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RC51 SP1 SP2 Parts Interchangeability


JZH

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I think I can do this...

 

"This" being: swap fork internals from SP2 to SP1.  We all know SP2 forks are "shorter" than SP1 forks, but my online research strongly suggests that this is simply a function of the SP2's monstrously long OEM top-out spring, rather than of any of the SP2's non-springy parts actually being shorter.  The US RC51 workshop manual doesn't even bother illustrating the SP2's internals, they're so close... (FWIW, I've found that the 954 workshop manual does show the maintenance procedures applied to the same type of fork parts that the SP2 has.)

 

(I have a set of SP2 forks that have been fettled by a well-known suspension tuner over here, so I was planning on using them as-is on my FP, but the "clamping zones" of the outer tubes of these forks are slightly different than those of SP1 outer tubes--not a lot different, but just enough to be incompatible with the lower triples I'm using (VFR1200*) and the height at which I want to mount the forks.

* Note: VFR1200 lower triple clamps have 55mm ID openings; in order to use SP1/SP2/929/954 forks (54mm OD) I will have to fit 0.5mm shims, but this is easily resolved.)

 

That said, there are some parts differences between the SP1 and SP2 fork internals, but I don't know if they would prevent swappage.  I currently have a pair of newly re-annodised SP1 outer tubes, good condition SP1 lowers and new bushings/seals ready to go.  I'm thinking that all I will need to do is fit the new bushings and seals to the cleaned SP1 uppers and lowers, and drop in the already assembled SP2 cartridges/springs/fork caps, oil and Robert's my mother's brother, right?

 

Cheers,

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I think we've discussed this before, but to answer some of your questions here:-

 

SP1 and SP2 fork tubes, outers and inners are each the same length. The shorter SP2 assembly just means there is more overlap (inner to outer) by default on the SP2 forks.

 

SP1 and SP2 outers are interchangeable, but the internal dampers are different, requiring different top caps and also the bottom 'knuckle', i.e. the axle clamp/brake mount would not simply interchange on their own. You'd need to use the correct damper assembly to suit the inner/lower fork leg.

 

As we know, the VFR1200F forks are Kayaba and not Showa like those of the RVTs so the top caps use different thread etc and so no swapsies there unfortunately.

 

The RVTs (i.e. SP1 and SP2) use the same 30mm offset (fork leg plane to stem) as 929 and 954 'Blades and RC45.

 

The VFR1200F and CB1000R both use 35mm offset.

 

VFR800s (that I've seen) have I think 40mm offset.

 

So although I know JZH is fully aware of this, other's should beware when swapping front ends because changing the offset will alter the trail, as will changing the length of the forks which will also change the steering angle (rake). Whether any of that is good or bad is up to the final user to decide. But be aware of what steering geometry changes have been incurred by any such swapping of parts.

 

Likewise with brakes. Swapping master cylinders and calipers may well change the leverage ratio and that can be good, or not so, and you don't want to be finding out the latter when too late. So make sure you understand what varying sizes of pistons (M/C and caliper) mean and also you'll need to take into account the mechanical leverage ratio of the lever. Radial master cylinders tend to provide greater leverage with long lever for the hand to pull, but short from the pivot to where it pushes on the piston. However this is also the case with other conventional M/Cs like those from the RVTs when compared to older type M/Cs such as the very common 14mm, 1/2" and 5/8" as Honda have previously used and which provide a lower leverage ratio.

 

The performance of hydraulic systems like brakes is all due to the mechanical and hydraulic advantage provided by the levers and pistons employed. Radial or not makes no difference and certainly having Brembo stamped on the side has NO effect whatsoever.

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Thanks, Ken, for the confirmation and additional information.  I think all I will need to do is to swap the SP2 outer tubes with the SP1 outer tubes, leaving all of the other SP2 parts exactly as they are now.  Which is perfect, because the forks are--apart from the outer tubes--perfect now.  

 

So I don't need to deal with it, but I'm curious about the cartridge/fork lower compatibility issue.  I'll have a closer look at the internals when I'm actually doing the swap (sometime this century, I'm fairly certain...), but by memory, I think you're right--the lower cartridge bolts are completely different, as are the lower castings to accommodate the different retention methods.  The SP2 has something like an M8 or M10 center bolt, I think, while the SP1 has a huge M20 threaded bottom "bolt", IIRC.

