Buying Tires for a Boxster

 
 

Measuring Tread Depth

Measure in 3 places across the width of the tire.  The lowest depth is the one you use in comparing tread depth. You can find the original tread depth in the "specs" area for each tire at Tire Rack.  Their site has videos showing how you can measure using a coin and what the recommended tread depths are and how they affect handling.  Or you can buy a "professional" tread-depth gauge from most auto parts stores for around $3.

You could read their tests or I'll cheat and just give you the results. The difference between a new tire and one worn down to 2/32 (legal limit in many states) in a test on a water soaked surface was an almost doubling of stopping distance! 4/32 deep tires took about 50% longer to stop than new tires.

New - 195 feet

4/32 - 290 feet

2/32 - 378 feet

Even more startling to me is that on a 2/32 tire, in stopping tests in the wet from 70MPH the new tire would have stopped the car where the worn tire would only have slowed the car to 55MPH!!!!  4/32 would only have slowed the car to 45!!!! 

They don't cite skidpad tests but the same issues that affect stopping distance would affect your staying on the road as you round the curve in the very wet.  The tire needs the depth in order to evacuate the water beneath the tread and get the tire "rubber" into contact with the pavement.  If it rides up on the water, it is like driving on ball bearings.  I recall driving behind a car once and seeing it hit a puddle just as it came to a bridge and then going off like a pinball bouncing off the sides of the bridge.  When I stopped, sure enough balding tires.

Depth does matter in the wet. 

In the dry, depth is not nearly as important as long as the depth is consistent (see below).

Tests done here at Tire Rack.

How long do they last?

Lots less than your average sedan tire.  You drive them harder and they probably have a softer compound to enhance their summer driving performance.  Most Porsche tires are of the summer ultra-high performance variety.

They go bad from punctures, misalignment, and age.  One of the problems with buying an older car with very few miles is it may have the original tires on it and they deteriorate with age and exposure to sun and weather.  Replace after 6 years. The tire date of manufacture is stamped on the tire and any good tire place can read it for you.

The rears typically last half as long as the fronts. You'll see people getting 5 to 20 thousand miles before they change their rears depending on the brand, the alignment, and how they drive. You can adjust the alignment to give better wear at the cost of some handling. I did and liked it.

Do track time and you can count the time they'll last in hours.  Most people who do more than a single DE (Driver's Education) experience have a set of track wheels and tires.  Track tires have less tread depth, a softer compound and a more solid tread.  Some are even sold as "not DOT approved" which means the Department of Transportation has not approved them for use on public roads.  Because of the solid tread and its inability to evacuate water away from under the tire,  track tires can be very dangerous in the wet.

Some of the cost of tires is mounting and taxes. Buy a tire that has to be replaced more frequently and you pay those costs more frequently too.  So the more expensive but longer lasting tire may not be such a bad bargain after all. 

Tire Rotation

You don't rotate tires on a Boxster like you do on a passenger car that has 4 or 5 of the same size tires.  Boxsters have different size tires on the rear axle from the front axle.   You may be able to rotate tires side to side by dismounting them if the tires have a symmetrical tread (not Pirelli Asimmetricos).   This is often done on the rears to balance out the wear on the edges but is expensive as it involves dismounting, mounting and balancing expense.   Be careful of the direction the tire tread is designed to point towards (indicated by an arrow on the sidewall) and don't get it pointing backwards.

All Weather ? 

Just means they aren't really great at anything. 

All tires are compromises in cost, traction, handling, wear, noise, heat resistance, ability to stay flexible at temperature, ability to evacuate water away from the tire, ice grip, snow grip, etc.  There is no perfect tire. 

A summer ultra high performance tire is optimized to handle like heck in wet or dry when the temperature is above 40F degrees.  Go lower in temperature or try to drive in snow and they are horrible and dangerous!   Don't believe me?  Try stopping at 80F and at 30F on those summer high performance tires and compare the distances.  It's measured in car lengths and that distance can mean ending up in someone's trunk. I "totaled" a Boxster that way once.

Snow Tires?

Yes they are a must if there is any chance you'll drive in ice or snow.

And they must be on all 4 wheels. 

Consider a spare set of wheels. You'll save enough on demounting, mounting and balancing costs over a couple of years to pay for the wheels especially if you buy them used on eBay.  Remember they don't have to be perfect, no one looks at wheels in the winter.

The limited road clearance the Boxster has means it can get hung up in deep snow. 

I just put the car away when it gets so I'd need snow tires.  I bought it to drive with the top down and I'm lucky it isn't my only car.

