How high can you go? (Gear Ratio)

[Kartorbust]

Now this frame, I like. A few angles, but I have tools and a brain

This isn't a plan. I'll just replicate-ish it by sight

View attachment 71280

Went ahead and added two SOLID steel spindle brackets to the cart. 4.95 each, but I'd rather buy then weld what holds my wheels in place, ESPECIALLY if I want to go over 50mph.

That frame has a pivot point on the back for shocks. That frame is the Arachnid from Spider karts. That much 1"x1"x11ga steel might be a bit heavy to keep it light weight enough, if you are going that high of gear. Even going to 14ga, it may be too heavy.

 

[ddowns46]

Karts and mini bikes that have high top speeds all have one thing in common: they turn a lot of RPM. Those drag bikes you see doing 80+ mph on Youtube are turning 9000 rpm minimum. They dont get to those high speeds with tall ratios and governed motors.

My advice to you would be to modify that motor to turn at least 6500 RPM safely. Then using one of the many online calculators, choose the sprocket sizes that will get you to 50 mph at 6500 RPM.

I run my sprint kart with a warmed over clone using 4.4 gearing and 11 inch tires. Still has plenty of kick off the line and will do 50mph no problem. My modifed 212 will do 60 on the same kart.

I would also reccommend a good quality adjustable stall clutch such as a hilliard flame/fury.

 

[itsid]

Well simple fact I know someone with a really high gearing (one I wouldn't ever recommend)
I don't say who, since otherwise .... one would want to try that and fail..

But yes, if you pay twice the amount for a quality clutch than you payed for your predator engine, you can gear pretty high.

Since sprockets are cheaper than a regular cheap lutch I'd suggest to just gear according to common sense (i.e. not higher than 6:1 for now) especially not with 15" wheels..
(take ddowns experience as a measure 4.4:1 on 11" tyres.. 4.4/11 conveniently .4 that times 15 and there you are 6:1!!
So you running 6:1 is the same as him running 4.4:1)
and work your way down slowly buying split sprockets and a few extra feet of chain

You will ruin a clutch at one point, one sprocket size up, and a new clutch and you'll be set.
You'll spent much less than for a racing grade clutch that way
(still you'll end up with not much gain at all if any.. but you at least know now!)
my best guess.. you'll even need to lower a hair (say 6.3:1)

'sid

 

[chancer]

You can run 3:1 on smaller tires and a fancy Noram clutch. I know the same guy as sid.
But this guy does not Put around. He gets the kart moving gets it up to speed and STAYS there!

Please listen to the advice you have been given here today. It is all good. and no one has insulted you...yet. but what you are talking about doing is not easy or normal.
People are here to help you we all want to help you but good advice that is ignored will get you nowhere here.

 

[ultralight01]

Thank you everyone. Modifying the engine, at least removing the governor, and getting a bigger sprocket is probably a good idea. The last time I removed a predator's governor, it didn't go so well (pull starter locked up, valves got out of whack, etc.). But maybe out of the box I can do it.

I'm not inexperienced with karts, but I'm also inexperienced with karts. So any advice is appreciated.

I'll draw up a frame similar to the one I found, with less steel. Thanks for the I.D., Kartor Bust.

If only you could get a 6000-9000 rpm engine for under $200. Now THAT would be a game changer. For now, I'm on a budget.

So what can I run without destroying a clutch?

Time to play with the speed calculator again.

 

[chancer]

With 15" tires. Maybe if your real lucky 5:1. Maximum

 

[ultralight01]

If someone can help me out here, I'm just trying to increase my knowledge.

There is too much friction for a clutch, even when fully engaged, at a high ratio, for it to survive the heat, breaking it?
Would a jackshaft increase torque allowing for a higher top speed? Or a TC (Which I have no idea what that does).