 

Ciao,

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10 hours ago, JZH said:

Thanks, Ken, for the confirmation and additional information.  I think all I will need to do is to swap the SP2 outer tubes with the SP1 outer tubes, leaving all of the other SP2 parts exactly as they are now.  Which is perfect, because the forks are--apart from the outer tubes--perfect now.  

 

So I don't need to deal with it, but I'm curious about the cartridge/fork lower compatibility issue.  I'll have a closer look at the internals when I'm actually doing the swap (sometime this century, I'm fairly certain...), but by memory, I think you're right--the lower cartridge bolts are completely different, as are the lower castings to accommodate the different retention methods.  The SP2 has something like an M8 or M10 center bolt, I think, while the SP1 has a huge M20 threaded bottom "bolt", IIRC.

 

Ciao,

 

Yes, the way the damper cartridges are bolted to the lower knuckle is different and so not interchangeable SP1 to SP2. However the latter does use the same cartridge type as the first 'Blades with radial brakes (04-07) and so those inner tubes/knuckles can be swapped. That's how I built the hybrid forks for my SP2 so it had true radial caliper mounts. I also shortened them to better suit the 929 'Blade top yoke I wanted to use as it's better looking.

 

As I think you've worked out, SP1 and SP2 outer tubes are interchangeable. Be aware that in the UK and certain other markets the SP2 had light gold outer fork tubes, but in some markets (like US I think) they continued with the same bronze colour of the SP1 we had here. So just the colour is no indication of whether a fork outer is SP1 or SP2. As you have discovered the outer shape is slightly different. Same diameters at the yokes, but I think they trimmed the SP2 tubes to be lighter and no doubt claimed better flex in the right places.

 

Let me know if you end up with a spare SP1 outer as I think I need one to make a good pair of forks.

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Sorry, Ken, I will end up with spare SP2 outer tubes, but the SP1 ones are what I need to get the full clamping area.

 

Interesting to note that the early CBR1000RR fork bottoms would interchange with the SP2 fork bottoms.  I'll keep that in mind!

 

Cheers,

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1 hour ago, JZH said:

Sorry, Ken, I will end up with spare SP2 outer tubes, but the SP1 ones are what I need to get the full clamping area.

...

Cheers,

 

Well now, I'd also be interested in a pair of SP2 outers as I have the innards left over from my hybrid ones. Can we talk about those?

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On 11/4/2017 at 2:52 PM, BiKenG said:

 

Well now, I'd also be interested in a pair of SP2 outers as I have the innards left over from my hybrid ones. Can we talk about those?

 

Sure, but they're not perfect.  A few gouges at the top you might be able to see here:

 

20160516_160823y.thumb.jpg.c1bd72f89e667b920e3abd155754b444.jpg

 

(The other tubes are some SP1 ones I had re-anodised last year.)

 

Ciao,

 

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2 hours ago, JZH said:

 

Sure, but they're not perfect.  A few gouges at the top you might be able to see here:

 

20160516_160823y.thumb.jpg.c1bd72f89e667b920e3abd155754b444.jpg

 

(The other tubes are some SP1 ones I had re-anodised last year.)

 

Ciao,

 

 

Doesn't rule them out. Keep me in the loop on those please John.

 

BTW, did you see that the CB1000R forks are 50/55 like the VFR1200F. Who knew. Not me obviously as I was sure they were 50/54. So I'm still struggling to find a 50/54 bottom yoke with 35mm offset. Maybe there isn't one.

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On 11/5/2017 at 12:49 AM, JZH said:

Sorry, Ken, I will end up with spare SP2 outer tubes, but the SP1 ones are what I need to get the full clamping area.

 

Interesting to note that the early CBR1000RR fork bottoms would interchange with the SP2 fork bottoms.  I'll keep that in mind!

 

Cheers,

Indeed. Very interesting. Might consider a radial brake upgrade to my bike at some point...

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12 hours ago, EX-XX said:

Indeed. Very interesting. Might consider a radial brake upgrade to my bike at some point...

 

If you're talking SP-1 or SP-2, the adapters to fit radial calipers are probably still available.

 

In fact virtually all these Showa forks can be swapped around. As long as the inner leg diameter is the same (43 mm for these and most others) any outer leg can be used. The overall length is then determined by the length of the damper assembly and although that can be modified (by shortening or lengthening the rod, within reason regarding the inner/outer overlap) the stroke cannot be so easily changed. In fact, it can't be changed at all.

