I have 20" Carrerra S for my summer set and 18" Boxster wheels with my winter tires. I don't push the winter set as hard as the summers, so I can't really comment on handling, but I honestly don't feel much of a difference in ride quality. The 18's have the extra inch of sidewall, which reduces the chance of a bent rim if I hit a pothole. Plus they are cheaper.

Chris Harris once bought a Cayman for himself, and I think he put 17's on. He likes to hang the back end out.

 

I have a 911 with 20 inch wheels and use a set of 19 inch wheels for my winter tires. I actually prefer the ride with the smaller wheels, more compliant on bad roads. I would gladly give up the handling gain for the better ride. However, I'm not sure I would drop to 18. Maybe you can take a test ride with a Cayman with 19's and see the difference?

 

I'm another Michigan guy, with a GTS Cayman that came with 20 inch wheels. You didn't say whteher you have PASM or the standard or x73 suspensions. I think that is the major ride quality variable for roads like ours.

Having said that, I can say that my 19 inch track wheels with Michelin Cup 2 tires feel better than the 20 inch wheels with P-Zero tires. Not necessarily better ride per se, but more compliant and more accurate at the same time. Sounds contradictory but that's my feeling.

For all around driving and not on tires as extreme as Cup 2s, my strong guess is 19 inch wheels with 40 section tires will feel a bit better on our roads especially if you don't have PASM.

 

I'll second this. I didn't notice a difference in ride quality going from my stock 20s to my winter 18s, or going back to the 20s recently. I was surprised!

 

For me the only downside is less bling. 20" wheels have very limited tire choices and they are very expensive. 18s have a better ride and nearly every decent tire is available at lower cost. Cayman Spec racing series runs only 18" tires encouraging a good supply of quality high performance tires.

 

Thanks for the responses, guys!

I'm kind of still leaning towards downsizing (for the record, I do *not* have PASM).

 

I had 20" wheels on a 981S. Porsche gave two recommended tire pressure settings for those wheels. One pressure setting was a "comfort setting" for everyday driving and the other, higher pressure setting was for high speed driving. The lower pressure was more comfortable.

 

I have the base 18" wheels and no regrets. The ride on surface streets which have varying degrees of quality (from decent to might-as-well-be-off-roading) is quite good. No PASM either. And handling is nothing short of perfect, so I doubt you'd be giving up anything measurable in that area.

 

First, make sure your tire pressures are slightly lower. 30 cold is 'comfort pressure.' Dealers like to put them to 40 cold and this will cause rougher than normal ride.

Yes 20 inch wheels with higher tire pressures ride rougher. Its actually why people get them. No one likes rubber band feel of handling (once they understand what it is). Riding on metal allows better handling at lower (street) speeds. I think the improve handling is worth the cost of ride comfort.

In my testing, 19 inch wheels and stock tire size give the best performance for this car, but the difference between 20 and 18 inch is less than you'd think. If you are considering changing wheel size because you aren't 'getting lexus comfort'...to put it bluntly...you probably bought the wrong car.

I have 20 inch wheels and like them...as you have the car longer you get the urge for more, so normally you don't want to go from 20 to 18 inch wheels. If you downgrade, you may notice degraded performance.

 

I've posted many times my personal preference for 18 over 20. My new 18's with RE-71R were delivered the other day. I should get them on the car this weekend time permitting. I'll try to remember to do some pics of change over and post them.

 

I have a CS, stock suspension, oem 20" wheels with oem p-zeros and oz 18" wheels with re-11's for track. Definite ride improvement with the 18s vs the 20s. The 20s look way better though.