Planet-9 Porsche Forum banner

61 - 73 of 73 Posts

·
Registered
Joined
·
51 Posts
Re: Nexen N FERA SUR4G

Interesting. I've been running RE71R's this season in the stock size (235/45 and 265/45) and been super happy. We made about 11 track days equivalent (counting days my wife and I both ran the car as 2x) and that included swapping the tyres on the rims after 5 or 6 days to even out the wear (both of our local tracks are anti-clockwise). I found 32 PSI to be a good sweet spot hot on both tyres.

Disadvantage is I called to order a new set and there are none to be had in this size right now. So I'm going to try out the Firehawk Indy 500 in 245/40 - 275/40 which will lower the car by .36" (it's a little over 1/2 shorter in diameter). I'm a little concerned about clearance with that but we'll see how they last and how they feel.

I drive my tyres to the track (The Ridge is about 100 miles down and then 100 back, and Pacific is a lot less than that), but do change them out for regular street driving. My spec for a tyre was consistent feel (no snapping and letting go, I want progressive sliding) and that I can drive home if it rains without being scared for my life. These have worked quite well for that. I'll report back after I've run the Firehawks at least one day.
I've been thinking about running the same RE71R set up you mention on my 2014 Cayman S. I like the idea of the 45 profile to help preserve factory tire diameter and ride height/ground clearance. Do you have any additional feedback on this set up?
Thanks!
 

·
Registered
Joined
·
832 Posts
Re: Nexen N FERA SUR4G

Please check out RE71R's in 255/35/18 f and 275/35/18 r, this setup is balanced. Some like 285/30/18 rear, but with shorter side walls, I do not have the room under the car for these as my ride is lowered 36mm by Ohlin coilovers and corner balancing, which could be an issure with a deep sump/skid plate.
 

·
Premium Member
Joined
·
5 Posts
Re: Nexen N FERA SUR4G

Please check out 255/35/18 f and 275/35/18 r, this setup is balanced. Some like 285/30/18 rear, but I do not have the room under the car for these as my ride is lowered 36mm by Ohlin coilovers and corner balancing with a deep sump/skid plate.
+1 on these sizes. Balanced is an accurate description.
 

·
Registered
Joined
·
156 Posts
Re: Nexen N FERA SUR4G

I've been thinking about running the same RE71R set up you mention on my 2014 Cayman S. I like the idea of the 45 profile to help preserve factory tire diameter and ride height/ground clearance. Do you have any additional feedback on this set up?
Thanks!
Beyond I really like it? Not really. I've got two sets of Apex wheels so I can run this setup, I tried the 245/40 275/40 setup on the Firehawk Indy500 and the car sit's noticeably lower, can't get my lift under the front any long so have to drive the front onto wood planks which is annoying. We did run through the RE71's in around 5 days of back to back running, I think after 3 we should of flipped sides and we could've gotten more. The firehawks btw are kind of bloody awful, the car oversteers on them no matter what I do to the pressures, but they are indestructible as far as I can tell. I'd like to see if any of the options wear longer while not being so much slower (The firehawks are 3-4 seconds a lap slower on a 2 minute circuit) but I'm not super stoked about running the car lower.
 

·
Registered
Joined
·
51 Posts
Re: Nexen N FERA SUR4G

Beyond I really like it? Not really. I've got two sets of Apex wheels so I can run this setup, I tried the 245/40 275/40 setup on the Firehawk Indy500 and the car sit's noticeably lower, can't get my lift under the front any long so have to drive the front onto wood planks which is annoying. We did run through the RE71's in around 5 days of back to back running, I think after 3 we should of flipped sides and we could've gotten more. The firehawks btw are kind of bloody awful, the car oversteers on them no matter what I do to the pressures, but they are indestructible as far as I can tell. I'd like to see if any of the options wear longer while not being so much slower (The firehawks are 3-4 seconds a lap slower on a 2 minute circuit) but I'm not super stoked about running the car lower.
Thanks for the feedback. I've been "finishing" a set of Michelin PSS 235/265 40 R18 on my 2014 Cayman S, and I hate the reduced ground clearance. I think I've made up my mind and will replace them with the RE71 in a 235/265 45 R18 like you have. Thanks again!

