My 7 year old son is going to be doing a triathlon which has a 5k (3mile) bike leg. He's pretty fast on his mini bmx bike which has a pair of Tioga knobbys on it. I hoping to find a supplier where I can order some 20x1 3/8" city slick tires to give him a little less rolling resistance for the bike ride on the road.
Does anyone know a brand/website where I can get some 20x1 3/8 slicks/city tires?
They're pretty common for recumbent riders I believe (at least, relatively speaking, since recumbent riders aren't that common themselves). Most bigger bike stores, online or otherwise, can probably get some for you if they don't already have any in stock.
just check some local dealers. if they dont have em, then they can order em and theyll be in 2 wks later at the most. and try to get something really high psi because the higher the psi, the less rolling resistance there is. that would help him even more.
BMX are 406mm, is that so? Apparently you dont get out to the race tracks much.
There are 4 common rim sizes for BMX Racing
451mm these are the narrow 20 inch rims for kids race bikes
406mm the common 20 inch size, most racers move to this size at age 13 14
520mm kids 24 inch cruiser class
507mm regular 24 inch cruiser class
The 20 inch naming convention refers to the outer diameter of the inflated TIRE not the rim, it is also only an approximation, there are few tire rim combinations that are actually 20 inches.
If you do the conversion from millimeters to inches you will see that 406mm is actually only 16 inches, this means that to get a 20 inch diameter you need a tire that has a sidewall height of 2 inches. When you put that tire on the rim you add the 2 inches at the top and bottom giving you a 20 inch diameter. In reality 20 inch tires range in diameter quite a bit but they refer to all of them as 20. For example, kids race tires come in 20 * 1 1/8 and 20 * 1 3/8, the narrower one has a 20 inch diameter but the wider one has a 21 inch diameter. The same is true of the wider tires, two common sizes on race bikes are 20 * 1.5 and 20 * 1.75, these have inflated diameters of 19.25 and 19.5 respectively. Check this next time you are at a track, it is pretty obvious during gate practice when there are kids and older riders on the gate at the same time.
It is also obvious if you ever try to use any of the gearing charts as the gearing is impacted by your inflated tire diameter.