Car Physics - Tire Side Bite

I'm trying to understand two concepts that seem to oppose each other. First is the idea that max grip is available when the load of the vehicle is balanced between the right and left side tires. Second is the idea of tire "side bite". I never heard the term "side bite" in all my years of sim racing. When I started racing oval karts, I found that this is a big topic of discussion. I have also heard it used in other forms of car racing. Side bite is essentially the amount of lateral force the tire can provide. This lateral force generally increases as the tire becomes more compliant to the road. Side bite is generally increased by raising the load on a tire, or reducing air pressure in the tire. So, the key seems to be the amount that the sidewall of the tire flexes. When I started racing karts, and thinking about setups, I could see that while cornering standard oval karts often transfer 90% or more of the total weight of the kart onto the right tires. I thought I was going to gain a big advantage by running more left side weight bias, and getting a better balance between the left side and right side tires in a corner, thereby increasing grip. But it doesn't really work that way. What I found out is that the more weight you get on the right side tires, the more "side bite" you get, and the more grip the kart develops. I have experienced this increase in grip myself. What surprised me is that you can have too much grip, and the kart will be slow. What you want is a balance that provides enough side bite to get through the corner, without getting so much bite that you "bind" the kart (which is another term that I had never heard). So, how does the idea of side bite reconcile with the idea of max grip occuring when balancing the loads on the left and right side? My only theory is that, if you can balance the load more evenly, that you could run a softer tire compound on the right side. By doing so you could maintain the amount of grip generated on the right side, and increase grip on the left side. I don't know if this would end up binding the kart up or not. In my only experience of testing this theory, I was running more left side weight than normal for karts, and ran a softer right side tire compound than anyone else in the race. I had a big advantage at the start. Starting on the pole, I ran off and hid during the first half of the race. Toward the end, one guy caught me, but wasn't able to pass. My tires didn't go away since my lap times weren't going up, he just got faster toward the end. I must be really bored! Racing won't start again here in Indiana for at least another month. :) Anyway, I'd appreciate any other ideas on this subject.

Left side weight is good when turning left, but you have to let the LR tire lift in the center of the corner to unload the kart. Then it has to sit back down on exit to get "forward bite". Another key thing in oval kart racing is air pressure. If you start too high then you come in too quick and fade at the end. Where as starting lower allows you to come in later. I run dirt down in Va, and NC and I'm assuming you run asphalt. I know on a rock hard track that is black as asphalt with rubber build up, we run the hardest damn Maxxis tires we can find (60+ on durometer) with only about 1/32 of rubber on the tire. In qualifying we up the air pressure to get the kart up to speed quicker "less tire flex, like a stiff shock" and it makes it come in much sooner since we only run 4 laps in qualifying. We reduce the pressure in the race, so we can last for 20 laps. Been working for me, ran very good this past year. I won a VDKA state race, and had several top 5 finishes in money races this winter. The big learning curve I had this past year was caster/camber. It has gotten very big in dirt oval karts, and helps a ton in maintaining corner speed. There are a lot of people running high amounts of camber in the RF tire now a days. --------------------------------------------- Thanks, Aaron Markham RATE MY CAR AT CARDOMAIN.COM! http://www.cardomain.com/id/amarkham *RIP Ayrton Senna & Dale Earnhardt*

I have seen a number of posts here about kart physics from you and a couple of other guys which make me think that kart tires just plain don't work like full size racing tires. Are there differences in the construction? Are kart tires bias ply or radial? Do they run inner tubes? Something has just got to be a lot different. "Pat Dotson" <[email hidden]> wrote in message news:[email hidden]...

