Gear set-up

[AMMiK]

I have a 21 speed diamondback MTB, model M05 (2008), with a 14-28 tooth cassette and 22-34-42 on the front.

I'm finding it difficult to get above 20mph on the flat, and as for cycling downhill, well my legs just whizz around ridiculously with nothing to work with when I'm in the lowest gear.

Sadly my bank manager lacks the enthusiasm I have to go buy a shiny new, purpose built carbon-fibre road bike, so for now I'll have to make do. And so was wondering what set-ups other riders have.

I'm doing the Isle of Wight Randonnee this year and also the London to Brighton this June. My bike weighs 17kg, plus with me on top at 100kg, that's a fairly sizeable couch potato that I'm pushing around!!!

 

[MacB]

Well a 42x14 gives you a top gear of about 75 gear inches and you could do with moving that closer to 100, if you get a new cassette with an 11t top that would get you to 95 gear inches, then decide how low you want to go. Do you use the 22x28 much? if not then maybe an 11-23 cassette.

The other thing to change would be tyres, if you haven't already, a slick 1.5" tyre(about 38mm) would make quite a difference on the road.

 

[garryfisherbike]

Remember that using 1.5" tyres will reduce your gear ratios as the wheel circumference is reduced.

 

[MacB]

Remember that using 1.5" tyres will reduce your gear ratios as the wheel circumference is reduced.

Yep, I based all of the above on a 1.5" for comparative purposes

 

[fossyant]

What Mac says - get a closer ratio rear cassette with an 11.

 

[mcshroom]

Just before you do that check that it's a cassette and not a freewheel (if you are not sure have a look at this page, or post up any markings on it and we can probably work it out ). If it is a freewheel then 14t will be the smallest you can get at the back (ok Sunrace do a 13 but near enough).

The other way to bump up the gearing is to change the chainset to a touring/hybrid/trekking one which will be something like 48/38/28t. Something like this one. That would up your top gear to 85in.

I did the same to my Rockrider 5.1 when i was commuting on it as I was spinning out at about 20mph, it upped my comfortable speed to about 25/26mph on 26x1.75 tyres. In my case I had to change the front mech as well but I'm not sure if that was because the old mech wouldn't work with the larger outer chainring or just that it was too bent and twisted to work anyway.

 

[AMMiK]

Brilliant, thanks for the advice everyone. Looks like I have some shopping to do!