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Better Understanding of Todays Track Lengths

Your comments to the woods of Northern Wi led me to think NE Wisconsin as I grew up in Wabeno so I definitely get the tight technical woods riding in that area as that's what I grew up riding - I'd definitely prefer the 129 personally for that area for sure although the 137 isn't totally out of its element there either - and your also 100% right that for the majority of the big high speed trails in the UP I would definitely recommend a 137 or 141 for the stability they have at speed.
 

MrSled said:
Im getting a LTX-LE.. dont get hung up on on what you are reading. Its not the gospel and some of us have other opinions on how sleds ride based on riding style, our own weight and what we expect out of the sled.
Click to expand...
AMEN!
 
I personally am a fan of the short track models. For top speed, you cannot beat the short track. Rotating mass is your enemy in terms of best top speed, and the track on a snowmobile is the worst method available for putting power to the ground for top end. It is basically a 40 lb flat tire, and the energy to rotate it is directly proportional to the square of the driver rpm. Double the driver rpm and you quadruple the energy needed to double the track rpm. (this is true for all components that rotate). Rotating components create a double-whammy, not only must the engine move them from a dead stop, but must also rotate them from the same stop. It has been estimated that a single pound of rotating mass is equivalent to 7 pounds of static mass. This is why light weight wheels, cranks, jackshafts, etc, net so much performance gain. Removing the heavy reverse gears in our chain cases would provide an increase you would feel on the trail.

So, adding 10 or 15 pounds for a 137 vs a 129 would be like adding 70 to 105 pounds of static weight.

The real advantages of the longer tracks (129 vs 121, 137 vs 129, etc) are the stability of the longer wheel base and the marketing appeal to the snowmobile buyers. The longer wheel base creates less transfer (skis down) and more high speed directional control. Manufacturers have also increased the pitches in an effort to save the expensive rods and clips (less are needed as you increase pitch) in an effort to give buyers what they want and still control cost to a certain extent. Interestingly, a longer pitch tends to create a more choppy radius as the track bends around the drivers and back wheels. At some point, too much pitch creates excessive bending forces.

I find that many people overestimate the amount of track on the ground as they contemplate the longer options. A 162 vs a 129, gives a track length increase of 33 inches, but only about 40% of the extra length is actually on the ground (40% of 33 inches = 13 inches). The rest is above the ground and over the top idlers and lost from in front of the approach angle of the rails. You can see that the difference in 129 vs 137 or even 141, is essentially immaterial. But, the added weight of these longer tracks is significant!

I think you will find that the guys and gals with the 129s are not feeling disadvantaged off trail as they follow their 137 and 141 tracked friends.

For what its worth,
Jim from Canton
 
Well jim for what its worth,i used to think just like you years ago,but today with the angle of attack,that the track rotates around,allows it better top speed,out of 144 or a 146 and even my old 136 attack ape,was just as fast top end as our shorties,121 at the time,and some of that was a drop in top gear from 24 to 23,and once the 121 was geared a like the 136 it was faster on top,but these are the old 2.52 pitch drivers and 121 length,but now with the lighter weight tracks in a 2.86 pitch track and better angle it just is not true,i have seen it on every occation,my Yamaha dealer in caribou kept telling me all his 2015 sleds in the xtx 144 length were beating all of his 128's in top speed,i just did not believe him,until I bought one and he was right.
 
Anyone know if the 7 tooth drivers on the 2016 Apex XTX 1.75" will have a loss of top speed as compared with the 8 tooth drivers on the 2016 Apex XTX 1.25" and Apex 129" track? I believe the number of driver teeth on both 2015 Apex XTX and shorty Apex were 9 teeth. Guessing the number of drive teeth were changed in 2016 to accommodate new track pitch?

Sent from my XT1055 using Tapatalk
 
Jim D said:
I personally am a fan of the short track models. For top speed, you cannot beat the short track. Rotating mass is your enemy in terms of best top speed, and the track on a snowmobile is the worst method available for putting power to the ground for top end. It is basically a 40 lb flat tire, and the energy to rotate it is directly proportional to the square of the driver rpm. Double the driver rpm and you quadruple the energy needed to double the track rpm. (this is true for all components that rotate). Rotating components create a double-whammy, not only must the engine move them from a dead stop, but must also rotate them from the same stop. It has been estimated that a single pound of rotating mass is equivalent to 7 pounds of static mass. This is why light weight wheels, cranks, jackshafts, etc, net so much performance gain. Removing the heavy reverse gears in our chain cases would provide an increase you would feel on the trail.

