Tires

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Overview[edit]

This page as it stands currently is just a brain dump of Van Swol. It is made up of logical reasoning, hear-say, and gossip. As such, until actual testing of tires on a baja vehicle (a suggested testing procedure is laid out below), take all information written with a grain of salt. (please revise this statement as updates occur)

Intro to Tires for a Baja Car[edit]

There are a number of special considerations to take into account when selecting tires for a Baja car vs for an ATV, UTV, or side-by-side.

The first one is limited power. Only ATVs designed for children are as limited on power as Baja cars. This is important to consider when deciding what size tires to get. Taller tires require more torque to accelerate and since they create taller gearing, REDUCE the torque put to the ground. Thus, any tire taller than 22 inches should be used with caution.

Limited power also means that if the rear tire is too wide, it may not break loose when the driver wants it to. Rear tires with large contact patch should thus be used with caution. Its possible that the shorter, wider tires used in the rear by sport atvs are short enough to overcome their increased surface area, but its worth noting that these tires are not used by any of the top teams.

Another thing to consider is the size of obstacle. Baja cars commonly encounter much bigger obstacles, at least when i comes to S&T tracks, than most trail-riders. So tires should be as tall as possible without compromising too much on acceleration.

One should also consider that the smoothed nature of most courses and the limited speed of the baja car means that tires don't need to be as tough. While 1 or 2 ply likely won't cut it, but 6-ply is overkill. Less plies means less weight and rotational inertia. I shouldn't need to tell you how important that is.

Last thing to consider also deals with ply, in regards to radial vs bias. Radial means the belts of the tire run the way the tire rotates, on bias they cut across. This means that radial tires run smoother and longer, neither of which we care about in baja racing, at the expense of cost, which we do care about. Additionally, due the nature of the construction, bias tires flex more and thus generally have better grip over rocky terrain, but will be effective at high slip angles. What that means is that bias tires will feel more 'mushy' and have a higher slip angle under hard cornering, but will 'let go' more gradually. Leaning the tire will cause it to pull harder in the direction its leaned (lean to the left, it will pull to the left). These attributes can be very beneficial if a car is set up to take advantage of them.

In summary, starting from a good middle ground of a rounded 22x7x10 4ply tire, reducing ply will allow more height or more contact patch (flatter or wider) at the expense of durability and sidewall stiffness (higher slip angles will ensue) and visa-versa. Bias in the front will be advantageous if running high castor and low KPI, otherwise radial will give a more planted feel. Bias should be used in the rear unless the rear has high camber change with travel or a more planted feel is desired.

Selecting Tires for Competitions[edit]

The important thing to here is remember that selecting a tire is like suspension, its all about deciding which compromises you're willing to make and which you aren't. The endurance race may only have a few muddy parts, but if there is going to be a mud bog event, and acceleration is in a poorly drained area. Then its important to have mud performance. But if every event is on hardpack, then perhaps mud bog will just have to suffer. The sections below will talk about what compromises result from the different tread types.

If possible, studied the soil of the area and take that into consideration, more on that below.

Selecting Tires for Soil Type[edit]

Particle size and consistency is the name of the game here. Here are some examples:

  • Silty and Clay Soils /Dusty
    • Kansas, Wisconsin, Alabama
    • Very small and consistent particles
    • Will pack very hard when dry
      • Hardpack tires will be advantageous in the dry
    • Very sticky and goopy when wet
      • Very important to have good mud tires if things are gonna be wet
    • This is very much a case of wait and see, have both tires on hand and watch the weather
  • Sandy Soils
    • Sand has been described as being very similar to a vicious fluid. It doesn't stick, it just moves out of the way when you push on it, wet or dry.
    • Sand tires will make a huge difference here. Running the wrong tires in sand will eat energy worse than a wet cvt.
  • Loam
    • Oregon, Rochester, Alabama
    • Loam is mix of the other two. Its the soil that people plant in. Its the all-rounder of soil
    • It moves easily but with some resistance when dry
    • Sticky but not gooey when wet.
    • Most tires will do fine, but this is where all-terrain and trail tires shine.

