8 tooth or 9 tooth extros?

[Super Sled]

Gents:

I have done a ton of research on this and even once procured then sold a MB drive shaft and 8 tooth extro drivers. I thought I wanted 9 tooth extros then. But now I am not so sure....

Here in my situation: I installed a tunnel extension to 144" this summer on the Attak. Sometime soon I also plan to either find rail extensions or have custom 144" rails created for my Mono that would include a slight tip up. So I plan to go 144" track.

I have narrowed my track selection to either a 144" back country or 144" Intense or Cross Country. But I don't need help with the track question. I have already removed my tunnel protectors. My question is what size drivers should I get?

I've been in contact with Micro Belmont, and I plan to order a new HD shaft from them for my Attak. They can have extro drivers already pressed on the shaft. Should I get 8 tooth or 9 tooth, that is the million dollar question.....?

Here are my thoughts:
9 Tooth Extros: Will keep gearing the same as I have now and thus have better gas mileage and most all will feel similar to the staock machine. Maybe a tad less track speed tho because stcok gearing is 23/38 and maybe need a tad more gearing to spin track. But all things being equal I prefer to stay 9 tooth to keep things status quo.

8 Tooth Extros: Will be a slight lowering of gearing by virtue of the smaller drivers, which might be an advantage to me, being that my sled is geared 23/38. It might assist to spin the 144" track (a tad anyways) faster. While I'd lose some top end and add fuel consumtion, maybe the benefit of a slight gearing reduction would outweigh the lost benefits of higher gearing. The 8 tooth would also allow for greater snow evacuation also as the track spins. As I write this I find myself leaning towards the 8 tooth, I guess.

Please keep in mind I'm only asking about what size drivers, not whch track or what gearing i should run. I am not switching my gearing at all, I'm staying with stock 23/38. I also run Super Rats, so I'm not worried about having to re-tune my clutching formula. You all can see my mods stated below, and I feel I have plenty of power to spin a 144" track. Heck, my Mt Viper has less power and torque and can quite handily spin a 151"!

Thoughts? And thank you all in advance...

 

[kinger]

Rule of thumb if your concerned about mpg, top speed, rolling resistance is to use as large of a driver as you can fit in there.

9T all the way.

Also going to 8T is not a SLIGHT decrease in gearing its a major one, equivalent to 2 of 3 top gear reductions.

Some go to great lengths to stuff 10T in there just because of the advantages of those. Bigger is better but its all a compromise.

Never heard of a issue of snow evacuation with any driver.

 

[Super Sled]

Thank you Kinger. You are right. Those were my initial thoughts, staying 9 tooth that is. Going to 8 tooth extros would be a pretty drastic gearing down, wouldn't it. Geez, why am i even laboring over this decision!!!!

 

[Mtnviper]

Normally it is better to go with larger drivers as they tend to be more efficient. The other advantage is a slightly reduced track approch angle when compared to 8 tooth drivers.
The main reason for going with 8 tooth drivers would be for clearance issues both at the front heat exchanger and at the front rail tips (when extroverts are used)
If you have a 1/2" or more clearance between the track lugs and heat exchanger with 9 tooths then you should be fine.
To check for rail tip clearance to the extrovert teeth. I like to use a floor jack under the front of the skid, then compress the skid upwards to move the rail tips at they're closest point to the drivers. Then using a straight edge, measure the clearance between your non-extrovert 9 tooth drivers and the rail tip.
Generally you'll want at least approx 1" clearance minimum depending on the extrovert tooth length. Extroverts are positioned directly in front of the rail tip and the extrovert teeth are usually 3/4" long.
It's best to check with the extrovert manufacturer to see how long they're teeth are and what they recommend for minumum rail tip clearance to be sure though.
To calculate effective gearing change when switching to 8 tooths, multiply your current 9 tooth gearing times 1.13.
for example
9 tooth gearing 20-40 (2 to 1)
2 x 1.13 = 2.26 to 1 with 8 tooths

Bill

 

[DAGE]

what you want to do is what I did during the summer, my Attak is now a 144" and I'm using 9T extro drivers and I know I won't have a hard time spinning the track and I know fuel economy won't be that bad

on my RX1 mountain I had 9T drivers and I could spin the 151" track like nothing, I was also getting slightly better mpg then my buddies Attak

 

[Super Sled]

what you want to do is what I did during the summer, my Attak is now a 144" and I'm using 9T extro drivers and I know I won't have a hard time spinning the track and I know fuel economy won't be that bad

on my RX1 mountain I had 9T drivers and I could spin the 151" track like nothing, I was also getting slightly better mpg then my buddies Attak

Thx Dage, that's what I'm thinking -- 9 tooth extros. Seems to be concenus. How did you extend you rails? Only companies I've seen to extend mono rails on Attak to 144" are Hartman's and Traxx USA. Or Ice Age can make custom 144" track rails......

