This post is about comparing the difference between using my 14" BBS wheels with 195/60/R14 tires and my 15" OEM wheels with 195/55/R15 tires. I think you might find my conclusion surprising.
First, what are the main differences. The 14" BBS wheels are from a 92-93 Miata LE and weigh 8.5 lbs each. I believe they are forged, very strong, and of high quality. Many people would probably avoid them because they look "fuddy-duddy" or "old-school" but that's not the topic of this post. The 195/60/R14 tire I have is a Dunlop D60 A2, a dinosaur of a tire that is H-rated and built for touring. Most 14" street tires only go up to H speed ratings.
The 15" OEM wheels are the 4-lug, 5-spoke alloys that come with the 2000 Protege ES (and probably subsequent model year LX's, if I'm not mistaken). Compared to 14's, the tires will have a shorter but stiffer sidewall and will most likely have more grip. You can easily find tires with V speed ratings (mine are Kumho Ecsta Supra 712, a decent 3-season tire), and they will be much more performance-oriented than H rated 14" tires.
Let's compare the estimated weights of the tire/wheel combos. Some of these figures are guesses, but they are qualitatively correct:
Wheel Tire Total
14" BBS 8.5 lbs. 16.5 lbs. ~25 lbs.
15" OEM 17 lbs. 17-22 lbs. ~35+ lbs
The main point here is that the 15" combo weighs about 10 lbs more than the 14" combo. We all know that reducing unsprung weight and rotational mass dramatically changes the driving dynamics of the car. With lower rotational mass, the car will accelerate and brake faster. With lower unsprung weight, the car's suspension components are dealing with a lighter load, and will react more quickly and will not have as "tough a job to do." Usually, these are considered desirable characteristics. Another side effect is that the steering feel is considerably different; with the light 14's, the steering feels too light because the steering is calibrated for the heavier 15's. But turn-in is quicker, since the wheels are lighter and take less effort to turn.
So far, you may be thinking, 14's for better acceleration, 15's for better traction and arguably better handling in most cases. But what about ride comfort? Well, we usually want a higher sidewall, softer sidewall, and a tire compound suited for touring for ride comfort. And for the most part we want the exact opposite for performance: lower sidewall, stiffer sidewall, and a grippier tire compound.
But in this case, the 14's did not yield better ride comfort. While the tire size did have all the "ride comfort" attributes, the 14's had something that was working against it: its weight. Let me explain. Assume that the Mazda engineers calibrated the suspension to handle a tire/wheel combo of ~35 lbs. What happens when we change the weight to 25 lbs?
Let's think about one of the main functions of a car's suspension, when traveling down a straight road. The suspension is going to react to changes in the road's surface by having the springs move up and down, while the strut is dissipating some of this energy into heat so that this movement is controlled. So what the suspension is doing is controlling the vertical (up and down) acceleration of the car. The simplified equation to describe acceleration is FORCE = MASS X ACCELERATION. The surface irregularities in the road are providing the force that is moving the car up and down. The mass (and I could be wrong here) is most influenced by your car's unsprung weight. This why engineers and enthusiasts pay so much attention to unsprung weight. So given the above equation, if we lower the unsprung weight (mass), the result is an increase in acceleration.
This is indeed what I found to be the case. With my 14's, the car reacts very quickly and even a little jerkily to bumps on the road. That's not because the 14's are inherently bad; in fact I think they are very very good. The problem I think is a miscalibration, because I had to be an ass and switch so many parts in my car. I put a 25 lb tire/wheel combo on a car that was designed to accomodate a 35 lb tire/wheel combo. Just today I put back on my 15's, and the result was an IMPROVEMENT in ride quality. This is especially noticable with aftermarket springs and struts, which exacerbate the above qualities (the car now reacts more quickly to bumps because of the increased spring rates and different valve rates of the struts).
The moral of the story: Yes, lighter weight is almost always better. But excessively light weight can result in undesirable ride characteristics, as my example illustrates. I think a good idea is to stay pretty close to the OEM wheel/tire combo. Extreme increases (for example, heavy 17's or almost any 18's) result in too slow of a suspension response. Extreme decreases (like my 14's) result in too quick of a suspension response. Most people like to plus size anyway so a good rule of thumb is to increase wheel size while maintaining the same tire/wheel weight. If you are going to "minus size," you're most likely preparing for winter and so you might even consider a HEAVIER rim (like steelies), but not too heavy. And finally, if you're going to autocross or road race, who cares about ride comfort, go with the lightest and strongest wheels you can find, in the size that is appropriate for what you're doing.
