Rc51 (Sp1/sp2) Forks Vs. Cbr1000Rr Forks

[JZH]

I've been commuting to work in London a few days a week and, though my "hot rod" FP is holding up, I've pretty much decided that I need another VFR... 

So, why not the exact same year and model I already know and love? 

 

And that means mods! 

 

So, do I go down the "tried and true" path to USD enlightenment?  Or do I really push the boat out, throw caution to the wind and experiment with another variety of early 21st Century Showa forks?

 

I have a set of 1000RR forks (I think they're usable), but when I took them apart years ago I recall thinking they seemed like cheapo imitations compared with the obvious quality of my SP1 forks.  But are they really worse?  I'm curious if anyone knows the answer to that?  Do the radial brake calipers make up for any difference?

 

(I've noticed that Honda has helpfully manufactured both a CBR954RR and a CBR600RR in the VFR's lovely PB-215C Candy Tahitian blue, so I can easily fit a matching mudguard--how convenient!)

 

Cheers,

[BiKenG]

A quick question guys. Anyone know the fork width of the CB1000R? It's either 214 or the narrower 204 but I seem to have misplaced this information. Anyone know?

[Mohawk]

P1 P2 M/C Comparison-3 32.00 34.00 14.00 Dia 16.00 17.00 7.00 Radius 803.84 907.46 153.86 Area 3215.36 3629.84 44.49

Ratio

That must have a higher lever ratio to get a good feel at the lever ! Otherwise the lever would hit the bar for sure. Obviously the higher the ratio the stronger the brakes, but the feel you get is determined by the lever ratio on the bar which has to be balacned against the availabe travel of the average humans finger grip.

[BiKenG]

The formatting makes your figures confusing. But 'feel' is totally subjective and not determined by any one factor. In truth, it's mostly just down to what one thinks 'ought' to feel right. Look how many say radial calipers 'feel' so much better which is utter nonsense as we know. But they believe it so it must be true. Same for using Brembo braking components, but that's another discussion.

All the master cylinders you quote use the standard lever. The so called 'radial' master cylinders have a much higher lever ratio and the crossovers (as I call them) on RVT, 929 and 954 'Blades are very similar in length of lever. We've discussed elsewhere why increasing lever ratio is a better trade off against hydraulic advantage. But the proof of the pudding and all that...

I have personally tried e.g. 14mm master cylinder (std. lever, no other possible alternative) with 27/30 calipers, e.g. FireBlades up to 1997, FireStorm and also the RC45 (and others no doubt). They are ok. Good at the time, but one can now do better. Actual braking performance of those different models varies in any case due to different disc sizes.

I have also used for many years that same 14mm master cylinder with the 32/34 calipers from the SP-1 and although I was using stainless braided hard lines and not the OEM rubber ones, however when new, there's no great difference (but the OEM ones do get worse in time). Anyway, I'm not sure what you're saying Chris, but that combo is exceptional and in NO way too soft.

If you instead use a 5/8" master cylinder, you will as you know get harder but less powerful brakes. If you reduce the caliper piston sizes, you will get even harder and even less powerful brakes. But harder doesn't necessarily mean better brakes and it reduces 'feel'. Conversely, a bit softer will increase feel - up to the point that they are too soft and the lever moves too far of course. As you say, there is a 'sweet spot', i.e. the best compromise, but in my experience I would say this is the 14mm with 32/34 calipers as I know from years of experience of using exactly this combo, it's very good.

When in an endurance race at Snetterton some years ago with an SP-1, my co-rider fell off in the wet and we had to find a replacement master cylinder. All we could scrounge was a 1/2" and so I had to then race with that. Initially it was frightening as the lever just came back to the bars so easily, but I then discovered I could pump it a few times and although still soft, the bike was pulling stoppies into the sharp right hander after Riches (Sears IIRC, but it's gone now) with just one finger. So yes, I would say that 1/2" master cylinder with the 32/34 calipers is TOO soft.

However, my calculations indicate that with 30/32 calipers, it might just work as the hydraulic advantage is closer to the 14/32/34, than it is to 12.7/32/34. BUT, I have not tried it yet. I will though to confirm either way. I'm optimistic.

I have also not tried 12.7/27/30, but that is even more likely to work and is also something I want to try.

BTW, the 14mm master cylinder provides greater overall advantage than the 'radial' type. IOW, its smaller piston outweighs the longer lever of the radial type. The 1/2" (12.7mm) even more so, but as we know, possibly too much.

BTBTW, the approx. 15% longer hand lever of the 'crossover' and 'radial' type is not the biggest factor. It is the short lever that presses on the piston that has the greater impact as that decreases by 25%. In any case, it is rather variable as to where the hand and fingers actually apply the pressure, whereas there's no such uncertainty about how far the piston is from the fulcrum (pivot).

