Find a tire shop that will allow you to try fitting certain sizes and types of tires on your car, or find a friend who has a tire/wheel combination you like and borrow them.
Good tires can increase your handling and braking significantly
Upgrade to larger wheels
This article is one in a series that have been released in conjunction with Wayne's
101 Performance Projects for Your Porsche Boxster. The book
contains 312 pages of full color projects detailing everything
from performance mods to changing your brake pads. With more than 950+ full-color
glossy photos accompanying extensive step-by-step procedures, this book
is required reading in any Boxster owner's collection. The book is currently available and in stock now. See The Official Book Website
for more details.
Check out some other sample projects
from the book:
For this project, I polled a number of people on a few Internet chat boards, in an attempt to figure out what the best and most popular combinations of tire and wheel sizes were for the Boxster. I confirmed what is inherently true about almost all hardcore Boxster owners: they love to modify and tweak their cars. Out of all the responses, no two were exactly alike. I've compiled and summarized the feedback here so that you can make an educated decision when equipping your ride.
Let's talk for a few moments on tires in general. Although you can write volumes on tire sizing and design, we'll try to cover the basics here. Tires are sized using a system that takes into effect the tire's aspect ratio. This aspect ratio is a function of the tire's height with respect to its width. An example of a common European tire size is 195/65R15. The number 195 refers to the width of the tire in millimeters. The second number 65, refers to the height of the tire as a percentage of the width. Therefore 65 percent of 195 would give a tire width of about 127 mm. The letter following the width and length is the tire's maximum speed safety ratings:
Q=99 MPH, 160km/h
V=149 MPH, 240km/h
S=112 MPH, 180km/h
W=168 MPH, 270km/h
T=118 MPH, 190km/h
Y=186 MPH, 300km/h
U=124 MPH, 200km/h
Z=149 MPH, 240km/h and over
H=130 MPH, 210km/h
Needless to say, a good Z rated tire should be more than adequate for non-suicidal driving! The last number in the tire size is the wheel diameter in inches. In this case, 15 refers to a 15 inch diameter wheel.
Tread is another important consideration in selecting a tire. You should select your tire based upon what type of driving you are planning on doing. With the Boxster, sometimes it's usually a bit more complicated, because some people don't drive them in all types of weather. With a family sedan located in a snowy environment, an all-weather tire is a natural choice. However, many Boxster owners do not drive their cars in the snow or the rain.
In an ideal setting, such as on the race track, flat surfaced tires called racing slicks are best because a maximum amount of tire rubber is laid down on the road surface. However, slicks have almost no traction in wet weather. The water has a tendency to get underneath the tire and help hydroplane the car by elevating the wheel onto a wedge of water as it is moving forward.
The array of choices for tire tread is way beyond the scope of this project. One rule of thumb is to make sure that you purchase a tire that is appropriate for your climate. Using a snow tire or all-weather tire on a Boxster that is rarely driven in the snow will significantly reduce the tires contact patch area and reduce cornering performance on dry roads. However, not equipping your car for bad weather can result in disastrous effects if you are ill equipped during an unforeseen storm. If you drive your car only during the dry summer months, then look for a conventional performance tire with a maximum contact patch area.
Another important consideration is the tread wear and traction. The tread wear refers to the average number of miles that can be put on the tires before they will need to be replaced. A tread wear indicator of 100 means that the tires should last about 30,000 miles. An indicator mark of 80 means that the tires will last 20% less, or 24,000 miles. Wear will be different for each car, and each driver's personal driving habits, but the various ratings are good for comparisons among different brands and different types of tires. Traction is related to the type of materials used in the tire. The more hard rubber is used in the tire, the longer the tires will last. However, the hard rubber provides much less traction. A rating of A' for traction is best. These tires will grip the road well, but will generally wear out faster than the B' or C' traction rated tires.