So, adding 10 or 15 pounds for a 137 vs a 129 would be like adding 70 to 105 pounds of static weight.

The real advantages of the longer tracks (129 vs 121, 137 vs 129, etc) are the stability of the longer wheel base and the marketing appeal to the snowmobile buyers. The longer wheel base creates less transfer (skis down) and more high speed directional control. Manufacturers have also increased the pitches in an effort to save the expensive rods and clips (less are needed as you increase pitch) in an effort to give buyers what they want and still control cost to a certain extent. Interestingly, a longer pitch tends to create a more choppy radius as the track bends around the drivers and back wheels. At some point, too much pitch creates excessive bending forces.

I find that many people overestimate the amount of track on the ground as they contemplate the longer options. A 162 vs a 129, gives a track length increase of 33 inches, but only about 40% of the extra length is actually on the ground (40% of 33 inches = 13 inches). The rest is above the ground and over the top idlers and lost from in front of the approach angle of the rails. You can see that the difference in 129 vs 137 or even 141, is essentially immaterial. But, the added weight of these longer tracks is significant!

I think you will find that the guys and gals with the 129s are not feeling disadvantaged off trail as they follow their 137 and 141 tracked friends.

For what its worth,
Jim from Canton
Click to expand...

So Jim , you are essentially disagreeing with what so many know as fact , that the longer 137 track is faster and has a higher top speed than the 129 track ! The Apex XTX is faster than the 129 !
Also , I don't understand how you think that only 40% of the additional track length is on the ground ?
IMHO , the answer can only be 50% !
I think, although not sure, that all the additional track length , goes in front of the rear axle , and half of the additional length has to be on the ground .
If the longer track is in fact faster than the shorty , then the additional weight is insignificant , and the continuous added traction is significant !
Maybe those who know , can chime in here .
 
Let's go a little deeper into some of the physical aspects of this discussion.

For those of you who think that 50% of the track is on the ground, consider this. Even when a track is laying on the ground uninstalled on the sled, like when you take it out of the box, less than 50% of it is touching the pavement. The bend in the track at both ends is not touching, and certainly all the length between the bends is off the ground. Even if you got two of your buddies to stand on each end and flatten in down as much as possible, you still will have less than 50% on the ground, although it would be fairly close to that number. Now, consider the track mounted in the sled with the big radius's on the drive axle and the rear axle; plus all the track that is off the ground between the drive axle and the rail where the hyfax first touches the ground. Then finally, consider the that the track follows a path that is not a straight line between the rear axle and the drive axle under the tunnel. It goes over the rear idlers up near the back of the seat, and this diversion from a straight line consumes even more track length. You don't have to take my word for it, simply sketch a track profile as they are installed in sled. It is roughly a parallelogram (a 'tilted' rectangle), best represented by the famous fast 10 rear suspension. Take the length of track that your sketch has touching the flat surface (ground) and divide it by the total length of track, and see how far from 50% you land!

In terms of approach angle, the SR chassis mounts the drivers in the same place for a 129 and 137. The rails for the 129 and 137 start in the same place (just under the foot wells). Both of these parameters determine approach angle. If on the other hand, you were to 'roll' your chain case (a practice that mountain sledders sometimes do to intentionally lower their drive axle and decrease their approach angle), or set your rear suspension back in the tunnel (sometimes done to use a longer track without adding rail extensions), you could 'change' your approach angle. But on the SR chassis, the axle and rails are in the same spots and only the length of the rail is different going out the back of the tunnel. With both sleds using the same settings on the spring preloads and limiter straps, the approaches are the same.

Some of the SR rear suspensions are uncoupled, and therefore will articulate quite differently compared to coupling, and will allow the suspension to drop its rear axle a lot lower during power transfer, to effectively change the approach angle and allow the sled to climb up onto the surface instead of plowing into it. But this is in deep snow and is not relevant when talking about top speed on a flat hard surface. Both coupled and uncoupled suspensions will have the same approach angle at top speed on a flat surface, given the same spring preloads and limiter strap settings.

