# Tire sizes - scratching my head



## Chilidawg (Sep 26, 2020)

I want to replace the rubber on my 1978 Schwinn Twinn tandem. They are 26x1 3/8inch. I bought two new 26 inch tires and they are too small. What am I missing?


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## rustjunkie (Sep 26, 2020)

there are different bead diameters for 26 x 1 3/8", sounds like you need the 597:





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						Tire Sizing Systems
					

Several different systems of size markings for bicycle tires are in existence. The modern ISO system is not as familiar as it should be, this article explains it.



					sheldonbrown.com


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## Chilidawg (Sep 26, 2020)

I never realized how many oddball parts are on these bikes. I am missing a seatpost which is 20.7mm with 5/8 top. Finally found a place to order them that won’t cost me 2x the cost of the part to ship.


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## GTs58 (Sep 26, 2020)

So what rims are on your Tandem? There are two Schwinn rims that will take a 26 x 1-3/8 tire, the S-6 and the S-5. On your existing tires there should be markings, get the sizing information and BSD if they're marked. Sometime tires will say for S-6 etc. I really can't see a big difference in a BSD of 7 mm in a tire size to where it will or will not fit. Having a clean rim around the bead makes a big difference when mounting new tires. Sometimes a lubricant is needed, I use Windex. On the cheap tires there's a better chance of the tire not being made to the correct size.


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## Chilidawg (Sep 26, 2020)

checked the tire and there it is


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## GTs58 (Sep 26, 2020)

That tire looks brand new. No cracks either.


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## Chilidawg (Sep 26, 2020)

The back tire has a 1 inch long split in the middle of the tread, so I thought I would get 2 matching tires.


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## Nashman (Sep 26, 2020)

Chilidawg said:


> I want to replace the rubber on my 1978 Schwinn Twinn tandem. They are 26x1 3/8inch. I bought two new 26 inch tires and they are too small. What am I missing?



The tire sizing attachment Rustjunkie/Mod supplied should help. Tires and rims and their sizes are a jungle. American ( early) tires are more standard, but once they get into the later 60's and above, it gets sketchy, and Canadian and British/European get crazier. Many of the old tire sizes are hard to find. Good luck, I think you have been helped by good folks, and I'll say, no better folks than Cabers.


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## Nashman (Sep 26, 2020)

Chilidawg said:


> I never realized how many oddball parts are on these bikes. I am missing a seatpost which is 20.7mm with 5/8 top. Finally found a place to order them that won’t cost me 2x the cost of the part to ship.



All part of the fun. Keeps us intense?


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## Archie Sturmer (Sep 28, 2020)

13/16” is a fairly common size for seat posts (in inches).


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## gkeep (Sep 28, 2020)

Try could switch out the rims with some iso 590 (26x1 3/8") from a 60s or 70s 3 speed like an old Raleigh. You'd have more tire choices.


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## Chilidawg (Sep 28, 2020)

Archie Sturmer said:


> 13/16” is a fairly common size for seat posts (in inches).



Maybe in the States. Nobody in Canada stocks them. The problem is the international shipping costs.


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## GTs58 (Sep 28, 2020)

Chilidawg said:


> Maybe in the States. Nobody in Canada stocks them. The problem is the international shipping costs.




Is there no Canadian based eBay?  

Jeeze, I just went to the Canadian eBay with a search for Schwinn seat post. 250 items and all but four items were not from the US. Two Canadian, one Puerto Rico and one from Japan.


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## Chilidawg (Sep 28, 2020)

GTs58 said:


> Is there no Canadian based eBay?
> 
> Jeeze, I just went to the Canadian eBay with a search for Schwinn seat post. 250 items and all but four items were not from the US. Two Canadian, one Puerto Rico and one from Japan.



I did the same search. The 2 Canadian ones we’re for seat post lights


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## GTs58 (Sep 28, 2020)

You guys up in Canada sure have it rough when trying to get Schwinn parts. Didn't Schwinn export bikes to Canada?


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## detroitbike (Sep 28, 2020)

here it is again

                                Dec 24, 2016                             


                                                                                                                       26" Tire sizes by Diameter...

S-2 ........... 559 mm (26 x 2.125 / 1.75) Balloon , mountain and middleweight
S-7 ............ 571 mm (26 x 1 3/4 ) Schwinn Middleweight
S-4 ............ 584 mm (26 x 1 1/2 ) 650b / Schwinn Welterweight AND todays new 27.5 tire designation
EA-3 ......... 590 mm (26 x 1 3/8) Lightweight
S-5 / S-6... 597 mm (26 x 1 1/4 - 1 3/8) Schwinn Lightweight (AKA as EA-1)


S5 was intended for 1 3/8" wide tires ( available in 20" 24" and 26" )
S6 was intended for 1 1/4" wide tires ( available in 20" 24" 26" and 27" )


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## GTs58 (Sep 28, 2020)

detroitbike said:


> here it is again
> 
> Dec 24, 2016
> 
> ...





May I copy and paste this in the *Schwinn Tire* sticky thread for everyone?


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