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I embarked on an experiment lately that may be of some use to others. I bought a set of 20" OE RS Spyders and refinished them in a polished aluminum powdercoat. When I installed the OE tires, I didn't care much for the bulge and how the wheels looked, compared to the tighter sidewalls in either the 21" Spyders or the similar versions on 911s or Panameras. My use for this car is in Florida and I don't need the extra sidewall for true SUV use. Given this was a spare set of wheels, I decided to try a set of Michelin PS4S sized two sizes smaller: 245/45/20 in the front and 275/40/20 in the rear. That took away the bulge in the sidewall and gave a slight OE stretch.
Compared to my PS4 SUV, these smaller tires are a total of 24lbs lighter and since the weight is the furthest from the wheel center, I can feel every pound of that weight loss. The Macan now feels more like a car and is more nimble, accelerates faster, and simply is more of a joy to drive, especially in the curves. Other benefits are a slight increase in gear multiplication from being just under 2% smaller in total diameter, better steering feel, better mpg and a slight 7mm drop in ride height.
Cons are: speedo is 1mph slower, fender gap increased by 7mm, less rim protection and the tires do not look as wide from the rear, compared to the 295s.
I added 15mm spacers to get them flush, since the tire is more inboard, and I am pretty happy with the look. Its more of a BMW or Tesla look but does the trick. If it wasn't an OE wheel, it may look a little too much like a "tuner", but given these are a spare set to compliment my 21" Turbos, the much improved performance gives me a good reason to switch every few weeks. Many spend big dollars on lighter wheels but tires are also an option and actually do make a difference, even on a 4,000lb SUV.
Removing unsprung mass will definitely aid in performance but doing it with smaller tires also reduces the contact patch. What is the overall benefit? I will leave that to the mechanical experts.
If it works for you, that's really all that matters.
Removing unsprung mass will definitely aid in performance but doing it with smaller tires also reduces the contact patch. What is the overall benefit? I will leave that to the mechanical experts.
If it works for you, that's really all that matters.
The risk of stretched tires aside from the reduced contact patch is debeading, particularly the rear tires under acceleration in colder than normal conditions.
Removing unsprung mass will definitely aid in performance but doing it with smaller tires also reduces the contact patch. What is the overall benefit? I will leave that to the mechanical experts.
If it works for you, that's really all that matters.
Good point about the contact patch. While I haven't measured, the sidewall bulge on the OE 265/45 and 295/40 plus the generous rim protection tells me that effective contact patch to the ground is not reduced by much, if any by going with a smaller size that is more fitted to the rim. I chose the tire carefully and with a Michelin PS4S that has a far superior compound to nearly any other street tire, I am confident that any loss in contact patch is averted by the superior grip, when comparing to another OE tire. Additonally, a narrower tire will place more surface pressure on the road which may lead to better hyroplane resistance. For my use and considering its an AWD SUV, I don't think that a huge contact patch is needed for dry grip under spirited street-legal conditions.
I am not advocating for narrower tires here but I don't think my pursuit of a better looking rim/tire combination has jeapordized any road safety. It quite frankly may have improved it with the handling and braking benefits of less unsprung weight. There is less a chance of tramlining too but at the cost of a meatier look, which is what I have my 21" set for.
The risk of stretched tires aside from the reduced contact patch is debeading, particularly the rear tires under acceleration in colder than normal conditions.
I addressed the contact patch in my post above but in terms of a stretched tire, this fitment is used in OE applications and the level of "stretch" equal to or less than what I have seen on other Porsche cars, including a Panamera that is parked next to me right now. A 245/45 on a 9" rim and a 275/40 on a 10" rim is an OEM approved size and within the operating range as sanctioned by major retailers and OEMs. Here's another photo of the profile if helpful:
I embarked on an experiment lately that may be of some use to others. I bought a set of 20" OE RS Spyders and refinished them in a polished aluminum powdercoat. When I installed the OE tires, I didn't care much for the bulge and how the wheels looked, compared to the tighter sidewalls in either the 21" Spyders or the similar versions on 911s or Panameras. My use for this car is in Florida and I don't need the extra sidewall for true SUV use. Given this was a spare set of wheels, I decided to try a set of Michelin PS4S sized two sizes smaller: 245/45/20 in the front and 275/40/20 in the rear. That took away the bulge in the sidewall and gave a slight OE stretch.
Compared to my PS4 SUV, these smaller tires are a total of 24lbs lighter and since the weight is the furthest from the wheel center, I can feel every pound of that weight loss. The Macan now feels more like a car and is more nimble, accelerates faster, and simply is more of a joy to drive, especially in the curves. Other benefits are a slight increase in gear multiplication from being just under 2% smaller in total diameter, better steering feel, better mpg and a slight 7mm drop in ride height.
