Ever since I added a fork brace to the VTR and loved it, I've been thinking of upgrading the front end to something beefier like many others have done but costs of USD forks have been prohibitive; especially when you consider that you have to get everything (wheel, spacers, axle, brakes, rotors, triple, clipons, fender). So I thought I'd look to see what else is out there.

Requirements: a minimum of new parts thus keeping costs down, more rigidity/adjustability, and these next two criteria would greatly narrow things down: keep my gixxer 6pot brakes and be able to use my superbike handlebar kit. Keeping it in the honda family would narrow it down further.

The popular 929/954/rc51 route would make it difficult to mount the bars or let me keep the brakes. Besides, good specimens go for big bucks. Older CBR900rr's are much cheaper but use an "old skool" 16inch wheel/tires combo. Latest cbr600/1000RR's have bigger steering stems and bearings so they would take too much modding/parts.

Looking further, I found the popular cbr600f4i has the larger 43mm tube diameter, a flat upper triple so I could easily mount the handlebar risers, the same head bearings as the VTR so the triples should bolt up, the same brake caliper spacing so my gixxer brakes would work, and are relatively cheap/plentiful on ebay.

HOUSTON, WE HAVE A POSSIBLE WINNER! So I got a set and proceeded to try them out.

Yup, straight bolt on affair. WOO-HOO!!!! The only things required besides the forks themselves are F4i triples, fender and possibly clip-ons (more on this later). The VTR axle, spacers, and the brakes all bolt up. I did need to shim the gixxer caliper bolts with washers to get the brakes properly centered on the rotors so I assume actual F4i spacers would prevent this. Dunno' for sure since I run a VFR750 front wheel and rotors (confused now?) :-)

So is this the perfect mod? No. The forks are 1/2 inch shorter and the triples' offset is shorter (less). What does this mean?

The shorter length means you can't really bolt clip-ons ABOVE the triple as there isn't enough length left to adequately grasp the tubes. Less offset means with the forks set to the same height as stock steering is slower so fork height will need adjusting thus also affecting available fork length above the triple.

After much experimentation on fork height, I found a sweet spot (for me): 28mm above the triples. Unfortunately as I said before, this is NOT enough height for the cbr clip-ons. So you'd either need to bolt them underneath the top bridge or utilize a handlebar mount kit as I did. Typical USD clip-ons that mount below the triple might have a higher rise than stock F4i's so they could be the answer for those who don't want to run a handlebar setup. Make sense?

So for much less than an USD setup but definitely less bling too :-( I gained excellent front end rigidity AND more adjustablilty as the F4i has both compression and rebound options. An additional plus for my weight (180lbs damn holidays!): stock f4i springs are the same rate (.800ish) as racetech's recommendation for the VTR (stock VTR is .500ish) so you are better sprung right off the bat thus further savings on this mod. Heavier riders will, of course, need higher rate springs but it will be much better right out of the box than the stock setup.

As with any mod, YMMV.

Me very happy. More later, pics too.

 

I had a feeling this was the route you were going to take when we were having our "discussions" on the brace post. I had to use Helibars under the triple on my GSXR1000 forks, (another way to keep the 6 pot brakes), but your way was much cheaper I'm sure.

It's amazing how much better some of the parts the cbr got that they could've used on the hawk somwhere through the years. Like maybe when they raised the price with no real upgrades!

 

Yeah, I've seen F4i sets go for as low as $200 (questionable ones even less), add a triple for $20-50, and a used fender $30-50 and you're good to go. All's that left is to decide on the handlebar solution.

Summation:

Pro's: Low cost, ease of installation, more rigid/feel, additional compression adjusment.

Con's: Low bling (looks like late stock/olive color), handlebar/clip-on mod.

I think if one ran low handlebar risers with a flat style bar, bar height would not be an issue with the fairing uppers (no trimming necessary). IOW, keep them at stock height or that of VFR bars.

 

Two other things, one minor/one major.

Major: Steering stops on the F4i triple appear to be the same (at least to me) thus tank clearance and turning radius seem unaffected.

Minor: The horn needs a slightly different mounting. Stock location faces back and would foul oil cooler. Using the same mounting hole, I faced it forward and juusst had enough slack in the wires with my high bars.

 

RC996 here. For some reason that account is inaccessible.

Doug. Less triple clamp offset yields more trail for a given head angle. So the stock head height should not have been more twitchy (?). remember, the offset moves the contact patch relative to the steering axis. So less offset moves the contact patch further aft of the steering axis. Good experiment!

Man I miss my bike!!!

I've got a full RC51 front end that will be coming up for sale. The fork outer tubes showed .020" and .017" TIR (total indicated runout). There is no buckling and actuation is smooth. I still need to disassemble and straighten them. They will be <.005" TIR.

More info later, as I get the time to work on it.

 

Here's a link to what we're talking about. Lot's of good info:
http://sportrider.com/tech/146_0310_art/

I realize now that I went the WRONG way the first time I set things up. The F4i forks are a 1/2in shorter than the VTR and to compensate I mistakenly raised them by that amount when I should have lowered by that amount thus I was off by an inch (nearly 30mm!!!). Heh, heh, no wonder it was steering fast! :-)

So, I slid the forks down in the triples till I found the sweet spot (for me) and that was 28-30mm of fork left above the top triples.

Lot's of fun doing this. I now greatly appreciate GP test riders, what they can do, and how quickly they can do it while dialing in new designs.

 

We need some pics superbling. Good job on a worthy mod.

 

We need some pics superbling. Good job on a worthy mod.

 

Here's how they look. Like I said not much bling factor so I just "had" to add a CF fender!

The compression adjuster is there just below the caliper mounts on the backside of the fork. The second photo shows the fork length available for clip-ons; not much. I don't know if there are any that short but I haven't looked either. I have very high bar risers (55mm). Shorter risers with a flatter rise handlebar should keep the overall height low enough to clear the fairings without any mods to them.

Click on the photos for a much larger version.

 

Very well done Doug!

I like the look of the CF front fender.

GSX-R 6 pots caliper + SS brake line + F4i calipers ( I imagine ) = a terrific brake upgrade!! I guess, don't pull too hard on the lever or your face will it the ground first!!!

Give us some feedback on how it ride with this new front end after a couple of ride!

And, if you can, post picture of the whole bike in order that we admire your work on the Superbling's machine!

Nice job again!

 

Right about the time I was putting all this together, a forum member (xcooper) sold me his ohlins rear shock. I sold my modified cbr954 penske to help fund the deal and thus had a stock shock on in the interim. So, I tried to dialed in the F4i front end while waiting for the ohlins to come in. The forks have a full race tech treatment but the stack and springs are calibrated for track instead of street so I really need to experiment with them. The ohlins is also valved for track.

I had the forks set at 28mm above the triples which is slightly lower than the stock VTR ride height to gain some handling speed. The F4i triples have less offset which is gives more trail/stability because it runs a much steeper head angle (nearly one degree less). Overall, the bike felt good but I really didn't feel like I was getting much return in terms of results on corner and exit speed. The bike definitely felt much better under extreme braking and bump compliance.

Now that I have the ohlins installed and dialed in, the handling has been transformed. I added about 5mm ride height as I wanted more steering quickness. I now realize that the stock shock was diluting a lot of the fork's qualities. Now that the rear isn't a problem, the front really shines. I ended up with both fork settings around 1/3 in and preload full soft. The shock is at 3/4's compression and 1/2 rebound and pre-load full hard.

My point being don't "waste" your money on a new front end if you're not going to upgrade the back.

 

back from the dead

I just got my f4i forks in the mail and hopefully will have them on by the wee hours of the morning