Author Topic: 3-7 21 shifting on High Timber MTB and Gear rations/sprocket teeth, Handle bars  (Read 436 times)

Offline wb3jma

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So I needed a new bike old folding was beat up. Bought a Schwinn High Timber 26" Model #S4009E Rather than a single gear set the front sprocket has 3. Before I bought this did not give it a single thought that my previous bike was 7 speed and this is 21 with the exception that the Shimano shifters have thrown me off. Right shifter is 1-7 sure no problem there but the left is a friction shifter has a - sign at the top and a + sign at the bottom and from the bottom and there are 10 clicks from + to - so I'm a bit baffled as exactly how this is controlling the front deraileur 3 sprockets to work with the backs 7 sprockets to produce a 21 gear range? Other than watch what sprockets it's on I'm not sure how to track and watching your sprockets instead of facing forward is not so good an idea. I do understand that from the manual it's best so as not to have the chain rubbing the derailers so the not to have an acute angle of the chain when it's on both the two smaller and two larger sprockets front to back but other than that?

Some help/advice along these lines is welcomed before I go and end up getting a set of shifters that are both numeric and easier to track gearing with. 

Also the sprocket set in the back is 14-28T and the front is 24-42T. I understand the changing the backset so you have 30,32 or 34 teeth will making climbing easier but if you change the back should you change the front as well? If so to what?

Finally the handle bars are not wide enough to make steering control optimal they measure across at ~ 24.75 inches or 630 mm so I'm sure I need a larger set and stem to go with it.

Thank you ahead of time for any advice and explanations!

Offline JenniferC

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I ride an 18 speed older mountain touring bike and I normally leave the front on the middle chain ring and shift the back according to what I need. If I want to go faster then I'll move the front to the larger chain ring and adjust my speed with the rear gears. It's not very often I use the smallest front chainring but when I do it's the same, keep the front where it is and do a finer adjustment with the rear gears. Hope that helps.

Offline wb3jma

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Point is where exactly is that in relation to a friction shifter that seems to have 10 settings?

Offline rickpaulos

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Suntour made the first ratcheting shift levers in the 1970s. Many tiny clicks in friction shifters. They really did shift easier and they held their position no matter how hard you pedaled.  With all the friction shift systems you (the rider) had to "trim" the derailleurs to keep the chain from grinding.  There have been a number of copycat levers since then.

For dropped bar road bikes since the late 1990s:

Shimano makes the STI left levers in many versions.

Some are 1 click only for double ring cranks,
Some are 2 clicks only for triple ring cranks
Some are many clicks (10).  these are much more tolerant of mismatched components and front derailleurs out of adjustment. It puts the task of "trimming" the front derailleur on the rider to keep the chain from grinding on the front derailleur cage. 

As you shift through the gears on the back, the chain angle varies from side to side and the chain will rub on the front derailleur cage. Some of the Shimano groups are designed to prevent that from happening IF they are set up correctly.  I've seen plenty of bikes from brand new to rebuilt that have mismatched parts so there is no way they will work that well. The 10-click left levers will work with just about any derailleur.

If you change the rear gears from a max of 28 to a max of 34, you will need to replace the derailleur with a longer cage version and get a longer chain.  (adding links to existing chains is a pita as they pretty much have to be identical brand & model of chain).   To go the next step of replacing the front crank set (and derailleur) to get lower gear ratios puts you well in to "it's cheaper to get another bike that has those gears already" territory.  If you really like the bike, get a donor bike that has the low gears you want.  I have a couple bikes with Shimano STX drive trains.  22-32-42 sprockets and freewheels up to 31t.  The mountain bike gears just work so much better and were made in lower gear ratios that the roadie touring sets.

A 22 tooth front combined with a 31 or 32 rear is a really low gear.  No problem riding up mountains with 100 pounds of camping gear on the bike.  Sure beats walking and pushing your bike or blowing out your knees.






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Offline wb3jma

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Suntour made the first ratcheting shift levers in the 1970s. Many tiny clicks in friction shifters. They really did shift easier and they held their position no matter how hard you pedaled.  With all the friction shift systems you (the rider) had to "trim" the derailleurs to keep the chain from grinding.  There have been a number of copycat levers since then.

For dropped bar road bikes since the late 1990s:

Shimano makes the STI left levers in many versions.

Some are 1 click only for double ring cranks,
Some are 2 clicks only for triple ring cranks
Some are many clicks (10).  these are much more tolerant of mismatched components and front derailleurs out of adjustment. It puts the task of "trimming" the front derailleur on the rider to keep the chain from grinding on the front derailleur cage. 

As you shift through the gears on the back, the chain angle varies from side to side and the chain will rub on the front derailleur cage. Some of the Shimano groups are designed to prevent that from happening IF they are set up correctly.  I've seen plenty of bikes from brand new to rebuilt that have mismatched parts so there is no way they will work that well. The 10-click left levers will work with just about any derailleur.

If you change the rear gears from a max of 28 to a max of 34, you will need to replace the derailleur with a longer cage version and get a longer chain.  (adding links to existing chains is a pita as they pretty much have to be identical brand & model of chain).   To go the next step of replacing the front crank set (and derailleur) to get lower gear ratios puts you well in to "it's cheaper to get another bike that has those gears already" territory.  If you really like the bike, get a donor bike that has the low gears you want.  I have a couple bikes with Shimano STX drive trains.  22-32-42 sprockets and freewheels up to 31t.  The mountain bike gears just work so much better and were made in lower gear ratios that the roadie touring sets.

A 22 tooth front combined with a 31 or 32 rear is a really low gear.  No problem riding up mountains with 100 pounds of camping gear on the bike.  Sure beats walking and pushing your bike or blowing out your knees.

Thank you that was informative.