Gear change from 20/42 to 19/43

ehna · Feb 19, 2012

I'm riding at 3000-4000 ft elevation and I want to change gears from stock (20/42) to 19/43!

What should I expect RPM wise ? Drop or Rise ??? :face-icon-small-con

Thanks!

lognomore · Feb 19, 2012

I ride a little higher then you but I did change the gearing like you're asking about. My RPM's really didn't change that I notice but the clutches run cooler. I think it is worth doing myself, easier on the belt.

gman086 · Feb 20, 2012

ehna said:
I'm riding at 3000-4000 ft elevation and I want to change gears from stock (20/42) to 19/43!

What should I expect RPM wise ? Drop or Rise ??? :face-icon-small-con

Thanks!

Stock gearing is fine for your elevation, especially if you just have the 155. Poo nailed the gearing unless you're riding at higher elevations (above 8,000 feet or so). If you're having belt/heat issues, send the primary to Carl's for balancing and their sheave mod and make sure alignment is good.

Have FUN!

G MAN

ehna · Feb 20, 2012

Thanks GMan!

The reason is, right now, I'm pulling barely 8000 rpm! I have the 163"

I'm having an argument with a friend and want to make sure before I actually do anything to the gearing! If I do it...

So a drop or a raise of RPM ???

Thx

Sixat38 · Feb 20, 2012

An old drag racer once told me lowering your gearing will raise your rpm. Slightly. Sometimes not even noticable. As far as a mountain sled is concerned, you won't notice a rpm change with just a gear reduction. Or rather tuning your rpm by a gearing change will most likely net you zero.

gman086 · Feb 20, 2012

ehna said:
Thanks GMan!

The reason is, right now, I'm pulling barely 8000 rpm! I have the 163"

I'm having an argument with a friend and want to make sure before I actually do anything to the gearing! If I do it...

So a drop or a raise of RPM ???

Thx

What Sixat32 said! Fix your clutching issues - should be 8,000 - 8,150. You CAN go with the black/purple secondary spring which is stiffer and keeps the sled in the lower ratios longer for better rpm recovery in the steep and deep (kind of like gearing down - I'd recommend it for the longer track). First make sure your primary spring isn't broken - has been a big problem. Also you should be running 64 gram weights for that elevation.

Have FUN!

G MAN

AdrenalineAddict · Feb 20, 2012

Gearing down will drop your RPM's slightly, you may not notice it much on the flatlands but due to a little less resistance when pulling a hill your backshift may suffer a bit. You may need to run a bit lighter in the primary, or a couple degrees less angle in your secondary, or possibly slightly more spring in your secondary if you have issues. 8,000 to 8,050 is exactly where you want to be.

IQRTurbo · Feb 20, 2012

What?

AdrenalineAddict said:
Gearing down will drop your RPM's slightly, you may not notice it much on the flatlands but due to a little less resistance when pulling a hill your backshift may suffer a bit. You may need to run a bit lighter in the primary, or a couple degrees less angle in your secondary, or possibly slightly more spring in your secondary if you have issues. 8,000 to 8,050 is exactly where you want to be.

I hope you did not realize what gearing change he is making..... He is asking about gearing DOWN. If you lower the gearing ratio, the motor will have less load on it and would pull more rpm.

Eh a

You may have to do the opposite of what is quoted above, but most likely no changes will be needed. You only dropped your top end 1:1 shift out speed at 8250 rpm by 6 mph.

I will guarantee if you marked your clutches with a black marker you are not using the top half inch of your sheaves with stock gearing. Stepping the gearing down will help in most every condition to better utilize more of your larger clutch sheave diameters, reducing belt temps.

What way are you running the ethanol key? Running good fuel and the non ethanol key will help the motor pull harder as well.

ryan_625 · Feb 20, 2012

I just went to 19/42 and loved the way my sled pulled. Really makes it come alive IMO. I am going to put a 43 in after I get my sled back together to see if it helps any more.

ReTodd · Feb 21, 2012

I went 19/43 and really didn't notice a rpm change...just noticed that it crawls around better in the tight trees but I also noticed that when I went head to head with my friends stock gearing that his initial track speed put him up on the snow much quicker. We dragged up a canyon and he jumped ahead by about 5-10 feet and then we stayed that distance all the way up the pull. Your clutch will shift out more to compensate for the lower gearing.

IMHO, leave your stock gearing in. My clutches don't seem any cooler to me.

Rt

FFLH · Feb 21, 2012

IQRTurbo said:
I hope you did not realize what gearing change he is making..... He is asking about gearing DOWN. If you lower the gearing ratio, the motor will have less load on it and would pull more rpm.

