Wednesday, July 5, 2017

mini at the track - part 3

I have planned to write more about the track day with the Mini a few days ago. I however hit the publish button inadvertently. I have been very much looking forward to taking the Mini out onto the track with the list of recent modifications to prove out the pudding so to speak. As we would have it that day turned out to be a hot and sunny day for end of June. I was hoping for a cooler day. I should have brought my sun brolly.

When I set out to make my 2005 Mini Cooper S more fun I set a number of objectives. I want to improve the performance but without going overboard. I carefully chose a set of modifications that would still maintain the driveability for daily use and significantly improve the performance on the track over the stock setup. It would turn out the entire cost of the modifications cost much less than my initial estimate, mainly due to my opting for a set of performance springs and dampers over the more costly good coilovers.

Here is the list of the performance modifications that I installed:

  • replace the stock 17mm rear sway bar with an Alta 22mm one and reused the stock drop links
  • replace the stock Mini Cooper S's performance springs with a set of Swift Sport springs
  • replace the stock Mini Cooper S's dampers with a set of Koni Sport dampers
  • replace the stock rear lower control arms with a set of adjustable Hotkichi adjustable ones
  • replace the stock front strut top mount with a set of fixed mounts with slight increase of camber
  • replace the stock supercharger pulley with a 15% reduction pulley (this makes the supercharger spin 15% faster)
  • replace the stock open differential with a Quaife limited slip differential (LSD)
  • replace the stock clutch and flywheel with a set of street-use single mass flywheel and clutch kit
  • replace the stock NGK spark plugs with one step colder range of same
  • in case you wonder I did not bother with a any engine tune after the modifications; nor have I changed the alignment of the car

I also later decided to carry out the "one ball exhaust" modification which I don't think improves the drivetrain power output by any measurable amount. I am more interested to the slightly increase of the exhaust sound and the weight loss.

It is a very short list of sensible modifications and the improvement is nothing short of dramatic even for road use. The question is how much better the car performs on race track over the stock configuration that I experienced 10 years ago?

In addition to the list above there are two things that I wanted to postpone under after the track day. They are a set of new and improved Falken Azenis extreme performance summer tires and a set of bigger front brakes from Wilwood. I really like the set of Falken Azenis tires but they are now 12 years old. I planned to wear them out in this track sessions and replace them with the new tires. Similarly with the brakes. I replaced the rotors and brake pads a few years ago and they are in like-new condition. I feel bad not to at least get some use out of them. By using them on the track I would also able to compare before and after of the Wilwood big brake kit.

The Mini with the modifications on the track is nothing less than dramatic over the stock configuration. It drives like a much better car as the difference on the road. The elements of the entire package complement one another. The car felt just right while one can always want more power, more brake, and more handling and traction for the track. In all fairness I am extremely please of the overall performance considering my initial goals.

I have not done any track days for 10 years and in all I had just 2 track days prior. Most other drivers in my group have much more experience. The performance of the cars are very diverse. My goal of the day was simple. Reacquaint with Portland International Raceway and come home with the Mini in one piece. I signed up in the intermediate group. The turnout was excellent and the event was full with over 30 cars in each group.

I considered getting a GoPro camera for the event but decided to wait as I was unsure of the event holders' rule and regulation on what they deem an acceptable safe setup. Soon I would learnt that the letters of the rules is much stricter than reality. I put on my $35 dash cam to record a few laps. The video and audio quality is not the best. The time stamps is wrong as well. On the front and back straights the Mini reached speed of over 125 mph in 5th gear. It could be higher if I am more confident of the safe braking point and begin accelerate out for the turns sooner and harder. It is so fun to drive wide open throttle at these segments. Compared to the stock suspension, the Mini now has very little lean and the handling feels very neutral with my blind luck setting the suspension variables. All this help reduce excessive tire wear compared to the factory suspension that is softer and with excessive understeering characteristic.

My first couple of lapse was a bit shaky in some turns. In no time my heel and toe was back and ver I didn't have any drama that whole day. I did have a few scares which all could be avoided if I didn't get timid and lifted off the throttle once settled into a turn. Next time I should do much better. Practice practice and drill. And by the way, I should mention that I have to keep remember to switch off the Mini's Automatic Stability Control (ASC) because the US corporate lawyers told the engineers that it should be an opt-out feature.

To prepare for the event I checked all the tires carefully. I swap the tires between the front and the back as the ones on the back have more tread left. I was expecting the tires last not much more beyond the track day.

rear tire (left) and the front tire (right) before the swap

I really like how the car feel with this set of tires on the light weight SSR Spec C light weight rims

The Mini ran very well all day and it is such a trill to be able to drive as fast as one's skills safely permit. On the front and back straights I gave ample opportunities for the much faster cars pass as you are required to. One car that really stands out being very fast was a Golf R. While I knew it is a very vast car I would later found out more about it.

