Everyone seems to have a build thread for their car, so now things are becoming serious, I thought I wouldn't deny Bertie the same honour.

I've written some about Bertie in My 2013 Season thread, and in my Early Start on 2014 thread, but this thread is to bring together all the information about changes to Bertie.

So the story so far:

For our first full season in Autocross, we were running Tristan, an 07 Cooper with sport suspension in novice H Stock. For a variety of reasons we decided to upgrade to a new 2013 model Cooper to be our autocross car. This brings us EDLC, a few more hp, and the ability to run 7" wide wheels (either 16" or 17") in next year's Street category. We're targeting H Street.

The new MINI we will eventually call "Bertie", named after George IV as he's our 6th MINI. We order him very similarly equipped to Tristan, as we do like Tristan a lot. There are a few extras in there which won't make him faster, but he's also going to be one of our daily drivers, so we also want him to be a good street car. Berties specs:

Lightning Blue + White Roof
Sport Package:
- Black Star Bullet wheels (17x7, partly to prove they're stock legal)
- Sports Seats
- DTC (which includes EDLC)
- Spoiler (extra weight)
- Front Fog lamps (maybe extra weight)
Sport Suspension
Carbon Black cloth/leather seating surfaces
Carbon Black color line
Pepper White interior surfaces
Rear fog lamp (essential)
Auto A/C (luxury, we like)
Mirror with Autodim, Homelink remote, compass
(Bluetooth and USB was standard)



We ordered him on May 19th, went into production immediately an arrived on June 30th, 6 weeks later, the fastest we've ever got a MINI. The first task was to break him in, which I did in three weeks by taking the long way to work. That allowed us to enter him in an Autocross on the 21st. I wanted to test him against Tristan to make sure there was nothing wrong and the test came back that Tristan was about 1 sec faster. So at that point we put his autocross career on hold and ran with Tristan for the rest of the year, with the intention of working out what the difference was.

Upon reflection we decided that the difference was oveersteer. Tristan had grown some oversteer during the year, and became somewhat of a handful for our inexperienced selfs. So we decided we'd try tuning in some oversteer. This probably short-circuited a whole bunch of experimentation which would end with us deciding we needed to tune in some oversteer.

In the meantime I set about sourcing some wheels for use in 2014 H Street, I'd be able to use them for non SCCA events (we also run with the BMW club) and save our competition tires which were wearing out. I'd decided I wanted to try 15x6.5" wheels. I was also going to try 225 wide tires, the only suitable tires were BFG Rivals in 225/45-15. We were running Bridgestone RE-11 in 205/45-16, they had almost the same diameter, but 20mm more tire. Looking around for tires, I was finding that the 15x6.5 size was out of fashion, and most of the good ones had been discontinued. I found a good price for some Ray's CE28N (all of 8.1lb each), so I ordered some. They were going to have to be special ordered from Japan. 6 months later they still hadn't arrived, and I'm not sure if they ever will, I need to chase the vendor. His price was several $100 cheaper than others, so I as prepared to put up with some flakiness.

As a stop gap, I looked for other 15x6.5" wheels and found that a lot of people advertised them, but no one had any in stock. If you ordered you'd fid they would just try to order from the manufacturer and find they were discontinued. I eventually tracked down some Rota Slipstreams from a local company. These are not actually legal for street as they have a +40 offset, rather than the allowed +42, but they'll do for now.

After the test vs Tristan, I got Bertie an alignment and had him corner weighted. He turned out to be 52lb heavier than Tristan, but that may be that I forgot I was getting him weighed and filled him up with gas. The cross weights are also not quite as good as Tristan. The corner weights are:
Corner weights (lb) with driver, competition trim:

835 821
568 506

Without Driver:

751 786
471 471

Total: 2479

The alignment specs are:

Camber Before -> After
LF -0.3 -> -0.7
RF -0.7 -> -0.7
LR -1.4 -> -1.5
RR -1.6 -> -1.5

Toe
LF 3/32 -> 0
RF 1/32 -> 1/32
LR 1/16 -> 1/16
RR 5/32 -> 1/16

The plan is to run Bertie in the autumn "Slush" season here while getting him ready for 2014. At the first event we just ran with the same setup we'd been using for Tristan, because I hadn't found the wheels yet. That would be our baseline.

