What is the best psi for street racing? This is a very common and highly-contested question in the world of racing. The air pressure in the tires is one of the most crucial considerations before a race, more so in cases with limited suspension adjustments available. As such, setting the tire pressure of your car to just the right reading is top on the to-do list of many drivers and enthusiasts. It can spell the difference between coming in last and carrying home the trophy.
This article explores the question of tire psi in depth. Remember, the goal is not only to get the best tire pressure for your car but also to maintain it for the major part of any race, regardless of the track and temperature conditions.
Ambient Temperature on the Race Track
Many racers now incorporate an infrared gun into their driving gear and tool set. This equipment helps you measure the temperature on the track and in the tires, without having to make physical contact with them. Generally, track temperatures are categorized into four:
· Hot – Temperatures above 130°F
· Warm – Temperatures between 106°F and 130°F
· Cool – Temperatures between 90°F and 105°F
· Cold – Temperatures below 90°F
Under all racing conditions, it is safe to always assume that the track temperature differs from that of the surrounding air. The track tends to remain at least 20 to 30 degrees hotter than the ambient air temperature, except on days with high cloud cover. This is because the dark pavement quickly absorbs heat from the sun and heats up itself.
Low PSI Vs. High PSI in Tires
Too much air pressure prevents your tires from wrinkling, leading to initial wheel spin. Initial wheel spin refers to when the tires spin during launch almost immediately after you hit the accelerator. This action can slow launching, causing you to lose your race. Fortunately, the remedy is to lower the tire psi, increasing wheel traction and allowing faster launching.
On the flip side, too low psi means inadequate air pressure, which can cause your car to experience reaction wheel spin. Reaction wheel spin happens when the tires are underinflated and wrinkle to excess, causing overreaction. The result is your car will hook at first then bounce as the tires unload.
Generally, a low but not too low psi is advisable because it allows the tire to adapt to the pavement surface, which improves friction and, in turn, traction.
Recommended Tire Pressures
Air pressure is determined by one too many factors, not the least of which are weight distribution, wheel size, and transmission. With that in mind, the following table should only provide a starting point for your vehicle psi. The numbers also only apply to drag radials and not to slicks.
· 2,500-3,000 pounds, more than 30 inches’ diameter – 8 psi and above
· Over 3,000 pounds, more than 30 inches’ diameter – 12 psi and above
· 2,500-3,000 pounds, less than 30 inches’ diameter – 16 psi and above
· Over 3,000 pounds, less than 30 inches’ diameter – 16 psi and above
Always keep track of your tire pressure during each pass of every race using a good quality tire pressure gauge. Once you have the initial psi (recommended pressure for your vehicle weight and type), using your gauge, adjust the air pressure until you achieve a hint of spin. You have the ideal psi when you can achieve the quickest 60-foot times.
Circuit Racing Tire Pressures
Consider the following factors when adjusting your tire pressure for a race:
· Weight Distribution
Cars that have a 50-50 weight distribution will need the same tire pressure in all four wheels. On the other hand, cars with a biased weight distribution should get 3 to 4 more psi on the heavy end (front or rear of the vehicle).
· Cold Pressure
Always record your cold pressures after a race and after your tires have cooled. If you have to begin another race without warming up, you can use your records to adjust psi.
· Race Direction
After a race, the wheels on the predominant direction side may run hotter than those on the other side. In this case, bleed them to the previous pressure,
· Rainy Conditions
When racing in the rain, you should start with higher cold pressures in the tires but aim for the same hot pressures. This is because the buildups will be slower than on a dry track.
Determining Tire Pressure for a Drag Race Car
Determining the air pressure in your tires is an easy-step process. The first thing you should remember is that you should always do it when the tires are cold or at an ambient temperature. In all instances, avoid checking the pressure immediately after a race or burnout.
It is also important to note that cars will respond to tire pressures differently depending on the type of tires. Racing slicks, for example, are designed to wrinkle and run better on lower tire pressure. Always start your psi at the recommended level for your car weight and tire type, then adjust the levels as you go until you get the ideal psi. To test for inflation, you should:
· Drive onto a clean pavement.
· Adjust the rear tires so that they both have the same pressure.
· Do a burnout (keep it short).
· Check the marks made by the tires on the pavement.
If the tire is overinflated, the mark left on the pavement will be light along the edges but will have a dark mark in the center. If it is under-inflated, the edges will be dark, and the center light to indicate cupping.
A lot goes into preparing your car to launch for a race, and achieving the best psi for street racing should be one of the easiest things for you to do. Running too much air pressure, as discussed, will cause your tires to bulge or crown, wearing the tread center faster and causing lost traction and premature wear and tear. Too low pressure, on the other hand, will cause excessive wear on the outer parts of the tread. Either way, you will only win your race if your tire psi is at optimum.