Eh a

You may have to do the opposite of what is quoted above, but most likely no changes will be needed. You only dropped your top end 1:1 shift out speed at 8250 rpm by 6 mph.

I will guarantee if you marked your clutches with a black marker you are not using the top half inch of your sheaves with stock gearing. Stepping the gearing down will help in most every condition to better utilize more of your larger clutch sheave diameters, reducing belt temps.

What way are you running the ethanol key? Running good fuel and the non ethanol key will help the motor pull harder as well.

I agree there is less load with a lower gear ratio, but that is where the confusion begins. RPMS are controled by the clutches. When they sense less load they shift more aggressively, potentially reducing engine rpms.

Clutching systems are calibrated to maintain proper operating rpms against a given load. Changing the load will affect shift out.

Another way to view this is to observe the rpms at 45 mph on a hardpak trail being much lower than 45 mph on a hard pull in the deep.

Less load experienced by the clutches equals more rapid shift out potentially reducing rpms.

AdrenalineAddict · Feb 21, 2012

FFLH,
Thank you for backing up my original post, there are many who don't understand the physics of centrifugal clutching and will spread backwards clutching advice. Lower gearing will always lower RPM's slightly due to the fact that your secondary will now sense less load from the track resulting in an overly aggressive upshift. Some will argue that the efficiency gained due to being in more efficient shift ratio will offset the aggressive upshift, but personally I've never seen it happen.

ryan_625 · Feb 21, 2012

I did see a drop in RPM from 8200-8250 to a consistent 8050, but it also feels stronger off the bottom and through the mid. Top it still pulls. My stock clutching also feels better with it geared.

I am not trying to argue against anyone here as I know that you guys know a bit more than me, but would elevation play into that much? I ride at 6,000+ a lot.

RockyMtn.Kris · Feb 21, 2012

Ok I gotta get in on this. This is an old conversation for sure. I spent quite a bit of time on this by using driveshaft and or jackshaft sensors to record and playback clutching and gearing changes. Rpms overall did not move much with gear chages, but I normally made small changes at a time. What I did find is that lower gearing is definately more efficient for mountain riding. The lower gearing will move the clutches closer to the desired 1 to 1 ratio then taller gearing. This means less belt heat. The second benefit is maintaining rpm while the load increases,(i.e. elevation or snow condition) plus quicker backshifts. I do think some people gear too low. As a general rule, I gear for for low 80s for top speed and clutch from there. Dont expect a gear change to blow your hair back, but you will like it boondocking and your belts will last longer.

gman086 · Feb 21, 2012

ryan_625 said:
I am not trying to argue against anyone here as I know that you guys know a bit more than me, but would elevation play into that much? I ride at 6,000+ a lot.

You bet it will! Sleds have more power at lower elevations so the "load" the clutch sees is MUCH different (lower)! That's why the lower elevation guys can even gear these up, mid elevation should STAY THE SAME as I stated (it's Poo's compromise gearing) and the higher elevation guys could benefit from gearing down. That's why I cringe when I see advice being thrown around on the forums without qualifying where you're using it. The OP clearly stated he'll be riding in the mid elevation range which is what the sled is geared for.

Have FUN!

G MAN

Norway · Apr 6, 2012

So, can I go steeper on the helix and capitalize on my sleds newfound torque to accelerate faster?

Thanks

a2jet16v · Apr 6, 2012

while people are talking clutching, my sba with the 2in track is slipping th ebelt in the primary on bottom. got the stock 66's in there, sled pulls the rpms fine, i have messed with the deflection to see if that was my issue, it wasnt. i am thinking i need to buy some after market weights, staying very close to my weight now and just adding some to the heel to get it to grab the belt better. but i don't want to loose it further up. i can look what i am currently running for springs/helix tomorrow. i am only riding 1500-3500 sometimes few hundred higher but not alot. ehna sorry not trying to hyjack your topic here.

snosub · Apr 6, 2012

a2jet16v said:
while people are talking clutching, my sba with the 2in track is slipping th ebelt in the primary on bottom. got the stock 66's in there, sled pulls the rpms fine, i have messed with the deflection to see if that was my issue, it wasnt. i am thinking i need to buy some after market weights, staying very close to my weight now and just adding some to the heel to get it to grab the belt better. but i don't want to loose it further up. i can look what i am currently running for springs/helix tomorrow. i am only riding 1500-3500 sometimes few hundred higher but not alot. ehna sorry not trying to hyjack your topic here.

do you have the 20/42 gearing and a 1115 belt on it?

a2jet16v · Apr 7, 2012

i have run the 20/42 and 19/42. and yes the 115 belt.

Gear change from 20/42 to 19/43

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