 

[chancer]

Well it is kinda like driving a manual tranny Car. If you try and continually start in 4th gear from a dead stop. Well you will probably stall. So lets say 3rd. You may get it going but you really have to burn and slip the clutch. and eventually the clutch will be bad.
same thing on a kart clutch.
3:1 is like 3rd or 4th gear.

once you get it moving at speed you would be alright. So if you ALWAYS had a hill to roll down from a stop and never slowed down. 3:1 will work.

 

[Poboy kartman]

Well...here it is...check out old videos of sandflat racers....

They have people PUSHING. them to get them going....

It's because they are geared so high...they can't move on their own from a dead stop.

 

[chancer]

Yep! you used to see that alot in Nascar too, as a car exits the pit stall the guys will give it shove tryng to help the driver not stall. Mostly overzealous crew guys though. LOL

 

[Kartorbust]

A jackshaft can help lower your gear ratio with the proper sprocket choices. A torque converter will help, but it'll still require a lower gear ratio than what you have currently, but will also give you extra ratios as the belt goes through the pulleys. A T/C works the same way as a CVT (continuously variable transmission) in fact some will use CVT as the name for a T/C on a go kart.

---------- Post added at 08:07 PM ---------- Previous post was at 08:05 PM ----------

The link may or may not work very well as I'm on my phone right now, but here's a good description of how a CVT works https://practicalmotoring.com.au/car-advice/continuously-variable-transmission-explained/

 

[ultralight01]

Alright. My goal is 50mph. Looks like I can achieve that with no governor (5200-5400RPM) and a 60T sprocket with a 12t clutch. 5:1

Good Gosh this next predator had better not lock up with no governor... My plan is to do it surgically, out of the box. No spilling out the cam and push rods twice like last time. Maybe the alignment will stay then... Or whatever went wrong when the plastic piece inside the starter snapped

By the way, I finished my Murray, and it's up for sale: http://portland.craigslist.org/grg/snw/5620726700.html I decided I didn't want to modify this kart, it's too big for what I want to build.

To build a sprocket+brake drum assembly is actually $38, whereas that combo piece with the tiny sprocket was $39. All Right!

I would buy a kart, but CR'sList is dry. Bone dry. Desert Dry. And full of "Crappy Gold In The Eye Of The Beholder" (rust buckets listed at $600)

So I might as well learn to use a welder.

---------- Post added at 06:46 PM ---------- Previous post was at 06:32 PM ----------

To Weld Or To Buy, That is the question. Right now the question is: Are $30 Pre-made front-wheel spindles recommended by members at DIYGOKARTS.

 

[landuse]

I think you have made a wise move changing your mind. 5:1 is a lot better tha 3:1. I am still worried it might be a bit too high though. Try it out and see if it works though. You can always get a bigger axle sprocket later on

Just remember, trying to go fast on a badly build kart is more dangerous that bungee jumping, and i am pretty sure you wouldn't go bungee jumping. Just make sure that you do everything right. Ask a lot of questions here and we will help you through it

 

[Poboy kartman]

Don't get me started....but ...YEAH! ! buy spindles.....or not....(you'll kill yourself either way.)

 

[ultralight01]

Wow, Poboy! The Negativity! Lol.

I'm thinking of starting a build thread, or, heck, entering the DIYGOKARTS build-off with very low odds of even an honorable mention. I'm assembling frame steel this weekend.

 

[Kartorbust]

I'm curious, what brand welder will you be using and will you be using gas or gasless flux cored.

 

[ultralight01]

It's my friend's welder, a wire-feed MIG (I think that's what a wire feed is). Gasless. It's an older high-quality brand is all I know.

 

[chancer]

Enter the build off!

 

[ultralight01]

I will! Does higher HP mean higher rpm with no governor? I'm looking at a power land 13hp.

 

[chancer]

No. Rpm is rpm, It sets your top speed. But HP gets you to your top speed faster.

But with more HP means ability to gear Higher. the 420 has a 1" shaft. means a much more expensive Clutch too. or TC.