A larger tire also increases the total footprint of the contact patch between the tire and the road. Ultimately, it is this contact patch area plus the load applied to the tire against the ground that affects stopping distance.
A common misconception about octane is that a higher octane level also delivers more horsepower. This is just flat not true. Octane, by definition, is merely a rating of the fuel's resistance to detonation. The higher the octane rating, the more resistant the fuel is to detonation. Assuming your engine is tuned to its optimal total ignition timing number and the engine does not detonate, there is no performance increase to be gained by using a higher-octane-rated fuel. So, if your engine runs fine on 91-octane pump gas, there is no performance to be gained by using 93-octane gas. But if the engine likes additional timing (for a turbocharged or high-compression engine application, for example), then using a fuel with a higher octane rating will be a benefit. This allows the tuner to dial in more ignition lead without suffering the damaging effects of detonation.
Finally, we found several posts on the Internet asking questions about mixing your own octane-booster cocktail by using stuff like toluene and other industrial chemicals. We've even seen questions about mixing kerosene with gasoline. Unless you are well versed in the highly specialized petro-chemical world of blending gasoline, you'd best leave those mad-scientist experiments to the professionals. As for kerosene, with an absolutely hideous octane rating of something like 20, use it to wash parts-but that's all.
Tire Size And Braking
Steve Huffman, Guntersville, AL: In What's Your Problem? in the Oct. '06 issue you say that increasing tire diameter increases stopping distances. I think you need to take a look at that statement again. You are not taking into account the fact that the larger circumference slows down the wheel. The lever effect is inconsequential here. A 245/45R17 tire rotates 811 revolutions per mile. A 275/45R22 tire rotates 657 revolutions per mile, a much slower speed. It's the same as if the vehicle were doing 45 mph with the larger tire versus doing 65 mph with the smaller tire. It's physically impossible for braking to be decreased. I have found that going from a 215 to a 235 on the same size wheel increased my stopping ability on my pickup. Of course, none of this banter takes into account that the increased wheel and tire weight also affect stopping and launching negatively.
Jeff Smith: As with many things in life, Steve, there is a sliver of truth to your theory. Let's look into this a little closer. The facts are that the leverage effect and weight are the main reasons larger-diameter tires and wheels affect braking-system efficiency. Think of this as a situation where the tire and wheel are leveraging a given amount of torque against the brake caliper. A taller tire and/or wheel combination increases the length of that lever. So a given amount of brake pressure applied to the rotor must work against a greater force applied through the length of the radius, which is the distance from the axle centerline to the road surface. If we increase this distance with a taller tire, it gives the vehicle force (the combination of vehicle speed and its weight) more leverage to use against the brakes.
'Cc Quickies
These are just more broken parts we know you love to see-as long as they belong to someone else! |  |