13" tire group buy

[Conserv]

On 2/9/2018 at 11:45 AM, Joesprocket said:

 

I'm with Paul. Incorrect speedo/odo is frustrating when it's due to incorrect tire size. 

 

Let’s be clear:  the original radial tire size for all ‘02’s, except the factory turbo, was 165/80/13.  The factory turbo tire size was 185/70/13.  The difference in outside diameter between these two is negligible, less than 1%.

 

One of the many tire size calculators is at tiresize.com:

 

https://tiresize.com/calculator/

 

They provide the following sizes:

 

165/80/13 = 23.4” in diameter

185/70/13 = 23.2” in diameter, .9% less than 165/80/13

175/80/13 = 24.0” in diameter, 2.6% greater than 165/80/13

175/70/13 = 22.6” in diameter, 3.4% less than 165/80/13

 

Thus, a 175/80/13 tire is slightly larger in outside diameter than the original 165/80/13 tires, just as a 175/70/13 tire is slightly smaller in outside diameter.  So if your speedometer was 100% accurate from the factory, and remains so today, a 175/80/13 or a 175/70/13 will introduce an error: your actual speed will be slightly higher or lower, respectively, than the speedometer indicates.

 

But this assumes your starting point is 100% accuracy of the factory set-up.  Hmmm?

 

My ‘76 is not typical of all ‘02’s, but it does represent a sizable subsection of 1976 U.S.-spec, 49-State cars.  As I’ve discussed previously, showing you excerpts from 1976 Roundels (copies below), BMW accidentally marked a large batch of speedometers intended for use in 3.90 diff cars with “W = 1.393”, but actually installed gearing for 3.64 diffs in those speedometers.  The period articles talk about a 7% error, but my ‘76, always shod with 165HR13 XAS tires, has had an approximate 9% error since new.  Given these facts, a non-original 175/80/13 would actually improve the accuracy of my speedometer.

 

My assumption, since I learned my car had a 9% error, is that a 7% error was created by the speedometer gear fiasco and the other 2% error arose from other system shortcomings or miscalculations.

 

My overall point is that most ‘02’s did not come from the factory with 100% accurate speedometers — my ‘76 being far worse than the likely norm — and you should bear that in mind as you examine your tire size choices.

 

(Since 1997, the dawn of my GPS era, the GPS providing a relatively reliable means to evaluate speedometer era, I have not owned a car with a 100% accurate speedometer.  Most are off by 2 to 5%.  These include new cars from Mercedes, BMW, VW, Audi, and Toyota.)

 

Regards,

 

Steve

 

 

 

 

 

Edited February 12, 2018 by Conserv

[joebarthlow]

9 minutes ago, Conserv said:

...

So, my point is that most ‘02’s did not come from the factory with 100% accurate speedometers — my ‘76 being far worse than the likely norm — and you should bear that in mind as you examine your tire size choices.

 

Regards,

 

Steve

 

 

 

 

 

 

 

I'm about 9% off in my '74, running 185/70s, but that's likely a speedo error not the tires

Edited February 9, 2018 by joebarthlow

[venoak]

A little off topic.

This gps based iPhone app was easy to use and confirmed that all my analog and digital speedometers were accurate to within 0.5 mph. If you have your phone mounted near, not in, your line of sight this could be a free option to repairing your Speedo. 

 

https://itunes.apple.com/us/app/gps-digital-speed-tracker/id901574501?mt=8

 

Alternatively, if you are in SoCal, North Hollywood Speedometer and Clock can/will check your Speedo for free if its out of the car.  Then repair/change it to your specs for a fee of course.

[PaulTWinterton]

48 minutes ago, Conserv said:

175/70/13 = 22.6” in diameter, 3.4% less than 165/80/13

 

 

I knew this topic would shed light on speedo/odo discrepancies.  

 

Thank you Steve for the archival info.

 

For me 3.4% is significant.  70mph on speedo is actually 67.9mph.    90mph is actually 87mph.  Add that to the gauge discrepancy...jeez.

 

Maybe I'll reconsider 185/70s in the future.  165/80s are just too skinny.

[jgerock]

Need tires for these.

[JohnS]

Love those Cosmic wheels Jim.  What's the width?

[Cruzr]

Need tires for these.

From the pic, it loiks like 5.5×13

Sent from my SM-G930V using Tapatalk

[jgerock]

1 hour ago, Cruzr said:

From the pic, it loiks like 5.5×13

Sent from my SM-G930V using Tapatalk
 

I guess folks don't keep up or view my Archived project blog..

 

 

[jgerock]

1 hour ago, JohnS said:

Love those Cosmic wheels Jim.  What's the width?

5.5" x 13" diameter  They are Mk2 sourced from a FAQ'r in Texas.

[mike472]

On 2/5/2018 at 8:21 PM, Conserv said:

 

There’s been discussion lately that Michelin has re-introduced the tubeless version of the 165HR13 XAS.  But I haven’t yet heard from anyone who has actually obtained a set of the tubeless version.  Anyone?

 

The XAS was introduced in ‘65 as a tube-type tire, but a tubeless version appeared, as best as I can recall, in the mid-‘70’s.  The tubeless version was never factory equipment on 2002’s, even my ‘76 came with tube-type XAS’s.  After the tubeless version appeared, however, I immediately switched to the tubeless version because, even in the late ‘70’s, when tire shops were more accustomed to tube-type tires than today, tube-type tires were a nuisance.