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> I'm trying to understand two concepts that seem to oppose each other. > First is the idea that max grip is available when the load of the > vehicle is balanced between the right and left side tires. Second is > the idea of tire "side bite". > > I never heard the term "side bite" in all my years of sim racing. > When I started racing oval karts, I found that this is a big topic of > discussion. I have also heard it used in other forms of car racing. > Side bite is essentially the amount of lateral force the tire can > provide. This lateral force generally increases as the tire becomes > more compliant to the road. Side bite is generally increased by > raising the load on a tire, or reducing air pressure in the tire. So, > the key seems to be the amount that the sidewall of the tire flexes. > > When I started racing karts, and thinking about setups, I could see > that while cornering standard oval karts often transfer 90% or more of > the total weight of the kart onto the right tires. I thought I was > going to gain a big advantage by running more left side weight bias, > and getting a better balance between the left side and right side > tires in a corner, thereby increasing grip. But it doesn't really > work that way. What I found out is that the more weight you get on > the right side tires, the more "side bite" you get, and the more grip > the kart develops. > > I have experienced this increase in grip myself. What surprised me is > that you can have too much grip, and the kart will be slow. What you > want is a balance that provides enough side bite to get through the > corner, without getting so much bite that you "bind" the kart (which > is another term that I had never heard). > > So, how does the idea of side bite reconcile with the idea of max grip > occuring when balancing the loads on the left and right side? > > My only theory is that, if you can balance the load more evenly, that > you could run a softer tire compound on the right side. By doing so > you could maintain the amount of grip generated on the right side, and > increase grip on the left side. I don't know if this would end up > binding the kart up or not. > > In my only experience of testing this theory, I was running more left > side weight than normal for karts, and ran a softer right side tire > compound than anyone else in the race. I had a big advantage at the > start. Starting on the pole, I ran off and hid during the first half > of the race. Toward the end, one guy caught me, but wasn't able to > pass. My tires didn't go away since my lap times weren't going up, he > just got faster toward the end. > > I must be really bored! Racing won't start again here in Indiana for > at least another month. :) Anyway, I'd appreciate any other ideas on > this subject.

>I'm trying to understand two concepts that seem to oppose each other. I don't think they oppose each other. I think it's different with a kart because they are so light. You can't get enough weight on the tire unless you "unbalance" it to favor the side you want to have traction. >without getting so much bite that you "bind" the kart The binding is partially because of the solid rear axle and the small circumference tires. That's another reason to lighten up the inside tire almost to the point of "bicycling" it. Bill Berry

"Haqsau" <[email hidden]> wrote in message news:b3p08a$1oq5o5$[email hidden]... > I have seen a number of posts here about kart physics from you and a couple > of other guys which make me think that kart tires just plain don't work like > full size racing tires. Are there differences in the construction? Are > kart tires bias ply or radial? Do they run inner tubes? Something has just > got to be a lot different. Karts are different in that they have no diff, when people say a kart is binding they mean they have both rear wheels on the ground and they are 'fighting' each other, they want to run at a different speed and this reduces rear grip. I thought oval karts used stagger to reduce this but we don't use ovals this side of the pond. If you try pushing a kart in a straight line and then round a corner you will find that this binding does make a difference! Without stagger at least, the idea is to lift the inside rear wheel when cornering at the limit as this gives more grip, with the correct amount of stagger or a diff this shouldn't be the case. It is critical to get wheel lift setup correctly as you also need both wheels on the ground for maximum traxction out of corners. If you look closely you will see some drivers lean outwards through some corners to lift the inside rear. I don't really know much about oval racing however. Paul

Thanks for the excellent explanation! :-)

Haqsau wrote: > I have seen a number of posts here about kart physics from you and a couple > of other guys which make me think that kart tires just plain don't work like > full size racing tires. Are there differences in the construction? Are > kart tires bias ply or radial? Do they run inner tubes? Something has just > got to be a lot different. They are bias ply with no innertube. One idea is that you have to get more weight on the right side tires to get heat into them. PD

WillyB4120 wrote: > I don't think they oppose each other. I think it's different with a kart > because they are so light. You can't get enough weight on the tire unless you > "unbalance" it to favor the side you want to have traction. You may be right about how light they are. I've heard people say that before, but in reading car dynamics books, the tire grip v. vertical load curves seem to be linear from zero force up to the limit of the tire. So it doesn't seem like the light weight of a kart should matter. > The binding is partially because of the solid rear axle and the small > circumference tires. That's another reason to lighten up the inside tire almost > to the point of "bicycling" it. Small circumference. Could you go further into why that makes a difference. Unloading the LR tire to the point of lifting is sort of a standard part of current oval kart setup theory, but with the right amount of stagger, I can't see why the inside tire should have to lift. Obviously, with a sprint kart and no stagger, lifting the inside rear makes complete sense. Thanks, PD

