Do Lower Profile Tires affect Speedometer Reading

[Ameer Antar]

I don't think that rule applies to all cases, b/c when the width is small, changes in the profile doesn't affect the total diameter as much when the width is larger. That's b/c the profile number is a percentage of the tire width. Keep in mind the tire diameter is what affects the speedo reading. The best thing to do is to figure out the total diameter of the original size and then try to find another size that is similar to the original diameter. 

Check out: http://www.mgbexperience.com/service/tirecalc.php
Use the last calculator to find out the original diameter and the new tire diameter. With those 2 numbers you can use the top calculator to see the difference in speedo numbers for the 2 tire sizes (the difference gets bigger the faster you go).

I think you should stick to the same size tires, unless you can get a smaller rim. If the wheel size is the same, you can change the profile, but you need to also change the tire width to keep the tire diameter the same (or similiar). I'm not sure about the 100, but for the 5000, you can't go too much wider than 205's, and you'll be getting less performance by going to a tire less than 205. Usually, you'll find more snow tire options at higher profiles, so the only real option is to find a 14" rim. Then you can increase the profile to try to get back to the original diameter. I also think it's good to stay as close as possible to the original diameter b/c a smaller tire will look funny on the car, and too big a tire may cause rubbing. Audi's have their own bolt pattern that only a few other car makers use on some models, but's not a common one like they use on Honda's or American cars. Good luck.

-Ameer


---- Original Message ----
Date: Wed, 09 Nov 2005 08:14:53 -0500
From: Kneale Brownson <kneale at coslink.net>
Subject: Re: Do Lower Profile Tires affect Speedometer Reading
To: <mboucher70 at hotmail.com>, <quattro at audifans.com>
Message-ID: <4.1.20051109081335.01678dc8 at pop.powerc.net>
Content-Type: text/plain; charset="us-ascii"

Minimal speedo difference, but for snow, it's recommended to go to the
slightly taller tire. So you should be getting 195 65 R15. 


At 08:03 AM 11/9/2005 -0500, mboucher70 at hotmail.com wrote:
>I'm looking at a pair of 'performance winter' tires. The size is 195 55 R15.
>
>My car's original equipment is 205 60 R15.
>
>I've read that for winter you should change the sizing by one each - that is
>either
>
>205 60 R15 or
>195 65 R15 or
>185 70 R14 if load capacity allows.
>
>I'm a bit confused by this rule. I understand that the tire profile change
>is ofset by a rim size change. So then, wouldn't 205 60 R15 and 195 65 R15
>give different speedometer readings, since the rim size is the same but the
>profile is different?
>
>Bottom line question is will moving from 205 60 R15 TO 195 55 R15 work on my
>car (1990Audi100) or will it change my speedometer readings?
>
>Other question, where is a good place to get inexpensive winter rims
>(Wal-Mart, etc)? It uses 6Jx15 rims. Are these standard rims, or
>specialized Audi rims? I've noticed that most Audis use the 5-bolt tires,
>but mine uses a 4-bolt.
>
>Thanks
>
>Charles
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