Please educate a noob about chainrings and teeth

[Scott-S]

Hi folks I had a search and either got lost in tech talk or drowned in adverts
Basically the chain rings on my 91 Lava Dome are junk and need replaced.

The bike isn't catalogue correct so I'm not averse to spec changes, however I would if at all possible keep them silver as per original look.
I have been looking for silver Shimano chainrings 5 arm 110 bcd with 36 & 48 teeth as that is what was on the bike.
I haven't got the small 24 tooth ring off yet so I have no idea of the bcd on it yet.

There has been very little in the way of choice available although a couple were black.

It's not going to see a lot of action, some mild forest paths/trails canal paths etc
Ive seen a few in 34 44/46/50 teeth but I have no idea what difference it makes to the gearing and ride and I don't want to mess anything up.
Can I change the tooth count and if so by how much?

Would somebody mind breaking it down for me as if I eat crayons for entertainment please?

Many Thanks
Scott

 

[Woz]

The 5 arm 110 BCD did have it's origins in the ATB / MTB era. 26, 36, 46 +/- about 2 teeth about the norm.

With the advent of 8 speed and a smaller rear sprocket 11T, chain ring sizes decreased to a more typical 22, 32, 42 triple in a later 94 BCD.

110 BCD is still interesting, because it was dusted off in the road bike world called a Compact Double - this I think is actually what you have found; typically a 34 inner and 50 outer.

With the riding you are doing - you may be able to get away with a single 34 or 36 on the front that does not need any pins or ramps to help shifting? Just a suggestion as getting rings can be bothersome.

 

[minor_LEGEND]

Personally I would buy a decent used chainset (period correct) & either swap it in or pilfer the rings from it. Many here will attest to that being a more cost-effective route to replacement than purchasing brand new rings.

Replacing what is on your Lava Dome should not be at all difficult. I have just bought a used (good) pair of 36/46 Shimano rings from a 1992 chainset on ebay for £20 with the bolts included, lifted straight from a Deore LX crank set.

 

[bikeworkshop]

Stronglight and TA still offer 110mtb sized rings.
Ask in your independent LBS if you still have one. We keep a few in stock and order quite often.

 

[bold stelvis]

I saw your images and I think you might be being hasty regarding the rings
some of the teeth that look "missing" are in fact not - they are a deliberate design feature to aid shifting
eg middleburn rings have what looks like 2 missing teeth on 2 sides of the chainring even from new:



is your assessment based on it actually shifting poorly or dropping the chain or just from looking at what you're assuming are broken teeth when you cleaned it?

 

[Scott-S]

Thanks very much for your time and help folks, greatly appreciated

I saw your images and I think you might be being hasty regarding the rings
some of the teeth that look "missing" are in fact not - they are a deliberate design feature to aid shifting
eg middleburn rings have what looks like 2 missing teeth on 2 sides of the chainring even from new:

is your assessment based on it actually shifting poorly or dropping the chain or just from looking at what you're assuming are broken teeth when you cleaned it?

Thanks bold stelvis, admittedly it's from seeing what I assumed was broken teeth after cleaning and my own inexperience in knowing any better.
I'll get back out to the shed in a day or so and have a better look, I probably (definitely) jumped to conclusions as my heart dropped and I thought I was going to be out a lot more money before I could get riding it.

 

[bold stelvis]

some guidance on replacement chainrings:

there are generally 2 common types of vintage 5 arm MTB triple chainsets about:

110BCD (outer and middle) with a 74BCD on the granny
94BCD (outer and middle) with a 58BCD on the granny

the other common standard was the 4 arm 104BCD until shimano started to use different and incompatible asymmetric 4 arm setups on every single new groupset release

as pointed out above 110BCD is also shared with a standard "compact road double" and many places that sell new chainrings will assume that is what is they are for (and will have limited sizes available accordingly)

TA and stronglight generally have the widest range of decent replacement rings though TA especially are not cheap - SJScycles or Spa are probably the best places to purchase in terms of range

note the smallest middle ring available on 110BCD is 33T (more commonly 34T) and on 94 BCD around 29T
the 74 granny ring BCD limits you to around 24T wheres as the smaller 58BCD inner on the other standard you can get down to 20T

 

[bold stelvis]

in terms of gearing:

22/32/44, 24/34/46, 24/36/46 or all quite common MTB triple setups - if you have a 32 or 34 on the back 24 is fine for a granny - 28T max sprocket on the back and you maybe want a smaller granny

 

[JCS]

I would either get a used set of Shimano chainrings/chainset or another option is replace the middle ring with a strong light from spa cycles.
If you’re just using the bike for light riding you might not need the granny ring, or even the big ring. So you could leave them as is and just use the middle ring (depending on how worn they are - if they are very worn then they will wear out your new chain)

 

[bold stelvis]

BETD also sell new middleburn rings which are very nice as well - IF they have stock (spendy but about the same cost as TA stuff)

https://www.mountainbikecomponents.co.uk/product-category/chain-rings/?bike_type=mtb