Go Back   DIY Go Kart Forum > Building Plans And Advice > Engines & Clutches

Notices

Closed Thread
 
Thread Tools Display Modes
  #41  
Old 05-16-2019, 07:27 AM
67StingrayJ 67StingrayJ is offline
Member
 
Join Date: Jan 2019
Posts: 73
Thanks: 3
Thanked 1 Time in 1 Post
Default

But my initial ratio is 7.5:1 so how is that like starting out in "3rd gear"? Isn't that the purpose of a CVT? to give you a high ratio to get started then transition into a lower ratio once you get going?
  #42  
Old 05-16-2019, 07:57 AM
J.S.@SMS's Avatar
J.S.@SMS J.S.@SMS is offline
Here 8am-? Mon-Fri
 
Join Date: Sep 2018
Location: Weeki Wachee Fl.
Posts: 670
Thanks: 63
Thanked 121 Times in 107 Posts
Default

What is the sprocket ratio. That is what is important. I could have used a 30 series on my Manco, and had a 8.1:1 reduction initially. But the 2.7:1 final ratio was just too high for the kart. But a 30 series works on my, much bigger, Streaker. The difference is, at the final stage the Manco has a 9t-27t (3:1) ratio, where my streaker has a 9t-60t (6.6:1) ratio.
__________________
For his personal safety, keep this one away from bicycles.
  #43  
Old 05-16-2019, 08:48 AM
landuse's Avatar
landuse landuse is offline
Moderator
 
Join Date: Nov 2010
Location: Pietermaritzburg, South Africa
Posts: 17,405
Thanks: 2,156
Thanked 3,482 Times in 2,840 Posts
Default

Quote:
Originally Posted by 67StingrayJ View Post
But my initial ratio is 7.5:1 so how is that like starting out in "3rd gear"? Isn't that the purpose of a CVT? to give you a high ratio to get started then transition into a lower ratio once you get going?
You stated that you have a 10T going to a 31T. How is that 7.5:1 and not 3.1:1?? And how is that not like starting in 3rd gear?

It is no use fighting us. We are only trying to help you.

Peace out....
  #44  
Old 05-16-2019, 08:51 AM
Kartorbust's Avatar
Kartorbust Kartorbust is online now
Senior Member
 
Join Date: Feb 2016
Location: Lincoln, NE
Posts: 2,885
Thanks: 614
Thanked 766 Times in 644 Posts
Default

Quote:
Originally Posted by landuse View Post
You stated that you have a 10T going to a 31T. How is that 7.5:1 and not 3.1:1?? And how is that not like starting in 3rd gear?



It is no use fighting us. We are only trying to help you.



Peace out....
His 7.5:1 is taking the low end of the 40 series multiply by his 3.1:1.


When you are gearing a kart, you do not take the CVT into consideration at all. Just the physical gears themselves. So the sprocket on the CVT or clutch and the axle.
__________________
In the age of information, ignorance is a choice.
  #45  
Old 05-16-2019, 10:50 AM
65ShelbyClone's Avatar
65ShelbyClone 65ShelbyClone is offline
Senior Member
 
Join Date: Jan 2018
Location: SoCal
Posts: 453
Thanks: 42
Thanked 180 Times in 150 Posts
Default

Quote:
Originally Posted by 67StingrayJ View Post
But my initial ratio is 7.5:1 so how is that like starting out in "3rd gear"? Isn't that the purpose of a CVT?
Because that's what your top end ratio should be closer to, not your takeoff ratio. You have to prioritize the top end ratio (3.1:1 in this case) because that will be limited by the engine's power. Ideally the CVT will have shifted fully at the engine's max power RPM and the kart's top speed. You currently have gearing for about 70mph at just 4000rpm. That's not likely to happen.
__________________
I'll show those guys who's in top place, I'll really give 'em a hotrod race.
  #46  
Old 05-16-2019, 12:18 PM
KartFab's Avatar
KartFab KartFab is offline
Senior Member
 
Join Date: Jan 2013
Location: Dallas, TX
Posts: 3,286
Thanks: 497
Thanked 1,452 Times in 1,026 Posts
Default

If you want to try it out, nothing is stopping you from running it with a small axle sprocket.
__________________
Free Go Kart Plans https://kartfab.com Go Kart Videos https://www.youtube.com/c/KartFab
  #47  
Old 05-16-2019, 12:30 PM
67StingrayJ 67StingrayJ is offline
Member
 
Join Date: Jan 2019
Posts: 73
Thanks: 3
Thanked 1 Time in 1 Post
Default

Quote:
Originally Posted by landuse View Post
You stated that you have a 10T going to a 31T. How is that 7.5:1 and not 3.1:1?? And how is that not like starting in 3rd gear?

