Jump to content

F4I Forks And F4I Rear Shock Info


simba

Recommended Posts

Hi there Guys,

Looking to get into the nitty gritty with the suspension on my 2004 VFR800. I mostly ride on the street (rough Canadian roads) with 1 -2 track days a year.

Due to my size and weight (5'8" and 135lbs) I find that the bike is actually over-sprung in the rear and takes alot of commanding to turn at low speeds.

I also wanted to add some more adjustability to the front forks as they seem under valved( harsh)

So far I have purchased a set of F4 or F4i forks (cannot tell due to being very similar but could be .66kg or .77 kg springs) along with a very good condition set of 4 pot calipers.

These will need to be re-sprung! but I'm unsure as the best way to do the calculations for the increase, (race-tech shows vfr800 with my weight should be .86 kg springs, but when using vfr weight on the CBR600F4i calculator it recommends .95 kg springs( seems too stiff)

If the .86 is the correct calculation is it possible to use the VFR800 springs in the F4 forks? (using the preload spacer to accommodate for slight length variations)

Also Any recommendations about Valves? Racetech? Ohlins? DIY??( I have herd of polishing the pistons and making your own stacks but dont know the science) I would also contemplate sending the valves to DM for upgrade( forks are currently disassembled)

My next questions relate to the rear shock, My expectations is that the F4i rear shock will also be the replacement for the VFR stocker.

Are there any higher performance shocks that could be fitted the the VFR? 600RR 1000RR GSXR1000? or do all these newer designs have fitment issues?

If i am to use the F4 rear shock as the best inexpensive starting point Again what is the best way to calculate spring rate, some results from Racetech show the stock 14.3 kg unit as acceptable for my weight, other times it says its too much?????

Once a spring is chosen, what should be done for valves? Racetech?, diy?, send to DM?

Open to any suggestions or ideas to improve the ride and performance!

Thanks in Advanced!

Link to comment
Share on other sites

  • Member Contributer

These will need to be re-sprung! but I'm unsure as the best way to do the calculations for the increase, (race-tech shows vfr800 with my weight should be .86 kg springs, but when using vfr weight on the CBR600F4i calculator it recommends .95 kg springs( seems too stiff)

RT basically consider the CBR as a sportsbike, expected to handle as such and be used as such (e.g. track days, smooth twisties), and the VFR as a sports-tourer.

Evidence for this is their 'Recommended Preload' which is 10 mm for the CBR and 15 mm for the VFR. This is IMO why inputting the VFR's weight on the CBR page yields a stiffer spring rate.

Link to comment
Share on other sites

  • Member Contributer

Are there any higher performance shocks that could be fitted the the VFR? 600RR 1000RR GSXR1000? or do all these newer designs have fitment issues?

If memory serves, these bikes all have a clevis as lower shock mounting point and a significantly lower linkage ratio than the VFR with correspondingly (much) lower spring rates. These will require some serious mods to be usable.

Older CBR 600 F and CBR 900/929/954 were more similar to the VFR but the V4 architecture and the LBS/ABS plumbing also puts physical space at a premium so even these do not fit all that well.

DMr offer the CBR F4 shock for the 6G and the 929 for the 5G. They are the best fit but they still require mods to get the proper length and access to the adjusters may not be all that great, especially preload on the 6G/F4 swap.

Link to comment
Share on other sites

  • Member Contributer

If i am to use the F4 rear shock as the best inexpensive starting point Again what is the best way to calculate spring rate, some results from Racetech show the stock 14.3 kg unit as acceptable for my weight, other times it says its too much?????

Not sure what you mean by 'some results' from RT. At your weight, RT recommend a 17.8 kg/mm spring for the 6G.

To 'calculate' spring rate you need to have some pretty accurate figures for sprung weight, weight distribution and, most importantly, linkage ratio. These are not very easy to come by and the linkage ratio is a VFR peculiarity (significantly higher leverage than most anything else on the market these days).

If you used another bike on the RT calculator and input the VFR's weight, that might give you acceptable results for the forks but the shock will likely be way off.

Link to comment
Share on other sites

  • Member Contributer

Due to my size and weight (5'8" and 135lbs) I find that the bike is actually over-sprung in the rear and takes alot of commanding to turn at low speeds.

That seems unlikely. Check your sag, adjust your preload accordingly and play with the damping adjuster a bit.

The (admittedly pretty rubbish) stock shock is softly sprung but can be adjusted very hard, especially at your weight. I'm over 210 w/o gear and it kicks like a mule if I give it too much preload and turn the adjuster near full hard.

