Fish73

Champion Motorsports
19X8.5-235/35/19
19X11-315/25/19

soltino

All i can say about the first pic is:

http://bigassfans.com

and applys to the tires too.

tino

MjRocket

Some of you gentleman might have wider tires, however im at SITM and Rick Dobson has 20" wheels on his car.

Crazy what can be achieved.

jheis

Why?

worf928

+1

There's a reason to go wide on the front: grip, neutral handling.

No reason except looks to go tall.

j.kenzie@sbcglobal.net

Looks.

You either like the looks or you don't. Sometimes it is a matter of getting used to a new look. When I put 18's on my car I liked the look, but I found myself tilting my head to the side, just to see the overall package differently. 20's might be too much of a change for me to accommodate. They do look cool though.
Dave

19psi

Do you mean a taller tire or wheel? The most dramatic I've seen posted is the 315 that Fish73 is using. It's a whopping 1% off a stock tire's height. At 80 mph, the speedometer will be off by 1 mph.

Or do you mean a taller wheel...if so, are you saying a stock 16" tire will handle just as well as a modern low profile tire?

RedRaider1

Jeff, the car looks great

worf928

First, there's nothing wrong with running a big - tall - wheel for the look. If you know what you're getting along with the look.

Imprecise terms. Wheel diameter and profile or tire sidewall height are better.
That's width.
Yep.
Possibly.

Here are the reasons in reverse order of importance to a 928:

If ultra-low profile tires (short sidewalls) were really better for handling we'd see them used more on race cars.

Short sidewalls, stiffer with less 'spring' to them, are going to hammer the suspension and suspension pickups on the chassis much more-so than tires with more sidewall. Stuff is going to wear more quickly. More vibration and force will be transmitted into the car. Metal fatigue needs to be considered. Tires, suspension, and body are a system. Dramatic changes to one without regard to the other will rarely result in overall improvement.

Related to the above 'system' argument, big wheels, especially larger diameter wheels, will be heavier than smaller wheels if all other characteristics are the same. A heavier wheel is more unsprung weight. That's going to compromise the ability of the suspension to keep the wheel planted (again, all other things remaining the same.)

If you can get a giant-sized wheel that's nearly the same weight as the stock wheel then that last argument is mostly nullified. An almost-light-as-stock 18" or 19" wheel is going to be very expensive though.

Last, a taller wheel takes more force to accelerate; it has a higher moment of inertia because most of the weight is at the rim and on a longer lever arm than a smaller wheel that weighs the same. That higher moment of inertia will rob horsepower transmitted to the pavement at rate of roughly 1% per inch. So, a 19" wheel will rob about 3% of the effective horsepower over the stock 16". A wider 16" wheel will also have higher inertia, but since the lever arm is the same the effect is not as dramatic.

Very last: I know folks are seeing new Porsches with 20" and 21" wheels. One important thing though: for many years the overall diameter of Porsche's wheel/tire combos (for non-SUVs) was in the high 24" range. Then, in the early-to-mid 2000s everyone went gaga for big wheels. Porsche followed suit and started putting big wheels on their cars too. But, they also up'd the overall wheel/tire diameter by almost 2 inches and opened up wheel wells to accommodate them. So, modern Porsches may sport taller wheels but they don't have much less sidewall height than our 20+ year-old Porsches. And we can't match them without going to almost-non-existent sidewalls or doing some series body mods.

For example: a 991-series 911 with 20" wheels runs a 245/35 with an ~86mm sidewall height. The tallest wheel you can run on a 928 and keep that sidewall height is a 245/35-18. We can't go to a much larger wheel/tire diameter because we're wheel well limited. A 245 on a 20" rim for a 928 (25 profile) has a ~61mm sidewall. That's a little more than half the sidewall of the stock 50-profile on a 16" rim. That's a lot less 'spring' between the tread and the rim.

So, yes, new Porsches with 20" wheels have lost more than an inch of sidewall height as compared to a 928 with 16" wheels. But, the suspension design and the technology used to design the suspension (and the rest of the car) have change dramatically too.

