Tire Size Tolerance: What You Need to Know

Hello,

I'm starting to think about buying winter tires.

In the summer, I use 195/55 R 15 tires with a full-size spare tire.

The recommended tire size is 185/55R15. I actually want to use that size as well, because narrower tires have a higher weight load per unit area.
However, I would like to avoid buying a separate winter spare tire, and in the event of a flat tire, I would like to use the summer spare tire instead.

Now, the two standard rolling diameters differ by at least 2%.
I know that the difference is less than your allowable spread within one dimension (, 5% / -2.5% results in a total maximum possible spread of 4%).

However, with an unfavorable combination (large summer tires and small winter tires), the difference can already be 6%, which leads me to the question:

"What is the acceptable level of permanent wheel speed deviation that the ABS can tolerate without causing malfunctions or errors?"

Fortunately, my speedometer no longer has its own sensor; it's fed data from the ABS system (removing the ABS fuse causes the speedometer to read zero).

Hi,

Regarding the ABS tolerance, I unfortunately can't provide any information, but I wanted to raise a point about the contact patch pressure of different tire widths:
http://www.dunlop.de/de/data/news/reifentest/rollederreifen5.html

But then there's still the question of weight ...

Roger wrote:

http://www.dunlop.de/de/data/news/reifentest/rollederreifen5.html ...

Ein interessanter Link - man lernt eben nie aus. Thank you .

Regardless of the size of the contact area, you can also see how, with a wide tire, it not only becomes wider, but also rotates "perpendicular to the direction of travel."
When there's water on the road, the old shipbuilding wisdom becomes even more relevant: length provides stability, while width causes slippage -> aquaplaning .

Quote:

But then there's the issue of weight

However, since my Polo weighs practically the same with 195 or 185 tires, the weight probably doesn't play a significant role here.

Quote:

When there is water on the road surface, the old shipbuilding wisdom becomes even more relevant: Length provides stability, while width causes slippage -> aquaplaning

That's true, but shipbuilders don't have the ability to increase the profile negative area. Unless they build catamarans .

I drive 225/45 R17 tires, and despite this size, I have never experienced aquaplaning. The Dunlop SP 9090 tires have a very pronounced directional tread pattern and a very high proportion of negative grooves. Unlike the 155/70 R13 tires on our previous Polo, the wider tires also seem to be up-to-date in terms of aquaplaning performance. Everything is possible, but potentially at the expense of durability.

But maybe someone will come back to your ABS topic later.

The contact area of a tire is roughly the size of a postcard. With narrow tires, the long edge is parallel to the direction of travel, while with wider tires, it's perpendicular to the direction of travel. So, it's not a huge area.

I initially used the Conti SP2 tires on my Golf 4 in size 205/55/16, and now I'm using them on my Audi in size 235/40/18. What's really strange is that this wider tire seems to be less susceptible to aquaplaning than the narrower one. However, my Audi only weighs just under 100kg more than the Golf, which is a negligible difference.

You can read the individual wheel speed signals from the ABS/ESP control unit (if you have a good one from Bosch), and then you'll see that the difference is very small.

'I used to test the ABS/ASR system on the rear axle of my Mercedes by mounting the spare tire (195/65/15) on one side and the wider tires (255/35/19) on the other. The result was that the ASR (traction control) worked perfectly, and so did the ABS (anti-lock braking system). However, the speed sensor on the rear differential would occasionally give a warning in tight, slow turns (like when turning around on a road). But the difference in tire size was quite significant. Within the normal operating range, the system worked flawlessly.'

Are you sure you should be using 195/55 and 185/55 tires? Wouldn't the 185 size have a higher sidewall?

Julian wrote:

But the difference in wheel sizes was already considerable. Within the normal range of both, the system worked perfectly well.

Okay, that already suggests a relatively high tolerance for different tire sizes.

Quote:

Are you sure you should be using 195/55 and 185/55 tires, as the 185 would have a higher sidewall?

Hm??

The slope height is determined by...
195 mm * 0.55 = 107 mm, or approximately 107 mm.
185 mm * 0.55 = 102 mm.

So, the 185 is about 5 mm lower - or what are you trying to say?

The slope height is determined by...
195 mm * 0.55 = 107 mm, or approximately 107 mm.
185 mm * 0.55 = 102 mm.

So, the 185 is about ~5 mm lower - or what are you trying to get at?

Hmm, shouldn't the sidewall height always be adjusted so that the tire's overall diameter remains as consistent as possible when you change the width?

So, in your case, it's 185/60 (= 111mm, only a 4mm deviation).

Julian wrote:

Hmm, the tire should always have an adjusted sidewall height so that the tire circumference remains as consistent as possible when you change the width, right? So, in your case, it's 185/60 (=111mm, only a 4mm deviation).

Oh, so you mean ?

However, the tires that come installed from the factory are actually 185/55 R 15 M+S.

Perhaps due to space constraints in the bike frame's internal compartment?
-> If 107 mm is already the maximum acceptable diameter, and if snow chains are to be usable, then the tire must be slightly smaller.

Hi,
If you are using four identical tires, an ABS malfunction should not occur, as the ABS system itself only evaluates the difference in wheel speed pulses. Regarding the speedometer, the deviation should be within the legally permissible tolerance for all tire sizes approved in the vehicle's documentation (I believe it was a maximum of +7% of the speedometer's maximum reading).

Regards,
Olli.