At the second Slush event we added the 15x6.5" wheels and 225 Rivals. He was maybe 0.7s faster.

Next was to address the suspension and (lack of) oversteer. My initial thought was that Tristan's shocks maybe going bad, and in the meantime making him faster at Autocross. So I looked around for somewhere with a shock dyno who could actually measure Tristan's shocks to see if that was where the secret sauce was. I asked around who had a shock dyno as the only one I know is with some friends down in Paso Robles (3 hours south of here). I was referred to Fat Cat Motorsports. When looking around their site it became obvious that they had similar ideas about shocks as I did (simple shocks, but matched to the suspension correctly).

So I eventually contacted Fat Cat with a view to getting custom shocks, and after a brief consultation ordered the shocks from them. They're going to be Bistein HD (which seem to be "B6"), but they'll be custom valved to match the suspension. The total cost of all that seems remarkably reasonable to me.

The other suspension tuning item was a rear sway bar. I'd been looking around to see if I could find an adjustable bar which could be adjusted to about the same as the sport bar we have, so we wouldn't suffer on the street, and be able to be adjusted stiffer for use at autocross, as stiffer rear bar seems to promote oversteer. What its doing is actually not allowing the rear suspension to work so well, so the rear loses some grip. If the rear loses grip first, you get oversteer. I'd always been suspicious of reducing grip, but Tristan had persuaded us it was the right thing to do.

In investigating this I came across the Tarett Engineering adjustable bar. I really like the way this worked, and that it was lighter than stock, so I inquired as to how stiff it was relative to the sport bar we have. I think they told me the wrong thing, that it was 2.3x to 5x as stiff. That put me off ordering it initially, not enough adjustability to the less stiff end. However, I think they misquoted and that's the stiffness compared to the regular Cooper bar. Compared to the sport bar its 1.4x to 3x as stiff. If they'd told me that I might have ordered it three months ago. However, I've now ordered one and its due to arrive tomorrow. It'll be fitted along with the new shocks by FatCat when the new shocks are ready.

Also part of the setup are three GoPros and the iPhone as the data system. One of the GoPros is mounted on a setback mount I made, so its positions just above your shoulder giving a view of cones and your driving. Outside the other two GoPros are mounted on the rear behind the rear wheels as "cone Cams", to see how close you're getting to the cones. Meanwhile I have the iPhone running Harry's Lap Timer, which talkes to an XGPS Dual 150 GPS unit with the special firmware which ups the fix rate to 5 Hz, and also to a GoPoint BT1 OBD-Bluetooth module.

This setup is good enough that its preventing me from getting anything "better". I've been considering getting a "real" data system, I've asked my friends at Veracity Racing Data about this (they're also the ones with the shock dyno), they don't seem to have anything which can do what the cobbled together system can do. The big advantages of the current system is that its portable so you can mark the start and finish lines on the course and you can get immediate feedback on your runs. I've used it to compare two runs while waiting for my next run. It'll show you where on course you're gaining or losing time and compare your revs, speed etc. Its been very handy. No "real" data system seems to have that immediacy. The closest they can suggest is a Race technology DL1 and a somewhat cobbled together system to connect that to an Android device running Solostorm.

I export the data from the Laptimer and use RaceRender to imprint it on my videos. I put the multi cam video together in Final Cut Pro.

Other more mundane things are the numbers we use. As there's two of us running, we need something easy to change between runs. I also wanted something that looks good, so I got modular panels from iZoom graphics. I've now got (not modular) panels for the class letters, so they're more visible.

I've also been using CG-Lock seatbelt latches to keep me in place, but for the last event I got a Schroth QucikFit pro harness. There are a couple of extra "tails" you bolt into the existing anchor points, but after that the harness just clips in. It clips into the regular seat belt receiver up front as well as an extra one at the lower seatbelt anchor. It also clips into one of the rear seatbelt receivers and an extra tail at the outboard seatbelt anchor point.