All good mental exercise.

[Terry]

This is a great brain exercise gents.

Reading through the different opinions and the associated maths, I have concluded that we might all have different ideas of 'perfection'. I only ride on roads, and like to use two-finger braking. As such my preference is a firm lever feel, not too much lever travel and controlled braking power, but not too much as I have had past experience with front lock-ups and crashing which I'm not in a hurry to repeat. So my ideal is the larger master cylinder, braided lines and some reasonably-sized calipers. I'm still leaning towards getting an 11/16" master off a CBR600RR to go with my CBR600F4i calipers.

[BiKenG]

That will work fine. All the options we discussed will work fine. We're just talking fine tuning really. And yes you're right, each has their own personal definition of perfection. However that can sometimes be clouded by what they perceive 'should' be good, rather than a clear objective analysis. If someone tries 2 different combinations and discovers one is absolutely better for them, then that's the one to choose, but picking the harder option in the mistaken belief that this means better brakes is misguided. As long as everyone has all the information 'at their finger tips' as it were, they can make an informed decision.

Terry is making a very valid point about the risk of locking the front. The more powerful the brakes, the more chance of this. As wth all things braking, it's a compromise - until you enter the realms of ABS which in theory should provide the best braking performance but with zero risk of locking up. My own view though is that I have never yet had occasion to deal with an automated system of anything that actually got it right all the time. My last year has for the first time been largely on a bike with ABS and twice it has decided to turn off the brakes at the front due to a perceived problem and I very nearly ran into the back of the vehicle in front while frantically squeezing the brake lever and cursing any braking security system that operates by preventing me from braking exactly when I need it. Yet in almost 50 years of riding bikes, I have NEVER been in a situation that would have been enhanced with ABS and in these instances I mention, it was a minor pothole that I would have hardly noticed while allowing for it, had I been in manual control of the brakes. So for me, statistically, ABS is a bad thing and I prefer to not have it and enjoy my (independent) control over the front and back brakes. My VFR1200 -> eVo4 project involved the elimination of the ABS and I'm much happier for that.

But that's me, others obviously love having ABS. But in the context of a 5th gen VFR, it's not an option so as Terry says, one might want to consider the maximum braking power available in the chosen combination of components.

A note of clarification - my preferred 14/32/34 combo does not feel soft in isolation. When tried in direct comparison to an empirically harder set up, you will feel some slight difference, but it's not something you'd notice otherwise. Ideally, you'd want to set up each alternative and try it to find what suits you best. In practice, hard to do. Hopefully this discussion will help others make their own informed decision.

[BiKenG]

Continuing this thread as it seems relevant.

How is Rake and Trail measured?

I know that sounds pretty dumb, but bear with me on this.

When manufacturers quote the above figures, do they mean as per measuring static sag, i.e. bike siting on it's suspension or as per dynamic sag, i.e. with rider on board, or even when loaded with e.g. luggage? Or is it a virtual measurement as it would be if the suspension was fully extended, i.e. with no weight on the suspension?

I cannot find this issue mentioned anywhere, but of course as the suspension moves, the rake and trail WILL both change. So it seems to me that trying to take into account any sort of sag would make the figures useless, without quoting exactly what the weight was on the front and the back, or by how much the suspension was compressed. Apart from the difficulties this would cause, it isn't the case. When those figures are quoted, there is NEVER any mention of suspension state.

So I'm thinking the most useful figures will just relate to that virtual state of the suspension being fully extended. Seems to me that's the ONLY figure that's worth quoting.

The reason I'm asking is because I'm putting together a suspension/geometry calculator that will give us some real data on what effect various changes will have as we modify them. So if you fit yokes with a greater or smaller offset, or change the length of the forks etc. I started out by including an average static sag, but it gets complicated (what about the rear etc) and it makes more sense to me to just use fully extended fork lengths as any figures are only useful as a comparison to standard anyway. However, for this I need to start with the quoted figures for the bike, and for which I need to know the suspension state.

Does anyone have any idea of what is the 'standard' way of quoting these figures?

[JZH]

Nope. But, FYI, you can download the demo version of Tony Foale's Suspension Kinematics software--a lot of it works fine (at least it did the last time I checked)--and play around with it.

Ciao,

[BiKenG]

Unfortunately Tony Foale's stuff is Windoze only. But in any case, it's one thing to calculate some figures, but another to have to make use of existing data with no qualification such as in what state the suspension would have to be to make the data applicable.

I think I'll stick with assuming fully extended. It is after all how we discuss fork lengths so makes it more digestible methinks.