A shorter track is lighter, and it takes less energy to move lighter vs heavier. It is the way the universe is set up and none of us can change that!

Jim from Canton
 
Jim D said:
Let's go a little deeper into some of the physical aspects of this discussion.

For those of you who think that 50% of the track is on the ground, consider this. Even when a track is laying on the ground uninstalled on the sled, like when you take it out of the box, less than 50% of it is touching the pavement. The bend in the track at both ends is not touching, and certainly all the length between the bends is off the ground. Even if you got two of your buddies to stand on each end and flatten in down as much as possible, you still will have less than 50% on the ground, although it would be fairly close to that number. Now, consider the track mounted in the sled with the big radius's on the drive axle and the rear axle; plus all the track that is off the ground between the drive axle and the rail where the hyfax first touches the ground. Then finally, consider the that the track follows a path that is not a straight line between the rear axle and the drive axle under the tunnel. It goes over the rear idlers up near the back of the seat, and this diversion from a straight line consumes even more track length. You don't have to take my word for it, simply sketch a track profile as they are installed in sled. It is roughly a parallelogram (a 'tilted' rectangle), best represented by the famous fast 10 rear suspension. Take the length of track that your sketch has touching the flat surface (ground) and divide it by the total length of track, and see how far from 50% you land!

In terms of approach angle, the SR chassis mounts the drivers in the same place for a 129 and 137. The rails for the 129 and 137 start in the same place (just under the foot wells). Both of these parameters determine approach angle. If on the other hand, you were to 'roll' your chain case (a practice that mountain sledders sometimes do to intentionally lower their drive axle and decrease their approach angle), or set your rear suspension back in the tunnel (sometimes done to use a longer track without adding rail extensions), you could 'change' your approach angle. But on the SR chassis, the axle and rails are in the same spots and only the length of the rail is different going out the back of the tunnel. With both sleds using the same settings on the spring preloads and limiter straps, the approaches are the same.

Some of the SR rear suspensions are uncoupled, and therefore will articulate quite differently compared to coupling, and will allow the suspension to drop its rear axle a lot lower during power transfer, to effectively change the approach angle and allow the sled to climb up onto the surface instead of plowing into it. But this is in deep snow and is not relevant when talking about top speed on a flat hard surface. Both coupled and uncoupled suspensions will have the same approach angle at top speed on a flat surface, given the same spring preloads and limiter strap settings.

A shorter track is lighter, and it takes less energy to move lighter vs heavier. It is the way the universe is set up and none of us can change that!

Jim from Canton
Click to expand...

So Jim , everything that you post is very interesting .
But theses are the facts that you are not getting .
The additional length of a track from 121 to129 , 0r 129 to137 , or 137 to 141 , will have 50% of the ADDITIONAL LENGTH on the ground , as it has been added to the part in front of the rear axle ! Obviously this doesn't apply to the tipped up rails on the XTX , and that is why it has the best of both worlds , and I don't understand why it is not currently in the line up . But I digress .
Also the additional weight of the longer track , is offset by the added traction , and that is why it is faster , when the lug heights and track sections remain the same . The 137 is faster than the 129 ! The Apex XTX 144 or 146 , are faster than the 129 !
That is part of the reason , so many TY'ers , are buying the SW137 , and not the 129 !
And those that do buy the 129 , will spend their next season looking at their friends back with the 137 ! unless they reflash , but that is another topic .
 
You guys are making my brain hurt....lol
One question tho
In the Viper or Cat is the 137 faster than the 129?
 
Do the exercise that I recommended first, before you continue down your path. (Sketch the track on paper and observe the physical state).

Think of it this way; how much of a tire is actually in contact with the ground? Not much because it is almost a perfect circle, only the flatness created by the weight of the vehicle makes the contact patch more than the geometrical zero tangent point of a circle/sphere contacting a plane. A track is essentially the same object with a much larger contact patch due to the 'flatness' of the profile. But still, more than 60% is up off the snow.

And, any additional length is subjected to the same physical constraints.

If you still disagree, I will bet you pink slips on this one.

As far as bench top racing, anyone can post anything on these forums, but that hardly proves anything. I can say that my 129 is faster than any 137 or longer track, but we all know that there are countless variables at play and it is impossible to isolate enough to prove anything in this virtual setting.
 