It is important to consider another factor in addition to tread wear when selecting a tire. Most tires have a shelf life based on the rubber's natural process of breaking down and becoming brittle. It doesn't pay to purchase a 30,000 mile tire if you are only going to be putting 3,000 miles a year on your car. After ten years, the rubber may be cracked and deteriorated beyond safe use, even if there is plenty of tread left on the wheel. This is also an important consideration if you are purchasing a car that has been in storage, or sparsely driven for many years. Although the tires may have plenty of tread on them, they may actually be dried out and ready to fail. If the tires develop cracks in the sidewalls from aging, they can blow out when heated up from driving. A blowout is a very bad situation, and can cause you to lose control of your car very quickly.
So, what tires and wheels can you fit on your Boxster? It all depends upon the wheel design, offset, and which tires you prefer to run on your car. With so many different combinations out there, it's impossible to fully document them in a mere few pages. I did create a wheel collage (opposite page) that you can use for ideas on which wheels to mount on your car. This array was assembled from photos of Boxsters and 996 Carreras I took at various meets and club events over a period of three years.
Expanding the pool of options, you can also use spacers to accommodate different wheels that weren't originally designed for your car. I recommend the use of hub-centric spacers, which are located on the hub by a machined center hole. This is opposed to the lug-centric spacers that are located by the position of the lug nuts alone (see Photo 6 of Pelican Technical Article: Big Brake Kit Upgrade).
With some older cars, the tire sizes that you can fit on the car may depend upon the condition of the car. Sometimes the chassis are perfectly balanced from left to right, and sometimes they are slightly off from being in an accident, or simply from body sag. It's best to find a tire shop that will allow you to try out several tires on your car in order to find the best fit. Go in the afternoon on a slow day and talk with your tire salesman to see if he will let you size the tires on your car. If he won't then go to a different shop: there are plenty of them out there willing to cater to you, especially if you are going to shell out some money for high performance tires.
If you want to go with larger diameter wheels on the Boxster, the best combination for 18 wheels would probably be 225/40/R18 in the front and 265/35/R18 in the rear. Moving up to 19 wheels, you would probably want to run 225/35/R19 on the front and 265/30/R19 on the rear. Different tires will look and perform differently with various wheels, so the best option is to consult with a good tire shop for their recommendations. You can fit 20 wheels to a Boxster, but at that point, the tire thickness is so small that the ride and handling suffers quite a bit. I don't recommend installing anything greater than 19 wheels. I currently run Genuine Porsche 18 Sport Design wheels manufactured for Porsche by BBS, on the project Boxster for this book. It's also important to note that Porsche has released a Technical Service Bulletin warning against putting 18 wheels on 1997 Boxsters because the early chassis aren't as reinforced as the 1998 and later cars.
With the wider wheels, the options for the installation of tires grow exponentially. The type of offset used on the wheel and the tire size will affect whether it will fit or not. The offset of a wheel is the distance of the center of the wheel from the edge of the mounting flange on the hub. Different wheels with varying offsets will affect tire sizing considerably, so make sure that you know which types of wheels and offsets you have before you attempt to mount tires to them. It's also important to keep in mind that Porsche made very similar looking wheels for the Boxster and the 996 Carrera, with the only major difference being the offset of the wheel. If you're buying used wheels, be sure that you purchase ones with the correct offset for the Boxster.
So after reading this project are you still confused? You should be, and rightly so. It would appear that there is a never-ending amount of options for tire sizing. The best way to figure out what type of tires to place on your car is to inquire around. Check on the Internet at the various technical bulletin boards, like the one at PelicanParts.com. I'm also fond of the TireRack.com website: they have useful tools there for determining the right wheel / tire combinations that will fit on your car. Regardless, you will find that everyone will have an opinion to share, and a wheel/tire option that they have tried on their car.
No matter which wheels you buy, you're going to want to make sure that you protect your investment with a set of wheel locks. The factory ones available from Porsche look pretty terrible though and I don't necessarily recommend them. Booth Designs makes an aftermarket set of locks and polished studs that are of extremely high quality and really look like they should be on your Boxster (available from PelicanParts.com).
