Author Topic: 72 tooth chain ring anyone? (Read 9602 times)

tonycollinet · « **on:** 29 May, 2010, 03:45:45 pm »

Friend has a folder (dahon style, cant remember the make) with 18 inch wheels. He wanted a large 72 tooth chain ring to get the gearing up a bit.

Laser cut from 2mm stainless steel. He'll have to grind the tips of the teeth down a bit, but he also had a spider cut from the centre, so he can mount the ring in a drill, spin it and apply angle grinder.

25 quid for both bits - not bad, seeing as the going rate online for such beasts seems to be upwards of £150

delthebike · « **Reply #1 on:** 29 May, 2010, 03:50:09 pm »

Wow! What size are the middle and outer rings?

Rhys W · « **Reply #2 on:** 29 May, 2010, 07:50:44 pm »

20p piece for scale. Nice touch.

Zoidburg · « **Reply #3 on:** 29 May, 2010, 07:53:41 pm »

Single ring set up?

Leave the teeth unprofiled and just give them a light polish to loose the sharp edges.

Deep teeth on a single ring is a good thing.

The only reason the one on it was profiled was because they just use an off the shelf ring from an FSA double chainset.

tonycollinet · « **Reply #4 on:** 29 May, 2010, 10:35:27 pm »

Word is (from the owner) that the profiling helps the chain on when it is offline.

Zoidburg · « **Reply #5 on:** 29 May, 2010, 10:37:52 pm »

Too much and it helps the chain unship.

It needs a bit of de-horning but not profiling like a double or triple ring, we rode with unprofiled rings on derailuers for decades.

Cudzoziemiec · « **Reply #6 on:** 30 May, 2010, 07:14:18 am »

Now we need a challenge to see if anyone has, can find, or will have made, a larger one.

tonycollinet · « **Reply #7 on:** 30 May, 2010, 08:04:35 am »

Something like:

http://www.thehubsa.co.za/uploads2/20090522_084735_Large_Chainring.jpg

MSeries · « **Reply #8 on:** 30 May, 2010, 08:48:46 am »

is 2mm stainless thick/stiff enough ?

tonycollinet · « **Reply #9 on:** 30 May, 2010, 09:06:08 am »

Yes - tis stronger than a standard Alu ring.

rogerzilla · « **Reply #10 on:** 30 May, 2010, 08:11:39 pm »

It could be noisy if it's not chamfered. The Surly stainless rings don't have much of a shape and are vocal (and it's not a nice noise) even with a millimetre-perfect chainline.

Mr Larrington · « **Reply #11 on:** 01 June, 2010, 10:28:04 am »

IIRC this had a ring of the order of 140T.

drossall · « **Reply #12 on:** 01 June, 2010, 09:37:59 pm »

I recall a clubmate doing some roller riding years back, and going for a record. No air resistance, so potentially very high speeds - I think he was trying to reach 100mph or something stupid. TA had a ring of something like 100T that you could arrange to borrow. Nearly as big as the crank...

rogerzilla · « **Reply #13 on:** 01 June, 2010, 09:50:24 pm »

100T would have a radius of 202mm (to the point where the chain pins sit), so even bigger than a crank. At some point the ring touches the floor or the chainstay, then you need a double chain system.

drossall · « **Reply #14 on:** 01 June, 2010, 11:27:26 pm »

Wasn't 100T then. It was big though

I think TA did commercial rings up to about 60T (mostly used by time triallists on the 5-speed set-ups that were then standard for weight-saving reasons) so could have been anything significantly more than that. 80T?

clarion · « **Reply #15 on:** 02 June, 2010, 09:16:42 am »

What size rings did Dave LeGrys use?

LittleWheelsandBig · « **Reply #16 on:** 02 June, 2010, 10:35:20 am »

Quote from: drossall on 01 June, 2010, 09:37:59 pm

I recall a clubmate doing some roller riding years back, and going for a record. No air resistance, so potentially very high speeds - I think he was trying to reach 100mph or something stupid. TA had a ring of something like 100T that you could arrange to borrow. Nearly as big as the crank...

Usually you need a long BB axle to keep very big chainrings away from the chainstay. This usually isn't a problem up to about 70t or so, depending on chainstay dimensions.

bobb · « **Reply #17 on:** 02 June, 2010, 10:42:27 am »

Quote from: clarion on 02 June, 2010, 09:16:42 am

What size rings did Dave LeGrys use?

I think "Large"

Although he did "double gear" it.

He's a nutter. I had a snout with him after he smacked down on the rollers at Mildenhall last year

Rhys W · « **Reply #18 on:** 02 June, 2010, 10:52:17 am »

Quote from: rogerzilla on 01 June, 2010, 09:50:24 pm

100T would have a radius of 202mm (to the point where the chain pins sit), so even bigger than a crank. At some point the ring touches the floor or the chainstay, then you need a double chain system.

Google "Bruce Bursford" or "Jose Meiffret" to see what this looks like!

clarion · « **Reply #19 on:** 02 June, 2010, 10:53:10 am »

If Dave LeGrys had had tyres made out of more than elven wings, he might not have had that blowout...

Yeah, I know he double geared for the record attempt, but it was still a pretty mental chainring.

Sigurd Mudtracker · « **Reply #20 on:** 02 June, 2010, 08:17:07 pm »

I have a 62T ring on my Moulton (17" wheels) - would have gone for a bigger one but the braze-on for the front mech set a limit on how far I could go. I therefore feel humbled.

tonycollinet · « **Reply #21 on:** 11 June, 2010, 06:01:22 pm »

And here it is with a bike attached. Not far off as big as the rear wheel....

MattH · « **Reply #22 on:** 11 June, 2010, 06:21:44 pm »

Quote from: tonycollinet on 11 June, 2010, 06:01:22 pm

And here it is with a bike attached. Not far off as big as the rear wheel....

Reminds me of this

or, in (slightly) more sane form

(Bruce Bursford's bike, as on display at Brooklands - more info here).

Rhys W · « **Reply #23 on:** 11 June, 2010, 11:40:03 pm »

There's something very pleasing about such a short, tight length of chain. Totally the opposite of these saggy, crossed-over, join-three-chains-together recumbent monstrosities.

Author Topic: 72 tooth chain ring anyone? (Read 9602 times)

Zoidburg

Zoidburg

Sigurd Mudtracker