Getting bigger chainset advice

Guile

I have a Hardrock Sport Disc 2011 which I basically use for commuting but I find I am riding in the top gear 80% of the time on the roads and when going downhill, the highest gear is too slow (I have slicks tyres on). I NEVER use anything but the biggest cog of the front 3 so I am looking to change it from a 42 to a 48, hoping to get some more speed.

Looks like it is just as cheap to replace the whole chainset as opposed to just the big cog. I am looking at some cheapo £20-£30 Shimano ones or is it better to replace the one ring?

Can somebody just tell me whether I will need to do anything else other than move the front derailleur up? Will I need a new chain? Will the gear system be compatible with bigger cogs? Thanks.

Bike spec: http://www.tredz.co.uk/.Specialized-Har ... _38372.htm

supersonic

What is your cadence when you run out of gears? Also what is the ratios of the rear cogs ie the smallest cog? Is it 11 teeth?

Twelly

If you bike is as it says in those specs, your top gear is 44t x 11t which should give you a top speed of about 30-36mph (80-100 cadence)

How fast do you want to go...

I have a road bike with a 52t big ring and my top speed (ever) on that bike is 41mph.

Guile

I would guess the cadence is about 100-120 revs per minute. But I have to freewheel on a small slope @ 120.

The smallest cog at the back looks to have about 11 notches.

Different chainsets have different amounts of notches? How does that affect which one I buy?

Guile

Maybe the Tredz site is wrong - Evans says it has a 42 on the front (http://www.evanscycles.com/products/spe ... e-ec024137).

Judging by the speed of the cars coming by me, I am not hitting 30mph. I would guess mid, low 20's.

It seems 19 of my 24 gears are useless.

styxd

It seems like you have picked the wrong bike for commuting on the road with.

Guile

styxd wrote:

It seems like you have picked the wrong bike for commuting on the road with.

Now I know that but it's too late. Changing the chainset should make a big improvement though, no?

Twelly

styxd wrote:

It seems like you have picked the wrong bike for commuting on the road with.

Agreed..

But it is still strange that you can't get anything more than mid 20's at 120rpm. Mind you, this is still pretty quick for an MTB. My top speed on my roadie may be 41mph but that was head down, top gear and down a big, long hill. I generally cruise at about 20-25 on my lightweight, skinny tyred road bike. If you are regularly riding at mid 20's on your MTB then I would just sit back and be happy with that.

If you want to go faster, get a road/commuter bike or get one with an engine attached.

supersonic

I agree with the above, 120rpm in a 44/11 gear is about 37mph!

A larger chainset ie with 48t (the max you can go really) will add less than 10%.

Twelly

I suspect you either aren't using the full range of your gears (maybe shifter indicators are showing top gear but derailleur hasn't shifted all the way?) or your estimates of cadence and speed are a bit out.

Even if you have a 42t big ring rather than 44t, you should still be flying along at a hefty speed when your legs are doing 120rpm.

Guile

The derailleur definitely shifts all the way to the big cog but you're right, my cadence estimates are probably inaccurate. I will try to count it today when I ride and come back. What I meant was when rolling down a slope, I can pedal at 120 but still not accelerate in the top gear.

bails87

Also, the cars will be overtaking because you're on a bike, not because you're going slowly! I'll be doing the best part of 30mph in a 20 zone or the high 30s in a 30 zone and they'll still try to get past.

But back to the gears, I bet you're not doing 120rpm. On a steady stretch of road count how many times your right foot goes through the 12 o clock position in a minute.

Twelly

Guile wrote:

The derailleur definitely shifts all the way to the big cog but you're right, my cadence estimates are probably inaccurate. I will try to count it today when I ride and come back. What I meant was when rolling down a slope, I can pedal at 120 but still not accelerate in the top gear.

As said above, your top speed will be in the region of 35mph so if you are going down hills faster than this then yes, you won't be able to pedal fast enough to keep up.

When you get to these speeds (down a hill) you will find you can actually go faster by not pedalling and just tucking in to the bike with your feet at the 3 o'clock/9 o'clock position.

OCLV74

Interested in this, because I'll mainly be on the road til I scope out where to go, and getting my fitness up! (I live in Birmingham centre near enough). I bought a nice light frame, got a bike on the cycle to work gubbins, transferred most of it to the frame, however when riding the bike I got from the shop, I found I simply stayed in the largest cog on the chainset the whole way home, even uphill! I hasten to add, I haven't ridden in near 10 years, although before that I did do maybe 300 miles a week on a mountain bike as part of my job. I did find it a little worrying that I was maxed out before I even started???? Perhaps a larger chain ring is in order? I'm starting to regret going 3x10, although when I get on the silly stuff, I'll bet I'll be glad.

Twelly

You have to remember what you are riding - a mountain bike. As soon as you use it for its intended use (mountain biking) you will find you will almost never need to go all the way to top gear and you will be very grateful for the low gearing when you get to that 30 degree rooty slope. Commuting on roads = road bike.

bails87

There's a lot of overlap between gears too. More so on the new 10 speed setups with a slightly smaller big ring and bigger granny.

E.g if you're on the big ring and a fairly big cog at the back, you could get the same gear by going to the middle ring and a smaller (harder) cog on the cassette. The big ring only adds about 2 gears, but gives a better chainline for the stuff that would be at the top end of the middle ring.

Guile

I guess my cadence was about 70-80 when topping out on the flat. I guess some people are going to say I need to pedal faster but 60 seems right to me.

Twelly

70-90 is supposed to be the most efficient but it depends on the person. Simple answer is - you have got a mountain bike. It is not designed to do 30mph on roads.

YeehaaMcgee

Guile wrote:

I guess my cadence was about 70-80 when topping out on the flat. I guess some people are going to say I need to pedal faster but 60 seems right to me.

at a cadence of 60, you'll be doing roughly 18mph with a 42 tooth chainring and an 11 tooth sprocket.
60 however, is a fairly slow cadence.

Guile

TwellySmat wrote:

Simple answer is - you have got a mountain bike. It is not designed to do 30mph on roads.

OK but I am still wanting to give the ring change a go even just to make a little bit of a difference.

For £20, I don't have much to lose.

Any advice on the technical aspects of it? Thanks.

Chunkers1980

Yes, make sure yourfront mech works for the size of ring chosen and it fits your cranks.

The Rookie

Much better in the long run to learn to pedal at an effective cadance than allow yourself not to bother by bodging it!

My Commuter has a 46T front and a 28-11 cassette, it runs on skinny slicks, I only use the top 2 gears going downhill and have been clocked by a guy from work (and on my GPS) doing near enough 40 downhill with revs to spare.

supersonic

Guile wrote:

TwellySmat wrote:

Simple answer is - you have got a mountain bike. It is not designed to do 30mph on roads.

OK but I am still wanting to give the ring change a go even just to make a little bit of a difference.

For £20, I don't have much to lose.

Any advice on the technical aspects of it? Thanks.

Sticking a 48 on means the jump to the next ring, the 32 will be 16t. Most mechs are only designed to handle 12.

YeehaaMcgee

Guile wrote:

Any advice on the technical aspects of it? Thanks.

Er, yeah. Just pedal faster.