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MTB gear changing question

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MTB gear changing question

Old 06-19-07, 02:58 AM
  #1  
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MTB gear changing question

I am a rookie so this may be a silly question, but I hear there are no stupid questions. I have an ancient MTB, (early nineties) that I am trying to rehab. Since I only ride in suburbia now I would like to change the gearing to make it more road friendly, (more speeds in the rear or bigger chainrings?). I started riding again a couple of weeks ago and I had completely forgotten what a pleasure it is to be out pedaling in the morning air. I hope this is not a pipe dream since I cannot afford a new bike right now. Here are the patients vitals:

The rear derailleur, front derailleur and crankset are all Shimano Exage 500LX. The shifters are Shimano units with no identification other than the Shimano logo.

Rear cassette is a 7 speed 12 / 28 Hyperglide, (I measured the dropouts 130 mm.)
Chainrings are Shimano SG 24, 36, 46 (110 mm BCD)

After spending several days searching the forum I never really found an answer to my question. I also searched ebay listings hoping to divine an answer but so far I have come up empty. I am reduced to imploring all the experienced mechanics out there in the ether to offer guidance. So if you were in my shoes, what would you do?
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Old 06-19-07, 03:30 AM
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You won't find a cassete geared much higher than that. I would suggest looking into a new crankset, it will probably be cheaper than trying to change all 3 chainrings. It may require a bottom bracket change and a new chain as well. Might be possible for less than $100.

First I'd get some cheap road tires. Try nashbar.com, performancebike.com
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Old 06-19-07, 06:11 AM
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+1 on the tires. Go with as narrow as you can stand (1 inch is the narrowest you can get, I think), and you'll be surprised at how much that makes up for your lower gearing. You're working hard now to overcome the knobby road resistance. Ritchey Tom Slicks come in 1 and 1.4in., I think.
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Old 06-19-07, 06:23 AM
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I have a similar setup for 'round town use, I took the granny off the front ring (I would have left it on just cause but the derailleur I had laying around could only handle a double) and I changed the rear cassette to 11-21. Technically you have the same gears almost with your 12-25, but I had 11-30 and I like the closer spacing of the other one for road use. Mine is a bit older though too I should mention, and I have 38-48 rings. I bet you could score a crank like that pretty cheap, or just get the rings and swap it out (mine is 110 too)

+1 on the tires, that's going to make the biggest difference. I run 1.25" wide Tioga City Slickers which are cheap and durable.
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Old 06-19-07, 10:01 AM
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I guess my question was a little vauge

Hey guys thanks for the quick replies.

I agree with everyone about switching tires. Last week I put on 1.25" slicks and that made an incredible difference! Altough the ride is nowere near as comfy it is A LOT faster. After re-reading my post I realized that my question was a bit on the vauge side. Being a newbie I forgot a to mention a couple of other ingrediants. The area I ride has hills, tall ones, short ones, long tall ones (my favorite to go back down!).

My point is I don't mind the granny since I use it daily. What bothers me is the lack of top end gearing. When I am going down some of these hills, or even a long downhill slope, I quickly run out of gears resulting in my just coasting, albeit a fast and exhilerating one. My dream is to really take advantabge of these long downhills and put the peadal down!
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Old 06-19-07, 02:14 PM
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One result of going to smaller tires is that it gears you down. If you are going from a 26x2' to a 26x1.25 means you are going from a 26" nominal diameter to a 24.5" ND. That's about 6%! ONE tooth difference on a 12T cog is 8.3%!
You can get cassettes as low (or high?) as 11-19. They don't have any cogs smaller than 11 unless you go to the Capreo "system". I have no idea how "adaptable" it is to your bike or the cost. It requires a special Cassette AND Hub. It's probably too expensive of an option.

What I would suggest (before you make any changes) is determine what the lowest gears you need are to get up your steepest hill. Fudge a little bit for that torrid day when you aren't feeling well etc.....
Go here and calculate the Gear-Inches required for your worst case hill here-
http://sheldonbrown.com/gears/
Try some other cassette options such as 11-19, 11-24 etc.
Then go ride some more and re-evaluate!
You may want to just consider doing some trading and go with a road bike. They tend to have bigger chain rings (52-53T).
BTW- Are you sure you have a cassette instead of a Free Wheel? I don't think a FW doesn't give you as many options as a cassette does. You can check with your LBS to make sure.
Also, when I got back into riding a couple years ago, I was constantly wishing I had a different cassette. A week later it was a different combination and the next week.....
I would suggest riding it a couple weeks before making any major decisions.
You could probably get a new cassette installed for around $30 if you carry the wheel in and have a sad, poor look
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Old 06-19-07, 04:16 PM
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Originally Posted by ddmann
My point is I don't mind the granny since I use it daily. What bothers me is the lack of top end gearing. When I am going down some of these hills, or even a long downhill slope, I quickly run out of gears resulting in my just coasting, albeit a fast and exhilerating one. My dream is to really take advantabge of these long downhills and put the peadal down!
1. What does your front derailleur look like? Does the shift cable run under the bottom bracket?
2. How much clearance do you have between your biggest chainring and the chainstay?

