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Date: 18 Sep 2007 18:11:55
From: peter
Subject: Gearing on MTB not tall enough, what to replace?
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I found the tallest gearing on my MTB not tall enough, both on road and on a
bike trainer. On the trainer, it feels like biking on a flat or slight
incline, but no where near hill climbing.
The chainrings are 42T, 34T, 24T, and the rear cluster is
11-13-15-18-21-24-28. Crank length is 175mm. Wheel is 26 inch. Trainer is a
kurt kinetic fluid I just bought. I was hoping it would provide more
resistance than it does. I use 42T to 11T gear ratio at all times on the
trainer.
Since 11T at the rear is the smallest possible, to increase the gear ratio I
can only make the front chainring larger. There is 1cm of clearance between
the top edge of the 42T chainring and the top of the front derailleur. Does
that mean I can replace the 42T chainring with something that is 2cm larger
in diameter (1cm larger in radius)? By my estimate this means a 46T
chainring. Doesn't seem like much. Are there larger front derailleur to
accomdate an even larger chainring? Or would I have to also make the
smallest chainring larger to keep the chain inside the front derailleur
(after raising it higher on the frame)?
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Date: 20 Sep 2007 09:13:47
From:
Subject: Re: Gearing on MTB not tall enough, what to replace?
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On Sep 18, 11:11 am, "peter" <nos...@nospam.com > wrote:
> I found the tallest gearing on my MTB not tall enough, both on road and on a
> bike trainer. On the trainer, it feels like biking on a flat or slight
> incline, but no where near hill climbing.
>
> The chainrings are 42T, 34T, 24T, and the rear cluster is
> 11-13-15-18-21-24-28. Crank length is 175mm. Wheel is 26 inch. Trainer is a
> kurt kinetic fluid I just bought. I was hoping it would provide more
> resistance than it does. I use 42T to 11T gear ratio at all times on the
> trainer.
>
> Since 11T at the rear is the smallest possible, to increase the gear ratio I
> can only make the front chainring larger. There is 1cm of clearance between
> the top edge of the 42T chainring and the top of the front derailleur. Does
> that mean I can replace the 42T chainring with something that is 2cm larger
> in diameter (1cm larger in radius)? By my estimate this means a 46T
> chainring. Doesn't seem like much. Are there larger front derailleur to
> accomdate an even larger chainring? Or would I have to also make the
> smallest chainring larger to keep the chain inside the front derailleur
> (after raising it higher on the frame)?
No problem. Stick a 48 tooth large ring on there--which gives a 117
inch high, which should be large enough for even the strongest pedal
masher--raise the front derailleur and you're off to the races. One
thing that will likely need to be adjusted just right is the chain
length because you're now wrapping a lot of chain. Better to make
sure that the big on big combination works--you're not supposed to use
it, but everybody does anyway--even it rubs a little in the granny/
small cogs combo--you should never need these anyway.
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Date: 19 Sep 2007 09:37:08
From: Mike Jacoubowsky
Subject: Re: Gearing on MTB not tall enough, what to replace?
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>I found the tallest gearing on my MTB not tall enough, both on road and on
>a bike trainer. On the trainer, it feels like biking on a flat or slight
>incline, but no where near hill climbing.
>
> The chainrings are 42T, 34T, 24T, and the rear cluster is
> 11-13-15-18-21-24-28. Crank length is 175mm. Wheel is 26 inch. Trainer is
> a kurt kinetic fluid I just bought. I was hoping it would provide more
> resistance than it does. I use 42T to 11T gear ratio at all times on the
> trainer.
>
> Since 11T at the rear is the smallest possible, to increase the gear ratio
> I can only make the front chainring larger. There is 1cm of clearance
> between the top edge of the 42T chainring and the top of the front
> derailleur. Does that mean I can replace the 42T chainring with something
> that is 2cm larger in diameter (1cm larger in radius)? By my estimate this
> means a 46T chainring. Doesn't seem like much. Are there larger front
> derailleur to accomdate an even larger chainring? Or would I have to also
> make the smallest chainring larger to keep the chain inside the front
> derailleur (after raising it higher on the frame)?