 

Since the late 1980’s, however, when Michelin transferred production of the XAS from their general tire production to their Michelin Passion division (predecessor name of the current Michelin Classic division), only the tube-type 165HR13 has been produced.

 

I am eager to see the tubeless version once again! But I also note that the Michelin Classic website, although it shows tubeless versions of some other XAS sizes, does not yet show a tubeless version of the 165HR13.

 

Regards,

 

Steve

 

In the mid 70's a car tuner by the name of Jack Clark out of Closter, NJ brought a tii up to Lime Rock that had the Alpina injection setup and a nice new set of Michelin XWX's in 185/70-13 mounted on a Ronal wheels.  It was the first time I had ever seen XWX's in a 13" size. Back then you usually saw those only on high end sports cars. I know they are recreating those in different sizes these days and this makes me wonder if they are making in 13" sizes again too.  They had a really interesting looking tread pattern.  Dog biscuit I'd call it.  The stock XAS's I remember were easy to lock up go into a slide when it was wet.  Really good in the dry though.  I wonder how much better these recreations are then the originals.  Thanks to modern tech in rubber and construction they are probably a lot better.

Edited February 10, 2018 by mike472

[Conserv]

12 hours ago, mike472 said:

In the mid 70's a car tuner by the name of Jack Clark out of Closter, NJ brought a tii up to Lime Rock that had the Alpina injection setup and a nice new set of Michelin XWX's in 185/70-13 mounted on a Ronal wheels.  It was the first time I had ever seen XWX's in a 13" size. Back then you usually saw those only on high end sports cars. I know they are recreating those in different sizes these days and this makes me wonder if they are making in 13" sizes again too.  They had a really interesting looking tread pattern.  Dog biscuit I'd call it.  The stock XAS's I remember were easy to lock up go into a slide when it was wet.  Really good in the dry though.  I wonder how much better these recreations are then the originals.  Thanks to modern tech in rubber and construction they are probably a lot better.

 

Mike,

 

The current version of the XWX in a 185/70VR13 size is called an XDX:

 

https://www.longstonetyres.co.uk/tyres/185-70x13.html

 

As you can see, current price for the XDX is $321 each.  Given the excellent performance of the Pirelli Cinturato CN36, at $156 each, however, the XDX has become a tough sale....

 

Best regards,

 

Steve

 

 

Edited February 10, 2018 by Conserv

[jgerock]

Historical stuff for Ray.

 

Make sure you folks read the right side about a certain 507 owner in PA... (aka Uncle Barry).

Sorry for the partial hijack Steve P.  Just going down memory lane (blacktop).

[Conserv]

On 2/9/2018 at 10:46 AM, Dirk02 said:

The Michelin XAS 165R13 tires currently on the market and which I have on the 2002 Cabriolet, are the FF (Formula France) type.

The FF tires were designed for racing and are softer than the regular tires. As can be expected, they offer better grip, but also wear much faster....

 

 

Dirk,

 

Have you actually “used up” a set of the current FF XAS’s yet?  If so, how many miles did you get out of them?  The set on my ‘76 has about 4,000 miles on it, without noticeable wear.  I can’t imagine they won’t go at least 20,000 miles, extrapolating from their current appearance.  But I’ve been wrong before!

 

If they, indeed, last 20,000 miles, at 2,000 miles annually on each of my ‘02’s, I’ll likely “time out” — that’s ten years for me — before I wear out any XAS.  I divide the cost by 10 years and, thereby, rationalize the cost of original tires.

 

Believe it or not, in 45 years of ‘02 ownership, I’ve never used tires other than XAS’s, with the exception of snow tires.  And I’ve never exceeded 35,000 miles on any XAS.  Most were probably gone by 30,000 miles.  This was consistent with ‘02-driving friends, who had similar driving styles!  One friend could not get more than 20,000 miles out of an XAS — this was in the ‘70’s — but his driving was scarier than most.  Other members of this forum have achieved 60,000 miles on XAS’s, in the old days, with the old tread compounds.

 

I keep hearing mention of the FF tread compounds — they go back to the inception of the XAS in 1965 — but I’ve yet to find a user who has “used up” a set of the current FF XAS’s.  And I’m curious.  Are modern FF XAS’s like the Michelin XWX series (e.g., 185/70VR13 XDX for ‘02’s), fantastically grippy but gone in 10,000 miles?

 

Certainly someone here has used up a set of modern XAS’s.

 

Regards,

 

Steve

 

 

 

Edited February 12, 2018 by Conserv

[Conserv]

On 2/9/2018 at 2:39 PM, PaulTWinterton said:

 

....For me 3.4% is significant.  70mph on speedo is actually 67.9mph.    90mph is actually 87mph.  Add that to the gauge discrepancy...jeez....

 

 

But, Paul, one needs a baseline in order to determine the existing speedometer error with the correct original 165/80/13 tires — a baseline you might not have if you’ve never run 165/80/13 tires.

 

Sure, a 3.4% error from running 175/70/13 tires could be a bad thing.  But if your speedometer happened to be off 3.4% in the opposite direction, you could wind up with 100% accuracy, thanks to undersized 175/70/13’s!  ?

 

Best regards,

 

Steve

 

 

 

Edited February 11, 2018 by Conserv

[Teelinger]

Not mine and no affiliation but thought I'd share in case someone was interested: 

https://sfbay.craigslist.org/scz/wto/d/set-of-4-vintage-gurney/6490562425.html

 

 

Edited February 11, 2018 by Teelinger