Kart width & offset

Eric85629

Member
I am new to the karting world & have been working on my 5 year old's jr flat kart. She is winning races and doing good but I have questions about the logic of where to position the tires (yes i know, one on each corner). I changed tires around which changed the width and it got me wondering if they tires are usually spaced to be even with the edge of the body or if there is a different logic that may require the front to be wider than the back, back wider than the front, have a certain tire stick out or in farther than the others.... Can some of you share your reasoning on how to set up the width?

BTW, when I changed things around I put the very wide right front on the left rear so both rear tires are the same width & I put the left rear tire on the right front. This tire was much narrower and slightly taller.

Glad I found this site, been reading lots of good advice
 

racing promotor

Moderator
I am new to the karting world & have been working on my 5 year old's jr flat kart. She is winning races and doing good but I have questions about the logic of where to position the tires (yes i know, one on each corner). I changed tires around which changed the width and it got me wondering if they tires are usually spaced to be even with the edge of the body or if there is a different logic that may require the front to be wider than the back, back wider than the front, have a certain tire stick out or in farther than the others.... Can some of you share your reasoning on how to set up the width?

BTW, when I changed things around I put the very wide right front on the left rear so both rear tires are the same width & I put the left rear tire on the right front. This tire was much narrower and slightly taller.

Glad I found this site, been reading lots of good advice
Your doing it all wrong, it would be easier to call someone to explain it, Carlson motorsports and So Co tire treatments numbers are on here, or check your PM you can call me.
 

alvin l nunley

Premium User
You're doing it all wrong! The fact that you're winning races Probably means your competition is doing it wrong too. You're just not doing it As wrong as they are. lol
 

Eric85629

Member
LOL! I know its not the right way but I'm working with what came with the kart & putting everyone's advice together to make decisions. If I heard right, both the right tires should be the same on wide wheels. The left tires I'm not sure about. The thought behind me putting the small tire up front was due to its larger diameter. I got the kart with a narrow, tall tire on the left rear. His explanation for that was it actually changes the gearing due to it being taller. My thought process was a taller tire on the front right will help the kart carry its speed through the turns. Its a fairly large track, 1/5 mile, the kart's top speed is about 26 mph and the kids don't even lift off the gas until the yellow is thrown. The first race I switched the tires around is the first time she actually caught the lead kart who has been winning 1st almost every race rather than being half a lap down. I would agree that as the karts become faster in other classes, the front right tire should be wider for more grip / better handling.

With all that said, I do want to know how to set up the kart correctly so I can change things around when she isn't in 1st any more & so I'm prepared for the faster classes or when I get her a modern adjustable chassis.
 
LOL! I know its not the right way but I'm working with what came with the kart & putting everyone's advice together to make decisions. If I heard right, both the right tires should be the same on wide wheels. The left tires I'm not sure about. The thought behind me putting the small tire up front was due to its larger diameter. I got the kart with a narrow, tall tire on the left rear. His explanation for that was it actually changes the gearing due to it being taller. My thought process was a taller tire on the front right will help the kart carry its speed through the turns. Its a fairly large track, 1/5 mile, the kart's top speed is about 26 mph and the kids don't even lift off the gas until the yellow is thrown. The first race I switched the tires around is the first time she actually caught the lead kart who has been winning 1st almost every race rather than being half a lap down. I would agree that as the karts become faster in other classes, the front right tire should be wider for more grip / better handling.

With all that said, I do want to know how to set up the kart correctly so I can change things around when she isn't in 1st any more & so I'm prepared for the faster classes or when I get her a modern adjustable chassis.

Your right side tires should both measure 34" in circumference.
Your LF tire should be 32 1/2".
Your LR tire varies depending on track size, chassis preference, and driver comfort. For a 1/5 mile track, let's just start with 32 3/4" and work from there.
Those measurements should be at race pressures.
Again, let's "assume" normal track conditions with 5 psi left sides and 6 psi right sides.
If you need to stretch or shrink tires to get them to these sizes, then follow the instructions found in several other threads on this forum. (Use the search feature located in the upper right hand corner of this page.)

Next we'll need to get the kart on some scales and get the front end lined out...One step a a time. :)



-----
🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
32 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 

mike97760

Premium User
Take a walk around the pits and notice how everyone else is set up, especially the adult karts. You will quickly see a pattern in setups.
 

Eric85629

Member
Your right side tires should both measure 34" in circumference.
Your LF tire should be 32 1/2".
Your LR tire varies depending on track size, chassis preference, and driver comfort. For a 1/5 mile track, let's just start with 32 3/4" and work from there.
Those measurements should be at race pressures.
Again, let's "assume" normal track conditions with 5 psi left sides and 6 psi right sides.
If you need to stretch or shrink tires to get them to these sizes, then follow the instructions found in several other threads on this forum. (Use the search feature located in the upper right hand corner of this page.)