Paul Laidlaw wrote: > Karts are different in that they have no diff, when people say a kart is binding > they mean they have both rear wheels on the ground and they are 'fighting' each > other, they want to run at a different speed and this reduces rear grip. > I thought oval karts used stagger to reduce this... Exactly. With the right amount of stagger, the inside rear doesn't really have to lift IMO. I understand what you are talking as far as binding the kart if the stagger doesn't match the turn. But I have also heard people refer to having too much side bite as binding. It's probably more properly referred to as being "tight". The car has enough grip to drive it anywhere you want. It's very easy to drive, but it's slow.

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> Without stagger at least, the idea is to lift the inside rear wheel when > cornering at the limit as this gives more grip, with the correct amount > of stagger or a diff this shouldn't be the case. It is critical to get wheel > lift setup correctly as you also need both wheels on the ground for > maximum traxction out of corners. If you look closely you will see > some drivers lean outwards through some corners to lift the inside > rear. > > I don't really know much about oval racing however.

Yes, ovals are different. Thanks, PD

Aaron Markham wrote: > Left side weight is good when turning left, but you have to let the LR tire > lift in the center of the corner to unload the kart. Then it has to sit back > down on exit to get "forward bite". Another key thing in oval kart racing is > air pressure. If you start too high then you come in too quick and fade at > the end. Where as starting lower allows you to come in later. I run dirt > down in Va, and NC and I'm assuming you run asphalt. Thanks Aaron. I mostly run dirt too. Kart setups work quite a bit differently from cars. It took about a year to figure out the differences. Even once you understand the mechanics of how a kart works, it's still hard to figure out what combination makes it fast. One of the most surprising things about karts is that you really do want to limit the amount of grip that you have to keep the kart "free" (free being the opposite of binding). Oh, BTW, if anyone is interested, there is a picture of my kart here: http://www.mindspring.com/~pdotson/index.html I used to be a regular here on RAS, but keeping the kart ready takes a lot of time. It's hard to get much sim racing done these days. I was box-stock track champion at a local track last summer, and won the Indianapolis Indoor series championship in stock-heavy this year.

> You may be right about how light they are. I've heard people say that > before, but in reading car dynamics books, the tire grip v. vertical > load curves seem to be linear from zero force up to the limit of the > tire. So it doesn't seem like the light weight of a kart should matter. You must be reading different car dynamics books than me! Tyres do not produce double the grip for double the vertical load, hence the overall weight and weight transfer does (or should) matter. I suspect it is simply hard to get the correct amount of stagger. Do the ovals you race at have constant radius corners and are all corners identical?

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> > The binding is partially because of the solid rear axle and the small > > circumference tires. That's another reason to lighten up the inside tire almost > > to the point of "bicycling" it. > > Small circumference. Could you go further into why that makes a > difference. Unloading the LR tire to the point of lifting is sort of a > standard part of current oval kart setup theory, but with the right > amount of stagger, I can't see why the inside tire should have to lift. > Obviously, with a sprint kart and no stagger, lifting the inside rear > makes complete sense.

I imagine small circumference and tight corners simply means you need lots of stagger, ie the wheels need to run at a greater percentage speed difference than if you used larger diameter wheels (like on a car). Now I think about it I was also under the impression that people use offset seats on oval karts to transfer weight to the inside? There is (or was last time I looked) some good setup advice at www.ekartingnews.com in the forums. You'll have to have a look through to find the good posts though. Paul

>Unloading the LR tire to the point of lifting is sort of a >standard part of current oval kart setup theory, but with the right >amount of stagger, I can't see why the inside tire should have to lift. There is another reason for lifting the inside tire. IIRC, we used to raise the RF spindle so when you turned left, the weight transferred to the right front tire like a teeter-totter effect lifting the LR in the process. This dug in the RF and really made the kart turn hard. We tried to run zero stagger because even the smallest amount killed the top speed. This was in a stock medium 5HP. As far as the seat being offset, it has to be for clearance with the engine. The driver sits right next to it. One other thing I learned was that the weight of your head and helmet could help you corner. When going into the turn I'd lean out a little and let my head roll as if I were looking around a corner. It actually did make a difference. Bill Berry

