Hey guys, need your help...so over winter after dropping the bike and bending one of the forks i got a full F4i front end.

anyways, today finally i took it out for a spin after it sitting dormant for the winter. first thing i noticed is that the front end is really twitchy, it REALLY wants to just drop over. when in a corner i physically have to push on the inside handle bar so it doesnt fall over even more (make a tighter turn). i'm sure that has something to do with the front end geometry...right now the F4i forks are installed what the stock VTR forks would be installed like....

thats one issue, issue number two is that the front end dives a lot under braking and comes up during hard acceleration. I thought the F4i front forks were supposed to be stiffer?

so what are people with the F4i fronts running suspension wise? any recommendations?

i'm 200 lbs if tht helps to help me setup the forks...

Much appreciated!

oh, and is it supposed to backfire like a **** with Yoshimuras? as soon as i let off the throttle it pops..

 

Enjoy the backfire cuz the rest of us do

As far as F4i fork legs go I don't know much about them but you can check with these guys:http://www.fireblades.org/forums/honda-cbr-600/

 

Some very wild stabs in the dark here.
The F4i front end reduced the trail and may be shorter so the rake is reduced too.(can't find specs so can't compare). Something seems wrong with the fork oil (waaay too light?.Not enough?) . Leaky exhaust joints somewhere.

 

Do the PAIR removal, found in the KB section, and that will reduce if not eliminate the backfire.

 

Falling in to a corner is generally caused by too much trail (the contact point on the tire creates too much leverage and causes it to steer further in the direction of the turn). Is the front end higher than before? The F4i may have less triple clamp offset, which gives you more trail for a given head angle. You will probably need to either raise the rear, by shimming the shock at the top or drop the front by raising the forks in the triple clamps to increase the head angle.

You need to dial in some damping, both compression (braking) and rebound (acceleration). Rebound adjusters are on top, compression on the bottom.

That should at least get you on to the playing field, so you can start on a baseline setup.

 

According to RaceTech info the VTR forks have a 0.585 kg/mm spring rate, the F4 has 0.750 and the F4i has 0.660. That's all fine and dandy, but it doesn't mean squat without knowing the rest of the set up .....

How far into the triple clamps are the forks? What's the sag set to? What oil is in there and how much? What do you have the rebound and compression adjusters set to? So many questions .....


Also, it just so happens that I have a pair of RaceTech S3732085 springs here that I was gonna put into those forks before you bought them from me. They are rated at 0.85 kg/mm, so they'd be a noticeable difference from what you have now. Think about if you'd like them. These are BNIB and you know i'll give you a good price.

 

If you're pushing on the inside handlebar that will make it turn tighter.

 

Truth.. counter steer ftw..

 

simple thing is just double check the tire air pressures. one of my bikes is very sensitive to air pressure giving that flopping feel otherwise, what RCVTR said.
To determine if your spring rate/spacer length is in the ball park you could start by just measuring sag. Finally, are the F4 forks same length as vtr?

 

Let me rephrase the push steering thing

this is at very low speeds, as in residential area, 15mph, before push steering comes into play...

you feel as if by pushing on the inside steering handle you are physically stopping the bike from turning even more...

i'm at work now but as soon as i get home i'm gonna adjust the suspension...thanks for the tips guys

 

Ahh, I thought so. Too high in the front.

Once you get a bit of speed, you steer the bike by turning the front wheel away from the center of mass, to make it lean over (countersteer). Then to stand it back up, you have to steer the front wheel back under the bike.

At very low speed you don't lean the bike over to turn it, you turn the front wheel in the direction you want the bike to go. Exceesive trail makes it turn more as it starts to lean over.

Set your damping in terms of clicks out from all the way closed (clockwise is closed). As a guess, I would say something like 12-15 clicks out from fully closed on compression and rebound. Somebody with experience with F4i forks can give you a better answer.

 

Actually, I'm thinking the opposite. The F4i forks that I have are shorter than the VTR's by a good amount (going by memory). This is by no means a direct swap! I'd say Red_Liner is running too steep a rake angle. That would cause the 'falling in' effect because the front end will be way too twitchy. In fact, I'd say it's borderline dangerous. It's also dangerous because your front wheel will probably be able to hit the front cylinder head on full compression. This is especially bad because, as noted, the F4i forks are way too soft for the VTR w/ 200lb rider.

Red_Liner: check everything out and I'll bet that you'll find it's a geometry issue.

 

Hmmm....

I recall the 600RR forks beig too short. 900RR too. that's when I decided to go with RC51 forks.

I thought the F4i forks were closer to the VTR. Doug (superbling) had them on his VTR, but not sure what he did to make them work.

Time for some measurements.

 

The F4i forks are most decidedly shorter than stock... How much I'm not sure of, but I'd say about the same as the 929/954 or there abouts... I checked a buddies F4i when doing research for my swap and decided against it, as they would need new springs for me... And I'm also at 200+...

With a 200 lbs rider on there they will be seriously short as they are compressed the same way as the soft OEM forks are...

Are you using the F4i triple tree? it's not a gull wing if I'm correct? Try finding a gull wing upper and a higher clip-on and it should put you back at stock height or close to it...

 

okay guys, problem has been solved.

as someone mentioned earlier, the tire was low on pressure, by a lot...

it was so weird to ride it to the gas station to get some air in, that at 40km/h letting go off the handle bars it would start to oscillate really bad, lol, imagine a really slow speed tank slapper...

anyways, got it up to proper pressure and she rides good.

reading up on the F4i front end on VTR's i raised the forks up in the tripples 30mm above the top tripple...which means that above the clipons they stick up a bit....but now everyone is saying that with the F4i forks being shorter i shouldnt do this....i think i'm going to lower them so they sit flush with the clipons

also, i'm a newb when it comes to suspension adjustments....so there are 3 adjustments on the F4i forks?

the little flathead screw on top which i take is for compression? the little fltahead on the bottom of the forks which is for rebound? and whats the 14mm screw on top of the forks for?

please enlighten me...

thank you!

 

I would try to maintain bike geometry as close to stock as possible, then tweak little by little from there. Yes, the F4i forks are shorter, though I don't remember by how much, but I'm thinking close to 20mm. By raising the forks in the triples an additional 30mm you are probably beyond the point of instability and fully into the danger zone. Getting the front wheel light could send you into a tank slapper that you won't recover from. Case in point: Generally a low tire pressure wouldn't give you a "slow speed oscillation" like you had. You should also ensure your steering head bearings aren't too tight. That could give you the same type of oscillation.

The other thing you comprimise is cornering clearance. Do NOT dive heavily into right handers with the forks like this. You'll drag the front header and lift the front wheel off the ground. This usually does not end in your favor.

I recommend setting them even with the clip ons.

Top screw is rebound. Bottom screw is compression. Top outer adjuster (with lines?) is preload.

 

Good call. 20 mm low in front is a lot. 50 mm is scary. Especially since you probably have too much sag as well.

If your forks are short, I would recommend that you get them spung properly for your weight. At 200 lbs, you probably need 1.0 kg/mm springs on a VTR. 0.95 kg/mm at a minimum. Go with spring rates recommended for your suited rider weight for a VTR, not an F4i, because the bike is heavier.