 

The sway bar arrived. I'm not sure if its the right one. It has an outer diameter of 25mm and an inner diameter of 17.7mm (being hollow), which I calculate should be as stiff as a 23.2mm bar.

They advertise a 23.8mm bar and a 25mm bar, I'm not sure which I have as its not clear if they're talking actual bar diameter of equivalent bar diameter.

I sent them an email for clarification.

 

I keep looking at your camber settings and I think I can see why you don't have any oversteer. Dialing up more rear camber has made the back of the car more grippy than the front. Are you able to go with camber plates up front? I am running -2.1front -1.4 in the back with a 23mm RSB on full stiff and it rotates nicely but I am not limited to any rules because I don't race and am not trying to stay in any particular class.

 

I'm not sure 0.1 degree rear camber makes that much difference, but they couldn't find any less (negative) camber and make the toe that small. Its interesting that Tristan came form the factory with less rear camber and toe, he could also be adjusted to even less than Bertie could be.

I am constrained by the rules, so I can't use camber plates. Camber plates were in the first draft of next years rule, but unfortunately that got dropped. So far just getting an alignment have evened out the tire wear significantly.

 

Bummer on the camber plates. No .1 difference in back wouldn't change much. You could look at going with a smaller front sway bar. Euro mini come with as small as 16mm, that would be considered legal no? That would help front grip a bit.

 

The usual way to address the oversteer (or lack of it) is to change the rear bar, which is what I'm doing. Stock classes have been able to change a choice one bar for a year or two now. Street still allows either bar to be changed.

16mm front bar? That's tiny, the regular Cooper rear bar is 16mm. Bertie's rear (sport) bar is 18mm and his front is 23.5mm (I measured, that's 4.5x as stiff as a 16mm). A 16mm front could be legal if it were the only bar you changed, under the allowance of changing one bar. It wouldn't be legal because its an option in Europe. Only US options are legal for Stock/Street, even then it has to be the complete package conversion if you want to change it. If you change the bar to another package's bar, you also have to change the springs. As shocks are free, and you're allowed to change one bar, you basically have to choose your springs, and match one bar to it, then you're free with the shocks and other bar.

There's the choice of regular, sport and JCW. It looks like I'm sticking with the sport springs and front bar, new rear bar and FatCat shocks.

 

I just had a thought, more of a general question. I've been thinking of stiffening the rear bar as a method of reducing rear grip, and I'm suspicious of reducing grip, seems counter productive.

But, isn't a stiffer rear bar actually moving grip from the back to the front, which seems like a very good thing. If its increasing front grip by trading rear grip for it, sounds like a very good trade. Or am I misunderstanding the situation.

 

WTF??? It's fine, it's a sway bar. You would just need to run the OEM bar in the back or the JCW rear bar if you do JCW springs.

Your example would be converting a regular SN95 chassis Mustang GT to Shelby GT specs. A lot more needs to be changed because of the nature of the package.

Read before you type...

http://www.scca.com/solo/content.cfm?cid=44517

 

That's exactly what I said, it'd be legal if it were the only bar you changed. That its an option in Europe is not what would make it legal, which seemed to be what Swimbaxter was asking.

 

I think it would help you understand it better if you did some reading on the physics behind what you are doing with the sway bars. There are quite a few good books out there that aren't too hard to understand without a strong physics background. The Fred Phun "How to make a car handle" book is an oldie but goodie.

Dennis Grant's website is good reading as well: http://farnorthracing.com/autocross_secrets.html

Not everyone agree with Dennis's car setup tactics, but he has pretty good descriptions of the physics.

