750 K6 fork. It was too stiff with 15-20mm spacer. Nylon spacer to be cut to fit. The instruction show a drawing about the preload and how the top nut can affect it. CB750 nut has inbuilt spacer. I added some washers to get a preload not ending up in too stiff fork. Maybe 2 washers of 3mm on each spring (6mm).
Oil level acccording to instruction that say minimum 140mm from top of tube to oil level with forks collapsed and no springs in.
I use Motorex 15W-30.
Fork is to the softer, can be a little bit stiffer, not much more.
Ok for street an inspired riding looking for flashing blue lights in mirrors.

[scottly]

I checked the level with no springs and the forks fully compressed: 8.5". Like I said before, this may be a bit low, but before lowering the level the forks seemed to bind up after about 2" of compression.
As far as spring rates, my bike is about 410 pounds with an empty gas tank, and I weigh about 130 pounds fresh out of the shower. The K7 springs don't feel excessively stiff to me, but the 550 springs with appropriate spacers might be a better match.
In the attached pic: K7 springs at the top, K1 springs with stock spacer in the middle, and 550 springs on the bottom. Notice that the 750 springs are all straight-wound, while the 550 springs are progressively wound.

 

[Scott S]

 I set the shocks to the softest settings all the way around (3 adjustments on 1100F shocks) and took 12cc of oil out of each shock. That definitely helped, but the front end is still a little stiff. I may try removing a little more oil.

 Eventually, I'll probably call Race Tech or Progressive and ge some replacement springs for both ends. Or, if I stumble across a set of 550 springs for the forks, grab those and make some spacers....just as an experiment if nothing else.

[Scott S]

I can get a set of Progressive fork springs, model #11-1104, for a really good price. These are the springs that come with a spacer. Here are some specs from the Progressive site:

 Free length: 19.12"/486mm
 Spring rate: 35/50 lbs./in or .63/.89 kg/mm
 Spacer: 1.30 inches

 If these are the ones that are softer WITHOUT the spacer, I'm thinking about giving them a try and then contacting Progressive about springs for the rear shocks.
 Any input on springs for the shocks? The 1100F shocks are ~13.25" from eye to eye and the spring itself is only about 8" long on the softest setting.
 What's a good length and spring rate to keep that approximate ride height on a ~415 lb. bike with a 180 lb. rider?

[scottly]

Here's a fork-spring rate chart someone posted here a while ago:

[Scott S]

 Looks like the fork springs might be just about right.
 Do you get the shock springs rates the same way?