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Gearing.

Snowmobile How-To's

 
 
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  #1  
Old 10-05-2007
Madcow's Avatar
Madcow
1050 one lunger
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Default Gearing.

this is basically my opinion and experience.

gearing a sled is a very overlooked performance increase. on most sleds you can change the amount of torque at the drive axle by 5-15 lb/ft with simple gear changes. to gain them gains to the track with engine mods you are looking at hundreds of dollars. you have lots of lost hp in the track itself and a percentange lost in the clutching. so changes in the chain case will tend to carry to the drive axle with little loss. if you take a sled in general for trail riding if you gear it to low you will have amazing power off the line and for ditch banging. but once you started to get on a flat smooth trail you will be shifted out at a very low mph or trying to keep up with your friends you will be trying to get into a big overdirve on the clutch's. as the clutching gets to 1-1 you have a small amount of efficiency loss. as you try to force the clutch into overdrive you really loose hp in a fast way. the slower you keep your secondary clutch spinning the more efficient the clutching will be. if you gear to tall you can start to have belt sqweel or burn if you dont reclutch on take off. you can have a bog or sluggish bottom end. in the rough stuff the sled might still have some hesitation to it or less pull. on flat hard trail you will be doing just fine but have slow accelleration coming out of corners. most sleds will hp out on top end before they run out of gear. meaning if you take a stock 700 dragon with a 1.25 ripsaw track and toss in some studs. lets say stock gearing is good for about 110mph. you take and do a couple 1/2 mile runs and get 104 mph. that is pretty good because you are getting close to 1-1 shift with a heavy hard to spin track. if you gear up to 120 chances are you might only see a couple mph gain on top end. after that you can gear up all you want and the sled wont pull any more top mph since the hp of the motor can only get you a little over 104.

usually you want to gear for about 10 mph more than you are going to go. on a heavier sled or a smaller motor sled you might need to gear a little closer to the projected mph you want to go. on a lighter or more powerfull sled you can gear very tall and have good take off with great top end.

belt burning with gear change. you hear a lot of people say that they geared higher but it just smokes the belt now on take off but I like the higher top end. usually what is happening is the motor has enough power so its not going to bog, and with tall gearing it takes a little more power to get moving, like starting a manual truck in second gear vs first gear. so when you punch the gas the motor pulls hard on the belt. the helix is also very aggressive at low end to shift up the clutch, the motor basically pulls the belt into the secondary enough to create a little slack and you get some burn. but since the machine is starting to roll the secondary is also trying to back shift some of the slack so you get a little smoke or sqweel but it goes away in a moment. usually what you need to do is go to a smaller helix on the starting angles to help hold the belt back, also the smaller helix angles have more natural bite on the belt with the same amount of spring pressure.

one minute I am telling someone to gear up and the next minute I am telling someone to gear down. because each situation is a little different. for the on/off trail riders a little lower gearing will pay off in the long run. you lost top end already with a longer track and deeper lugs, so pure top speed doesnt matter. but getting moving in deeper softer snow with as little trenching as possible is more important. so if you gear down several teeth so you have the power now to baby the sled moving instead of having taller gearing where you slowly give it gas and you can feel the sled wanting to start to move and when it gets enough power to start to move it spins out. also the lower gearing helps keep the rpms up a little bit, keeps the clutches engaged a little more solidly meaning a lot less stress on the belt and clutches.

over the years I have done testing and basically all the clutch tuning can only go so far for performance. once I seemed to hit a wall for speed I geared up a little bit. the speed came up at the same rate of gearing so you gear up a little more and the speed came up a little more.
pros doing drags where there is positive traction accually went quicker as they geared a little higher than they wanted to go. but the oval guys lost lap time when gearing a little taller since they lost a tiny bit of acceleration coming out of corners.
gearing for drag racing/ditch banging you might be suprised at how much gearing your sled can actually pull. for the heck of it I ran some 200 foot drags against some f cats. both sleds seem to have equal traction. I was geared at a 1.4 ratio. according to most shops that is way to tall for trail riding let alone drag racing in short distances. but it worked very well. since traction very limited no matter how much I geared down to help acclerate faster I would have just spun more. same with running a 144 1.25 track. 23-41 worked amazing for off trail riding and did ok on the trail for top end. that gearing got me about 100 on the mph calculator and on the ground it got me just shy of that. if I was in hard pack snow it went to 98 mph, if I was in 2 feet of fresh snow it went to 98 mph. with the same track on in the deeper snow with 24-39 gearing I could get the top end up to the 110 mark and had good drivabilty for starting out and picking trees. with the 25-37 gearing it had about the same top end but now you could feel a little hesitation on getting the sled rolling in the deep snow.

for the cost of all the aftermarket stuff out there gears can offer some of the best improvments for the least amount of money. for 350 dollars you can add a can, or a set of reeds to add 2-3 hp to the motor. or for about 65 dollars you can add a couple percent of torque to the track for a deffinate increase. gearing is the best compliment you can do with a clutch kit or motor work.
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  #2  
Old 10-05-2007
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98PSI700RMK
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Default Gearing.

bravo VERY well stated...
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  #3  
Old 10-05-2007
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Summer Sux!!
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Default Gearing.

I get very puzzled looks from many of the locals when I try to tell them that my '93 Wildcat will hit 110 mph on Hard Pack and yet will go from a standing start on deep snow with almost no track spin (it is even better with the 1" lug track).

The original clutching on this was for higher elevation from the factory.
After I changed the track (121X15X1) and put the new clutch on with OEM settings for this area/elevation, and dialed in the secondary. I only lost about 3 mph top end and it will still pull from a standing start in deep snow (2/3 ft) without getting buried.
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  #4  
Old 10-31-2007
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Default Gearing.

I don't remember where I got these from but(if they upload) I've attached 2 files. First is a Gearing recommendation chart for Polaris Snowmobiles. Second is a gearing calculator, it will let you calculate your hypothetical top speed determined by what gears you want to input
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  #5  
Old 10-31-2007
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Default Gearing.

Possibly here?:

http://www.slednutz.com/index.php?op...40&topic=197.0

If yours are different I'll upload them into the other thread. The more the better.
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  #6  
Old 10-31-2007
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Default Gearing.

No I've had them for quite a while now.
I completely forgot about that topic, the ones I uploaded are basically the same but slightly different in aesthetics
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