It is no use fighting us. We are only trying to help you.

Peace out....
I'm not fighting anybody, just asking for justification and clarification. Anyone can make a claim, but backing up that claim takes intellect. I'm keeping things civil yet challenging everyone to prove me wrong.

You keep saying I have a gear ratio (3.1:1) that's like starting out in 3rd gear but I have a valid point that nobody can seem to contest. I'm not starting out in that gear ratio, I'm starting out in a 7.5:1 ratio. Can you explain WHY one wouldn't count the CVT as part of your gear reduction? Isn't that the point of a Transmission?

If the cart is struggling to get to speed, won't it slow down effectively reducing it's gear ratio?

YES or NO. Is a 7.5:1 gear ratio sufficient enough to get the cart moving, and possibly pull it's occupants up a hill?
  #48  
Old 05-16-2019, 02:49 PM
Kartorbust's Avatar
Kartorbust Kartorbust is online now
Senior Member
 
Join Date: Feb 2016
Location: Lincoln, NE
Posts: 2,885
Thanks: 614
Thanked 766 Times in 644 Posts
Default

When you are figuring gearing on a go kart or buggy you do not include the gearing from the CVT at all, only the sprocket from the cvt and axle. So no, your current gear ratio on the kart is not sufficient enough to be used.
__________________
In the age of information, ignorance is a choice.
  #49  
Old 05-16-2019, 03:49 PM
67StingrayJ 67StingrayJ is offline
Member
 
Join Date: Jan 2019
Posts: 73
Thanks: 3
Thanked 1 Time in 1 Post
Default

Quote:
Originally Posted by Kartorbust View Post
When you are figuring gearing on a go kart or buggy you do not include the gearing from the CVT at all, only the sprocket from the cvt and axle. So no, your current gear ratio on the kart is not sufficient enough to be used.
I'm going to take your word for it, but I really wish someone could tell me why. Again, I'm not trying to be difficult, just looking for solid reasoning. As they say in the Show Me state, "Show Me".

What's the difference if had a clutch instead of CVT where there was only engaged (at 1800 rpm), or not engaged. If I had a 7.5:1 ratio in that regard, how is it not acceptable to the initial gear ratio I have now?
  #50  
Old 05-16-2019, 04:10 PM
bob58o's Avatar
bob58o bob58o is offline
Sick, Tired, and in Debt
 
Join Date: Jan 2016
Location: Under the Rothschild Whip
Posts: 7,516
Thanks: 3,226
Thanked 2,247 Times in 1,740 Posts
Default

First of all, of course you include the reduction from the CVT when figuring gearing on gokart or buggy. The above statement doesn't make any sense. That's like saying you don't include the transmission or axle ratio when figuring the gearing in a car.

At 3600 RPM, IF THE TC SHIFTS TO HIGH GEAR, the buggy should be traveling 62 mph. Do I think you are going to get that heavy buggy moving 62 mph? Probably not. So either the TC isn't going to fully shift out or you are not going to rev to 3600 RPM.

So I do agree that the gear ratio is not optimal. Like KartFab mentioned, a more reasonable speed would be around 40 mph at 3600 RPM. That would be using a 4.8 :1 sprocket ratio. 5.4 :1 would be even better.

---------- Post added at 04:10 PM ---------- Previous post was at 03:50 PM ----------

Quote:
Originally Posted by 67StingrayJ View Post
I'm going to take your word for it, but I really wish someone could tell me why. Again, I'm not trying to be difficult, just looking for solid reasoning. As they say in the Show Me state, "Show Me".

What's the difference if had a clutch instead of CVT where there was only engaged (at 1800 rpm), or not engaged. If I had a 7.5:1 ratio in that regard, how is it not acceptable to the initial gear ratio I have now?
Let's assume a 7.5 :1 sprocket ratio with regular clutch and 18" tires.
If the clutch starts to engage at 1800 RPM, then the vehicle should be traveling 13 mph at that engine speed. If we include the fact the clutch is not FULLY locked up until an even higher RPM (say 2500 RPM or so), then we realize that the clutch will be slipping until the vehicle is traveling around 18 mph. The clutch will be slipping, getting hot, and wearing out when you are traveling at speeds less than 20 mph. So if you stop and go often or cruise around at low speeds, the clutch will wear out faster than if you run at high speeds on long open roads for extended periods of time.