Cons are: speedo is 1mph slower, fender gap increased by 7mm, less rim protection and the tires do not look as wide from the rear, compared to the 295s.
I added 15mm spacers to get them flush, since the tire is more inboard, and I am pretty happy with the look. Its more of a BMW or Tesla look but does the trick. If it wasn't an OE wheel, it may look a little too much like a "tuner", but given these are a spare set to compliment my 21" Turbos, the much improved performance gives me a good reason to switch every few weeks. Many spend big dollars on lighter wheels but tires are also an option and actually do make a difference, even on a 4,000lb SUV.
24 lbs off the tires and wheels is equivalent to 10X or 240 lbs off the chassis. Its the reason I run HRE wheels that save me 10-11 lbs/wheel or about 400 lbs off the chassis compared to the stock alloys. This you can definitely feel in performance.
24 lbs off the tires and wheels is equivalent to 10X or 240 lbs off the chassis. Its the reason I run HRE wheels that save me 10-11 lbs/wheel or about 400 lbs off the chassis compared to the stock alloys. This you can definitely feel in performance.
Yup, that is a super nice gain! I'm sure those wheels were very pricey but anyone can start with the tires for a more economical way to go. I had a set of forged GT replica wheels that were a few pounds lighter than the RS Spyders but I like this design enough (and that they are OEM) to stick with the minimal weight penalty for now.
I am always on the lookout for a good deal on something more lightweight though. Tire weight was always an afterthought until I realized the difference on paper and then in-person.
Another tire option is 255/45/20 and 285/40/20. Those are more for better looks (less sidewall bulge) than weight savings. Those will be slightly wider and taller than my setup but not as light. Their diameter is 29" which is an OE size vs. 28.7" on the ones I went with.
There is a 255/45 PS4S for the front but the rear 285/40 is only in a PS4 for the Taycan which is the same tread pattern but heavier due to a higher load rating and noise absorbtion material.
For how much weight are the PS4s rated in comparison to the PS4 SUVs?
The PS4 SUV are 108 and 110 for the F & R. Those are overkill considering the N0 Latitude 3 are 104 and 106. The PS4 SUV provided amazing traction but have a heavier weight and can ride stiff at higher pressures, especially when paired with the swaybar and spring mods on the car. Considering they are designed for many SUV models, using them on a "lighter" Macan results in a less comfortable ride but a noticeable decrease in sidewall flex. That turned into a flatter cornering experience, even when it was on stock suspension, so big gains there on performance.
The PS4S I am using are considered Extra Load and are 103 and 106. Those are just about OE spec and ride very comfortably while providing a next-level handling experience.
People always underestimate the effects of weight loss until they find out for themselves. Good for you for doing this. Also, your tires aren't "stretched".
Sit at a table and do curls with one arm.
Now do it with a 6# weight. Approximately 1' from your elbow.
You have just experienced the additional torque of 6 lbs ft it takes, to curl the weight.
Now multiply by 4.
There's a physics formula for this, but I can't remember it from 60 years ago.
People always underestimate the effects of weight loss until they find out for themselves. Good for you for doing this. Also, your tires aren't "stretched".
Thank you! I have always adored wider wheels and tires but on AWD suburban SUVs, it doesn't make much sense to lug around that extra weight.
Sit at a table and do curls with one arm.
Now do it with a 6# weight. Approximately 1' from your elbow.
You have just experienced the additional torque of 6 lbs ft it takes, to curl the weight.
Now multiply by 4.
There's a physics formula for this, but I can't remember it from 60 years ago.
Yup I lift almost every day so I am very familiar with leverage and I agree there is a good formula out there to figure the effects of weight loss or gain on the outer edge of the rotating assembly.
Common sense tells me that the rotating mass further away from the center plays a larger role in overall torque needed to achieve a velocity demand.
If I can feel 24lbs on a 4,000lb car, it must be significant. While these tires aren't cheap, It's definitely cheaper than investing in a new set of lightweight wheels. I like my approach better since I can keep OE wheels and reappraise my direction once these tires wear out.
Yup I lift almost every day so I am very familiar with leverage and I agree there is a good formula out there to figure the effects of weight loss or gain on the outer edge of the rotating assembly.
Common sense tells me that the rotating mass further away from the center plays a larger role in overall torque needed to achieve a velocity demand.
If I can fell 24lbs on a 4,000lb car, it must be significant. While these tires aren't cheap, It's definitely cheaper than investing in a new set of lightweight wheels. I like my approach better since I can keep OE wheels and reappraise my direction once these tires wear out.
Another parameter to look at is wheel diameter. As wheel diameter goes up so does wheel weight, while tire weight drops. They tend to balance out but I think smaller diameter rims with higher profile tires still are lighter than larger diameter rims with low profile tires.
02-23-2024, 12:09 PM
Lighter Tires = Better Performance