This photo shows how the aspect ratio of the tire changes with the change in wheel size. In general, you do not want the outer circumference of the wheel to change: this will affect handling and also change your speedometer readings. So, when you go with a larger wheel, you must go with a lower profile tire. The lower profile tire results in less of an air pocket under the car, and this typically reduces the ride comfort. This photo shows some examples of three rear wheel options for the Boxster. It is generally my recommendation to run 18 wheels for the best combination of looks, performance, and ride.
The upgraded, polished lug nuts really look great on the Boxster. If you use them, be sure to use what is known as a soft socket (also available from PelicanParts.com). This special socket has a softer inner liner that will allow you to install your lugs without damaging them. If your center caps are looking aged, then you can try removing them and sanding them with some fine grit sand paper. The outer plastic covering on the crests gets old and cloudy after many years, and a few minutes of sanding can improve the overall appearance tremendously.
Here's a collage that I created
from photos I took at the many events that I have
attended over the past few years. Hopefully,
this can give you some ideas when you're looking for a
new set of wheels for your Boxster.
Comments: Hi can you please advise if these wheels and tyres will fit my 2001 Boxster 2.7 Please.
Porsche 911 996 Carrera 4S 19" Alloy wheels with Michelin tyres.
Came off 2002 Carrera 4S.
Rear 19 x 11 J E.T 52
Front 19 x 8.5 J E.T 45
Michelin Pilot Sports N2
Rear 305/30 ZR19 102Y
Front 235/35 ZR19 87Y
October 19, 2014
Followup from the Pelican Staff:
These are the sizes I know will fit your car.
I opened a post in our forums. A Pelican community member may be able to answer your question.
- Nick at Pelican Parts
Comments: hi wondering why the limit of the tire size...if coil over kit is installed on the car can 20" tires then be used with maybe a different wheel offset??, or some other no-no reason for larger than 18" wheels???
October 14, 2014
Followup from the Pelican Staff: I am not 100% sure. I opened a post in our forums. A Pelican community member may be able to answer your question.
- Nick at Pelican Parts
Comments: Hi Wayne,
I'm Sam from Malaysia, I have a 2009 boxster S sitting on a set of original Conti SC3 rubbers. My front 235/40 ZR 18 still has 50% tread, unfortunately the rear need a replacement. Dialed half a dozen of local Conti dealers, and none of them could offer me a pair of Conti SC3 265/40 ZR18 no stock since a while according to these dealers.
Now I have no choice but to fall to Michelin. I opted for a pair of rear 265/40 ZR18 Pilot Super Sport and cross brands with the front Conti 235/40 ZR18 for the time being. I was thinking that I could replace the front Conti as well with Mich PSS 235/40 ZR18 when time comes.
To my surprise, Mich PSS 235/40 ZR18 are no available in my country.
Weird though! cos PSS 225/40 ZR18 and 245/40 ZR18 are available and why not 235?
Michelin business strategy probably, lol....
My question are;
Can I shoe my front with a pair of PSS 245/40 ZR18? Does the slightly wider tyres affect the handling, stability and performance?
August 27, 2014
Followup from the Pelican Staff: Below are the tire sizes that will fit your vehicle.
Original Front Size 1: 235/40-18
Original Rear Size 1: 265/40-18
Original Front Size 2: 235/35-19
Original Rear Size 2: 265/35-19 - Nick at Pelican Parts
Comments: I own a 2005 Boxster and am looking for some wheel lug bolts that Do Not rust. I do not have spacers and am trying to find what size lug bolt to buy. Porsche parts will not tell me the size as they want me to buy their's that will rust. I wanted to buy from Boothe Designs, but heard they were out of business. Do you have any recommendations? THX for your time, Steven
July 19, 2014
Followup from the Pelican Staff: Most will rust once they are worn a little. Give our parts specialists a call at 1-888-280-7799. They can help you find the right part.
