Crank ring compatability?18-28-38 triple?

[Trikeyohreilly]

I am trying to build up a custom crankset but I've not got a proper understanding of the subject as I have only brought stock before.

I know it needs to be a five arm and have been advised by the maker of the 18 tooth chain ring that it needs to be 110/74 bolt circle. What I don't quite get is which of the three rings goes where. I'm trying to build it up to be 18 tooth lower ring a 28 tooth middle with a 38 or 40 tooth large ring.

Normally, do the middle and large ring bolt to the 110mm BCD or is it the middle ring (along with the small ring) on the 74mm BCD? If so does a 28 tooth 110mm BCD ring even exist?

Thank you. Ed

[beardy]

Middle and outer both go on the 110bcd boltholes.

To the best of my knowledge 34 teeth is the smallest that you can buy for 110bcd.

I dont think that you can get an 18 tooth on a 74bcd either. I thought 24 was the minimum there.

[Tigerbiten]

The smallest which is normal is 40-30-22t but thats on a 96/54 BCD 4 arm MTB spider.
It is possible to drop the inner to 20t, they are rare so it's a case of if you can find one.
After that your looking at something like a Mountain Tamer Triple adapter.

What type gear range are you after ??
22t/32t on a 700c wheel is around a18" gear or around 3.5 mph.
Much smaller and you start to have real difficulties balancing.

[Trikeyohreilly]

Thanks beardy. It's as I feared. I don't think my plan is coming off.

Hi Tigerbiten. It was for my trike with a proposed Mountain Tamer. Looks like 18-28-38 was only possible with the no longer avalible Quad. 18-34 is no good I don't think. I emailed Tom at MT but I'm not expecting good news.

Thanks Ed

[freeflow]

Middleburn do a 94/58 spider. The 58 bcd 22 tooth chainring looks like there is enough metal to get down to l8 tooth.

But why isn't a 40/30/20 chainset enough?

[freeflow]

Opps. Just checked online and what I remebered as 40/30/20 is actually 40/30/22.

Best I can see for a 58 bcd is 20 tooth TA chainring

http://www.spacycles.co.uk/products.php ... b0s113p906

[CJ]

What do you want the middle for? I'm very happy with 20,40 on a Middleburn Incy spider. With an 11-34 cassette there is enough overlap between the two gear ranges, plus the outer is small enough that the inner is needed only on steep hills, as to render a middle ring superfluous. And doubles shift more reliably - in this case by an SLX double mech designed for outer rings of approx 38.

There are no triple mechs however, designed for outer rings that small. This might or might not be a problem depending on whether this tricycle has something like a chainstay in a position to interfere with the tail end of whatever mech you try to shift this with.

[Trikeyohreilly]

CJ, I'm honoured. Thanks.

I had just been coming to a similar conclusion. I had been looking at a Schulmf BB drive but couldn't afford, then I realised that two chain wheels that far apart do a similar thing.

I was playing with SBs gear calculator and its not as bad as i had thought. 18-38 give me 9.3 to 59.2 gear inches. Not as low or as high as I had hoped for (as low as possible to around 69") but moving to 18-40 teeth would bring me closer and within the 22 tooth capacity of my front mech. 44 would be ideal.

The greater overlap would, I think make it easier to get used to than a mountain drive.

This topic started as "lowest possible gear in a trike" in the non standard hpvs section.

Thanks. Ed