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Discussion Starter · #1 ·
I was wondering if anyone out there could take a moment to explain the concepts behind large front sprockets. I've been told that 15 tooth front gearing is the most common general gearing for 421 cubs, with a 42,43,44 rear depending on the tire,arm,HP, rider weight, etc. I'm focused on finding out WHY a 15-43 is better than say a 14-40. I've got the spread sheets that show FINAL gear ratios. But many people tell me that the motor/trans "likes a bigger front sprocket". Anybody care to shed some light on the topic. (I've got a friend with a 421 cub on alky that's going to try a 15-47 ???) Does that sound right?? Ultimately, I'm looking to find an ideal gearing for my 472 Powervalved Cheetah. I should be in the 100-105 HP range on gas. Stock frame,+8 or +10 arm, 210LBS rider, 72rollout 11 paddle Extreams (for now). Any thoughts on the concepts/facts as well as gearing selections for my setup would be very helpfull. THANKS, Sand Fan, JOHN.
 

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Hopefully some good info comes from this, I can't quite remember what I've read in the past so I'll let someone who's fresh on it chime in. I run a 13/42 gearing on my 421 cub though, might go to a 14/42 not really sure, I kinda like it, can launch in 2nd and makes 3rd hit HARD. Just my experience.
 

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Well the larger sprockets make it easier for the chain to roll around it. I would say dropp that down to a 45 in the back to start out.
I've never had a 421, but on my 4 mill stock cylinder I ran 15/41 with 12 extremes, +10.
175lbs. And 16/43 on my 10cub.
 

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I always ran 15/43 with 12 haulers on my 350's and 15/41 on my 421 with 14 extremes,both 73 rollout,both 1-5's launching in 2nd.We always tried to gear up to let the tires bite more outta the hole.With it geared too low you'll blow the tires off and be outta gear quick.You've got the torque to pull the gear,use it to your advantage.
 

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I haven't heard a whole lot of people say that a larger sprocket is better for the motor, but it is certainly better for the sprocket and the chain. The more teeth that the chain can wrap around the less likely you are to break it or round the teeth off.
 

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QUOTE (Koolguyson @ May 15 2009, 08:35 AM) index.php?act=findpost&pid=42691I haven't heard a whole lot of people say that a larger sprocket is better for the motor, but it is certainly better for the sprocket and the chain. The more teeth that the chain can wrap around the less likely you are to break it or round the teeth off.


I agree.

Also.. the larger sprockets have a "reduced radial bend" of the chain around the sprocket. Possibly creating less drag?? Just a theory...
 

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Discussion Starter · #11 ·
Everybody's seen something like this....http://www.sprocketcenter.com/g/4156/gear-ratio-chart.html
I would think that a final ratio of 2.93 would be the same if you did it with a 14-41 or a 15-44. I would think that either way the motor is seeing the same final force working against it. The tire should also have the same amount of leverage working on it. Stock is 14-41. Why go to a 15-44? They should be the same. I don't want to get into a debate on theory of drag (larger front sprocket means chain has wider bend to make around gear = less drag) because then we would have to debate the extra resistance that feeding extra sprocket teeth into and out of a larger rear sprocket would add to the topic. LOL. But over the years I've heard plenty tell me the trans/motor just "likes" a bigger front sprocket, so go big in front, then just go bigger in back to balance it out. My case saver won't fit a 15T gear. I've also seen some very fast slightly moded banshee's that had WAY TOO MUCH tire for the mods they had, but they just geared the piss out of the motor and made it work thru gearing advantages. ( I've raced some guys that had 12 and 13 tooth gears with 44 in the rear and I was left asking "How in the hell is that guy runnin' that fast" ) Well I've explained my thoughts......Any profesors out there wanna' help me with my schoolin'? On the other question....With a 105+HP motor (I should be about the same as a 421 cub on alky...maybe a little more torque) Running a +8 arm, 22X11X8-11 paddle extreams (72" rollout), 210 LBS. rider, with no bar, on a sand track with a little clay mixed in "West Michigan Sand Dragway" (wet packed sand, great traction) What would you guys advise for gearing? THANKS For your input on both parts of the question.
 

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Are you gonna run is dune ready or strut it for the track John? I would say, since you cant fit a 15t front, just try the stock ratio, then throw a different sprocket on the rear, depending on how far you make it, and if your running out of gear to early or late, remember you wanna be wide open passing the gate in 5th gear so gear accordingly.....
 

