tyre scrubbing/ kart bogging down

[4wd_for_field]

i just finished my first full build of a manco kart/quad hybrid, and was all excited to take it for its first run. but, to my disappointment, the engine clutch combo was fit to drive it and the clutch was slipping terribly! thing is, this combo worked before with the same wheels and tire setup,but in the standard configuration. could me splitting and putting it on my kart have affected it that much? check out
to see it.
any help would be seriously appreciated, thanks!

 

[karl]

clutch was slipping terribly!

What kind of clutch? Right now all I can say is fix it.

tyre scrubbing

Fix it?

No info, so thats all I can give you.

 

[4wd_for_field]

sorry,
the clutch is a hilliard heavy duty thats rated to 10 hp i think?
its brand new with less than an hours use.
Well its running quad tires, so i'm wondering maybe is there too much contact patch on the road?
thatnks!

 

[Doc Sprocket]

I'm a little lost here- you said you have the same engine/clutch/tire combo that worked before, so what exactly did you change? Whaddya mean, "splitting it"?

 

[4wd_for_field]

well i took the front end off of a quad, and converted it for my kart. i "split" the joints that was holding the front together, you should see it in the pictures.

 

[karl]

you should see it in the pictures

I dont see the pictures.

 

[Doc Sprocket]

Nor do I. What exactly do you mean by tire scrubbing- details, please.

 

[4wd_for_field]

woops sorry i thought i had the build thread shown, here it is:
http://www.diygokarts.com/vb/showthread.php?t=13059
the tires seem to be being "pushed" across the surface instead of turning, causing the engine to bog and the clutch to slip..

 

[Doc Sprocket]

Front tires are scrubbing, or rears?

I just ran thru your thread- those rears appear much larger than the original rear tires. Have you altered the gear ratio to match the new rear tires?

 

[TorqueRanger]

Front tires are scrubbing, or rears?

I just ran thru your thread- those rears appear much larger than the original rear tires. Have you altered the gear ratio to match the new rear tires?

He is pretty much have the same problem as i do with the tire being to large for a clutch.... Check out something I just read

LINK



Changing the size of the tires. Putting on tires that are larger than what came with the kart will result in clutch problems. Tires exceeding 13" in diameter stress out a clutch if the kart is not properly geared for the larger tires. If you are driving on smooth flat terrain than you may be able to get by with 14" tires but once you get on hilly terrain, deep grass, then you are putting additional strain on the clutch, which will cause premature wear. Big tires look cool on a go kart but you create your own problem changing to a bigger tire when the clutch isn't designed to handle them. If you have tires over 15" tall you are required to use a torque converter instead of a centrifugal clutch. Do not install rims larger than six inches if your go kart is equipped with a centrifugal clutch.
5) Weight: A centrifugal clutch is designed to be able to move a certain amount of weight. Once the weight limit is exceeded, then the life of the clutch will be shortened. A good rule of thumb is the kart and driver (and passenger when it is a two seat kart) should not exceed 400 pounds. The kart weighs around 150 pounds add to this the driver (and passenger weight, if it is a two seater kart). If you know ahead of time that you will exceed the 400 pounds then buy a torque converter go-kart and avoid the problems of burning up the clutch asking it to do more than it was designed for. A torque converter has a variable speed system between the driver and the driven pulleys so it can improve upon this ratio, which gives the torque converter an advantage over a straight clutch system. It improves the ratio by approximately 3:1 and can turn larger tires and drive at slower speeds without doing any damage to the clutch system. A torque converter is a more expensive system initially but it will last longer and is more trouble free when maintained.

 

[Doc Sprocket]

Well, sure- but in the first post, he stated that the engine/clutch/tire combo was the same.

However, the pictures say differently. If the gear ratio was not lowered by at least an equivalent percentage- that's THE problem. Example- going from 14" to 20" tires. That's a 30% increase in tire size. Let's suppose you have a 6:1 ratio. You must increase that by at least 30% to compensate for the larger tires, so that would equal 7.8:1.

Now remember- that equal percentage equation compensates for tire diameter. It does NOT compensate for added weight, rolling resistance, frictions, etc.

 

[racerc2000]

was the original kart a live axle? from the build post ide say no.

live axle will kill your turning on hard ground.

if its not something you've driven before. the same kart with the only diff being single or live axle. they will feel like night and day

and depending how your front suspension is setup and the tall tires. you might be getting roll over. bottoms of your tires pointing inward and taking a turn rolling the tire past the tread.

can you lower the front at all? it may lack the weight to be at the suspensions resting height. as it was designed for when on the quad. spindle angle and ackermann how are they?

