mmarshall

While it is true that suspension tuning also plays a role, all else equal, tires do, in fact, determine the amount of ride harshness or smoothness one will feel in the cabin, not just the amount or type of road-noise encountered. It gets back to the simple laws of physics. All else equal, less rubber in the sidewalls means less sidewall-flex over bumps and impacts. That means less-aborbtion/cushioning of the road shock and impact-force...so the shock-force has to go somewhere. And where does it go?......usually, of course, into the suspension and shock-absorber damping, where the design, type, and firmness of the shock-damping and suspension/bushings themselves (and the amount of sound insulation in the vehicle structure) will determine how much of it ultimately reaches one's ears (and the seat of one's pants). The seat-padding itself, of course, can also play a role, as, all else equal, the softer the seat cushion, the less road-shock will be transmitted through to your body. The flip side to all of this, of course, is that all of this cushioning means a vehicle that excels in comfort (the type of vehicle I tend to prefer) but is less-amendable to "sport" or "aggressive" driving in tight corners, for a sports-car feel. Most drivers/buyers, of course, are not interested in a sports-car or sport-sedan feel...and the dense traffic in many areas, today, more or less precludes that type of driving anyway. Some vehicles, of course, particularly upscale ones, have variable shock-damping with a NORMAL/COMFORT/SPORT (or even SPORT-PLUS) adjustment, which tries to combine the best of both worlds in shock-tuning and steering-effort....sometimes succeeding, sometimes not. I've seen vehicles where the setting-adjustment makes a big difference...others where it is all but useless. Last, it should be pointed out that, no matter where or how you set the adjustment-position or the way the suspension is tuned, all else equal, a lower tire sidewall will mean less rubber, over bumps and impacts, to flex and cushion the rest of the tire and wheel from damage from the impact. Many expensive tires and alloy wheels, particularly low-profile ones, are damaged and/or replaced each year from these impacts (the neglect of our road and bridge-infrastructure repair is now paying its price). The landfills and junkyards are full of them, and a huge amount of money is spent on tire/wheel repair or replacement, whether from insurance companies, road-hazard warranties, or right out of people's own pockets.

Johnhav430

LOL putting this to bed would be like expecting everybody to understand what octane represents. (You know, the 'I switched to 87 and my mpgs went down!'). Or even calculus, because imho calculus helps to understand mph which in turn is related to mpgs (how do you calculate mph, instantaneously?)

When I was a young lad I had a brand new Porsche with forged aluminum wheels. The tires were 16". Sixteen inches. On the rears were 245/45-16. 45 series, which was incredible at the time.

Today, my DD is a 13.5 y.o. LS. The tires are 245/45-18. The difference between this car, and the Porsche, is 2" worth or rim, and additional unsprung weight. Imagine having 2" less rim, and the material being forged instead of cast aluminum? Did the Porsche inherently ride poorly due to having 45's? No.

My coupe has 35's in the rear, and the ride is just fine. I just think that man wants a number to evaluate goodness, without the background, and that's why debates go around and around. 93 good. 87 bad. 65 good. 45 bad. $132,900 good. $132,899.99 bad. Sony called it the megapixel conundrum. my .02

mmarshall

One thing you have to keep in mind, on rear or mid-engined Porsches, is that no matter what tire size you have, the center of gravity, with the heavy powertrain behind the driver, is rearward enough for the relatively light front end to have quick steering response (and avoid understeer) without having a truck-firm suspension that will jar you and transmit a lot of sharp impacts. Because the load on the front tires, from less weight, is lower, they can do more of the steering itself and not have to, at the same time, overcome the inertia and kinetic energy of the vehicle's weight. The more even center of gravity also allows superbly short braking distances because, on sudden braking, the rear-weight bias is transferred forward to the approximate center of the vehicle, which throws a (roughly) equal weight of the braking force on all four of the brakes, not just the overburdened two front ones. Lastly, when one considers what a new Porsche costs (you yourself hinted at it in your post above) one can understand how or why the engineers were able to include very high-quality suspension parts that, simply by themselves, are well-above what one will find in more bread-and-butter, more run-of-the-mill vehicles.

Toys4RJill

Wow. Didn’t know the Q7 goes to 21” rims

Toys4RJill

Yes. This all makes sense. I do know a Maybach has 40 on the front, 35 on the rear, and they are Good Year F1 tires. So suspension tuning plays a bigger roll

mmarshall

role.

Roll is what the tires do.

geko29

Ours is a 2018, and those were the largest factory wheels for that year. The 2019 has optional 22". 20" is standard on the Prestige models (optional on Premium Plus) for both years. Nothing smaller than 18" will clear the front brakes.

Toys4RJill

Wow. That is just crazy.

geko29

Why? It's still four inches of sidewall--overall diameter 29.9"

Toys4RJill

cuz they just keep getting bigger and bigger. Nothing to do with sidewall, more with auto design. I like the larger wheels we are seeing.

tex2670

It's not really crazy on an SUV.

It's crazy here:

tex2670

Everyone does. That's why car companies won't stop with the larger wheels--customers like the look.

SW17LS

Thats not really accurate. The cushioning effect that a tire has on bumps absolutely has an impact on how a car rides.

When you step on a stone wearing a pair of leather soled house slippers, or a pair of running shoes which one transmits more of the sharpness of the stone to your foot? The more sidewall the thicker the "sole", the more cushioning. Thats just physics.

If you drive the same car on smaller wheels and larger wheels you absolutely will feel a difference in ride. I've owned the same car on 18s with 50 series tires and 19s with 45 series tires and despite the 460L having air suspension and a longer wheelbase, the sharpness of that initial bump or pothole hit is definitely sharper with the 19s. Overall, the 460L rides better because its more planted and isolated with less vibration, but that initial strike the firmness is definitely threre.

As for road noise, you might be surprised that a slightly lower profile tire might actually be quieter

Interesting YouTube Comparison:

Johnhav430

I gotta tell you, nobody should not go to a "FREE" BMW Ultimate Driving Experience event. C'mon, it's free. You don't have to sell your email or phone# or any of that.

They start with the very basics--what happens when you accelerate? What happens when you brake? Why your grandpa was taught hands at 10 and 2, and why since 1992 nobody does that anymore. Where you should begin a turn, where you should exit. And where I am headed....how tires actually work for the vehicle.

And they were not like Porsche--Porsche told me always on the gas, always on the brakes, i.e. full on. Never, ever, in between (coasting). BMW does not have you drive like that at their events (you are allowed to coast), but they will push you further than what you do on the road.

My dad would get on me when I started listing out facts, but did not know the background behind them. It seemed like this thread wanted a YES or NO answer to series, i.e. 45. Is it good, or bad. There is a heck of a lot of more info needed to answer. Today it seems we want one measure of goodness, understanding is optional.

Are staggered tires better? In general, no, from the factory? Yes.

Johnhav430

I only mean this in a nice way. But please, the next time you take a pic of my car and want to post it on the internet? At least ask first!!!