Jason Rhoades also covers some of the physics on his Camaro build blog: http://www.rhoadescamaro.com/build/?page_id=481

Typically what the sway bars (or anti-roll bars) are doing two things:

1. Limiting total body roll.

2. In part, determining how much of the lateral weight transfer gets sent to each tire.

Limiting body roll can be useful because it limits camber loss due to body roll in most cases. This is especially helpful in cars that have suspensions which don't gain much camber in compression travel. The front suspension of the Minis is a prime example of this. How much the body of the car rolls is a function of a bunch of different parameters, but the combined stiffness of the front and rear anti-roll bars is part of the equation.

When a car is corning, weight is transferring from the inside tires to the outside tires. Roll bars do not directly change the magnitude of the amount of weight that is transferred, but they do change the distribution of the transfer between the outside tires. If 500 lbs is being transferred at a given point in time, the sway bars help determine how much of that 500lbs is going to the front outside tire and how much is going to the rear outside tire.

Keeping it brief, due to tire behavior, cars work better when the tires are more evenly loaded. By increasing the rear roll stiffness with a stiffer rear sway bar, you are increasing the amount of weight that is transferred to the outside rear tire and reducing the amount of weight that is transferred to the outside front tire. For a front heavy Mini, this amounts to making the mid corner weight distribution between the front and rear tires more even, which results in more total grip.

The next consideration is balance (oversteer/understeer) of the car at the limits of traction. Because sway bars affect weight transfer, they also affect the balance of the car. Ideally you want to get the most traction, while also having desirable balance characteristics. You can have a car this is well balanced, but not necessarily making as much grip as possible. You can also have a car that makes close to "max" grip, but doesn't have good balance. The nice thing about increasing rear sway bar stiffness on the Mini is that it typically both increases grip and improves balance.

 

I heard back from Tarett this morning. Both their sway bard have an outer diameter of 25mm. (They say 1", but I measured 25.0mm). The wall thickness seems to change to effect the stiffness difference. They said the bar should have a wall thickness of 0.156" (3.9mm) which is what I measure.

That makes the bar a bit stiffer than I'd want at its softest, but we'll see how it works for us.

The other unknowns in the stiffness equation are material, lever arm length. They say its 4130 chrome-moly steel, I don't know how that compares to standard. Without removing the wheel it looks like the standard lever arm is 7", the Tarret is adjustable from about 4" to 8".

 

That's the conclusion I was coming to. It makes me much more enthusiastic about the change.

Physics is my thing, I'll have a look at the link you posted.

 

Your reply would make it difficult for a novice to understand what you meant. In your first statement above, you, in essence, imply that you'd have to build a MINI One if you wanted to run a 16mm bar up front, when in reality, you could run a full-tilt GP and put that tiny front bar on.

Please clarify things for me if I'm in the wrong here, but it seems like you contradicted yourself...

 

Yes. Legal.

 

It's not an option but a standard FSB on a MINI One in Europe. You can buy them used on ebay for pretty cheap.

 

The euro mini front bar would be considered the same as any other aftermarket front bar in terms of rules legality because it did not come as a factory option here. You can change the front bar to whatever you want so long as the rear bar is left "stock" - with "stock" matching the suspension package you have (base, sport, JCW).

When the rules only allowed the front bar to change, it wouldn't seem unreasonable to try a smaller front bar to get a better balance with the "stock" rear bar. However, with the change in rules to be able to change front or rear (but not both), most are choosing to increase the rear bar stiffness since it both improves the balance and increases total roll stiffness.

 

I already tried once. The clarification is

Means the legality of the 16mm derrives from it being a one bar change. The availability of the option in Europe does not make it a legal option in the US. The availability of the 16mm bar in Europe does not change anything with respect to the US rules.

You're reading it as: the reason it is not legal is because it is an option in Europe.

My intent was: It would not be made legal in the US by virtue of it being option in Europe.

As I said, I was responding to: The gist of what I was saying was it would be legal because you can change one bar.

Being an option in Europe does not matter. Only options supplied to the US matter to the Solo rules.

 

It depends on which allowance you want to use. There is the allowance to use a package conversion and the allowance to change one bar.

You're free to change one bar arbitrarily because of the allowance to change one bar.

If you've already used you one bar allowance, you would have to use a package allowance to change the other bar. In effect you'd have to build a MINI one to change a second bar to the 16mm one. (But you couldn't as the MINI one is not a US model.)

