A Story of Unscientific Tyre Testing

by Adrian Streather RO Swiss-European Region TIPEC (SERTIPEC) .

Introduction

This article is all about tyre testing. The results are totally subjective and unscientific however I hope that my efforts can provide just a little insight into tyre selections.

One can only get the best out of ones Porsche with the correct tyres for your needs fitted. We all have different conditions in which we drive, we all drive differently and very few tyres are great in every category. Porsche publish their recommendations for summer and winter tyres every year in their magazine Christophorus. They also issue Technical Service Bulletins but in recent years Porsche seemed to have stopped doing this. The last one I have is dated 1995. Various Auto Clubs around the world do similar things as do many of the respected motoring magazines. I highly recommend that these publications be read as well to ensure you have all the possible data. New tyres for a Porsche is an expensive business and getting it right first time is the goal.

Test vehicles

Porsche 911 (964) Carrera 4 rego AR5029

Porsche 944 (1985.5) rego AR23953

Togetherness

Tyres tested

Note one: I received no support from any of the tyre manufacturers.

Note two: I have not and cannot comment on the aquaplaning abilities, or lack thereof any of these tyres. The 944 has never been in the situation and the 911C4 does not aquaplane. Not on me anyway. AWD and extra weight in the front which is not present on most other Porsches.

Bridgestone S01

These were the tyres that were installed on my 911C4 when purchased it. my C4 was completely stock standard with standard original 1990 design wheels. 6JX16 on the front and 8JX16 on the rear. This was the first time I had used or driven on Bridgestone tyres on a Porsche, previously I had been a Pirelli person. The S01 was the best tyre I had ever driven on. In the dry the grip was excellent. In the wet the grip was excellence and even in the snow after being caught out a couple of times these S01s worked well past my expectations. The S01 certainly did nothing to assist or reduce the inherent understeer of the 911C4 in standard set up but my opinion on the S01s is that they are an excellent high performance tyre. On criticism is that they did wear quickly, especially on the inside of the fronts on the AWD C4. They were not what I would call noisy on the road, they were smooth but when worn the C4 made you know that the tyres were worn. Unfortunately S01s are no longer easily available. Some stock still remains here in Europe but they are very hard to find. Some of the Tuning firms have stocks of them for their modification programs but I have not found a tyre store with stock.

The 911C4 with its original wheels and SO1s and Gail of course

Michelin Alpin Pilot

If you live in Switzerland and want to drive in winter you need winter tyres. In fact if you live anywhere that has a true winter climate you should not venture out without winter tyres. The 911C4 was a complete mystery for myself in winter so this time I went with the official Porsche winter tyre recommendations for 16 inch wheels in winter.

So what can be said about these tyres. They have a low speed rating, 190kph maximum. I have had them up to 260kph just to see how they would go. Answer, not good.

These tyres are brilliant in the snow and ice. Never felt safer. In the wet as long as the road surface was cold, less than 7 degrees centigrade. No problems at all. Unfortunately as the road surface warmed or the road was dry, the performance of these tyres fell away rapidly. In the dry four wheel drifts are very common as the understeer causes some concerns, to me anyway, when you push it a little hard. As soon as spring arrives these tyres need to be removed and replaced. of course only bad luck means its snows after you put your summer tyres on. These tyres also wear very quickly in the dry so gentle driving is required before they can be replaced.

Next winter I shall wait to the last moment to replace them and I will get them off at the first opportunity. To be completely fair though. These tyres are brilliant winter tyres and they ensure safe driving with the 911C4 regardless of the weather. I highly recommend them.

Now I also tested these tyres on the 944. Just for fun. The 944 being RWD is severely limited in use in the mountains. However I would still highly recommend these tyres as winter tyres for the 944 should you be able to drive around in winter. In the flat areas of the world I would see no major problems and the 944 and the Michelins would make an excellent combination. I did not feel any major changes in the balance of the 944, without power steering my 944 understeers anyway and the 205/225 combination seemed to reduce this understeer as compared to the all round 15 inch 215s previously installed.

Winter, what else can I say

Tread Comparison Between P7000s and the Michelin Alpin

Bridgestone S02 Potenza

Well what can one say about these tyres. The best tyre ever manufactured for a 16 inch wheel and installed on any model Porsche. I have used these tyres on the 911C4 and the 944. They provide brilliant grip in dry and wet and even in the snow. Not that I recommend anyone use them in the snow. I was forced to once on the 911C4 and they handled the job very well. The SO2 is the first tyre that I have ever had total 100% confidence in under all circumstances. I have pushed both Porsches very hard wearing these tyres and never have I been let down by tyre or Porsche. On a negative side, the SO2s tend to wear more quickly, they are quite expensive and they do have a high road noise level. I still think they are brilliant and safe tyres and well worth the purchase.

