Bicycle Mechanics - popsigh

Hello, I am an old Irishman not too well informed about bike mechanics, I always had someone do it for me. my American wife had an old [15 years] Schwinn tricycle in her shed and it only needed new tires and tubes. I bought these and fitted them and while the front went on beautifully the two rear tires [ same size ] will not seat properly, it seems as if they are too big but they are the same size as the ones I removed. Can anyone help.
Thanks for reading.
Popsigh.

Schwinn was and is notorious for using non-standard sized tires and labling with a standardized size tire. If you're not using a Schwinn brand tire the tire won't fit. This means if you have a Schwinn 20 x 1 3/4 on the bike and you grab a 20 x 1.75 tire off a rack the new tire won't fit. Even if you think both tires should be the same size.

I would bet the front wheel has been replaced at some point with a standard dia rim so it worked while the rear Schwinn rims did not. If you still have the old tires look for an S-7 or S-6 next to the tire size. You need to match up those codes to the new tires. The LBS should be able to get them. There is also a difference between 1.75 and 1 3/4s when it comes to bike tires.

I think that the bike still has the same wheels but I must admit that I just bought 3 tires of the same size but not Schwinn's. Thanks for your help.

I live and learn. Thanks for the info, I will check further.