3 speed / 5 speed build
 

Looking for some tips on a build/convert I am wanting to do. I am wanting to change my road bike into either a three speed or a five speed. I am not wanting to go with an IG rear hub, I am wanting to run either three cogs or five cogs in the rear - I just haven't decided if I want to go three speed or five speed yet. Nonetheless, I am wanting to use a single chainring up front and space the rear cogs out so that the middle cog is inline with the front chainring. If I choose to go with a three speed, this will put one cog both sides of center, and if I choose to go with a five speed, two cogs both sides of center. My questions are regarding shifting. I am thinking about using a down tube shifter or a flatbar shifter as this is being done on my flatbar roadbike. Are there different size cog spacers I will need to match either a 8,9, or 10 speed shifter? I know that if I use a downtube shifter I can always operate in friction mode, but I would much rather use index shifting. Are there larger cog spacers that I could use to take up some of the wider areas on both sides of the cogs? Also, I am wanting to get a new rear der. as the current one is a long cage Sora and I wanted to use a short cage seeing how not that many gears are going to be used. Can I assume that the rear der. can be either 8, 9, or 10 speed? Lastly,do you see any problem of having nothing up front for a chain guide? The biggest shifting in this scenario would be the five speed and then at that it is only moving either two cogs up or two cogs down from center. Do you think a chain guide is still in need? Thanks for the help.

Apart from the modest amount of weight saving to be had from getting rid of some sprockets and switching to a short cage RD, and some novelty/style features, your build seems kinda pointless.
Why don't you get a 9-speed MTB shifter, a 9-speed "corncob" (close range) road cassette and be done with it? If you insist you can always turn the limit screws all the way in so that you no longer have access to all the gears.

If you were intending to keep the original range, and chucking some of the intermediate sprockets I'd advise against it. Get the jump too big and the bike just won't shift.

Can't really help you with the spacers. One option is simply to disassemble a handful of used cassettes and get the spacers from them. People who have the parts & the tools sometimes use (plumbing) pipe which they cut into custom spacers. If youy want to throw good money after bad you can always buy a SS kit or two, and use the spacers out of them.

I'm with dabac; missing cogs makes very little sense. But IMO you should use 7spd, cause the 5mm spacing is far more tolerant of shifter cable degradation and doesn't need adjustment all the time.

Yep, cog width matters too. http://www.sheldonbrown.com/cribsheet-spacing.shtml

As for whether you need a chain guide, I reckon you'll have to find out for yourself. The short-cage derailleur may help, imparting more of the derailleur's spring tension to the chain, and getting the chain length just right should help too.

Thanks for the replies guys. If I keep it as an 8 or 9 speed and only the single front chainring, wouldn't there be too much chain cross when in the higher and lower gears? This is why I was limiting it down to either 3 or 5 cogs. I have plenty of old freewheels that I can take apart for the spacer, and those are the kind of spacers I was referring to.

Ok, lets say that I go the 1x7 route - would that still be too much chain cross when on the first and seventh cogs?...

To clairify - yes, I was planning on finding the correct spacing to use with whichever shifter I was going to run and adjust the upper and lower rear der. limits to only sweep the five cogs. Then just use the "active" index's on the shifter - i.e. if I were using a 9 speed shifter and only five rear cogs, I would use the shifter as 3rd to 7th gear and have a couple dead spots both high and low.

I hope I am explaining this ok. I appreciate the advice, opinions, and help guys!

Well, hereabouts there are plenty of people using 1x9 on their singletrack MTBs, which seems to work out just fine. When I'm on the middle front I run the whole range at the rear, and it doesn't seem to do any significant damage.

If you insist, you don't want to be shifting into a dead stop. If you forget about where you are, pulling the derailer hard against the limit screw can mess things up. Better then to block the higher gears with the limit screw, and the lower by the cable length. I.e. not use the mid range of the shifter, but the end.

You could very easily build a 5 or 6-speed setup using a standard freewheel. Chain for it will probably be sold as 8-speed chain. Doing it this way will reduce the wheel dish, and eliminate the need for a custom cassette.

What type of shifters do you use at the moment? Downtube shifters can still be obtained in 5/6-speed. If you're looking at using a 8/9/10-speed shifter and cassette with lots of spacers, it's more worthwhile to leave them in. People run 1x9 setups on mountain bikes without much of a problem.

High and low are only 15mm away from the centre. It'll be fine. You might get a little bit of extra chain wear on the edge gears, but since you were prepared to do without those gears, you won't be using them that often, will you?

Also, they'll be a bit less efficient than your middle gears, but that's still a lot more efficient than being in the wrong gear.

The Kyle/Berto bicycle drivetrain test found no efficiency losses due to cross chaining all the way across nine cogs when using modern chain.

I've seen rear derailleur only drivetrains from as far back as the early 1930s that had front chainguides. I have every reason to expect one to make your life happier and less stressful, too.

O_o

Sweet!

Thanks for all the replies everyone, much appreciated. Well then... it looks like either a 1x7, 1x8, or 1x9 is in the works. So, is it confirmed that a short cage rear der. will work with up to 9 rear cogs (Shimano 105 SS to be exact)? What type of front chain guides are out there? I could rig up a dummy front der. but if they make specific front chain guides that would be better. Thanks again!

Given that a short cage rear derailleur is good for say, 53/39 x 11-23, it should be good for a single ring and like 11-whatever fouls the upper jockey wheel.

Once again, don't worry about a chain guide until you go dropping the chain - how else would you know if it's unnecessary?

Go to a screw on freewheel hub, and you can buy 5 speed freewheels, still..

or you can get a duplex freewheel, 2 cogs, for single speed hubs.

Here's the freewheel pimp!

; )

Actually, a SS hub with a 3-speed freewheel would be cool. Might have to make your own, though.

I managed to find a 3-speed freewheel on ebay. Not sure whether it's meant for 3/32" or 1/8" chain though.

http://cgi.ebay.co.uk/Sprocket-Wheel...item43a6bd44ad

I have a 7 spd. no problem using the full range in the back with no chainguide.

When it comes to chain guides, I haven't been able to find any reliable way of knowing if they are needed or not. I've found a few bikes that throw chains to matter what, and a few that have never thrown a chain. High tension on the chain should help, but sometimes it isn't enough. Other times the chain just doesn't budge on the biggest hits.

I like taking some cheap chainrings, grinding off the teeth and using them as a guide.

You can also take a nice looking front derailer and just lock it in place with the limit screws.

Or you can buy one of the fancy Paul versions for about ten times the price.

The listing specifies 3mm tooth width, which would require 1/8" chain.

Thanks to everyone for the information. I read above that chain length is important when doing this. What would be a correct chain length for something like this (1x8). Perhaps pictures of the rear der. on the smallest cog and then on the biggest cog would help...

Chain length is a function of the chainring size(s), cog size(s), chainstay length, and derailleur capacity, so it is difficult to provide an answer via remote viewing. Just buy a long chain and trim it to fit properly.