#1: With that 11 tooth back there, your high gear is approximately 99." That
should be sufficient for pretty decent speed on the road; it would take a
faster ride than my group normally does (and they ride pretty fast) for me
to have to use a higher gear than that.
#2: Your front derailleur is made for the radius of the chainring size you
have now. You can raise it a slight amount and use a 44, but it will not
shift very well with a 46. Most significantly it will have more difficulty
shifting from the smallest to middle chainring, and also from the middle to
the smallest. It would probably be easiest to pick up an inexpensive
road-style triple crank and appropriate front derailleur if you want
super-high gearing. Keep in mind that you might also run into
shift-lever/front-derailleur compatibility issues.
Are you running small (26x1) tires? That exacerbates the gearing situation,
since it lowers your actual gear. You could bump up to the largest
smooth-tread tire (26x2 or so) and get a significant increase in high gear.
--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com
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Date: 19 Sep 2007 17:57:39
From: peter
Subject: Re: Gearing on MTB not tall enough, what to replace?
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"Mike Jacoubowsky" <mikej1@ix.netcom.com > wrote in message
news:VecIi.4936$Sd4.4816@nlpi061.nbdc.sbc.com...
> #2: Your front derailleur is made for the radius of the chainring size you
> have now. You can raise it a slight amount and use a 44, but it will not
> shift very well with a 46. Most significantly it will have more difficulty
> shifting from the smallest to middle chainring, and also from the middle
> to the smallest. It would probably be easiest to pick up an inexpensive
> road-style triple crank and appropriate front derailleur if you want
> super-high gearing. Keep in mind that you might also run into
> shift-lever/front-derailleur compatibility issues.
The middle chainring have some damage, so I may upgrade all three rings.
If I make all three chainrings larger, could I then avoid the derailleur
issue?
Other than number of teeth, is there any difference between road and mtb
chainrings?
> Are you running small (26x1) tires? That exacerbates the gearing
> situation, since it lowers your actual gear. You could bump up to the
> largest smooth-tread tire (26x2 or so) and get a significant increase in
> high gear.
It never occured to me tire width has an effect on gearing.
I have a 1.25 right now. I will look for a wider one.
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Date: 19 Sep 2007 22:10:21
From: Mike Jacoubowsky
Subject: Re: Gearing on MTB not tall enough, what to replace?
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>> #2: Your front derailleur is made for the radius of the chainring size
>> you have now. You can raise it a slight amount and use a 44, but it will
>> not shift very well with a 46. Most significantly it will have more
>> difficulty shifting from the smallest to middle chainring, and also from
>> the middle to the smallest. It would probably be easiest to pick up an
>> inexpensive road-style triple crank and appropriate front derailleur if
>> you want super-high gearing. Keep in mind that you might also run into
>> shift-lever/front-derailleur compatibility issues.
>
> The middle chainring have some damage, so I may upgrade all three rings.
> If I make all three chainrings larger, could I then avoid the derailleur
> issue?
It's the radius of the chainring that causes some of the trouble; the front
derailleur is approximately matched to the radius of the chainring. Moving
to a larger set of chainrings will still result in a mismatch (and
less-than-optimal shifting).
> Other than number of teeth, is there any difference between road and mtb
> chainrings?
Generally, no. Smaller mountain bike chainrings tend to be made of steel,
and mountain bike chainrings in general use smaller bolt circles. But the
chainring designs are pretty much the same.
>> Are you running small (26x1) tires? That exacerbates the gearing
>> situation, since it lowers your actual gear. You could bump up to the
>> largest smooth-tread tire (26x2 or so) and get a significant increase in
>> high gear.
>
> It never occured to me tire width has an effect on gearing.
> I have a 1.25 right now. I will look for a wider one.
That sounds a bit funny; obviously "width" per se has no effect on gearing,
but a wider tire is also taller, and that's what makes the difference.
--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com
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Date: 19 Sep 2007 16:07:48
From: Marz
Subject: Re: Gearing on MTB not tall enough, what to replace?
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On Sep 18, 1:11 pm, "peter" <nos...@nospam.com > wrote:
> I found the tallest gearing on my MTB not tall enough, both on road and on a
> bike trainer. On the trainer, it feels like biking on a flat or slight
> incline, but no where near hill climbing.
Yes, funny how a bike designed for off road use doesn't perfrom that
great on the road.
> The chainrings are 42T, 34T, 24T, and the rear cluster is
> 11-13-15-18-21-24-28. Crank length is 175mm. Wheel is 26 inch. Trainer is a
> kurt kinetic fluid I just bought. I was hoping it would provide more
> resistance than it does. I use 42T to 11T gear ratio at all times on the
> trainer.
How fast are you pedaling, what's your cadence? What are your goals
while using the trainer, endurance, V02max, sprinting, leg strength,
general fitness, etc? I've found that most home trainers don't offer
enough resistance to really help with leg strength, for example I can
adjust the stationary bikes at the gym to a point where the wheel is
stuck or requires massive effort to move it. Something I can't do with
my mag trainer, even while using my road bike.
> Since 11T at the rear is the smallest possible, to increase the gear ratio I
> can only make the front chainring larger. There is 1cm of clearance between
> the top edge of the 42T chainring and the top of the front derailleur. Does
> that mean I can replace the 42T chainring with something that is 2cm larger
> in diameter (1cm larger in radius)? By my estimate this means a 46T
> chainring. Doesn't seem like much. Are there larger front derailleur to
> accomdate an even larger chainring? Or would I have to also make the
> smallest chainring larger to keep the chain inside the front derailleur
> (after raising it higher on the frame)?
You can adjust the height of the front derailleur to fit a 52T if you
wanted. You'll need a new chain too, which may mean a new rear cluster
and may make the bike pretty crap for offroad use.
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Date: 19 Sep 2007 08:09:13
From: David Bonnell
Subject: Re: Gearing on MTB not tall enough, what to replace?
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On Sep 18, 4:11 pm, "peter" <nos...@nospam.com > wrote:
> I found the tallest gearing on my MTB not tall enough, both on road and on a
> bike trainer.
What about on the trails? Do you really need a MTB?
> On the trainer, it feels like biking on a flat or slight
> incline, but no where near hill climbing.
It never will. Your position and weight distribution relative to the
bike change when climbing a real hill, but that isn't the case on
trainers. On a flat, the faster you go, the more wind resistance you
encounter...this effect is generally what trainers mimic (more
resistance with more effort).
> The chainrings are 42T, 34T, 24T, and the rear cluster is
> 11-13-15-18-21-24-28. Crank length is 175mm. Wheel is 26 inch. Trainer is a
> kurt kinetic fluid I just bought.
I had a 42-32-22 on my MTB and (i) never used my granny ring and (ii)
very quickly ran out of gears when on a slight downgrade (or even on
the flat). I 'upgraded' to a 48-36-26 and no longer have any troubles
using the full range.
> resistance than it does. I use 42T to 11T gear ratio at all times on the
> trainer.
Maybe the trainer can be adjusted? I'm not familiar with it, sorry.
> Since 11T at the rear is the smallest possible, to increase the gear ratio I
> can only make the front chainring larger. There is 1cm of clearance between
> the top edge of the 42T chainring and the top of the front derailleur. Does
> that mean I can replace the 42T chainring with something that is 2cm larger
> in diameter (1cm larger in radius)? By my estimate this means a 46T
> chainring. Doesn't seem like much. Are there larger front derailleur to
> accomdate an even larger chainring? Or would I have to also make the
> smallest chainring larger to keep the chain inside the front derailleur
> (after raising it higher on the frame)?
Most deraillers can be moved up or down to accommodate most chainring
sizes.
Shimano generally recommends 2mm between teeth and derailleur cage
(1cm is a LOT of room, possibly necessary due to your larger-than-
normal middle/granny rings).
If your drivetrain isn't heavily worn, get a 46T chainring to replace
your 42T. You will likely need a longer chain to accommodate this
setup. Check the specs on your front and rear derailleurs to ensure
they can handle the new gearing. For example, Shimano FDs are
typically designed for a 12T difference between top/middle chainrings,
and 22T difference between top/granny. Coincidentally, a 46-34-24
meets this spec exactly. If your setup isn't Shimano or if you've got
some really old kit, this 'advice' may be irrelevant.
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Date: 19 Sep 2007 18:09:30
From: peter
Subject: Re: Gearing on MTB not tall enough, what to replace?
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"David Bonnell" <dbonnell@gmail.com > wrote in message
news:1190214553.592447.240350@n39g2000hsh.googlegroups.com...
> On Sep 18, 4:11 pm, "peter" <nos...@nospam.com> wrote:
>> I found the tallest gearing on my MTB not tall enough, both on road and
>> on a
>> bike trainer.
>
> What about on the trails? Do you really need a MTB?
Hehe. Probably not. But MTB was "in" a while back. Just like people who buy
SUVs now -- how many go off road? I did go trail riding once.
>> On the trainer, it feels like biking on a flat or slight
>> incline, but no where near hill climbing.
>
> It never will. Your position and weight distribution relative to the
> bike change when climbing a real hill, but that isn't the case on
> trainers. On a flat, the faster you go, the more wind resistance you
> encounter...this effect is generally what trainers mimic (more
> resistance with more effort).
I'm not complaining about riding posture, just the resistance. Althought I
haven't tried, I think doubling the resistance of the trainer would give me
what I want. If the manufacturer are smart, they would provide an option to
mount a second resistance unit on the trainer.
> I had a 42-32-22 on my MTB and (i) never used my granny ring and (ii)
> very quickly ran out of gears when on a slight downgrade (or even on
> the flat). I 'upgraded' to a 48-36-26 and no longer have any troubles
> using the full range.
Sounds like a good idea. I may try that too.
> Most deraillers can be moved up or down to accommodate most chainring
> sizes.
> Shimano generally recommends 2mm between teeth and derailleur cage
> (1cm is a LOT of room, possibly necessary due to your larger-than-
> normal middle/granny rings).
>
> If your drivetrain isn't heavily worn, get a 46T chainring to replace
> your 42T. You will likely need a longer chain to accommodate this
> setup. Check the specs on your front and rear derailleurs to ensure
> they can handle the new gearing. For example, Shimano FDs are
> typically designed for a 12T difference between top/middle chainrings,
> and 22T difference between top/granny. Coincidentally, a 46-34-24
> meets this spec exactly. If your setup isn't Shimano or if you've got
> some really old kit, this 'advice' may be irrelevant.
Thanks for the tips.
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Date: 19 Sep 2007 00:55:30
From: me
Subject: Re: Gearing on MTB not tall enough, what to replace?
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On Tue, 18 Sep 2007 18:11:55 +0000, peter wrote:
> kurt kinetic fluid
I looked up some details on this trainer and it has
"speed sensitive resistance" i.e. the faster you go, the
harder it is to pedal. Are you getting up to speed?
I would expect with that gearing if the trainer is set
up right it should provide a good work out. If on road
gearing is also too low,i.e. you are spinning out in top
on flat roads then maybe you are a very strong rider?
Are you used to road gearing? It is possible to put bigger
chainring on, the normal highest for a MTB is 48 I think.
I don't see why you couldn't put a road triple derailleur
on and take it up to 52 or 53.
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