Would a 60t sprocket give me any take-off power?

[speed1]

Have been using the speed calculator on here (great tool) want to acheive around 30 mph for street riding...Have 1 go-kart set-up as follows : 15"tires , 3600 rpm, 72 t sprocket and 12 t centrifical clutch and according to my GPS it gives me 25.4 MPH...The new 1 we are building I would like to achieve 32 MPH...To do that I would need to put a 60 t sprocket on it and the rest the same as the other kart I have...My question is this...The 60t sprocket calculates to 32 mph with 15" tires, 12t clutch and 3600 RPM . will that give me ENOUGH TAKE-OFF power, or should I usr a 72t sprocket (which takes off fine now) and remove the governor from the 212 cc HF engine with the 60t sprocket? Thanking you in advance for your expertise...Bob

 

[mysteryboy28]

remove the governor only if you'd enjoy the constant fear of death by flywheel shrapnel.

smaller axle sprocket means more speed and less torque. period. if you have plenty of torque with the 72t sprocket, then you SHOULD be ok with the 60t. torque loss will be obvious (especially depending on weight of kart and driver), but the gain in speed might be worth it for you. i would do it, especially with 15 inch tires!

ditch the centrifugal clutch (ew. just, ew.) and get a TAV2 torque converter. centrifugal clutches have NO balls. avoid them at ALL costs! sell a kidney if you have to, or donate blood 7 days a week...

 

[speed1]

I thinkk I will leave the Gorvernor ALONE , there was 1 word in your answer that kind of scare me "DEATH" ...I will look at BMI for the TAV2 torque converter and go with that and still keep my kidney or have to sell blood...Thanks for the quick reply and add the converter to my parts list...Bob

 

[mysteryboy28]

eBay is a good cheap place to get a TAV2.

for the 3/4" shaft here is a good one:

http://www.ebay.com/itm/Comet-30-TA...25902?pt=Go_Karts&hash=item1c25ac308e&vxp=mtr

check what size shaft you have on your motor before buying!

 

[r_chez_08]

Go ahead, take the governor off, leave stock springs and get a tav2 if you can afford it. A 60t sprocket and governor removal or adjustment would work fine.

Tbh though, if you are not planning on riding offroad, I would stick with the centrifugal clutch and get a billet steel flywheel for $60 and 18lb springs for $5 or so, and a decent header from free to $40 and air filter, around $15-20

 

[speed1]

r_hez do you have the governoor off of your kart? What kind of set up do you have on it?

 

[Doc Sprocket]

remove the governor only if you'd enjoy the constant fear of death by flywheel shrapnel.

I sincerely hope you're kidding.

 

[Jcotz]

Speed1, governor removal is something that is potentially dangerous, but if you don't over-rev the engine or hold it wide open for extended periods of time then you should be fine. In all honesty it is mostly personal decision, but it is good to know both sides of the argument.

 

[r_chez_08]

r_hez do you have the governoor off of your kart? What kind of set up do you have on it?

Yep. My kart is currently in rebuild process. See my clone thread in the engines and clutches section, I hope to be getting 12hp from it.

However it will be getting a billet rod and a new flywheel of some description, but I ran for a while with no governor and otherwise stock motor.

When rebuilt, I will have 18" tyres, 9:60 ratio.

 

[speed1]

Yep. My kart is currently in rebuild process. See my clone thread in the engines and clutches section, I hope to be getting 12hp from it.

However it will be getting a billet rod and a new flywheel of some description, but I ran for a while with no governor and otherwise stock motor.

When rebuilt, I will have 18" tyres, 9:60 ratio.

Nice!!! When do you expect to finish it? We have decided to oder: 15" tires , 60t sprocket and according to the speed calculator it'll give us 32 mph which is plenty when you're that low to the ground and then if we feel we need more speed we'll take off the governor which will give 45 mph if the RPM goes to 5000 ...It is a fun project when we are done we'll have 2 karts one that goes 25 mph and one at 32 mph, I am having a blast learning from all you guys ...Jcotz, you are correct it's always good to know both sides..You can't never learn enough ...Bob

 

[Doc Sprocket]

Speed1, governor removal is something that is potentially dangerous, but if you don't over-rev the engine or hold it wide open for extended periods of time then you should be fine. In all honesty it is mostly personal decision, but it is good to know both sides of the argument.

We've covered this a bazillion or so times on this forum. In addition to Jcotz's points-

1) Keeping the stock valvesprings tends to act as a natural rev-limiter. Up in the 5000-5500 RPM range (depending on engine), valve flutter- which is the inability for the valves to open and close completely in time for the next cycle- will not allow the engine to spin up any faster. It is widely accepted that this RPM range is "safe".

2) at UNSAFE speeds, your connecting rod is much more likely to fail first- and is a lot less, ahh, SPECTACULAR.

 

[mysteryboy28]

I sincerely hope you're kidding.

so you endorse removing the governor then? hmmm... i see a new project for myself in the near future...

 

[fallguy]

Yeah i thought the valve float would keep it at a safe RPM, if you do the valve springs then the connecting rod will be the next weak link.

after you install a billet con-rod i dont know what will let go next.

