17's vs. 18's performance

[mjw930]

I just purchased a very clean 8500 mile 2003 Boxster S that has the 17" turbo twist wheels (dealer swap out when bought new) with the factory AVS Sports. I WILL be replacing these tires ASAP with either the N spec Pilots or the PS2's but before I do I'm looking at bumping up to 18". I like the idea of the 225 and 265 contact patch but I understand the trade offs in ride quality (possibly mitigated with more compliant tires like the PS2's) and cost. I'm also thinking that the 17's could become track / autocross wheels and tires (DOT Spec R compounds)

I would like some real world comments on the performance difference between 17" wheels and 18" wheels on an S. I'm looking for comments from people who have tracked the car or have experienced both sizes in demanding road conditions. Comments on ride quality count too

I know that sometimes what might seem intuitive (larger tires = better grip) turns out to be wrong in the real world. The combination of 205's and 255's might be the sweet spot for the Boxster S. I don't know the answer so I'm asking the question.

Thanks in advance,
Mark

[Brucelee]

In my experience, the 18s are a very nice addition for handling and performance. I DO NOT notice a degredation between these and the 17s. Look better too!

[savinor]

I have an extra set of 18" Turbo twist wheels with N rated P-Zero tires mounted and balanced. The set has 8411 miles on them and are in excellent condition. The tires measure 30% worn by tread depth. I replaced them with new wheels. If interested I can send high resolution pictures.
Rich

correct me if im wrong...i ve been told 17 to 18 ....you lose 1second off your 0-60
and for a porsche boxster...this is not good. i too am considering this 17 to 18 change in rim size. my car is lowered 1.3 inches and with an 18 inch rim...look out.

i say get the 18, but find the lightest rim on the market...

[mjw930]

I just found out that the 17's are NOT Porsche rims, they are Mille Migla Cup 3's.

The dealer installed them as a swap according to the service record, they are checking to see if they swapped them for aftermarket (something I wouldn't expect a dealer to do).

Man, I'm pissed!!!!!!!!

[Brucelee]

I don't see how this would be possible!

Originally Posted by KronixSpeed

correct me if im wrong...i ve been told 17 to 18 ....you lose 1second off your 0-60
and for a porsche boxster...this is not good. i too am considering this 17 to 18 change in rim size. my car is lowered 1.3 inches and with an 18 inch rim...look out.

i say get the 18, but find the lightest rim on the market...

[savinor]

When changing from 17 to 18" rim the tire size is also changed (lower profile). The results are almost the same diameter wheel. Therefore no change in the 0-60 time.

[mjw930]

Generall, 0-60 times are effected by 2 things, weight and size. Assuming the same weight and size the straight line performance is unchanged.

I'm looking for information about the car's driving dynamics, especially in demanding conditions, I'm not concerned with 0-60 times.

Ok, here's the situation, The original owner acknoledges the swap of the factory 17's with MM 17" Cup 3's (turbo twist). He had no qualms and the wheels are in mint condition. I have the selling dealer in a position that they will offer me some compensation either in a check or new tires. They are a Mercedes dealership so they handle Michelin's (what I want).

Now, the tough decision, do I take the cash and try to find some reconditioned or take off factory 18's or do I keep the Aftermarket 17's and use the cash to put new tires on them? Also, with the MM's I have 7.5" and 9" widths so I have the option of doing 225/45x17 on the front. Here's my dilema, do I put the "N1" spec Michelin "Rib" Pilot Sports in the 205/50 and 255/40 sizes or go with the new PS2's (I have these on the V70R and love them) in the 225/45 and 255/40 size?

Decisions descisions........

Mark
'03 Boxster S

[savinor]

I had 17" on my 99 base model and have 18" on my 2000 S. The handling is somewhat different because of suspension but the 18" wheels have almost no sidewall flex and the ride is not signifcantly different. A little harder but after 20 minutes you don't notice it. The 18" combination take tires out of the equation until the tire start to slide sideways.

[FASTBMW]

I heard that the rear suspension needs to be beefed up when you upgrade to 18". Something about porsche upgrading the rear body or something. Did I hear incorrect?

[savinor]

I believe the upgrade came in 1998 or 1999. At that time 18" was offered as an option.