- Nick at Pelican Parts
Comments: Hi Ive just got a 987 Boxster S and am looking for a set of wheels to put winter tyres on - my question is can I fit 17 inch wheels on a Boxster S or must I go with 18's?
i'd rather have the taller sidewalls for winter driving if possible, but I can't find an answer
July 12, 2014
Followup from the Pelican Staff: If you keep the same tire width and circumference, you can go with a 17.
Rear: 235/50-17- Nick at Pelican Parts
Comments: Hi I have just puchased a 1997 Boxster 2.5 right Hand drive, but i live in Germany 6 Months of the year, I have to Change my tyres and my front light beams to pass the German MOT, any help would be nice,, -thanks.
June 23, 2014
Followup from the Pelican Staff: The headlights may need to be adjusted? I am not sure what it failed for, so hard to say.
I would get the vehicle aligned if it is wearing tires. - Nick at Pelican Parts
Comments: I have a 2014 Boxster S front offset ET57 and rear ET45. Want to change the wheels, same size afferent design. Guys at tire shop assure me new wheels with ET45 front and ET49 rear will be perfectly OK. Your thoughts would be appreciated.
June 10, 2014
Followup from the Pelican Staff: I don't have any experience swapping wheel offset around I opened a post in our forums. A Pelican community member may be able to answer your question.
- Nick at Pelican Parts
Comments: I recently purchased a rim to replace a cracked left front.
It turns out the rim width measurement is 11" which I did not measure and they assured me it fit the tire dimensions. It now rubs at times and I am assuming the only solution is to purchase a correct rim with the correct dimensions.
May 30, 2014
Followup from the Pelican Staff: I would agree with your assumption. You will need the correct rim. - Nick at Pelican Parts
Comments: Dear Sir,
I have a Boxster from 2001, with original boxster 17" wheels. I would like to install 15mm spacers on all wheels, and off course install high quality with high yield strength bolts that compensate the difference 15 mm longer.
Will this negative influence the handling of the car ?
April 27, 2014
Followup from the Pelican Staff: It should not cause a negative effect. Theoretically, it will improve handling. Have the vehicle aligned once you are done. - Nick at Pelican Parts
Comments: Can I use 3mm spacers on my 99 986 without changing the lugs?
March 4, 2014
Followup from the Pelican Staff: No. Porsche did not design the factory suds to be used that way. - Nick at Pelican Parts
Comments: For 2006 Cayman S planned to put on winter wheels Front: 225/45 18 and Rear 255/45 18 whereas stock size is: Front 235/40 18 and Rear 265/40 18. The overall diameter would be slightly larger but still within 3%...should this be ok?
January 10, 2014
Followup from the Pelican Staff: Not sure of the clearance issues, as I stick with factory spec tires myself. I opened a post in our forums. A Pelican community member may be able to answer your question. - Nick at Pelican Parts
Comments: I have purchased new wheels for my 2000 Boxster, 17"x8.5 front & 17"x9.5 rear. Right now I have the stock 17" 17”x7 front / 17”x8.5 rear wheels on my car and blew one front tire. I'm getting ready to buy 2 new tires because the 3 Pirelli’s I have now are in really good shape, but I can't see buying only 1 tire. I want to move the rear 255/40ZR 17 to the front and put the 2 new tires on the rear. Can I go a little wider on the rear, if yes, what? Is it a good idea to put the new ones on the back or the front? I’m also looking at mixing tires, keeping 2 Pirelli’s and buying either 2 Michelin’s or Goodyear’s, any suggestions? Not really liking the Pirelli’s but they are like new.
January 6, 2014
Followup from the Pelican Staff: I would check the tirerack site for the maximum tire size you can use. I don't have much experience installing varying tire sizes on these vehicles. - Nick at Pelican Parts
Comments: Response to Ryder. I have a very nice set of Michelin Alpin snows which are 205 50 17 front and 255 40 17 rear mounted on ROH rims off a Boxter. They're taking up space in the basement. If you're in Ontario PM me if you can use them. Username is 14carrot
November 25, 2013
Followup from the Pelican Staff: Thanks for the input on this one. We appreciate the help.