Basic Research 

Go to Tire Rack and enter your car and driving preferences and read reviews and owners comments about tires.  Pick the one in the price range you want to spend.  Ask about the experiences of others in the online forums. You'll get lots of opinions.

Brands

In reply to a guy who was having problems in the rain that forced him to drive at 3MPH around a wet curve and wanted to know what we used, I posted this:

We use about a dozen brands and types of tires....

And everyone has their opinions and biases.

It is hard to get good comparison information about tires.  And people who have opinions are frequently comparing old, used tires like yours with new tires newly balanced and possibly with a new alignment.  And self justifying the wisdom of their purchase...it is human nature.

I'll bet most of your problem is worn tires and alignment. And any tire you buy will be better.  Never even slid in the rain in the Boxster unless I meant to .... and I don't drive 3 MPH and I know how to control a slide.

I've had 5 designs on Boxsters.  All were used when I got them, 2 because of used-car purchases and one because I bought some wheels and they were already on them.  So I have experience in driving worn tires and comparing them to worn tires.

1. Pirelli Russo Asimmetrico/Russo were on my first Boxster.  Good tires.  Good grip.  Quiet.  Drove them about 6k miles.

2. Yokohama AVS ES100 were on my second Boxster.  Fabulous grip wet and dry.  Noisy to the point where I couldn't wait to get rid of them.  Drove them about 3k miles.

3. Michelin Pilot Sport Ribs were on a set of wheels I bought, no idea how many miles on them when I bought them.  I'd driven 16k+ miles on them and they had another 4k left on the rear judging from the tread depth but they got to be 7 years old and were replaced based on age and the above wet weather stopping distances. (I have the rear alignment set to favor wear over grip). More tread depth of course was on the front. Very good grip wet and dry.  Quiet.  Expensive.  No longer available.

4. Replaced with PS2 N3 tires. I like the Ribs better based on 500 miles of driving.


Getting lots of comments are the Sumitomo HTR Z III and Kumho Ecsta SPT as much less expensive but still very good.  Few say they are as good as Michelin PS2s but they are less than 50% of the $. 

If you buy the PS2s, be aware that there are at least 3 model numbers sold under the same marketing designation and, if you want the Porsche approved version, you have to buy by model number and not by marketing name of the tire.

I'll confess to a bias in favor of Michelin tires. I've probably bought (or influenced the buying of) 25 sets for family cars  over the last 35+ years.  3 family cars have them now.

Also note I live in a moderate climate (DC and now NC) and don't drive the Boxster in the snow so I only have summer tires.  Your needs could vary.

Go to www.tirerack.com which is a great place to research reviews and prices.  Many buy through them, have them ship the tires directly to one of their recommended mounting shops (listed on the tirerack web site)  and  have them mounted locally.  Look especially at the comments from users who drive Porsches.

Porsche Approved ? (N0, N1, etc)

You'll get a lot of opinions about using Porsche "approved" tires (labeled N0, N1, N2, etc with the number being the generation of the tire and not indicating any increasing goodness.  All it means is some manufacturer decided they wanted Porsche approval to enhance their sales so they submitted samples for testing and then Porsche works with the manufacturer to tune (change) the way the tire is made so that it provides the dry, wet and curves handling and safety specifications that Porsche feels their cars need. 

Sometimes a tire is available in one size with the N rating but the in the size you need isn't N rated.  Just means the manufacturer didn't submit that tire for "approval" either for marketing or technical reasons.  

Two tires that are Nn rated will not perform the same, they may have very different feel, handling, and performance characteristics. 

Sometimes a tire is available with or without the Nn rating for a small (~$10) difference.  No way of knowing if the tires are built the same way and just not labeled or not.  

Some people swear by tires that are not Nn rated, others figure Porsche must know best.

TireRack has a discussion on Porsche Approved tires here

 

2 or 4 Tires ?

Are you replacing all 4 or just the rears? How much tread is still available on the fronts?  Most people get a set of rears and then the next time replace all 4.

Is it safe to have wide differences in tread depth on the same axle?  No.  The old tire should have 70% or more of its original tread depth for optimum safe handling with a new tire on the same axle.

Can you have different tread types on the 2 axles?  You can, not optimum.  Wouldn't even be allowed in some countries.

At least put same depth and same tread design on an axle.

Option 1: Stick with what you have and replace only the 2 rears. Then next time plan to change all 4.

  Pro: Keeps the tread pattern and handling characteristics mostly consistent.  Moderate cost.

