June 28th, 2017

Go Kart Tires: The Right Kind, The Wrong Kind, The Ugly Kind

Tires, The Right Kind the Wrong Kind: Which Kind Should I use?

Tires come in all sorts of shapes and sizes and are designed, obviously primarily to get grip to the road.

But they have a second use and that is to dissipate material around from them for instance mud or water.

The basic tires for use for racing, if you have ever looked at them they’re flat.  That is why they call them slicks.   The reasoning for that is, they are not expecting any rain and they are trying to maximize the surface area of grabbing for the tire on a piece of pavement.   The wider the tires typically the more grip you have.  

There is a dynamic that occurs with tires and that is that they have a moment of inertia or rotational inertia, which increases with obviously the mass of the tire and diameter of the tire. 

We’re strictly talking about tires here we are not talking about rims here...
Rims do have effect on the rational mass of a tire system. But we are more talking about the tires and  the right tires to use. 

Am I choosing the right tire or the wrong tire? 

It depends on what you are trying to do with your go kart.  If you are trying to go off road, the best kind of tire would be a knobby style tire.  The purpose for that is because when you are trying to corner, You need to corner!  You don’t need to be sliding into trees, you need to grip into the dirt and move over.  And it is most advantageous when the material underneath, the pavement if you will, is very moist or very moveable.  

The more grip you can get, the more knobs you can get into the surface the better off you are.  Also they aid in acceleration, so that you can spin out and get your vehicle to get going forward.  So if you are going off roading, the best would be to have a knobby style tire. 

If you are dealing with a pavement style tire, there are different kinds.  There is the grooved style which is designed to disappate water, if you ever were driving in water conditions.

 

Just as a side note:  Riding in water is very difficult with a gokart, because water sprays off the wheels.  The water comes spraying off tangentially off the wheels like fans, but they spray straight up in the air, and it will get in your face, get all over your goggles, helmet.  You will want to make sure that you wear a helmut, and some goggles, or at least a helmet with a visor on it.  You will get soaked, so you are going to need to wear a suit, or clothing that will at least repell the water.  You obviously are going to need to wear some pants that don’t absorbs water as well.   I’ve done it myself, but it is very dirty and very wet and very cold, especially if you are going fast.  Because the water will tend to evaporate off of you, and act as a refrigerator.  Believe it or not, there are refrigerator or air conditioning systems that use water as a medium for removing heat…but I digress…

Using tires that have grooves in them, they are designed so that the tire itself can get down to the pavement and disappate the water out.  That is just the treading.

 

Side Walls Probably One Of The Most Important Considerations
There are different style sidewalls, and this is probably the most important thing to you as a consumer, you may want a stiff side wall, or you may want a soft sidewall, it depends on the application.  If you are dealing with an offroad application, you may want a softer tire so that the tire acts as a suspension unit itself.  It helps cushion the load when you are hitting heavy bumps and rough terrain.   

But on a go kart that you are dealing with on a track, you want some stiff sidewall tires.  The reason for that is when you try to corner the tire itself will actually bole over or bend.  It is not something that you want to happen.    You can change the geometry of you front wheels so that they are canted a little bit that helps in cornering, in that the forces will tend to go more vectorly through the tire and cause it to bend less. 

If all that you have is a tire that is relatively low grade and you have a certain style rim, it wouldn’t hurt to put your tires at an angle so that tires won’t bend.  But the better of the options would be to get a tire that doesn’t bend and has a very stiff side wall.  You are going to pay more money for that.

The tires that I use are basically turf tires.  They work relatively well, especially for the ones in the rear.  I would actually advise using a larger tire in the front because they are stiffer, they have a stiffer side wall.  The tires that I have on my go kart right now, has a smaller front tire.  The reason for that is because that is what I had.    I got it off of a gokart and that is what it had. 

Tire Size Up Front...
The smaller tire up front is typically what you find on older go karts.  The reasoning for that is it is easier to steer, there is less kick back in the stearing system, less rotational intertia in the tires, and it is more manageable.

I personally don’t like the smaller tires because they bole over, or bend in turning.  Larger tires are usually put in the rear for traction in power and cornering.

If you look at a racing go kart that has a fifty-fifty weight distribution, typically the rear tires are larger, they are designed for traction during acceleration and for cornering, because you have a little bit more weight in the rear, and the front tires have less weight on them, that is why they are a little bit smaller. The diameter are typically the same, but the widths are different.

Speed Rating of Tires

As far as speed is concerned, tires can be speed rated and balanced it depends on how fast you are going.   I am not abrogating going much beyond 30 mph, that is the kind of go kart I like, but there are gokarts that go up, well towards 70 mph, some even 120 mph.  Those type of gokarts obviously have to have balanced, speed rated tires.   

