Bigger Tires - Lower Gearing?

[Hikyle2]

I have been wanting to go bigger with my road bike tires for a while, I currently run Challenge Paris-Roubaix Tires that are about to wear out. I was going to run a 35mm tire, like a slick Gravel King tubeless. Do I need to consider having lower gearing because of the bigger tire size? Will it make any difference when running an 11/28 cassette? I have a 50/34 in the front as well.

[mhespenheide]

It makes a slight difference, but not much. About a gear if you go from 25's to 35's or thereabouts.

The bigger issue, usually, is that you're on rougher surfaces or gravel and dirt and therefore there are spots where you won't be able to stand up out of the saddle and muscle like you would on pavement. At that point, lower gears become much more of an issue.

[Clean39T]

I have been wanting to go bigger with my road bike tires for a while, I currently run Challenge Paris-Roubaix Tires that are about to wear out. I was going to run a 35mm tire, like a slick Gravel King tubeless. Do I need to consider having lower gearing because of the bigger tire size? Will it make any difference when running an 11/28 cassette? I have a 50/34 in the front as well.Definitely search out an 11/34. Rougher roads and gravel call for more nuanced power output on climbs...and having some lower gears helps there..

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[Burning Pines]

11-28, what is this, 2014? Yeah get lower gears not because of ratios or whatever but because comfort is the new cool. Life is stressful and we all need lots of pneumatic suspension and at least 1:1 to make it tolerable imo.

[martl]

It makes a slight difference, but not much. About a gear if you go from 25's to 35's or thereabouts.

not even that. A tire of 35 or 40mm width has about 4-5mm bigger a diameter compared to a 25-28mm. If you do the math, that results in a difference of about 1/4 of 1 gear.
Riding with a cadence of 85, this means the 34/34 gear will give you 11 instead of 10.8km/h and the 50/12 is 45.7 instad of 44.8.
You will get the same speeds if you lower your cadence from 85 to 83.

[marciero]

not even that. A tire of 35 or 40mm width has about 4-5mm bigger a diameter compared to a 25-28mm. If you do the math, that results in a difference of about 1/4 of 1 gear.
...


True on the low end, if you compare going from 25-35 tire with 34/25 to 24/28 gear, which are adjacent on 11-28 cassettes. But note that adjacent gears-even those separated by a single tooth- are not evenly spaced.

Using tire circumferences of 2168 and 2105m for 35 and 25mm tires, resp, (found online Cateye chart) gives about 5mm difference in radii for the following relative increases in gear ratio

25 to 35 tire: 3%
50/12 to 50/11: 9%
34/28 to 34/25: 12%

So this agrees with your 1/4 gear on the low end, which is the end you would be concerned about. But more like 1/3 gear on the high end.

[cp43]

I like this gear calculator: http://gear-calculator.com/

It has two things that can help you out here, it accounts for tire size, and it allows you to compare two setups.

I would suggest putting in your existing gearing/tires, and comparing with that with the new size. That will give you some idea of whether or not you think you'll notice the difference.

Also, I think it would be worth while to get the bigger tires, and ride for a while with the existing gearing. If it's too tall, get the wider cassette. If not, job done.

Chris

edit: assuming you're running 10 speed, here's the comparison: Gears (http://gear-calculator.com/?GR=DERS&KB=34,50&RZ=11,12,13,14,15,17,19,21,24,28&UF=2135&TF=90&SL=2.6&UN=KMH&DV=gearInches&GR2=DERS&KB2=34,50&RZ2=11,12,13,14,15,17,19,21,24,28&UF2=2185).

[Hikyle2]

Thanks, I’ll try out the gear calculator for sure. It’s not necessarily that I want to ride steeper gravel roads, it’s more for comfort and maybe opening up paths on my normal rides that I would shy away from. I’d also commute more on my road bike with bigger tires I think.