I'm thinking that, if it was my bike, I'd replace the 46 chainring with a 50 That will give you a lot faster downhill gear. A 50 tooth chainring will obviously have a larger diameter so that's why you need to check the chainstay clearance.

The other issue is the front derailleur. A road front derailleur will match the arc of the larger chainring better so it will sit closer and work better. The catch is that all road front derailleurs are downpull. You'll also be exceeding the designed gear range of the derailleur by about 4 teeth, but I'd try it anyway.
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Old 06-19-07, 05:39 PM
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Thanks for that link Bill I put it into my favorites folder. While I am riding for the next few nights I will pay close attention to which gears I am using for each type of terrain. Usually I just pedal away and enjoy the ride so hopefully I won’t forget to look! I try to avoid the really steep hills for the weekend early morning ride when the traffic is light. I have already noticed that I spend very little time in the 24 chainring unless I am climbing. The 36 is nice when I am on the backside of a roller or starting up from a stop light. Once I am heading back down a hill I shift into the 46 and pedal as fast as I can. I have noticed that the dudes on road bikes who fly by me on a regular basis seem to have HUGE chainrings.

Retro Grouch you and I seem to be of the same mindset on this. Turning around in my chair to stare at the bike and....the cable comes up from the bottom and your right the cage matches the diameter of the 46 nicely. Evidently a 50 tooth chainring is in my future. I will check out Nashbar and Performance. With any luck I can put a little life into the old girl.
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Old 06-20-07, 01:59 PM
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To add to Retro's advice- You may be able to get away with the same FDER, by "optimizing" it for the 2 largest rings IF you can get by just using them. Using the smallest ring in this condition may result in you throwing the chain off the smallest ring on a too frequent basis. They do make "chain guides" to help alleviate this problem. Here's an example. There are others.
http://www.gvtc.com/~ngear/

Your FDER needs to be slid up the tube a little bit to accomodate the larger ring. Make sure it's a "clamp on" type, if you plan on going to a bigger ring.
Now a bit of math-
46/11= 4.182
50/12= 4.167
Basically, going to a 50T ring with your current cassette OR going to an 11T cassette with your current ring gives you virtually the same "high" gear!
To me, the cassette change is less hassle, and is easier to "undo" in case you change your mind.
That would lead to the question of "which" 11?
11-12-13-14-15-17-19
11-12-14-16-18-21-24
11-13-15-18-21-24-28
With the 11-19, you WILL need to use the small ring often. IS 24/19 a low enough gear?
With the 11-24, you give up the 13. I also have a 12-28 and would love a 13!
With the 11-28, you have the same 4 "low" gears as the 12-28, but reduce the 3 upper gears by 1 T. You also give up the 12T!
12-14-16-18-21-24-28 (for comparison)
Things to ponder!!
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Old 06-20-07, 01:59 PM
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Sorry for the "double. Something went wacko
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Old 06-20-07, 02:39 PM
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+1 with Retro, I did the big chainring swap and had the LBS adjust the FDerailler for me. I did have to give it a li'l extra push on the rapidfire, but it worked on all 3 rings. I was actually able to participate on the downhill.
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Old 06-20-07, 08:03 PM
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Your FDER needs to be slid up the tube a little bit to accomodate the larger ring. Make sure it's a "clamp on" type, if you plan on going to a bigger ring.
Now a bit of math-
46/11= 4.182
50/12= 4.167


Yes it is a clamp type, I wonder if I would need to buy a longer cable also?



