Mechanical Grip

[team9]

Here is a LSD, though I have not tried it. Been thinking about it since I am having the same problem as you. The stock LSD's just don't do as well as I would like for a tight autox course.

http://cgi.ebay.com/ebaymotors/OBX-LSD-BMW-E30-E36-325i-M3-E28-E34-525i-535i-Z3-2-8L-_W0QQcmdZViewItemQQhashZitem2a0fd74cc9QQitemZ180654394569QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories#ht_2766wt_939

[Jean]

Yeah, I am not sure if it's best to rebuild the factory diff with 4 new clutches or go with OBX + new hardware..

[wildstoats]

You might want to check out http://www.diffsonline.com/. I have not dealt with them personally but they could be a good resource.

[Jean]

You might want to check out http://www.diffsonline.com/. I have not dealt with them personally but they could be a good resource.

They have been mentioned before, with not such stellar remarks especially for their asking prices.

[PrinceE30]

The guys winning nations are using the widest tire they can fit on the car. With the softest compound (Hoosiers without a doubt right now).

The "right" tire is more important that the widest tire possible. Look at Mike Simanyi, 2010 SM National Champion and 2011 Runner-Up. He *could* run any size / width tire he wants but he runs 285/30/18. When autocrossing, making the car wider is a determent to speed at which you can run through the course. Balance is more important than overall width and driving the car is far and above the most important factor.

Bigger tires are always faster. A lot of the theory about contact patch and tire pressure and weight and such never really applies - Bigger tires WILL generate more grip, always.

I'd recommend getting a cheap infrared thermometer/pyrometer and recording tire temps inside/outside/center on each wheel after every run.

Read the entire site "Autocross to win" by Far North Racing. It's easily the best AutoX resource on the internet.

Additionally, if you cannot get the tires to the proper temperature when maximum grip happens, good luck with massive A6s. Going too wide and increasing height is another potentially detrimental issue that can come up. It's something you can ONLY solve by testing, not by bench racing.

Additionally, though Far North is an interesting read, the author doesn't have a lot of street cred in the autocross community. A local Atlantan and current EVO School driving instructor drove his Talon a number of years back and was less than impressed. If you want to autocross fast in a BMW, talk with the following people:

Bob Tunnell
Mike Simanyi
Alex Schipkov (E30s)
Toby Larson
Mike Shields
Neal Tovson

Are you wanting to play in a specific class? If so, read the rules and go from there. VERY FEW SCCA autocross classes allow wings.

As someone who has spend the last 3 years developing (2 of which I actually own the car) a STX E36 328is, the best things you can do is get a lot of seat time and always be trying something out. However, only try one thing out at a time. Too much and you'll muddle the data and get nothing useful out of it. Here's an idea of the amount of time I spent on various things on my car, for example:

6 months and 6-7 autocrosses nailing the alignment
8-10 months getting proper spring rates (still a work in progress)
1-3 events over the course of a month getting proper shock settings.

We're about to start work this season with new tires (RS-3s), stiffer front sway bar (potentially softer springs) and if we gain enough grip - softer rear springs. I expect this to take until around mid-late July. At that time we'll keep the car in its fastest incarnation through Nationals at the end of August.

The point is, to get it right, it's a lot of work. However, on the bright side...you get to stand on the shoulders of giants and learn from what others have already done. There is a HUGE amount of information out there to learn from. Talk with Alex Schipkov. He's a wealth of information and an INCREDIBLY nice guy. Talk with Terry Fair at Vorshlag Motorsports. They built an ST 318is last year and got a lot of good data with respect to spring rates and shocks (they couldn't run at LSD so I had to tune accordingly). One thing I certainly learned is that you can only learn so much via the internet. You have to start testing yourself or you could go on a while goose chase. I spend almost 8 months believing I was running "the right" spring rates on my E36 and when I finally started to soften the rear of the car so much I am running the same rates front and rear I found that the "best practices" of the overall BMW community doesn't translate well into the highest level of autocrossing. Live and learn!

Great luck and feel free to ask questions on some of your mod ideas...there's been some tidbits of good data on this thread and it's a good place to start.

[Jean]

Thanks! I am running SM, so the rules do allow more than ST or DSP classes :)

Keep the good info coming guys, there is really no way around it car will need more tire sooner than later. The 225/50 v710s on it barely had a few weekends on them, last full season was ran on rt615s before I got these. I'll have to run these until they wear before spending money on new wheels/tires.

[m_dudey]

Hey Jean,

Come out to the May 14 BMW autocross down in Marina! I know it's a bit far for you but I'd love to see your car run.

[rwh11385]

In addition to what Corvallis and Prince posted about lots of factors and needing to spend lots of time to test and fine tune... there's probably a lot of helpful reading you can do. It's probably difficult to tweak your car's handling through the intrawebz, but if you read up you probably can get informed and be able to draw conclusions after testing, and then present what you've discovered.

http://www.amazon.com/How-Make-Your-.../dp/0912656468 - How to Make Your Car Handle by Fred Puhn - This book helped tons and probably where you ought to start.



And books from vehicle dynamics and/or vehicle design and fab course reading lists:

http://www.amazon.com/Chassis-Engineering-Building-Performance-Handling/dp/1557880557/

Step-by-step guide to enhancing road handling ability. Topics include: center of gravity, roll center, tire technology, front and rear suspensions, brakes, shocks and springs, and chassis design.

http://www.amazon.com/Absorber-Handbook-Wiley-Professional-Engineering-Publishing/dp/047051020X/

"The Shock Absorber Handbook, 2nd Edition" provides a thorough treatment of the issues surrounding the design and selection of shock absorbers.

http://www.amazon.com/Competition-Car-Suspension-Practical-Handbook/dp/1844253287/

"Allan Staniforth who runs his own business tuning suspension for competition and road going cars is a long-acknowledged expert on the subject."

http://www.amazon.com/Racing-High-Performance-Tire-Using-Balance/dp/0768012414/

"Based on 15 years of research on tires, Paul Haney's The Racing and High-Performance Tire presents clear, non-academic explanations of how and why tires really work."

http://www.amazon.com/Tires-Suspension-Handling-Second-R-168/dp/1560918314/

"An introduction to the control, stability, handling and cornering behaviour of four-wheeled vehicles. Subjects discussed include aerodynamic forces, steady state vehicle handling characteristics, transient handling characteristics and lateral oscillations."

[Jean]

Hey Jean,

Come out to the May 14 BMW autocross down in Marina! I know it's a bit far for you but I'd love to see your car run.

I'll be in Stockton on the weekend before that, what are you running?

[e304me]

I have a metrix motorsports diff and it is amazing. %40 lockup.

[nando]

out of curiosity, have you done any measurements with an accelerometer to see what kind of cornering grip you have now?

[Jean]

I have not. I've looked into camera setups and the ones with acccelerometers are out of my range. Do you use one?

[nando]

I have a $20 3-axis chip plugged into my ecu :p

[nrubenstein]

I have not. I've looked into camera setups and the ones with acccelerometers are out of my range. Do you use one?

You might try Harry's LapTimer Pro. $15 gets you datalogging + video if you have an iPhone, or access to one.

[Jean]

I have an android g2x, looking on app market now. I wonder how accurate these are though?