Now if we switch the regular clutch with 7.5 :1 sprocket ratio to your TC with 3.1 :1 sprocket ratio, not much changes on the low end. But now, at lower speeds, the belt (or possibly the driver unit internals) will be slipping instead of the clutch.

If we look at the top end, the regular clutch with 7.5 :1 sprocket ratio would be traveling 26mph at 3600 RPM which is very doable (even with a heavy buggy).

3600 RPM with 3.1 :1 final drive ratio would be 62 mph. Not very likely for a heavy buggy. So like I said in the previous post, either the TC isn't going to shift out completely (meaning you are going to stay in a lower gear at all times) or the engine isn't going to rev to where it is making peak HP. The point of the TC is to keep the engine at the RPM where it is making peak HP at all times. In order to keep the engine at peak HP RPMs, the TC will stay in lower gear. This limits the range of the TC and somewhat defeats the purpose.

I see many people giving advice who have zero experience with "big blocks" and/or 40 series torque converters. My heavy buggy with 420cc, 40 series TC, and 18" tires has a 5.45 :1 sprocket ratio (60T :11T).
__________________
History doesn't repeat but it rhymes Name a successful fiat currency in the last 5k years
The Following User Says Thank You to bob58o For This Useful Post:
PullHorse (05-16-2019)
  #51  
Old 05-16-2019, 04:22 PM
KartFab's Avatar
KartFab KartFab is offline
Senior Member
 
Join Date: Jan 2013
Location: Dallas, TX
Posts: 3,286
Thanks: 497
Thanked 1,452 Times in 1,026 Posts
Default

So when i first started messing with gear ratios on go karts i got a small axle sprocket and wanted to see how fast i could go.

What basically happens is if you gear with a small axle sprocket on a torque converter, the drive unit makes some really funny sounds and you slip your belt until all of a sudden it locks up fully when you start creeping forward. If the axle sprocket is too small, and the belt is fully engaged, it may even stall the engine or cause it to lug lug lug until you pick up a little more speed. Once you get going and actually hit the engines power band, its not so bad and the torque converter actually functions as it normally should.

That point between you being completely stopped up until the engine hits the power band on a normally geared go kart or mini bike is usually overcome with very little belt slippage.

Since you are running a little more hp, i think you will probably just spin the belt more and eventually get going rather than having the torque converter engage fully. IT will be a real jerky feeling when it does suddenly engage.

That is what happens at very low speeds. You might actually find it enjoyable to be going 40-60 mph in the powerband, but it will be a struggle for the belt and kart to reach that speed initially. It just wears the belt out and heats the drive unit up because of all the friction. Who knows, you might even see some belt smoke if you dont have enough teeth on the axle.


I havent done this with a 40 series, but the 30 series really did struggle to get going. Id assume you would have a similiar experience.

We often see people post about "why is my clutch burning up" and it is because someone swapped out the torque converter/jackshaft reduction for a centrifugal clutch.

We dont often see people post about "why is my torque converter burning up" because its actually kind of hard to ruin a torque converter when you gear with a smaller axle sprocket, it just mainly eats belts and you dont get those little butterflies in your stomach from acceleration. The end result is you just get poor jerky acceleration and your engine will lug down or smoke the belt because the kart cant accelerate like it is supposed to.

You can actually gear for a slightly higher top speed with a torque converter from the initial reduction, but it is not proportional to what you would think for a centrifugal clutch. All else the same, a 25 mph (centrifugal clutch) go kart can be geared for 35 mph with a torque converter, but not THREE TIMES FASTER. More like 40% faster, not 300%....

Again, nobody is stopping you from trying it out. Sometimes the best lessons are learned from doing and seeing what happens.
__________________
Free Go Kart Plans https://kartfab.com Go Kart Videos https://www.youtube.com/c/KartFab
The Following 2 Users Say Thank You to KartFab For This Useful Post:
bob58o (05-16-2019), Kartorbust (05-16-2019)
  #52  
Old 05-16-2019, 04:48 PM
67StingrayJ 67StingrayJ is offline
Member
 
Join Date: Jan 2019
Posts: 73
Thanks: 3
Thanked 1 Time in 1 Post
Default

bob, KartFab,
Thank you both for taking the time to spell it out. I'm not fighting anyone on switching to a larger sprocket on the axle. It's just a lot of work and worth understanding before cutting the rear end up. I have a 60 tooth that can install so we'll see how that works out.

