nondo

Hi there. I currently have a Decathlon's B'twin 7 (https://www.decathlon.co.uk/btwin-7-id_8076847.html). Chainrings are 48-38-28 and 7-speed cassette 14-28. I'm going to pull a heavily-fully-loaded BOB trailer for a couple of months, mostly on flat roads, but 20% in mountains.

I've been training but it turns out that pulling it on steep uphill with no sort of granny gear will not only force me to stop every 500m, but eventually injury me on the long run. So i'll consider changes, and as i'm totally newbie i'm asking for your help.

1 - Taking a look a Sheldon Browns gearing calculator, i could change the smaller chainring from 28 to 20. The lower gear would no longer be 28gi, to become 20gi... i think that would be enough for no-hurry-touring?!
Does it make sense? Would this be feasible? (I mean, compatibilities and other stuff i may be totally unaware)

2 - With the loaded bike i'll never use the higher gears. I know it would be wiser to upgrade the crankset, but wouldn't that be more expensive?

3 - Help me!


(Also, you're free to comment whether the bike is inappropriate for touring. It's just i'm on a budget and i'll rather spend it on the road, even if i go slower...).

Thanks in advance.

chasm54

You certainly want a low gear of no more than 20". My own gearing for touring goes down to 18", and while I very rarely need to go that low, it isn't unknown and I am not pulling a trailer. However, I'd question whether simply swapping out the 28 for a 20 is the way to go - the drop from the 38 to the 20 is colossal. Look at putting a bigger sprocket on the back.

Or, look at the bike. Any bike is appropriate for touring, as long as you are comfortable on it and can stay comfortable during long days in the saddle. BUt all that suspension is going to be very wasteful of energy, and really isn't any good to you if you are staying on roads or trails. It absorbs force that ought to be used in pushing you forward. I hear what you say about being on a budget, but a pre-owned touring bike might not be too expensive and if your tour is two months long, would be likely to make a massive contribution to your enjoyment.

fietsbob

min gear of a 74 bcd chainring is 24t, can't be smaller than the bolt circle
that attaches it.
your crank has to have a 56 or 58 bcd granny gear mount for a 20t

Sram makes a cassette with a 34t or a 36t biggest cog, for the rear..

nondo

Thank you for your replies.

chasm54: The suspensions would be no problem, since they can be "turned off". I enjoy the bike, have done small tours (no longer than three days) and i feel comfortable with it. Also, i'm not so committed so seriously to long daily distances.

Buying a new bike is completely outside my plans, unless i have to spend more than half of the value of this one replacing gearing system. And i live in Portugal, where touring is not common, and used touring bikes are not be easy to find.

Still, i have some doubts on what you wrote. From the gearing calculator i see there would be a gap somewhere, but i would rather have it there than in low gears eheh

My last question to you would be: how much would cost the cheapest option of replacing gear, in your opinion? (Considering i would be satisfied with 18'' as lowest...)

fietsbob: sorry but i couldn't understand your reply, what's "bcd"?

Bezalel

For a couple months tour, I'd suggest a rigid frame and fork. If you insist on using this bike, I'd suggest that you replace your crankset with a 22-32-44 chainring combination. Your current chainrings are likely to be riveted on so you may have to also replace the cranks.

BCD = Bolt Circle Diameter

Doug64

The bike will be OK, if you can figure out a way to come up with lower gears.

Suggestion: Think about a small chainring, if you have interchangeable rings, with 26 or 24 teeth. This will shift much better than trying to go to a 20 tooth low, which I don't think you can do anyway without changing cranksets. Most front derailleurs are at the edge of their range with a 12 tooth difference in ring size. Shifting up from a 20 to a 38 ring would probably not work.

Then change the rear cassette to a 14-34 which would also require a new rear derailleur. You might be able to do both things within 100 USD. This would give you low of 20.4 with a 26 and an 18.8 with the 24 tooth chainrings. From the information on the Decahtalon website it is not possible to tell what components the bike has or figure out options.

Portugal is a great place to cycle. We started a tour in Lisbon last summer and our route through Portugal took us through Evora, Beja, Serpa, and then into Spain. Good luck on you trip.

AngrySaki

I also think a new crankset is probably your best option.
I was able to get a 22-32-42 mountain bike crankset a couple of years ago for about $60USD that's held up fine (TruVativ Isoflow).

nondo

Thank you for your feedback. Forgive my newbiness, and here it goes again:

Doug: from what i see in the sheldon brown calculator, a cassette for 14-34 needs to be 9-speed, correct? Is it because i need more speeds that i need to buy also new derailleur?

AngrySaki: I visited a store today, and a brand new cheap shimano 22-32-44 was exactly what the dude proposed me (he said 30€). He said it should be enough, but i'm really carrying heavy load, tent, kitchen & food, and 22'' as lower might not be enough as chasm54 pointed.
Also, the guy said no ring could be changed alone: all the crankset needs to be replaced.

So, assuming that i would keep 7-speed in the back (mega-range freewheel 11-34), with a new 44-32-22 crank set i would have 18.1'' as granny and 25.7'' as a second gear and 26.4'' as the third. I know they're kind of spaced, but my point is to travel, even if i do it slowly (as i said, steep mountains are a fraction of the trip...) Does this sound stupid?

bicyclridr4life

My bike came with a 48/38/28 crank and 14/28 six speed freewheel. I pull a trailer everywhere I go. I changed the crank to a 46/36/22 and upgraded the freewheel to a 14/34 seven speed.

bicyclridr4life

No, it does not have to be a 9 speed. I just upgraded my bike to a seven speed SunRace 14/34 freewheel (was originally a 14/28 six speed)

Provided the crank rings are not welded together, or integral with the spider, you should be able to change them individually.

nondo

I suppose the crank rings are welded, because the dude said it wasn't possible to change only one ring, and i should buy another crankset. How could i confirm this by myself?