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Discussion Starter · #13 ·
Dune ready. I could take the case saver off if I had to. I'm trying NOT to be TOO far off from where I want to be. I've got the stock style carrier for now and you can only move up and down a few teeth either way before you run out of adjustment and need to lengthen or shorten the chain. I'm looking for someone to be a good "Crew Chief" for me now, so I don't have to spend the entire Memorial Day Weekend being my own "Pit Crew". I've had more than my fair share of weekends spinning wrenches. ( NOTE: Don't any of you go buying ANYTHING with the TRINITY name on it! TRINITY parts carry a 2-stroke form of V.D. and your quad/motor will never be the same again! ) At this point I just wanna' get some seat time! I've got a 13-14-15 front and a 42-43-44 rear.
 

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Great topic guys im in the middle of figuring a different gear set up for my bike and would like some input. My build is a midrange or dune port 65 hp im 205lbs. +4 swinger 14-41 gear now tires 21-12-8 9 paddle extreme. I like out the hole in 1st but need to short shift to 2nd and would like to gear it up for 300' drags. Should i buy 15t up front or 40-39 for rear? Help, need input. R.O. 68. Motor is a pump gas 350 w t-5s great pipes for this build.
 

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Discussion Starter · #16 ·
Well, I'm happy to see the amount of feedback and input this topic is getting so far. Maybe everyone could post what they run as a reference. Size motor, Est. HP, tire size, # of paddles, type tire, length of arm, rider weight and finaly the gearing. Also type of riding matters too. I drag in WET sand (sometimes standing water) so I might need more gear than a guy who rides in fine dry sand like glamis. If we get enough input here it will give everybody a good base of info to draw from.
 

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i ran a 15 38 on my trail pump gas 350 its more load on the motor dyno said it would hit 93mph in 6th.. the bike "reacted" better to that and i felt with the broader powerband i use the extra gearing helpd put it to the ground.. and made it ride nicer not as much shifting while i was crusiing it around..

i also ran 15-38 and 15-40 on my bigger alky motors also. with 1-5 transmissions. with an override and a 1-5 i use 1st to take the "shock" of the launch and then let 2nd pull me out of the hole.. most time on the dunes i wont make it to 5th but its there just in case...

the ones i get a kick out of are the 16 and 17 tooth fronts..
 

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Discussion Starter · #18 ·
You have to tell the tire size or all info is worthless. A 18" tire, 20" tire, and a 22" tire will all need different gearing. They don't charge by the word here. Post your FULL ride setup so each person can judge whether your setup is close enough to theirs to be a help or if your too far from their setup for your info to be helpfull to them. We have to know if it's apples to apples. A guy with a 350 with toomey t-5's isn't going to want to copy the gearing from a guys 10mil. So he's got to know what the "bigger motor" is.
 

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"I would think that a final ratio of 2.93 would be the same if you did it with a 14-41 or a 15-44. I would think that either way the motor is seeing the same final force working against it. The tire should also have the same amount of leverage working on it. Stock is 14-41. Why go to a 15-44? They should be the same. "

You would think so - but the leverage IS different & is the reason for larger sprockets.

Think about the distance from the center of the axle to the edge of a 41t - lets just say 6". Now put a 45t & measure again...say 8" That difference (even with the final g/r being the same) acts as a torque multiplier due to the longer "lever" - nearly for free. The same holds true even with primary gear sets - If you net the same final, while using a set of 2.68s over 2.86`s - more-torque will be at your disposal.

At least this is how I understand it.
 

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That makes sense.


Here's what I run:

Rider Weight Engine Size Swingarm Tire Chassis Gearing Best e.t

185 lbs 421 cc + 8 78 ro 15 stg ext stock 15/44 [email protected] mph

185 lbs 593 cc +12 78 ro 15 stg ext stretched stock 16/43 3.85 @ 83mph

135 lbs 593 cc same same same same [email protected] 86 mph

135 lbs 421 cc +12 72 ro 15 ext susp. chromoly 15/43 3.93 @ 78 mph

185 lbs same same same same same 4.11 @ 74mph

200 lbs 392 cc +7 72 ro 14 ext stock 15/42 4.23 @ 75mph

I'll have more to post after this weekend I hope. Also some numbers for a 610 cc. Most of these times are on a heavy Track, either at Gilbert or Outlaw Sanddrags.


Well, I spaced all of that out, but it runs together when I submit the post. Hope ya'll can sort it out.
 
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