Change gearing through tire size?

[Merlin07CS]

My new (to me) 987.1 Cayman S needs new shoes. I've got Carrera Sport 19" wheels and both current tire sizes are non-standard: 245/35/19 front and 275/30/19 rear. I'm considering going down to 18" OZ wheels (8.5"f, 10"r) for a lighter setup, while also doing an R-suspension conversion (20mm/0.79" lower). And while I'm at it, I have the opportunity to tweak the car's setup further with tire options. I'm not planning to track the car. Really just looking for a fast canyon-road setup that's still tolerable in town. 

Thinking of 245/35/18 front, 265/35/18 rear, with 5-7mm spacers, for a little more square tire setup. Obviously, this also means similar sidewall height to stock 19s but they're about an inch shorter. The upside is lighter weight and 3.8% shorter effective final drive (better gearing/acceleration/responsiveness?). The downside? Fuel economy on the freeway. Looks maybe, but I'm not overly vain. Drops the front end another 1/2" below the R, so may be getting close to impractical on speedbumps and the like?

 

Anyone else try this? Thoughts? Observations?

(Also considering just buying a second set of OZs for a taller 235/40/18 and 265/40/18 set of all-seasons to swap around as needed.) 

[MartinF6]

Personally, I'm not a fan of really low profile tyres.

 

For really fun road driving (as opposed to track days), I'd vote 17s not 18s. If you get some 987.2 gen 2 17s, the fronts wheels are a bit wider and will accept 225s. The rears are 235s, for a very nearly square setup. 987s feel miles more lively and engaging on the 17s.

 

The factory-spec 205 fronts on the 17s are a bit understeery. But with the 225s, the front end is really positive and overall there's more than enough grip for road driving, but with much more feedback. In my experience, the car feels quicker, too. Not quite sure why. The 17s are much lighter and will have less inertia, so that could contribute, but you wouldn't think enough to actually feel?

 

Anyway, I've piut 17s on three different 987 3.4s (one gen 1 and one gen 2), and the result is always the same. Much more fun on back roads.

 

I run my current 987.2 3.4 on 17s with Bilstein PSS9 Damptronic coilovers set to Cayman R ride height and also have a DSC Sport controller box so I can tweak the damping rates with a laptop. 

 

I've actually got two sets of 17s, one of each style from the gen 2 987. These are the 987.2 Cayman 17s.

 

 

 

Edited February 26 by MartinF6

[MartinF6]

And these are the 987.2 Boxster 17s.

 

Anyway, the 17s are a bit of a hard sell because most people want the bigger wheels for looks. For my money, 18s are the perfect 'look' on 987s, 19s are too big. But for me these cars drive so dramatically better on 17s, so I just have to live with the way the smaller wheels look. You can't see them when it matters most - when you're behind the wheel!

 

Honestly, these cars are such a thrill to drive on the smaller wheels. They feel dead behind the eyes on 18s and 19s by comparison. But I would recommend increasing the fronts to 225s from the factory 205s on the 17s. The 205s are lovely for steering feel, but they're just too understeery. You also lose quite a bit of braking performance on the 205s. The 225s do take away a tiny bit of steering feel, but make for a better overall compromise.

Edited February 26 by MartinF6

[Merlin07CS]

Hmm, this is a pretty interesting take. I've read at least one other person who swears by 17s, but as you imply, most people probably haven't tried it. So, obviously, no brake clearance problems on the S with 17s then? I would think the ride would be improved as well with extra sidewall and narrower width than the stock S setup. I'll have to look into this and see if I can source some 17s to try. Thanks for the out-of-the-box perspective.

[Merlin07CS]

9 hours ago, MartinF6 said:

And these are the 987.2 Boxster 17s.

 

Anyway, the 17s are a bit of a hard sell because most people want the bigger wheels for looks. For my money, 18s are the perfect 'look' on 987s, 19s are too big. But for me these cars drive so dramatically better on 17s, so I just have to live with the way the smaller wheels look. You can't see them when it matters most - when you're behind the wheel!

 

Honestly, these cars are such a thrill to drive on the smaller wheels. They feel dead behind the eyes on 18s and 19s by comparison. But I would recommend increasing the fronts to 225s from the factory 205s on the 17s. The 205s are lovely for steering feel, but they're just too understeery. You also lose quite a bit of braking performance on the 205s. The 225s do take away a tiny bit of steering feel, but make for a better overall compromise.

Do you happen to know the width of the wheels you're running, front and back? Thanks

[MartinF6]

Sorry, you will need some slim spacers for the front to clear the front calipers on a 3.4S. I have 6mm hubcentrics, I believe 5mm is sufficient. Rears are fine.

 

17s are 7J front, 8.5J rear. Note, that is for the Gen 2 17s. The Gen 1 17s are half an inch narrower on both axles and the fronts are a bit too narrow to take 225s, so I'd recommend the Gen 2 versions as shown in my images. They're cheap to buy as nobody wants them. I paid £150 for one set with decent tyres! Albeit they came with the 205 fronts.

 

I'd suggest picking up a set, then grabbing the 225 fronts (225/50 will maintain exactly the same rolling radius as the factory spec 205/55 tyres) and see what you think. As these things go, it's not a huge investment to give it a go.

 

Tyre choice is a little tricky to get the 225/50 fronts and 235/50 rears. I run Yokohama Advan V105, which is probably better than any of the N spec tyres for the 17 inch wheels. Not sure if you can get those over the pond.

Edited February 27 by MartinF6

[Merlin07CS]

10 hours ago, MartinF6 said:

Sorry, you will need some slim spacers for the front to clear the front calipers on a 3.4S. I have 6mm hubcentrics, I believe 5mm is sufficient. Rears are fine.

 

17s are 7J front, 8.5J rear. Note, that is for the Gen 2 17s. The Gen 1 17s are half an inch narrower on both axles and the fronts are a bit too narrow to take 225s, so I'd recommend the Gen 2 versions as shown in my images. They're cheap to buy as nobody wants them. I paid £150 for one set with decent tyres! Albeit they came with the 205 fronts.

 

I'd suggest picking up a set, then grabbing the 225 fronts (225/50 will maintain exactly the same rolling radius as the factory spec 205/55 tyres) and see what you think. As these things go, it's not a huge investment to give it a go.

 

Tyre choice is a little tricky to get the 225/50 fronts and 235/50 rears. I run Yokohama Advan V105, which is probably better than any of the N spec tyres for the 17 inch wheels. Not sure if you can get those over the pond.

Good to know about the spacers. I've found a set of 17x7, 17x8.5 Boxster/Cayman wheels for sale, so I may give it a try. Looks like I can either mount a set of 225/45 and 245/45 Pilot Sport 4S, or 225/50 and 235/50 or 245/50 Continental ExtremeContact all-season. Thinking I may still try the wider 18s for when I want more stick. If I decide one set can do it all maybe I'll sell the other. Thanks.

[MartinF6]

For road driving, the 225/235 amost square setup has plenty of stick assuming high performance summer tyres. Not sure how much you'd lose with the all-seasons.