Tiagra Gear Ratios

[clockhammer]

I bought Mavic Aksiums a few months ago and the LBS fitted a Tiagra cassette as that's what was on my old wheels. I use the old rear wheel for turbo training and when fitting it on the bike today I noticed that the largest gear looks a bit bigger than on the Mavics. I had not noticed this before.

This got me counting teeth and it seems that the cassette on the new wheels is a 12-28 and cassette on the old wheels is a 12-30. My Crankset is a 34/50 in case that matters.

My question is will the 2 fewer teeth make much difference? Perhaps a silly question and not really important at all but I'm sure someone here will know all the maths behind it. I do feel faster on the Mavics compared to the old stock Giant wheels.

I'm thinking that it will obviously make severely steep hills a little harder but by how much in terms of %, if it can be measured like that?

thanks

 

[HLaB]

It hard to say, like for like you've lost gears but that is likely to be offset largely by the lighter wheels and perhaps by a smoother transition between closer spaced gears. It may also force you to ride slightly harder which can result in a faster ride. It may also be partly the placebo effect of the new wheels

 

[Rickshaw Phil]

This is where knowing about gear inches helps. If you like doing the calculations yourself you divide the number of teeth on the chainring by the number of teeth on the sprocket and multiply that figure by the diameter of the wheel (including tyre).

Alternatively put the numbers into an online gear calculator. The figure you get at the end represents the diameter the wheel on a penny farthing would have to be to give the same gear ratio.

Using a nominal figure of 27 inches for the wheel diameter I get 32.78 gear inches for the 34 chainring to 28 tooth combination and 30.6 inches for the 34 to 30 combination. It's not a huge difference but you'd probably notice it on a long slog of a climb.