 

[4wd_for_field]

sorry i havent been very up to now so i will give a complete background on the build:

5 years ago, i asked to get a quad, but was dismissed as they are too "dangerous".

so not giving up, i decided to build a kart.

i built the frame and all, and bought a quad to use for wheels, but then decided to use it for suspension too.

to do this, i cut it in front of the engine, and bolted/welded it to my original frame.

to this frame, i used the engine/clutch/live axle combo you see here.

before this build was finished, my friend offered me the manco kart seen in the pictures for €40 ($50-60). the original plan was to fix it up and sell it for a profit, but in the mean time, the engine packed in.

so, with my original design a bit below par (designed by an 11 year old me in fairness) i decided to bring it up to scratch with the streamlined manco frame, and my drivetrain/wheels.

when test run on my original kart, the system worked much better. the only thing that has changed from that original body is that the frame is different, and the steering geometry has changed. so i am just wondering is steering geometry alone enough to cause the kart to bog down?

 

[Doc Sprocket]

It is conceivable. Perhaps the alignment is bad enough that while the kart is being forced forward in a straight line, the tires actually are pointed elsewhere. This would be a toe-in (or -out) problem. A conributing factor might be the suspension not resting in a position that allows the correct alignment, due to the effects of bump steer. While you're checking things, ensure that the bearing preloads are acceptable, the wheels spin freely, etc. Here' a question- when you try to drive forward, does the front suspension try to compress? Its very hard to tell from the pics, but it looks like your shock towers are dead vertical. Is there any kind of caster angle in there?

 

[4wd_for_field]

yeah there is no caster, its dead vertical. i think another problem is that i have too much camber i it, which is causing the steering to roll, which is not alone dangerous, but adding to the problem as its impossible to control. i have checked the toe already and its dead straight!

 

[racerc2000]

one thing to remember is that a quad... humm how to say this.

its not a flat track racer unless modded to do so. the stock setup is pretty neutral when sitting at the oem weight. but it handles the same with a 150lb person compared to a 250lb person.

its like from the factory they are setup to work everywhere just good enough. but need to be modded to work better in a more controlled environment.

lean is also not present in a kart as the roll center is much lower then a quad. on high speed turns a quad will lift one side off the ground a kart wont. and. a quad has the power to push right through the tire drag.

if you have the ability I would suggest adding rod ends to your front arms and making them adjustable. adding a shock mount down your towers could help with the shock tuning. it can have 4 or 5 positions to mount the upper. it will change the height and also the angle. that working together with adjustable arms and you can dial it in perfectly.

The MOST important thing to remember is...........ONLY MAKE ONE CHANGE AT A TIME !!!!! Doing one change at a time will allow you to get a better feel for how your suspension is responding to the changes. Making more than one change at a time will just confuse you because you won't know which change made a desired or undesired effect.


btw do you have any sag built in? can you lift your front end with the tires staying on the ground? most quads have 20-30% ride height sag

front is 20% on avg rear 30% from wheels off ground shock travel to loaded with you sitting. if you have 10" travel it should be about a 2" diff. im guessing you have none or very little.

 

[Doc Sprocket]

I agree! Especially with the droop. Way too many time I see folks set up suspension to ride at full droop at all times. Without writing a novel, I disagree with this practise. I believe that with a full tank of gas and the riders weight (and any other incidentals beyond the karts curb weight) the kart should sag a bit. 20-30% sounds like a good figure. Amongst other reasons, this will much better allow the kart to follow the terrain, keeping all four firmly planted.

If the caster is at zero (shock towers dead vertical) I can't help but think that powering the kart forward might cause the suspension to drop a bit in front, causing the wheels to toe out and plow (or scrub). I'm not sure if this is the case here, but I would be tempted to tip the shock towers back 10* or so, set the ride height as mentioned above by softening the springs, extending the towers upward, or whatever it takes, and adjusting the tie rods to achieve 1-2* of toe in.

 

[4wd_for_field]

i was just out with the kart ther, and i thought i'd check the clutch. it seems the shoe has sections of it which seem untouched, but other parts were clearly trying to engage.

also, once i had the clutch back on, it was very easy to move the kart with my hand by just turning the clutch, is there something wrong with the clutch either?

 

[Doc Sprocket]

Due to gear reduction, it should be easy to roll by hand with the clutch drum. Is it any easier than it was before?
There are a few different clutch designs out there, and some do not put the entire shoe in contact with the drum. Pics of clutch may help.