Basically, going to a 50T ring with your current cassette OR going to an 11T cassette with your current ring gives you virtually the same "high" gear!
To me, the cassette change is less hassle, and is easier to "undo" in case you change your mind.
That would lead to the question of "which" 11?
11-12-13-14-15-17-19
11-12-14-16-18-21-24
11-13-15-18-21-24-28
With the 11-19, you WILL need to use the small ring often. IS 24/19 a low enough gear?
With the 11-24, you give up the 13. I also have a 12-28 and would love a 13!
With the 11-28, you have the same 4 "low" gears as the 12-28, but reduce the 3 upper gears by 1 T. You also give up the 12T!
12-14-16-18-21-24-28 (for comparison)
Things to ponder!![/QUOTE]


Hey I checked into the 11T cassette today by visiting Sheldon's site. Apparently I would need to get a slightly different hub to accomadate the smmaller gear. Probably not a huge issue I will do some more research tonight. Since I have put smaller tires onto my old MTB the 11T gear is a pretty good idea.

I also looked into a 50T chainring iwth 110 BCD spacing. My research ran into a bit of a snag on this one. Matching the chainrings teeth to the rear cassette which is a 7-speed may be a bit challenging. It looks like different "speed" cassettes use different spacing between each gear, and the chain matches these "widths". I am not sure yet whether a 9-speed chainring will co-operate with a 7-speed chain. I will do more research tonight.

BTW on my ride last night I paid pretty close attention to which chainring and gears I was using. I spend close to 90% of the ride in the big ring, only use the little ring for climbing, about 5%, and the middle ring I use a lot for starting from stop signs and smallish hills.


Once again thanks for the suggetions and support folks. With all your help I am learning enough to make smart decisions rather than the expensive lame ones.
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Old 06-20-07, 09:25 PM
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With your current rings, if you need a lower gear than Middle-1 (36/28), then an 11-19 won't work.
36/28 =1.29 = 31.5 gear-inches
24/19 =1.26 = 30.9 gear-inches
IF you have to change the FH body, It would also almost make sense to upgrafe to an 8-9 speed. Of course that means new shifters & chain, plus a more expensive cassette. At that point, you may be better off looking for a used road bike.

BTW, what bike do you have? Year???? Indexed shifting?
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Old 06-20-07, 10:09 PM
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Here is a pic of the ancient one.



It is a Mongoose IBOC Comp, I am not sure of its production year my best guess is 1990 or 1991. It now wears a set of 26 x 1.25 Forte slicks which was a great decision.

The rear derailleur, front derailleur and crankset are all Shimano Exage 500LX. The shifters are Shimano units with no identification other than the Shimano logo.

Rear cassette is a 7 speed 12 / 28 Hyperglide, (I measured the dropouts 130 mm.)
Chainrings are Shimano SG 24, 36, 46 (110 mm BCD)
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Old 06-20-07, 10:35 PM
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Once upon a time I swapped out my 2.2" knobbies for some of those skinny 1.25" tires. Perhaps it was the 180mm cranks I ran for my long legs, or maybe even the steep curve around the block I loved to take at speed, but the bottom bracket height was lowered signifigantly, and not taking that into account, caught a pedal and yardsaled in the intersection.

It seems to me that some larger slicks would still give you a low rolling resistance (especially at higher pressures) and at the least not lower your gearing. For higher gears, HG70 7-speed cassettes are available in 12-21, 13-23 and 13-26 spreads.
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Old 06-21-07, 07:06 AM
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Originally Posted by ddmann
Your FDER needs to be slid up the tube a little bit to accomodate the larger ring. Make sure it's a "clamp on" type, if you plan on going to a bigger ring.
Braze-on types have vertical adjustment, too. Not sure how you can tell whether it has enough before buying the ring, though.
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Old 06-21-07, 08:51 PM
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Wordbiker said

Once upon a time I swapped out my 2.2" knobbies for some of those skinny 1.25" tires. Perhaps it was the 180mm cranks I ran for my long legs, or maybe even the steep curve around the block I loved to take at speed, but the bottom bracket height was lowered signifigantly, and not taking that into account, caught a pedal and yardsaled in the intersection




Boy do I hear you on that one! Within the first 10 seconds after switching over the slicks I realized that I was sitting significantly lower in the saddle. I recieved the tires as a gift from a friend of a friend who was quite excited that I was going to revive by bike. I just can't say no to FREE.

Today I put new pedals on the ancient one. They are Wellgo 95B which imitations of the performance FOrte` campus pedal. Pretty cool I think since I can use the platform side until I can afford some fancy schmancy shoes!

Still looking for a 50T 110 mm BCD chainring, but I have not given up quite yet.

Last edited by ddmann; 06-21-07 at 09:01 PM.
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