Yes, I know I should always go off the ETRTO tire sizing, but the Dahon folder I just picked up has tires that are in such awful shape that I can barely read the 20x1.75", and nothing else. It is an older bike that I can't find much about online. Are there any goofy tire variants in this size that I have to worry about?

Also will take any recommendations on tires (preferably Contis, as I get a substantial corporate discount) for city commuting use.

There are 406 and 451 wheels.

Most of the 20x1.75 should be 406, and I would expect that on a Dahon.

But, if in doubt, measure.

I think Schwalbe makes some durable 406 semi-slick tires. Marathon, Marathon Plus, and maybe Durano or Ultremo.

Decimal (e.g. 20x1.75) is 406. Fractional (e.g. 20x 1 3/8) is 451.

Sheldon Brown's page on tire sizes says that 20" tires in decimal inch widths are ETRTO 406 mm, whereas 20" in fractional inch widths are (with some exceptions) ETRTO 451 mm.

Can't speak to 406s but I've been using Schwalbe Duranos and/or Panaracer Minits Lites in 451s and have been happy with both (I buy whichever is cheaper when I'm shopping for tires).

As long as you stay with 406mm ERTRO sizing you will be good. There are 2 20" tyre sizes; the other one is 451mm. Typically that one is indicated in fraction of an inch width e.g. 20x1-3/8". The 406 is indicated in decimal width, e.g. 20x1.75".

I am using Conti Ride Tours at 1.75 on my Zootr Swift and like them. They are heavier tires made for touring.

Thanks, you all have confirmed what I suspected!

What's good in 406 tires is related to use.....hate flats Schwalbe marathons are good. Want speed, then Kojaks are good. Need a softer ride perhaps Big Apples. All tires are a compromise between rolling resistance, flat protection, handling, cushioning and price if not other concerns. I have been using 1 1/2 Kenda Kwests on my Swift and Nano with no troubles, really.

there wont be wide 451

(an old 451 wheel BMX in the LBS, a moto sprint bike , looks drastically different, placed next to the typical 406 BMX stunt bike..


from Sutherlands : 406 rim, bead seat circumference is 1274 , OD 422..

451 circumference 1416 , OD 463




...

My go to tire is Schwalbe Marathon Green Guard. Surprisingly fast for a heavy tire, nice ride and good flat protection. Have 3k miles on my Xootr Swift and good for at least another 3.

Have a look at the BMX tyre section of your local bike store. I've had a good run with a varied selection of Maxxis, Vee Rubber and even Schwalbe BMX tyres. The advantage is you can select a tread pattern that closely matches your actual riding surface. The competition tyres are surprisingly light but be aware that some have soft compounds.

BMX tyres are available in 406 (most common) and 451.

I use Schwalbe Marathon Plus for the ultimate in puncture resistance. This comes at a price - ride quality and response does suffer.

Conti Sport Contact IIs seemed to have been the fastest rolling 20". These have been supplanted in Conti line-up with the Contact Speed - perhaps narrower than you want to ride in the city?

There are currently three city/trekking conti tires for 20" wheels.
1. Contact in 1.40 and 1.75
2. Ride Tour in 1.75
3. Contact Speed in 1.10