  Con: Don't get the fun of changing.  Don't get the tires you might really want right now.

Option 2: Change only the rear 2 with another brand/pattern.

  Pro: Moderate cost.

  Con: Most inconsistent handling. May not be an issue in normal highway driving but in the wet and at the limits or in an emergency? 

Option 3: Change all 4 with less expensive tires

  Pro: Consistent handling.  Moderate cost.

  Con: All tires are built with compromises.  What did the cheap tire leave out to get to this price point?  It can be nothing but advertising and profit that make the difference.  Hard to tell.

Option 4: Change all 4 with the tires you really want

  Pro: Get best tire this way.  Totally new experience.

  Con: Costs as much as 70% more than options 1, 2 or 3 

Replacing just one!

So you have a blowout or a non-repairable flat.  And you have 3 perfectly good tires.  What to do?

The general rule of thumb is, as I said above, "At least same tread depth and same tread design on an axle".  So what is "same depth"?   With 70% of original tread depth or more it is safe to replace just one tire.  Get much below that and you are violating the "same depth" rule and it starts to get dangerous because you are creating different traction on each side of the car and a different ability to evacuate water away from the contact patch.

By keeping the tread depth nearly the same and the tread pattern the same, you are maximizing the effectiveness of anti-slip brakes and Porsche's Stability Management (PSM).

If you do get just one tire, watch the wear on the older tire and don't let it wear down to where it has no tread depth just because you are trying to get maximum use out of the replacement tire.  Remember tread depth differences can cause accidents. 

Accidents hurt ...your pocketbook ... your insurance rating ... your health...someone else

 

Metal stems? 

Not for me because they add weight and make the tire hard to balance.  Same comment about tire pressure reporting stems.

Where to buy tires

Would I go to the dealer?  Only if the dealer is price competitive. I'd do some comparaison shopping first.

Would I go with TireRack?  Only if they are price superior when all services, taxes and shipping is included.  A tie goes to the local shop.  Ask the local to match TireRack's price.  They often will when they know there is competition.

Where would I go?  To a tire specialist who has Hunter equipment and is recommended by local Porsche owners (tell us on where you live on one of the online forums and maybe someone here has local experience).  Why the recommendation?  Porsche wheels are big, and expensive.  Big means the forces operating on them are large and tougher to balance than the average tire.  Expensive means you don't want the tire mounting process to scratch them.

Alignment

Alignment for a Porsche is important.  And choosing an alignment shop which knows Porsches is the right thing to do. Alignment ought to cost $150-200.  Consider a shop that records the before and after values for you.  Consider asking them to adjust the toe-in on the rears to as near zero as they can for best wear (prevents excessive inside edge wear). 

Notice that alignment is specified not as a specific number but as a range of numbers, any of which can be acceptable.  

You want someone who understand how each of these values affects tire wear and handling and can pick the right numbers for your needs.  That means the alignment shop must understand your needs before they do the alignment so talk to them.

You can get the alignment with the old tires on.  As long as you are sure that the wheels aren't bent.  An argument for waiting until you have the new tires on is that the tire installer should check that the wheels are true before even demounting your old tires.  I had this done on an Acura I had where I knew one of the wheels might be out of true.  I had 3 bent wheels!  If I had the car aligned using the bent wheels, I would have only torn up the new tires.

The best place to get an alignment is not necessarily the place that installs your tires.  More convenient, yes.  But expertise counts a lot especially in a Porsche. For a stock suspension...


 

Front: 

Rear:

 

Other Tips 

I take digital pictures of the wheels before I gave the shop the car just to prove that any damage they did was their fault and make sure the shop knows I'm taking those pictures.

Before you take it in, check to see if you have wheel locks and, if you do, do you have the special socket attachment that allows removal of those locks.  Look in your toolkit or the pouch on your spare tire.  If you don't have it, visit your dealer and borrow their set of 30 and figure out which "number" socket your car was fitted with.  A dealer wanted $108 for a new replacement set and $60 to remove the old locks.  You can buy just the replacement key for $25 from:

McGard
1-800-444-5847
385 California Rd.
Orchard Park, NY 14127

Or maybe now is the time to get some plain studs and get rid of the locks entirely.  New studs are around $7 each.  Once I had a tire going flat and the last trip to another dealer had lost the lock socket.  I bought the studs from the dealer conditioned on my borrowing the dealer's sockets for use in his parking lot.  I figured out which one fit my locks, removed the locks, installed the new studs and was on my way in 30 minutes. 