 

Added in red below.



My sincere suggestion... Save some money. Instead of setting the car up using the priciest parts with the priciest data acquisition systems, invest here first...

http://www.evoschool.com/

I'm not only a student... I'm also an instructor.

 

I'm not sure what your problem is, for the most part you seem to be agreeing with me, but not doing it in a very agreeable manner. This will be my last comment on the matter.

There was a suggestion that a certain bar would be legal. The post seemed to suggest that the legality would be because it was an option in Europe.

My response was:

1. It would be legal because you could change one bar. That's sec 13.7.

2. Its legality does not depend on it being a European option.

3. Once you've exhausted 13.7 if you want to change a bar, it must be part of a legal package. The legal packages available are standard, sport and JCW.

That's what I said, do you disagree with any of those points?


I've already signed up once, but the school was cancelled. You're not being a good advertisement for the school.

 

Leave it at one and two. Nice and concise... Zero chance of misinterpretation.


Sure I am... This is a sport where 90% of one's success is based on the driver, not the total sum - or exclusivity of - parts going on the car. A number of people on this forum have been posting threads chronicling how much or how many cool parts are going on the car, yet the driver is a component that is being left out of the equation, regardless of reason. Evolution Performance Driving Schools help and it's worth even a 3 hour drive to attend one.

The MINI is a car where one could simply put tires on it, along with an alignment, and go out and win races. Cubic dollars do not need to be spent to have cubic loads of fun. Spend less, drive more.

 

I prefer spend more and drive more.

The hardware is mainly to just give me no excuse, if I don't do well its my problem, not the car's. If I can pick up an extra second or so without me getting better, I'll take it. A couple of my main rivals are less than a second in front of me. I have hard evidence of a deficiency in the car, so I'm keen to fix that. I hadn't originally intended to go this far modding the car this fast, but with the data staring me in the face, its pushing me.

I also consider the data system to be part of the driver improvement. If you don't know what you've been doing (wrong), you can't get better.

So far, I'm quite pleased with my progress in the sport, I'm doing better than I ever expected to, but there's plenty of scope for improvement. Part of that is down to not only driving at most opportunities, we got to almost all rounds of the championship (we missed the one they moved the date), we did a few extra events (4 BMW and 2 Fresno for me), as well as doing two schools (Fresno and BMW club).

By preference I'd be at an Evo school right this minute, I had paid for it, but it was cancelled much to my annoyance. The Evo school was part of my plan for world domination next year.

 

Can you post any pictures of the interior? I like your option choices.

 

I should make an effort to get some better interior shots.

 

As I said, Physics is my thing (I'm a Physicist by training), and also that web site is one of my favorites about car setup. I like a lot of what he says. But by Physics I mean the principles involved, that site does go into a lot of detail about the mechanics involved, which is interesting but some of it has washed over me as just a bit too detailed.

However, as you brought up the subject, I just reread the sections on weight transfer and balancing. There's a very interesting, and practical, nugget in there, that in order to balance a car, the proportion of the roll stiffness (front to rear) should be the same as the proportion of the weight distribution (front to rear). If the front is stiffer than that, you'll get understeer, if the rear is stiffer, oversteer. That's something I can calculate.

As I mentioned, I have the corner weights, so Bertie has a 60.7% front weight distribution (with driver). But the sport suspension has a 23.5mm bar up front, and an 18mm one at the back. That gives the roll stiffness (at least the contribution from the bars) as 74.4% to the front. So by that model, Bertie should understeer.

A quick and dirty calculation would suggest that to equalise the bars to the weight distribution, you'd need a 21.1mm rear bar. The bar I've got is supposed to be the equivalent of a 22mm bar when set to its softest, that's not too far from what you want. That's moved the stiffness balance 4% backwards.

Its interesting to have some theoretical reason for the bar thicknesses that people throw around. The sport bar is 18mm, 19mm is a mild change, 21mm is quite radical, 23mm or more is a bit extreme.