[Rush2112]

I talked to Jamie Daugherty about this exact subject. If I understood him correctly he has not been able to exactly replicate a manufacturers claimed rake and trail whether the suspension was fully extended, set for static sag, loaded, etc. IIRC, he uses them as a reference for comparison between bikes, or between different set-ups on the same bike rather than chasing some holy grail of rake & trail numbers that will make your bike handle like a GP bike.

I believe the manufacturer reported rake & trail numbers are theoretical from engineering drawings and calculations and most likely based on the suspension at full extension.

[BiKenG]

Then Jamie and I are in agreement. The TRAIL figure I have for the VFR800 is 100mm. But they also quote RAKE at 25.5° and with the diameter of the front tyre at 600mm (120/70x17, work it out), the TRAIL calculates to 98.7mm. It's not a big difference, but it should be exact. There's no manufacturing tolerance involved here. The TRAIL is calculated from wheel/tyre RADIUS, fork OFFSET and RAKE. The first 2 are absolute and we use the RAKE as quoted by the same source (Honda) as we're getting the spurious TRAIL figures.

Actually, I just looked in the Owner's Manual to check the tyre size in case I had that wrong. Nope, that is the correct size. BUT, in there the TRAIL is quoted as 95mm. So the first TRAIL figure I had was wrong. Can't remember where it came from, not Honda though obviously, so let's ignore that first one. It's now even worse. You cannot get 95mm TRAIL from 25.5° RAKE and 40mm fork OFFSET and that RADIUS. Please someone correct me if I'm wrong.

So I think for the purposes of comparing different forks, we should assume forks fully extended and ignore Honda's quoted TRAIL and instead start from the calculated TRAIL with standard forks. Then we can compare the figures with different fork lengths, offsets etc. Or even different front tyres if anyone wants to go that route.

Thing is, to make such fork comparisons, we need to know the resulting RAKE, from which we can then calculate TRAIL. But to get the RAKE for any given fork length, we need to compare back to the original. So from the quoted RAKE and std. fork length we can calculate a headstock angle figure that is the one fixed parameter whatever the fork length. From that we can calculate the RAKE for any fork length. That parameter is unimportant apart from its use in other RAKE calculations so I won't bother including it. Just the final figures we need.

I'll post a simple chart later with some obvious examples, but we could work it out for any fork.

[JZH]

Update:

Need to change the topic photo, as I've put a deposit on a tidy box-stock one-owner '01 with 22,000mi, which has silver wheels and different "VFR" decals on the fairings.  I much prefer black wheels, but as the wheels will be replaced with an 8-spoke rear from my FP and an SP1 front wheel, I won't have to live with it for long! 

Ciao,

[RVFR]

Nice, we never had the Blue here :( Very nice ;)

[Switchblade]

Congrats ...

[Lorne]

Update:

VFR800Fi1.jpg

Need to change the topic photo, as I've put a deposit on a tidy box-stock one-owner '01 with 22,000mi, which has silver wheels and different "VFR" decals on the fairings. I much prefer black wheels, but as the wheels will be replaced with an 8-spoke rear from my FP and an SP1 front wheel, I won't have to live with it for long!

Ciao,

Say it ain't so, John Everyone knows that white is the best wheel colour :tongue2:

[JZH]

Sorry, Lorne, I have been totally against honky wheels since I powder coated my FL's wheels ca.1991. In fact the 8-spoke rear wheel I'm going to use on this bike is the very same wheel!

Anyway, the bike is here now. I had it delivered this afternoon, so I haven't actually ridden it yet, but the engine sounds sweet! Of course, we will need a few mods...

Might have to start a new thread. "Beware the Blue Peril"?

Ciao,

[Rush2112]

That's an AWESOME To Do List!

Looking forward to seeing more of the Blue Peril!

[Switchblade]

Gonna be good ..

[RVFR]

Wow you got a few trinkets there on that list huh, That Ohlins though may be tough to find, I mean they are out there, but $$$ in France whew!! to much for my blood.

[Cogswell]

That's quite a to do list. Looks like it all might have cost more than the bike. Looking forward to photos of this build!

[Lorne]

John,

Blue 5th gens were never very common in my neck of the woods. Too bad 'cause it is an awesome colour.

Are the Tommaselli 'bars adjustable in two axis?

I was going to suggest painting/plating the heat shield for a brighter look until I noticed you're opting for the cf look - very tidy.

Looking forward to seeing the final result.

[JZH]

Yes, probably would double the cost of the bike... Still, compared with the yellow bike's totally shameless excess, it almost looks like a bargain! I have many of these bits already, mainly because I had already acquired all of the fork swap parts for my FP. Those are SP1 forks, though, and I'm going to try to find a set of SP2 forks, because I like gold...

