235 section rear tyres

[ed80]

Sorry if this has been discussed before, I couldn't find anything when I searched.

I need new rear tyres on the 17" wheels I picked up. I was thinking of going for 235/45 rather than 255/40, to give a slightly better balanced car, and much cheaper tyres. Porsche switched to this ratio in the 987 from what I have seen, so was wondering if anyone else had done it. Fronts are the standard 205/50.

Cheers,

Ed

[Bike Loon]

I wouldn't put narrower than recommended on. Rolling radius will be -1.17% but my concern would be the narrower tyre will make it much more tail happy in the wet as less surface to grip

[That986]

30 minutes ago, Bike Loon said:

I wouldn't put narrower than recommended on. Rolling radius will be -1.17% but my concern would be the narrower tyre will make it much more tail happy in the wet as less surface to grip

This. Need that rear grip to balance the front. 

[PaulQ]

3 hours ago, ed80 said:

Sorry if this has been discussed before, I couldn't find anything when I searched.

so was wondering if anyone else had done it

Yes, but with 225 on the front. Works very well. 

 

2 hours ago, That986 said:

This. Need that rear grip to balance the front. 

You do know that Porsche spec 235 rears on the 987.?  986 16's had 225. 

[PaulQ]

3 hours ago, Bike Loon said:

I wouldn't put narrower than recommended on. Rolling radius will be -1.17% 

That's the speedo. 235/45 is a tad bigger then 255/40

[That986]

2 hours ago, PaulQ said:

Yes, but with 225 on the front. Works very well. 

 

You do know that Porsche spec 235 rears on the 987.?  986 16's had 225. 

The car in question is a 2001S. If the owner fancies something tail happy go for it, personally speaking i like to grip round a corner. 

[Bike Loon]

Exactly, Why would anyone want less grip? ?

[PaulQ]

13 minutes ago, That986 said:

The car in question is a 2001S. If the owner fancies something tail happy go for it, personally speaking i like to grip round a corner. 

What makes you think it would be tail happy.? 

[That986]

6 minutes ago, PaulQ said:

What makes you think it would be tail happy.? 

Because the boxster (especially the S) is endowed with brilliant front end grip from those 205 tyres. even more so if you step up to 18s and put 225 tyres on. It's quite easy to spin up a 265 tyre (trust me, it is) so a 235 would be even easier. Couple that with great front end grip and you get tail happy. 

Personally speaking i'd stick to the 255. Not only will you get better grip but the ride will more than likely be better as well due to the increase in sidewall. 

[PaulQ]

6 minutes ago, That986 said:

Personally speaking i'd stick to the 255. Not only will you get better grip but the ride will more than likely be better as well due to the increase in sidewall. 

Well I've done the comparison, but with a 200 bhp car. 255/40 has LESS sidewall height then 235/45, not more. 

[Bike Loon]

Bet less tyre in contact with the road. Also, I wonder how you stand with the insurance company if you crash on tyres that are narrower than the manufacturer put on the car

[PaulQ]

If in doubt ask your insurer, but they won't be interested unless your fitting something that less then the manufacturers minimum load rating which it's not. 

[PaulQ]

@ed80 if you want any advice, feel free to send me a private message. 

[That986]

1 hour ago, PaulQ said:

Well I've done the comparison, but with a 200 bhp car. 255/40 has LESS sidewall height then 235/45, not more. 

Ok then. 

[PaulQ]

9 minutes ago, That986 said:

Ok then. 

Yes it is. This was one of the reasons I did the swap from 255 to 235 as I was looking for a bit better ride quality. It helped a little, but could have been just down to the softer compound of the tyres. 

[That986]

1 hour ago, PaulQ said:

Yes it is. This was one of the reasons I did the swap from 255 to 235 as I was looking for a bit better ride quality. It helped a little, but could have been just down to the softer compound of the tyres. 

Ok, well done. 

[ed80]

Thanks for all the feedback. I found some more reports of it on Pistonheads too, the consensus there was that it was worthwhile.

I am going to give it a go once I have painted my wheels. I will report back on how it goes. I am pretty sure that even 235 width Michelins have to be grippier than 255 Acceleras

[PaulQ]

Go 225 ?

https://www.pistonheads.com/gassing/topic.asp?t=1346868

[Mr96er]

The Chap who owned Mr Kaplan had 225s all round to square up the stance with an impact on the handling that promotes drift characteristics. I immediately swapped it back but forgot to check the alignment.  So a month later I had a spin when it looked like this...

leave it alone would be my advice. Porsche had plenty of dabloons to spend on getting it right. 

[ed80]

13 hours ago, Loz987 said:

The Chap who owned Mr Kaplan had 225s all round to square up the stance with an impact on the handling that promotes drift characteristics. I immediately swapped it back but forgot to check the alignment.  So a month later I had a spin when it looked like this...

leave it alone would be my advice. Porsche had plenty of dabloons to spend on getting it right. 

I am not sure why different sized tyres would cause the car to be misaligned so badly, and why that should be relevant to my car (which is not misaligned).

