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Racing tires, tubes and
slicks: the real story Mickey Thompson Tires answers questions about the rubber that meets the track Story and photos by Dale Wilson
Your tires, both front and back, play a crucial role in whether or not your drag car is a successful round-maker and/or money maker. With the advent of wrinkle-wall slicks some 20 years ago, plus new radial compounds, new racing wheel technology, real-rubber racing tubes and the like, racing tires and what you can do to them and with them to make them hook, have lately become more of a science than a black art - pun intended. Coming up with a new set of slicks, tube and front tires for our latest bracket endeavor, our "Yeow-eee!" front-engine dragster, caused us to stop and wonder --- what is our best combination? If we go with this-and-this slick size and that-and-that wheel size, are we going to have enough clearance between the "pooch" of our slicks and the dragster’s side panels? Should we run tubes or not in our front tires? How much air should we pump into the new slicks? How much of a burnout? And on and on … We called on the experts at Mickey Thompson Performance Tires and Wheels in Stow, Ohio for answers to our questions. We got plenty. So herein are our Top 10 questions on the rubber that meets the road - in our case, the drag strip - directly from the source, M/T’s man-in-the-racing-field, Frank Papp. a
d v e r t i s e m e n t
What is the largest drag tire I can put under my car? Answer: There is no guideline. However, some racing classes, of course, have rules limiting tire size. Use a tire size that can best utilize the space available without interfering with the car’s sheet metal, suspension, etc. What is the approved rim range for M/T slicks? Answer: The tread width plus or minus one inch. But the sidewall measurement will change with rim width. The rule of thumb is four-tenths of an inch for each one-inch change in rim width.
What is the advantage to running a stiff sidewall slick? And, if there is no stiff sidewall slick in my size, what can I do to stiffen the sidewall of my slick? Answer: The advantage of a stiff sidewall is that there is less tire wrap or sidewall distortion, thus the tire reacts better at launch. This is especially good for heavy cars, or cars with a suspension that can absorb the initial launch. If you are running a fixed-suspension car like a dragster or an altered, you need the tire to absorb the launch, thus you need a softer sidewall. There are two ways to stiffen the sidewall. One way is to run tubes, to help support the sidewall, and another is by matching the tread width with the wheel width, or going one inch wider on the wheel width.
No. 4 - Do I have to run tubes in my slicks? You should run tubes in any tube-type tire. Note: Some M/T race tires are tubeless. Tube-type tires will leak air through the sidewalls. As pressure drops, heat increases, and the chance of tire damage or failure is increased. Tubes will also aid in absorbing some of this heat. Also note: Mickey Thompson Tires has a race tire spec sheet available that will tell you what size tube should be used in your drag tire. Contact the company. No. 5 - What size hole do I need in my wheel to accommodate M/T racing tubes? Most racing wheels come with the proper hole size already drilled. If you wheel won't accept the valve stem, you must drill the wheel to five-eighths of an inch. Be sure to deburr the hole and clean the wheel before mounting the tire and tube. We have actually used a quarter to block off the existing hole, but again, consult an M/T advisor on this.
No. 6 - Should I use rim screws with Mickey Thompson slicks? Starting line launches can cause the rim to spin inside the tire, which
can be hazardous. If you are not sure your rim is doing this, mark the
tire and wheel with a line to gauge tire slippage on the wheel. Also,
check for tire slippage when you check your tire pressure after each pass.
If it moves one-half to one inch, you should use rim screws. But do not
use rim screws on radial tires unless they move on the rim.
No. 7 - Should I check the circumference before I run my tires? How much of a circumference variance is acceptable on my tires? The short answer to the first is yes. A variance of three-quarters of an inch maximum is acceptable. Note: Each pair of M/T slicks we have received has been marked at the factory with the circumference noted on the face of the slicks. A difference in circumference can cause the car to pull one direction or the other, which can affect elapsed time. If the difference is more than three-quarters of an inch, increase the inflation in the shorter tire until the rollout is one-half to one inch larger than the desired rollout. But DO NOT exceed 40 psi in doing so. Also note: This can be done only when the tire is new.
No. 8 - What kind of burnout is recommended with Mickey Thompson slicks? For cars with automatic transmissions, on the first pass or two, do a fairly hard burnout. After that, a light burnout should be sufficient. For standard --- meaning hand-shifted --- transmissions, like with Stock Eliminator cars, no burnout or a short, dry burnout is sufficient. Generally, tires work better with a lighter burnout than a heavier one.
No. 9 - Are Mickey Thompson slicks directional? Answer: Yes, including radials. Rotation arrows are imprinted on the sides.
Do I need tubes in my Mickey Thompson front drag tires? No, you don’t need tubes for M/T front racing tires. |
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© Competitionplus 2005
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