3 auto-x last year, 2 so far this year out of a 6 event season. I am running on my street tires and up until this last event I was running on the original 34 year old shocks with 121,000mi on them. I'm running a consistent 10% behind the leaders, pretty good for a beginner in an antique car I think, but a lot farther back than it sounds in this kind of competition. My street tires may make it through the summer, maybe. They are definitely showing some stress.
Here we are having fun on the street tires, summer '22. That's our head instructor riding shotgun to help me out. I was having a tough day.
Not that I am any great driver - I have a long way to go, but I know my tires are a problem. The fast cars are running Hoosiers (racing slicks) I have ridden in some of the instructor's cars with them and what they can do on the right tires is mind bending.
My gearing is an issue as well; we're running 2nd gear courses and my RPMs are low so the car is not super responsive. The 3.2 liter engine makes peak torque at 4,800rpm and peak horsepower at 5,900. These 30-50mph courses are lucky to get me much over 4,000rpm. It can be tough running against modern turbo-charged cars with lots of electronics (ABS, traction control) and so on when my sleepy old car can't even get on the cam. I actually did a few runs early on leaving it in 1st gear and winding out! Fun, but probably not a great tactic in general. Could get expensive.
Ideally I would want to
Lower my gearing
Lower the car for better handling
Get better tires for better grip
And as it happens, we can do all 3 if we are mildly clever without affecting its day to day practicality.
First I purchased a used set of Porsche 944 rims. The 1986 and earlier 944 has wheels with the same 23mm offset as the stock Fuchs on the 911. The 911 came with optional 16" wheels which are what are on my car, but came standard with 15" wheels. The stock wheels were 6" wide up front and 7" wide in the back. Mine has 7" in front and 8" in the rear. Net net, 7" all around is not going to be an issue, and the 23mm offset is correct. The so-called "Phone dial" wheels are not popular options on a 911 (some people really hate the look) so they are also inexpensive. It's not a fashion show (ok, maybe a little bit...) and if I can place better with ugly wheels, well all the better. It was under $100 a wheel to get in the game. The most reasonable set of Fuchs I saw was over $1300 plus shipping and was 6" fronts and 7" rears. 6" is narrow for what we're trying to do which only makes it harder to find tires.
Normally the wheels and tires on a 911 are staggered, with the rears being wider in deference to the majority of the mass being back there (roughly 60%) but we're going to make due with a square setup and see how it goes.
(My car has 7" Fuchs up front and 8" in the back - a popular tweak of its time period. The 8" are originally from the Turbo. )
So, now we have 15x7 wheels all around. How do we address all 3 items in the list?
For #1 - we can lower our gearing by using tires with a smaller diameter. If the whole wheel assembly has to turn more to go the same distance, we have effectively reduced our gearing.
For #2, the same idea in #1 applies - a smaller wheel assembly will lower the car. If we reduce the diameter of the tire by 2", we will lower the car by 1".
For #3, the obvious one, we will find tires that accomplish #1 & #2 that are track/auto-x tires. These are tires that are optimized for auto-x events and track days. Not quite racing slicks, but close.
As an added bonus, smaller wheels and smaller tires should be a bit lighter as well.
The stock tires in back are 225/50-R16. That tire diameter is 24.9". To lower the car I needed to find the widest tire that will fit on a 7" rim, in a 15" size and that has a diameter as close to 23" as possible. (really 22.9 but...) A 225/45-R15 gets us there and will fit on a 7" wide rim. A 23" diameter wheel assembly. Boom.
The fastest cars run tend to run on Hoosier racing slicks. They are also very expensive (around $330 a tire). I opted to save some money and get something else. I was trying to find used slicks but not having much luck. There is still a lot of stuff on the car to refurbish on a 35 year old car, and then there is getting a real alignment & corner balancing, so I need to conserve funds for all that. Plus I have a lot to learn about driving first. So I grabbed a "square" set of Toyo Proxes R888R (square meaning all the same) to run on. These are a tick more than 1/2 the price of the Hoosiers. Fine for where I am as a driver, and they will accomplish the goals - which include saving my street tires.
Gearing
The circumference of the stock tire is 78.22591" (PI x diameter of 24.9". Yes, geometry class finally paid off!)
The circumference of the racing tires is 72.25657"
The difference is 5.96902" - almost 6" less distance for every rotation of the wheel.
How much less? 5.96902 / 78.225591 = 7.63% less.
And that is our gearing difference. :) Net net I am a bit closer to peak torque at speeds I will actually see on the track. Hopefully it will help a bit. Every little bit helps. Here is how it actually works out with my real gearing and tires (both sets). Fast courses with 40-50mph will still be where I am strongest.
The speedometer will be wrong, but I won't care on a track.
Tires are here and mounted!
All 4 fit in the back on the way to the garage, but only with no tires. With the tires they are a tiny bit too tall and rub the roof liner. I can get 3 in back and one in the passenger seat so I do not need to buy a roof rack. That's another $500 we don't have to spend. And yes, that window sticker is from a photo of Gus, our German Shepherd. My daughter had it made for me for good luck. <3
A great & simple diagram of what offset is. The 911 wheels have a 23mm positive offset.
Beneath the years of crud and brake dust you can just make out 15x7J (15" wheel, 7" wide) and "ET23.3" which is the offset. (23.3mm) "ET" is from the German, "Einpress Tiefe" or 'insertion depth'. #Therewillbeaquiz
And here is the Porsche part number, also cast into the wheel.