When Porsche created the Boxster, it was very much a parts bin special using lots of bits of 996. There are many reasons why they may have chosen 255 section rears that had nothing to do with performance, not the least of which is it allowed them to specify N-spec tyres that were already certified for the 996. I cannot think of any other reason why two cars as different in power and weight distribution as the Boxster and 996 Carrera should have exactly the same tyres.

If the 205/255 tyres are perfect for the Boxster, then why did Porsche change to 205/235 on the 987, and why do 16" (the original standard size, and probably where most of the development happend) wheeled boxsters use 205/225?

[Mr96er]

My apologies,

I didn’t mean to suggest the alignment had been adjusted for the tyre set up, merely that it’s prudent to check and mine was rather compromised.

not sure about the parts bin special assertion. My understanding was they were developed together though actually production of the 986 predates the 996 by at least a year. So who's parts bin could had really been robbed? Surely that would be the boxsters, right? 

As for many reasons why they changed tyre recommendations, I’m inclined to believe that Porsche would apply their design philosophy consistently and not stray far from their Teutonic principles of efficiency.

  

[Terryg]

I'm curious about the better balanced bit, mine is currently the best balanced car I have ever had and at a ridiculously cheap price. I just bought some excellent tyres for a very reasonable price also so I am highly sceptical on the value of either of these objectives, however if it is what you want to do just go for it. I would then suggest you join one of the drives run by many of the forum members so you can really evaluate the efficacy  of this change against standard cars 

[Pothole]

15 hours ago, ed80 said:

I am not sure why different sized tyres would cause the car to be misaligned so badly, and why that should be relevant to my car (which is not misaligned).

When Porsche created the Boxster, it was very much a parts bin special using lots of bits of 996. There are many reasons why they may have chosen 255 section rears that had nothing to do with performance, not the least of which is it allowed them to specify N-spec tyres that were already certified for the 996. I cannot think of any other reason why two cars as different in power and weight distribution as the Boxster and 996 Carrera should have exactly the same tyres.

If the 205/255 tyres are perfect for the Boxster, then why did Porsche change to 205/235 on the 987, and why do 16" (the original standard size, and probably where most of the development happend) wheeled boxsters use 205/225?

 

No, the 986 was not a parts bin special 'using lots of bits of the 996'. The 986 and 996 were developed in tandem as two variants of the same car on the same platform, one mid engine and one rear engine. Porsche could easily have had tyres specific to the 986 developed. Indeed it did. The 16-inch option for the base Boxsters involves 16-inch N spec tyres that are unique to the Boxster.

The 987 thing is also a red herring. It's a different car and it's perfectly reasonable to have different tyre sizes.

That said, I agree, it's a nonsense that exactly the same tyres are 'perfect' for both the 986 and 996 despite the very different weight distribution of the two cars and it highlights that decisions other than pure driving enjoyment come into the equation. The big tyres on the 986 in 17 and 18 inch spec are about fashion and idiot proofing and in that context there's not a huge amount of value in finessing the result to the nth degree so no need to develop tyres specific to 986 and 996 when one spec will do.

When the 996 went to 3.6 and 320hp, I guess they felt they needed to go even bigger to maintain the fashion look and huge safety margin, hence the 285s on that model.

 

[Pothole]

re the OP, in short, good idea. I'll definitely be going to 235 rears on my 986S when my current rears wear out.

As standard with 255 rears and 205 fronts, 986 Boxsters are chronically over tyred at the rear. It really dulls the chassis and makes for a marked and excessive understeer bias.

I ran 205 fronts and 235 rears on my Cayman S for three years 60k miles. The 235 section rear was plenty re grip for road driving but allowed a little access to adjustability and yaw. Did not turn the thing into a drift machine, you still had to be very, very deliberate if you wanted to get the rear moving. And that's with an addition 40-odd hp over a 986S.

People will inevitably bleat about how Porsche knows best and spent x amount of money on refining the set up. But it's ultimately b*ll*cks in my view. Perfecting the balance for driving pleasure is not the only consideration when Porsche was signing these cars off. Fashion for wide, low profile tyres that look 'sporty' is also in the mix, as is making the car as idiot proof as possible for the lowest common denominator of driver. It does not follow that dialling out a little of the significant quantity of understeer is going to turn the car into a death trap.

I'll repeat that. 205 fronts and 235 rears is not going to make a 986S 'tail happy'. It will still be understeer biased, just not as understeer biased as the factory 205 / 255 stagger. 

I think if you wanted these cars to drive really, really sweetly in road terms, you'd go for the factory 16-inch wheels with 205 fronts and 225 and that would be just fine for the 3.2 engine. But I don't think the 16s will fit over the Boxster S brakes. I had to use spacers on the front of my 987S to get the front wheels to clear the calipers, but my guess is that spacers aren't going to do it re 16s on a 986S.

[PaulQ]

We are taking small differences here. I found changing the fronts from 205 to 225 was more noticeable then going from 255 to 235 on the rears, but neither is exactly earth shattering. Might try some 205/225 in all season/winter. then we won't get any shyate weather.