Shilun

My frame won't allow the fitting of a FD, so I'm planning to install a double/triple and change by hand. Do I need to follow any of the usual advice about size differences between chainrings, or am I free to fit any combination that I like - for example 52/22 double or 52/30/22 triple? Also, since there is no FD shifting, is there any likelihood of the chain coming off a chainring while simply cycling along? Finally, are there any other issues which I need to be aware of? Thanks.

blamp28

Will one of these work?




https://www.bikemannetwork.com/biking/p/CC-XTEFD

roadfix

Just curious, why doesn't your frame allow fitting of a FD?

JanMM

good question

Barabaika

The seat tube can be very fat, have a strange shape, or made from plastic; or it's a double suspension bike.

BCRider

I'm curious as well. The only bikes I can think of that won't have a stub or seat tube for mounting the FD do are some of the super serious DH bikes that are intended for single rings up front.

But to answer your question..... Yes, you can shift by hand just fine. I would not do it on the fly through since you risk a rather messy accident. But for stopping and shifting it so you work with a range I don't see any issues. But I'd avoid any serious cross chaining if you do so other than in the middle ring.

Joshua A.C. New

A pleasant anecdote:

My friend Dan was, oh, 11 or so. Naturally, we rode BMX bikes a lot and coaster brakes were the order of the day. His chain popped off the outside and, being the person he was, didn't want to stop. So he reached back and put it back on the sprocket with his pinkie. That is, he put his pinky in between the chain and the sprocket. Because it was a coaster brake, he couldn't just pedal backward. He had to pedal his finger all the way through. It broke it pretty good. It looks pretty normal now, twenty years later.

Old School

I am not quite sure how you manually "shift" a double or triple with no FD. That conundrum aside, I assume that a manual shift would be accomplished at 0 mph and 0 rpm or you might risk serious hand injury...

aley

You don't need to follow the usual advice about size differences between chainrings, as long as your RD can take up the difference. You may have trouble finding a double crank that will fit extreme ratios of chainrings, though; for example, the 22 you mention would probably be on a 58mm or 64mm bcd, while the 52 would be 110mm (or 130, or 135); good luck finding those two bolt circles on a single crank, even a triple!

mtnbiker4791

Another option is look for a sram 3x7 or 3x8 hub. 3 speed internal that takes the place of the triple crank and gives you the 7 or 8 spd rear end. They work very well alittle heavier than a triple grank but would be more convinent and possibly safer.

I_bRAD

You take the chain in your hand, and move it to the desired ring!

52-22 won't be a problem as long as you get a long cage RD and the rear has less than a 15T range. You could probably stretch that to 17 in a pinch, but with 30T on the front you could definitely get away with a close range (like 11-21 or 12-23) on the back unless you live in some mountains.

due ruote 

Eeek! Hopefully most fixed gear and ss riders know about this danger as well. Seems as likely as not the digit would be removed rather unceremoniously.

Pista Largo

Recall the tour prologue a couple of years ago when David Millar threw his chain, costing him a stage win. (Well, it's just the prologue, but it's still a stage). The team mechanic had prepared his bike by removing the front derailleur and inner chain ring, ostensibly to save weight, and believing them to be superfluous in the short flat TT.

I do not know, but have always suspected that Millar's remaining chaining was of the standard ramped-and-pinned variety that is cleverly designed to easily derail the chan, and that this contributed to his untimely mishap.

I think you would be well advised, to use old style, unadorned, no tricks chainrings.

blamp28

E Type Derailleurs like I posted above are for just this type of application.

roadfix

I'm still waiting to hear from the OP.

Shilun

Sorry for the delay in getting back to you. Anyway, here are the answers to some of your queries:

1] The bike in question is a 20-inch folder (Giant Halfway) with a chunky frame and no discernible tube around which to fit a FD.

2] I don't think the E-type derailleur stretches to a 50 or 52 tooth chainring. I believe 46 is the limit, although someone may correct me on that.

3] I plan to switch chainrings at 0mph!! I'm not brave enough to try anything else. However, I do seem to remember reading about a guy who rigged up an extended tent-peg contraption to reach down and make the change on the move. Anyone else read that?

4] Good point about the ramped chainrings. That's really my main concern - whether or not the chain will suddenly jump off, for example when under pressure on a steep hill.

Please keep the comments coming - they're all helpful.

Barabaika

The best variant is to use a Sturmey Archer internal hub. It works well for folders.
https://www.sturmey-archer.com/
https://sheldonbrown.com/org/raleigh-twenty/index.html

TireLever-07

The old Simplex & Huret FD's had a long toggle switch sorta thing.The, "Suicide Shifter". Not long enough by modern bike standards.Back when the front chainrings were closer in size to each other.I'd too vote for an internal hub.Those Nexus Dahon's(7 Speed) are like $400,the single speed is around $200.

BCRider

It should only be a problem if you're cross chained enough that the pins or ramps can touch the side plates. This can also occur if things are close from the pedalling related flex. I'm sure we've all had FD's set up that don't rub except when pushing hard where the frame and pedal setup flexes that little bit extra.

orange leader

I'm unsure if you're looking for more range or just higher range, but if the latter, then it seems it would be cleaner to just replace the cassette, with one with smaller cogs, or just replace the chainring with a larger one.

I looked up the specs online, and it comes with a 13-28 tooth cassette and a 48 tooth chainring. and those are fairly small wheels, so you're geared low (at least by my standards as i'm a masher). Your highest gear is only a 3.69 ratio, which is only slightly higher than on my fixie commuter (with 700C wheels), which I rarely spin out on. With your small 20" wheels, i'd guess you do, and often. I have only found one hill which I could not climb on my fixie, due to my ratio being too high, and if I'd started it with any momentum, i'd probably have been able to manage it.

My point is, try just the larger ring, and/or smaller cogs, and you won't be spinning out.

Shilun

Ideally, I would like a range in gear inches of about 95 down to 23. With an 11-34 on the back, I still can't quite make it. A 40-tooth chainwheel would give me down to about 24 at the low end, but the high end would be in the 70s - doable, but not ideal. Even the Capreo setup, with its 9-tooth small cog, won't help. I think, all in all, the hand shift is the only solution.