 

It can be possible to swap around damper rod assemblies, but how their top and bottom fittings vary can restrict what will fit with what.

 

Be aware however that Honda have used some Kayaba forks and they seem to prefer a 55 mm bottom yoke clamp diameter and a different thread for the top cap.

 

JZH, let me know when you're done with those SP-2 outers John. :smile:

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9 hours ago, BiKenG said:

 

If you're talking SP-1 or SP-2, the adapters to fit radial calipers are probably still available.

 

In fact virtually all these Showa forks can be swapped around. As long as the inner leg diameter is the same (43 mm for these and most others) any outer leg can be used. The overall length is then determined by the length of the damper assembly and although that can be modified (by shortening or lengthening the rod, within reason regarding the inner/outer overlap) the stroke cannot be so easily changed. In fact, it can't be changed at all.

 

It can be possible to swap around damper rod assemblies, but how their top and bottom fittings vary can restrict what will fit with what.

 

Be aware however that Honda have used some Kayaba forks and they seem to prefer a 55 mm bottom yoke clamp diameter and a different thread for the top cap.

 

JZH, let me know when you're done with those SP-2 outers John. :smile:

Thanks for that.

 

I read one of the threads where you explained the relative differences (or lack thereof) comparing radial to axial mount brakes in terms of outright performance.So, while it's good to know that the lower leg swap can be done, gut feel is that there's no compelling need to do so at present. The brakes I have are well and truly good enough for any use to which I'd put them (including advanced riding courses/track days).

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I have these on my RC-Tuono, with the Brembo Monoblocks, and radial M/C - works almost too good!

 

 

http://www.superbikeunlimited.com/730-2000-2006-honda-rc51-sp1-sp2-radial-caliper-mount-kit.html

 

 

 

RC_Tuono.jpg

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I find the oem brakes on my SP more than adequate and shudder to think what more powerful brakes would do.

 

I saw someone lay down a darkie with the front tyre of a 4th gen RC36 with upgrades brakes... :491::goofy:

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20 minutes ago, Dutchy said:

I find the oem brakes on my SP more than adequate and shudder to think what more powerful brakes would do.

 

As I've said before, braking power is all about leverage and friction. The former is determined by the relative ratios of hydraulic piston sizes (Master Cylinder and calipers), M/C lever design and disc size (plenty of potential with all that to customise to one's personal preferences). The latter is governed by pad and disc material (can't really improve on what Honda have figured out there). Nowhere in the mathematics is there anything about the direction of the caliper mount bolts. Simply changing that will NOT improve your (potential) braking performance. Any such swap will often also involve other changes that do affect braking and mask the fact that the axial -> radial change (or vice versa) made f**k-all difference. 

 

If you want to fit radial calipers for the bling, I'm all for that - go for it. :smile:

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Since we are brushing on the topic of brakes, I will share one thing I found while rebuilding brake calipers for a couple different projects:

In addition to being different diameters than the SP2/954RR, the SP1 and 929RR front calipers have aluminum(?) alloy pistons where the later are heavier steel pistons.  It's not so much a big difference, but this is unsprung weight.  If you are looking for every advantage, this might be worth pursuing, but I didn't care given my modest abilities and usage.  I would be surprised if the difference added up to 1 lb.

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In all my meanderings with these calipers, I never noticed that. Makes me wonder what the RRW/X and radial ones have.

 

What it does mean is that there’s Al pistons available in 30, 32 and 34 mm which covers all sizes. So any of those Nissin axial calipers can have Al pistons. I wonder if they would also fit the Tokicos. How different can they be. 😀

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I can confirm that the 929 calliper pistons are alloy with some kind of low friction costing & they are very light. You can now get replacement Titanium pistons in common sizes, which is a great material for brake pistons, as it does not transmit heat well thus keeping the brake fluid isolated from the heat. It’s lighter than steel (-40%), stronger than alloy, thus les distortion & does not corrode so ideal for brake application.     

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Well yes, but don't forget Ti is actually 50% heavier than Al and in a brake caliper piston I don't see distortion as being a problem. I don't really think heat transfer is an issue on the road either.

 

However, although hard anodised Al is likely to resist corrosion pretty well, there's no denying you can't beat Titanium for staying shiny.