Despite all the research, I test fit the wheels on the car to look for any possible interference. They can rub things, or hit things and of course have to clear the brakes. In the old 911 the oil lines in the rear wheel well are a particular concern, wide rims or strange offsets can result in issues there. These look fine. This is looking down into the rear driver's side wheel well. (forwards is up)
Looking through the wheel to get a better view of clearance around the brake caliper. Looks good!
Mounted, balanced & all ready to go! I have to figure out the best way to stuff them into the car along with a small jack and electric impact gun (to remove them) and a torque wrench (to put them on) I scrubbed and power washed the wheels a few times to get as much crud off as I could.
Mid July Update
The first outing with the new tires was on the 15th. I re-built most of the front suspension (not strut inserts though) and got a basic alignment done to even things out a bit.
I packed up some tools, my little jack and all 4 wheels inside the car. It was tight, but it all fit.
I used the dog's seat cover on the passenger seat.
Swapping wheels in the pits. An electric impact gun and a paddle extension for the factory jack point makes taking them off 2 at a time pretty quick.
It sits a little funny but not too bad.
The course featured a 200ft dia skidpad as it's first big turn which gave me a good chance to get used to the car with all of the changes. It was also a pretty fast course with some long straightaways and big sweepers. With close to -1 deg of camber up front and about -1.5 in the rear it is ready to oversteer before it will understeer, or close to it with the narrow rear tires. I used stock tire pressures (29/34) and it was very smooth and predictable. I finished 5th in P02 by a few tenths of a second but i was much closer to the folks ahead of me this time. I was .206 seconds behind the 4th place finisher and .334 seconds behind the 3rd. So I think we're 'in the mix' now. My class, P02 is a neat mix of Boxters, Caymans and Carreras.
September 2023
I travelled up to Ayers MA for the PCA Zone-1 Auto-X. it was a lot of fun, a huge track (close to a mile?) on an old airfield with slaloms and other course features we just don't have the room for at our normal venues. It was a faster "momentum" track, so I was running 45-60MPH in second the whole way. The Toyos just melted on the first day, never really giving much traction or turn in. That was disappointing. I also developed an oil leak which caused a bit of smoke at the end of day 1. I had started the day with 4 DNFs in a row and I honestly did not know what I was doing wrong. The course organizers took a handful of the new kids having the same issue around slowly (following a Honda CRV) to hopefully figure out the error in our ways. This made all the difference for me and really exemplified the kind of sportsmanship the group brings to bear. The track was more than 2X larger than anything some of us were used to. I also reviewed my own video and found some mistakes at lunch. That $25 iPhone suction cup mount has really been helpful.
Initially I was going to head back home on Sunday due to my oil leak but realizing they were short staffed and my leaving would pull someone off of some other post. So I decided the right thing to do was come Sunday to work my shifts (all the racers work these events, a great practice!) and then a few more experienced air-cooled folks told me not to worry about my oil - that they all "sweat" a bit when they are hot. So I ran on day 2, but left my street tires on and kept an eye on my engine temp and oil leak(s). And I shaved off 4 seconds! My Continental street tires did great. Much better turn-in, more responsive. I was still one of the slowest cars there, but as it turns out I was the only car in my class so I trophied! Hey, a win is a win. ;) And the car did great, traveling 150 miles each way getting great gas mileage (close to 30mpg!) and wonderful to drive with the re-built front suspension and proper alignment.
Photo: Paul Cantrell (yes, I purchased a copy of this(!) although this is a screen shot here) He took some wonderful photos. This was from Day 1, on the Toyos.
And here is what they looked like at the end of the day! (melted)
I am still looking for used Hoosiers, even though they will drop me into Improved (where I will get curb stomped) the experience of learning how they respond will be beneficial. Also feeling how the car changes will help me drive better in general.
I finished up the 2023 season on my street tires and ended up 34th out of 101 cars. I am very happy about my progress from just 3 events last year and 4 this year.
Seat time is really key so I also attended a pair of car control clinics at Lime Rock put on by the SCDA. These pair wet skidpad drills (learning to drift basically) with runs on their auto-x course to work on smoothness, technique and lines. It's a ton of fun, if a little rough on your tires.
The skidpad is pretty tricky at first, and nearly everyone spends a lot of time spinning out.
The old 911 has a combination of great traction and not a lot of horsepower so I could not break the car loose with just the gas; I had to take an eliptical path, then upset the car with drop-throttle oversteer and once the car got upset I had to get on the gas (literally floor it) but not try to correct. Essentially the opposite of what you do on the track (don't upset it, and if it steps out you correct quickly). My first session I spun over and over, but my 2nd session I did pretty well. I can go about 1/4 of the way around in the wet. Hard to say because if I didn't spin, the other car on the skid pad did so I'd have to stop to give them room.
Photos below by Vincent Nardone / Petrolhead studios (purchased for non-commercial use)
On the auto-x course (above). I gave up one session to ride shotgun with an instuctor and he was so smooth it really clued me in to where I am trying to get to. Now I feel like I can see the goal, even if I can't accomplish it yet! I can put a turn or two together, they can put all the turns together lap after lap. It's going to take practice.
Wet skidpad - leaning nearly as much as we did in the dry (above)
Different angle - this is really throwing it in the wet, trying to kick out the rear. Compare to the below, cornering hard in the dry. Not much difference.
Here you can really see why you want to run negative camber - when the chassis rolls over and the suspension compresses, you want the wheels to stay straight up and down. You can see the front tire here is angled out a little (normal during a turn, this is what caster does) but not much. The rear tire looks almost perfectly vertical.
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