Jim D said:
Let's go a little deeper into some of the physical aspects of this discussion.

For those of you who think that 50% of the track is on the ground, consider this. Even when a track is laying on the ground uninstalled on the sled, like when you take it out of the box, less than 50% of it is touching the pavement. The bend in the track at both ends is not touching, and certainly all the length between the bends is off the ground. Even if you got two of your buddies to stand on each end and flatten in down as much as possible, you still will have less than 50% on the ground, although it would be fairly close to that number. Now, consider the track mounted in the sled with the big radius's on the drive axle and the rear axle; plus all the track that is off the ground between the drive axle and the rail where the hyfax first touches the ground. Then finally, consider the that the track follows a path that is not a straight line between the rear axle and the drive axle under the tunnel. It goes over the rear idlers up near the back of the seat, and this diversion from a straight line consumes even more track length. You don't have to take my word for it, simply sketch a track profile as they are installed in sled. It is roughly a parallelogram (a 'tilted' rectangle), best represented by the famous fast 10 rear suspension. Take the length of track that your sketch has touching the flat surface (ground) and divide it by the total length of track, and see how far from 50% you land!

In terms of approach angle, the SR chassis mounts the drivers in the same place for a 129 and 137. The rails for the 129 and 137 start in the same place (just under the foot wells). Both of these parameters determine approach angle. If on the other hand, you were to 'roll' your chain case (a practice that mountain sledders sometimes do to intentionally lower their drive axle and decrease their approach angle), or set your rear suspension back in the tunnel (sometimes done to use a longer track without adding rail extensions), you could 'change' your approach angle. But on the SR chassis, the axle and rails are in the same spots and only the length of the rail is different going out the back of the tunnel. With both sleds using the same settings on the spring preloads and limiter straps, the approaches are the same.

Some of the SR rear suspensions are uncoupled, and therefore will articulate quite differently compared to coupling, and will allow the suspension to drop its rear axle a lot lower during power transfer, to effectively change the approach angle and allow the sled to climb up onto the surface instead of plowing into it. But this is in deep snow and is not relevant when talking about top speed on a flat hard surface. Both coupled and uncoupled suspensions will have the same approach angle at top speed on a flat surface, given the same spring preloads and limiter strap settings.

A shorter track is lighter, and it takes less energy to move lighter vs heavier. It is the way the universe is set up and none of us can change that!

Jim from Canton
Click to expand...

I agree rotating mass is Energy expensive. But of the lbs added for increased track length very little of it actually rotates so although there is a penalty it is SMALL. One could argue the only rotating mass is the track and the idler wheels.
Always been interesting to me that some longer track models are apparently 'faster'.
 
Jim D said:
Do the exercise that I recommended first, before you continue down your path. (Sketch the track on paper and observe the physical state).

Think of it this way; how much of a tire is actually in contact with the ground? Not much because it is almost a perfect circle, only the flatness created by the weight of the vehicle makes the contact patch more than the geometrical zero tangent point of a circle/sphere contacting a plane. A track is essentially the same object with a much larger contact patch due to the 'flatness' of the profile. But still, more than 60% is up off the snow.

And, any additional length is subjected to the same physical constraints.

If you still disagree, I will bet you pink slips on this one.

As far as bench top racing, anyone can post anything on these forums, but that hardly proves anything. I can say that my 129 is faster than any 137 or longer track, but we all know that there are countless variables at play and it is impossible to isolate enough to prove anything in this virtual setting.
Click to expand...
You are correct with about 40% on ground because i measured my 128'' Apex next to my buds' 121" Apex. It was about 3'' on ground. BUT, although your theories make sense on paper, not always in reality. CASE IN POINT: Me & bud at 121'' ran neck & neck from off the line to top end. With my 128", i walked away from him on bottom & beat him on top also. We were both FLABBERGASTED 'cuz it went against all THEORIES. 3'' times 15'' is 45 inches squared on ground. Those 45'' really hooked up! Also i believe on top i wasn't spinning as much. Spinning at any speed is a waste. It's also possible my Ice-Ripper was a better track on top than his 121'' Ripsaw with 96 studs. Both tracks weighed the same also. BTW he bought a 128'' Ripsaw the following week...and we're even again...
 
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