Tire sizes explained

[mrelwood]

Looking into the available tire sizes for your EUC for the first time is confusing. This boils down to EUCs being a rare vehicle group in that can succesfully use either (e-)bicycle or motorcyle tires. The sizing designations in these groups are both measured and reported differently, so you have to be sure to know whether the tire is made for a motorcycle/scooter/moped or a bicycle/e-bike/EUC when shopping for a new tire.

 

Bicycle tires

18 x 3.0  :  Tire diameter class (inches) "x" maximum tire width (inches). This is the imperial designation type we are most familiar with, as this is what reads on almost all factory install EUC tires. Although, the first number is neither the rim diameter nor the actual outer diameter, but more like a size class that fits on a rim that is 4" smaller. For example, 18 x 3.0 tire has a much larger outer diameter than a 18 x 2.5 tire, but as they are in the same size class, they both fit on a 14" rim. The designated width is usually the maximum width of the tire, but the actual measured width can be as small as 2.65" (Chao Yang H-5102).

76-355  :  Actual tire width (millimetres, mm) "-" rim diameter (mm). This is the ETRTO stardard for a Chao Yang H-666 18 x 3.0 tire. Since the width is the actual width of the tire, an 18 x 3.0 tire could also be for example 75-355.

Then there are the French 700A/B/C sizes, but they are 27" bicycle tires, so nothing we are interested in.

 

Motorcycle tires

2.75 - 14  :  Carcass width (inches) "-" rim diameter (inches). This is the imperial motorcycle standard. The width does not include any tread pattern shapes and knobbies, so a 2.75 - 14 tire can have a maximum width of as much as 3.1". Notice that here the width is written before the diameter, and instead of the "x" they are separated by a "-". A few rare shops mess these up though, so while the product page title may read 14 x 2.75, the tire can actually be 2.75 - 14. Or even vice versa, such as the 14 x 2.5 tire that I received when I ordered a 2.5 - 14 tire...

2 3/4 - 14  :  Width (inches) "-" rim diameter (inches). While mathematically identical to the above, all I know is that the width of a 2 3/4 tire is different to a 2.75 tire. This is a rare (and likely outdated) style though, and I haven't found EUC suitable tires that are written in fractions.

80/90 - 14  :  Width (mm) "/" height (% of width) "-" rim diameter (inches). This is a metric replacement for a 2.75 - 14 motorcycle tire. While the 80mm width should point to 3.15", for a reason unbeknownst to me, 80/90 - 14 is mentioned as a direct replacement for a 2.75 - 14 tire in motorcycle tire compatibility charts. I have actually been running a 80/90 - 14 tire on my MSX for the past few weeks. At least the IRC SN-26 80/90 - 14 fits the MSX without rubbing, but other models may not.

The height of a 2.75 - 14 tire is about 100% of the width, so a 80/90 - 14 tire has a slightly smaller outer diameter. Comparable to a 18 x 3.0 though.

With motorcycle tires there is more variation between the size specification and actual measurements, so there is more risk of a tire not fitting an EUC. Luckily shaving the side edge of a tire is easily done with a belt sander, angle grinder, or just letting the tire run against a concrete wall or a rock etc.

Edited July 31, 2020 by mrelwood

[Sai]

On 7/30/2020 at 11:22 PM, mrelwood said:

Looking into the available tire sizes for your EUC for the first time is confusing. This boils down to EUCs being a rare vehicle group in that can succesfully use either (e-)bicycle or motorcyle tires. The sizing designations in these groups are both measured and reported differently, so you have to be sure to know whether the tire is made for a motorcycle/scooter/moped or a bicycle/e-bike/EUC when shopping for a new tire.

 

Bicycle tires

18 x 3.0  :  Tire diameter class (inches) "x" maximum tire width (inches). This is the imperial designation type we are most familiar with, as this is what reads on almost all factory install EUC tires. Although, the first number is neither the rim diameter nor the actual outer diameter, but more like a size class that fits on a rim that is 4" smaller. For example, 18 x 3.0 tire has a much larger outer diameter than a 18 x 2.5 tire, but as they are in the same size class, they both fit on a 14" rim. The designated width is usually the maximum width of the tire, but the actual measured width can be as small as 2.65" (Chao Yang H-5102).

76-355  :  Actual tire width (millimetres, mm) "-" rim diameter (mm). This is the ETRTO stardard for a Chao Yang H-666 18 x 3.0 tire. Since the width is the actual width of the tire, an 18 x 3.0 tire could also be for example 75-355.

Then there are the French 700A/B/C sizes, but they are 27" bicycle tires, so nothing we are interested in.

 

Motorcycle tires

2.75 - 14  :  Carcass width (inches) "-" rim diameter (inches). This is the imperial motorcycle standard. The width does not include any tread pattern shapes and knobbies, so a 2.75 - 14 tire can have a maximum width of as much as 3.1". Notice that here the width is written before the diameter, and instead of the "x" they are separated by a "-". A few rare shops mess these up though, so while the product page title may read 14 x 2.75, the tire can actually be 2.75 - 14. Or even vice versa, such as the 14 x 2.5 tire that I received when I ordered a 2.5 - 14 tire...