- Nick at Pelican Parts
Comments: 2003 Boxster with winter tires. Last year I put winter tires on the rear only - closest size I could find was BLIZZAKK WS70 245/45 r17. I'm wondering for this year if there is a front winter tire that will work close to 205/50/R17 as tire rack has none in R17 on R16. Should I be switching to R16s front and back or can you run r17 rear and r16 front?
The vehicle isn't driven in snow per se, but my understanding that the Z rated tires it has will not perform well once the temperature dips under 7ºC 45F which happens here in Canada even on clear sunny days in the winter. Any suggestions?
November 3, 2013
Followup from the Pelican Staff: If you desire snows or winter tires, i would switch to a wheel and tire combo that will work. Possibly a 16" set with the right tire size will work out. - Nick at Pelican Parts
Comments: I have 986 Boxster S 2001 with 18" wheels with 225/40 and 265/35 tyres. The wheels are orginal Porsche with ET 50 52. What do You think of spacers to my car? If You recomend that, which thikness shuld I go for? I don´t want any problems, only better handling and look
August 20, 2013
Followup from the Pelican Staff: Generally spacers are used to accomidate wheels that are not the exact fit for your car. If you give our parts specialist a call, they may be able to help you sort out what thickness spacer you can run with a stock wheel. 1-888-280-7799- Nick at Pelican Parts
Comments: I acquired a price of steel in my 2011 Boxster S. a quality tire shop ws quite comfortable installing an internal patch. They didn't really wnt to commit to 150 mph with the patch!
Looking in the owners manual and callin The Tire Rack I gather the tire needs replacing. The car has about 7,000 total miles. Thus 4 tires. Expensive.! Yikes.
What are others thoughts on this issue
June 9, 2013
Followup from the Pelican Staff: I would replace the damaged tire. As much as a problem the extra cost seems, piece of mind is priceless. The other tires, have the tread depth measured to see if they need replacing.- Nick at Pelican Parts
Comments: What is the tire size you recommend on a 19" wheels for the 02 base model boxster?
June 2, 2013
Followup from the Pelican Staff: I pulled this excerpt from the tech article:
Moving up to 19” wheels, you would probably want to run 225/35/R19 on the front and 265/30/R19 on the rear - Nick at Pelican Parts
Comments: Hello, I need to change the front tire of my 2005 Boxster.
Few years ago I mount 2 Sumitomo HTZRIII on the rear. As I am very happy with tme I would like to mount same brand on the front.
However they do not sell the original size 205/55ZR17.
I think of mounting 225/50ZR17 instead as the diameter is exactly the same and the extra 20mm of width should not matter too much.
What do you think about that? Will it fit?
May 31, 2013
Followup from the Pelican Staff: You have to match the tire size that is currently on your vehicle. - Nick at Pelican Parts
Comments: I have a '99 Boxster with the factory upgraded handling package and 205/50/17 front and 255/40/17 rear. I drive the car at HPDE events at Road ATL and Putnam, IN and want to buy a set of wheels with racing slicks just for the track. Do you think I will have any problems going up to a 225/35/R19 front and 265/30/R19 rear? Or should I only go up to 18"? Will I need spacers?
May 22, 2013
Followup from the Pelican Staff: I would stick with 18 and try to match the tire outer circumference to what you currently have.- Nick at Pelican Parts
Comments: 2005 Boxster S 987 with KW Coilovers
Maybe I could try a different size. Front: 235/35/18, Rear: 265/35/18 with a low profile tire. with wheel sizes 18X8.5 & 18X9.5. My only problem is would be the offset...any tips?
