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That is my end goal, I want to run 17x9 rims all around with either 245/40/17 or 255/40/17 tires. I am thinking of using the Direzza ZII because they are a little more precise and require more precision in input than the rivals, so they should be a better tire to help learn on as they will reward good driving techniques and not reward the bad.
The problem is finding a set of four 17x9 rims that aren't custom and thus expensive, or needing to find two pair of rear wheels from a 911. This is why I was leaning towards another pair of 16x8 and 225 tires for now.
You know, i tried stuffing the 17x9 10 spoke 996 targa rims w/ 255's i have on the front of my s2 and it wouldn't clear the outer fender with the spacer on that you have to run to clear the hub with newer rims. 16x8 w/ 245's should work though. Can't you mount 245's on an 8?
Re-11's would be another good tire choice but i'm not sure if they have that size...
You know, i tried stuffing the 17x9 10 spoke 996 targa rims w/ 255's i have on the front of my s2 and it wouldn't clear the outer fender with the spacer on that you have to run to clear the hub with newer rims. 16x8 w/ 245's should work though. Can't you mount 245's on an 8?
Re-11's would be another good tire choice but i'm not sure if they have that size...
Interesting, I thought the 17x9 and 255 would clear, since I have heard a 275 on a 9 would fit....
The RE-11 is the only street tire in a 245/45/16 though will fit on an 8" rim, there are a bunch of 225/50/16 tires though. Which is kind of a bummer because I like the clubsport/d90 rims on the S2. I'd like to stick with street tires for the moment, from the learning to push the car standpoint.
Hmm ill have to try it again, i didn't set the car down on the wheel i just mounted them while it was in the air and it looked like it would hit. I could be wrong. In fact i hope i am, i really want to go 255 all around.
I have 225/45-17's on front and and 255/40-17's on the rear, on 993 Cup II wheels. I recently put on RE-11A tires, based on previous (excellent) AutoX and DE experience with the tires my Cayman.
I'll be trying them out at a DE next weekend, and will see how things go for real.
I had 16x8 968 rims with 245 Rs on the rear. No problem.
In '03 I had 17x8.5 Boxster Crabs (base '00? Boxster rims) with 255 pilot sports on the rear of my first S2. They rubbed the left quarter. I tried to roll the fender, but ended up grinding the inner lip. I think I finally ground off enough about four days before the car was stolen.
So I got a great deal on some 964 Cup 1 wheels (replicas) in 7.5x17 F & 9x17 R so I went ahead and picked them up. If I find a pair of matching 9x17 I'll grab those later but I plan on using these as track wheels for the moment. So now the question is which tires to put on it....
I bought a 19mm M030 adjustable rear sway bar to dial out the understeer that is likely to come from the staggered setup. Since the current stock setup has more understeer than I like (stock 26.8F/16R).
The tires I am looking at are BFG Rival, Dunlop Direzza ZII, Hankook R-S3 in 225/45/17 Front and either 245/40/17 or 255/40/17 Rear. What choice would you make for the mixed autocross and weekend warrior role?
I am leaning towards 225/245 on Rivals after a chat with a rep from TireRack...
I am not a fan of over-tiring rims especially with a macphereson strut suspension because it is very likely that the tire will wear out quickly due to the soft sidewall rolling under.
I have driven on a 225/45/17 on a 7.5" wide rim and it works pretty well, so I am kinda stuck there for the front until I get another pair of 9x17 for the front.
Does the 225/255 balance as well as the 225/245? From TireRack the Rivals measure 8.5" tread wicth for the 225, 9.1" for the 245 and 9.5" for the 255.
So it has been a while because I was busy with taking care of some engine upkeep and also replacing all my old rubber bushings for new Powerflex Black Series bushings. Once I got all that done I headed down to another SCCA autocross in May and now I figured I should update this since I was quite happy with the car, collected some data to support my not-so-perfectly-calibrated butt, and before I go changing things (I have stiffer springs, torsion bars and camber plates en route ).