The rear deraileur is a Shimano Altus. How do i know if it is compatible with 14-34?

If it is possible to change only crankset + chain + 14/34 freewheel, i can get away with less than 100€, and i think it's worth it!

Doug64

This would work fine. the 44 tooth chainring /11 tooth rear cog will give you about 28mph at 90 RPM. The 22/34 low end will give you a pretty good granny gear.That is the same high end/ low end gear ratios I have on my touring bike.

pacificcyclist

My ex-RIP 26" touring bike was a full suspension bike made by BMC. There are a lot of people who tour with suspension bikes no problem either with BOB or with touring racks either locally or globally. I even toured with a lady who had a $50 Canadian Tire (Crappy Tire in Canada) full suspension from Vancouver to the Queen Charlotte Islands with the same gears -- lots of walking for her and lots of waiting for me but she made it!

Yes, there is no problem with your bike. But I would make some modifications.

To get lower gears, just replace the whole crankset with an Alivio 42-32-22 mountain gear as I think your front derailleur can be lowered enough to accommodate a smaller 42 ring. The Alivio crank is heavy, chain rings are welded but is tough. It's cheap as well -- I paid like $30 US for it last time. I think your stock crankset (Altus?)also have welded chain rings. With the rear, you can replace it with a Shimano CS738 HG-50 7 speed 13-34 cassette. 22/34 should give you low gears to climb steep steep hills. Again, it's $30 for this in the USA/Canada. You can get the Shimano Altus to work with a 34 at the back, but it may grind a bit the last time I modified one bike. Since you won't be using 34 all the time, this should last a good while before the tour ends. As with anything, you need a new chain.


Hope this helps.

Bezalel

https://techdocs.shimano.com/media/te...9830686243.pdf

skilsaw

I put a 10 sp 11-34 on the back and 48-36-26 on the front of my first bike.
Pull a Burley Nomad on road tours.

My other bike has regular 9 sp MTB gearing.
Ride it loaded with panniers in off-road tours.

At times, I wish I had the MTB gearing on the first bike.
I have to walk it up long hills of 13% plus.

Doug64

nondo,

After pulling 50 lbs of groceries in my trailer up a steep little hill today in a 26-34 (lowest gear on my cyclocross bike), I really want to reinforce the idea of getting lower gears on your touring bike

Northwestrider

Going with a 20t chain ring up front, I believe you'll find is very expensive. If you go with 22-32- 42 up front and a 36 cog in back on the cassette, I think you'll be fairly happy.

djb

I second the idea to put a mtn bike crankset on 42/32/22 or .44/32/22 and a rear cassette of at least 32 teeth. You should stay within your budget and the lower gearing really will make a difference for enjoying the trip and being easier on your knees.
Bon dia

indyfabz

By checking to see if there are bolts (usually hex bolts) that allow you to remove each chain ring from the crank.

djb

Remember though that an alvio mtnbike crankset at 30 euros, even if you can't change the rings, will.last year's and years and years. A single chainring can easily cost more. This crankset will be the most cost effective way for him to go.

nondo

So, following your advice, i'll opt for a new 42/32/22 crankset, opting for a rear cassette of 11-34 (since i have to buy a new one, i'll play it safe with a 17.5 granny) and a new chain.

My last doubt is whether or not my Altus derraileur is compatible or not with the new setup. The datasheet https://techdocs.shimano.com/media/te...9830686243.pdf mentions capacity of 43T (?), largest sprocket 34T (ok), smallest sprocket 11T (ok) but says it is supposed to be used on 8 sprockets! (But heck, if it works on my current 7 gear setup...!)

Thanks so much for your help.

pacificcyclist

Yes, the Altus is compatible the last one I installed but that was on a 8 speed system. DO NOT CROSS SHIFT from big chain ring to big cassette ring (43T/34T) which is what the warning on the upper front chain ring rear cassette sizes. But since you have a 42T front, it's ok for a short period of time. A word of advice. When you are climbing steep hills, REMEMBER to shift your front derailleur to the front granny chain ring BEFORE you shift to the biggest cog (cassette ring) at the back. That way, you won't put a lot of stress on the poor derailleur. Good luck on your tour!

Bezalel

Regarding changing your cassette, I think your bike uses a Freewheel and not a cassette. The way to check is by looking for a model number, if it starts with MF it's a freewheel if it starts with CS than it's a cassette.

Capacity is a simple concept. Any time you shift to a chainring or cog other than the largest ones, the derailleur cage needs to take up that much chain, so if you have a 22-44 crankset you need a capacity of 22 and for a 11-34 cassette you need a capacity of 23 which would require a total capacity of 45.

Derailleurs don't care how many speeds you have all indexing is done at the shifter, as long as the model number matches the datasheet you can ignore the speed spec and concentrate on the other specs.

djb

good explaining.

his link to his bike seems to indicate that it uses a "7 speed cassette", funny that it would use 7 and not 8 speed stuff as the bike cant be that old, but if thats what it is, then thats what it is....
Ive seen 7 speed cassettes on sale at a store here in Montreal at reasonable prices, so they are around.