Selecting Tires for Mud[edit]

Front[edit]

The idea here is to have a surface that offer resistance when the tire isn't point straight. This usually takes the shape of a line of closely-placed, tall knobs along the center line. They may be direction so they have more traction on one side to aid with turning. Other knobs are widely place to allow for the mud to be flung off as the tire spins.

Rear[edit]

These usually take the shape of a series of V shaped treads. The tip of the hits the ground first. This is so the tire can scoop but the as the tire spins, the mud slides to the outside and off. They will clog if not mounted correctly.

Selecting Tires for Hardpack[edit]

Contact patch is the name of the game here. Knobs are close together so more rubber hits the road. Notice this is the opposite of mud tires who have wide spacing to allow for better self-cleaning.

Selecting Tires for Sand[edit]

Front[edit]

See Front Mud Tires, except that reason for having widely spaced knobs is for floatation, more on that below

Rear[edit]

Since sand is like a fluid the idea here is to scoop and float. Scoop means that idea is to funnel as much sand in one push as possible, more sand means more push. Float means that if the tire has scoops too close together, it will dig down instead of forward. Its interesting to note here that while mud tires will do poorly in their mud configuration, simply switching the direction of mud-tires will make them perform very well in sand.

Another trick is to significantly lower tire pressures as this will cause the tires to deform more and work better as scoops. This technique also works best on mud tires.

Suggested Tire Testing Procedure[edit]

Overview[edit]

This page as it stands currently is just a brain dump of Van Swol. It is made up of logical reasoning, hear-say, and gossip. As such, until actual testing of tires on a baja vehicle (a suggested testing procedure is laid out below), take all information written with a grain of salt. (please revise this statement as updates occur)

Intro to Tires for a Baja Car[edit]

There are a number of special considerations to take into account when selecting tires for a Baja car vs for an ATV, UTV, or side-by-side.

The first one is limited power. Only ATVs designed for children are as limited on power as Baja cars. This is important to consider when deciding what size tires to get. Taller tires require more torque to accelerate and since they create taller gearing, REDUCE the torque put to the ground. Thus, any tire taller than 22 inches should be used with caution.

Limited power also means that if the rear tire is too wide, it may not break loose when the driver wants it to. Rear tires with large contact patch should thus be used with caution. Its possible that the shorter, wider tires used in the rear by sport atvs are short enough to overcome their increased surface area, but its worth noting that these tires are not used by any of the top teams.

Another thing to consider is the size of obstacle. Baja cars commonly encounter much bigger obstacles, at least when i comes to S&T tracks, than most trail-riders. So tires should be as tall as possible without compromising too much on acceleration.

One should also consider that the smoothed nature of most courses and the limited speed of the baja car means that tires don't need to be as tough. While 1 or 2 ply likely won't cut it, but 6-ply is overkill. Less plies means less weight and rotational inertia. I shouldn't need to tell you how important that is.

Last thing to consider also deals with ply, in regards to radial vs bias. Radial means the belts of the tire run the way the tire rotates, on bias they cut across. This means that radial tires run smoother and longer, neither of which we care about in baja racing, at the expense of cost, which we do care about. Additionally, due the nature of the construction, bias tires flex more and thus generally have better grip over rocky terrain, but will be effective at high slip angles. What that means is that bias tires will feel more 'mushy' and have a higher slip angle under hard cornering, but will 'let go' more gradually. Leaning the tire will cause it to pull harder in the direction its leaned (lean to the left, it will pull to the left). These attributes can be very beneficial if a car is set up to take advantage of them.

In summary, starting from a good middle ground of a rounded 22x7x10 4ply tire, reducing ply will allow more height or more contact patch (flatter or wider) at the expense of durability and sidewall stiffness (higher slip angles will ensue) and visa-versa. Bias in the front will be advantageous if running high castor and low KPI, otherwise radial will give a more planted feel. Bias should be used in the rear unless the rear has high camber change with travel or a more planted feel is desired.

Selecting Tires for Competitions[edit]

The important thing to here is remember that selecting a tire is like suspension, its all about deciding which compromises you're willing to make and which you aren't. The endurance race may only have a few muddy parts, but if there is going to be a mud bog event, and acceleration is in a poorly drained area. Then its important to have mud performance. But if every event is on hardpack, then perhaps mud bog will just have to suffer. The sections below will talk about what compromises result from the different tread types.