To answer your question: Take two identical 928s. Keep one of them on the OE forged slotted 16" rims and stick a set of cheap cast 18" wheels on the other but keep tire section widths and tire make/model the same. The 16" shod 928 will out accelerate the 18"-equipped 928 and will likely out-handle it on most public roads. However, put some nicely-light, forged 17" or 18" wheels with more front section width on the latter 928 and the story changes. The former may still out-accelerate the latter a bit, but the latter will most-likely out-handle the former. But, that's due to changing the width not the height.

A lower-profile tire may feel less 'squirmy' than a higher-profile tire. But, that feel doesn't necessarily translate to better grip or better over-all handling if the 'system' is thrown out of kilter.

Start throwing well-considered suspension modifications into the mix and everything changes though.

Big wheels with low-profile tires look cool. Just don't expect them to improve the car unless you've considered all the components carefully.

Cole

This is backwards. Porsche has often been in the lead with larger diameter wheels.


Just look at the stock 16s that came on the 928. Almost nothing else on earth had wheels larger than 15" at the time.

worf928

Bottom line for TL;DR: big wheels that are not very expensive are usually heavy and kill overall handling; They may result premature wear of various things (including driver's buttocks.)

No disagreement about the distant past. But, it took 20 years to go from 15" to 17" rims. Then in the last ten years we've gone from 17" to 20" and 21". I don't know if Porsche was a year-or-two ahead or a year-or-two behind. I didn't mean to imply that Porsche was behind (or ahead) of the trend. Nor was that an important element of the text. I don't think they were the cause of the trend though. A quick google of some representative cars doesn't provide a smoking gun.

I suspect that their marketing guys figured out that buyers wanted bigger wheels at the same time everyone else's marketing guys figured it out. If you'd like to do the research, feel free. I'll bet you can make it a cultural anthropology master's thesis

I remember the trend as a 'cultural thing.' Possibly originating from the Ricer crowd?

Folks like the look. I don't blame them; I like it too.

19psi

Uh...YOU are the one who used the term "tall".

That would be why I mentioned the whole 1% difference thing.

That's why they are on every performance built car made today from Corvettes to Lamborghinis.
And as Cole mentioned, the 928 was pretty much at the forefront with a 50 series 16" back in the old days. Even a Cayenne uses a lower profile.

Materials have gotten much lighter in the last 3 decades.

Except the added weight of the 16" tire will cancel out the larger wheel weight (if a cheap wheel of same width is used). Factor in that most 16" tires are now designed more for OLDER trucks and SUVs and it gets worse yet.
I have the same 928 with both sets and know that there's no difference in acceleration and I know what handles much better. My original 16s are decoration in my office and if they ever get put back on, it'll be for original show reasons only.

Cole

Or.....you could just chalk it up to technological acceleration like many thing in our world.


Took us decades of tube TVs before the first flat screens. Now you can watch a movie in better than HD resolution on a tablet while on a plane.

Better alloys, rubber compounds and manufacturing scale have made it feasible at many levels to make bigger wheels.

upstate bob

-and curiously the guys with 79 corvettes religiously stay with 15" wheels. Some even need raised white letters

Cole

It's also a bit of a false assumption to say that tall sidewall tires "always" ride softer and are therefore easier on suspension, etc.

f1 is a perfect example of the ability of a tall size wall tire to be stiff enough in a performance setting. Many old school performance tires have really stiff sidewalls in an effort to gain lateral stability.

Tire technology has come a long way. Sidewall stiffness and height isn't the only factor in the ability of the whole tire carcus to have lateral grip or conversely, a nice ride/transmission or absorption of impacts to the rest of the car.


Bottom line is that a low profile tire can ride better than a tall sidewall dependent on the constriction of the tire and the rubber compound. My 19s ride MUCH nicer than the rocks of 16s they replaced.

Wear on suspension components is more than just impacts too. A wallowing, undulating, tall sidewall tire *could* be putting more demands on the suspension points than just the impacts of a larger but more stable wheel/tire combo. Think more shaking, wiggling, steering input going through a joint for every movement of the suspension.

Too many variable to really make much of a judgement either way really.