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I recently bought my first Porsche a lovely 2013 (pre Tyre Pressure Monitoring System) 981S Cayman. It has 19" aftermarket wheels (Carrera Classic lookalikes) on it. I was very happy with it but unfortunately a bus driver decided not to look when he was moving into my lane and scratched both left side wheels (among other damage). The car is being repaired at the moment and I have a choice of wheels to replace all 4. As it was no fault the bus insurance is paying for everything. I would like to have 4 proper Porsche wheels on my car and I like the look of the Carrera Classics but they come in 20" and I am a bit worried about the effect of these on the ride quality of the car as mine is really comfy and smooth and I really value that, and I don't want to end up with a hard bumpy ride, and also problems with the speedo etc (although I understand this can to some extent be corrected with low profile tyres). I dont much like the look of the other 19" wheels that I have been offered by the garage, and so I am a bit stumped as to whether to go for the 20" carrera classics with low profile tyres or perhaps another 19" original Porsche wheel or just to get replacements for the aftermarket ones I already have. I would be most grateful for any advice on this.
 

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You also need to consider that you have more tire options with the 19"s than the 20"s. However I like my 20"s. Some tire installers will charge more as the diameter goes up. Some won't install on 20s.
 

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I have the 20" Carrera Classics with summer tires and 19" BBS CH-R with winter tires.
The difference in comfort is minimal. The difference in safety (aka if I hit a pothole or something) is something you should also be concerned about.
As long as you stick to the preferred tire sizes, you can change the tire size from the display to the right of the rev and, thus, the speed will be adjusted.
As an option on 19", I really like the 718 Boxster S wheels.
 

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Discussion Starter #5
I have the 20" Carrera Classics with summer tires and 19" BBS CH-R with winter tires.
The difference in comfort is minimal. The difference in safety (aka if I hit a pothole or something) is something you should also be concerned about.
As long as you stick to the preferred tire sizes, you can change the tire size from the display to the right of the rev and, thus, the speed will be adjusted.
As an option on 19", I really like the 718 Boxster S wheels.
Thank you that is helpful but my 2013 981S doesnt have Tire Pressure Monitoring and so I am not sure that the tire size can be adjusted on the display as you say from your more recent model - but I will ask this question of the garage thank you.
 

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OP, I was positively shocked when I drove Cayman GTS on 20" wheels. It shouldn't feel that good with that tiny strip of rubber on it. That said, it is 100% true that you might destroy both tire and the wheel on a bad road very easily (I did it with 19" wheel) and it is also true that your choices of tires to pick from become quite a bit more abundant when you go from 20" to 19" to 18" in progression.

Lastly, why don't you try to see what wheels are available as parts on Britain's Porsche web page? Or you can find wheel codes here (search page for "wheels"), then view the wheels with Google search ...


Porsche 718 (982) equipment codes

Good luck!
 

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Discussion Starter #7
OP, I was positively shocked when I drove Cayman GTS on 20" wheels. It shouldn't feel that good with that tiny strip of rubber on it. That said, it is 100% true that you might destroy both tire and the wheel on a bad road very easily (I did it with 19" wheel) and it is also true that your choices of tires to pick from become quite a bit more abundant when you go from 20" to 19" to 18" in progression.

Lastly, why don't you try to see what wheels are available as parts on Britain's Porsche web page? Or you can find wheel codes here (search page for "wheels"), then view the wheels with Google search ...


Porsche 718 (982) equipment codes

Good luck!
Thank you - I will have a look
 

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Mine came with 19s and I swapped to 20s and honestly I can’t tell the difference.


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Ok some education here.
1)The way a tire rides depends on the sidewall height. ex a 40 will be better riding than a 35 or certainly a 30.
2) Look on Tirerack for the listing of OEM tire spec's for your car. You want something that's the same diameter. That's what effects your speedometer accuracy. See #4
3) Yes the insurance company is paying now but you need to consider tire replacement cost in the future. 19" are cheaper and have more choices than 20"
4) OEM 19" wheels/tires are 235/40-19 26.4" & 265/40-19 27.4" Not the performance choice but a better ride you want. Go with Michelin PS4s highest rated tire for great ride and street quality. The 20" are 235/35-20 & 265/35-20 same heights cost $135 more with worst ride but better performance.
If it was my choice I would go with OZ HLT or BBS LM-R wheels and Michelin PS4s tires in 19"
 

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worst ride
That's debatable. Again, I swapped from 19's to 20's and there literally feels no difference to me.
 

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;) How appropriate hitting that milestone
 

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That's debatable. Again, I swapped from 19's to 20's and there literally feels no difference to me.
If you stayed with the same tire sidewall there really shouldn't. But what offer happens is you go from say a 235/40-19 to a 235/35-20 then less sidewall cushioning can make a difference if both had the same suspension.
 

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If you stayed with the same tire sidewall there really shouldn't. But what offer happens is you go from say a 235/40-19 to a 235/35-20 then less sidewall cushioning can make a difference if both had the same suspension.
If you stayed with the same aspect ratio as the 19”, you would have a taller tire with the 20”. That would cause all kinds of other problems. 19 & 20 aspect ratios are what they are to keep the tire diameter the same but results in less sidewall on the 20”. In any case, there’s not a enough difference to feel worse with the 20” in my experience.

