Fw: Re: Wheels

[Larry C Leung]

From: Larry C Leung <l.leung at juno.com>
To: antar at comcast.net
Date: Thu, 21 Oct 2004 22:55:00 -0400
Subject: Re: Wheels

Bear in mind, an auto manufacturer, as I stated, can, and does test the
combination to ensure their liability is covered. So, Audi can certainly
take the "risk", because they've evaluated the combination ON THE
VEHICLE. Extreme rim/tire sizing is dependent upon:

-Tire/rim fitment
-Vehicle weight
-Gross Vehicle weight
-Corner loads
-Dynamic Corner Loads
-Expected Vehicle Usage
-Projected Tire Life/Wear

Tire Manufacturers, by the nature of them being unable to test EVERY 
possible combination, and yet, as you've noted, they still bear liability
responsibility. So they are cautious in their recomendations. Since
you, nor I, nor the original poster, are likely to be able to test their
vehicle under all possible conditions, prior to being in an accident
avoidance manuver, I feel it's opening yourself up to possible liability
(yes, you didn't sell the advise, but...) if something happened, so
to err on the side of caution is somewhat advisable. Depending upon
profile, a majority (search TireRack's website)of  tire manufacturers 
don't support a 6" rim on their 225 tires. Yes, there may be some 
tire manufacturers that do support it, BUT, it's tough to make a 
GENERAL rule about that without knowing the specifics. 

Would I run 225's on 6 rims. Yes, I have, in experimenting during my
Solo2 years, on a 2200 lb A2 GTi. But that was controlled conditions, 
and at comparatively low speeds (hard to get much past early in 3rd 
gear). Would I do the same on the street? Not on your (actually, my) 
life. Would I do the same on an autocross with a 3600 lb type 44, or
even a 3400 lb B4 or 5 car? No way. Car weighs too much, consequences
too high. 

My point, is careful making recommendations without knowing specifics,
especially when operating at the extremes of a piece of machinery or
equipment of which safety is of issue. Yes, you can state specific cases
that do work, but by being on the extreme, they can't be generallized. 

LL - NY, temporary safety nazi, especially when the guy next to me may be
following my advise....



On Thu, 21 Oct 2004 22:32:36 -0400 Ameer Antar <antar at comcast.net>
writes:
> I understand your cautiousness, but really, 7" is NOT "ALREADY" below 
> the manufacturer's suggestion. 7" is what Audi uses, and they do not 
> manufacture tires. I've looked at several tires that are sized 
> 225-50-16, and their recommended rim width is 6-8", so there's no 
> danger, unless manufacturers want to slit their own throats (I'd say 
> the flop between Firestone and Ford should've put these people on 
> notice).
> 
> I felt that 6" was cutting it close, but I don't think they are a 
> danger. As the Yokohama site explains it, you increase the softness 
> of the ride when reducing wheel width, due to the shape of the 
> sidewall. The other extreme will increase the performance (they 
> didn't say safety), but will also increase negative aspects, like 
> ride harshness and tracking on cracks in the road (a symptom of 
> over-responsive steering). Everything really ought to be balanced 
> somewhere in the middle... So 7.5" is actually not ideal; it's 
> making some sacrifices, but not in safety. As long as the tire 
> manuf. approves the size, it's OK. Manufacturers build a decent 
> margin of safety into these ratings to account for extreme 
> conditions, so being very close to the extremities will get you by 
> for a while, but as I mentioned in the first email, you should 
> replace the tires with a better size when they wear out, or even 
> replace the wheels to match the tires. It all depends on $$... I 
> really don't think safety is an issue here (esp. given the manuf. 
> ratings), it's about what the person is looking for and how much 
> they have to spend for that.
> 
> -Ameer
> 
>    ----Original Message----
>    From: Larry C Leung <l.leung at juno.com>
>    Date: 10/21/04 8:39:01 PM
>    Subject: Re: Wheels
>    
>    There is an inheritly LARGE difference between a 7" rim and a 6" 
> rim,
>    7" is ALREADY below what nearly all tire manufacturers suggest as 
> 
>    a minimum rim width for a 225mm width tire, and the car 
> manufacturer
>    has the luxury and responsibility to test the safety of the 
> combination.
>    
>    Do you really wish to be the test pilot for this application? 
>    
>    The whole percentage thing is ONLY a guideline, it's not a rule. 
> The
>    rules are set by the tire manufacturer. Only they truely know the 
> limits
>    of their tire. In reality, it's really a tire mfg/car mfg 
> combined
>    effort, 
>    although reasonable corner weight info may be enough to confirm 
>    things for the tire mfg alone. 
>    
>    The only application I've seen allowing 225's on 6" rims is on 
> several
>    DOT R (race) tires, which have a MUCH narrower range of expected 
> 
>    uses and conditions from street tires (but being DOT rated, they 
> have
>    the same liabilities). Tire manufacturers were forced to make 
> this
>    combination
>    work due to at least the SCCA's rules for Solo Stock and Showroom 
> Stock
>    racing. I rather doubt they'd consider this range ideal for the 
> tire.
>    I've seen
>    no other application allowing this narrow a rim for this wide a 
> tire. 
>    
>    I'd also imagine that this is a rather difficult combination for 
> the tire
>    wrench to seat properly. 
>    
>    IMHO, it's NOT a good idea, I'd prefer to NOT be driving next to 
> 
>    a car so equipped. 
>    
>    LL - NY, protecting mine (and possibly your own) flanks
>    
>    
> 
>