Very specific Porsche wheel sizing question
 

I've done a lot of searching and haven't found anyone who's used this setup yet.
I have a 2000 Porsche Boxster S with:
Front- 18x7.5 ET 50
Rear- 18x9 ET 52

Current stock Tires:
Front - 225/40R18
Rear - 265/35R18

I just bought a pair of used Panamera wheels that are:
Fronts - 19x9 ET 60
Rears- 19x10 ET 61

Tires on the Panamera wheels:
Fronts 255/45R19
Rear - 285/40R19


Long story short they are way too big, should've known.
Someone with experience sizing wheels for our 968s please tell me what tires sizes I will need not to have rubbing issues. Thanks in advance

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Your wheels dimensions are not lining up. Both the front and rear of the wheel can not be the same sizes. The back will be wider with a different offset then the front wheels. Need to know what the exact numbers are between the front and rear wheels.

You're right, I left out some key information and didn't realize. I just updated it now thanks for the help if you end up knowing what I need

Its looking like I'm going to need some spacers if I want these wheels to work and not hit the suspension but I don't want them to poke out, again if someone with a little more experience could share some knowledge thatd be very helpful

Try this link...you can plug in all you data and get before/after fitment.

https://www.rimsntires.com/specspro.jsp

I used a website with a calculator very similar to that one. My issue is trying to find out how much room on the inside I'm worried about and how much poke coming out I can get as well as what tires I will need for everything to fit

This wheel calculator vizualises how much the new wheel moves / differs from the OEM wheel:

REIFENRECHNER | ET Rechner | Abrollumfangrechner | Felgenrechner

If you want predict exactly, measure everything with the OEM wheel and calculate to the new one. But keep in mind that changes on the suspension will also affect if the wheel will fit or not.

Regards, Markus

the tire sizes you have are pushing the limit of what the car can accept, so fitment will be very sensitive to offset. without the tires, aim for 40 in the rear and 45 in the front; 20 and 15 mm spacers respectively.

you want to use the Fronts - 19x9 ET 60 Rears- 19x10 ET 61?
I'd get 18mm spacer for the front and 20mm spacer for the rear.
get tires that are 25inch diameter something like 225 35 19 and 265 30 19

You think I can get away with putting that skinny of tires on 9" wide wheels and 10" wide respectively

225 would be too narrow for the front. The optimal rotation speed for a set of tires that would fit would be 235/35/19 front 275/30/19 rear. The actual speed will be 0.8% greater than the speedo reading from your original set.

I would call ECS Tuning (google it) and see what they would recommend for spacers. You can buy a kit with spacers and proper length lug bolts from them.


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willtheyfit.com is your friend.

Alright I have come up with a final set up for the rears.
275/30R19 with a 20mm spacer

in the fronts I want to run 235/35R19 but the biggest spacer I can run is a 10mm
a 10mm spacer will put me flush against the fender for the face of the wheels but I will have an inset of 19mm

In other words these new wheels will stick into the suspension parts 19mm more than stock

Is that too much? Can I get away with this setup and not damage anything

Only way to know that is to get behind the wheel and measure back to the struts.

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225 35 19 will fit a 9 wide fine. Very slight stretch but it's within specs.

You'll potentially have 2 issues with a 235. The diameter is about 25.5 which will make a slow car slower. You're going the wrong way in diameter.
Depending on the height of your car and offset, with a 235 can/will rub when you turn. At almost full lock, it can/will rub on the wheel liner.

225 is not recommended for a 9" wheel, 235 is the minimum recommended. Will it fit, yes, is it dangerous, yes and looks amateur to me. A 225/40/18 tire has a 25.08" diameter and a 235/35/19 tire has a 25.47" diameter. The 235 tire will work fine if he gets the wheel spacer correct, plenty of people here running 235 front tires.

Going 235 front 275 rear tires gives almost an identical rotation speed of 492/km front 491/km rear, which will feel much more stable then his old setup of 500/km front 495/km, less twitchy feeling, along with the extra tire patch to the road. There is less sidewall height, which means less tire flex, but at the cost of a rougher ride.

As for the car not being as quick off the line. I wouldn't worry about that unless he is running 1/4 mile drags all day and you would go by the rear tire size, not the front when calculating this and we are looking at 0.8% difference there. The car would actually be faster on the top end. Personally I bought my Boxster for the way it handles, not because it was a drag monster, which it isn't. Enhancing the handling would be way more important than the 1/4 mile time when dealing with the wheel and tire setups. There are more pros vs cons on his new setup if done correct. If he wants to have a faster 1/4 mile time, much better places to put your money to give the engine more power to do that job with this car.

From my understanding, you can get away with a 17mm inset to the suspension on the front. So 12mm spacers would fix the inner issue. That would leave you with 21.1mm poke to the fender. Also remember that the 235/35/19 tire will be 10mm closer to your wheel opening then your 225/40/18 tires. If you can't get that to work, then you can't use those wheels.