If possible, studied the soil of the area and take that into consideration, more on that below.

Selecting Tires for Soil Type[edit]

Particle size and consistency is the name of the game here. Here are some examples:

  • Silty and Clay Soils /Dusty
    • Kansas, Wisconsin, Alabama
    • Very small and consistent particles
    • Will pack very hard when dry
      • Hardpack tires will be advantageous in the dry
    • Very sticky and goopy when wet
      • Very important to have good mud tires if things are gonna be wet
    • This is very much a case of wait and see, have both tires on hand and watch the weather
  • Sandy Soils
    • Sand has been described as being very similar to a vicious fluid. It doesn't stick, it just moves out of the way when you push on it, wet or dry.
  • Loam
    • Oregon, Rochester, Alabama
    • Loam is mix of the other two. Its the soil that people plant in. Its the all-rounder of soil
    • It moves easily but with some resistance when dry
    • Sticky but not gooey when wet.
    • Most tires will do fine, but this is where all-terrain and trail tires shine.

Selecting Tires for Mud[edit]

Front[edit]

The idea here is to have a surface that offer resistance when the tire isn't point straight. This usually takes the shape of a line of closely-placed, tall knobs along the center line. They may be direction so they have more traction on one side to aid with turning. Other knobs are widely place to allow for the mud to be flung off as the tire spins.

Rear[edit]

These usually take the shape of a series of V shaped treads. The tip of the hits the ground first. This is so the tire can scoop but the as the tire spins, the mud slides to the outside and off. They will clog if not mounted correctly.

Selecting Tires for Hardpack[edit]

Contact patch is the name of the game here. Knobs are close together so more rubber hits the road. Notice this is the opposite of mud tires who have wide spacing to allow for better self-cleaning.

Selecting Tires for Sand[edit]

Front[edit]

See Front Mud Tires, except that reason for having widely spaced knobs is for floatation, more on that below

Rear[edit]

Since sand is like a fluid the idea here is to scoop and float. Scoop means that idea is to funnel as much sand in one push as possible, more sand means more push. Float means that if the tire has scoops too close together, it will dig down instead of forward. Its interesting to note here that while mud tires will do poorly in their mud configuration, simply switching the direction of mud-tires will make them perform very well in sand.

Another trick is to significantly lower tire pressures as this will cause the tires to deform more and work better as scoops. This technique also works best on mud tires.

Suggested Tire Testing Procedure[edit]

Overview[edit]

This page as it stands currently is just a brain dump of Van Swol. It is made up of logical reasoning, hear-say, and gossip. As such, until actual testing of tires on a baja vehicle (a suggested testing procedure is laid out below), take all information written with a grain of salt. (please revise this statement as updates occur)

Intro to Tires for a Baja Car[edit]

There are a number of special considerations to take into account when selecting tires for a Baja car vs for an ATV, UTV, or side-by-side.

The first one is limited power. Only ATVs designed for children are as limited on power as Baja cars. This is important to consider when deciding what size tires to get. Taller tires require more torque to accelerate and since they create taller gearing, REDUCE the torque put to the ground. Thus, any tire taller than 22 inches should be used with caution.

Limited power also means that if the rear tire is too wide, it may not break loose when the driver wants it to. Rear tires with large contact patch should thus be used with caution. Its possible that the shorter, wider tires used in the rear by sport atvs are short enough to overcome their increased surface area, but its worth noting that these tires are not used by any of the top teams.

Another thing to consider is the size of obstacle. Baja cars commonly encounter much bigger obstacles, at least when i comes to S&T tracks, than most trail-riders. So tires should be as tall as possible without compromising too much on acceleration.

One should also consider that the smoothed nature of most courses and the limited speed of the baja car means that tires don't need to be as tough. While 1 or 2 ply likely won't cut it, but 6-ply is overkill. Less plies means less weight and rotational inertia. I shouldn't need to tell you how important that is.