When I track the Mini 10 years ago, the most frustrating part is at turn 2 the left front wheel would be spinning in the air as I power out of the turn in second gear. No more this frustrating drama now with the superior suspension setup and the Quaife LSD. The 15% supercharger reduction pulley is the most conservative modification for the Mini drivetrain one can do. The increase of the power output for me is very noticeable (while some complain that the difference cannot be felt). While I am still far from finding the safe braking point on the front straight I noted 125 mph in 5th gear. The other thing that I observed is the maximum boost pressure is 15 PSI, which indicates the supercharger is in excellent condition and there is no air leak downstream of the supercharger, and the boost relief valve is working well. I have not data point of the boost pressure with the stock pulley but I read that is about 11 - 12 PSI. To give some perspective 15 PSI is about an increase of 1/2 atmosphere. That means an engine is supplied with that much more air than without forced air induction!

Driving on the track, the whole time that was utmost in my mind is I could use more traction and improve my track driving skills. Never once that I thought I want more power. While I really like the set of Falken Azenis tires they are now over 12 years old and it is not a surprise to me they are not as grippy as they should be - thought not by much compared to when they were quite new. I could feel the difference in their traction before warming up, warmed up, and gotten very hot. There are better R-like compound tires but with the 16 inch wheels the selection is very limited. In my research the Falken Azenis is probably the best track tire for my 16 inch SSR wheels. Most R53 Mini owners have 17 inch wheels, except those are heavily into autocross. Autocross was what first led me to choose 16 inch wheels. I just really like the low unsprung mass feel of the 16 inch wheel and tire combination.

In all the Mini accumulated about 55 miles during the event and that is a lot of driving. We had three sessions and the track workers are some of the best people that are out there to keep you safe. Most of the folks that I met at the event are ones that I want to be my friends, and I have total comfort driving side by side with them on the road over the majority drivers these day and age, and you get my drift. Oh. I should add that that 55 miles consumed over half tank of petrol. Definitely one of my best smile per gallon fuel economy.

By the last 2 lapse I notice some vibration from the steering wheel, and the car does not run as nicely. It was not as sudden onset, but progressively gotten worst. On the way home the condition of the Interstate 5 road surface was so poor that it masked the roughness, except the slight pulling to the left of the steering wheel. It was too dark and I was too exhausted to check that night.

The next morning I put the Mini up on jack stands so I could check all 4 wheels. This also allow me to swap the front with the back easily in case I need to trouble shoot which tire is bad. I was also concerned that I might have knock the front end off alignment when riding the FIA curbs. It is very unlikely since I never hit any aggressively or at the wrong spot. I also wonder if one of the brake discs is warp from excessive heat, and causing drag and pulsing of the steering wheel.

The right rear tire has the most pick-up from the track, as this wheel has the most easy job at the clockwise race track. The pick-up did not get a change to be rubbed off so they accumulated.

Before the suspension modifications the tires always has very significant wear along the outer edge, especially the front tires. The tires worn so little and no sign of uneven wear from this track day - attributable to the much stiffer springs and better dampers as well as the stiffer rear sway bar. The fixed camber plates that I install does increase the negative camber slightly at the front. Hence I am very pleased with the suspension.

the left rear tire has less pick-up than the right rear

Inspecting the left front wheel it did not take long to spot the problem. The outer part of the contact surface bulges more than the right front wheel, suggesting belt separation. Once have both wheels off and compare them side by side it became very obvious.

the diameter of the left front tire (right side of photo) is more than half inch more due to belt separation inside the tire

Like the saying goes, you are better be careful what you wish for. I thought the track day would use up what is left of the threads of this set of tires, but instead the heat and pressure finished it off. I did check the tire pressures after the first session and they were not excessive and I bleed them down slightly.

The brake rotors all got a good workout at the track. There are definite wears just by running the finger across the rotor surface. I would now feel better of taking the perfectly good front brake parts off.

The Mini paint did not suffer from any debris except some rubber deposits from the car in front. On the adjustments of the suspension I have no indication at this time any needs changing. These are the rebound damping of all 4 dampers, the stiffness (3 discrete steps) of the rear sway bar, and the front and rear alignment of the car.

I have a set of new and improved Falken Azenis RT616K+ tires ordered. At the mean time I put the heavy factory wheels with all season tires back on. They are 50 aspect ratio instead of 45 and the Mini does not handle as well is very noticeable.

Once the new tires are installed I would also put on the Wilwood front brake kit. I love love this little fun car.

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