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Carter
03-19-1998, 11:20 AM
Last night launched the first <A HREF="http://www.windycitybmw.com">Windy City BMW CCA</A> meeting for 1998. I arrived late and missed the first half. After the refreshment intermission, the rest of the meeting belonged to guest speaker John Rastetter, midwest representative of <A HREF="http://www.tirerack.com">The TireRack</A>. His appearance last year focused on choosing the right tire, compounds, characteristics, suspension, etc. This time it was mostly about wheels.<p>I'll try to post as much as I could remember during his highly informative presentation...<p><H3>WHEELS: THE GOOD, THE BAD, THE UGLY</H3><br>He first began by mentioning the importance of selecting the right wheel and why the good ones cost what they cost. Much of it goes into the amount of manufacturing. He showed four samples of the same wheel — each going through various stages of the manufacturing process. Cheap alloy wheels are more or less cast into a hole in the ground. The better ones are cast by machines that themselves get heated and cooled to control the aluminum alloy's properties. He mentioned how tremendous pressure was used to eliminate imperfections in the super-heated alloy. After the casting, the rims don't look much like what they're supposed to. The edges get roll-forged to reach their final form. One of the last things to finish the process is it goes through a pellet bath to polish and strengthen the wheel.<p>He mentioned that the better wheels should place its weight on the axle hubs...others stress the lug bolts. Some of the more generic wheels use a composite plastic shim to transfer the wheel's weight to the hub. Over time, this plastic may fail and crack.<p><H3>IT'S THE ROAD, STUPID!</H3><br>There <B>was</B> some brief recap about tires...<br>He's convinced me to never pay attention to someone's antecdote about how long their tires last. Tire wear depends greatly on where you live. Period. Your local municipality isn't gonna haul material from a quarry three states away. They're gonna use whatever's available to them in making your local roads. He bought his collection of "roads" from various states and locations...each offering very different degrees of abrasion. In Greenville, SC, they mix a smooth-ish quartz-like rock into their asphalt. In Huntsville, AL, they use rock from a riverbed. In Florida, they use crushed seashells. You can actually see bits 'n pieces of them embeded in his sample road-chunk! For places that use concrete, they brush the surface to intentionally put texture into the road. With continuous traffic, this "texture" <I>does</I> wear smooth (and also wears your tires). He pointed out where you see signs that say "Slippery When Wet," it's because it's cheaper to put up that sign than to fix the road! The absolute worst surface is gravel. As the loose rocks shift under the tire, it chips away the material.<p>He also explained as a tire wears, the individual rubber blocks get worn closer and closer to its base. This essentially makes that block less wobbly (sways less). What this means is as your tire wears, your dry-handling performance increases. Autocrossers will sometimes claim the exact replacement tires they bought have had its rubber formula changed by the manufacturer...when the reality is the new tire feels different from his/her worn-down set solely because of the difference in the height of the blocks.<p>There was a question about how long a tire's rubber last. Tires have a shelf life of maybe 6 or 7 years. When they're mounted and exposed to the elements, the rubber is good for about 5 years...sometimes less. He warned against cars that were left out in the hot sun day after day...the tires would reach a temperature of 140&#176; Farenheight! Not a good thing for the rubber compound's longevity.<p><H3>YOU'RE FULLA GASses!</H3><br>By far the <B>most</B> intruguing portion of the discussion was when someone asked him about what the racers are filling their tires with. At the microscopic level, rubber is sorta like spaghetti. The constant stretching and compacting means that the air inside escapes. Not by a <B>huge</B> amount, but it does. The air molecules pass through and in some cases a tire might lose 1lb of pressure per month.<p>At the race pit, the crew has tanks and tanks of nitrogen. They use these tanks to power their wrenches. Nowadays, they're also using nitrogen to fill their tires. Since nitrogen molecules are larger, it lessens its exodus through the tire rubber. Air is generally made of oxygen and nitrogen. Having no oxygen inside our tires will diminish the rate of oxydation to that portion of the wheel's alloy. Nitrogen's also a "drier gas". Unlike oxygen that can combine with hydrogen to form water, pure nitrogen can't do that...and eliminates chances of moisture inside the tire.<p>The ultimate benefit of tires filled with nitrogen is that it's less prone to expanding and contracting with changing temperatures. Used to be that race crews who see 70 degree weather one day and 90 degree the next will have to cope with the tire's fluctuating pressure. Nitrogen maintains a more constant tire pressure.<p>So what now, keep a 5ft tank of nitrogen in the garage? That'd be a pain to work with. He mentioned there was one company offering a unit that took air and pushed it through membranes to give a greater-than-95% nitrogen...described as a scrubber machine. Whatever it costs, it's probably not a feasible solution. The TireRack is currently investigating how to make this whole nitrogen-thing widely accessible. They're looking into shipping tires and wheels filled with nitrogen...better still, to have places that hold track events keep these machines. Let's say you have your tires replaced with nitrogen for maybe $10 and in the future it'd cost maybe a nominal dollar to top-up.<p><H3>HOME STRETCH</H3><br>As the presentation ended, many long-time CCA members stepped forward with unsolicited praise that <A HREF="http://www.tirerack.com">The TireRack</A> is a top-notch company with the expertise to back it up. Everyone on the other end of their 800 number knows their stuff. All their tires are reviewed on their paved 5&#189; acre test lot...and often on BMWs no less. In the end, I was satisfied with what I heard and have decided I would <B>only</B> go to <A HREF="http://www.tirerack.com">one place</A> for my next set of tires. It'd be great if John R. could show up at the Reunion and field some specific questions from the rest of you!<p><B>OK, brain's empty</B>. Flame suit <B>ON</B>. :)<p><A HREF="http://www.mcs.net/~carter/z3reunion"><IMG SRC="http://www.mcs.net/~carter/oz/z3carter.gif" ALT="Carter" BORDER=0 HEIGHT=130 WIDTH=130 ALIGN=LEFT></A><BR><BR><BR>Carter<BR>'96&#189; <FONT COLOR=#000000 FACE="Arial,Helvetica,Swiss,Sans">Z3 <I>_<B>7</B>_<B>7</B>_<B>7</B>_<B>7</B></I></FONT><BR><FONT COLOR=#FF0000 FACE="Serpentine,Arial,Helvetica,Swiss,Sans">—<B><I>roadster</I></B>—</FONT><BR CLEAR=ALL>