May 10, 2013
Followup from the Pelican Staff: My suggestion is to talk to a rim dealer and see what they say. Use the tech article and see if there is a size that suits your needs, if not, you're going to have to do some footwork to figure out what will fit. - Nick at Pelican Parts
Comments: Can I use 235/40/18 and 265/40/18 on my 2003 Boxster ? It now has 225/40/18 and 265/35/18
February 25, 2013
Followup from the Pelican Staff: Those tire sizes are very close and should fit. How ever if you have them installed check all clearances from the tires to the body before driving. Also the larger rear tires will change your overall gearing, engine RPM to road speed. You can go to most of the tire makers sites or the Tire Rack site to check the dimensions of different tire sizes.
- Denny at Pelican Parts
Comments: Are you aware about some chassis structural issues after mounting wide/low profile tires my 986 has 265/30/19 and 225/35/19?
December 4, 2012
Followup from the Pelican Staff: In The tire and wheel article a Porsche bulletin is referenced about early Boxster chassis issues with larger tires and wheels. You did not state the year of your car in your question. If your year Boxster had 19" wheels as a factory stock or optional size you should be fine.
Denny at Pelican Parts
Comments: I have a 2001 Boxster and am I'm looking at some 17" wheels from a Cayman. The front offset is the same at 55mm, but the rear wheel offset is 48. Porsche says the Boxster has 50mm rear offset. Will that 2mm really make a difference? Meanwhile, on my stock 17s, the front lugs are flush with the wheels, while the back are like an in in the socket. Is this right?
October 17, 2012
Followup from the Pelican Staff: Yes the recessed lugs on the rears is normal. 2MM is a very slight difference so they should fit. Check to see if the tires are the same in width and height. The only way to know for certain is mount them up and check all clearances.
Denny at Pelican Parts
Comments: CAn the 18" front wheels and tires be used on the rear of a boxter without any spacers ? I'm looking to drive cross country and want a quieter tire
October 16, 2012
Followup from the Pelican Staff: I would not recommend this modification. It will upset the balance and safety of your car.
Denny at Pelican Parts
Comments: Can 235/40-18 tires fit on a 2000 Boxster non-S without any modifications or clearance issues?
July 8, 2012
Followup from the Pelican Staff: They should fit. I would see if you try them with the wheels you are planning on using. - Nick at Pelican Parts
Comments: I am looking for 18" track tires for a 2005 Boxster S, will be mounted on 18x8, 18x10 BBS wheels. I have run Michelin Sport cups for several years on a 911, but cannot find stock size in any track tires for the Boxster. I really don't want to go back to a street tire, any suggestions?
March 19, 2012
Followup from the Pelican Staff: I would recommend checking with your local high performance tire shop if your area has one. Also you can check with Tire Rack. They stock a wide selection performance tires and should have a recommendation that could work for you.
Denny at Pelican Parts
Comments: I bought a 2002 Boxster recently. Front wheel is 235/35ZR19 whereas rear wheel is 275/30ZR19. Are these wheels OK? They certainly look good but they also look a bit oversize!
March 17, 2012
Followup from the Pelican Staff: You listed tire size not wheel size. Yes those tire sizes are oversize for your Boxster. You did not state that you are having any fitment or rubbing issues so you are probably ok. As a reference a taller tire changes your engine RPM to speed ratio. A taller tire decreases acceleration.
Denny at Pelican Parts
Comments: Can I fit 265 40 18 on rear of my boxster 2.5 1997...
Will it affect the handling etc
January 21, 2012
Followup from the Pelican Staff: Yes a change in tire size, brand or model of tire within a brand will affect handling. You have an early Boxster and there is a factory bulletin on tire size from Porsche about chassis issues on the early cars. It is referenced in our MISC-Wheels article to which you posted your question.
Denny at Pelican Parts
Comments: I'm about to buy used and long distance a pair of 8x17 Fikse wheels for my 2000 Boxster S track car. The seller says the offset is 43mm, as estimated over the phone by someone at Fikse. The wheels are not made anymore and are off a 1996 Carrera narrow body. Concern has been expressed by my shop that the offset may be too small. Does anyone know if these wheels will work on my car? At the moment they are mounted with used Hoozier R6s.
