輪胎胎紋的寬度, 同一寬度尺寸, 為何部分輪胎看似比其他較大或細? (持續更新) Tire width, with the same width size, why some models appear larger or smaller? (to be updated continuously)

 *English version below*

有部分人曾經都提過有關輪胎寬度問題. 新購買同一尺寸的輪胎對比下, 看似比較寬身/窄身.

❓係肉眼上既錯覺 , 定 實際尺寸真係有唔同?  

今次我會幫大家搜羅, 盡量每一個尺寸, 每一款 (就算係同牌子), 唔同製造地點都度下到底條條呔既寬度係咪真係有分別. 

🚙係呢樣之前, 要先幫大家重新了解一下, 輪胎既寬度

**注: 由於係用人手, 用拉尺去度, 一定會有誤差. 另外, 輪胎寬度應該係以裝左上呔鈴, 有足夠輪胎氣壓, 未有裝上汽車前測量. 只可用作為參考之用. 今次只係想睇下, 咁多款呔下其實只係我地肉眼上既錯覺, 覺得一啲呔好似比另一款呔較大/較細.

**特別注意既係, 一款同一尺寸, 同一製造地點, 但唔同製造日期, 係會有機會有輕微誤差. 過去係某啲輪胎廠係根據製造日期批次去回收有問題既輪胎.

肉眼上既錯覺 (optical illusion), 其中必定會了解到 "Müller-Lyer illusion" 及 "Ponzo illusion" - 兩條相同既橫線但看起來好似一長一短, 及兩條相同既直線看起來一高一底.

普通既直線都會令到視覺上產生錯覺. (大部分) 輪胎 (我個人認為) 都係一樣. 胎紋上既設計, 包括主要排水紋及其他周邊細少既槽會影響視覺上睇出黎既寬度.

而呔肚位上所示既寬度, 其實係由一邊既呔肚位去到另一邊既呔肚位, 並非係呔紋既寬度. 所以, 一條 205/55 R16 既寬度為 205mm, 接觸地面既呔紋並非係 205mm.

呔肚位所示既寬度有國際認可要求. (下文叫佢做"總寬度"), 但呔紋的寬度並沒有特別固定要求. 但暫時我所量度既呔款當中, 大家呔紋的寬度其實都係差不多相同.

(輪胎所示既總寬度, 上圖輪胎尺寸為 205/65 R15)

上圖所顯示的兩款不同輪胎, 其實肉眼上既寬度看似不一樣(相可能睇唔出), 但量度下, 呔紋寬度及總寬度都係差不多一樣. 而總寬度都係205mm

相信唔少人都會察覺到, 係 www.tyrehood.com 能夠俾您選擇既寬度, 每個寬度之間都差 10mm. 

根據European Tyre and Rim Technical Organisation (ETRTO), Tire and Rim Association (TRA) , 每個尺寸製造出 10mm 之差, 其實有多個原因. 當中, 10mm 之差先會令輪胎有些少增加性能(e.g. 咬地性能) 

除此之外, 輪胎寬度都有 "可接受範圍". 應該係大約3%之間. (e.g. 205) 總寬度都有機會可能係 198mm, 211mm etc

有可能呢個原因, 引致部分呔睇落好似有些少窄身啲或寬身啲

問題黎啦 ❓❓❓❓❓❓❓❓❓

Q1: 會唔會每一款既同一尺寸輪胎都會有不同既呔紋寬度呢? 
Q1a: 會唔會每一個牌子其實都有一個特定既標準去製造出呔紋寬度呢?

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Q2: 每個尺寸既總寬度都有10mm 之差, 會唔會有部分輪胎尺寸總寬度寫 (e.g. 255), 但實際可能係 250mm? 更有可能係246mm ? 大於"可接受範圍"?

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Q3: 有冇可能兩個不同尺寸 e.g. 205/55 R16 vs 215/55 R16, 總寬度相差 10mm, 但呔紋寬度係一樣長?

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Ans: 呢個就係我今次會幫大家收集既數據. 下回分解.

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Some have enquired about the physical width of a tyre. Purchasing the same size, why different models look wider or narrower than the other?

❓ Is it an optical illusion, or the size physically really different?

This time I will try to gather as much data as possible, with different sizes, different model and different manufacturing place to ascertain if the width of each tyre (even of the same brand) really has a difference.

🚙But before that, let's understand more about TIRE WIDTH

**Note: There will be a human error in measuring the width of the tire (using measuring tape). The standard of measuring tire width is supposed under the following conditions:

- Has installed on a rim
- Sufficient tire pressure
- No loading.

Hence, this experiment is just for reference with no accurate data. It is supposed to find out if the look of a tire that looks narrower or wider is simply due to optical illusion.

**Another Note: A batch of same size, same model, same manufacturing place but different manufacturing date could have a slight variation on the measurement. After all, tire manufacturer recall tires based on manufacturing date. 

Talks about optical illusion, we will surely come across "Müller-Lyer illusion" and "Ponzo illusion" - Two horizontal lines with the same length but one looks longer and the other one look shorter, 
and Two vertical lines with the same height, but one looks higher, the other one looks shorter.

In this way, I believe that (most) tires that look wider or narrower due to tread design with different styles of rib, block, sipe.

The width of the tyre shown on the sidewall is actually the length between one point of the tyre (inner) sidewall, to the other point of the (outer) sidewall. The width shown IS NOT tire tread width.

Therefore, a 205/55 R16 tyre has a 205mm width. The tire tread width that touch the ground IS NOT 205mm

The measurement of the tire size has an international standard. But tire tread width does not have a fixed standard. So far, the tire sizes that I have measured by now have around the same tread width and overall width.

(Tire width shown with red lines. Both tires are 205/65 R15)

The two tires shown on the above image actually looks physically different in width. (You may not see it inside the photo). But both tire tread width and overall width (which is 205mm) are the same after measurement. 

Some may discover that www.tyrehood.com only allows you to select a width with 10mm increment. According to European Tyre and Rim Technical Organisation (ETRTO), Tire and Rim Association (TRA) , tire should be manufactured at least 10mm difference due to a varies of reasons. One of them is a 10mm difference can only prove to have slight improvement of performance (e.g. traction).

In addition, the width of the tire size also have a tolerance of around 3%. (e.g. 205) overall width, actual physical width could be 198mm, 211mm etc.

As such, this may result in some tire model looks narrower or wider.

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Q1: Does each model have different tire tread width?

Q1a: Does each brand actually have their own standard for tire tread width?

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Q2: With an 10mm difference in width, will there be tires with size overall width (e.g. 255), but actual physical width is 250mm, or even narrower, 246mm in which greater than the international tolerance?

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Q3: For two different size e.g. 205/55 R16 vs 215/55 R16, overall width is 10mm but tire tread width is the same?

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Ans: The answer is going to reveal next time after data gathering.