# Does the size of a bike tire matter when going up and down hills?

I am doing science fair and my question is if the size matters when going up and down hill on a bike. I looked all over your site and I couldn't find anything about the size of a tire for going up and down a hill, but I did find something about the size of a tire help for going on flat ground but I'm not sure if the same will apply for going up and down hill. Sorry for the bother but it would really help me out if you could answer my question.

• Road or Mountain biking down hill? Nov 10, 2020 at 19:04
• What do you mean by size? And look up "gear inches". Nov 10, 2020 at 19:07
• Also look up the term "mechanical advantage." Nov 10, 2020 at 20:54
• Are you talking about the diameter of a wheel, and how gear ratios and wheel size transform torque on the crank to force applied to the road, or width, inflation pressure and rolling resistance of a tire? Nov 10, 2020 at 21:04
• Possibly diameter / width of tyre? Does tyre pressure matter? How about rolling resistance? Nov 10, 2020 at 21:05

I assume you're testing a tyre's width, not its total radius because that would change the rim size.

I'm also taking this as "how to design a tyre test " because otherwise you're asking for opinions, which would not be very Scientific, and would also be off-topic.

There's a lot of things to vary. Good scientific tests try to fix all the variables except one, which may not be possible.

Assuming that adding weight makes a climb harder - that's easy to test by adding some non-functional weight, and timing it.

However testing if a wider tyre helps, will add weight as well, which we know from previous test will hinder the ride. But how would you test if the wider tyre alone without the added weight is of benefit, or not.

To test "Is X better than more/less X" will require you to isolate, or at least account for:

• rolling circumference (A wider tyre has a subtle increase in the distance it rolls per revolution, which slightly changes the gearing)
• tyre pressure (wider tyres have lower recommended pressures)
• tyre rolling resistance (how much it deforms as you ride)
• tyre grip
• tyre wear
• tyre construction (Ideally test a tyre that comes in multiple widths in the same model, and not test a commuter tyre against a race tyre)