Gearing ratio question

Howdy I think I know the answer to this however I’m after the desired gearing of 14 63 giving me a final drive of 4.50. I do not have a 14 driver and decided to use a 15 68 combo giving me a final drive of 4.53 very similar final drives . Is there any disadvantage of utilizing a larger driver and ring gear to accomplish this desired final drive or should I be ok? Thank y’all
 

racing promotor

Moderator
First off regardless of what the chart reads you would use a 15/67 not a 15/68 ( and some cases only a 66 ), then really you will not know until you try it there could be a disadvantage then again could be an advantage depending on what your competition is doing, there is a best front driver size for all tracks and classes size & shape of the track, how much grip it has, there are plenty of cases where track starts out a certain size and increases one driver as the day goes on, how much momentum you can make determines front driver size ,the more momentum the bigger the front driver, and in most cases the lower the H.P the bigger the front driver how ever there are exceptions to this.
Before I would want to give an opinion on the 15 being OK I would ask what class and weight, How much out of the throttle are you while racing laps,
How did you determine the 14 / 63 being correct & would your class be the same class ?
 
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This is for my 8 year old sons jr champ purple plate flathead on a 1/6th mile track. So I’m learning even if the final drive ends up almost the same, how you achieve that final drive can still affect the kart one way or another? I can understand the concern of the larger rear having a tendency to dig into the track..
 
As far as the 14/63 being desired.. this is what was recommended to me by the leaders and was witnessed by me them running this gearing
 
I guess what I’m trying to say is, in my head as long as the final drive ratio is the same or very close to the same, it doesn’t matter which gears you use to obtain that ratio. Am I wrong?
 

racing promotor

Moderator
I guess what I’m trying to say is, in my head as long as the final drive ratio is the same or very close to the same, it doesn’t matter which gears you use to obtain that ratio. Am I wrong?
It doesn't matter as much to obtain the ratio, however it does matter in the fact that it could cost you a race, on track results with R.P.M will never end up changing by 5 teeth difference provided you were hitting your target R.P.M before the change.
 
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racing promotor

Moderator
As far as the 14/63 being desired.. this is what was recommended to me by the leaders and was witnessed by me them running this gearing
Being a champ kart reduces your chances of the bigger front driver end up being an advantage VS a disadvantage, If your son is newer racer needing seat time yet anyway, your OK to start on the 15 front driver But IF you do use a 67 or even a 66 NOT the 68. As it does not show up as much UNTIL the driver is MAXIMIZING MOMENTUM.
 

OVALTECH1

Premium User
I wouldn’t run a flatty on a 15 driver at bonneville... just saying. As said above once you get up passed the 65/66 gear it’s gets sketchy cause there isn’t a lot of ground clearance there. I would switch to a 13 personally before going up. It’s a Flathead on a cage. That’s a lot to get rolling.
 
We won a LOT of races (and several championships) running a 15 driver at this fellow's track (jr1 champ with purple plate flathead.)
There's more to gearing than track size alone.
Restrictor plate racing is all about momentum and being real smooth behind the wheel. I was fortunate to have two fairly smooth drivers over the years so we could free our karts up and let'em roll.
It's all a matter of corner rpm drop and power band of your engine.
Gear for your engine, the track, and your driver. It all has to work together.

14:63 will get you in the ballpark.
15:64 will walk the dog on them if you have your ducks in a row. ;)


-----
?Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
30 years of service to the karting industry
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 

alvin l nunley

Premium User
Howdy I think I know the answer to this however I’m after the desired gearing of 14 63 giving me a final drive of 4.50. I do not have a 14 driver and decided to use a 15 68 combo giving me a final drive of 4.53 very similar final drives . Is there any disadvantage of utilizing a larger driver and ring gear to accomplish this desired final drive or should I be ok? Thank y’all
Are you familiar with "base circles"? Using your examples, I see very little difference between the gears you're planning to use. A difference of .0364 in ratio could hardly, in my opinion, make much difference. You may find differently. You might try a 15/67 for even less difference. -.0264
A lot has been written about changes in gear sets with the same ratios, do a little research, there are pros and cons in favor of both sides. b_c ratio 1.jpg
 
We won a LOT of races (and several championships) running a 15 driver at this fellow's track (jr1 champ with purple plate flathead.)
There's more to gearing than track size alone.
Restrictor plate racing is all about momentum and being real smooth behind the wheel. I was fortunate to have two fairly smooth drivers over the years so we could free our karts up and let'em roll.
It's all a matter of corner rpm drop and power band of your engine.
Gear for your engine, the track, and your driver. It all has to work together.

14:63 will get you in the ballpark.
15:64 will walk the dog on them if you have your ducks in a row. ;)


-----
?Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
30 years of service to the karting industry
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
Agree Brian! I haven't raced there for a couple years but I personally seen the boys getting it done.
 
First, if Brian says run a 15/64, run a 15/64. This "ratio is a ratio" discussion is as old as karting. I was one of those guys, then I got a few years of experience. It does matter once you have everything else 99% perfect. A combo with a smaller driver will pull better out of the corner, but flatten on top end. A bigger driver will pull better at the end of the straightaway, but be lazy off the corner. Lap times will usually be the same, it's just a matter of where you want to be better. I always liked smaller driver combo because you could get a nose under coming off the corner.
 
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