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245mm on the front would be better. Maybe some 255's will fit.
Steering at parallel parking speeds might be a little heavier but it's worth it.

If you need a little more fender lip to tire clearance while at full lock you can roll the fender lips up a little with a wood base ball bat. There are posts on how to do that.
You use the bat like a prybar against the inner fender well while rotating the bat as you pull outwards on the handle of the bat while rolling it along the fender lip edge to bend it upwards.
The paint could crack while doing it and carefully heating the fender lip with a heat gun should soften the paint enough to keep it from cracking.
Put a few layers of heavy tape like duct tape or gaffer's tape on the fender lip to protect the paint while bending it up a little with the rotating baseball bat.

It's gonna leave scratch marks around the baseball bat. Walmart has nice low cost wood ones.
Old 09-12-2018, 04:29 PM
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I'm running 255/315 now and have for years. I don't like the heavy feel and tramming on the street so I want to try narrower tires. My tires are coming up on 5 years old so if I change the fronts, I'll need to change the rears too, otherwise I'd just change the fronts and see how it works.

I've never driven a Porsche 935DP or Lamborghini Countach but they ran 205 (or 225) fronts and 345 rears so it's not too odd. And I never read about them being terribly understeering cars. Of course I would adjust my sway bars after tire installation to get a proper test of the new sizes.

Another thought is trying to put the 225 and 275 tires on the 9 and 11.5 wide wheels as they are and see how they work even though both would on wheels a 1/2 inch over what's allowed by the tire manufacturer.
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Old 09-13-2018, 07:03 AM
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I run 215/50/15's on 8" rims (measures the same as a 225) and 335/35/15's on 13" rims on my 935DP. Tires are Michelin TB15. Fairly aggressive on the street, but no where near the limit, works fine. I also ran the 215's on a 9" rim with no issues. The front shocks are re-valved Bilsteins by SmartRacing which made a much better progressive shock. You could also play with the front/rear sway bar settings to dial out some of the under steer if you experienced it.
On our '75 iroc race car I used 245 fronts and either 295 or 315 rear Hoosiers.
I found a 1" wider rim lowers the tire diameter by 1/2".
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Old 09-13-2018, 09:06 AM
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If this fella doesn't feel over tired nobody does, ha!




It's gonna take more than one of our custom mufflers to break those tires loose!

I've always ran the widest tires I could on any car I've owned, simply because I like the way it looks. Yes if you put skinny tires on a car it will be more nimble, it will turn quicker and accelerate quicker. I simply don't care, the cool factor trumps all! Sluggish? Turn up the boost!

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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8

Last edited by RarlyL8; 09-13-2018 at 04:48 PM..
Old 09-13-2018, 04:42 PM
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Those front rims are wider than the tires.
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Old 09-13-2018, 07:08 PM
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I was running 235/40/17 on the front, and 275/40/17 on the rear of my car, the previous owner raced with these sizes and did very well. I've recently switched to 255/18 & 315/18 R888 and lover the look of the width and sticks great on track, but the front is pretty twitchy on the road over every little bump & change.

FYI a well respected instructor at my local PCA & BMW groups had a super hairy 930 track car, he said 235 / 295 section width was best handling in his opinion.
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1975 Carrera / 965 tribute w/ 1989 3.3 turbo 8.5:1, K27 7200, 964 cams, euro CIS, TEC1 dual plug, rarlyL8 headers & outlaw pipe. 915/68 trans, kevlar clutch and lightweight pressure plate.
Old 09-14-2018, 04:07 AM
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I just installed 255/40-17 and 315/35-17 last night. I only had time for a couple mile drive and I'm pleasantly surprised at the feel. I really didn't notice a huge change.
I was worried the steering would feel heavy and the car would chase the ruts. So far so good.
I did go with the Nitto NT05 street tires, so maybe that helps the ride quality.
I'll report back after the drive to Rennsport.
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Old 09-14-2018, 06:01 AM
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Car won't chase ruts unless the alignment is off, such as track specs instead of street specs. I keep my rears aligned totally flat to the ground, fronts stock street spec. Tires wear even, track straight and handle very well and predictable.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 09-14-2018, 09:13 AM
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So my -1.6 camber is making my front end twitchy on the street?
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1975 Carrera / 965 tribute w/ 1989 3.3 turbo 8.5:1, K27 7200, 964 cams, euro CIS, TEC1 dual plug, rarlyL8 headers & outlaw pipe. 915/68 trans, kevlar clutch and lightweight pressure plate.
Old 09-14-2018, 09:30 AM
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Mine is -1.5 camber, 1/8" toe out front, 0/0 rear. Mine doesn't feel twitchy.
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Old 09-14-2018, 10:35 AM
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Quote:
Originally Posted by RarlyL8 View Post
Car won't chase ruts unless the alignment is off, such as track specs instead of street specs. I keep my rears aligned totally flat to the ground, fronts stock street spec. Tires wear even, track straight and handle very well and predictable.
Thanks, thatís my next step after tires.

At this point changing tires is as much about trying something different as it is about fixing something. The slightly stretched look is growing on me, so Iíll try 225/275 on my current 9/11.5 wheels.
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Old 09-14-2018, 11:05 AM
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My 275 rears looked pretty stretched already on 11" wheels.
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Old 09-14-2018, 01:30 PM
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Quote:
Originally Posted by David View Post
Thanks, thatís my next step after tires.
At this point changing tires is as much about trying something different as it is about fixing something. The slightly stretched look is growing on me, so Iíll try 225/275 on my current 9/11.5 wheels.
Tire construction & compound will of course determine the final net effect, but maximizing the wheel width to a tire (max stretch) inherently stiffens the side wall and quickens the responsiveness of the tire. Beyond track events, I find this makes a noticeable difference when running canyons & mountain roads and when making high speed corrections on an on/off-ramp / freeway interchange.



Old 09-14-2018, 01:31 PM
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Quote:
Originally Posted by Noah930 View Post
My 275 rears looked pretty stretched already on 11" wheels.
Could you post a pic?
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Old 09-15-2018, 04:45 AM
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Agreed. Here’s 11” with 275
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Old 09-15-2018, 06:40 AM
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Old 09-15-2018, 06:40 AM
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Old 09-15-2018, 06:44 AM
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Matching the actual tire width to the wheel width has a really big impact on the visual aspect as well as the handling. All tire brands are not created equally. There seems to be no adherence to any QC when it comes to calibrating whatever measuring device they use to determine the advertised size of tires. The Pirelli 345/35-15 I had on the Red Rocket were a full 3/4" more narrow than the corresponding 345/35-15 Yokohamas. The 315/35-17 tires I settled on for the Gray Slant run large. They fully filled out the outer 13.25" bead/bead custom wheel making them look larger and also handle better with less sidewall movement. They feel very stable and predictable.

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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 09-15-2018, 06:52 AM
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So what fat tires (315/35/17) are people using. I was looking at the Goodyear F1's. But they seem to be almost twice as expensive as the alternatives.
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Old 09-15-2018, 08:09 AM
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This is the Nitto 315 fit. I want to get a slightly thinner spacer and pull the wheel in flush.




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Old 09-15-2018, 08:53 AM
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