WillyB4120 <[email hidden]> wrote in message news:[email hidden]... > >Unloading the LR tire to the point of lifting is sort of a > >standard part of current oval kart setup theory, but with the right > >amount of stagger, I can't see why the inside tire should have to lift. > > There is another reason for lifting the inside tire. IIRC, we used toraise the > RF spindle so when you turned left, the weight transferred to the rightfront > tire like a teeter-totter effect lifting the LR in the process. This dugin the > RF and really made the kart turn hard. We tried to run zero staggerbecause > even the smallest amount killed the top speed. This was in a stock medium5HP. > > As far as the seat being offset, it has to be for clearance with theengine. > The driver sits right next to it. One other thing I learned was that theweight > of your head and helmet could help you corner. When going into the turnI'd > lean out a little and let my head roll as if I were looking around acorner. It > actually did make a difference. > > Bill Berry Lifting of the inside rear tire on a kart is pretty standard. It is called a jacking effect and happens in both oval and sprint karting. I always thought it was a simple way to get a kart to turn without having to deal with the effects of not having a diff in the kart. Dave

I race road courses up here in Saskatchewan, Canada. I use an american built Coyote chassis and find that the physics of the kart and tires can be drastically different than the same tyres on a European chassis. This is because chassis flex is very important for grip. A stiff sidewall on my chassis gives me more grip on the front and turning in. A softer compound tire gives me less grip probably because the sidewall flexes too much...go figure. As far as unloading the rear, When the kart is turning left, the LF tire bites first and lifts the left front corner of the Kart.With a proper setup, this will transfer weight to the right rear because of the way the chassis flexes thereby unloading the left rear tire to allow the kart to floww through the corner. If the setup in the rear is to narrow this can result in "bicycling" which means the LR lifts too high and in some cases the kart can flip over . Happened to me once ehhe http://members.shaw.ca/wjen/wjen/index.htm Bengal Pat Dotson wrote:

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> > I'm trying to understand two concepts that seem to oppose each other. > First is the idea that max grip is available when the load of the > vehicle is balanced between the right and left side tires. Second is > the idea of tire "side bite". > > I never heard the term "side bite" in all my years of sim racing. > When I started racing oval karts, I found that this is a big topic of > discussion. I have also heard it used in other forms of car racing. > Side bite is essentially the amount of lateral force the tire can > provide. This lateral force generally increases as the tire becomes > more compliant to the road. Side bite is generally increased by > raising the load on a tire, or reducing air pressure in the tire. So, > the key seems to be the amount that the sidewall of the tire flexes. > > When I started racing karts, and thinking about setups, I could see > that while cornering standard oval karts often transfer 90% or more of > the total weight of the kart onto the right tires. I thought I was > going to gain a big advantage by running more left side weight bias, > and getting a better balance between the left side and right side > tires in a corner, thereby increasing grip. But it doesn't really > work that way. What I found out is that the more weight you get on > the right side tires, the more "side bite" you get, and the more grip > the kart develops. > > I have experienced this increase in grip myself. What surprised me is > that you can have too much grip, and the kart will be slow. What you > want is a balance that provides enough side bite to get through the > corner, without getting so much bite that you "bind" the kart (which > is another term that I had never heard). > > So, how does the idea of side bite reconcile with the idea of max grip > occuring when balancing the loads on the left and right side? > > My only theory is that, if you can balance the load more evenly, that > you could run a softer tire compound on the right side. By doing so > you could maintain the amount of grip generated on the right side, and > increase grip on the left side. I don't know if this would end up > binding the kart up or not. > > In my only experience of testing this theory, I was running more left > side weight than normal for karts, and ran a softer right side tire > compound than anyone else in the race. I had a big advantage at the > start. Starting on the pole, I ran off and hid during the first half > of the race. Toward the end, one guy caught me, but wasn't able to > pass. My tires didn't go away since my lap times weren't going up, he > just got faster toward the end. > > I must be really bored! Racing won't start again here in Indiana for > at least another month. :) Anyway, I'd appreciate any other ideas on > this subject.