Last thing to consider also deals with ply, in regards to radial vs bias. Radial means the belts of the tire run the way the tire rotates, on bias they cut across. This means that radial tires run smoother and longer, neither of which we care about in baja racing, at the expense of cost, which we do care about. Additionally, due the nature of the construction, bias tires flex more and thus generally have better grip over rocky terrain, but will be effective at high slip angles. What that means is that bias tires will feel more 'mushy' and have a higher slip angle under hard cornering, but will 'let go' more gradually. Leaning the tire will cause it to pull harder in the direction its leaned (lean to the left, it will pull to the left). These attributes can be very beneficial if a car is set up to take advantage of them.

In summary, starting from a good middle ground of a rounded 22x7x10 4ply tire, reducing ply will allow more height or more contact patch (flatter or wider) at the expense of durability and sidewall stiffness (higher slip angles will ensue) and visa-versa. Bias in the front will be advantageous if running high castor and low KPI, otherwise radial will give a more planted feel. Bias should be used in the rear unless the rear has high camber change with travel or a more planted feel is desired.

Selecting Tires for Competitions[edit]

The important thing to here is remember that selecting a tire is like suspension, its all about deciding which compromises you're willing to make and which you aren't. The endurance race may only have a few muddy parts, but if there is going to be a mud bog event, and acceleration is in a poorly drained area. Then its important to have mud performance. But if every event is on hardpack, then perhaps mud bog will just have to suffer. The sections below will talk about what compromises result from the different tread types.

If possible, studied the soil of the area and take that into consideration, more on that below.

Selecting Tires for Soil Type[edit]

Particle size and consistency is the name of the game here. Here are some examples:

  • Silty and Clay Soils /Dusty
    • Kansas, Wisconsin, Alabama
    • Very small and consistent particles
    • Will pack very hard when dry
      • Hardpack tires will be advantageous in the dry
    • Very sticky and goopy when wet
      • Very important to have good mud tires if things are gonna be wet
    • This is very much a case of wait and see, have both tires on hand and watch the weather
  • Sandy Soils
    • Sand has been described as being very similar to a vicious fluid. It doesn't stick, it just moves out of the way when you push on it, wet or dry.
  • Loam
    • Oregon, Rochester, Alabama
    • Loam is mix of the other two. Its the soil that people plant in. Its the all-rounder of soil
    • It moves easily but with some resistance when dry
    • Sticky but not gooey when wet.
    • Most tires will do fine, but this is where all-terrain and trail tires shine.

Selecting Tires for Mud[edit]

Front[edit]

The idea here is to have a surface that offer resistance when the tire isn't point straight. This usually takes the shape of a line of closely-placed, tall knobs along the center line. They may be direction so they have more traction on one side to aid with turning. Other knobs are widely place to allow for the mud to be flung off as the tire spins.

Rear[edit]

These usually take the shape of a series of V shaped treads. The tip of the hits the ground first. This is so the tire can scoop but the as the tire spins, the mud slides to the outside and off. They will clog if not mounted correctly.

Selecting Tires for Hardpack[edit]

Contact patch is the name of the game here. Knobs are close together so more rubber hits the road. Notice this is the opposite of mud tires who have wide spacing to allow for better self-cleaning.

Selecting Tires for Sand[edit]

Front[edit]

See Front Mud Tires, except that reason for having widely spaced knobs is for floatation, more on that below

Rear[edit]

Since sand is like a fluid the idea here is to scoop and float. Scoop means that idea is to funnel as much sand in one push as possible, more sand means more push. Float means that if the tire has scoops too close together, it will dig down instead of forward. Its interesting to note here that while mud tires will do poorly in their mud configuration, simply switching the direction of mud-tires will make them perform very well in sand.

Another trick is to significantly lower tire pressures as this will cause the tires to deform more and work better as scoops. This technique also works best on mud tires.

Suggested Tire Testing Procedure[edit]

Testing of tires should be done in each of the above conditions. Comparisons will be done by measuring the max g-forces able to be sustained in a turn at low (under 10mph), medium(10-20mph), and high speeds(20+mph), and from a standstill (rear tires only). Tires should then be chosen by selecting a tire that will offer the best point balance.