2 3/4 - 14  :  Width (inches) "-" rim diameter (inches). While mathematically identical to the above, all I know is that the width of a 2 3/4 tire is different to a 2.75 tire. This is a rare (and likely outdated) style though, and I haven't found EUC suitable tires that are written in fractions.

80/90 - 14  :  Width (mm) "/" height (% of width) "-" rim diameter (inches). This is a metric replacement for a 2.75 - 14 motorcycle tire. While the 80mm width should point to 3.15", for a reason unbeknownst to me, 80/90 - 14 is mentioned as a direct replacement for a 2.75 - 14 tire in motorcycle tire compatibility charts. I have actually been running a 80/90 - 14 tire on my MSX for the past few weeks. At least the IRC SN-26 80/90 - 14 fits the MSX without rubbing, but other models may not.

The height of a 2.75 - 14 tire is about 100% of the width, so a 80/90 - 14 tire has a slightly smaller outer diameter. Comparable to a 18 x 3.0 though.

With motorcycle tires there is more variation between the size specification and actual measurements, so there is more risk of a tire not fitting an EUC. Luckily shaving the side edge of a tire is easily done with a belt sander, angle grinder, or just letting the tire run against a concrete wall or a rock etc.

Great info, thank you. Any idea for 16x3.0 wheels? Ks 16, nik+? 

[mrelwood]

2 hours ago, Sai said:

Great info, thank you. Any idea for 16x3.0 wheels? Ks 16, nik+? 

Plenty. They follow the same pattern as other sizes. Not exactly sure what you mean though.

[Sai]

7 hours ago, mrelwood said:

Plenty. They follow the same pattern as other sizes. Not exactly sure what you mean though.

Lol should have elaborated properly. I mean a 16x3.0 will be a 12 inch motorcycle tyre? I see alot of 12 1/2 and was wondering if they would fit. 

[mrelwood]

Yes, 2.75-12 or 60/100-12 and maybe even 80/90-12 are the maximum motorcycle tire sizes to fit a 16x3” EUC. 12 1/2” will not.

Edited August 9, 2020 by mrelwood

[Unventor]

I found this website today. 

https://www.tacomaworld.com/tirecalc?tires=80-80r14-80-90r14

[mrelwood]

On 12/6/2020 at 12:46 PM, Unventor said:

I found this website today. 

https://www.tacomaworld.com/tirecalc?tires=80-80r14-80-90r14

There are many tire size calculators around, but they all consider the width designation of the tire as an absolute, which it never is.

 Here’s a photo of a 18”x3.0” tire of an MSX facing a 3.00-12 scooter tire. The actual measured widths - tread shapes excluded - are 70mm and 78mm (72 and 83 with tread). That’s 2.76 and 3.07 (2.83 and 3.27) inches.

My 80/90-14 tire measures 71mm (77mm), 2.8” (3.03”).

 

Edited December 7, 2020 by mrelwood

[upbnsfrrfan]

So a tire designated as 3.00-18 size is also the same as a 18x3??? Just curious as I saw some nicely treaded tires from Aliexpress but I wonder if they will fit the 14" rims from gotway etc...

Motorcycle tire 2.50 2.75 3.00 18 inch anti slip and wear resistant front and rear outer tire| | - AliExpress

Edited April 15, 2021 by upbnsfrrfan

[fbhb]

2 hours ago, upbnsfrrfan said:

So a tire designated as 3.00-18 size is also the same as a 18x3??? Just curious as I saw some nicely treaded tires from Aliexpress but I wonder if they will fit the 14" rims from gotway etc...

A tire designated as: 3.00-18 in size is measured via motorcycle format i.e. rim diameter, so those dimensions are way too large to replace the 18x3 bicycle tire as used on an EUC! 

If any tire is listed for sale in motorcycle format and then it needs to be a 2.75-14 to fit as even a 3.00-14 will measure up far too wide for most of our 18inch (14" rim) EUCs.

Edited April 15, 2021 by fbhb

[upbnsfrrfan]

Oh okay. Got it  Thanks 

[Kagenin]

I'm gonna go ahead and call my S18 tire swap a success for now... but now I'd like to adjust the speedometer and odometer to compensate for the change in diameter.  EUCWorld has such a feature, so I may as well use it so I can figure out fast/far I'm actually going.

The stock tire was the ChaoYang H-5102, which says "18x3.0/76-355" along the side.  I've replaced it with an IRC TR-1 in 2.75-14, a dual-sport tire with a knobby tread, that I ordered off Amazon Japan.

https://www.amazon.co.jp/dp/B0042ZBYAY

The specs there state a 5mm tread depth.  The tire seems bigger, which would mean that with the motor spinning at the same RPMs, I'm going slower, but further, correct?

Anyone know how or where I can calculate that out?