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Here is another data point. I have 20" wheels for summer (currently PZero but switching to PS4+ soon) and 18"wheels with Dunlops) for winter. I notice very little difference in ride. YRMV. I got the 18" for more sidewall on winter roads.

Base 981's were sold with 18" but 19" or 20" were available at extra cost. The S models came with 19" with 20" as an option. The sidewall gets progressively shorter, but the tire outside diameter is constant within a few %. Despite claims to the contrary, it is my understanding that the only real difference is looks. Track junkies tend to use 18" or smaller.

A number of people indicate that a larger variety of 19" tires are more available. That was not my experience, at least in my jurisdiction. If it matters to you, there are a limited number (ususally three or four) of Porsche approved tires (N-spec) for each model and wheel size. The approved tires document can be obtained from Porsche websites.
 

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(1)The sidewall gets progressively shorter, but the tire outside diameter is constant within a few %. Despite claims to the contrary.

(2)A number of people indicate that a larger variety of 19" tires are more available. That was not my experience.
(1) as the image I posted above shows.

A bit of nerdy info if others don’t already know: the middle number (35-40etc) is the sidewall height as percentage of the section width (235). So 235/35, the sidewall height is 35% of the 235 width in mm. 235mm x .35 = 82.25mm (or 3.24”) The 19” has a higher percentage of width therefore the sidewall is taller but the tires are virtually identical in overall diameter. You can theoretically play around with these numbers to try and get a tire that’s wider but no taller, IF there exists such a configuration.

The graphic shows how much taller the 20” would be with the same aspect ratio.

(2) this has been my experience as well. Also with cost. There is a negligible difference in price.


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Good points and explanation of the comparison of the ratio.
But your first graph proves my point. Most people go from a 235/40-19 to a 235/35-20 with very close diameters which recommended because it doesn't mess your speedometer reading up. When they do this they get worst sidewall ratio. In your example -13.5% which is why everything else being equal, they get a worst ride.
If on the other they chose tires with a higher diameter, the ratios remain the same or close and they say, I didn't notice any difference in ride.

You certainly explained it better.

As for racer using 18" which I did. It is because the tires are much cheaper AND more available. You can experience the available problem going from 19 to 20 also. I had to get 19" front and back instead of the 19F & 20R since there weren't any 20" big enough. That is, unless I went to slicks which didn't want to because got rid of my trailer and car carrier years ago and drive to and from the track.
 

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Good points and explanation of the comparison of the ratio.

(1)But your first graph proves my point. Most people go from a 235/40-19 to a 235/35-20 with very close diameters which recommended because it doesn't mess your speedometer reading up. When they do this they get worst sidewall ratio. In your example -13.5% which is why everything else being equal, they get a worst ride.

(2)If on the other they chose tires with a higher diameter, the ratios remain the same or close and they say, I didn't notice any difference in ride.

You certainly explained it better.

(3)As for racer using 18" which I did. It is because the tires are much cheaper AND more available. You can experience the available problem going from 19 to 20 also. I had to get 19" front and back instead of the 19F & 20R since there weren't any 20" big enough. That is, unless I went to slicks which didn't want to because got rid of my trailer and car carrier years ago and drive to and from the track.
(1) I don’t know that I’ve heard of anyone going up a size from 235/40-19 to 235/40-20. This is not a specified size for the 981, so not a particularly good idea. It will also throw off abs/wheel speed sensors due to the rear tires rolling a different rpm. Most people go to that size because it is the correct size for a plus one wheel i.e. 19” to 20”. The lower sidewall is a function of this plus one and considered a trade off to the larger wheel size. And again, the ride being worse is a matter for debate, but to each their own.

(2) see (1)

(3) not sure I’m following you here but I think you are saying:
Tires for tracking a car are more available and affordable in 18”. I didn’t notice a big decrease in tire options from 19”-20” and as I said, some 19” were only a few dollars cheaper than 20” negating the 19” vs 20” being cheaper debate. I’m not sure what you mean about no 20” being big enough either. Unless you mean you wanted to run staggered sizes front to rear and there were no 20” tires for racing.

I think the main reason for using 18” in racing is less centrifugal inertia and weight, reducing unspring weight. Meaning 18” are generally lighter and the car will handle easier and quicker on track at speed. Less centrifugal force being 2” less diameter. The GT4 Club Sport uses 18” if I’m not mistaken.

I remember years ago when I had my 986 in for service. I had 18” turbo look II wheels and was given a Boxster with the standard 17” wheels as a loaner. It was very noticeable how much quicker it felt steering and tossing it around.


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Big enough - As for not being able to find tires big enough I am talking from my current car's needs (2019 Corvette Grand Sport) those tires are +5 front and +7 rear sizes larger than Porsche's tires.

I didn't point out the lighter weight of 18" tires but clearly that is a benefit.

Lower Price - I went +2 sizes bigger 255-18 & 285-18 and purchased RE-71R's with wheels, TPMS, Porsche center caps, valve stems, mounting, road force balancing, nitrogen filled, and free shipping all for $3000. Try doing all that with 20".

For you to have an ABS problem you really need a very large different in stagger. I experienced it when I had a 2.5" different. I was using these much taller rear tires because I was purchasing lots of 10 used Hoosier's tires (used for 3 lap qualifying only) from a race series car for $1000 including shipping.
 
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