Traction Questions - Porsche 718 Forum
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post #1 of 6 Old 05-19-2019, 12:46 PM Thread Starter
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Traction Questions

I track six, two-day, events per year. Two days ago, I hit the leading end of an apex berm and ruined a tire. My intention was to replace all four tires after this event, so no problem there. I am going to get Michelin Sport 4S replacements. However there are two ways I can go on my 20 inch Porsche rims.

1. Stock sized tires (235/35/20 and 265/35/20) OR slightly oversized tires (245/35/20 and 285/35/20)

If i get the stock sizes, I can get N spec tires. If I buy the oversized tires, I can still get the 4S tires but they won't be N spec.

Questions: 1. Will slightly oversized tires make enough grip difference to give up the N spec rating?
2. Will slightly oversized tires mess with my traction control nannies? I know that my speedo will be slightly off.


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post #2 of 6 Old 05-20-2019, 12:26 PM
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I use 19" Michelin Pilot Sport 4S tires for track days and they are excellent. They are not N rated. They are the correct size for the car based on Porsche's specs.

Can't comment on the oversize tires as I have no experience with that.

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post #3 of 6 Old 05-20-2019, 02:51 PM
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I understand the idea behind "wider = more traction", but wouldn't Porsche engineers have put on wider tires as OEM if they were more appropriate or "better"?
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post #4 of 6 Old 05-20-2019, 03:48 PM
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Originally Posted by cbarra View Post
I understand the idea behind "wider = more traction", but wouldn't Porsche engineers have put on wider tires as OEM if they were more appropriate or "better"?
There's always tradeoffs. Wider may be better for traction but they they may need to beef up suspension, there might not be enough room, etc. The car is a "system". we tweak it for our own needs.... and risks.
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post #5 of 6 Old 05-20-2019, 09:39 PM
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I think with increasing tire size there are cost and road noise/comfort trade off that Porsche is addressing in non-GT cars.

I have the 4S on my car and I notice the car does slide a little (though remarkably balanced and controllable) so I think the tires could be slightly larger for my style of driving (mountain type roads) and when I wear them out I will go larger.

I know at least two people that have put GT4 spec Cup 2 tires on their 718 so Front: 245/35 ZR 20, Rear: 295/30 ZR 20. David Lemmens on here has 255/35/20 and 305/30/20s.

If you compare GT4 vs 718 GTS lightening lap times at VIR by Car and Driver with the above tires the GT4 has slightly better corner speed than the 718 which catches up a little on the straights. The GT4 is 2.7 sec faster which can be attributable to the larger and stickier track tires and a little bit more aero. I think the GTS would be a little faster with the GT4 wheels and tires.

So I think if you don't mind a little bit of extra road noise and adjusting for slight speedo changes then 245/35/20 and 285/35/20 is a good choice. Perhaps also check if the 285/30 is a better fit or go to the 295/30.

If you don't drive in the rain much I'd consider the Cup 2s or even the Nitto NT01 or similar which should be faster again.

If your car is also still under warranty then you may also want to check with your dealer that they will be Ok with you installing slightly larger tires. Though I've never heard of this being a problem within reason. After all the percentage increase is minimal.

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Last edited by don; 05-20-2019 at 09:50 PM.
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post #6 of 6 Old 05-28-2019, 12:45 PM
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i run 245 front and 275 rear nitto nt01 on 18" wheels for the track and have not had any problems.

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