Or is now the time to get a set of chrome or stainless ones to get rid of the dull and scratched finish the stock ones have after a while?

You don't need to do an alignment unless the wear on the old tires shows you need it.  And the dealer could still do the alignment even though you bought tires elsewhere. You can have an alignment done with the old bad tires still on the car...but a good tire shop checks the wheels aren't bent and one I found 3 of the 4 wheels were bent so an alignment wouldn't be wise until the wheels were straight.

The wheel centers should have the pointed end of the crest pointing toward the stem according to the purists and concours-entering folk.   Mine don't.

Check your tire pressure whenever the temperature changes by 30 degrees.  Amazing how tires perfectly right for 80F suddenly aren't right at 45F.

And check the tire pressure on your spare! 60 PSI

Some Ratings

Summer Ultra High Performance Tires (not for use in lower than 40F/4C temperatures)

Tests done on 225/40ZR18 tires. Not done on a Porsche and not done with differing sizes front to back axle. N-rated version not mentioned so probably not tested. Done the summer of 2007 so the results may change based on tire reformulations. Others listed but these are the tires people most frequently mention. Listed in their order of overall score. Price not a factor in scoring.


Michelin Pilot Sport PS2

Excellent (3) Dry Braking, Wet Braking,Hydroplaning

Very Good (4) Dry Handling, Wet Handling, Noise,Rolling Resistance

Good (1) Ride

Fair (1) Tread Life

 

Pirelli P-Zero (not P-zero Rosso)

Excellent (4) Dry Braking, Wet Braking, Dry Handling, Wet Handling

Very Good (3) Hydroplaning, Noise, Ride

Fair (1) Rolling Resistance

Tread Life Not available nor its absence explained

 

Bridgestone Potenza RE 050 A Pole Position

Excellent (3) Dry Braking, Wet Braking, Hydroplaning

Very Good (3) Dry Handling, Wet Handling, Noise

Good (2) Ride, Rolling Resistance

Fair (1) Tread Life

 

Goodyear Eagle F1 GS-D3

Excellent (1) Hydroplaning

Very Good (6) Dry Braking, Wet Braking, Dry Handling, Wet Handling, Noise, Tread Life

Good (1) Ride

Fair (1) Rolling Resistance

 

Continental ContiSportContact 3

Excellent (1) Wet Braking

Very Good (6) Dry Braking, Dry Handling, Wet Handling, Hydroplaning, Noise, Rolling Resistance

Good (1) Ride

Fair (1) Tread Life

 

Kumho Ecsta SPT

Excellent (1) Hydroplaning

Very Good (5)  Dry Braking, Wet Braking, Dry Handling, Noise, Rolling Resistance

Good (2) Wet Handling, Ride

Fair (1) Tread Life

All Season Tires?

There is no such thing as a perfect tire. Just as Ultra High Performance Summer (UHPS) tires will be better in warm weather and snow tires better in the snow and ice, you can't expect all season tires to be as good as the specialized tires in either season.   When Consumer Reports did its ratings of 15 different all season tire models, it found them around 2 of 5 rating points inferior to UHPS in the dry and wet.  And surprising to me was, of the 15, only 5 were as good as "very good" in the snow and 5 were "fair" or "poor".  If you really want to get around in snow and ice, you need 4 snow tires!  And among snow tires, some are better in snow and others are better on ice.  This is a case where you really have to set your priorities and read the reviews with what your conditions are liable to be in mind.

Where all season tires can help is that their blend of "rubber" doesn't get as hard as the UHPS "rubber" does and so all season tires can be driven in cold weather (specifically on cold roads where the road temperature is less than 40F).  Their noise will probably be a bit louder and their rolling resistance greater (mileage less).


Wheels 

Pictures of Porsche-supplied wheels

 Wheel weights


There are good safe wheels made by aftermarket suppliers that fit our Boxsters.  There are also cheep imitations that look the same but which are heavier and or less sturdy.  A wheel that bends is no bargain (I just replaced 3 on another brand of car.).  Unsprung weight is the enemy of good handling.  There are no new $150 per wheel bargains to be had.   And if it sounds too good to be true, it probably is.

However, just reported is this site that is said to sell real Porsche wheels for about 25% of what the dealers sell them for. Ask if they are new or repaired/repainted.

Another source.

Individual repaired wheels can be had here.   Or here.    Or hereOr on eBay.

Thinking of different size tires.  Look here to see how they will affect things like speedometer/odometer readings.


Mike Focke's Porsche Boxster Web Pages

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