Changing the Gearing on the RC51
has some extremely tall gearing, according to
calculations & actual tests it is capable of speeds
close to 75mph in 1st gear. A quick & easy mod is to
replace the OEM 40 tooth rear steel sprocket with an
aluminum 42 tooth sprocket.
By lowering the overall gearing with the taller rear sprocket you theoretically lose some topend speed in favor of quicker acceleration which is perfect for the RC51 as no one needs a 172mph top speed on a street bike anyway, but the real truth is you don't lose any topspeed on the RC51 because the stock engine is not capable of pulling redline in top gear with the OEM sprockets. You actually get more topspeed when you can actually rev out a slightly lower gearing plus it's much more beneficial to have the quicker acceleration while at the same time easier on the clutch when taking off from a standing start as the now lower gearing requires less clutch slippage & lower engine revs to get the bike rolling.
For those of you that are curious here is an Excel Spreadsheet RC51 Gearing Calculator that can be used to calculate gearing changes on the RC51
The gearing can be lowered even further by going down 1 tooth on the front sprocket which is roughly equivalent to going up 3 teeth on the rear sprocket and the most popular gearing selection by far is the 15/41 set. I literally sell 20 of the 15/41 Kits compared to 1 of ANY other gearing combination. You may end up short shifting in the lower gears to keep the front end planted instead of using the motor to it fullest potential to keep you going forward, but this is a small price to pay for the overall benefit of the lower gearing. You also have to contend with increased compression braking from the motor which is a bit of a problem on any large displacement V-twin without a slipper clutch. Too much compression braking combined with an aggressive clutch release will have the rear wheel locking up as you are trying to enter 1st & 2nd gear corners at optimum speed & trust me when I say it's no fun to have your rear wheel hopping all over the asphalt when you are trying to set up for the corner on the other hand do it right & you will start to learn the technique of "backing it in".
All things considered the 42 tooth rear sprocket is the simplest way to lower the gearing as it requires the least amount of effort & expense ($50-$70). The stock chain will accommodate the 42 rear & also allows you to shorten the wheel base a little bit on the bike as you will have to push the rear wheel forward to compensate for the larger sprocket when setting chain slack. It should also be pointed out that with the stock chain & a 42 tooth rear sprocket that if you choose to run a 180 series tire that you might have clearance problems with any hugger you may have fitted or the tire might even expand at high speeds & literally rub the swingarm. The shorter wheel base makes the bike handle slightly quicker, but also seems to cause some rear grip issues when really picking up the pace In this case the 15/41 combination can be a great asset as it actually allows the rear wheel to be placed further back in the swingarm. Steel rear sprockets are available have become the rage in the last few years. Apparently most owners are looking for longevity rather than outright performance and they get that with the Steel Rear Sprockets and at a cheaper price as well. That being said some of the hardcore trackday guys and or racers are still buying Aluminum sprockets and with that here is what you need to know:
Aluminum Sprockets: Never buy an aluminum sprocket that is not Hard Anodized. The Hard Anodizing process greatly extends the life of the sprocket & is easily worth the extra $10 or so it costs for them. The OEM rear sprockets are steel & are built for durability, but the extra weight of the streel versus a lighter aluminum sprocket makes the bike harder to stop, steer & accelerate due to the additional rotating mass on the wheels. I mean you bought a top of the line high performance sportbike you might as well do all you can to get the most out of it & aluminum sprockets, even though they are going to wear out faster than steel they are still pretty damn cheap mods in the scope of things. If you can buy an $11,000 bike you oughta be able to spend $60-$70 on a sprocket every now & then plus if you keep you chain maintenance done properly especially proper chain slack then you can get some incredible mileage out of them.
I have tried just about every single brand of sprocket known to man, even used to pay big bucks (about $90 each & waited forever to get them) for the Renthal's cause I figured if the HONDA team used them they must be good (WRONG!) I have had issues with them being out of round and the hard anodized Renthals wear very quickly compared to other brands. The hard truth is those companies GIVE those sprockets away to race teams by the bucketfulls so they can say that a Pro Race team uses their products and gain market exposure. In all the years I have been testing & selling sprockets I will rest my reputation every single time on the AFAM brand. They are without a doubt the best. They don't advertise their process, but I used to have aluminum fittings & bungs hard anodized when I was in the rotational molding business & the coloration of the AFAM sprockets looks just like they have impregnated their hard anodizing process with teflon. This would go a long way towards explaining why their sprockets last so long, but again they don't make any claims to this at all it is just something I have observed. Having said that that the latest offerings from AFAM seem to be moving away from the teflon impregnation and more towards standard hard anodizing so there is some uncertaintly as to their longevity, but they still seem to be lasting longer than any other brand I use or sell.
There has also been a resurgence in steel rear sprockets lately, but these are new designs called "superlight steels". They are made in the 520 pitch, but are machined out to reduce weight and while they do weigh more than aluminum sprockets they are still significantly lighter than the OEM steel sprockets and with proper chain maintenance will last a very long time when compared to aluminum sprockets.
I can also throw my
opinion out for 3 more things with great certainty:
SuperSprox: Everytime I turn around on a message forum someone brings up the issue of SuperSprox sprockets. This is where they take an aluminum hub and rivet a steel out ring of teeth to it to give the user the best of both worlds etc... As far as I am concerne nothing could be further from the truth. The cost of the Supersprox sprockets is much higher than the cost of a quality aftermarket hard anodized aluminum sprocket and WAY higher than a steel rear sprocket. Here is the real kicker for me though as I had to order one of these for a very insistent customer not too long ago and when I weighed the 530 Supersprox sprocket it actually weighed MORE than the OEM steel sprocket it was replacing. Seems ridiculous to me to spend more money for less performance...
