Bottom Gear Change

[Shootinstick]

I'm thinking about gearing my Attak down a little for next season. I'd like to gain a little more out of the corners without sacrificing too much top end. With my weight (285 in gear) it is seldom I can pull full top end now unless the conditions are really perfect, so I don't think gearing down will hurt me that much. I'm just undecided between a 39 tooth or a 40 tooth bottom. Top will stay the stock Attak 23 tooth. Anyone tried either or both and what did you find?

 

[blade072]

I'm thinking about gearing my Attak down a little for next season. I'd like to gain a little more out of the corners without sacrificing too much top end. With my weight (285 in gear) it is seldom I can pull full top end now unless the conditions are really perfect, so I don't think gearing down will hurt me that much. I'm just undecided between a 39 tooth or a 40 tooth bottom. Top will stay the stock Attak 23 tooth. Anyone tried either or both and what did you find?

I run a 22/40 and love it. You will have to play around with clutching to dial in your RPMs. Another advantage is that you can use the stock chain.

 

[SledFreak]

23/40 is a good combo as well. Use 23/40 and a swap your track for a Cobra and you will see a big difference in corner to corner acceleration.

 

[LJ 452]

I used a 22/40 on my Apex and it was much better. I could still see 110+ on the speedo in the right conditions but even that was more than needed. Corner to corner for me is more important. Oddly enough the RPM's stayed right at 10600 out of the hole and would slowly climb to 10900 when WFO. So no need for me to play with clutching. With the transfer set at anything past mid it would pull like a mule. 0-85 mph is a blast. Highly recomend 22/40, as said you can use the stock chain. With 23/40 you can as well but the tensioner is backed out quite a bit. Top gears a cheap (even the Yamaha ones) so at least try it.

 

[ROCKRTX]

Geared down wont hurt,i run 23/40 on my apex rtx and it very strong,can still see 110 MPH and even more on good condition.i have tested all combo from 24/38,23/38 and 23/40.

24/38 is good for fuel economie.

23/38 is faster on ice!

23/40 is faster on snow! ( where you ride 98% of the time )

22/40 you will loose top end over 23/40

 

[LazyBastard]

22/40 you will loose top end over 23/40

Unless you overdrive...

 

[SpecRTX]

LB,

I've tried overdriving before and have run into inconsistent results. One run it holds RPMs, one run it doesn't. Have you had this happen?

 

[LazyBastard]

Never, but I have heard of the problem.

The issue is that when you can overdrive, it means that whatever speed you're going, there's ALWAYS room to shift further, which means that the big end has a greater degree of sensitivity. In order to use overdrive effectively, you need to minimize variations.

There are a few things to consider when overdriving;
1) You need to overdrive BOTH clutches,
2) You need to LOCK your secondary.
3) Your clutch calibration needs to be more or less insensitive, which may mean using non-OEM weights.
4) *MUST* gear down when you overdrive. Anyone trying to use it to pick up top end or reduce fuel consumption is fighting an impossible battle.

The purpose of overdriving is controlling overrev when gearing down to increase BOTTOM end.

I've never tried overdriving on a 2-stroke, but I would imagine that because of the sensitive nature of the engines and clutching, that it would be very difficult to get that balance consistently.

I also haven't run an OEM belt with overdrive. Don't know if it makes any difference in this regard, but I use gates xtreme belts.

If you don't mind my asking, WHAT did you try to overdrive? Was it your RTX (or other Yam 4-stroke), or was it some previous (2-stroke) sled? And what clutching were you using? Did you make any additional adjustments to the clutching after the overdrive?

 

[blade072]

Never, but I have heard of the problem.

The issue is that when you can overdrive, it means that whatever speed you're going, there's ALWAYS room to shift further, which means that the big end has a greater degree of sensitivity. In order to use overdrive effectively, you need to minimize variations.

There are a few things to consider when overdriving;
1) You need to overdrive BOTH clutches,
2) You need to LOCK your secondary.
3) Your clutch calibration needs to be more or less insensitive, which may mean using non-OEM weights.
4) *MUST* gear down when you overdrive. Anyone trying to use it to pick up top end or reduce fuel consumption is fighting an impossible battle.

The purpose of overdriving is controlling overrev when gearing down to increase BOTTOM end.

I've never tried overdriving on a 2-stroke, but I would imagine that because of the sensitive nature of the engines and clutching, that it would be very difficult to get that balance consistently.

I also haven't run an OEM belt with overdrive. Don't know if it makes any difference in this regard, but I use gates xtreme belts.

If you don't mind my asking, WHAT did you try to overdrive? Was it your RTX (or other Yam 4-stroke), or was it some previous (2-stroke) sled? And what clutching were you using? Did you make any additional adjustments to the clutching after the overdrive?

What do you do to the primary and secondary clutches to overdrive?
Thanks

 

[SpecRTX]

LB,

I tried overdriving my 06 RTX when it was geared 24/40. I also have an Ulmer Stage 2 in it, so I could adjust the weights. Like I said earlier, one run would pull 10,700. However, later that day it might only pull 10,000. My secondary is not locked but I do have an overdrive helix. The method I used to overdrive was a speed sheave. I have always run the OEM belts it. However, I've had great results with Gates on my old Thundercats. With my "new" 23/40 gearing I was considering trying overdriving again.

 

[LazyBastard]

Thats a HUGE range. 10000 is way too low, so the overdrive is causing overshifting. You definitely want to lock the secondary. What kind of spring and helix are in the secondary? The secondary, being torque sensitive, is the likely culprit for variations like that. Before going into secondary calibrations, you want to get the gearing right, otherwise the overdrive isn't going to gain you anything. That and... with the right gearing, your secondary may not need much (if anything) done to it. (besides being locked down).

Also, you see what I mean when I say that you need it geared way down, right? It should NEVER have the opportunity to shift too far like that.


@blade072: primary clutch fixed sheave - machined for overdrive or replaced with an overdrive sheave. Secondary clutch helix - either an overdrive helix, or put some washers on the studs below the helix to space it out further.

 

[Shootinstick]

I ordered a 40 tooth bottom gear and pulled my gearcase apart tonight. Upon doing so I see the bottom gear has a bearing pressed in that according to the parts list is separate from the gear. Guess I will have to order a bearing tomorrow so I don't have to remove the old one from the 38 gear.

For those that have done it, how tough is it to install the bearing? Does it just press in, do I have to heat the gear and/or chill the bearing to get them together?

 

[SledFreak]

I had my dealer do it.

 

[yamadog1]

bearing

very easy to do, i ordered one, the next time pushed the bearing out, if
i can do it anyone can.

 

[SpecRTX]

I'll take your advise on locking the secondary. For overdriving, I'll be using a speed sheave. Because the speed sheave is thicker than the stock sheave, I'll measure the difference in thickness from the back of the sheave to the start of the cut angle and compare it against the stock one. I'll use that number when measuring my 15mm offset.

For my secondary, I'm using whatever helix came with the Ulmer stage II. The spring is silver Yamaha set at 6-3.

For my primary, I'm using whatever spring came with the stage II and my super tips set with 7 grams in the heel, nothing in the middle and 2 in the tip.

I'm assuming when I overdrive, I'll have to remove about a gram from the tips and possibly a gram from the heels.