Changing the gearing on an Avanti Metro 8c
- Biffidus
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Changing the gearing on an Avanti Metro 8c
Postby Biffidus » Mon Sep 10, 2012 10:40 pm
By my reckoning I'd be looking for a 26T front sprocket. Any ideas on the best way to proceed? Has anyone tried something similar? Can I avoid replacing the cranks somehow?
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Re: Changing the gearing on an Avanti Metro 8c
Postby rkelsen » Mon Sep 10, 2012 11:13 pm
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Re: Changing the gearing on an Avanti Metro 8c
Postby Biffidus » Mon Sep 10, 2012 11:53 pm
I haven't taken it apart yet to see how it attaches.
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Re: Changing the gearing on an Avanti Metro 8c
Postby MattyK » Mon Sep 10, 2012 11:57 pm
You can get a 24 t sprocket in 1/8" width but that is less than a 1-gear downshift
Currently she has a 25" low gear. A 26T ring will give her 17" of satisfaction (and a 52" top gear)
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Re: Changing the gearing on an Avanti Metro 8c
Postby rkelsen » Tue Sep 11, 2012 9:52 am
I'd look for something second hand.
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Re: Changing the gearing on an Avanti Metro 8c
Postby rkelsen » Wed Sep 12, 2012 8:53 am
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Re: Changing the gearing on an Avanti Metro 8c
Postby MattyK » Wed Sep 12, 2012 10:58 am
The chainring looks like a stamped steel piece, it will be separate from the crank arms - possibly a 3 bolt pattern (looks like I can see one nut on the arm at about 11 o'clock). You will however probably have to remove the right crank to replace the ring, and you would probably need a custom replacement eg from Cycle Underground.
If you're going to custom fab (and you probably need to), you might also consider just custom fabricating a larger rear 3-spline sprocket instead. (Assuming there is clearance on the chainstay) 38/32 would get you the same gearing as a 26/22.
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Re: Changing the gearing on an Avanti Metro 8c
Postby find_bruce » Wed Sep 12, 2012 2:14 pm
Ok moving on to comments that may actually assist, biggest rear cog I have seen commonly available is 24 teeth - available for a 3/32 chain from sjscycles.
The IGH forum on MTBR has plenty of information from people who have run low ratios. The lowest I have seen is 29 x 26
It seems a 24 or 26 teeth sprocket may require you to bend the cassette joint to clear the sprocket. Haven't seen anyone going anywhere near as big as a 32 at the rear. Some rough calcs indicate a 32t sprocket will be something like 130 mm diameter
To avoid the expense of custom manufacturing, you may need to go both directions with a 24 t sprocket and 32 t crankset
Have you thought about coming from another direction to make hill climbing easier with an electric assist - may even work out cheaper as well as keeping the GLW happy
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Re: Changing the gearing on an Avanti Metro 8c
Postby MattyK » Wed Sep 12, 2012 3:31 pm
Basked on that MTBR link people clearly make custom sprockets.
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Re: Changing the gearing on an Avanti Metro 8c
Postby Biffidus » Sat Sep 15, 2012 12:08 am
No. There are good reasons why that's not an option but I'd rather not go into that here. We had an electric assist bike before this one but it was heavy and harder work than a decent IGH. A decent quality kit might be an option in future but I was hoping for a simple solution so she can cycle up the short hills near our house.find_bruce wrote:Have you considered advising the GLW to HTFU ?
I'm going to take the cranks off when I get time over the next few weekends and see how the front gear is attached. Hopefully it will be something I can then go hunting for replacement parts online.
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Re: Changing the gearing on an Avanti Metro 8c
Postby find_bruce » Sat Sep 15, 2012 8:23 am
While you are looking at the bike, have a good look at the rear sprocket- if you can get it to fit, a custom sprocket as suggested by Mattyk may be the simplest solution, although you may need to move the chain guard.
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Re: Changing the gearing on an Avanti Metro 8c
Postby rkelsen » Sat Sep 15, 2012 10:40 am
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Re: Changing the gearing on an Avanti Metro 8c
Postby Biffidus » Sat Sep 15, 2012 9:32 pm
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Re: Changing the gearing on an Avanti Metro 8c
Postby mitzikatzi » Sat Sep 15, 2012 10:01 pm
You can also do this with some older square taper shimano cranks.
that is a 28t chainring
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Re: Changing the gearing on an Avanti Metro 8c
Postby MattyK » Sun Sep 16, 2012 12:31 am
Far as I can tell - not likely. They seem to use different approaches to bottom brackets, rather than the 68mmx1.1375732238263" you probably have. They use cranks arms with a pin on the inner face that engages a single hole on the chainring, so you would have to swap BB, cranks and chainring.Biffidus wrote:How about BMX components? Are they compatible with other types of bikes?
Pretty sure you will be able to pull this off with just a custom chainring. Show us pics with the chainguard off.
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Re: Changing the gearing on an Avanti Metro 8c
Postby find_bruce » Tue Oct 09, 2012 1:30 pm
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Re: Changing the gearing on an Avanti Metro 8c
Postby MattyK » Sat Oct 13, 2012 10:24 pm
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Re: Changing the gearing on an Avanti Metro 8c
Postby Biffidus » Sun Oct 14, 2012 2:28 pm
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Re: Changing the gearing on an Avanti Metro 8c
Postby Comedian » Sun Oct 14, 2012 3:06 pm
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Re: Changing the gearing on an Avanti Metro 8c
Postby rkelsen » Sun Oct 14, 2012 5:25 pm
The chainring is pressed on. You can't buy replacement rings for this type of crank.
I still reckon that something like this is probably the cheapest way out:
http://www.ebay.com.au/itm/MOUNTAIN-BIK ... 1102391985
Just use the small ring.
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Re: Changing the gearing on an Avanti Metro 8c
Postby Biffidus » Sun Oct 14, 2012 11:56 pm
rkelson: The plastic bits seem to just rotate in place - I suppose they could be damaged. The bike shop suggested I might need to replace the cranks as well.
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Re: Changing the gearing on an Avanti Metro 8c
Postby Comedian » Mon Oct 15, 2012 7:37 am
Mate I take that on board. I know you mentioned you'd tried the electric thing ...Biffidus wrote:Comedian: Smaller tyres won't do much - I want to move it down by about 2-3 gears which is a significant change.
But our story is I bought my wife a lovely Cannondale Adventure with an IGH to ride to work on. She tried it a few times. But the hills... it was just too much with all her gear in it etc. I rode the thing and it took my commute from like 30-35 minutes on my hybrid to 45-50. So, I got her one of these and she hasn't missed a commute since. Her commute is about 35 which is fine and she doesn't even need a shower at the other end. With the geared motor hub she gets up the **really** steep hills that allows her to bypass the worst of the traffic out our way... another win.
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Re: Changing the gearing on an Avanti Metro 8c
Postby Biffidus » Sun Oct 28, 2012 1:14 pm
It appears to be a Prowheel brand chinese crank and the sprocket seems to be permanently attached.
Edit: the local bikeshops I tried were no good. Anyone know where I can get a square-taper crankset (preferably a double rather than a triple) that will take 64 or 74mm BCD chainrings? I'd rather not replace the bottom bracket.
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