Adding a larger chain-set to a mountain bike Can i replace a 24/34/42 MTB chainset with a 24/38/48 MTB chainset while still using the same 7 speed cassett, chain and shifters.
My old mountain bike from the 90s had 24/38/48 MTB chainset and when i stood up and pedaled on flat roads i could get to 40mpg while now on my 2019 29er with 24/34/42 MTB chainset &amp; 12-32 7 speed cassett i struggle to reach 30pmg while pedalling like crazy
EDITED: So it appears, i have a Formula DC22 rear hub, not sure if this help anyone to tell me if a 11-28 cassette will fit on it. Trek say i need to buy a whole new back wheel if i want to change the cassette. Here are some images of back wheel and cassette.
Another option - change out your cassette to one with an 11-tooth smallest cog.
Per Sheldon Brown's gear calculator, pedaling at 100 rpm on a 42-tooth chainring and a 12-tooth cassette cog results in a speed of 28 mph.  Going to a cassette with an 11-tooth small cog, at 100 rpm that's 31 mph.  Getting up to 120 rpm results in a 37 mph speed.
And 37 mph on level ground is really fast on a bicycle - as in &quot;speed reached in the final sprints in Tour de France stages&quot; fast. 30 mph on a bicycle is fast, too.  If you're not struggling to reach 30 mph on a bicycle on flat ground, you should be riding in the Tour de France.  An average-size rider has to sustain a power output of 400 watts or so to go 30 mph - while riding an aerodynamic time-trial bike.  Sustained power output from cyclists who have never raced rarely exceeds 150 watts.
40 mph on level ground while riding a mountain bike with 26&quot; wheels?  You would have had to have a 48-tooth chainring and and 11-tooth cog and be riding at 120 rpm to do that.
So if you hit 40 mph on that old 26&quot; MTB, you should be able to hit almost that fast with your 42-tooth chainring on your 29er just because of the larger wheels - as long as you have a cassette with an 11-tooth small cog.
But at the end of the day, bigger gears do not make you faster.  The speed you can sustain depends mostly on how much power your body can generate.  The biggest limiter after that is how aerodynamic you and your bike are.