 

Did I say I like Titanium. 😁

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This has nothing do with the mathematics of braking force, but weight is also a factor, and why modern is good.

On my  1988 gsxr 711 streetfighter, I changed from 1991 model USD forks and 6 pot axial brakes to K4 forks and radial callipers.

4.4kgs lighter, off the front end, just from swapping forks and callipers.

 

My MT09 monoblock callipers are considerably lighter than the K3 (I think) pad per piston gsxr 600 callipers I have on my VFR.

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On 11/5/2017 at 11:48 AM, BiKenG said:

 

Doesn't rule them out. Keep me in the loop on those please John.

 

BTW, did you see that the CB1000R forks are 50/55 like the VFR1200F. Who knew. Not me obviously as I was sure they were 50/54. So I'm still struggling to find a 50/54 bottom yoke with 35mm offset. Maybe there isn't one. 

 

Ken, it sounds like you've determined that the CB1000R triple clamps have 35mm offset - can you please confirm or deny?

 

Is there a reason you do not want to use 0.5mm shims like JZH is using on his VFR1200 lower triple clamp?

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Yes, the CB1000R (up to '17 anyway) is 35mm offset. So you could use a CB1000R top yoke and put regular bars on a VFR1200F.

 

I AM using 0.5mm shims for my 54mm Ohlins in the VFR's 55mm bottom yoke and indeed supplied JZH with both his yoke and shims. It was a quick fix and yes, it works. But I'm a perfectionist and can't help wanting a true 54mm bottom yoke to actually fit the forks. So far I've not found anything suitable 'off-the-shelf'.

 

Of course I'd really like to find out the clamp dia. and offset for the new '18 CB1000R which actually has a very nice looking bottom yoke. When Honda make a bike with fairing, they don't bother making the lower yoke look nice. The clamp area with bolts is just stuck on the outside and not very attractive. That's another reason for thinking about making my own. I could have the correct fork clamp dia. and also make it look better with the bolts tucked out of the way. Being a naked bike, the new CB1000R one is better looking. Anyone know the dimensions?

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8 hours ago, sfdownhill said:

 

Ken, it sounds like you've determined that the CB1000R triple clamps have 35mm offset - can you please confirm or deny?

 

 

I sorted those offset #'s out while building my blue streetfighter. I used a CB1000R top and custom billet bottom to fit my CBR1000RR 50/54 forks. 

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17 hours ago, BiKenG said:

Yes, the CB1000R (up to '17 anyway) is 35mm offset. So you could use a CB1000R top yoke and put regular bars on a VFR1200F.

 

I AM using 0.5mm shims for my 54mm Ohlins in the VFR's 55mm bottom yoke and indeed supplied JZH with both his yoke and shims. It was a quick fix and yes, it works. But I'm a perfectionist and can't help wanting a true 54mm bottom yoke to actually fit the forks. So far I've not found anything suitable 'off-the-shelf'.

 

Of course I'd really like to find out the clamp dia. and offset for the new '18 CB1000R which actually has a very nice looking bottom yoke. When Honda make a bike with fairing, they don't bother making the lower yoke look nice. The clamp area with bolts is just stuck on the outside and not very attractive. That's another reason for thinking about making my own. I could have the correct fork clamp dia. and also make it look better with the bolts tucked out of the way. Being a naked bike, the new CB1000R one is better looking. Anyone know the dimensions?

 

Thanks for the data Ken. I appreciate the way you navigate the permutation forest, and I share some limited portion of your purist spirit - as functional as 0.5mm shims are, they're not quite...just right. I hadn't noticed the aesthetic difference between Honda's 'inside' and 'outside' triple clamps. That the cowled units are-square cut and utilitarian while the naked bikes' triples have a design aspect is now clear.

 

12 hours ago, SEBSPEED said:

 

I sorted those offset #'s out while building my blue streetfighter. I used a CB1000R top and custom billet bottom to fit my CBR1000RR 50/54 forks. 

 

Ah, custom billet. It's fascinating how together those terms end up describing a component that meets all desired specifications. Seb, I recall mention that you were going to start manufacturing your own line of custom triple clamps - the date and chronology escape me, and so reduce my recollection to a vague hunch. Is the badass blue streetfighter's lower triple of your own making?

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Where is the best cross-reference information for Honda upper & lower triple clamps? (And other compatible models too.)

