sprockets and gear ratios

[john swenson]

hey friends and engineers, don't recall reading on the site about this. anyone have a general idea regarding : say you have a 21 tooth sprocket driving a 21 tooth sprocket. if you drop the drive sprocket down say 1/4 of the no. of teeth, have much top speed is lost but how much power is gained ? or maybe only 2 or 3 teeth ? any general idea or is it only figured out by actual drive testing ? i'm sure there are mathematical formulas but that's out of my expertise. thanks john boy va.

[msafi65]

I change gear ratio at the large gear on the jackshaft on max II and buf truck. Stock newer 2 is 15-27 trany to jackshaft and 21-22 down for total reduction of 1.88-1. Mine is 15-34 and 21-25 down 3.309 total reduction. I've not checked the speed but it's still faster than I like and never lack for power now. 16 hp Briggs on rubber tracks. Buffalo truck is another story. They have the capacity for such heavy loads that I found early belt failure common. The lowest gear one I've tried is 15-37 to jackshaft and 21-30 down. Total reduction was 2.57:1 now is 3.52:1. This vehicle top speed is 14 mph but will climb or pull at just over an idle. Belt life is greatly increased. If you go much bigger than 34 tooth on the jackshaft clearance to axle gear on short side is a problem. Hope this gives you some answers.

[john swenson]

msafi65, thanks for reply. still not quite understanding. mine is a max 2 also. so your saying there are 15 teeth on the tranny sprocket and 27 0n the jackshaft. then 21 down from jackshaft to 22 on the triple sprocket at the center axle and front and rears. so you changed the jackshaft to a 34 tooth and and then 25's on the triple center and front and rear axles to match ? so you basically increased the size of the driven as compared to reduce the size of the drive sprocket ? so you added 7 teeth on the jackshaft and 3 0n the triple and axle sprockets. could you get almost same result by just going less teeth on the jackshaft ? change the 21 to maybe a 16 or 18 ? leave the center triple and rear and front axles stock 22. thanks for helping me understand. john boy va

[Model Citizen]

[msafi65]

I made all my sprockets and chose 34 tooth jackshaft because I stock them for repairing MAX IV rear drives. the tooth count I give for stock is for a late model with #530 oring chain on the drop chain. The ones with # 60 drop chain were 1:1. I wanted to get a bit lower gear ratio without adding more diameter and causing clearance issues. 34 divided by 15 =2.26:1 which is standard for MAX IV. I run heavy pulling a trailer in swamp so speed isn't an issue. 35 tooth sprockets fit with out changing adjusters ,all you do is add links to main drive chains. Hope this clears up the muddy waters.

[john swenson]

thank you both, got it now. in the redesign i'm doing on my max i will be able easily to change sprocket sizes on the jackshaft going down to center axle triple. i'm going to experiment using the clamp on style sprockets from mcmaster carr. once you by the hub, sprockets are easily switched for testing. looking for moderate speed like yours, with more low end power. i don't do much flying around. will keep you posted. john boy va.