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Prior owner installed 20" 997T/991.1 wheels. Bought the car about a month ago, 245/35/20's and 295/30/20's (Michelin SS K1's) are old (2014's), bald and I blew one out yesterday at my first autocross event. So, need new tires, at least.
Whole thing has me thinking though, should I move down to 19's or even 18's for better performance, both on-road and autocross? I love the look of the 20's but am not sold on them for a 997. I have read arguments where the 997's suspension was obviously designed for 18's and 19's and running 20's doesn't make sense but I'm not an engineer so I have no idea.
A set of forged 19s will do it all well. Less tire sidewall flex than you'll have with 18s and they look better than 20s. The same wheel and tire pairing in a 19 will also be lighter than that in a 20. Offsets on your current rear wheels alps look wrong with too much poke. Is your car a NB that has WB wheels on it?
We (my son and I) are running 19"s with Bridgestone RE 71R's all around (305's on back) on our 2005 997.1 Carrera S. This is a great all around tire and a lot of people run them as their go to tire.
A set of forged 19s will do it all well. Less tire sidewall flex than you'll have with 18s and they look better than 20s. The same wheel and tire pairing in a 19 will also be lighter than that in a 20. Offsets on your current rear wheels alps look wrong with too much poke. Is your car a NB that has WB wheels on it?
Yes, it's a NB. The current 20's which the PO put on the car are the 991 Sport Design II's which are 8.5/ET51 and 11.0/ET70. They definitely fill out the wells, and although I'm usually not a big fan of newer-generation wheels on older cars or 20's on a 997, I have to admit they look really good on the car in person - not too much poke.
That said, I am officially addicted to autocross after one day and am now interested in setting the car up as best as possible for it, while still using it as a DD (not many miles). Besides the weight savings of going down to 19's, I'm wondering if the larger tire diameter of my current setup (almost an inch taller than what came on the car) is hampering acceleration time - figuring larger diameter takes longer to accelerate? Like I said, clearly not an engineer.
We (my son and I) are running 19"s with Bridgestone RE 71R's all around (305's on back) on our 2005 997.1 Carrera S. This is a great all around tire and a lot of people run them as their go to tire.
So funny you say that. There was a guy at the event with an '06 997-S with those tires on 19" OZ wheels and he was absolutely crushing it, basically keeping up with all the modern cars including the caymans and 911's. He swore by the Bridgestones and after doing some research yesterday, I now understand why.
What are the specs - width/offset - on the 19's you are running and do you daily drive the tires as well or are they dedicated track tires?
a lower center of gravity will help as well. there is a lot of info out there on Rennlist. you can search very easily by using google. like this "search term site:rennlist.com". Where "search term" is whatever you want to find out about.
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@Jasper234 - I am running 19 X 8 1/2 ET50 on fronts with RE71R 235/35 -19 and 19 x 11 ET 55 on rear with 302/30R-19 (Current wheels are fifteen52 Formula GT in Asphalt black). The RE71R's are wear rated 200 so you get a great overall street/track performance tire IMO. There is a little bit of a "tire sing" at speed, but my exhaust drowns out that noise
It is not a daily driver... both a street and occasional AX & Big Track car.
Last edited by Gmanscott; 09-30-2019 at 11:30 AM.
Reason: addl info
Thanks Gary, very helpful. I am beginning to feel like I may have to take the plunge and buy a dedicated set of autocross wheels/tires with the bridgestones sounding like a bit much for a DD.
Maybe just get some very economical/well behaved street tires for the 20's and then some 19's with the bridgestones. Will just arrive early to track and switch them out.
They weren't kidding when they said this would be both addicting and expensive! A little bit hesitant to venture onto the full-length track as I understand that to be exponentially more expensive than autocross.
a lower center of gravity will help as well. there is a lot of info out there on Rennlist. you can search very easily by using google. like this "search term site:rennlist.com". Where "search term" is whatever you want to find out about.
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Well duh, thanks Fined. Did as you suggested and came across the dedicated "Autocross" forum under "Performance and Competition Discussion Areas". I knew there had to be a dedicated forum on the subject.
A lot of AX'ers do just what you wrote. Also, do not be intimidated by Big Track experience for you and your car. A lot of PCA regions have DE (Driver's education) days at local tracks as well as well as other organizers. It is a drive at your own pace and you are grouped with others of similar capability. Go to www.motorsportreg.com and you can look at events in your area. Once you get a taste of what your car can do in the hands of an experienced driver, you will fully appreciate the Porsche experience better. Again, brakes and tires are the expense, but the trade off is well worth it! My son (19) and I are headed to Spring Mountain Motorsports Track in Pahrump Nevada in mid October for 3 days of track fun. He has been AX'ing for 3 years and won his class (CC12) last year and is leading again this year. Needless to say... he kicks my *** on lap times, but we are both having a great time!
Here is clip from last year at Spring Mountain... TURN THE SOUND UP
What class are you planning on competing in? Also, do you just want to have fun or are you looking to be competitive at a certain level (local, regional, national)? I would look at those things first. I haven't looked into auto crossing 911s but there is often a preferred setup based on tire availability and class rules and that will end up driving the tire selection. If you're just out to have fun then this matters less.
Besides the weight savings of going down to 19's, I'm wondering if the larger tire diameter of my current setup (almost an inch taller than what came on the car) is hampering acceleration time - figuring larger diameter takes longer to accelerate? Like I said, clearly not an engineer.
If the total tire diameter / rolling circumference is larger with this 20" setup than it would be with a 19" setup, for something having the same weight, you're correct. The larger diameter setup will be slower to accelerate and slower to stop because of angular momentum. If it's heavier too, that makes it even worse. You won't believe how much more nimble going to a lighter setup will make the handling and steering of your car and the more unsprung weight you can get the better. Forged wheels with PCCB brakes is amazing.
I think every application is different but I believe if you keep the width constant and only alter diameter the 18s will be faster in this case due to lower angular momentum.
A lot of AX'ers do just what you wrote. Also, do not be intimidated by Big Track experience for you and your car. A lot of PCA regions have DE (Driver's education) days at local tracks as well as well as other organizers. It is a drive at your own pace and you are grouped with others of similar capability. Go to www.motorsportreg.com and you can look at events in your area. Once you get a taste of what your car can do in the hands of an experienced driver, you will fully appreciate the Porsche experience better. Again, brakes and tires are the expense, but the trade off is well worth it! My son (19) and I are headed to Spring Mountain Motorsports Track in Pahrump Nevada in mid October for 3 days of track fun. He has been AX'ing for 3 years and won his class (CC12) last year and is leading again this year. Needless to say... he kicks my *** on lap times, but we are both having a great time!
Here is clip from last year at Spring Mountain... TURN THE SOUND UP
Gary that is too awesome and it is amazing how similar a situation I find myself in right now. I have a 16 year-old who is chomping at the bit to get going and a 12 year-old behind him. Sounds like you are having an amazing time with your son and I am hopefully looking forward to something similar. There is a track day coming up over here which I will be sure to go to as well as another few autocross events as well. Cannot wait.
09-29-2019, 12:59 PM
18's, 19's or 20's for Autocross?