 

[blueironranger]

definitely stay with 9's, I tried to put 9's on my MTX phazer but I couldn't get my skid to bolt back in with 9's in there. I have the adjusters all the way in with 8's

 

[DAGE]

what you want to do is what I did during the summer, my Attak is now a 144" and I'm using 9T extro drivers and I know I won't have a hard time spinning the track and I know fuel economy won't be that bad

on my RX1 mountain I had 9T drivers and I could spin the 151" track like nothing, I was also getting slightly better mpg then my buddies Attak

Thx Dage, that's what I'm thinking -- 9 tooth extros. Seems to be concenus. How did you extend you rails? Only companies I've seen to extend mono rails on Attak to 144" are Hartman's and Traxx USA. Or Ice Age can make custom 144" track rails......

what I did is I switched to 121" rails so I could get a tipped extension, I went with muffin works tunnel and rail extensions

 

[lawmanbsi]

Thx Dage, that's what I'm thinking -- 9 tooth extros. Seems to be concenus. How did you extend you rails? Only companies I've seen to extend mono rails on Attak to 144" are Hartman's and Traxx USA. Or Ice Age can make custom 144" track rails......

I would think Muffin works would make you a set. He may not list them on his site. probably not a common upgrade. When I got the 136" Expert X skid I called him and asked. Thats what he told me. Call him he's seems like a pretty good guy. Even exchanged my tunnel support for me after a year. I don't have an RA dial anymore.

I Know you don't need any help with the track selection (as I have read the "first post") but, you can remove the Intense from your list as it doesn't come in a 144".

I would think that the 9T would be better as it's closer to the tips, it should be less likely to let the rails stab the track. no experience here but, at least it may provoke someone who know to pipe in.

 

[sleddingfarmer]

You could switch to 2.86 pitch drives, drop down to 8 tooth drivers would you have enough clearance to run a 2.5" track? If you switched to 3.00" drivers you can get a 141" track with 2.25" lugs.

If you're looking for max floatation, will a 16" wide track fit in your tunnel?

16" or 15" wide 146" long tracks are available 2", 2.31" or 2.5" lug height. Probably the best way to go about doing something like that would be to just buy a complete Summit suspension. You'd be saving quite a bit of weight in the process I bet...and can probably pick up a suspension for less than a set of rails from Iceage.

You could maybe even avoid stretching out to 144 all together if you can fit a 16" wide track in there, just get a 16"x137"x 2.31" lugs. That thing would really float and dig! Just gotta see if you can 8 tooth 2.86 pitch drivers, and if you'd have enough clearance. I know the 1" extra in length isn't a problem if you use stock size drivers, but dropping to 8 tooth you would probably have to go to larger rear axle wheels.

I probably didn't help you out any with your decision

 

[Super Sled]

Thx all! I believe a felow TY'er has just answered my prayers and has some unused Doo 2.52 pitch 9T drivers collecting dust and happens to live right by Micro Belmont. I may be able to just buy those from him installed on a MB heavy duty shaft. Dang, I love this site, guys on here are great people!

Mike

 

[Ratpack]

If you stay with a 9 tooth and run a 2" track there is about enough clearence to get a piece of paper between you track and tunnel. That is when you would have a problem with getting the snow out. We have always gone to 8 tooth and never changed gears. I am droping one tooth on the gear this year, but that is for the mountains. We have done this to 11 sleds and no one ever said anything about the gearing being a problem. Good luck to you.

 

[Mtnviper]

8 tooth 2,86" drivers are just a hair larger then 9 2.52" driver's.
Link to driver specs page http://fourstrokesolutionsllc.webs.com/ ... edtech.htm

Bill

 

[sleddingfarmer]

8 tooth 2,86" drivers are just a hair larger then 9 2.52" driver's.
Link to driver specs page http://fourstrokesolutionsllc.webs.com/ ... edtech.htm

Bill

Oh yeah, I guess I should have known that, I switched from 2.86 8 tooth drivers to 9 tooth 2.52 and they were pretty much the same. My bad.

Thats a lot of good info on the site