Next we'll need to get the kart on some scales and get the front end lined out...One step a a time. :)



-----
🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
32 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
Great info, thanks. My track has a max diameter of 34.5 on the right rear so I'm assuming I can adjust your measurements to that limit. About air pressure; I was talking with the clone drivers and heard most run around 7 psi. For these kids karts that weigh in around 230 pounds, should the pressure stay the same or be higher? Also related to pressure, our track does not have much clay, is usually very rough, and gets dusty by the second heat. How should kids tires be set up with those conditions?
Since this is my first season in karts I did ask the other teams with the faster kids which is where I got the idea of the skinnier tire in the right front (less rolling resistance). The first race I switched that tire, she filled the gap which was always half a straight away. The next race she won. I understand what I'm doing is all wrong, but its fun seeing simple changes make a big difference. Looking forward to actually knowing what to do
 

Eric85629

Member
Take a walk around the pits and notice how everyone else is set up, especially the adult karts. You will quickly see a pattern in setups.
Unfortunately there aren't too many kids racing. There have been a total of 7 or 8 different kids this season with 4 consistently showing up, 2 of which are newbie families (me included). There just aren't many karts available here in AZ. I'm entertaining the idea of getting people together to make a trip out east or mid west to bring back a trailer load of predator karts to help get more families into it.
 

mike97760

Premium User
Unfortunately there aren't too many kids racing. There have been a total of 7 or 8 different kids this season with 4 consistently showing up, 2 of which are newbie families (me included). There just aren't many karts available here in AZ. I'm entertaining the idea of getting people together to make a trip out east or mid west to bring back a trailer load of predator karts to help get more families into it.
I guess you missed the part about checking the adult karts, too. No, they aren't the same, but they are similar. Bringing in more newbies won't answer you chassis/tires question.
 
Unfortunately there aren't too many kids racing. There have been a total of 7 or 8 different kids this season with 4 consistently showing up, 2 of which are newbie families (me included). There just aren't many karts available here in AZ. I'm entertaining the idea of getting people together to make a trip out east or mid west to bring back a trailer load of predator karts to help get more families into it.
Do you have a fixed gear ratio along with your tire size max for this class?
If so, then definitely max out your right rear tire to that size, and make the left rear only slightly less. Get way up on air psi (it'll be like a pogo stick to drive but it'll be faster than your competitors on that fixed gear. Some kid karts will even run narrower tires on all 4 corners just to reduce the drag and increase roll speed. I certainly wouldn't be opposed to that either, as that's what we did with my youngest son's kid kart (Comer then JRLO206) with fixed gear and tire size. If you're running the 3.5 Predator, you might try stretching some 5.00 or 6.00 tires on narrower wheels and over-inflating them for roll speed. Otherwise, stick with the standard tire sizes and just get up on air. IF the car looses too much sidebite, then add bite back in the tires with chemical rather than dropping the air back to normal psi. FWIW 20-22 psi is not out of the question on a kid kart on dirt.
 

Eric85629

Member
Do you have a fixed gear ratio along with your tire size max for this class?
If so, then definitely max out your right rear tire to that size, and make the left rear only slightly less. Get way up on air psi (it'll be like a pogo stick to drive but it'll be faster than your competitors on that fixed gear. Some kid karts will even run narrower tires on all 4 corners just to reduce the drag and increase roll speed. I certainly wouldn't be opposed to that either, as that's what we did with my youngest son's kid kart (Comer then JRLO206) with fixed gear and tire size. If you're running the 3.5 Predator, you might try stretching some 5.00 or 6.00 tires on narrower wheels and over-inflating them for roll speed. Otherwise, stick with the standard tire sizes and just get up on air. IF the car looses too much sidebite, then add bite back in the tires with chemical rather than dropping the air back to normal psi. FWIW 20-22 psi is not out of the question on a kid kart on dirt.
Yes, fixed ratio of 4.5 & tire size of 34.5 max on right rear. Your input about narrower tires & higher pressure for less drag is in my line of thinking. I know as speed and power increase, alot will change but as long as it drives straight & corners good every little bit helps. Tire prep is limited to washing with water but they allow tread or slicks. Lately Ive been running 9psi everywhere except the right rear which i just fill till its as big as allowed. Running bone stock predator 212 with a red plate
 
First, don't just jack the air up to get the tire size where you need it.
You want to "stretch" the tire and "size" it with heat and psi a week in advance to raceday. Use the search feature located in the upper right hand of this page to find many discussions on "sizing" "stretching" "shrinking" tires.
Next, do the same with the other four corners of your car -- you will want some stagger (front and rear) but not nearly as much as the other classes without fixed sizes and gear ratios. Keep your rear stagger to a minimum for now -- just to get some roll speed. You need enough that the car will roll through the corners, but not so much that it drags rpm down the straights. Next, get up (way up) on air. 20-25 psi is fine. The car will ride like a pogo-stick, but it will be considerably faster. If the kart becomes too free in the corners (ie not enough grip,) then go back down a few psi at a time until you get the sidebite needed to hold the track.
Kid kart racing is all about roll speed and momentum. (not entirely different than adults in that respect actually) Just takes a different mindset to get the car up out of the track with that limited HP and fixed gear ratio.
 
I am new to the karting world & have been working on my 5 year old's jr flat kart. She is winning races and doing good but I have questions about the logic of where to position the tires (yes i know, one on each corner). I changed tires around which changed the width and it got me wondering if they tires are usually spaced to be even with the edge of the body or if there is a different logic that may require the front to be wider than the back, back wider than the front, have a certain tire stick out or in farther than the others.... Can some of you share your reasoning on how to set up the width?

BTW, when I changed things around I put the very wide right front on the left rear so both rear tires are the same width & I put the left rear tire on the right front. This tire was much narrower and slightly taller.

Glad I found this site, been reading lots of good advice
Your chassis Manufacturer should have a baseline setup for Junior classes.

We're just starting to. I question of your daughter's big gain had little to with that tire change and more to do with her getting comfortable enough to put her foot in it.

My kid ran his 4th race last night and went from 2 Seconds off the pace to .3 back. It had nothing to do with what I did and everything to do with him being comfortable effort to get up on the wheel and GO!

Get a baseline setup, keep notes, adjust one thing at a time, if it doesn't help, put it back.

Good luck!
 
Top