btothek

Hi all. I'm a little new to the whole tire size world and it's a little overwhelming. My main question is bellow but here is a little back story:

Just moved to Boston and I plan to cycle commute. I was going to rent a bike but opted to instead buy something used.

I picked up a Trek 7000 (old grey mare) and later went to REI the other day to pick up some supplies related to safety and maintenance. One of those things I was strongly recommended to buy was a patch kit and a spare tube. I didn't have the bike with me so they looked up the tube size for me: 700 x 35/43.

When I get home I realize my tires are two different sizes. 700 x 32 C in the rear and 700 x 38 C in the front.

So I am guessing that the tube I purchased is too big for the rear tire and too small or for the front, or is 35/43 a range of size based on inflation?

Also, is there a good reason to have the tires mis-matched like this? I'm assuming the 38 on the front is for better comfort?

Also... can anyone elaborate on what the "C" stands for in the sizing? It's printed that way on the tire.

Back story: I ride all the time in Cincinnati where I hail from, but not often as a commuter. My bike there is a Marin Larkspur, basic but solid hybrid. I love riding it recreationally on trails.

I wear a helmet, a Gyro AEON and a high visibility jacket. Brought that with me to Boston.

So I just purchased a bell, a helmet mounted mirror and front and rear lights.

Apart from my basic concerns about my tires, am I missing anything?

I know, I know... too many questions. Thanks for bearing with my noobyness.

b to the k

10 Wheels

Tubes expand when aired up in the tire.

It should be good to use.

I have used tubes of all sizes in different tires.

JohnDThompson 

Tubes expand to fill the space available to them. The caveats are that too narrow a tube will be stretched thinner and more prone to puncture and too wide a tube can make it difficult to seat the tire. But there's a fairly broad range between those concerns.

And the "C" given in tire sizes is a confusing anachronism. Whenever possible use the ETRTO/ISO size designations instead.

dsbrantjr

You will also need a pump to inflate your spare tube; I use a Topeak Road Morph G which mounts on the bike frame and has an accurate-enough gauge. A floor pump is nice for home use, but you will need a pump with you for on-the-road repairs. I don't care for CO2 inflators myself, although others use and recommend them; air is free and you'll never run out.

As already mentioned the tube is close enough to work fine; a little smaller or larger than the tire size will be OK.

The "C" in the tire/wheel size is the common one (ISO/ETRTO 622mm); 700a and 700b are unusual and you needn't concern yourself about them.

Here's a discussion if you are interested: Tire Sizing Systems

fietsbob

NB The balloon animals did not start out that way..

Wanderer

There are two different reasons for mismatching tires. I do the former.

1. Wider on rear for more comfort and capacity, smaller on the front for quicker and more precise steering.

2. Wider on the front for better steering in soft surfaces, smaller on the back for more speed(they think).

MHO

btothek

Thank you all for your help! I'll keep the 700 x 35/43 tube I bought as my spare.

Having the wider tire in the front, that makes sense?

I have a JoeBlow floor pump back in Cincinnati, and a Cannondale bike frame pump but I didn't bring either due to size of suitcase concerns.

Should I try the C02 or spring to ship either of my pumps to me?

btothek

Good explanation. I think I'd prefer to swap mine around so the wider is on the rear but I'm not sure it's worth the trouble right now.

DiabloScott

You have a tube sized for tires that are 35-43 mm wide.
And you have one tire that's labeled as 32 mm wide,
and one tire that's labled as 38 mm wide.

So your tube will almost certainly fit your 38mm tire just fine, but might be a little too much material to stuff into the 32mm tire.

The other factor here is that tire labels are frequently bigger than the actual diameter, so your 38mm tire might actually measure 33 mm on your rims... this is a little game that tire makers play.

When buying tubes, you should also make sure you get the right kind of valve.

And the other reason for mismatched tire widths front and rear is the previous owner just used whatever happened to be handy when they needed a new tire.

btothek

Both are Shrader valves, this I know!

So my 32 might not fit my spare tube. Hmmm... I might roll the hard 6 on this and not shell out for another tube... or... would it be better to return the tube I have and get something smaller that could work for both?

Bill Kapaun

Since this tube is a spare, I'd take it back and get the next smaller size.
Get something that covers 32 AND 38.
Using the tube you have for the 32mm tire makes installing a bit more difficult and allows for the possibility of having the tube fold over on itself resulting in a crease.

btothek

^^Thanks! Good Advice everyone. Going to get something that will cover both tires.

best,

b to the k