How hard (moreso costly) is it to put a modern drivetrain on a vintage mtb?

[retrobiker273891]

I am interested in going this route as I want a specialized hill climbing bike with no suspension with a super low gearing.

Newer bikes which are called 'gravel bikes' fit my purposes down to a t apart from the £1.5k and up price tag, generally. I suppose as they are still somewhat niche so no economy of scale.

Conversely modern mountain bikes with low gearing setups, in my pricerange (£3-500) have budget sub-par suspension forks. Besides, no suspension is purported to be much more efficient for hill climbing.

I thus got the idea to get an oldschool rigid mtb for the frame and then put a modern drivetrain on it which would have far lower gearing than the older classics.

Will this be a terrible problem in terms of compatibility?

I have had mixed messages. A lot of outright naysayers saying it is a fools errand and I should just buy a new bike as doing up an old one would cost more than buying a new bike.

There have been the odd responses indicating that it shouldn't be a problem so long as the old frame has 135mm dropouts, same as today's mtbs, which most after 1990 do from what I have been told, is that right? Also the crankset should have the same spacing on old bikes as new correct? 69mm is it?

I would be looking to pay around £400 total upper limit. If I was nearing the objective and invested I would not mind going over that but that is my soft limit.

From what I am gathering from this forum I could get a serviceable functioning vintage for around £200 then factor another £200 for a modern drivetrain.

I looked it up (have done a lot of learning in the past couple of weeks as had no real interest in biking and parts since the 90s) and it seems I could buy a crankset with 22 teeth front for £54 (https://www.sjscycles.co.uk/chainsets/sunrace-triple-chainset-with-detachable-rings-423222t-170mm/). That should give pretty low gearing regardless of the rear freewheel/cassette, and/or I could up the back, if a 7 speed, to 34t or 32 depending on if the wheel was freewheel or freehub.

I have also seen a few older bike cranksets go as low as 24t inner chainring so getting a base bike with that could save a big chunk.

I was thinking that would probably be the cheaper route compared to getting the popular 1x drivetrains available now. Although there is a cheapish option of big dinnerplate 1x for £150 (https://www.mbr.co.uk/reviews/groupset/microshift-advent-x). I do think it would be super cool to have a contemporary drivetrain but might be less compatible. Would depend on whether the old bike came with free hub already or not as I am guessing a new wheel with modern hub would take a big hit to the kitty.

I read some old ones have hubs anyway (is that right?), which would be compatible with newer cassettes, and even though 7 speed you can just remove the smallest cog (which is inconsequential to me since I am making for going up hills and just cruize down or on flats anyway) since the spacing and format is just the same bar the one cog.

So does this sound a reasonable goal given the budget? It seems that option 1 might be cheaper if I didn't have to change whole back wheel/freewheel to cassette and getting the majority of the lower gearing from the smaller front crank. I am thinking maybe 1 first and have the option for 2 down the road.

Another disparagement has been that if I buy a retrobike I will end up finding everything is ceased up and the parts extremely hard to replace and cost hundreds to find appropriate parts for it and that retrobikes are useless for riding, only good for looking at. From looking at the vibrancy of the market on this forum this sounds, in large part, nonesense. Is that right?

To be clear, I don't want it just as a project to look at, I will want to ride it as my main steed, so the possibility to replace parts if they wear out will be salient.

Any other considerations?

 

[bikeworkshop]

You can't take a cog off 8 cassette to make it 7 - the spacing between sprockets is different - so you're restricted to a 7 speed cassette if you're using a 7 fhb and shifter.

You'd be better off using square taper mid 90s triple, 22,32,44 if you're on 7.

Modern 1x mtb kit with low gear is possible but you'd need to spend way more than £200 for it not to be either low quality or a bodge. There are quite a few design changes that need to be considered, it doesn't mix well with 3x7 period parts.

 

[retrobiker273891]

You can't take a cog off 8 cassette to make it 7 - the spacing between sprockets is different - so you're restricted to a 7 speed cassette if you're using a 7 fhb and shifter.

You'd be better off using square taper mid 90s triple, 22,32,44 if you're on 7.

Modern 1x mtb kit with low gear is possible but you'd need to spend way more than £200 for it not to be either low quality or a bodge. There are quite a few design changes that need to be considered, it doesn't mix well with 3x7 period parts.

That is not the common knowledge on the subject of cassettes:

https://www.mtbr.com/threads/8-speed-cassette-on-a-7-speed-hub.738283/
So are 22t old school cranksets available? The lowest I have seen is 24 so far.

All old tech and 22t and max old freewheel/cassette would probably be the path of least resistance yes? Say 22 (inner chainring)/34 (max size freewheel) x26 to give 16.8 gear inch low gear would rival most modern 1x drivetrains.

 

[Guinessisgoodforyou]

The spacing is wrong. Internet says doable, in practice, crap gear change.

 

[retrobiker273891]

See this from other cycle

The spacing is wrong. Internet says doable, in practice, crap gear change.

See this from other forum from a long time poster:

that is a cassette hub. Cassette hubs are an old idea, but as we know them today were made by shimano, starting in the 1970s, and became popular in the 1980s. A 7s cassette is a fairly rare bird these days, but the good news is that you probably don't need to buy one.

There are two main options here
1) retain 7s shifting
2) fit something more modern.

You can make up any 7s cassette you like, using cogs from any cassette you like, provided you do two things. First, be sure to respect the capacity limits of the RD (although these limits can sometimes be altered eg. using a hanger extender). Second, ensure that the pitch in the installed cassette is exactly 5.0mm, if necessary adding ~0.1mm shims. which can be cut from a coke/beer can.

A 7s freehub body will accept a variety of n-1 cassettes, for example 8/9, 9/10, or 10/11, but you will also need a new RD + shifter + chain in many cases. The usual way of doing a n-1 cassette is to remove the smallest cog, which may require a different lockring (although I have used a spacer made from old spoke here).

Anyway, the other question is, what is the smallest chainring on oldschool cranksets? Do they indeed have 22t as smallest or is 24 the lowest they go?

 

[Imlach]

I've done it but the low end shifts suffers in particular. With 8 speed shifters it works fine. Answer to all your woes is friction

 

[Guinessisgoodforyou]

See this from other cycle

See this from other forum from a long time poster:



Anyway, the other question is, what is the smallest chainring on oldschool cranksets? Do they indeed have 22t as smallest or is 24 the lowest they go?

Exactly what I said the spacing is wrong. He has changed/altered spacers. Have a great day.

 

[retrobiker273891]

I've done it but the low end shifts suffers in particular. With 8 speed shifters it works fine. Answer to all your woes is friction

What is the smallest tooth crank from older bikes? If I can get down to 22t the issue can be avoided altogether by just getting max compatible freewheel on the back, which is 34 from what I saw, and just getting a tiny front chainring.

 

[Imlach]

The stronglight kitted to my Spesh was 42/32/22. Plenty of those around for cheaps. Can always just replace the granny with a smaller.

 

[retrobiker273891]

The stronglight kitted to my Spesh was 42/32/22. Plenty of those around for cheaps. Can always just replace the granny with a smaller.

Well the thing with replacing, from what I read is compatibility issues as bcd mm are all different and for the tiny 22/20t ones they ask for 64bcd which seems like only few cranksets do.