These tyres are currently installed on the 944 and will remain installed until they wear out or I sell the 944. The 205/55ZR16 front and 225/50ZR16 rear combination really works on the 944. I have taken the 944 out in warm and dry conditions and wet and cool conditions. I really drove it hard on some of the toughest high speed and low speed corners through hairpin bends anyone can find anywhere in the world. Real James Bond type roads. The uncomfortable and inherent understeer of the non power steering equipped 944 was very nicely reduced. Never to oversteer but I like a little bit of understeer. Many will say that these tyres are too expensive for an old 944 but personally I feel they are worth every penny and they allow the 944 owner/driver to extract a little bit more from the abilities Porsche built into the 944. The road noise problem is reduced a little bit on the 944 as compared to the 911C4. However this might be down to the fact that a high speed the 944 makes more noise where as the 911 gets smoother as the speed increases. Rear engined versus front engined I guess.

911C4 with the SO2s installed on 16 inch 993 Cup Wheels

944 with the SO2s installed

215/60R15 Pirelli 5000 tested on 944 only. These were the tyres that the 944 was purchased with. A Porsche delivered option at the time. Not a recommended choice in my opinion. These tyres are too wide all round for a non power steering equipped 944. They cause massive understeer and the 944 is difficult to manage. Hurts the shoulders sometimes and under braking they also offer little control. Not a very good wet road tyre either. Good grip in the dry once the understeer is mastered but they get worse in the wet. Road noise level is okay but not my ideal choice.

205/55VR16 Semperit tested on 944 front only. These tyres are again not what I would recommend. The 16 inch 205/225 combination is highly recommended on the 944 in my opinion and is a huge improvement on the 215s all round, chalk and cheese really but these Semperits are just to hard and inflexible and they squeal easily under load. Good wearing tyre. Road noise level is good but again would never be a tyre of choice.

225/50VR16 Goodyear Eagle VR50 tested on 944 rear only. Same comments as above not my ideal tyre choice for a Porsche.

Yokohama A008P Assymetrics and Yokohama AVS Assymetric Combination .  These tyres in their 17 inch sizes are Porsche N0 rated. This combination works extremely well on the 911C4. 205s up front and 255 on the rear. I am not convinced that this combination can be bettered for road use. Track use I would recommend 225s up front but not for normal use. There is some evidence emerging that the stress placed

911C4 with Yokos Installed

Pirelli P7000

I was hoping to be able to write a glowing report on these tyres. Unfortunately I cannot. I cannot write a negative report either. I would say these P7000s would be an excellent high performance tyre on any auto type except a Porsche 911 (964) C4 or any other 911 for that matter, especially the C4s.

The P7000 17 inch version is not Porsche approved or N rated. They provide adequate to slightly good performance on dry road of varying temperatures and good to very good performance in the wet. Heating the tyres up does not really seem to make much difference. You can see on my C4 that these tyres have been used because I have nice brown rims on the side walls. They are much quieter than the Bridgestone SO2s and they are quieter than the Yokos but where they need to perform at their best, they do not. With my somewhat heavily modified suspension on the C4 the P7000s still cause a four wheel drift which I did not have with the Yokos. I have certain stretches of road which I can duplicate the same conditions over and over again. Play with speeds and other parameters. I feel that this gives me a quite good comparison between tyres. The P7000s just do not perform to what I need or fell confident with. As I said they are good tyres, I would certainly recommend them for autos like the Audi RS2, RS5, Audi TT etc but not for the 911s. Balance is not one of the high points of these tyres. They are also expensive so I would certainly look at other tyres anyway. One thing I have learned is that the N rating does affect design of the tyres. With the Yokos I had no wheel rub despite my efforts to cause it. The P7000s which are the same technical size rub at full left lock when going backwards. This is caused by the design of edge better the tread and sidewall. It is more vertical than the Yokos.

911C4 with Pirellis Inside on the way home to be installed

The P7000s Before Installation

Summary

From my testing I have come to a conclusion which some with disagree with but I must state. “If you own a Porsche 911 then purchase Porsche recommended N rated tyres”. I would also extend this to all model Porsches because the 944 is so much better with the Bridgestone SO2s fitted (pity about the lack of power). Whilst I cannot say what the N rating consists of I have worked out basically what it means.   N0=Very High Performance Tyre low on comfort. N1 thru N4 shows lowering of high performance specifications and an increase in comfort (comfort being ride comfort). Remember these ratings are on standard set-up 911s. When you lower and stiffen the suspension these N ratings and the affect on your own 911 may not be as you expect.

Final Note

I also had a couple of sets of Pirelli PZero Cs, given to me to test. Due to cost reasons and not wanting to damage my 911 Turbo wheels more than necessary with all these tyre changes I have decided not to personally test them. I have more than enough evidence to make the following statement.

Pirelli PZero C is a great track tyre, It is a great tyre to install on your Porsche to drive to and from the track as well. They are great in the dry and not so good in the wet on the track. They are not road tyres which will provide year round driving pleasure because firstly they will wear out fairly quickly and they a really are a superb high performance tyre. I have driven a 911 (964) Carrera RS shod with these tyres and all I can say is awesome!!!. Pirelli have a brilliant tyre here but I do not recommend them for normal road using Porsche owners. Please do not mix up Pirelli PZero Cs with other forms of the Pirelli PZero Series.

Ciao,

Adrian