Keith F
03-19-1998, 08:06 PM
The Tire Rack is <b>the best!</b> I turned to the Tire Rack when I lived in Podunk, N.C. The local shops could order the RE-71's I wanted for my loyal Honda CRX Si. The cost <b>per tire</b> mounted and balanced would be just a few dollors shy of what The Tire Rack would ship me the entire set for. I have to disagree on the knowledge of the guy on the other end of the phone, though. When I finished with my RE-71's, they were no longer made in my size. A Tire Rack dude told me that the RE-930 was a direct replacement. <b>Buzzz!!!</B> Sorry. But we do have a lovely parting gift for you!<p>When I ripped up one of my Pilot HX's, I unfortunately decided to replace the whole set. Bought them from Sears next door to where I work. I used an ad from The Tire Rack to get a reasonable price from them. To make a long story short, after the experience with Sears, I will not stray from The Tire Rack anytime in the forseeable future.<p>I'd love to see a Tire Rack rep at the reunion!<p><br><b><FONT FACE="Arial"><FONT SIZE="3"><FONT COLOR="#000000">K</FONT><FONT COLOR="#151515">e</FONT><FONT COLOR="#2A2A2A">i</FONT><FONT COLOR="#3F3F3F">t</FONT><FONT COLOR="#545454">h</FONT><FONT COLOR="#696969"> </FONT><FONT COLOR="#7E7E7E">F</FONT></FONT></FONT><FONT FACE="Arial"><FONT SIZE="3"><FONT COLOR="#7F7F7F"> '</FONT><FONT COLOR="#666666">9</FONT><FONT COLOR="#4D4D4D">6</FONT><FONT COLOR="#343434"> </FONT><FONT COLOR="#1B1B1B">Z</FONT><FONT COLOR="#020202">3</FONT></FONT></FONT> <FONT FACE="Arial"><FONT SIZE="3"><FONT COLOR="#4F95FD">/</FONT><FONT COLOR="#000000"></FONT></FONT></FONT><FONT FACE="Arial"><FONT SIZE="3"><FONT COLOR="#490587">/</FONT><FONT COLOR="#000000"></FONT></FONT></FONT><FONT FACE="Arial"><FONT SIZE="3"><FONT COLOR="#FF0000">/</FONT><FONT COLOR="#000000"></FONT></FONT></FONT><FONT FACE="Arial"><FONT SIZE="3"><FONT COLOR="#BFBFBF">M</FONT><FONT COLOR="#BFBFBF">4</FONT><FONT COLOR="#BFBFBF">4</FONT></FONT></FONT> <FONT FACE="Arial"><FONT SIZE="3"><FONT COLOR="#000000">B</FONT><FONT COLOR="#0D0C08">l</FONT><FONT COLOR="#1A1810">a</FONT><FONT COLOR="#272418">c</FONT><FONT COLOR="#343020">k</FONT><FONT COLOR="#413C28"> </FONT><FONT COLOR="#4E4830">a</FONT><FONT COLOR="#5B5438">n</FONT><FONT COLOR="#686040">d</FONT><FONT COLOR="#756C48"> </FONT><FONT COLOR="#827850">B</FONT><FONT COLOR="#8F8458">e</FONT><FONT COLOR="#9C9060">i</FONT><FONT COLOR="#A99C68">g</FONT><FONT COLOR="#B6A870">e</FONT></FONT></FONT></b>

BuzZ3
03-20-1998, 08:01 PM
<br>: The ultimate benefit of tires filled with nitrogen is that it's less prone to expanding and contracting with changing temperatures. Used to be that race crews who see 70 degree weather one day and 90 degree the next will have to cope with the tire's fluctuating pressure. Nitrogen maintains a more constant tire pressure.<p>Ummm<br>Pressure is directly related to temperature and volume<br>Pressure is P<br>Temp is K (in Kelvin)<br>volume is v<br>c is a constant (usual called gamma)<br>Here is the "Adiabatic Change" forumla:<br>PVc=k<p>So if the volume stays the same, when the temp increases, the pressure changes by <B>EXACTLY THE SAME AMOUNT NOT MATTER WHAT THE GAS</B><p>The thing that they MAY be talking about is that since N2 has a different mass than O2 for the same volume/temp/pressure, it may either take longer to heat up or shorter to cool down, something like that (that's where gamma comes in BTW)<p>-BuzZ3

//Mster
03-21-1998, 01:24 AM
Is'nt he saying that less of the gas is likely to escape which means it is more stable over time and temperature fluctuations? I think that is what he said.


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