Link to comment
Share on other sites

Are there any higher performance shocks that could be fitted the the VFR? 600RR 1000RR GSXR1000? or do all these newer designs have fitment issues?

If memory serves, these bikes all have a clevis as lower shock mounting point and a significantly lower linkage ratio than the VFR with correspondingly (much) lower spring rates. These will require some serious mods to be usable.

Older CBR 600 F and CBR 900/929/954 were more similar to the VFR but the V4 architecture and the LBS/ABS plumbing also puts physical space at a premium so even these do not fit all that well.

DMr offer the CBR F4 shock for the 6G and the 929 for the 5G. They are the best fit but they still require mods to get the proper length and access to the adjusters may not be all that great, especially preload on the 6G/F4 swap.

This is what i suspected about the newer bikes.

I will be pulling all the linked braking and associated brackets. Is the 929 shock preferred if it can be made to fit?

I have herd there is a special wrench that makes the f4i preload more feasible.

If i am to use the F4 rear shock as the best inexpensive starting point Again what is the best way to calculate spring rate, some results from Racetech show the stock 14.3 kg unit as acceptable for my weight, other times it says its too much?????

Not sure what you mean by 'some results' from RT. At your weight, RT recommend a 17.8 kg/mm spring for the 6G.

To 'calculate' spring rate you need to have some pretty accurate figures for sprung weight, weight distribution and, most importantly, linkage ratio. These are not very easy to come by and the linkage ratio is a VFR peculiarity (significantly higher leverage than most anything else on the market these days).

If you used another bike on the RT calculator and input the VFR's weight, that might give you acceptable results for the forks but the shock will likely be way off.

Due to my size and weight (5'8" and 135lbs) I find that the bike is actually over-sprung in the rear and takes alot of commanding to turn at low speeds.

That seems unlikely. Check your sag, adjust your preload accordingly and play with the damping adjuster a bit.

The (admittedly pretty rubbish) stock shock is softly sprung but can be adjusted very hard, especially at your weight. I'm over 210 w/o gear and it kicks like a mule if I give it too much preload and turn the adjuster near full hard.

Ahh i must have been using the wrong calculator when I was crunching some numbers. Makes me wish I could go try more suspension settings, (damm snow!) as I haven't gotten this bike to turn at low speed as I would like.

So 0.90 springs for the front and 17.8 for the rear. Would the stock 0.85 vfr springs work in the F4i forks?

Any suggestions on re-valving either the forks or the rear shock?

Thanks for replying RC36!

Link to comment
Share on other sites

  • Member Contributer

I have done pretty much what you're planning (front forks re-sprung, revalved, brake de-linked, CBR929 shock installed), but on a 5th gen, and have also changed the suspension and brakes on my VTR1000F.

For the fork you could buy RT parts (specifically a compression Gold Valve which comes with a handy bag of shims) and work out your own shim stacks (RT provide some good guidance), and make up spacers as needed to suit the springs that you have. You can use PVC pipe for spacers, very easy to cut and cheap. As long as the springs you are using aren't too long (ie they stick out the top of the extended forks) then they'll be fine with the correct spacer. For the shock you could make up an extended clevis to offset the shorter shock, and try the standard spring first.

Or...you could buy all the correct parts from Jamie Daugherty who will provide you with the specific bits to suit your weight and preferences. He modifies the shock itself to make it longer, and alters the shim stack as well, and provides a rider-specific spring. IMO his fork part pricing is the same or a little below RT, for very similar parts, and his modified shocks represent very good value.

One thing that may help your bike turn in is raising the rear and/or dropping the front to steepen the geometry. You can slide a spacer between the shock clevis and the frame (up to 5mm is pretty common) which will drop the back wheel by around 25mm, and the forks can be slid up through the clamps by up to 10mm before any hard parts make contact. This will make the steering livelier and more eager to drop into bends without affecting high speed stability too much. However in the first instance I'd make sure that you were running tyres that aren't badly worn e.g. squared off at the middle, as that will have a big effect on turn in.

  • Like 4
Link to comment
Share on other sites

  • Member Contributer

Would the stock 0.85 vfr springs work in the F4i forks?

Any suggestions on re-valving either the forks or the rear shock?

Both bikes have 43 mm RWU forks and RT use the same spring reference (FRSP S3732) for both bikes so it seems likely that they will swap just fine.

I know RT say that they are 0.85 but that figure has been questioned on this board (0.74 has been quoted). They are also definitely dual rate springs (taper + uneven spacing of the coils).

As for re-valving, forks are relatively easy to work on but it's a messy and time consuming job especially if you go your own way and have to go through several iterations.