 

On my 5th gen, I plan to replace my OEM/Traxxion forks and delink the brakes. I've recently purchased a complete of SP2 forks, triples, axle and brakes, but now see that may be a mistake. Previous posts describe a hybrid SP1/SP2 fork with mixed outers and inners; what is the difference in length between the two? Or alternatively, what makes the SP2 incompatible with the 5th gen? As for frame pitch or steering stem rake, I already have my OEM forks raised in the triple clamps and my Penske topped out to maximum rear ride height.

 

Thanks in advance,

Kirk

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The SP1 and SP2 forks are somewhat different.  The SP2 is shorter, but that can actually be changed internally.  It's probably no more than 30mm difference, but maybe someone else knows for sure.  But I've read that shortening the cartridge top out spring can make the SP2 as long as the SP1.

 

The two outer tubes have the same clamping dimensions (54x50), but the SP2 has a somewhat limited clamping area, which might not be a problem for you but was for me.  My particular lower triple clamp was in the SP2's non-clamping area, so I had to swap upper tubes for SP1.  I'm not aware of SP2 forks being a problem with a 5th gen fork swap. 

 

The calipers are visually identical, but the piston sizes are different (and they use different size master cylinders).  The caliper brackets on the SP2 are also much beefier and they are not interchangeable with the SP1 caliper brackets.

 

The SP2 lower triple has a larger diameter steering stem, so I think the problem may be that there are no bearings that match the VFR frame ID and the SP2 stem OD.

 

Most people seem to use 929/954 upper triple clamps with the SP1 lowers, as this combination results in about 10mm more fork tube above the triple clamp so you don't have to mount clip-ons below the triple clamp.

 

What wheel are you using?

 

Ciao,

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12 hours ago, JZH said:

The SP1 and SP2 forks are somewhat different.  The SP2 is shorter, but that can actually be changed internally.  It's probably no more than 30mm difference, but maybe someone else knows for sure.  But I've read that shortening the cartridge top out spring can make the SP2 as long as the SP1.

 

...

 

The calipers are visually identical, but the piston sizes are different (and they use different size master cylinders).  The caliper brackets on the SP2 are also much beefier and they are not interchangeable with the SP1 caliper brackets.

 

The SP2 lower triple has a larger diameter steering stem, so I think the problem may be that there are no bearings that match the VFR frame ID and the SP2 stem OD.

 

Most people seem to use 929/954 upper triple clamps with the SP1 lowers, as this combination results in about 10mm more fork tube above the triple clamp so you don't have to mount clip-ons below the triple clamp.

 

As john said, but also:-

 

To clarify, all the RVTs' (SP-1 and SP-2) fork tubes are the same length. It is only the overlap which means they end up a different length and that's down to the internals. Overall though, they are the longest suitable USD forks used by Honda.

 

Of those visually identical (colour notwithstanding) axial calipers The SP-1 and FIreBlade RRW/X calipers are 32/34, 929's are 30/34 and almost all the rest are 30/32 which is the same as all Honda's radial calipers. The Master/Cylinder bore sizes have varied, but a regular 14mm such as used on many VFR's (or also available with external reservoir as per RC45) will work perfectly. Better in fact than any RVT M/Cs. Don't try a 12mm M/C though as in my experience that is way too small and the lever comes back almost to the bars.

 

The SP-2 stem is too fat at the top to fit the VFR headstock (as John said, no suitable bearings) so the SP-2 stem and top yoke is no good. The bottom yoke is same as SP-1 though, it's just the stem that needs changing.

 

What you need to be aware of though is that the RVT, 929, 954, RC45 offset is 30mm whereas the VFR's is 35. So the swap we're discussing here will increase the trail by a bit less than 5mm. Whether that is of any significance is up to you. Many have done this and say it's no problem. Dropping the front (or conversely raising the rear) will steepen the forks reducing the rake (steering head angle) and decrease the trail, so that could be used to (partially) compensate for the decreased yoke offset. FireBlade forks are (approx. 2") shorter and would automatically mean a lower front end, so if you want to do that and not have fork tube's protruding above the top yoke, use 'Blade fork legs.

 

I've not yet ridden a VFR with 30mm offset fork yokes, but I'm so sure it won't be a problem, I'm doing that on my VFR.

 

Of course, there are a multitude of other fork/front ends available from other manufacturers, but I've not looked into that. To my mind, fit Honda bits on a Honda. Simple.

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