Hi all

First time here go easy on me,

I have a Trek FX 7.1 with 700C tires
read 700x35 on the tire

I want to replace the entire tire and wheel with one that is labeled 700x28C for the sake of adding a electric hub motor to it,
I am just wondering if this will new tire/wheel will fit? as I no nothing of what these numbers mean, any insight would be more appreciated

Hello namesake.

The 35 and 28 refer to the tyre's width (i think it's millimeters), so the 28 is slightly narrower than the 35 and may give a slightly less comfortable ride because of it. Also, as you are going slightly narrower you don't need to worry about having enough clearance in the frame, a problem which may present it's self if you were going wider. The 700 refers to the size of the wheel, If you stick with a 700 wheel you should have no problems with fitting.

As noted, the "700" refers to the rim diameter which is actually 622 mm across the bead seats. The 35 and 28 refer to the tire width, also in mm, so a 700x28 tire has a beadseat diameter of 622 mm and is 28 mm wide when installed. If you look on the tire side wall you should see the numbers 622-28 or 28-622. Any tire labeled 622 will fit your rims unless it is extremely narrow or extremely wide. Neither 28 nor 35 are a problem and you could exchange the 28 mm tires on your new wheel with the 35 mm tires on your old wheel if you wish.

The only problem you may encounter is you may have to readjust the brake pads. The width of the wheel is probably a little different. As stated, you can always go narrower as you are planning to do but you may encounter brake clearance and frame problems going wider. You won't encounter this problem.

Okay - I came up with this on a search and I have a, well, similar question. Hopefully similar enough not to be considered a hijack. My tires are labeled with the logo and 23-571, and have an additional stamp elsewhere on the tire that says 26x1. I haven't seen any in the places I've been looking that are anything other than "700." Are my tires *that* much smaller than every other 56cm bike on the planet?

Your rims and tires are not 700C but what is commonly known a 650C (ISO 571) and were sometimes used on small frame bikes to keep the rider's toes away from the front wheel on tight turns and on triathlon and time trial bikes as they were a bit more aero. 650C tires are available but not nearly as common as 700C so you will have to look around.

BTW, the most common 26" size these days is the mountain bike ISO 559 and there are several other "26 inch" size rims and tires, none of which are interchangeable with your 650C or each other, so be very careful what you buy.

Respectfully, that doesn't make sense. If you have an electric hub wheel the size of the rim will dictate the possible tires that can fit on it. My gut feeling is that an electric hub wheel will be on the wide side and putting a narrow tire woudn't be recommended. If the rim could take a 28mm tire I wouldn't do it unless you were very light as the added weight and wear would benefit from a wider tire and most likely one that is fairly puncture resistant, ie. heavy. So whatever benefit you're seeking from a narrower tire will be complicated by the greater wear and harsher ride. Are you sure your electric wheel can take a 28mm tire and why are you going for that size of tire?

Thanks a ton for the info, and confirms my gut feeling. Frankly, the wheels/tires just flat out look small. What I can't figure out is that it's a 56cm bike, it that considered "small?" We'll see how broken Japanese works at the LBS finding tires... ;-)

Back to the OP, your electric hub will have a different 700c rim to the original one. It will be the same diameter but the width may vary a bit. Rims have a range of suitable tyre width.
Is there any advantage in replacing your 35mm with 28mm?
28mm is a fairly sporty size for hybrid bikes and good for longer commutes. Electric bikes are heavier and less able to be bunny-hopped over obstacles, potholes and rough stuff. Most electric bikes come with fatter tyres to absorb this impact.
You can re-use your existing tyre and inner tube and replace it with another size when it wears out.

Its not the size of the bike that determines the wheel size, it is the design of the bike. I have a 56cm frame bike that has 650c wheels, and that was how it came from the factory. It is a triathlon bike.

I would consider a 56cm frame size to be "medium".