BTW, If I were going to run 245/275 40 R18, I'd run the Hankook RS4. I've done track days on other cars with them, and I really like the performance and wear. If they made them in a 235/265 45 R18, that is what I would definitely buy.
 

·
Registered
Joined
·
25 Posts
Re: Nexen N FERA SUR4G

Please check out RE71R's in 255/35/18 f and 275/35/18 r, this setup is balanced. Some like 285/30/18 rear, but with shorter side walls, I do not have the room under the car for these as my ride is lowered 36mm by Ohlin coilovers and corner balancing, which could be an issure with a deep sump/skid plate.
For a 981 I cannot recommend a 255/35 and 275/35 in -R18. They are a full 1.5" shorter than stock. The preferred setup would be a 245/45 and 265/45 -R18 for near stock heights (limited tire selection), 245/40 and 275/40 -R18 for better tire selection, or 255/35 and 275/35 in -R19. I just ran the RE-17R 255/275 -R19 setup this weekend and it was wonderful! I cannot put my car on the two-post lift with the track wheels installed now so the reduced height is real!
 

·
Registered
Joined
·
832 Posts
Re: Nexen N FERA SUR4G

Ride height is a personal preference, the car works with either 18's or 19's just fine. The question is weight transfer, tire/wheel weight, tire contact patch and gear ratio. The bigger diameter the tire, the shape of the tire patch that touches the road is different. The higher the center of gravity, height above ground, the more significant the weight transfer, both across the car and forward and aft. Taller sidewalls do give you a more comfortable ride as the sidewalls do have spring rates, but is that what the track business is about? I do not recommend bottoming out your car either. That is why stiffer spring rates/coilover shocks are used to control the ride height. The 18's give a better acceleration out of corners as well. Tire/wheel wt is significant, changing the wheel rate between 18's and 19's, so with more wt, suspension has to work harder to keep the tire patch in contact with the road. Lastly, the 35 sidewall flex slightly less than the taller 40 or 45 tires which means better turnin responsiveness. The GT4 Club Sport comes with 18's. I race against one who has 5 sets of 18's, mostly Hoosiers. I have three sets of wheels/tires, all 18's Titan 7 TS-5 with Hoosiers, 255/35/18 f & 275/35/18 r, Signature SV104 with RE71R's same size and OEM with Michelin PS4's same size.

- 18's are preferred because;
less weight transferred due to lower ride height
less wheel/tire weight which effects the wheel rate/spring rate/shock valving
better gear ratio to accelerate out of corners
less expensive

So, 18 inch wheels usually lowers the ride height which is about our track perspectives
 

·
Registered
Joined
·
25 Posts
Ride height is a personal preference, the car works with either just fine.
Ride height adjusted by tire diameter should have no impact on the suspension geometry. This is why the car works with either. There comes a point where the chassis is simply too low for bump clearance, though. I can't say if a 25" tire puts the chassis too low but, as I said, my 26" tires now puts the chassis too low to put on my 2-post lift. At that chassis height on my S2000 I had issues on really bumpy tracks. Just to be clear, ride height adjusted by stack height, spring rate, spring perches, etc does change suspension geometry and that is not what we're talking about here.

The question is weight transfer, tire patch sq in and gear ratio. The bigger the wheel, the less tire patch is touching the road....
The contact patch of a tire is not decreased with a bigger "wheel", which I'm sure you meant a larger diameter tire. The shape of the contact patch changes in width and depth, but not area.

To overly simplify the effect of the contact patch when increasing tire diameter:

* The contact patch increases in width and becomes shallower in depth
* The slip angle becomes peakier
* The tire cools more efficiently

I suggest you try to find a copy of The Racing & High-Performance Tire: Using Tires to Tune for Grip & Balance by Paul Haney. It is a fantastic read. I'm going to dig up my copy and read through it again...
 