Hope you've learned as much as I have from this experience. Comments and flames are certainly welcome, since I am always eager to learn more.
First, what are the main differences. The 14" BBS wheels are from a 92-93 Miata LE and weigh 8.5 lbs each. I believe they are forged, very strong, and of high quality. Many people would probably avoid them because they look "fuddy-duddy" or "old-school" but that's not the topic of this post. The 195/60/R14 tire I have is a Dunlop D60 A2, a dinosaur of a tire that is H-rated and built for touring. Most 14" street tires only go up to H speed ratings.
The 15" OEM wheels are the 4-lug, 5-spoke alloys that come with the 2000 Protege ES (and probably subsequent model year LX's, if I'm not mistaken). Compared to 14's, the tires will have a shorter but stiffer sidewall and will most likely have more grip. You can easily find tires with V speed ratings (mine are Kumho Ecsta Supra 712, a decent 3-season tire), and they will be much more performance-oriented than H rated 14" tires.
Let's compare the estimated weights of the tire/wheel combos. Some of these figures are guesses, but they are qualitatively correct:
Wheel Tire Total
14" BBS 8.5 lbs. 16.5 lbs. ~25 lbs.
15" OEM 17 lbs. 17-22 lbs. ~35+ lbs
The main point here is that the 15" combo weighs about 10 lbs more than the 14" combo. We all know that reducing unsprung weight and rotational mass dramatically changes the driving dynamics of the car. With lower rotational mass, the car will accelerate and brake faster. With lower unsprung weight, the car's suspension components are dealing with a lighter load, and will react more quickly and will not have as "tough a job to do." Usually, these are considered desirable characteristics. Another side effect is that the steering feel is considerably different; with the light 14's, the steering feels too light because the steering is calibrated for the heavier 15's. But turn-in is quicker, since the wheels are lighter and take less effort to turn.
So far, you may be thinking, 14's for better acceleration, 15's for better traction and arguably better handling in most cases. But what about ride comfort? Well, we usually want a higher sidewall, softer sidewall, and a tire compound suited for touring for ride comfort. And for the most part we want the exact opposite for performance: lower sidewall, stiffer sidewall, and a grippier tire compound.
But in this case, the 14's did not yield better ride comfort. While the tire size did have all the "ride comfort" attributes, the 14's had something that was working against it: its weight. Let me explain. Assume that the Mazda engineers calibrated the suspension to handle a tire/wheel combo of ~35 lbs. What happens when we change the weight to 25 lbs?
Let's think about one of the main functions of a car's suspension, when traveling down a straight road. The suspension is going to react to changes in the road's surface by having the springs move up and down, while the strut is dissipating some of this energy into heat so that this movement is controlled. So what the suspension is doing is controlling the vertical (up and down) acceleration of the car. The simplified equation to describe acceleration is FORCE = MASS X ACCELERATION. The surface irregularities in the road are providing the force that is moving the car up and down. The mass (and I could be wrong here) is most influenced by your car's unsprung weight. This why engineers and enthusiasts pay so much attention to unsprung weight. So given the above equation, if we lower the unsprung weight (mass), the result is an increase in acceleration.
This is indeed what I found to be the case. With my 14's, the car reacts very quickly and even a little jerkily to bumps on the road. That's not because the 14's are inherently bad; in fact I think they are very very good. The problem I think is a miscalibration, because I had to be an ass and switch so many parts in my car. I put a 25 lb tire/wheel combo on a car that was designed to accomodate a 35 lb tire/wheel combo. Just today I put back on my 15's, and the result was an IMPROVEMENT in ride quality. This is especially noticable with aftermarket springs and struts, which exacerbate the above qualities (the car now reacts more quickly to bumps because of the increased spring rates and different valve rates of the struts).
The moral of the story: Yes, lighter weight is almost always better. But excessively light weight can result in undesirable ride characteristics, as my example illustrates. I think a good idea is to stay pretty close to the OEM wheel/tire combo. Extreme increases (for example, heavy 17's or almost any 18's) result in too slow of a suspension response. Extreme decreases (like my 14's) result in too quick of a suspension response. Most people like to plus size anyway so a good rule of thumb is to increase wheel size while maintaining the same tire/wheel weight. If you are going to "minus size," you're most likely preparing for winter and so you might even consider a HEAVIER rim (like steelies), but not too heavy. And finally, if you're going to autocross or road race, who cares about ride comfort, go with the lightest and strongest wheels you can find, in the size that is appropriate for what you're doing.
Hope you've learned as much as I have from this experience. Comments and flames are certainly welcome, since I am always eager to learn more.
