From Rogue RC51
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.
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:
1. DID chains are the best period.
2. RK chains used to be great, but suck ever since they got bought out back in about 2000
3. Vortex sprockets wear out way way way too fast...
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.
With a 520 conversion you typically save about 4lbs of rotational mass which reduces gyroscopic precession and makes a big difference in the handling of the bike. It's proven hp on the dyno as well...
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.