kaiserschmarrn

I just blew a 1-1/2" tear in my rear Bontrager stock tire and innertube this weekend. I had to carry it a few miles back to the car. So, I am going to have to be replacing, and I will do both at ine time. After searching best hybrid tire choices, I came upon the Continental Grand Prix 4 Season. I am looking for a faster road tire option that has less rolling resistance. This seems like a possible good choice. There is only one problem that might come up. I think that my tires are 700 x 35 mm, and the Continentals seem to only be offered in 700 x 32 mm as the only close fit. How do you know if alternate sizes can fit this rim, and will this tire size fit my rim properly?

Thanks,

Danny

Sardines

Which year is it? You can get the info on the Trek website? Going narrower isn't going to be a problem. It does lower your top gear a tad but otherwise it's ok. Ride will also be a bit more harsher. Try the Grand Prix Urban or Gravel King Slick or Semi Slick @ 35mm.

t2p

pictures of a bike with 32mm GP4S (top pic) and 35mm GK SS (bottom pic)

the 32mm GP4S measures 32mm ; 35mm GK SS actually measure around 37mm

also had 32mm GK SS on this bike at one point; they actually measured around 31mm

the bike feels faster on smooth roads with GP4S installed

Arete One

I'm thinking of going from 700x38 to 700x32. Why does the narrower tire lower the top gear?

Sardines

The circumference and diameter of the tire usually shrinks slightly with a narrower/thinner tire, because of how the profile of the tire sits on the wheel. It's miniscule but can affect gearing a smidge, as the narrower tire's circumference is smaller. Then again, you gain on weight (lighter), aero and rolling resistance, which will cancel out that and more.

hokiefyd 

Short answer: yes, it does. By how much? Using nominal numbers a 38mm tire is about 698mm tall and a 32mm tire is about 686mm tall, a 1.7% decrease. Those are just nominal numbers, and assume both tires' profiles are fairly uniform, etc. Critically, it also assumes you're talking about tires that are actually 38mm wide/tall vs. 32mm wide/tall, instead of tires labeled 700x38 and 700x32. Many tires don't inflate up to quite as large as advertised. It is possible that the specific 700x32 tire you have is about the same actual size as the specific 700x38 tire you have.

In general, however, yes, a smaller tire will reduce your top gear.

Edit: I missed your question...why? It lowers the top gear because it has a smaller diameter. A tire with a larger diameter will move the bike further with one full revolution than a tire with a smaller diameter. At the same tire rotation speed (which is driven by your pedaling cadence and gear ratio), your bike will be moving a shorter distance with the shorter diameter tire. Again -- the difference here is relatively small -- fewer than 2% change. But, it's there in theory.

Arete One

That makes sense. Thanks.

kaiserschmarrn

Thanks for the heads up on the Continental Grand Prix Urban. I was unaware of that tire and it did not come up in a search for best hybrid bike tires. The specs. looked pretty good compared to anything else that I found in a search, and the prices were better. Hopefully it is enough of an upgrade from the OEM Bontrager H2. I tend to ride mostly on street conditions with some hard packed very fine gravel mixed in. I got the stock 700C x 35.

Danny

mdarnton

I run 32 mm studded tires in the winter on my FX 1 disc, no regrets.

Max is spec'd 37 mm without fenders, 35 with.