historical accuracy, was: <VV> Tire gurus

[airvair]

Thank you Bruce! That is extremely well stated, and something with which 
I fully agree. The big problem with the 7.00-13 is that it is HUGE for a 
13" tire, probably the largest one ever built, and nothing today even 
comes close. The reason Corvairs have 13" rims and no larger has to do 
solely with GM corporate policy. Management decreed that compacts were 
to have ONLY 13" rims. Corvairs honestly could have benefitted from a 
14" rim option. We collectors certainly could have....  (G) BTW, that 
policy has fallen by the wayside, as my '03 Cavalier has 16" wagonwheels 
on it. EGAD!!

FYI I understand that the way antique car clubs like the AACA get around 
the "no exact size available" problem is to require the closest size 
that IS available, then if and when the correct tire DOES become 
available, to require its use.

That said, I wonder if the powers that be in CORSA are listening? Hello 
out there? Anybody home??

-Mark

Bruce Schug wrote:

> On Mar 28, 2005, at 12:20 PM, airvair wrote:
>
>> All this discussion brings up a point. With regard to historical 
>> accuracy, is it better to preserve the factory LOOK of the (factory 
>> stock) car, or it's speedo's mechanical accuracy? In this case, is it 
>> better to have a tire with the diameter that LOOKS like an authentic 
>> 7.00-13, or one who's size is chosen merely to allow the speedo to 
>> function accurately? And if radials end up adversely affecting the 
>> look, should they be banned in stock classes?
>>
>> As stated before, I dislike the undersized look of (most all) present 
>> radial tires. Like any car, wide-open wheel wells (what you get when 
>> the tires don't fill the openings) don't look good. The downside is 
>> that with 13" wheels, it looks like we are pretty much stuck with 
>> undersize-looking tires (when they're radials.)
>>
>
> Mark,
>
> I haven't seen any other opinions posted about this, so I'll give you 
> mine.
>
> The CORSA rules for tire sizes were written when most Corvair people 
> were under the misconception that a 7.00-13 was 24.1" in diameter and 
> the 6.50-13 even smaller. This misconception apparently came about 
> because of a misunderstanding between "loaded" diameter (twice the 
> loaded radius) and actual static diameter. As a result of the research 
> I did about ten years ago plus the "discussion" of this topic that has 
> gone on in here, I think most people who have paid attention to the 
> subject now understand that this was incorrect. Even my staunchest 
> opponent emailed me privately one day and told me he had figured that 
> the original 7.00-13 was just about 25.3" in diameter, something I had 
> been trying to explain to him for years.
>
> There still exists those who believe the CORSA rules should be set by 
> tire manufacturer's charts of "replacement" sizes. My opinion of these 
> charts is that they are meaningless because they typically refer to 
> load ranges, which to me, don't mean anything when it comes to 
> specifying a modern tire that is the true equivalent to the original 
> bias tires.
>
> When we discuss this issue, some turn it to a matter of speedometer 
> accuracy. To me, speedometer accuracy has nothing to do with this 
> issue. I know how to get an accurate speedometer if that's what a 
> person is after.
>
> The essence of this discussion is simply, which modern tire LOOKS LIKE 
> an original Corvair tire. To me, this has to do with static diameter, 
> nothing else. (Obviously whitewall width too, if we are referring to 
> whitewall tires.) With this in mind we can study the diameters of 
> original tires and modern tires and easily and accurately conclude 
> that the 185/80-13 is essentially the replacement for the 6.50-13. The 
> 6.50-13 varied quite a bit in diameter and the 185/80-13 falls within 
> this window. Unfortunately, as you know, there is no modern equivalent 
> currently being produced for the 7.00-13.
>
> Regarding the CORSA rules, I think the current rules which allow, even 
> REQUIRE tires much different than the original tires make a joke out 
> of CORSA Concours competitions. This is like going to an AACA meet and 
> seeing modern radials on classic cars such as Corvettes, forty-Fords, 
> GTO's, etc. Can you imagine such a thing? It just wouldn't happen. 
> These cars are required to have the original tires if they are 
> presented as original cars.
>
> CORSA has several different classes for cars depending on how stock 
> and original they are. Since I'm not a concours guy and don't want to 
> get my CORSA Concourse rules out of the drawer, I'll just refer to the 
> class as more stock and more relaxed classes. We won't discuss the 
> modified classes - obviously any tire can be used by those 
> participants. But in the most stock classes - I think they're factory 
> stock restored and unrestored, I think original tires should be 
> required. Because original 6.50-13's are readily available this isn't 
> a problem for those cars with that size. For those requiring 7.00-13's 
> it's a different story.
>
> I think Corky Coker or some other vendor would make 7.00-13's if 
> someone would buy them (they don't buy them because CORSA doesn't 
> require them). I think it would take a rules revision like this to 
> force the issue. I'd give cars a grace period to meet the new tire 
> rule, maybe three years. That would give Corvair people time to 
> persuade someone to make these tires. Maybe someone like Cal Clark or 
> Lon Wall would have to put up some money and buy a quantity of these 
> new 7.00-13's to get the job done. Unfortunately, if this tire were 
> not available, there would not be any of those cars in the more stock 
> classes.
>
> I think the relaxed stock classes could be allowed to use modern 
> equivalents. The 185/80-13 would fit the bill for replacing the 
> 6.50-13. As mentioned before, there is no modern equivalent for the 
> 7.00-13. The only solution I see here is to allow the 185/80-13 as a 
> substitute replacement for the 7.00-13 too. I see no reasonable way 
> around this. The reproduced 7.00-13 could be used on these cars too, 
> but if the owner wanted a modern tire, the 185 would have to do. I 
> don't have any illusions of getting a tire company to make some 25.3" 
> diameter 195/80-13's.
>
> Bruce W. Schug
> CORSA South Carolina
> Greenville, SC
> bwschug at charter.net
>
> CORSA member since 1981
>
> '67 Monza. "67AC140"