Shift RPM Explained Deeper
The following is a tech article that is really a conversation I have several times a day on the phone and thought I would just put it in text for anyone to read.
What is shift RPM?
Should be called shift phase RPM really and it is the RPM the engine is running during the shift phase of the clutch which is basically from the time you start moving until the belt fully shifts out or moves as far as it can on the clutches.
The purpose of the CVT clutch system is to try and maintain a particular RPM during this phase where the engine makes most of it's power for maximum acceleration. The tachs on a RZR are very slow responding, you are at shift speed a whole lot longer than your tach tells you that you are due to the slow response. I usually tell people to get the belt warm, get rolling and floor it until top speed while watching the tach and it usually will level out around 45-60 mph depending on which RZR and the tach will either slow way down or actually stop then once the belt is fully shifted out past that point the RPM will tick on up to whatever top speed RPM is which is basically the engine speed that the vehicle is capable of. People with bigger tires, added weight etc drag down speed and rpm at top speed due to load. We can adjust shift speed with the clutch or clutch kits such as the Dalton kit we sell to get the RPM where we need it for maximum performance.
Also there is no shift feel, you are not looking for a shift or feel a shift, it is simply a term used to describe what is going on. Your CVT is shifting from low ratio (idling) to high ratio (fully shifted out) the whole time. The engine will sound like it is changing rpm too during shift phase but what you are really hearing is a load change on the engine. Easy to prove by running one on a dyno, during shift phase the graph has RPM flat.
Ok now we know what it is, so what about it?
A black and white answer is there is just one shift speed for any particular vehicle we need to shoot for when setting our clutch up. But that is really just for a group of people who I say use their RZR for it's intended purpose which is fast trail riding, on and off the throttle. Let's use the XP 1000 as an example. For this kind of rider we would set the clutch up for the engine to have a shift RPM of around 8300 RPM and it will work well.
But what if you are a rock crawler? Slow technical rider? Or even a duner? Well 8300 may not work for you very well. I like to say that when you are trying to clutch for maximum performance for whatever you are doing then clutching gets specific and requires you to adjust accordingly. A slow rider, rock crawler, mud guy is more concerned about belt grip more than anything and rarely gets into actual shift speed because he does not floor it and haul butt that much. So, I usually tell that guy to set his XP 1000 to a shift rpm of about 8100 and he does that by adding a bit more weight into the flyweights. What this does for him is makes his clutch engage sooner and with more clamping force on the belt. However, this heavier set up would not be as good as the higher shift rpm for some fast trail riding but it would do pretty good in some short drag races. This group of riders need to know that a RZR of any kind normally does not do well going slow. The larger and more powerful machines such as the XP 1000 have a harder time going slow due to weight of the machine, the powerful engine and the fact the clutch has to come in and squeeze the belt to get you moving add up to a decent amount of potential belt issues. It also does not help that the majority of this group normally has larger tires to accomplish the style of riding they do for clearance.
Duners, well these guys need more RPM due to the added load of the sand and the climbing up the dunes and it dragging them back down. Again using the XP 1000 as an example I would say a shift RPM of around 8500 RPM would work for these guys.
If a duner who set his clutch up to run in the dunes took his RZR rock crawling the most likely thing that would happen is a good bit of belt slippage due to the lighter weights.
I want to add something here that is not so much about shift speed as it is about people trying to adjust top speed rpm with a clutch adjustment. First, don't do this as this, it is not how it is done. Can you adjust rpm at top speed with clutching yes but you should not, you should set shift speed with the clutch and what you get what you get at top speed.
Example: A XP1000 owner who got his ECU flashed and raised his rev limiter and lets say it was at 9500 instead of 8500 and wants to hit it or run near it. Sure he can take weight out of the flyweights to get there but how is it doing it? He is getting the flyweights so light that the primary clutch can no longer close all the way and he just screwed up shift RPM which in turn just screwed up his acceleration and less belt grip at slow speeds. It will have less acceleration now but yes he is at the new higher rpm at wide open but it is wrong. Does he actually drive at those speeds and RPM much? No and regardless even if he does, he could run the same top speed or maybe faster with lower rpm by not doing that. My point is, set shift RPM where it should be and top speed RPM will take care of itself, it will be whatever you have enough power to pull you to. I use a 5 speed car, once you shift into 5th gear you are a the mercy of how much power you have to speed on up. In a five speed car, you would push in on the clutch and let it slip a bit to make rpm go while at top speed would you just so you can see the tach go up?
Who benefits the most from a clutch kit? The duner and the fast trail rider more so because belt slippage is not a concern and they want performance. Can a slow rider benefit? Yes of course but not the same way the other two can.
Here at Hunterworks we don't just give a canned response to what you have. I listen and hear your application then help you figure out what we need to do that best then tell you the limitations of that set up when used for anything else such as mentioned trying to go duning with a rock crawler set up.
Hope this has helped clear up shift rpm a little more
Got any questions give me a call