[Paxx]

So my last thread on clutching got a little derailed because of an issue that my machine was having, so I decided to start a new thread with some specific discussion around Olav Aaen's speed diagram.

As soon as I read his book and saw the speed diagram, it made a few things click for me. I'm a visual learner and found that the diagram helped my comprehension immensely. I've attached a couple of screenshots of his speed diagrams below. (excuse the handwritten notes, they were on the PDF copy I had)

In his book, Olav suggests that a typical low ratio is 3:1 and a typical high ratio is 0.8:1. When viewing the two attached drawings (both from his book), it appears that the low/high ratio lines that are plotted are actually different from each other, they don't intersect the same points on each diagram.

So I guess my first question is; at a 3:1 low ratio should the line always be plotted consistently on the speed diagram? - the same question applies to the 0.8:1 ratio line. Or does this change depending on the specific machine and how it is set up, how much power it produces, etc.

My next question depends on the answer to the first question I suppose - If the low ratio and high ratio can be plotted consistently on the graph, how do you actually calculate the angle of the lines?

Understanding that the stock low ratio on a 2014 XP1000 (as an example) is 2.6:1 low ratio, how would you accurately draw this line? If the lines can be consistently plotted, they will be in a different position on the diagram for our example vehicle (2014 XP1000) than what is shown in Olav's book.

And my final question - can anyone tell me what the overdrive ratio is on these machines? I know the low ratio is the 2.6:1 but I really have no idea what the overdrive ratio is.

Looking forward to discussing this in more depth - I think it has the potential to be an amazing tuning tool for me in the future when my understanding is a little more solid.

I have a ton more questions, but I need to know the answers to these ones before I can move on haha. :grin

 

[FordTruckMan]

Slope intercept is all I got for you. y=mx+b. The ratios you mention appear to visually line up with the slope of the lines. Ration of 3:1 is a slope of 3. Rise over run, so up 3 over 1. Get a piece of graph paper and plot it out to see. 0.8:1 is same thing but closer to 45° angle because it's closer to a 1 to 1 slope.


Or, I am completely wrong lol.



BUT, if I'm not, then it would make sense that the concept was to plot the min an max slope, note the desired shift speed based on where the engine makes power, and use that to illustrate the usable area of the graph where shifting would occur. I could see how this would help when tuning.



A disclaimer, I have done exactly zero work with a RZR or snowmobile clutch. All of my work has been with a yamaha ultramatic setup. I take that back, I did get rid of my square pucks (thanks Todd) lol.



Maybe someone smarter than me can chime in haha!

 

[Paxx]

Thanks for the input!

I've been thinking about this quite a bit and at first, I think I would have agreed with you but as I was imagining different scenarios, I think I may have changed my mind. Maybe... ha ha

Let's use this following hypothetical example...

Vehicle 1 - A 200hp fully built duning RZR with a 3:1 start ratio

Vehicle 2 - A 107hp stock 2014 RZR with a 3:1 start ratio

Obviously, vehicle 1 is going to hit 10mph much quicker than vehicle 2. The question is, will it hit 10mph at the exact same RPM just because they are both a 3:1 ratio or will vehicle 1 get there at a different RPM because it produces more power?

If the 3:1 ratio determines the slopes of the shift lines, regardless of power output, then it would be quite easy to map out the ideal shift curve based on whatever the vehicle ratios are. If not, this gets quite a bit more difficult because every vehicle will have a slightly different speed diagram based on engine performance...

What are your thoughts on that? I'm still wrestling with which outcome is correct ha ha.

 

[FordTruckMan]

Thanks for the input!

I've been thinking about this quite a bit and at first, I think I would have agreed with you but as I was imagining different scenarios, I think I may have changed my mind. Maybe... ha ha

Let's use this following hypothetical example...

Vehicle 1 - A 200hp fully built duning RZR with a 3:1 start ratio

Vehicle 2 - A 107hp stock 2014 RZR with a 3:1 start ratio

Obviously, vehicle 1 is going to hit 10mph much quicker than vehicle 2. The question is, will it hit 10mph at the exact same RPM just because they are both a 3:1 ratio or will vehicle 1 get there at a different RPM because it produces more power?

If the 3:1 ratio determines the slopes of the shift lines, regardless of power output, then it would be quite easy to map out the ideal shift curve based on whatever the vehicle ratios are. If not, this gets quite a bit more difficult because every vehicle will have a slightly different speed diagram based on engine performance...

What are your thoughts on that? I'm still wrestling with which outcome is correct ha ha.

Well assuming all clutching and drivetrain components were identical, regardless of the motor hp or even type, the same engine RPM would result in the same vehicle speed up until the clutch ratio begins to change. Even then, the differences would be limited until you approached higher speeds due to the required torque to continue to accelerate the vehicle.

Think of it this way, once the primary sheaves have reached engagement rpm, the engine output shaft and the rear tires are effectively locked together, save for belt slip. The only thing that determines change in vehicle speed after that is change in engine RPM or change in drive ratio of the CVT.

So, let's assume you have two setups as you said, one with high hp and one with standard hp. They would in reality never be clutched the same because their respective ideal shift speed would almost certainly be different. However, assuming they were clutched the same, they would both have a fixed 3:1 ratio from engagement speed to shift speed. The higher hp engine would likely get there faster, but the engine RPM and ratio are still going to be the same.

At least, that's how I understand it.

 

[Paxx]

Appreciate this back and forth, it's helping me work through this in my mind.

So now let me throw in another variable...

Vehicle 1 - running 32" tires
vs
Vehicle 1 - running 28" tires

So would the larger tires on the same vehicle allow you to reach speed faster, therefore changing the speed/rpm ratio, (larger diameter tire covers more distance per revolution) or will the larger tires bog the engine down that little bit that causes the speed/RPM ratio to stay the same?

 

[Paxx]

The reason I'm diving so deep into this is that I've got 3 buddies of mine with xp1000's and we are about to embark on getting our clutches dialled in.

Each of us has a slightly different setup so I'm trying to figure out if I can print a bunch of blank speed diagrams with lines pre-plotted at a 2.6:1 low ratio for them and a 3:1 low ratio for myself (I'm running an aftermarket clutch) and it will accurately depict the shift out on the line.

If this ratio is a constant, then it will make this a much easier task having that tool!