I don't know which shock I will actually use; depends on what I can find on eBay, mainly. (But an Ohlins would match the SP2 forks!)

The Tommasellis are double-adjustable and very solid (I already have them). They may not be necessary with long enough forks. I've also got some Helibars to try, once I get to that stage of the conversion.

I've also already got the "enutniatS" from my yellow bike and the Motad/Predator exhaust, as well as the Harris cf hugger, so I don't really have a lot of parts left to acquire.

My favourite part of these mods is the 954 front fender--a perfect match for the VFR's PB-215C blue, for that "factory" look...

Ciao,

[BiKenG]

...Those are SP1 forks, though, and I'm going to try to find a set of SP2 forks, because I like gold...

I don't know which shock I will actually use; depends on what I can find on eBay, mainly. (But an Ohlins would match the SP2 forks!)

Just to clarify, are those pictures what you have or what you want? Reason I ask is that the forks in the photo ARE SP-2 and not SP-1. Also, the rear shock shown has the 'clevis' at the bottom (as needed on the RVTs), but certainly the 5th Gen and I suspect later VFRs need an 'eye' type mount at the bottom, same as the top.

Do you have a neat way to modify a shock with clevis type bottom mount to eye type? Something I've been pondering as I have an SP-2 shock I want to use on my 5th Gen project so I will need to change the lower mount. I wondered if you had already studied this and sorted out a solution.

Also, regarding discs, the SP-1 front wheel will accept discs from SP-1, SP-2,929,954 and CBR1000RR4-7, but they're not all the same diameter. The 929 used 330mm and the RR4/5 used 310. But the RVT forks only suit 320mm. Also, some were thicker and therefore heavier. I'm sure you know all this, but just in case not I thought I'd mention it.

Of course later FireBlade discs will also mount on that wheel, but the offset will be wrong, so don't go that route.

[Rush2112]

...Those are SP1 forks, though, and I'm going to try to find a set of SP2 forks, because I like gold...

I don't know which shock I will actually use; depends on what I can find on eBay, mainly. (But an Ohlins would match the SP2 forks!)

Just to clarify, are those pictures what you have or what you want? Reason I ask is that the forks in the photo ARE SP-2 and not SP-1. Also, the rear shock shown has the 'clevis' at the bottom (as needed on the RVTs), but certainly the 5th Gen and I suspect later VFRs need an 'eye' type mount at the bottom, same as the top.

Do you have a neat way to modify a shock with clevis type bottom mount to eye type? Something I've been pondering as I have an SP-2 shock I want to use on my 5th Gen project so I will need to change the lower mount. I wondered if you had already studied this and sorted out a solution.

Also, regarding discs, the SP-1 front wheel will accept discs from SP-1, SP-2,929,954 and CBR1000RR4-7, but they're not all the same diameter. The 929 used 330mm and the RR4/5 used 310. But the RVT forks only suit 320mm. Also, some were thicker and therefore heavier. I'm sure you know all this, but just in case not I thought I'd mention it.

Of course later FireBlade discs will also mount on that wheel, but the offset will be wrong, so don't go that route.

Aren't the RR 6/7 rotors 320mm with the same offset as the 4/5 but about 0.5 kg lighter?

[JZH]

Sorry, the pics are of the planned mods.

 

But, I do already have:

SP1 forks, lower yoke, discs, axle & spacers

Race-Tech Gold Valve kit & straight-rate springs (needs installing)

SP1 wheel (needs re-coating)

CBR954 top yoke (needs powdercoating)

Tommaselli adjustable clip-ons (probably need some new grips...)

CBR600RR3-4 calipers (32/30) & 11/16" master cylinder

VFR750FL rear wheel (needs re-coating)

Michelin PR4s (need re-mounting)

Bridgeport 90-degree valve stems

Harris CF rear hugger

Predator stainless steel headers for '00-'01

Staintune high-mount slip-on

Factory Pro Shift Star Kit

Xexon headlight conversion (needs finishing!)

Suzuki TL1000 (Shindengen series-type) reg/rec

VFR800 clutch pressure plate (needs powdercoating...)

 

Oops, used the wrong pic of the Ohlins.  Definitely doesn't have a clevis:

[Edit: I don't know how, but I would expect that a good Ohlins centre could modify the shock.  It would be a strange design if Ohlins had used a completely different method of getting the right ends on their shocks.]

Ciao,

[BiKenG]

Aren't the RR 6/7 rotors 320mm with the same offset as the 4/5 but about 0.5 kg lighter?

Yes, that sounds about right. The RR4/5 discs are 310mm but do seem thicker.