 

[jamyers]

so you endorse removing the governor then? hmmm... i see a new project for myself in the near future...

See the latest sticky for info on governor removal.
http://www.diygokarts.com/vb/showthread.php?t=16518

 

[klicky96]

Without the governor removed, he would still probably get around 4-4,200 RPM right? Well with using the calculator, with 15" tires, 12T Clutch, 72T Axle, running at 4,200 RPM, he'll get 31MPH. This meaning, the setup he is using will give him what he desires. I've never used a 212cc Harbor Freight so i don't know the exact maximum RPM while still governed, so I just estimated. But with that, he'll get what he wants. Before you guys ask, yes, there is the effect of gravity, friction, air resistance, etc. But thats just at 4200RPM. If it goes to be around 4,600RPM, then he will excel his desired speed.

 

[r_chez_08]

Nice!!! When do you expect to finish it? We have decided to oder: 15" tires , 60t sprocket and according to the speed calculator it'll give us 32 mph which is plenty when you're that low to the ground and then if we feel we need more speed we'll take off the governor which will give 45 mph if the RPM goes to 5000 ...It is a fun project when we are done we'll have 2 karts one that goes 25 mph and one at 32 mph, I am having a blast learning from all you guys ...Jcotz, you are correct it's always good to know both sides..You can't never learn enough ...Bob

I hope to finish late June, I am doing exams ATM so cannot work on it .

IMO I would leave the 72 and adjust the governor, and install a free flowing exhaust and intake. This will allow you to get to around 4300 rpm and acceleration will not be damaged.

 

[klicky96]

I hope to finish late June, I am doing exams ATM so cannot work on it .

IMO I would leave the 72 and adjust the governor, and install a free flowing exhaust and intake. This will allow you to get to around 4300 rpm and acceleration will not be damaged.

Shouldn't he already be able to hit 4,300RPM though?



Also, to really go into detail, a 15" Tire fully pumped up should actually be about 16-17" Tall. So the speed with a 72T Sprocket at 3600 RPM is actually 29-30 MPH. Then Calculate in the friction and air resistance and you'll get about 27MPH.

 

[speed1]

This is what we ordered last Saturday...1" live axle, 60t sprocket , chain and all necessary stuff to finish up te rear end, according the calculator I should get around 32mph and if the 60t sprocket dosen't move my fat a** we'll replace it with a 72t and take off the governor...Hopefully we'll get the parts from BMI by friday and have it ready to go sat. or sunday ...Will post pictures at that time...Bob

 

[r_chez_08]

Shouldn't he already be able to hit 4,300RPM though?



Also, to really go into detail, a 15" Tire fully pumped up should actually be about 16-17" Tall. So the speed with a 72T Sprocket at 3600 RPM is actually 29-30 MPH. Then Calculate in the friction and air resistance and you'll get about 27MPH.

Yeah sure, he could reach it, however the simple mod of a filter and header adds approx. 1hp at around 4k where the torque curve starts to tail off.

Also, I am sorry, but I do not agree. Tire sizes vary a lot, some may be slightly under, some the same, and some slightly over advertised size. I have never seen one 2" larger on diameter though.

Also, sure air resistance and friction slow down the kart, but if the engine is turning 3600rpm, the axle will turn 720rpm whatever. The only loss would be in the clutch and from the tire to the ground, where slippage would occur. Drag, weight and other factors just put a higher load on the engine.

 

[Doc Sprocket]

Shouldn't he already be able to hit 4,300RPM though?

Not without adjusting the governor setting. Even then, 4300 is unlikely. Expect 4000, perhaps up to 4200.

Also, to really go into detail, a 15" Tire fully pumped up should actually be about 16-17" Tall. So the speed with a 72T Sprocket at 3600 RPM is actually 29-30 MPH.

Not to bust your hump, but I want to know where you're getting this stuff. Seriously. 99 times out of every 100, tires measure under the advertised size, as inflated to specified pressure. It is very rare they end up being larger- and to tell someone they can expect an additional 2" diameter on a 15" tire is just uncool. In MANY years of playing with things with tires, I long ago learned that there is just no substitute for a tape measure, as the advertised sizes just aren't accurate. When calculating gearing, I always advise people to measure the actual loaded diameter of the tire. For greater accuracy, multiply the static loaded radius by 2 (from the ground to dead center of the hub). For the ultimate in accuracy, chalk the tire, and a start point on the ground. With the kart fully loaded including the driver (and tires at spec pressure), have someone push the kart while observe the chalk on the tire. Push until the tire does 3 or 4 full revolutions, and mark the spot on the ground where the chalk on the tire indicates a full revolution. Measure the distance travelled, and divide that number by the number of revolutions the tire has turned. The result is the average dynamic loaded circumference, and will yield the most accurate calculation for gearing, speed, RPM, WRPM, etc. This is how I calibrated my speedometer, and then used the average of 6 long GPS passes to verify. If your calculation method requires a diameter number (and not circumference), divide the circumference by PI.

Then Calculate in the friction and air resistance and you'll get about 27MPH.

Do you have a calculator for this? I'd like a copy...