[Tawpie]

The way I would have done it (it's a little late now though) would be to:

1. put a mark on the H-5102
2. measure the distance travelled for 1 revolution of the wheel
3. mount the TR-1
4. put a mark on the TR-1
5. measure the distance travelled for 1 revolution
6. compute the % difference
7. enter into EUC World

But since you can't do steps 1 and 2 easily, maybe someone else can do them for you?

[Unventor]

36 minutes ago, Kagenin said:

I'm gonna go ahead and call my S18 tire swap a success for now... but now I'd like to adjust the speedometer and odometer to compensate for the change in diameter.  EUCWorld has such a feature, so I may as well use it so I can figure out fast/far I'm actually going.

The stock tire was the ChaoYang H-5102, which says "18x3.0/76-355" along the side.  I've replaced it with an IRC TR-1 in 2.75-14, a dual-sport tire with a knobby tread, that I ordered off Amazon Japan.

https://www.amazon.co.jp/dp/B0042ZBYAY

The specs there state a 5mm tread depth.  The tire seems bigger, which would mean that with the motor spinning at the same RPMs, I'm going slower, but further, correct?

Anyone know how or where I can calculate that out?

Some websites have a tire compensation calculator.  The one I looked at were the difference between irc SN26 80/80-14 vs 80/90-14

That calculated to about 6 or 7%if I recall correctly. 

[mrelwood]

4 hours ago, Kagenin said:

the motor spinning at the same RPMs, I'm going slower, but further, correct?

If you’re going further in the same amount of time (1 revolution), you’re going faster. That’s what a larger tire does.

[fbhb]

4 hours ago, Unventor said:

Some websites have a tire compensation calculator.  The one I looked at were the difference between irc SN26 80/80-14 vs 80/90-14

That calculated to about 6 or 7%if I recall correctly. 

@Unventor is correct with what he has advised here regarding online calculators.  This is a link to a very good one that I have used recently: 90/90-R14 vs 90/80-R14 Tire Comparison - Tire Size Calculator | Tacoma World

[mrelwood]

On 4/20/2021 at 5:33 AM, fbhb said:

@Unventor is correct with what he has advised here regarding online calculators.  This is a link to a very good one that I have used recently: 90/90-R14 vs 90/80-R14 Tire Comparison - Tire Size Calculator | Tacoma World

The tire sizes don’t always seem to be at all that precise in practice though. I only have closer experience with two models, IRC SN-26 and Heidenau K66, and the difference is huge.

 On the SN-26, the difference between the 80/80 and 80/90 was barely noticeable even with the two new tires right in your hands.

 On the K66 though, the difference is huge. The 80/80-14 is a very small tire. The difference was in the same class as between many 2.75-14 and 2.50-14 tires.

 Which kinda sucks. But in EUCs we usually want to optimize the available space in much more detail than what matters in motorcycles.

[lubokkanev]

Is it true that all the 18 to 21 inch wheels today have the same size rims? For example the Sherman, S20, S18, V11, RS19 etc?

Is the difference just the space they have, for a taller tire? Or are the tires also the same sizes?

Edited December 9, 2021 by amomymous

[RagingGrandpa]

10 minutes ago, amomymous said:

all the 18 to 21 inch wheels today have the same size rims? For example the Sherman, S20, S18, V11, RS19 etc?

All of those are a 14 inch diameter rim. And you could add the older narrow wheels to that list, like 18XL.

Rim width varies. Typically the mounting seat is 40mm. Sherman went to  60mm. S20 we don't know yet.

13 minutes ago, amomymous said:

Is the difference just the space they have, for a taller tire?

The EUC width, and height, matters a lot.

13 minutes ago, amomymous said:

are the tires also the same sizes?

No.

For example:

• 18XL is narrow and cannot fit the popular AT tire, K262 2.75-14
• MSX/MSP fits K262 2.75-14 nicely
• V11 and MSuper RS have a touch more shell width than MSP, and so 'wider' models of tire can fit like Pirelli Angel 80mm
• Sherman has the most clearance of the wheels you mentioned, and can fit slightly larger tires like Shinko 244 2.75-14 (despite the same size marking, its tread dimensions are much larger than K262).

hth

[Hxx8scootr2022]

Can I go from a 10x2.125 to a 10x3 offroad tread on my hx x8 scooter? I want to go a little bigger or an offroad tire without issues 

[RockyTop]

20 minutes ago, Hxx8scootr2022 said:

Can I go from a 10x2.125 to a 10x3 offroad tread on my hx x8 scooter? I want to go a little bigger or an offroad tire without issues 

I don’t know anything about scooters. I suspect that the diameter of the 10x3 is going to be a bit taller and almost an inch wider. 
@mrelwoodis the expert on tires. He might stop in soon. 

[mrelwood]

23 hours ago, Hxx8scootr2022 said:

Can I go from a 10x2.125 to a 10x3 offroad tread on my hx x8 scooter? I want to go a little bigger or an offroad tire without issues 

Not knowing anything about scooters, I’ll throw in a few guesses.

 From 2.125” to 3” is most probably too big a step for the rim, the fork, and to the fender as well. You might be able to go up to 2.5”, but measure everything well before buying the tire (if such a size even exists in 10” tires).