Naturally if you are racing the RC51 then your gearing may need to be much lower than discussed above and many of us are running 15/43 on track only RC51's, but for the average street rider the 15/41 combination is without a doubt be the most popular. As the RC hasn't been in production for over a decade most owners have already switched to a 520 chain conversion as well. Personally I am of the opinion that if your bike is brand new, save the money & simply swap out your sprockets & use your stock chain (530 or 525) & when it finally comes time to replace the chain then swap to the 520 conversion.
530 vs 520 conversion
Ok this question comes up a lot. The difference between a 530 & a 520 is that the 520 chain is slightly smaller in width & of course with that it weighs less. Less weight means you can spin up the rotating mass faster (better acceleration). People incorrectly get the idea that the 520 chain being lighter & smaller is inferior to all 530 or even 525 chains and that is simply not the case when the quality of the chain is taken into consideration. A high quality 520 Chain like the DID ERV-II stuff is just as strong as the OEM 530 chains they are replacing or at least close enough that the issue of accelerated wear is just not an issue. Now if you are buying cheap 520 chains from lesser brands then yea you may very well have longevity problems, but stick to the DID brand and you need not worry about the quality. I have personally used DID ERV3 chains for almost 2 decades now on everythign from RC51's to GSXR1000's to my new ZX-10R and we recently used the same DID ERV3 520 chain with Alloy sprockets for an entire race season on our 205rwhp BWM S1000RR race bike and had zero problems so I know damn good and well they work and the newer DID ZVM-X chain is rated even higher than the ERV3.
With proper chain maintenance and slack
the high end DID 520 X-ring chains will last as long as
any OEM 530 chain which are traditionally lower quality
used to meet a price point.
If you are switching to a 520 chain you must buy 520 sprockets to go with it! You cannot use the OEM 530 sprockets with your new 520 chain nor can you use 520 sprockets with a 530 chain (yes people have asked this)
Typically if you are racing the bike & need every ounce of help you can get go ahead & switch to the 520 conversion now (new chain & sprockets).
If your bike is new (chain & sprockets are in good condition) & primarily a streetbike or just an occasional trackday machine then I suggest just swapping out the sprockets in the same 530 pitch & leaving the OEM 530 chain on the bike. When the time comes that you do finally wear out the OEM 530 chain then you can decide at that time if you want to do the 520 conversion (I would) since you generally have to replace both the chain & sprockets together anyway.
Let's talk chain
This just recently came up in conversation on another message forum where a couple riders had complained about their fairly new X-Ring high end chain had the x-rings literally falling apart. Many years ago I had personally experienced a similar issue with an OEM o-ring chain and what had happened is I had used a very stiff plastic bristle brush to clean the chain and the bristles actually started to tear at the rubber o-rings and cause them to fall apart. the o-rings are under pressure between the side plates so the slightest nick in them will cause the abrasion to tear further under tension. In these recently reported incidents though the owners were stating that they did not use stiff bristle brushes etc, but there was a common denominator in that they were all using Motul Chain Cleaner. Now while the ingredients in the chain cleaner might not be caustic to the rubber o-rings or x-rings that does not mean that the propellant inside the can to get that detergent to the chain isn't. When I pulled the MSDS sheet on the chain cleaner it showed Butane & Propane as ingredients and both of those are deemed unsatisfactory for use with EPDM rubber. It was also stated in the Motul literature that the product was supposed to be applied in short bursts whereas the users were simply spraying it out of the can in long durations and rotating the wheel slowly by hand to coat the chain with the cleaner. This prolonged spraying allows the propellant in the can to saturate the rubber o-rings and start to deteorate them instead of evaporating quickly. Don't misconstrue I am not opposed to using Motul Chain Cleaner I am simply saying that if you do not use it correctly you may be subjecting your o-ring chain to premature failure. Additionally it is highly likely that it is not just Motul Chain Cleaner that this would be an issue with. I am reasonably sure other cleaners and even other brands of aerosol chain lubrication also contain propellants that are harmful to the rubber o-rings so too much of a good thing can easily become a bad problem.
I was asked about my own chain maintenance and what I
recommend. The short answer is I use WD-40 for cleaning
and light lube at all times. When I
take the time to actually lube the chain properly it is
usually Repsol Chain Lube. for the sake of
clarification I am not a fan of Repsol products as I find
their engine oils to be very inferior, but their chain
lube product is excellent. It sprays out of the can in a
very fine, atomized and controlled mist and is easy to
clean up if you get any overspray.
With OEM gearing most Japanese bike speedometers are designed to indicate about 7-8% faster than you are actually traveling at freeway speeds (around 70mph).That error is non-linear in that as you increase speed the error grows so by the time you are at an indicated 130mph the speedo error may be as high as 13-14%. At the same time if you are traveling at an indicated 35mph the speedo is almost perfectly accurate. it is designed that way by the engineers.
If you change your gearing ratio then you alter that error. By lowering the overall gearing to say 15/41 sprockets you have increased what was originally a 7-8% error at freeway speeds to about a 12-13% error. That is why there are several versions of speedo recalibrators on the market.
After all of that if you still have questions please feel free to contact me and I will answer you promptly
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