Fork conversion to Gen 7 forks and triples?

[sfdownhill]

Has anyone tried using VFR1200 triples and forks for their Gen 3-6 front end conversion?

Does anyone know of any significant reasons not to use VFR1200 forks and triples on earlier gen VFRs? 

JZH wisely observed "Most people would say that if no one has ever done a particular VFR mod, there's probably a reason. Oh. Yeah, that does make sense..."

In searching and following numerous fork upgrade / fork conversion threads on this and several other websites, it strikes me as odd that no one has mentioned or posted a conversion of earlier Gen VFRs to 7th Gen USD triple clamps and forks. I did see one person [JZH, as quoted above] use VFR1200 triples on his Gen 3, though he did not specify whether he intends to use VFR1200 forks as well. 

JZH stated pros and cons of VFR triples pretty clearly:

Pros:
- sturdy upside down configuration
- radial brakes
- 35mm triple clamp offset [Closer to Gens 4-6 40mm offset than most sportbike USD triple clamp offsets which are 30mm]
- Honda steering bearing compatibility
- Usable steering stop tabs [With slight modification]

Cons:
- to use the VFR1200 triples on the RC36 Gen 3, the upper fairing bracket needs to be cut and modified
- the lower VFR1200 clamp is an unusual 55mm diameter [Almost all other USD forks use a 54mm bottom clamp]
- the upper VFR1200 triple clamp is not a true gull wing like the popular CBR929 upper clamp, so it does not provide extra space to mount handlebars above the triples when using forks shorter than stock.
- it's not easy to find VFR1200 triple clamps

And one more downside I've noticed:

- Only the Deluxe Model VFR1200 forks have rebound adjustment

[CandyRedRC46]

How does the length of the 1200 forks compare to the 750/800's?

[JZH]

If I had been able to find a complete set to buy I probably would have bought them.  Recently, on UK eBay there has only been one guy selling a full set--minus the steering stem.  Given that you cannot buy the stem separately from Honda, and removing it is something only done for a good reason, I cannot understand why the stem would be missing...

 

Anyway, I didn't know about the lack of rebound adjustment on the US-spec "standard" model's forks, but neither version has compression adjustment, does it?  To put this in context, I think some/most of the other radial USD Showa forks do have adjusters for both, e.g., CBR1000RR, so the only real advantage I can see for the 1200's forks would be length--but I don't even know if that is the case. 

 

Ciao,

[Egg on Leggs]

I remember reading that Honda did not fit USD forks to the 8th gen as the frame was not up to the task.

[sfdownhill]

Thanks for the responses.

 

CandyRed - I'm trying to determine the length of the Gen 7 forks. I've posted the question 'what is the length of Gen 7 VFR1200 forks?' here and on the other site Gen 7 forums, so hopefully a Gen 7 owner will measure his and let us know. My Gen 5 forks are 764mm when unloaded/extended.

 

JZH - I saw those UK Gen 7 forks and wondered about the lack of steering stem; I agree with you that it would be the last piece to be snatched. I'd definitely send any forks to Jamie Daugherty. Based on his thorough explanation of how rebound is the critical adjustment and low speed [standard] compression adjustment is a nice but not critical accessory,  I'd give up compression damping adjustment for forks with better geometry for my installation..

 

Eggs - Honda's choice of RWU forks on Gen 8 remains a puzzle. Why didn't they design a chassis strong enough to integrate with modern fork technology?

[JZH]

FYI, Race Tech would say the opposite about the relative importance of compression and rebound.

 

I asked the stemless-forks eBay seller what was up and he mentioned that he had bought them that way and that I could buy the stem from Honda.  Bzzzzt.  No, I couldn't, and the rest of his story was simply not believable.  I wasn't sure it was him, but I recalled that a few months earlier there had been someone selling a VFR1200 lower triple with a "non-OEM" steering stem.  Why?  What the hell has been happening to all the seventh-gen steering stems in this country?  Just weird.  Anyway, stems can be fairly easily pressed in and out, but I didn't want to deal with the mystery.  Good luck with your quest...

 

Ciao,

[Mohawk]

12 hours ago, sfdownhill said:

Honda's choice of RWU forks on Gen 8 remains a puzzle. Why didn't they design a chassis strong enough to integrate with modern fork technology?

 

It's a space thing. By using the same frame as the 6th gen, they would need a larger offset to maintain the same steering lock angles. Ask anyone that has fitted USD SP1/2 (RC51) front ends, they lose a lot of steering lock, unless you get custom triples made. The VFR already uses a large offset, so to add USD's properly they would need a silly amount & that would affect the handling dynamics badly.

