Cadillac STS-V Series ForumForum specifically for Cadillac STS-V series discussions. With 469 horsepower, this is the most powerful production Cadillac ever made.
Sorry to be pendantic. Most of my ire for big wheels and tires is reserved for those boneheads who put massive mud tires and wheels on jacked up trucks. From the point of view of the brakes and suspension, they've done the equivalent of loading the bed with concrete while raising the center of gravity at the same time. The impact of you're large wheels would be much much smaller, and you've lowered the center of gravity. It wouldn't surprise me if overall your car would be faster around the track now than when stock.
I completely agree with your whole quote about large diameter tires on a performance car, and technically I agree with the statement quoted above.
However, as both the owner of a stock STS-V (with stock wheels as it shall remain), and as a bonehead with a large jacked up Chevy Silverado pickup truck with large wheels and tires, I can tell you that the modifications done to the truck were done for a completely different reason. Neither high speed cornering nor blistering quarter mile acceleration are among those reasons.
The truck I have is awesome to drive in the mud and snow, and has great ground clearance that I would not get in a stock truck. It does affect the handling slightly, but not as much as you may think. It actually has very good road manners and still retains very good acceleration, almost the same as a stock truck of the same year. A friend of mine owns a stock 2001 Silverado, and I have driven it frequently so I know the differences, and they really are not that much. He wants to lift his, but his wife won't let him.
Trucks like that are never meant to be corner carvers (that's what the V is for), but they are meant to be able to pretty much go anywhere over most anything (including Hondas) and that they are very good at. Modern lift kits and tires do little harm to handling while providing a lot of benefits for offroading and suspension durability.
I should add that as a matter of style I think you've done a very nice job. It looks way cool and you've done a good job of avoiding temptation toward excess on the outer treatment.
Handling is largely subjective unless you're in a timed race (at which point subjective is meaningless and objective is everything). By going to a larger diameter wheel, you have moved a relatively heavy component (the outer rim) further away from the axis, thereby increasing its rotating velocity. The rotation amplifies the amount of mass, causing the brakes, steering, etc., to "see" more "weight" regardless of the total weight of the entire wheel at rest. So maybe the 20" rim is a few onces lighter than the 18/19" rims it replaced, but the weight that remains has been moved in the wrong direction. I'll wager that when rotational effects are factored in, the 20" one is "heavier" in real life on average and is WAY heavier at high speed.
The performance advantages of large diameter wheel and low aspect ratio tires are an interesting study. I'll leave you with this thought: No pro racing team, anywhere, runs a wheel diameter or aspect ratio as extreme as what is currently fashionable with the street racing crowd. Now maybe the street racers have outengineered all of Formula 1, LeMans, Indy, and NASCAR, or maybe, just maybe, there is a point at which a taller wheel and lower sidewall no longer is a great idea.
Sorry to be pendantic. Most of my ire for big wheels and tires is reserved for those boneheads who put massive mud tires and wheels on jacked up trucks. From the point of view of the brakes and suspension, they've done the equivalent of loading the bed with concrete while raising the center of gravity at the same time. The impact of you're large wheels would be much much smaller, and you've lowered the center of gravity. It wouldn't surprise me if overall your car would be faster around the track now than when stock.
i see your point...after i did the suspenion and the wheels on the V it felt so much better then stock.
The truck I have is awesome to drive in the mud and snow, and has great ground clearance that I would not get in a stock truck. It does affect the handling slightly, but not as much as you may think. It actually has very good road manners and still retains very good acceleration, almost the same as a stock truck of the same year. A friend of mine owns a stock 2001 Silverado, and I have driven it frequently so I know the differences, and they really are not that much. He wants to lift his, but his wife won't let him.
Trucks like that are never meant to be corner carvers (that's what the V is for), but they are meant to be able to pretty much go anywhere over most anything (including Hondas) and that they are very good at. Modern lift kits and tires do little harm to handling while providing a lot of benefits for offroading and suspension durability.
I appologize to anyone who actually uses their truck as an offroad vehicle. Obviously, there are very good reasons for outfitting a truck in that manner. Because the overall subject was style versus substance, I should have made it clearer that I was referring to people who go for the "look" and never take the truck offroad, or at least never take it offroad in a situation where the enhancements really are required (e.g., road hunting for pheasants doesn't count).
I should add that I just got back from Phoenix and was shocked at the number of 4wd SUV's and "posuer" trucks that clearly never went into the desert, all in a climate that never sees snow or even much rain. In my not at all humble opinion, these people are boneheads--they've sacrificed safety for style, and a style that had no correlation with what they actually do. There were a few trucks and Jeeps that clearly were used offroad and I had no gripe with them.
We'll have to disagree on the "little harm" contention. The laws of physics are what they are, and while a jacked up truck with big, thick-lugged tires might seem "fine" during normal, 20%-of-the-limit tooling about, there is no way that it hasn't significantly compromised the brakes and handling in 100%-of-the-limit situations. All in a vehicle (truck) that was not built for handling or braking to begin with.
Large diameter wheels with very low profile tires generally loose a little traction on acceleration compared to the stock setup with similar tires.. The thickness of the tire sidewall allows the contact path to lengthen on hard acceleration or braking. You can compensate for this with stickier compound tires. Larger wheel can assist in cornering if the wheels are wider, or the cg of the car is lower with the new wheel/tire combo.
Wheels do 2 things.
Weight. Rotational mass = 8x.
Assist in efficiently transferring friction from the tire to the car.
Ideal wheel, weights the least, and keeps the most tire to the road while minimizing drag.
Large diameter wheels with very low profile tires generally loose a little traction on acceleration compared to the stock setup with similar tires.. The thickness of the tire sidewall allows the contact path to lengthen on hard acceleration or braking.
Which is why we see those tall, soft rear tires on drag racers.
But to be honest, I've yet to get my head around the whole contact patch thing. Moving to a wider tire does not increase the contact patch. The size of the contact patch is dictated by the vertical force applied and the air pressure in the tire. The tire's width only is relevant to determining the shape, not the area. Newton's standard friction equations say the size and shape of the contact patch is irrelevant. Newton was wrong.
But why? Why is long and narrow better than short and wide for acceleration? Obviously, force is being applied through a longer parallel axis, but I just don't see why this makes a difference, since the amount of contact remains the same. I keep banging my head against a wall.
Edit: I might have figured this out. It only took me decades. It isn't the amount of contact patch or friction. It's the leverage applied by the wheel to the contact patch. A long patch has more leverage and thus is better able to resist the torque being applied through the wheel. Newton wasn't wrong. He's just not relevant. This is simple geometry. It also explains why a wider tire has more resistance to lateral force.
Force, Angle, Friction.
Changing one, changes the other. The contact patch is determined by the angle of the force and its size. Forces come from all directions, vertical, horizontal, torsional, etc. All that matters it the additive sum of the force with direction.
So to accelerate faster you turn worse, drag tire. You change your parameters to get what you want.
For looks, nothing matters, it's subjective.
..after i did the suspenion and the wheels on the V it felt so much better then stock.
