too low of gearing?

[high time]

I agree. I like this thred....

I don't agree that shift out is 1 to 1. That would mean the the diameter the two ends of your belt are the same size. They are only that way somewhere in the middle. I think what Aaen means is that that is the most efficient spot. At that point the clutches react the best.

Belt deflection is a key part of all this. I have noticed that many of our sleds are leaving no belt wear marks on the top edge of our primary. That's either a non achievable top end or a belt too loose.

I've always felt that 20 x 43 gears gave me a top speed of about 80 to 85. With my belt tight, I can break a belt if I try to go faster. My belt goes right to the top of the primary.

I've also found that there isn't much change in clutching with a change in gear ratio. Lower gears feed back less load and thus faster upshift. This shows little or no effect at the bars. Most of us figure it would increase RPM it doesn't often have much affect. It just uses a different spot on the cluch face.

Owen

 

[ruffryder]

As far as clutching and gearing go you should be chasing your heat more than worrying about numbers I think. Get your temps down while holding onto your rpm, flat upshift, good backshift and do it without running out of gears and grenading belts and you're probably doin ok...

Agreed. Though, I am not looking for actual numbers, more some generalities of what had to be changed and the direction of changed for reference sake.

 

[winter brew]

Lower gears means your clutches will see less load from the track....so generally a guy can go with slightly steeper helix or less secondary spring preload for starters.
Someone mentioned watching the heat....good advice. Feel both clutches and if one is hotter that tells you where to go to lessen slippage and gain efficiency.

 

[LRD]

Shortstop,
You definitely have a point as far as rotating mass is concerned. I'd like to see some definitive results of that type of experiment. My first inclination would be negligible. Just a few years ago there was a big push to decrease rotating mass, you don't see that theory being pushed much today. An example of why my reasoning would lean towards negligible would be this, if you were out riding on a given day and threw 1/2 of a paddle off your track (difference in gear weight) would there be a performance gain?

I have a successful low rotating mass experiment (at least as far as my right thumb and my butt goes). In 2005 I built a 550 fan summit into a 629 big bore at only 395 lbs. It worked well and I got familiar with the goofy Lite primary (8lbs without a ring gear).

Well in 08 bought a XP TNT at 399 lbs and long tracked with 16 X 137 X 1.75 and got the weight down to about 360 lbs ( now 365 lbs with a 15 X 141 X 2.25, this track weighs only 42.5 lbs). One of the many ways I did it was losing 4 lbs on the primary clutch.

I bought a takeoff Lite primary from a 600HO Snow Hawk. Going from 12 lbs on the end of the crank to 8 lbs is amazing. The rotating mass has more effect the closer it gets to what is actually rotating everything (and RPM its spinning), that would be the end of the crank. The other quality of this clutch besides low weight is the weight is near the center rather than the outer edge which makes for a lot less rotational mass (flywheel effect).

As far as big losses in the drivetrain I thinks it's the driveshaft pulling the track across the top of the tunnel over the rear axle. The driveshaft can't push the track under the skid, so its the track being pulled under the skid and over the rear axle and back up to the drivehaft. Lots of extra friction.

Duane of Paragon fame used to work with Dale of CNA Pro skis up by Thief River. One of the top secret sled experiments there was a rear driven drive axle. Supposedly great gains. If you have a head for this stuff, think about it, our drive system is pretty dumb but no easy light way to get away from it.
There is a rear axle drive suspension system on the market out now but pretty complicated.

For you guys with carts the Doo Lite (PowerBlock clutch) would be perfect, very light 8 lbs. and very simple to tune, spring and weight washers. I tune mine with high rate springs and straight angle helix in the rear. Very aggressive. A friend also has a longtracked TNT but had the stock 12 lb TRA, his felt kind of mushy when you give it throttle, while mine is crisp, instant response at the track with mine while the TRA lag's big time. He now is running a Polaris primary which is still 2 lbs lighter than TRA and much crisper.

Good Luck

 

[2XM3]

Just to play devils advocate, what about the added weight from the larger bottom gear?

I run wahl bros aluminium bottom gear, never had a issue just change it once a year. very light

 

[go high fast]

The efficiency theories are more related to clutching rather than gearing. The gearing issues come into play when you have more load on the track due to fat *** riding your sled, heavy wet snow or steep hills. No ratio adjustment in these cases and you find the secondary shifting out too soon and down go rpms and power and up goes temp on clutches and belt. With the big 193 tracks of today it is even more important. The other adjustment often made with the gear change is go with less angle on the helix and a stiffer rear spring. This is a change that impacts efficiency as now more power is needed for shift out leaving less power to the track but still a good move if the conditions are as stated above.

 

[1Mike900]

Can one replace the clutch pin bolts with titanium bolts? I would assume they should be strong enough for high RPM use? That is why I don't like 8.5" clutches too much as the extra weight is further out. 8 to 8.125 would be plenty dia. and quicker revs if the Ti bolts will work. Now I see why larger rear idlers are more efficient, never thought about the driver compressing and pulling thing. Also another question is the drive train only seeing half the weight of the track when locked up with the snow? And then it's full weight once breaking traction?

Mike