·
Registered
Joined
·
832 Posts
That sounds like a great read. Ordered it from Amazon $70.00. Have any of the readers used tire softeners like Hot Lap II? The tire text book by Haney covers this subject. I was not aware such products existed.
 

·
Registered
Joined
·
156 Posts
Yup Ride Height is a personal preference, most things posted here are, Imstimpy and I have simply stated that it's our preference not to run that much lower on 18" wheels, and instead go with stock height.

I've found two issues, one is that it's harder to lift my car now (my big floor jack and lift don't clear with the lower height tyres especially now that I have an x73 suspension on) and that I hate worrying about scraping the nose when I drive to and from the track. With the stock sized 18" I get great performance and don't have to worry, so I'll go that route.
 

·
Premium Member
Joined
·
973 Posts
agree with ground clearance and lift problem
have GT3 18" with 255/285 and it's on the ground being 1.5" lower than stock 20's
but $ saving rules for me
wheels 71RE's mount balance TPMS nitrogen and delivery was $3100
don't think you do that for less than 5K with 20's
going to 255/295 or 305 for next year
have to check availability
 

·
Registered
Joined
·
832 Posts
Unfortunately Bridgestone 18's in RE71R's top out at 285/30. So you would have to go to another tire to get a wider footprint in the rear. Not sure why they stopped at 285/30/18's. I would like to try 295/35/18's if they were available from Bridgestone/RE71R.
 

·
Registered
Joined
·
832 Posts
Ride height adjusted by tire diameter should have no impact on the suspension geometry. This is why the car works with either. There comes a point where the chassis is simply too low for bump clearance, though. I can't say if a 25" tire puts the chassis too low but, as I said, my 26" tires now puts the chassis too low to put on my 2-post lift. At that chassis height on my S2000 I had issues on really bumpy tracks. Just to be clear, ride height adjusted by stack height, spring rate, spring perches, etc does change suspension geometry and that is not what we're talking about here.


The contact patch of a tire is not decreased with a bigger "wheel", which I'm sure you meant a larger diameter tire. The shape of the contact patch changes in width and depth, but not area.

To overly simplify the effect of the contact patch when increasing tire diameter:

  • The contact patch increases in width and becomes shallower in depth
  • The slip angle becomes peakier
  • The tire cools more efficiently
I suggest you try to find a copy of The Racing & High-Performance Tire: Using Tires to Tune for Grip & Balance by Paul Haney. It is a fantastic read. I'm going to dig up my copy and read through it again...
imstimpy- read the book you suggested, well center of gravity is cited in many calculations in your book. Reducing the tire diameter by using 18" wheels/tires, as you pointed out lowers the car and more importantly, the center of gravity. Many different equations all revolve around that important CG number. So, for many readers, who do not have garage racks that need wooden ramps to allow the car over the cross bars, well that is the owners decision. It does not change the fundamental calculations of weight transfer, which is described on pg 211 between three Cup cars ride height and wt transfer. The cited example shows CG of 16, 15.5 and 15. and depending on the G forces the wt transfer is very significant. So a quote from pg 211, "So the weight transfer increases with the weight of the vehicle and the CG height and it decreases with a wider track." There are many other examples of where CG is cited as again pg 216 "A lower CG generated less weight transfer resulting in more equal load on inside and outside tires, and that improved overall grip." So, there appears to be many factors supporting a smaller tire, as evidenced by the GT4 Club Sport usage of 18's. Its not because of the tire cost either.
I use a 3 ton floor jack on the front jack pad to change my wheels after each event. I only change one wheel at a time, but both can be changed by that jack position.
I have not had my front lip hit any road objects, sidewalks, ramps, or bumps. Maybe its my 400 lbs/in f spring rate that keeps the nose safe. But, I am very careful in parking stalls where there are concrete wheel stoppers.
 
61 - 73 of 73 Posts
Top