[sfdownhill]

9 hours ago, JZH said:

 

FYI, Race Tech would say the opposite about the relative importance of compression and rebound.

 

 

 

Perhaps Daugherty's approach is his own, and from posts/threads I've read, most of his VFR fork conversions that include external rebound adjustment are rebound-only cartridge kits. This is probably because VFR forks do not have any provision for external compression adjustment and VFR owners willing to change major fork components to get compression damping are in the [vast?] minority.

 

I looked around on Racetech's site in an attempt to find their 'rebound philosophy', but they have little in the way of description in their support section or FAQs. Is there an easy way to describe how they approach the compression/rebound relationship?

[JZH]

Sorry, I probably should have read your comment more closely!  Re-valving is one thing; adjustment is another.  Race-Tech historically did not offer Gold Valve kits for cartridge fork rebound valves at all, deflecting constant queries by saying that it was much more important to get the compression damping right, and that there was no benefit from changing the rebound valve body.  They later relented and now offer Rebound Gold Valves for most bikes--but I suspect that is simply to satisfy the demand, rather than the need.  That's the Race-Tech opinion I was referring to, but I see now that you were speaking of having the ability to make adjustments on the bike, and yes, I agree that having effective rebound adjusters is more important than having compression adjusters.  I'd also say that having preload adjusters is even more useful in a practical sense, but most bikes have those already.

 

[Edit: Paul Thede's Race-Tech Motorcycle Suspension Bible contains thorough discussions of the Race-Tech approach, but in a quick scan I was not able to find anything about the relative merits of compression and rebound adjustment.]

 

Ciao,

[VFROZ]

In most bikes, rebound pistons have large ports, probably why Rcetech never bothered to make them.

Not so on the VFR800 5th and 6th. Even the VFR750 had much bigger rebound ports, and if you want to save money, asking a suspension shop for old discarded 20mm rebound Pistons will greatly improve the 800's suspension as long as you redo the stacks. 

I know that on my bike, with high flow compression valves and VTR lowers and rebound adjustment, I was limited to how good I could get the compression until I replaced the rebound valves. 

This made the biggest difference to the whole package. 

Another thing to note is a lot of people are confused about slow speed adjustment. 

Technically it is slow speed that is being opened or closed, but it affects high speed a lot as well. 

As you open or shut the slow speed citcuit, you are either giving more or less work for the shim stack to do. 

As far as suspension tuners go, they all have their own philosophy on how to achieve the best results, there is no one right approach, but there is a lot of crap tuners out there, that's how I learned to do my own work. 

[sfdownhill]

Great info gentlemen - thanks. It's not often that two separate responses on a single suspension issue dovetail together.

 

JZH, thank for reminding me about the Racetech Bible. I'll do some reading in it. That Racetech would focus their early marketing on the compression valves they were selling at the time makes a lot of sense.

 

OZ, your experience with upgraded rebound valves enabling better compression control helps me understand more of the big interaction picture. Slow speed circuit adjustment shifting the point at which the shim stack takes over is another point of clarity.

[VFROZ]

2 hours ago, sfdownhill said:

Great info gentlemen - thanks. It's not often that two separate responses on a single suspension issue dovetail together.

 

JZH, thank for reminding me about the Racetech Bible. I'll do some reading in it. That Racetech would focus their early marketing on the compression valves they were selling at the time makes a lot of sense.

 

OZ, your experience with upgraded rebound valves enabling better compression control helps me understand more of the big interaction picture. Slow speed circuit adjustment shifting the point at which the shim stack takes over is another point of clarity.

 

You explained it better than me.

That is correct, adjusting the slow speed circuit, changes where the shim stacks take over. 

A very open slow speed port takes care of damping until the fork is moving too fast for the circuit to cope with the oil flow, once this happens the shim stack needs to open to allow flow. This set up gives you a plush ride, but you sacrifice bottoming out and not coping with really bad road surfaces. 

A very closed slow speed port flows very little oil, so it doesn't take a lot of fork speed to open the shim stack. This set up gives you plenty of front end feel, but makes for a harsh ride specially on crappy roads. 

Getting the balance right is the hard part. 

On top of this you also have oil height and viscosity to play with. This affects bottoming out and dive under brakes. 

I like a bit of dive to load the front wheel, I also like control on very bad roads at speed. But I don't like harshness at cruising speeds, so it took a lot of experimenting to get it where I'm happy. 

Only changing the rebound valves with very high flow ones allowed for this to happen. 

Did I mention unsprung weight?