The Powerflex bushing install was pretty straightforward thanks to all the people that have posted about various other such adventures with replacing spring plate bushings. I did end up having to sand the aluminum carriers a bit because I wanted a tight fit but not a whole lot of stiction so while I could have assembled the suspension without modifying anything I went ahead and sanded it anyway. The ride to and from the autocross was not any noticeably harsher; to be completely honest I am not sure I can feel the difference between the old rubber and new bushings, however what I did notice was that the car did not feel like the rear end was wandering under hard corner entry during this autocross compared to previous one before the bushings. This might also be due to me not trail-braking as aggressively this time versus the last time as I noticed that the trail-braking was causing issues for me to transition onto power without having the rear end slide out from under me.
The car felt right on the edge of neutral with a little understeer in the tight hairpin and maybe a touch of oversteer in some of the higher speed transitions. What is really cool is that I was able to gather some data that I believe supports my interpretation of the car's balance. Below is a scatter plot of Lateral Acceleration [G force] vs Yaw Rate [deg/sec] colored by GPS Speed [mph]. The lines on the graph are lines of neutral yaw given a certain speed and lateral acceleration based on simple physics of circular motion, using centripetal acceleration (Ay = V^2/R) and yaw rate (YR = V/(2*pi*R) * 360) and combining those yields the equation of those lines for a given speed as Yaw_Rate [deg/sec] = (180 * Lat_Acc [G] * 32.16) / (pi * Speed [mph] * 1.466); the extra numbers are conversion factors to account of units. Now that the math and physics lesson is over, the plot rather simply shows if the car is yawing faster or slower than the neutral yaw rate. So the dots and lines are colored per speed meaning if the green dots are above the green line than I was possibly oversteering and if they are below the green line I was possibly understeering.
Now there are a few caveats to this, in an autocross the speed changes quickly and I have yaw rate and accelerations logging at 25 Hz while the GPS logs at 10 Hz meaning some of the speeds are not representative of the actual vehicle speed during the maneuver. Second the balance of the car is influenced by driving style and the preferred balance of a car is based on what the driver likes meaning that this plot doesn't tell me anything more than I was somewhere in the neighborhood of neutral which I liked. Plots like this are great for finding places where the car deviates from the preferred trend with a quick glance, not so much telling you why or how it is deviating from the trend.
Ok, enough of that plot and onto a common plot that I really like because it's fun too look at it ... The Traction Circle!
This one is pretty self explanatory, the cool part is that I calculated based on a dyno of another 944 S2 that 2nd should be capable of between 0.4 and 0.45 longitudinal G's and this plot shows I am just barely under 0.4 so the engine isn't doin' too shabby!
To continue with some information overload on autocrossing these wonderfull 944's I captured two videos of the front and rear wheels on the left side of the car during my fast run at autocross. These tires aren't the stickiest of tires but are bad either (BFG g-Force Sport COMP-2) and even with them at 40 psi, the -1.2 deg of camber up front wasn't enough to fight the sidewall rollover.
Well that's it for now, I am going to crank in some more camber (-2.5 front and -2 rear) for the June autocross and then install new camber plates and 300 lbs/in springs with 28mm torsion bars for the July autocross.
Last edited by L Cubed; 06-04-2015 at 10:49 AM.
Reason: Fixed video links
have you tried a plot comparison at maybe -1.4 degrees up front or lowering the rear ride height...everything else being equal to see how the plot changes?
have you tried a plot comparison at maybe -1.4 degrees up front or lowering the rear ride height...everything else being equal to see how the plot changes?
I have not, but will make a similar plot from the next autocross I attend where I will have more camber front and rear and the rear ride height lowered some because I notice that I had the rear left a bit higher than the rear right after I reassembled the rear end with the new bushings.
I should also have a string pot on the car to measure steering angle next time which will be another layer to look at it!
nice..be cool to see how the data population shifts.
I kinda liked the rear squatted with the old spring plate bushings...probably slower but definitely more entertaining keeping the intended path. having janky bushings made it more fun to pitch it into the apex.
I installed new rubber bushings all around except power flex black in the the front lowers...1 degree in front and 1.5 in the rear. zero toe all around. it is a good compromise for how and where she is driven.
05-21-2014, 02:15 PM
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