If you do not have a balanced tire you are going to run into some serious vibration issues.   And you will notice, that even at a simple 20 mph, that if your tire is not balanced, that you will have some vibration going up through the steering system and through the axels, so it would be a good idea to invest in a quality tire if you are planning on spending any extended periods of time at speed.

Front Tires Wear Out Faster...

Typically the front tires will wear out a lot sooner than the rear tires.  And the reason for that is that you will be doing a lot of cornering, and the cornering is really hard on a tire, it will just chew it right up.  If your alignment is off, it will chew the tire up as well.  

So always make sure that your alignment is correct and you will save your tires.  Make sure that the cant of your tires as well is relatively flat on the road, other wise you will be eating those tires up and they will have an odd wear pattern.  It will chew the inside of the tire up, and you will have almost a conical tire after awhile.   

If that is the way that you are designing your front steering system, then a good idea would be to rotate the tires.  Actually flip the tires on the rims so that you can get both sides of the tire to be worn.    But ideally it would be better to have the tires sitting flat on the ground, for good wear.

For more information on wear and steering systems refer to steering systems section (Go  Kart Building 402).  One thing to understand, is that if your steering system is not set up properly you will eat up front tires and relatively quickly.   And that is why you have a steering point in the steering system so that the tire has a point of contact.  Also, as we said before a misdesigned system will contribute to steering feedback or steering vibration as well as misbalanced tires.

Tire Plying...Whats That?
 
Tires come in plies.  There are different types of plies.   You can get steel plies, or nylon cord ply.   If you want more information on actual tires I would suggest that you visit the tire manufacturer sites.

You can also get tires that have no tubes in them.  Some racers run tires without tubes, and the reason for that is that it reduces the amount of rotation inertia. 

But as far as,  if you are making your own go cart,  I would highly recommend that you put a tube in the tire, because you are going to run into a lot of aggravation, especially if you are using an old rim from an old lawnmower.  You want to not have to worry about the tire going flat all the time, so I would suggest that you invest in some tubes.  Tubes keep the tires from going flat.  

Also make sure that when the neck of the filler nipple comes out the rim that it is not being pinched. You can aid in preventing tears by actually wrapping a little electrical tape around the nipple as it exits the rim.  Now another way that you can also take a file to the rim edge and file off the sharp corners to prevent it from cutting into the tube.    And another way, also as well is to take a piece of electrical tape wrap in the hole to keep it from digging into the filler neck. 

Tire Care...Tire Pressure Is Important For Wear Ect...
As far as tire care is concerned,  make sure that you check your tires every time that you go out.    One way that I do that is that I just jump on the tires and make sure that they have the same kind of pressure feel to them.  You can use a tire gauge and make sure that you do not over pressure it.  

Typically a tire is rated at 10 psi to around 35 psi, it depends on how large and what style tire it is.    The higher the pressure, obviously, the harder the tire.   If you want a hard tire for stiff sidewall cornering, but one of the things that happens when you over inflate a tire, the center of the contact tread tends to crown out, and you will wear the center of the tire more than it need to be.  So typically the way you inflate a tire is to make sure it is as it is designed, so it will not have a crown on it.  It will actually sit flat on the road. 

If you under inflate your tires the center of the tire will not actually wear properly.  The edges will.  It is important that you the tires to the rated pressure, to make sure they are contacting the road as the design intended.

If you are driving off road it is not as critical.  Like I said before, you can have your pressures a little bit lower so that you are not killing your go kart frame.  

It is an aid to have the pressures a little bit lower when you are driving out in softer conditions.  One of the things that you need to be aware of is that the softer the tire the more grab, and if you are doing any stunts or side cornering it will actually grab more than you would expect and you may tend to get into a rolling or flipping situation before you really realize it.  

Tire Pressure Is Important For Stability

So  understand that a softer tire has more grip and when you do a cornering operation, or actually try to do a wipe out of some sort, you may actually grab tighter than you wanted to and put the go kart into a roll.

If you are afraid that a go kart could get into a roll, then one of the things you need to do is to take a look at the roll center of the go kart and actually calculate how much force is required to tip the go kart over with a man in it. 

You will want to lower the center of gravity of the go kart by getting it as close to the ground as possible.  
This is beyond tires at this point, but it is important to understand the roll characteristics of the go kart.

For example if you have really sticky tires and you do not have the go kart really set up properly you can actually roll it.  The discussion of suspension systems and stability is discussed in other articles.
 


 
 

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