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pros and cons of 20" vs 19" vs 18"

How does the wheel height change the stiffest of the tire sidewall ? It doesn't. The ratio of the tire does. a 35 or 40 sidewall on a 18, 19, 20 or 21 is the same stiffest.
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You are exactly right. However to maintain identical tire diameter, increasing the wheel diameter means changing the tires ratio to a lower profile, thus increasing the stiffness as you said.

Awesome looking Spyder by the way!


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Re: pros and cons of 20" vs 19" vs 18"

Except for the top it's like looking in a mirror
 

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Re: pros and cons of 20" vs 19" vs 18"

I've got another question. My 2014 Cayman S came with 20" wheels and OEM Pirelli tires. When pulling out of the dealer's parking lot the front end had a "bumping" sound at low speed with a hard angle turn. Similar to pulling out of your driveway to get into the road. I was told by the dealer that the bump or clunk was normal and nothing to be concerned about. Once the car is up to speed the front end noise disappears. However, I took my car into a tire dealership to order some new tires and the serviceman told me that this front end noise was odd and that I should get it checked out. Anyone else know what I'm talking about?
 

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Re: pros and cons of 20" vs 19" vs 18"

I've got another question. My 2014 Cayman S came with 20" wheels and OEM Pirelli tires. When pulling out of the dealer's parking lot the front end had a "bumping" sound at low speed with a hard angle turn. Similar to pulling out of your driveway to get into the road. I was told by the dealer that the bump or clunk was normal and nothing to be concerned about. Once the car is up to speed the front end noise disappears. However, I took my car into a tire dealership to order some new tires and the serviceman told me that this front end noise was odd and that I should get it checked out. Anyone else know what I'm talking about?
Look up Ackermann effect. It's been discussed many, many times on P9.
 

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19" and 20" wheels are all about the look with zero performance advantage. 18" are the choice for all GT3 Cup and GT4 Clubsport race cars and tire availability is a lot better with 18s. That said, if you like your 20" you can keep your 20".

https://www.yokohamatire.com/motorsports/racing-series/porsche-gt3-cup-challenge

https://www.porsche.com/internation...ngcars/cayman-gt4-clubsport/featuresandspecs/
Hi,

If I go with 18" for track and would like to go with something like RE71R, what tire sizes would you recommend? It only has 245/40/18, 245/45/18, 255/35/18, 255/40/18 and rear 265/35/18, 265/45/18, 275/35/18 and 285/30/18...
 

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Steve,
Thanks for the reference to the Ackermann effect. I hadn't heard of it before. Wikipedia explains it well and then adds:
Some racing cars use reverse Ackermann geometry to compensate for the large difference in slip angle between the inner and outer front tyres while cornering at high speed. The use of such geometry helps reduce tyre temperatures during high-speed cornering but compromises performance in low-speed maneuvers.
I don't know if modern Porsches have reverse Ackermann but it would further explain the pronounced tire skipping mentioned.
Bern
 

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Hi,

If I go with 18" for track and would like to go with something like RE71R, what tire sizes would you recommend? It only has 245/40/18, 245/45/18, 255/35/18, 255/40/18 and rear 265/35/18, 265/45/18, 275/35/18 and 285/30/18...
I'm interested in hearing more about this too. I'd like to run 18's for auto-x on my 2014 Cayman S. It sits on 19s now with the standard 235/265 40 rubber. I was thinking of mounting RE71s in 235/265 45 on the 18s to keep the overall diameters between the two sets w/in .1 inch.
I know that the 2014 owners manual only allows for 18" winter tires on the Cayman S. It also recommends the 235/265 in a 45 profile for those winter tires. It only recommends 19 and 20 inch tires for summer performance set ups.
Love to hear thoughts on performance and handling issues going from 40 to 45 profile on a high performance tire. My thoughts: negligible.
 

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I'm not sure what Bridgestone has available but I run Nitto NT-01 in 235/40-18 and 275/40-18 for DE. They fit and wear without any complications. These have a smaller diameter than stock and lower the car a bit but I"m happy for that at the track.
Bern
 

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I'm not sure what Bridgestone has available but I run Nitto NT-01 in 235/40-18 and 275/40-18 for DE. They fit and wear without any complications. These have a smaller diameter than stock and lower the car a bit but I"m happy for that at the track.
Bern
Thanks for your input. Can you tell me the specs on your wheels (width and ET)? Thanks!
 