>When the kart is turning left, the LF tire >bites first and lifts the left front corner of the Kart. Don't you mean the RF bites first?? Bill Berry

Actually it is the left front that starts the left turn on a kart. Ackerman also plays a roll which is an adjustment at the point where the steering columnis conneced to the tie rods. This allows the left wheel to turn in slightly before the right. The castor lifts the left front corner of the kart which causes the chassis to twist slightly depending on how stiff the chassis is. This will transfer weight to the outside rear. There are definately many other variables that have been coverd\ed in this thread that definately contribute, some even more so. WillyB4120 wrote:

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> > >When the kart is turning left, the LF tire > >bites first and lifts the left front corner of the Kart. > > Don't you mean the RF bites first?? > > Bill Berry

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>Actually it is the left front that starts the left turn on a kart. >Ackerman also plays a roll which is an adjustment at the point where the >steering columnis conneced to the tie rods. This allows the left wheel >to turn in slightly before the right. The castor lifts the left front >corner of the kart which causes the chassis to twist slightly depending >on how stiff the chassis is. This will transfer weight to the outside >rear.

O.K. I see what you're saying. The tire that "bites" in my mind is the RF, but yes, the way the LF lifts that corner and starts the weightntransfer is valuable in setup. Bill Berry

"Paul Laidlaw" <[email hidden]> wrote in message > > You must be reading different car dynamics books than me! Tyres do > not produce double the grip for double the vertical load, hence the > overall > weight and weight transfer does (or should) matter. The tire curves I have seen *are* close to linear up to about 400 lbs. The total weight of a kart is less than that. The most load a kart tire will ever see is about 200 lbs (except for high banks). So, if the curve is really linear for the range of loading, then there isn't any advantage in reducing weight transfer, is there? > I suspect it is simply hard to get the correct amount of stagger. > Do the ovals you race at have constant radius corners and are all > corners > identical? Depends on the track. It isn't hard to figure the right amount of stagger to run when both ends of the track are the same. If the track is egg shaped, I would generally set the stagger for the tight corner. > I imagine small circumference and tight corners simply means you need > lots of stagger, ie the wheels need to run at a greater percentage speed > difference than if you used larger diameter wheels (like on a car). Stagger usually ranges from 3/4" to 1.5". That's not really a lot. > Now I think about it I was also under the impression that people use > offset > seats on oval karts to transfer weight to the inside? Yes, but the amount of left side bias is small compared to the amount of weight that transfers on a kart. Typical left side weight on an oval kart is about 56%. At 1G, a typical kart will transfer around 30% of the total weight of the kart to the right. > There is (or was last time I looked) some good setup advice > at www.ekartingnews.com in the forums. You'll have to have > a look through to find the good posts though. Or, better yet for ovals, www.4cycle.com :)

"Pat Dotson" <[email hidden]> wrote in message news:[email hidden]...

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> "Paul Laidlaw" <[email hidden]> wrote in message > > > You must be reading different car dynamics books than me! Tyres do > > not produce double the grip for double the vertical load, hence the > > overall > > weight and weight transfer does (or should) matter. > > The tire curves I have seen *are* close to linear up to about 400 lbs. > The total weight of a kart is less than that. The most load a kart > tire will ever see is about 200 lbs (except for high banks).

True, but you have only seen data for tyres that are designed to take loads much higher than a kart so is that true for kart tyres? I freely admit however that I don't know how far from linear a kart tyre is with a normal load. > So, if the curve is really linear for the range of loading, then there > isn't any advantage in reducing weight transfer, is there? There may not be very much, and hence unloading the inside rear may well be optimal. > Yes, but the amount of left side bias is small compared to the amount > of weight that transfers on a kart. Typical left side weight on an > oval kart is about 56%. At 1G, a typical kart will transfer around > 30% of the total weight of the kart to the right. So even with an offset seat you still aim to lift the inside rear wheel I take it? > > There is (or was last time I looked) some good setup advice > > at www.ekartingnews.com in the forums. You'll have to have > > a look through to find the good posts though. > > Or, better yet for ovals, www.4cycle.com :) Paul