18" or 19" rims on GT4
09-21-2015, 02:16 PM
#17
A reduction in wheel diameter does not lead to a reduction in tire rolling radius if the tire profile is changed correctly. I have 20 inch S wheels with summer tires on my base 991 and 19 inch Tire Rack wheels with winter tires. The 19 winter tires are higher profile and give the same ride height and effective gearing as the 20s. They are also less vulnerable to winter pothole damage. A similar situation applies for base 991's ordered with either standard base 19 or optional S 20 inch wheels, same ride height, same effective gear ratio.
IIRC we also have to get one inch narrower wheels up front in order to run 19-inch wheels? Or was it in the rear?
09-21-2015, 02:24 PM
#18
For autocross I'd be tempted to try 255-35-18 and 295-30-18. Front is .5" shorter that rear vs .2" shorter stock, shouldn't confuse ABS or TC much. It would drop the car by nearly 1" and drop 2nd gear by 5 mph- a significantly improvement for AX.
09-22-2015, 06:49 PM
#19
Rennlist Member
If you want to keep a large OD it seems you might as well stick with 20s- Hoosier will be bringing 235s, 265s, 295s and 315s next year.
For autocross I'd be tempted to try 255-35-18 and 295-30-18. Front is .5" shorter that rear vs .2" shorter stock, shouldn't confuse ABS or TC much. It would drop the car by nearly 1" and drop 2nd gear by 5 mph- a significantly improvement for AX.
For autocross I'd be tempted to try 255-35-18 and 295-30-18. Front is .5" shorter that rear vs .2" shorter stock, shouldn't confuse ABS or TC much. It would drop the car by nearly 1" and drop 2nd gear by 5 mph- a significantly improvement for AX.
I simply bugged Nitto (along with other rennlisters) enough, and they listened. Hoosier and Nitto will make the size if enough people ask.
Now, tons of 997 guys enjoy the CORRECT rear tire size, which is 305-35-18. I would urge the GT4 guys to request the correct 18" downsized tires. 19" is fine and easier to clear brakes, but with the correct wheel, or more compact caliper, 18" is more ideal for long term track use, weight, and simply looks more appropriate for motorsport use. GT4 cup will come with 18" wheels.
09-22-2015, 07:14 PM
#20
18s do allow more access to slicks- nice assuming you're willing to chuck the warranty.
09-22-2015, 07:26 PM
#21
Burning Brakes
18" tires also tend to be more affordable. Yes, I know owners of 6-figure cars shouldn't complain about running costs, but it's still preferable to minimize them wherever possible.
10-02-2015, 02:02 AM
#23
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Here's the deal guys, 18's can fit, but they require specific offsets and widths.
For example, Finspeed's F14 wheel will fit. He has already confirmed the 18" front wheel clears the 991 GT3 brakes, so they will clear ours.
The rear will fit easily, but requires a 18x10.5" wheel, ET44, if you want to avoid using alot of rear camber to clear the toe-link. The problem is tire sizes, there are currently not any 18" tires with more ideal sizes, which need to be:
245-45-18 and 295-40-18 (or 285-40-18).....these will keep rolling diameters the similar and keep your TC/PSM happy if you keep it on.
I would start asking Nitto and/or Hoosier to make these sizes. It will likely take a year or so, but would be well worth the effort.
For anybody who thinks its too tall of a tire, or the "sidewall is too big"...that's total hogwash. I run 245-40-18 and 275-40-18's on my 987, and they are perfect. I never get any "ice mode" or ABS problems, compared to the fairly regular complaints of those running the 275-35-18 rear. Those sizes provide a much better load rating as well.
285/295-40-18 on the GT4 would be great.
For example, Finspeed's F14 wheel will fit. He has already confirmed the 18" front wheel clears the 991 GT3 brakes, so they will clear ours.
The rear will fit easily, but requires a 18x10.5" wheel, ET44, if you want to avoid using alot of rear camber to clear the toe-link. The problem is tire sizes, there are currently not any 18" tires with more ideal sizes, which need to be:
245-45-18 and 295-40-18 (or 285-40-18).....these will keep rolling diameters the similar and keep your TC/PSM happy if you keep it on.
I would start asking Nitto and/or Hoosier to make these sizes. It will likely take a year or so, but would be well worth the effort.
For anybody who thinks its too tall of a tire, or the "sidewall is too big"...that's total hogwash. I run 245-40-18 and 275-40-18's on my 987, and they are perfect. I never get any "ice mode" or ABS problems, compared to the fairly regular complaints of those running the 275-35-18 rear. Those sizes provide a much better load rating as well.
285/295-40-18 on the GT4 would be great.
If you make a post, I'm sure more Rennlisters will join in the cause
10-02-2015, 02:52 AM
#24
Pro
Thread Starter
For track use I use 295/30/18 or 295/35/18 in combination with the front 235/40/18 and never had any problems on 987.2. If anything its better with the lower dia and gives more acceleration due to the lower effective gearing.
Can anyone trial fit these? I cant get any yet for a test fit just yet (no stock in my state).
Yokohama Advan Racing TCIII. Designed to fit 997 GT3RS.
Rear:
18x11.0J / 130 / 5 / 30mm offset.
Front:
18x8.5J / 130 / 5 / 35mm or 51mm offset.
Yokohama Advan Racing TCIII have the biggest barrel possible to go over large calipers like on 991.
Can anyone trial fit these? I cant get any yet for a test fit just yet (no stock in my state).
Yokohama Advan Racing TCIII. Designed to fit 997 GT3RS.
Rear:
18x11.0J / 130 / 5 / 30mm offset.
Front:
18x8.5J / 130 / 5 / 35mm or 51mm offset.
Yokohama Advan Racing TCIII have the biggest barrel possible to go over large calipers like on 991.
10-02-2015, 01:19 PM
#26
Drifting
I'm certain that by next spring we will have many options, 
10-04-2015, 11:57 PM
#27
Pro
Thread Starter
Can get Yokohama Advan Racing TCIII to fit the rear now so tried the Yokohama Advan Racing TCIII on the front but they just scrape on the calipers, so looks like 18" is a total bust now. Dont hold any hope for any 18" to fit now.
10-05-2015, 03:21 AM
#28
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I didn't think rears would be a problem but the front was what I suspect... I have a set of Volks TE37 I want to try but I have a feeling it may scrap the calipers as well
10-05-2015, 03:31 AM
#29
Pro
Thread Starter
Rear: We had not finalized the correct offset and it looks like it needs to be a 10" rim ideally.
Anyway, no point as the fronts scraped.
I read how the cup cars have smaller monoblock calipers so as to fit 18".
Anyway, no point as the fronts scraped.
I read how the cup cars have smaller monoblock calipers so as to fit 18".
10-05-2015, 03:48 AM
#30
I know Forgeline 19s (barely) fit over the 410 mm PCCBs. Calipers are effectively the same as the 380 mm cast iron. The math suggests the right barrel 18s should have .1" more clearance. If we know the barrel ID of the TCIIIs we should be able to compare and confirm.