The thing that gets me, the engine previously on the cart was only 150cc, it had a CVT (not sure on specifics, but definitely small) and that CVT was connected to a 15 tooth drive gear to a 31 tooth on the axle. I was able to move the buggy in sand, with 2 full grown adults. However, it was a struggle therefore I elected to upgrade engine and put a 40 series on.

I can't help but wonder, if that worked (not admirably I admit) then why wouldn't an engine nearly 3 the size and a stronger CVT, with better gear reduction work for my set up?

I'm going to try it one last time with the 31 tooth on the axle before I cut things up. The bench mark will be if I can take 2 full size adults up a hill. If not, then I'll make the adjustments to frame for the 60 tooth.

Thanks everyone for their help, and patience. I'll be sure to post my results and give you all the opportunity to say " I TOLD YOU SO" should that be the case.
  #53  
Old 05-16-2019, 07:59 PM
cleatusj cleatusj is offline
Junior Member
 
Join Date: Apr 2019
Location: Granbury, Texas
Posts: 20
Thanks: 0
Thanked 10 Times in 9 Posts
Default

Quote:
Originally Posted by 67StingrayJ View Post
I'm not fighting anybody, just asking for justification and clarification. Anyone can make a claim, but backing up that claim takes intellect.
You provided the justification, when you stated it struggled to take off. The clarification will come, when you experience a lower gear ratio.

Those that have responded to you are expressing their knowledge of what they have experienced, by trying different ratios.

It takes knowledge to make a valid claim, but " Intellect" would be the faculty of reasoning and understanding objectively, especially with regard to abstract or academic matters.

Understanding Ratios, takes knowledge, backed by experience and facts, not anything abstract or academic.

No one here wants to tell you I TOLD YOU SO. We just want to help each other reach a point that our machines act like we want them to.
The Following User Says Thank You to cleatusj For This Useful Post:
landuse (05-17-2019)
  #54  
Old 05-17-2019, 01:15 AM
landuse's Avatar
landuse landuse is offline
Moderator
 
Join Date: Nov 2010
Location: Pietermaritzburg, South Africa
Posts: 17,405
Thanks: 2,156
Thanked 3,482 Times in 2,840 Posts
Default

Knowledge is really about facts and ideas that we acquire through study, research, investigation, observation, or experience. Wisdom is the ability to discern and judge which aspects of that knowledge are true, right, lasting, and applicable to your life. Wisdom is the application of knowledge.
  #55  
Old 05-17-2019, 08:26 AM
KartFab's Avatar
KartFab KartFab is offline
Senior Member
 
Join Date: Jan 2013
Location: Dallas, TX
Posts: 3,286
Thanks: 497
Thanked 1,452 Times in 1,026 Posts
Default

150cc has a geared transmission too...

If you want to check the math, just look up the specs for your buggy. Max speed and max rpm, then solve for gear ratio and you will find there is some additional reduction going on BEFORE the 15t output
Attached Thumbnails
s-l500.jpg  
__________________
Free Go Kart Plans https://kartfab.com Go Kart Videos https://www.youtube.com/c/KartFab
  #56  
Old 05-17-2019, 10:01 AM
LightningTeg's Avatar
LightningTeg LightningTeg is offline
Member
 
Join Date: Sep 2018
Posts: 75
Thanks: 8
Thanked 16 Times in 13 Posts
Default

Quote:
Originally Posted by bob58o View Post
I see many people giving advice who have zero experience with "big blocks" and/or 40 series torque converters. My heavy buggy with 420cc, 40 series TC, and 18" tires has a 5.45 :1 sprocket ratio (60T :11T).
Just curious what the weight of your "heavy" buggy is?

I've got a 6:1 ratio (10T Drive to 60T Driven) and it scoots out from a dig. I wouldnt mind maybe a 5.5:1 to get a little more top end out of it, but I love kicking the *** out on demand.

I think mine is 650lbs without people. Doesnt really seem to notice when people are in it either...
Closed Thread

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 08:40 PM.