Reworking an OEM Showa typically requires drilling and tapping to install a nitrogen valve, a safe way to compress the spring (downright dangerous amounts of force required) and you'll have to find someone who can recharge the nitrogen when you're done. Might be more trouble than you've bargained for.

RT will give you a generic kit of loose parts and (vague-ish) instructions on how to select a suitable shim stack. DMr will send you a custom pre-assembled shim stack. There are other vendors (Öhlins, Penske ...) but I don't know what their kits look like.

Don't want to discourage you. Just trying to give you a fair idea of what you're letting yourself in to. :wink:

Link to comment
Share on other sites

  • Member Contributer

So 0.90 springs for the front and 17.8 for the rear.

I am certainly no expert but based on what I could gather (from this board, Öhlins, my own experience with 0.90 fork springs) that sounds fairly reasonable to me. Should give you a firm setup (on the sport side of sport-touring) but nothing like race hard.

I reckon (own calculations) that will give you about 35 mm of front-end sag @ 15 mm of preload which is a good ballpark for spirited riding on public roads.

Note that spring rates play a fairly minor role in how harsh your suspension will feel. Damping is mostly what causes harshness (aside from excessive friction) so bumpy/crappy roads are not a good reason to go to lighter springs.

Shock spring rate on the 6G should be about 20-22 times the fork spring rate. Taller/heavier guys should aim for 22, 20 for shorter/lighter folks.

Feel free to question my 'wisdom'. :wink:

  • Like 1
Link to comment
Share on other sites

  • Member Contributer

Just checked my records and the DMr recommendation for your weight class is 0.85/18.77 (1050 #/in actually as he uses US made springs) for a ratio of 22+.

I hope he'll forgive my audacity if he reads this but my own research suggests that this shock spring rate to fork spring rate is a bit on the high side for lighter riders. Might serve you well if you ride with pillion/luggage, though.

  • Like 1
Link to comment
Share on other sites

Wow Thanks for all the Help guys!!!!

I agree that i will try the stock VFR 0.85 springs before I go buy a set of Ohlins 0.90 units.(not very hard to change after)

The next purchase will have to be the Racetech valves, weather they are from Racetech or from Jamie (would love to give him a lil extra $ for some baseline shim stacks) im not sure yet.

Forks are apart and working on sandblasting/ repainting the lower legs.

In regards to the rear shock, I have no issue with making some custom adapter for my wall mounted automotive spring compressor to remove the spring and I have talked with a few locals that will recharge the shock for a reasonable cost.

Again would love to buy the valves from Jamie, Its clear now that i have a game plan I should get in touch with him and is wisdom!

Will prolly do the forks first but will look at the rear shock shortly after.

Thanks again for the help guys!

Link to comment
Share on other sites

Wow Thanks for all the Help guys!!!!

I agree that i will try the stock VFR 0.85 springs before I go buy a set of Ohlins 0.90 units.(not very hard to change after)

The next purchase will have to be the Racetech valves, weather they are from Racetech or from Jamie (would love to give him a lil extra $ for some baseline shim stacks) im not sure yet.

Forks are apart and working on sandblasting/ repainting the lower legs.

In regards to the rear shock, I have no issue with making some custom adapter for my wall mounted automotive spring compressor to remove the spring and I have talked with a few locals that will recharge the shock for a reasonable cost.

Again would love to buy the valves from Jamie, Its clear now that i have a game plan I should get in touch with him and is wisdom!

Will prolly do the forks first but will look at the rear shock shortly after.

Thanks again for the help guys!

Stock fork springs are .744 like mentioned, not .85.

Personally at 135 lbs I would test and measure rider & free sag before any spring change from stock on either end first. I wouldn't think you would need too much of a spring rate increase except maybe the rear at a stock 15.3. Seems like a 17kg or abouts should in the ball park.

If you are de-linking the brakes and removing all associated items especially removing the mini rear subframe from the rear of the frame that supports the brake lines and blocks then the 929 shock will work nicely and has the same spring rate as the VFR's 15.3 kg.

The F4/F4i forks are shorter, I think on my bike ther was only an inch or so above the top triple clamp. I ran stock F4i clip-ons, but they hit the top of the side fairings at full lock.

post-301-0-25651800-1452902960.jpg

post-301-0-46429800-1452902981.jpg

post-301-0-07765100-1452902997.jpg

post-301-0-73532200-1452903102.jpg

post-301-0-73524600-1452903119.jpg

BR

  • Like 3
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

By using this site, you agree to our Privacy Policy.