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Just a picture to illistrate a couple of 18's; Titan 7 TS-5 17.1 lbs f and 18.5 lbs r , 9 in f offset 46 and 10 in r offset 35 with Hoosiers A7's; Signature SV-104's 18.0 lbs f and 19.5 lbs r, 9 in f offset 47 and 10 in r offset 35 with RE71R's , Tires for both Hoosiers A7's and Bridgestone RE71R's are 255/35/18's f and 275/35/18 r. Both wheel sets are Forged monoblock. No rubbing on either tire sets.
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The criteria for making a choice here are all so subjective.

A 20" wheel and tire have more "unsprung weight," standing alone a negative in a serious track car or race car.

On the other hand, a 20" tire has a stiffer sidewall, a positive attribute in a serious track or race car (simply put, less sidewall deflection and thus higher g-force potential).

A 19" tire may "communicate" slightly better in track-speed cornering as the wheel begins to slide under load. This is more or less important depending on your skill level. The price of that communication is diminished mechanical grip.

These are almost irrelevant factors in a moderately driven road car. In that context, you are mainly weighing looks against wheel damage issues.

I have a racing background and retain a strong high performance bias even for street driving. I am relatively careful around potholes and bumps. I like the look of my 20's and the feel on the street and track. I have had no issues with wheel damage. I would personally not change to a smaller size, especially 18s, where availability of tires is an issue. Also, 18s change the gear ratios ( not so with 19s, which have the same overall diameter as 20s). Again, this is so subjective and debatable.
Apparently all the racing Caymans run on 18’s.
 

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Another subjective data point here ... my 2015 Boxster with standard suspension came with 20" wheels and Nitto NT555G2 tires. I pretty quickly swapped the tires for PS4 All Season, and that plus using the "comfort" tire pressure (i.e. reducing it a couple pounds) helped, but the ride was still pretty thumpy. Recently I installed 18" wheels, also with PS4 All Season tires, and the difference in ride is quite noticeable to my butt. I figured that Porsche's engineers spec'd the Boxster with standard suspension and 18" wheels/45 aspect tires for a reason. I was starting to look at replacement cars with PASM, but it was a lot cheaper to just switch the wheels. My use case is street driving on the winter-weary roads of SE Wisconsin. YMMV!
 

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I recently went down to 18" wheels for the track using 295/35/18 and 265/35/18. Aside from the amazing grip on the semi-slick M compound tires what I also noticed was the change in the gearing which is kind of now like a GT3, very short! This is due to the wheels being much smaller and the relatively lower max RPM of the engine and the earlier shift points. To maintain the 20" wheel size I would need 45 profile tires, but the 35 is fine for the track.

I'm not sure if the car is accellerating much faster, as the smaller wheel does give you a bit of free torque, but definitely have to recalibrate all my gear changes on the track. I wont be going back to 19s or 20s simply because there aren't proper motor sport tires in those sizes. With that said there are still some very fast 19" and 20" R compound tires like RE71-RS and even Cup 2s, but the proper motor sport tires are just a little faster and much surprisingly much better in the wet.
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I posted this video a while back of my GTS with new 18" track tires realling in these GT4s. Now these guys are normally faster than me but with the new tires I was faster in the wet and able to keep up with them in the dry.

 

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Your video of a partly wet track is exactly where the RE71RS would work very well. The problem in the US is the 18 in size availability right now.
 

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Your video of a partly wet track is exactly where the RE71RS would work very well. The problem in the US is the 18 in size availability right now.
The second GT4 (981) actually has 19" RE71RS tires. In the dry he is usually faster than the 718 GT4 on Cup 2s and myself. There is also another 981 GT4 driver who is even faster than these two guys on RE71RS. So definitely a bit of driver involvement but also RE71RS is faster tire than Cup 2. I would definitely use them if I had a GT4 given 19" is smallest possible wheel. Or maybe try A052 or Trofeo R.

However, motor sport 18" medium compound semi-slick tire is faster again (e.g., A050 in my case or Z221), particularly in the wet/damp, although I think maybe the second GT4 guy's RE71RS tires may have been going off a litlte as I also passed him in the dry, but I will ask him next time.
 

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The only thing that I can see missing is sidewall height for pothole resistance, which may or may not be a consideration depending upon the condition of the roads that you drive on. Someone can correct me if I am wrong but I have never seen definitive evidence of noticeable performance gains related to sidewall height.

The main reason people get "dubs" is aesthetics - many think that more wheel and less tire looks better. My car came with 20's. Right now it has 18's with my winter tires. I like the look of both.

The other factor is Porsche - the wheel diameter generally goes up with the price. Base Box/Cay get 18, S get 19 and GTS get 20.
I run 20” in the summer months and 19”(factory installed) in the winter. I have not noticed any difference in handling, only difference in the look
 
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