November 30, 2011
Followup from the Pelican Staff: In general, the wheels that are made for the 996 Carrera will *not* fit the Boxster without some modifications, spacers, or rolling out the fenders. I'm not sure about aftermarket wheels, but I would probably tend to avoid the ones made for the Carrera, and try to find ones with the proper offset for the Boxster. This goes for Genuine / OEM wheels as well. - Wayne at Pelican Parts
Comments: I am looking at a set of 18" Carrera Sport Design for my 02 Boxster S. 10" rears and 7.5 front. Do you know which spacer and do you sell them? Do I need longer lug bolts front and rear? I currently have the 17" Twist with 55 offset front and 50 rear if that matters.
June 27, 2011
Followup from the Pelican Staff: As far as I know, there are no spacers that will allow 996 wheels to fit the Boxster - they are just too wide. I suppose that you can change the wheel offset by machining the wheel, but I would not recommend that, as it would probably compromise the safety of the wheel. There are plenty of properly-sized Boxster wheels out there - I would look for the ones manufactured specifically for the Boxster. - Wayne at Pelican Parts
Comments: Can I fit 235/40/19 front and 285/40/19 tires rear on my 2006 carerra 2 without experiencing handling and rubbing issues? I like the looks of a 19" wheel, but don't like the low tire profile. Thanks!
April 12, 2011
Followup from the Pelican Staff: Different tire manufacturers have different sizes of tires, even if they have the same spec (i.e. one brand of the same size tire may fit differently than another brand of the same sized tire). The sizes you mention *should* fit - the 19" wheel uses a lower profile tire to keep the outer circumference of the wheel the same. I had 19" wheels on my 996, but I took them off and put back 18" wheels on, as I didn't like the low profile going that thin, and I also didn't really like the looks. - Wayne at Pelican Parts
Comments: I just purchased a 2002 porsche boxster with it original michellin pilot sport tires that need replacing. I drive fast but not very aggressive. Do the tires have to be specifically replaced with a Porsche N specification tire or will any well branded performance Z rated tire work as well?
March 7, 2011
Followup from the Pelican Staff: Z rated tires can be used at speeds in excess of 149 mph. I don't think most people will be traveling at those speeds, so the Z-rated tires should be more than adequate. - Wayne at Pelican Parts
Comments: read you 2005 Boxster tire sizing article... i am replacing tires and found few options available in the exact size of 235/40/18-front, 265/40/18-rear. several tires, such as Bridgestone, BFG, even Mich have suggested sizes such as 275/35/18 on rear and 225 or 235/40/19 -front. in your experience do you think i will have a clearance problem if I use the 275 size on the rear ??? thanks
July 12, 2010
Followup from the Pelican Staff: Tire sizing is not an exact science - the same sized tire from two different manufacturers will often fit completely differently. I would find a tire shop that will allow you to "try on" the 275s on the lift. I have no experience running the 275s, but I would think they might fit on some cars. Each car is different too, and sometimes the left/right tolerances in the fenders is not exact. I.E. the extra wide tire may fit on one side but not on the other. Hope this helps, - Wayne at Pelican Parts
Comments: Once you replace the wheels I upgraded from the factory 17" to a nice Porsche compliant 18" with approved spacers for the rear, how to program the tiptronic ECU to correctly report the right speed on the speedometer?
June 7, 2010
Followup from the Pelican Staff: Putting slightly bigger wheels on a Porsche is different than putting them on a 4WD truck. When you put them on a truck, your outer diameter changes (usually accompanied by a lift kit or something like that), and then your speedometer is off. When you update from 17 to 18-inch wheels on a Boxster or 996, you are going to use a thinner profile tire, so that your outer diameter is the same. Hence, your wheels turn at the same speed, and you don't need to adjust / alter your speedometer. - Wayne at Pelican Parts
Check out some other sample projects
from the book: