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  1. #1
    Senior Member hamiltonian's Avatar
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    Gearing, MTB -> Road Tank

    I have two questions. The first one should be simple: are the teeth on chainrings supposed to be uniform? They look chewed on my old hardtail MTB—some of the tops are squared off as if broken, and others seem distorted into irregular shapes. The chain seems to work okay with no bumps or clicks, and everything shifts okay. When I have this bike on my trainer, I can also see that the rings are bent, and wobble a bit.

    So I was thinking that I could justify changing the crankset, and since I'm repurposing this bike as a road tank for rougher roads and gravel, I was wondering if I could add a couple higher gears in the process. Currently I have 24-34-42T, and I was wondering if I could get a large ring of 48T without needing to change any other components. This would give me a top gear of 113.5 gear inches, I think. Would even a 52T be possible?

    I suppose the key here would be the front derailer. The cassette is 11-13-15-18-21-24-28T, Alivio shifters, Alivio/STX derailers.

    Okay, so here's yet another question: the highest gear on this bike calculates to 99.3 gear inches (26in wheels). Is that correct? I usually ride this bike in the next lowest gear (84 gear inches). This seems high. My single speed bike is ~70 gear inches, and doesn't feel that much different.

    Anyway, I changed out the knobby tires for something more roadworthy, and that made a huge difference. It's not a showstopping bike, but it cost my friend $10 at a church sale (free to me, since it's too big for him), and it has a Tange sticker on the frame, so I think it's worth a little effort to tweak to my needs. Mostly I want to do rail trails in my area. I also need to do hills, since I live on the edge of the Niagara escarpment, but I won't be doing any dirt or mud trails.

    I hesitate to use the term "cyclocross" in relation to this bike, but if I wanted to buy something to fill its role, it would probably be a Cross Check.

    Here's the bike after I changed the bars but before I changed the tires. Obviously I don't want to spend a lot of money on this bike, but I think it has potential.

    Mongoose-01.jpg

  2. #2
    7-speed doomsday prepper ThermionicScott's Avatar
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    High gears aren't helpful at all for rough roads or gravel. Consider that when you're climbing a gravel hill, you'll want to stay seated so that the rear wheel doesn't spin out, and you won't be descending at fast enough speeds to want anything over 100.

    How often are you in top gear, and you can't pedal fast enough to increase your speed? Especially on a mountain bike?

    P.S. From your description of the chainring teeth, you're probably seeing the specifically-designed teeth that aid shifting. A picture would help.
    Quote Originally Posted by chandltp View Post
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    Quote Originally Posted by hamiltonian View Post
    ..... are the teeth on chainrings supposed to be uniform? They look chewed on my old hardtail MTB—some of the tops are squared off as if broken, and others seem distorted into irregular shapes. The chain seems to work okay with no bumps or clicks, and everything shifts okay. When I have this bike on my trainer, I can also see that the rings are bent, and wobble a bit.
    No the teeth on modern chainrings are not uniform. Several teeth are intentionally modified to speed and improve shifting. This is normal and intentional. As to the wobble, unless it's very minor, it does indicate damage such as hitting something with the ring. If the bend is not too bad, the rings can be straightened by the judicious application of an adjustable wrench with the jaws tightened to firmly grasp the ring.

  4. #4
    Senior Member Retro Grouch's Avatar
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    I've got a 48/32/22 crankset on my beater with an LX front derailleur and LX rapid fire shifters. It shifts fine. I think of it as a compact double but with a bail-out granny.

    I'd think that in your case, if you raise your derailleur a tad, all you'd have to buy would be a 48 tooth chainring. Your derailleur arc looks to me like a 48 would match it perfectly.

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    Yeah, your description of the irregular teeth sounds like the shaped and ramped teeth designed to improve shifting. THese have been pretty common on bikes since the early 1990s.

    Less expensive cranks and chainrings can get distorted over time from the forces involved in riding, shifting, crashing, loading and unloading the bike fromt he trunk of your car, etc. If it doesn't rub or grind so as to make it a problem, then it isn't a problem.

    But I agree with the idea of getting bigger rings for the front. A 42-11 is a pretty small biggest gear, and this will be made more noticable if you switch to smaller tires. According to the SHeldon Brown gear calculator, your speed (with 26 X 2.1" tires) and spinning at 100 rpm (a reasonable cadence to maintain with some effort) will put you at about 47 km/h (less than 30 mph), which is not too fast going down a hill. If you changed to a 46 tooth big ring, you likely would not need to change your front derailleur for this switch and you would have a speed of about 52 km/h at 100 rpm.

    A few other observations:

    -Your stem is almost definitely up past the maximum height line. It even looks like it is starting to bend a bit from the extra stress caused by the extension. If you leave it this way you are likely to need facial reconstriction surgery in the near future.
    -your saddle is canted severly nose-down and this will put loads of extra pressure on your hands, which may explain why you have your bars so high - having the saddle tilted like that will give you feeling of falling forward and many people erroneously think this is happening because the bars are too low.
    -THat is a big bike frame - probably a 22 or 23" frame, which is best suited for someone 6'2" or taller. If you are not that tall then the bike is likely too big for you and it will be tough to get it to fit properly. A whole 'nother used bike of similar quality may cost $100 or so, but you may get much more enjoyment out of it. I cannot say for sure, though, becuas I have not seen you on the bike.
    -Those tires are probably quite good for loose dirt, but for gravel and any hard surface, a tire with less tread will give you superior traction and probably roll a lot easier.

    -(edit) the stem also has a tonne of forward extension... we used to call an extra long stem like that a 'fishing rod.' If the bike is a big size for you then that will greatly exascerbate the problem as the frame already has a long top tube and the extra long stem forces you to reach out even further. New (or used) stems are available in lots of lengths and rises and do not cost much money.
    Last edited by DCB0; 08-28-12 at 10:22 AM.

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    Quote Originally Posted by Retro Grouch View Post
    I've got a 48/32/22 crankset on my beater with an LX front derailleur and LX rapid fire shifters. It shifts fine. I think of it as a compact double but with a bail-out granny.

    I'd think that in your case, if you raise your derailleur a tad, all you'd have to buy would be a 48 tooth chainring. Your derailleur arc looks to me like a 48 would match it perfectly.

    I don't think the chainrings on that crank are replaceable. He will have to buy a whole new crank to change the gearing.

  7. #7
    Senior Member hamiltonian's Avatar
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    Quote Originally Posted by ThermionicScott View Post
    High gears aren't helpful at all for rough roads or gravel. Consider that when you're climbing a gravel hill, you'll want to stay seated so that the rear wheel doesn't spin out, and you won't be descending at fast enough speeds to want anything over 100.

    How often are you in top gear, and you can't pedal fast enough to increase your speed? Especially on a mountain bike?
    What I want this bike for is road as well as MUPs and rail trails, with patches of rougher asphalt and gravel, and some country gravel roads. I want more speed for the road parts. It's very easy to hit top speed on this bike, and I don't need MTB functionality. If I keep it a triple crank, won't I have gears low enough for my purposes?

    Quote Originally Posted by ThermionicScott View Post
    P.S. From your description of the chainring teeth, you're probably seeing the specifically-designed teeth that aid shifting. A picture would help.
    Yes, from the other replies, I think that the teeth are designed to be that way. I was thrown because my other bike that I counted teeth on is 30 years old, and the teeth on that one are uniform.

  8. #8
    Senior Member hamiltonian's Avatar
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    Quote Originally Posted by Retro Grouch View Post
    I've got a 48/32/22 crankset on my beater with an LX front derailleur and LX rapid fire shifters. It shifts fine. I think of it as a compact double but with a bail-out granny.
    That's the kind of setup I was hoping I could make work. Mine is a beater, too, pretty much, and I don't want to spend for a whole new geartrain.

  9. #9
    Senior Member hamiltonian's Avatar
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    Boy, am I ever glad I posted a pic of the bike. You sure made some interesting points here.

    Quote Originally Posted by DCB0 View Post
    A few other observations:

    -Your stem is almost definitely up past the maximum height line. It even looks like it is starting to bend a bit from the extra stress caused by the extension. If you leave it this way you are likely to need facial reconstriction surgery in the near future.
    -(edit) the stem also has a tonne of forward extension... we used to call an extra long stem like that a 'fishing rod.' If the bike is a big size for you then that will greatly exascerbate the problem as the frame already has a long top tube and the extra long stem forces you to reach out even further. New (or used) stems are available in lots of lengths and rises and do not cost much money.
    I bought a new stem, but I was stymied by the way the brake cable goes through that hole in the existing stem. Do I need to drill a hole in the new stem? Anyway, I'd replace it immediately if I knew how. I hate the stem that's on there, and yes, now that you mention it, I can see the bend.

    -your saddle is canted severly nose-down and this will put loads of extra pressure on your hands, which may explain why you have your bars so high - having the saddle tilted like that will give you feeling of falling forward and many people erroneously think this is happening because the bars are too low.
    I hate that saddle, and perhaps that's part of the reason why. I'll adjust it right away.

    -THat is a big bike frame - probably a 22 or 23" frame, which is best suited for someone 6'2" or taller. If you are not that tall then the bike is likely too big for you and it will be tough to get it to fit properly. A whole 'nother used bike of similar quality may cost $100 or so, but you may get much more enjoyment out of it. I cannot say for sure, though, becuas I have not seen you on the bike.
    I'm 6'2" and I have two other bikes of similar size that are nice to ride. This bike is uncomfortable because of that stem, I think.

    -Those tires are probably quite good for loose dirt, but for gravel and any hard surface, a tire with less tread will give you superior traction and probably roll a lot easier.
    I changed the tires already, and they're much, much better on the road now.

    Thanks for the critical view of my bike. That helped me a lot.

    Now, how can I replace that nasty stem?

  10. #10
    Still spinnin'..... Stealthammer's Avatar
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    Quote Originally Posted by DCB0 View Post
    I don't think the chainrings on that crank are replaceable. He will have to buy a whole new crank to change the gearing.
    Actually I believe that the chainring bolts are on the backside of the crankset and that the chainring are replacable, but a new crankset would probably cost abot the same as three new chainrings....

    OP: I run a compact road crank on my commuter MTB with a 34/50t and a 11-26t cassette. Where I live this works out great but you might want an 11-28t or an 11-32t, which your current rear derailleur should handle fine.
    Last edited by Stealthammer; 08-28-12 at 11:52 AM.
    Just your average 'high-functioning' lunatic, capable of passing as 'normal' for short periods of time.....

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  11. #11
    Senior Member CACycling's Avatar
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    Quote Originally Posted by hamiltonian View Post
    I bought a new stem, but I was stymied by the way the brake cable goes through that hole in the existing stem. Do I need to drill a hole in the new stem? Anyway, I'd replace it immediately if I knew how.
    You'll need something like this: http://www.niagaracycle.com/product_...ducts_id=12337 for the brake cable.

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    Senior Member hamiltonian's Avatar
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    Quote Originally Posted by Stealthammer View Post
    OP: I run a compact road crank on my commuter MTB with a 34/50t and a 11-26t cassette. Where I live this works out great but you might want an 11-28t or an 11-32t, which your current rear derailleur should handle fine.
    I have an 11-28T cassette on there that I'm happy with—what I want to know is, will something like this work with my front derailer? And are there any compatibility problems that might involve something other than the FD?

  13. #13
    Senior Member hamiltonian's Avatar
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    Quote Originally Posted by CACycling View Post
    You'll need something like this: http://www.niagaracycle.com/product_...ducts_id=12337 for the brake cable.
    Is that compatible with a quill stem? I don't see how to fasten it to anything, unless it simply snugs to the stem.

    ETA: Or do I have to take off the headset to put it on? Man, I hate being such a newb.
    Last edited by hamiltonian; 08-28-12 at 12:42 PM.

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    Senior Member hamiltonian's Avatar
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    Here's an updated pic—I hope the bike looks a bit more rideworthy. I'll figure out what to do with the stem, but for now I just lowered it so it's not unsafe to use. The seat should be better, and those are the new tires.

    Mongoose-02.jpg

    I appreciate all criticisms. I'm not kidding.

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    Quote Originally Posted by hamiltonian View Post
    Is that compatible with a quill stem? I don't see how to fasten it to anything, unless it simply snugs to the stem.

    ETA: Or do I have to take off the headset to put it on? Man, I hate being such a newb.
    There are two types of cable hangers that look like that - there are ones that clamp directly onto the quill of the stem and ones that replace the spacers between the two nuts of the headset on the fork. Either will work. I prefer the type that go on the fork because then you can adjust your stem without buggering up your brakes.

    I don't know what size headset your bike has so I cannot suggest a specific model. Check your stem for the size stamped near the max height line... it is either 22.2mm , 25.4mm (or possibly 21.1mm) diameter. If it is 22.2 or (I think) 21.1 mm, then you need one that fits that size (to go on the stem) or on a one inch headset. If it is 25.4 then you need a 25.4mm quill mount or a 1-1/8" headset mounted one.

    Here is one more option:
    http://www.niagaracycle.com/product_...c95716eb9e5307

    You will likely need a new cable and housing for your front brake.

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    Quote Originally Posted by hamiltonian View Post
    Here's an updated pic—I hope the bike looks a bit more rideworthy. I'll figure out what to do with the stem, but for now I just lowered it so it's not unsafe to use. The seat should be better, and those are the new tires.

    Mongoose-02.jpg

    I appreciate all criticisms. I'm not kidding.
    Those tires look much better. Keep them pumped up to the max pressure (probably around 65 or 80 psi) for maximum performance.

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    Quote Originally Posted by hamiltonian View Post
    I want more speed for the road parts. It's very easy to hit top speed on this bike.


    ?? Top speed is determined by the rider's ability, not the gearing range, unless it is exceedingly low. A 113" gear will not make you go any faster on the level, and will only marginally increase your speed on paved downhills in comarison to tucking down and coasting. Do what you want but I have not seen anyone who could increase their speed on the level by riding in a 113" gear. You would be very hard put to get above 30mph on that bike in neutral conditions, a speed that can easily be handled in a 90" gear.
    Last edited by cny-bikeman; 08-28-12 at 01:58 PM.
    There's no such thing as a routine repair.

    Don't tell me what "should" be - either it is, it isn't, or do something about it.

    If you think I'm being blunt take it as a compliment - if I thought you were too weak to handle the truth or a strong opinion I would not bother.

    Please take the time to post clearly so we can answer quickly. All lowercase and multiple typos makes for a hard read. Thanks!

  18. #18
    7-speed doomsday prepper ThermionicScott's Avatar
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    Quote Originally Posted by cny-bikeman View Post
    ?? Top speed is determined by the rider's ability, not the gearing range, unless it is exceedingly low. A 113" gear will not make you go any faster on the level, and will only marginally increase your speed on paved downhills in comarison to tucking down and coasting. Do what you want but I have not seen anyone who could increase their speed on the level by riding in a 113" gear. You would be very hard put to get above 30mph on that bike in neutral conditions, a speed that can easily be handled in a 90" gear.
    Yep, I forgot to mention that if you're maxing out a 100" gear going downhill (30 MPH at a reasonable 100 RPM), the best way to go faster is to stop pedalling and get into an aero tuck. That lets you save energy for the next uphill.
    Quote Originally Posted by chandltp View Post
    There's no such thing as too far.. just lack of time
    RUSA #7498

  19. #19
    Senior Member hamiltonian's Avatar
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    Quote Originally Posted by DCB0 View Post
    I like that option the best, actually. At this point, though, I think I should take the bike over to my local mechanic (or bike co-op), because I don't want an iffy job on my front brakes. I'm pretty green with bike mechanics, which is a situation I'm seeking to change, but it will take time and experience.

    Those tires look much better. Keep them pumped up to the max pressure (probably around 65 or 80 psi) for maximum performance.
    I pay a lot of attention to tire pressure because I'm a big guy—6'2" and ~300 lbs. That's likely why I bent that stem so easily as well, since I really haven't ridden it that much.

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    Senior Member hamiltonian's Avatar
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    Quote Originally Posted by cny-bikeman View Post
    ?? Top speed is determined by the rider's ability, not the gearing range, unless it is exceedingly low. A 113" gear will not make you go any faster on the level, and will only marginally increase your speed on paved downhills in comarison to tucking down and coasting. Do what you want but I have not seen anyone who could increase their speed on the level by riding in a 113" gear. You would be very hard put to get above 30mph on that bike in neutral conditions, a speed that can easily be handled in a 90" gear.
    If what you're saying is that I can increase my speed by increasing my cadence, then I understand you. But for context, this isn't a bike project for sport—my intentions are pragmatic. I mainly want this bike to take me 15 miles across country via combined street, road, and rail trail of varying surface quality to visit my sister and niece. When the going is good, I want to go, and I don't necessarily want to kill myself in the going.

    If I can't improve on what I have, that's good news indeed, because I'd rather not put anything extra into this bike. But I'm not sure that I can't benefit from a larger large chain ring. Will it not be easier to go faster if I have one?

  21. #21
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    Quote Originally Posted by hamiltonian View Post
    If what you're saying is that I can increase my speed by increasing my cadence, then I understand you. ....But I'm not sure that I can't benefit from a larger large chain ring. Will it not be easier to go faster if I have one?
    In a word, NO. What I was saying was not that you can go faster by spinning faster in a given gear (which is true) but rather that in general you CANNOT go faster by pedaling a higher gear. Your current high gear is 42-11. On a 26 inch wheel that is a 99 inch gear. It only takes 100 rpm to move that gear at 30 mph. Within limits lower gears are more efficient, both from a physiological and mechanical perspective. Spinning even moderately provides better blood flow, better cardio exercise, and less muscle fatigue. The drive train will be under lower and more even load and therefore convert less of the input power to heat and deflection, and the bike will track straighter.

    The only circumstance where you could conceivably go faster with a 113 in gear is if you were pedaling down a fairly steep, long hill. But if your goal is to go 15 miles in good time w/out too much stress then pedaling downhill is a waste of energy, as you could be coasting (or pedaling lightly to keep your muscles warm) in preparation for the uphill.

    The final thing to consider is that if you change only the 48 you are potentially causing more shifting and fewer commonly used gears, as all the gears on the large chainring will be higher. Right now, at 100 rpm and using all but the largest (cross-chain) cog in back you are covering 13.5 - 30 mph. If you go to a 48 tooth the low end goes to 15.5 mph and even your 2nd highest is 29 mph. So if you drop much below 15mph you would have to shift to the middle chainring AND then shift the rear cassette as well. On the other end you will hardly use the high gear at all, the 2nd highest not that often. That means less ability to match gear/load to terrain, which will make the ride harder and slower. Even if you pedal at a more modest rpm pretty much the same thing applies.

    Stay with what you have. What will make the miles go easier is more miles, not more equipment and time spent ordering and fiddling with it.
    Last edited by cny-bikeman; 08-28-12 at 03:17 PM.
    There's no such thing as a routine repair.

    Don't tell me what "should" be - either it is, it isn't, or do something about it.

    If you think I'm being blunt take it as a compliment - if I thought you were too weak to handle the truth or a strong opinion I would not bother.

    Please take the time to post clearly so we can answer quickly. All lowercase and multiple typos makes for a hard read. Thanks!

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    Senior Member hamiltonian's Avatar
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    Quote Originally Posted by cny-bikeman View Post
    In a word, NO. What I was saying was not that you can go faster by spinning faster in a given gear (which is true) but rather that in general you CANNOT go faster by pedaling a higher gear. Your current high gear is 42-11. On a 26 inch wheel that is a 99 inch gear. It only takes 100 rpm to move that gear at 30 mph. Within limits lower gears are more efficient, both from a physiological and mechanical perspective. Spinning even moderately provides better blood flow, better cardio exercise, and less muscle fatigue. The drive train will be under lower and more even load and therefore convert less of the input power to heat and deflection, and the bike will track straighter.

    The only circumstance where you could conceivably go faster with a 113 in gear is if you were pedaling down a fairly steep, long hill. But if your goal is to go 15 miles in good time w/out too much stress then pedaling downhill is a waste of energy, as you could be coasting (or pedaling lightly to keep your muscles warm) in preparation for the uphill.
    This is the best news possible, actually. If there's no clear way to improve the gears for road use, I'll quite happily save the time and money and use the bike as it is.

  23. #23
    johnliu@earthlink.net jyl's Avatar
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    On a mountain bike with road tires, with a typical recreational / casual / novice rider, at a cruising speed that he can maintain for an hour on a flat road - a bigger chain ring won't make a difference.

    That speed will be sonewhere between 14 mph and 17 mph, depending on the rider. Your current gearing is easily able to handle that.

    Yes, "on paper" a bigger chainring will let you reach a faster speed before you "spin out" (reach your maximum rpm). Maybe, instead of 29 mph at 100 rpm with your current gearing, on paper you'd be able to do 33 mph at 100 rpm.

    But in the real world, that won't happen, because you don't have the legs and lungs to push a mountain bike with the current gearing at 29 mph for more than ten minutes at best, riding solo on a flat road absent a big tailwind. That's not a dig on you, that's true for any recreational / casual rider, and indeed is true for most riders out there.

    Give it a try. Put an inexpensive cycle computer on the bike (like a $20 wired one), find a flat open road, start pedaling, get up to 29 mph and see how long you can keep it up. You'll see the theoretical difference from different gearing is irrelevant, the motor just doesn't have the horses.

    So that leaves downhill. If you are going down a moderately steep descent, run the right tire pressure, get in an aero tuck, and you'll quickly be coasting faster than you can pedal regardless of gearing. Especially a big guy.

    Admittedly there might be a descent that is so gentle that a tuck only gets you a 30 mph coast, and a bigger gear would let you turn 100 rpm at 35 mph. So over a mile you'll save maybe 20 seconds. Does that really matter? If it does, there is another solution. Train yourself to spin faster, like 120 rpm. It is not hard, you can definitely learn it.

    Bottom line, don't mess with your gearing until you have several months of daily riding under your belt, including plenty of time going flat out in your highest existing gear at 100-120 rpm.

    At that point, you might find yourself wanting a road bike rather than trying to make a mountain bike into a road machine. In my experience, take a mountain bike and change the deep knobbies for slick tires, you gain 2-3 mph of cruise speed. Swap that for a road bike and you gain another 2-3 mph. The effort it takes me to cruise at 15 mph with my daughter's old Hardrock with full knobbies, will have me doing 20 mph with my (not expensive) vintage road bike. So if you get all about going from point A to point B fast via roads, you will want a different bike.
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  24. #24
    johnliu@earthlink.net jyl's Avatar
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    Oh, looking at the second picture, I have these suggestions.
    - Lower the stem further, get the handlebar a couple inches lower than the seat, and get that bent part of the stem tucked deeper into the steerer tube. You will be in a more aero and more powerful pedaling position and the visible bend in the stem still makes me nervous.
    - Add some inexpensive bar-ends ($5 from the used bits box at a bike coop) to give you an alternate hand grip that puts you in an even lower, more aero position.
    - Make sure your seat height is right, often people have their seat too low and their legs can't fully extend. They ride like someone waddling around in a constant crouch (duck walk). That is not powerful.
    - Finally, give the bike a once over, make sure freewheel is oiled, chain lubed, hub bearings greased and adjusted, rims true, tires hard, etc. We (people) are relatively weak motors, even little amounts of drag (mechanical or aero) make a significant difference.
    - My MTB is similar to yours, same general era and also a hard tail. Last week I rode it around Lake Tahoe, 75 miles, hit 40+ on the descents, a bit under 5 hours total ride - so these old MTBs can cover ground fine, if we do our part and don't expect to be cruising fast.
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  25. #25
    Senior Member hamiltonian's Avatar
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    Quote Originally Posted by jyl View Post
    Bottom line, don't mess with your gearing until you have several months of daily riding under your belt, including plenty of time going flat out in your highest existing gear at 100-120 rpm.
    That sounds good. I was originally going to wait and see how it went over time, then I got to thinking. Sometimes it doesn't pay to think until you have adequate data.

    At that point, you might find yourself wanting a road bike rather than trying to make a mountain bike into a road machine. In my experience, take a mountain bike and change the deep knobbies for slick tires, you gain 2-3 mph of cruise speed. Swap that for a road bike and you gain another 2-3 mph. The effort it takes me to cruise at 15 mph with my daughter's old Hardrock with full knobbies, will have me doing 20 mph with my (not expensive) vintage road bike. So if you get all about going from point A to point B fast via roads, you will want a different bike.
    I do have an old Nishiki road bike, but I think it's too delicate for the rail trails I want to use. I just wanted to make the MTB suit my purposes as well as possible, and if it's okay how it is, I'm good with that.

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