Caveat: 17mm inset to the suspension was with 18" wheels.

^^ :rolleyes: sure

A 235/35/19 front with just a 12mm spacer leaves you just 3mm closer to the suspension and pokes out 7mm more than 225/40/18 Those are pretty small numbers.

With the rear setup using just 12mm spacers you are 2 mm closer to the suspension and stick out just 8mm...again no issues.

I personally don't think you need such big spacers.

My .02 cents

Can you elaborate more?

I just purchased 12mm & 20mm hubcentric spacers
I think the tires I will run are 235/35R19 and 275/30R19

Did you get the correct length lug bolts also?

If you can get the rear tire in the 265 I'd say go for that instead. Those 19"x10 will be heavy for that little flat 6, Porsche wheels or not. If you can find any ways to save weight on the rear wheels, do it.

Not that it would make a huge difference compared with the 275, but it will sure help a bit

That makes a big change in the driving characteristics. Takes away the near identical ration speed between the front and rear tires, less sidewall on the 265, which would ride rougher and possibly make the car feel not near as planted in the rear while cornering and hitting bumps. Just doesn't seem worth it to me to give up better handling for a little weight saving in the tire. Like I said before, plenty of ways to add power then to give up the better handling. These cars were not rocket ships in the first place. If you want that, do some mods!

I see, was just trying to save our friend here 1~2kg on the rear end. Dunno about handling... my forged ADV6 (V1 SL Series) are lighter than the stock wheels that came with that car. So light I can do wheelies when passing over speed bumps.

Grip, ah that. the trick is to find the cheapest possible tires you can find(in China!) and warm them up real good before hitting it. The rubber "melts" basically: Velcro-mode-ON! Excellent for the dusty Shanghai industrial Park, early Sunday morning, 0400am, cops & kids sleeping....

Is that what you meant by driving characteristic? :D

If you don't have PSM, why would the rotational speed of the front vs rear matter?

If your front tires are rotating at a different speed then the rear, you will get a unbalanced feeling when turning. I can feel it when I go from my summer tires to my winter tires. On my winter tires the front and rear tires spin at much different speeds and steering input needed is way more then I like. It just doesn't feel as stable and balanced with you constantly having more input into the steering wheel. My front winter and summer tires rotate at the same speed (so I am used to the rotation speed of the front tires) the summer and winter rear tires do not rotate at the same speed. With my summer tires rotating at near identical speeds (1km per rotation difference in rotation speed) the unbalanced feeling is gone and rolling thru corners is a breeze with less input needed to the steering wheel. Completely different feeling of security while cornering. I can even feel this when changing lanes on the highway, just not a good balanced feeling to me.

That's my personal experience and I will always try to get the front and rear tires spinning at the closest speeds possible.

I think the weight difference actually depends on the tire manufacture and performance series.

Looking at General Tires G-MAX AS-03 tire, Tirerack shows the 265 weighs 1 lbs less then the 275, but their 275 weighs only 24 lbs. Click on specs.

https://www.tirerack.com/tires/tires.jsp?tireMake=General&tireModel=G-MAX+AS-03&frontTire=63WR9GMAS03XL&rearTire=73WR9GMAS03XL& vehicleSearch=false&fromCompare1=yes

Looking at Sumitomo HTR Z III tires, Tirerack shows the 265 weighs 1 lbs more then the 275 series. Click on specs.

https://www.tirerack.com/tires/tires.jsp?tireMake=Sumitomo&tireModel=HTR+Z+III&fr ontTire=63YR9HTRZ3&rearTire=73YR9HTRZ3XL&vehicleSe arch=false&fromCompare1=yes

Looking at Goodyear Eagle F1 Asymmetric 2, Tirerack shows the 265 weighs 1 lbs more then the 275 series. Click on specs.

https://www.tirerack.com/tires/tires.jsp?tireMake=Goodyear&tireModel=Eagle+F1+Asy mmetric+2&frontTire=63YR9F1A2XL&rearTire=73YR9F1A2 XL&vehicleSearch=false&fromCompare1=yes

Looking at Yokohama S.DRIVE tires, Tirerack shows both tires weigh the same at 26 lbs each. Click on specs.

https://www.tirerack.com/tires/tires.jsp?tireMake=Yokohama&tireModel=S.drive&fron tTire=63YR9SXL&rearTire=73YR9SXL&vehicleSearch=fal se&fromCompare1=yes

Looking at Continental EXTREMECONTACT DW tires, Tirerack shows the 275 weighs 3 lbs more then the 265 series. Click on specs.

https://www.tirerack.com/tires/tires.jsp?tireMake=Continental&tireModel=ExtremeCo ntact+DW&frontTire=63YR9ECDWXL&rearTire=73YR9ECDWX L&vehicleSearch=false&fromCompare1=yes

Is Tirerack correct on the weights?


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Your brake bias will also change resulting in diminished braking performance. The smaller diameter wheels will tend to lock up before the larger diameter ones.