Magic Pie 20" Tire

[MonkeyMagic]

Hey chaps

Still trying to source a decent tire for my 20" cast wheels. The problem is 20" BMX tires are actually a bit too big. I did some measurements and came up with the following:

Magic Pie 20" cast wheel diameter  = 1265mm 
Standard BMX 20" wheel diameter      = 1280mm

Magic Pie inside wheel width (wall to wall)        = 31mm
Standard BMX inside wheel width (wall to wall)  = 22mm

So basically I am thinking I need a slightly smaller, and can cater for a pretty wide tire like 3.5" or something..

Does anyone have any hints or advice on this? Maybe people who ride motorbikes.

I found this Michelin tyre that I think may fit but not sure at all...

Its a Michelin Commander 90/90-19 52H or something a bit thinner... Any tips?

[Bikemad]

So basically I am thinking I need a slightly smaller, and can cater for a pretty wide tire like 3.5" or something..

Does anyone have any hints or advice on this? Maybe people who ride motorbikes.

I found this Michelin tyre that I think may fit but not sure at all...

Its a Michelin Commander 90/90-19 52H or something a bit thinner... Any tips?

Unfortunately that 90/90-19 52H tyre will be way too big for your wheel!

The diameter of a motorcycle tyre relates to the tyre's internal bead diameter, whereas bicycle tyres use the outer tyre diameter for their sizing.

The front tyre size on my 750 Honda is a 100/90-19 57H and has an outside diameter of approx 25":


The 130/90-16 rear tyre has a much smaller inside diameter, yet the outside diameter is almost the same as the front one.

My Fantic Chopper moped originally had 16" tyres front and back, but the the outer diameters were very different:

16 x 5.00 tyre on the rear and 16 x 3.00 on the front.


The same 16 x 5.00 tyre on the rear, but now with an 18 x 2.50 on the front.

Monkey, you will need to accurately measure the bead seat diameter on your rim to be able to find a tyre that will fit it correctly:



Outer diameter minus (depth from outer edge to bead seat x 2).

Let us know what your BSD is in mm.

Alan
 
P.S. Do you think "V" brakes would work OK with those 20" cast wheels?

[MonkeyMagic]

Hey thanks Alan, and laughing at the thought of actually going to a motorbike tire distributor with my wheel and asking for that size!

I took the measurement as best as I could from the tyre seat lip to lip, im near certain its 400mm or slightly less.
Absolutely have no clue in the motorbike tire world... cheers for the help

As for the V-Brakes, I chose that as a no no as there is not really much room at all to play with, plus the fact I would have to mount the caliper anyway, so I just opted for a disc brake (I am still yet to hook up a bracket for the activator)

I really only use regen and the front brake, I have the front wheel set on 25% regen and now the rear wheel is off I notice nothing... I'm scared to turn it up because of the rear wheel failing on the weekend. It was set at 70% regen. When I fix it I think I will set both the wheels to 40/50% which is definitely okay for the front not to lock up or slip at high speed.

Here are some pics of the wheel and tire size etc..


 

[MonkeyMagic]

some more..

[MonkeyMagic]

and these..

[MonkeyMagic]

Would you agree looking at my pics now I think they are actually a 19" rim? You can even notice the wheel height difference from the back to front on the side view of the bike, I do like the strength and width

[GM Canada]

What does it look like if you do a side by side comparison of the new and old wheels? I think it looks like your tire is too large because the rim is wide and when deflated the tire falls to the center of the rim giving it more room.

Gary

[Leslie]

Check this out

http://en.wikipedia.org/wiki/ISO_5775#Rims

The standard diameters of straight-side and crotchet-type rims are:

    194, 203, 222, 239, 248, 251, 279, 288, 298, 305, 317, 330, 337, 340, 349, 355, 357, 369, 381, 387, 390, 400, 406, 419, 428, 432, 438, 440, 451, 484, 489, 490, 498, 501, 507, 520, 531, 534, 540, 541, 547, 559, 565, 571, 584, 590, 597, 609, 622, 630, 635, 642

The standard diameters of hooked-bead rims are:

 270, 321, 372, 422, 459, 473, 510, 524, 560, 575, 611

http://www.sheldonbrown.com/tire-sizing.html



This guy must really know his rim sizes! Look at that eagle thing on his helmet



May Bee these are the differences here,

Does .75 Equal Three Quarters?

    Note that the inch-based designations sometimes express the width in a decimal (26 x 1.75) and sometimes as a common fraction (26 x 1 3/4). This is the most common cause of mismatches. Although these size designations are mathematically equal, they refer to different size tires, which are NOT interchangeable. It is dangerous to generalize when talking about tire sizing, but I would confidently state the following:

20 x 1 1/8  
20 x 1 1/4  451 mm    Juvenile lightweights, BMX for light riders, some recumbents
20 x 1 3/8
   
20 x 1 3/4   419 mm    Schwinn juvenile

Both marked as 20" but a good 31mm difference.

http://www.sheldonbrown.com/harris/tires/419.html

[Sundsvall]

I’ll only show the most common sizes and not the French for each size. The French standard is, just as the inches, about the outer diameter but in mm and the only common today is the 700 size. It’s by my opinion a must to leave these inches to history and focus on the accurate ETRTO.

Inch   ETRTO   French
28”     635     
28”     622       700
26”     559     
24”     507     
20”     406     
20”     451     

Edit:
Sorry, but the ETRTO have been adopted by ISO and is now the correct standard to refer to.

Try to find the ISO size on the tyre, I’m pretty sure it’s the less common 451. GM have 635, 622, 559, 507 and most likely 406 mm as they in each of the other sizes have chosen the most common.

Oh btw, Sheldon Brown died in 2008 by a heart attack. His site is still going strong though and really is something to learn from.

Peter

[Bikemad]

Monkey, I think your rim is probably meant to be 406mm Bead Seat Diameter. I only found one tyre with a 400mm internal diameter and that was a very narrow 1" wide tyre.

Harris Cyclery have a large selection of 20" metric BMX tires with a 406mm Bead Seat Diameter.

They even have a wide 20 x 2.3" tire named after you!

I think a 20 x 3.0" tire (72-406) should fit the rim if you really want to go for wide tires, but there are not many of those to choose from.

Alan
 

[GM Canada]

They even have a wide 20 x 2.3" tire named after you!

Alan
 

Ha Ha Ha, How do you find this stuff Alan!

Gary

[GM Canada]

This guy must really know his rim sizes! Look at that eagle thing on his helmet

Ha Ha Ha, The forum is like a comedy show tonight

[MonkeyMagic]

Lol the "Curb Monkey" - sounds like me occasionally on a early sunday morning

Wow great info here, thanks heaps for the tips. Looks like I have a bit of hunting to do...

[Bikemad]

How do you find this stuff Alan!

Seek, and ye shall find

This advice was given a long time ago, but it still applies equally well today.

All this lovely information is freely available on the Internet, all you have to do is find it!

Alan