987 Base tire / wheel upgrade help

Fitment question: Would like to upgrade tire/wheel set on my '05 987 base. Current car has stock wheels w 205/55/17 front and 235/50/17 rear. Wheel Size Front 17 x 6.5 Wheel Size Rear 17 x 8 Considering replacement stock wheels w 235/40/18 front and 255/35/18 rear - from an '07 987 model S. Wheel Size Front 18 x 9 Wheel Size Rear 18 x 10 Rolling radius is > than 3% difference on the rears - will that cause a problem with any of the cars systems? Anyone have experience with similar upgrade or advice? Buying used so returns would be a problem. Thanks

A great combo would be 255/35/18 f and 275/35/18 r on those 18 x 9in f and 18 x 10 in r. or 245/40/18f and 275/40/18r in Michelin PS4 's. What you need is either a 20 or 30 tireside wall difference front to back to keep all measurements cool. If you are looking to reduce weight, the Titan 7 TS 5 or something similar, light weight, Forged, 9 in f and 10 in r in 18 inch. I currently have 3 sets of 18's. OEM with Michelin 's Titain 7 TS 5's and Signature SV-104 in 9 " f and 10" r. all with the tire pressure sender units. An enthusiast on PistonHeads a while ago called CMOOSE who had a Cayman S with 17 in rims really liked the ride of those wheels and tires . I like the 18, specifically the 35 side wall ones with stiff side walls like the RE71R. They have incredibly fast response reflex in the side wall which I really like for fast turnin rates. The down side is they are stiff and noisy. Tires have a spring rating so you can tell which ones will transmit a bump sharply and which ones will roll over it with more smoothly. CMOOSE favored more smoothly. So he setup his car to favor this type of drive style. the down side is canyon driving, Autocross, performance driving, like Porsche Tours of any kind, which favors the stiff walled tires and the car that can control those tires .

I had the base 17' tire and wheel setup on my '08. I ended up going with 18" BBS SR wheels with Continental ExtremeContacts - 235/40-18 up front, 265/40-18 in the rear. The wheels are 18x8 and 18x10, respectively. I've noticed no difference in speedo calibration or anything else. No other issues to speak of other than my tire choice. The 17s were Michelin Pilots, and I ended up going with the "ultra high performance all season" Continentals. Mostly because I will drive all year round as long as there's no snow or salt on the road (I live in Cleveland, OH). There's a noticeable difference in handling, especially in the bite on the initial turn-in. It doesn't feel quite as connected.

Apex1 - thanks for your reply....if I purchase the used set of tires /wheels mentioned in this post - I will go with your size recommendation. It keeps all the ratios the correct. Joliver3 - your car looks great with those wheels - my '05 is the same Guards Red color. Thanks for the reply.

The stance could be improved with both lowering springs and wheel spacers. The color and silver wheels are great.

Can anyone confirm fitment for the off-set of the following wheels for my '05 base 987 Boxster: Rims are : 9x18 ET52 - front 10x18 ET65 - rear Should these fit w/o use of spacers? Planning to mount the following tires on these new (used) wheels: 235/40/18 - front 265/40/18 - rear Thanks in advance for all responses..

OEM are 57 f and 43 r.. I rear will need a super large spacer to get the wheel tire away from the rear suspension. Why do you care about spacers as these wheels were not made for the Cayman or Boxster ? The question should be how can I make these wheels fit and look good. With the OEM wheels I have with the 43 off set in the rear, I can run a 23 mm spacers to push the wheels out to almost the finder lip. In the front , I can use a 19 mm spacer to push out the 57 offset wheel to the front fender lip.

That's a great look. The wheels I'm purchasing are OEM but they're off a 987.2 S. I have a 987.1 base. Since posting earlier today I've taken a close physical look at the clearance and entered the specs in the handy calculator here: Wheel Offset Calculator Use our wheel offset calculator to visualize the new tire position when changing wheel and tire sizes. Convert wheel offset and backspacing to calculate the correct setup for your vehicle. tiresize.com Snapshot of the changes in the rear: The new wider wheels and different offset will bring the inner sidewall 1.33" closer to the suspension. So I will use 1.25" spacers for the rear. The change in the front is minimal but I plan to use .5" spacers there. Initially I wanted to avoid spacers, but I'm getting comfortable with the idea and certainly don't mind the improved look of moving the wheels outward. Thanks

Great, Please post a picture when you get the wheels/ tires /spacers all together on your car. Then let us know what you intend to do next . Maybe lowering springs and B8 shocks. That will improve your stance. Polish it up and post your picture.

Turns out the person selling the tires and wheels provided an incorrect spec. The wheels are very close to the original Claw pattern stock wheels only wider but the offset made the fitment almost identical to original (WRT clearances). Thanks all for the help, I learned a bit about wheels and fitment. I'm running the tires that came with the wheels for now.. Requested pics : the tires

Looks like its ready for some canyon driving.

That's a great complement - and accurate...Thanks The ride on rough roads is a little harsher but the steering response is noticeably improved (was already good)... Might add .5" spacers all around just for wider stance...

After a while canyon driving, you maybe ready for better springs/shocks/swaybars. The spirngs would be from 2008 RS 60 Spyder model and B8 shocks. The swaybar would be Tarett adjustable. When autocrossing. there was a red Boxster simular to yours. He had a lot of body roll in corners, which stiffer springs and swaybars would correct. Adjustable swaybars would allow you to change the balance f to r reducing the understeer. The lower stance of springs would reduce the tire to fender top gap to go with the wheel spacers to improve the overall stance.

Thanks for the upgrade advise Apex1, these sound like good future upgrades to consider. I'd also like to find the right exhaust system to increase output and get a deeper exhaust note without being loud. I'll keep the community informed as I make changes. Appreciate everyone's help.

boxbox their are a set of Boxster H& R springs for a Spyder for sale for $100. Maybe a deal as springs usually once they settle they are good for life.