Transmission compatibility advice

[halhorner]

Hello, a request for some advice please....
On my bike I currently have a 10 speed Tiagra 4700 34/50 chainset, and a 10 speed 12-28t cassette. Front mech is Tiagra 10 speed, as are shifters. Rear mech is Shimano 105 10 speed.
I am considering swapping to a wider range rear cassette as I have started getting into longer audax events (up to 300km) and on several occaissions have wished I had a lower gear towards the end of the ride.
I think I could quite easily swap to another 10 speed cassette with a bigger ring (say 12-30t)... However I worry that the jumps between gears could feel a bit clunky if I did this.
Could a better solution be to go for an 11speed cassette (say 11-30 or 11-32) which would give smaller incrments? Would this work with my existing 10 speed chainset & shifters? I appreciate I'd need a new narrower 11 speed chain and probably longer cage rear mech, but I dont really have the budget available to upgrade the chainset or shifters (which rules out swapping to a triple).
Thanks in advance for any advice 

[Torslanda]

You would need  shifters as the Tiagra wouldn't shift across the whole cassette. There are only 9 shifts available.

You can go to a 34 cassette on 4700 on the short cage mech IIRC but yes, your gears would be wider spaced. Swings & roundabouts. Climbing gears or closer ratios. Unless you can find a 'junior' cassette (something like 15-34?), junior racers are limited to a 'low' top gear. No idea why, I don't race.

[halhorner]

Good shout on the 'junior' cassette - I see Miche do a shimano compatible 10 speed cassette in 13-30 for £30. Think they are designed for youths who don't have strong enough legs yet to turn a big gear in a race so should suit me fine! Cheers.

[Brucey]

but 30T is only 2T different from 28T.

You don't say that your high gears are not too high to be useful very often, but I'd wager that they are. Needless to say an 11s cassette won't work with 10s shifters; not enough clicks, amongst other things.

Might I suggest that you try a smaller chainset?  If you get (say) 28, 46T rings then you top gear is about 8% smaller but your bottom gear is about 20% smaller.

Spa sell a modified triple to be worked as a compact double, which is otherwise a rare thing. Ring sizes as suggested work OK  with this chainset I think.

cheers

[Karla]

You would need  shifters as the Tiagra wouldn't shift across the whole cassette. There are only 9 shifts available.

You can go to a 34 cassette on 4700 on the short cage mech IIRC but yes, your gears would be wider spaced. Swings & roundabouts. Climbing gears or closer ratios. Unless you can find a 'junior' cassette (something like 15-34?), junior racers are limited to a 'low' top gear. No idea why, I don't race.

It's supposedly to preserve their knees.

[quixoticgeek]

You would need  shifters as the Tiagra wouldn't shift across the whole cassette. There are only 9 shifts available.

You can go to a 34 cassette on 4700 on the short cage mech IIRC but yes, your gears would be wider spaced. Swings & roundabouts. Climbing gears or closer ratios. Unless you can find a 'junior' cassette (something like 15-34?), junior racers are limited to a 'low' top gear. No idea why, I don't race.

Based on the box for a 4700 mech I have next to me. Limit for short cage is 11-28. Limit for medium cage is 11-32 on a triple, and 11-34 on a dual chain ring.

I wish they did a 46/30 chainset in the tiagra range. a 50/11 is just bonkers huge for most people...

J

[yorkie]

You would need  shifters as the Tiagra wouldn't shift across the whole cassette. There are only 9 shifts available.

You can go to a 34 cassette on 4700 on the short cage mech IIRC but yes, your gears would be wider spaced. Swings & roundabouts. Climbing gears or closer ratios. Unless you can find a 'junior' cassette (something like 15-34?), junior racers are limited to a 'low' top gear. No idea why, I don't race.

It's supposedly to preserve their knees.

...and to ensure that they compete on a fair and equal standing. Plus it encourages them to learn to race using tactics rather than the biggest kid winning every week by mashing the biggest gear.

Sent from my Mobile Phone using Tapatalk

[Torslanda]

Oh, ok.

If they're all the same top gear then the strongest will still win in a sprint, surely? Rhetorical question BTW.

Thanks for the clarification about the mech, too. That will certainly save some embarrassment.

[sojournermike]

@hallhorner

As Brucey has said, 11 speed won't work as it has the wrong number of shifts and a different cable pull ratio.

In 10 speed I suspect that you'd get a 12-30 cassette to work readily enough (might need a longer chain), but it isn't much lower.

FWIW, I've grown to like the 12-30 on my 10 speed bike. The gaps are OK if you're not in a rush everywhere. 11-32 is a different kettle of fish...

4700 is a four arm chainset, so you will probably struggle to find a smaller ring without buying a new chainset and bottom bracket.

Following Brucey's logic, you could get a 46/30 chainset from Spa and bottom bracket and a 12-30 cassette (or just keep your 12-28 and see how it goes). Lower gears at 30:30 and the top gear of 46:30 will give you about 30mph at a cadence of 90ish. Probably fast enough?

This may be easier than the custom cassette route, but your call.

Mike

[halhorner]

Thanks everyone - good food for thought. Will report back on what I go with and how it rides.

[Brucey]

this compares 50,34 with 46,28 using the 12-28T cassette.

http://www.gear-calculator.com/?GR=DERS&KB=28,46&RZ=12,13,14,15,17,19,21,23,25,28&UF=2185&TF=90&SL=2.6&UN=MPH&GR2=DERS&KB2=34,50&RZ2=12,13,14,15,17,19,21,23,25,28&UF2=2185

you have lost the top gear but you still have a 105" gear (on 35mm tyres) and you have gained two lower ratios than before. In the upper midrange you have traded 74" and 84" gears for potentially more useful 72" and 80.5" gears.

cheers

[halhorner]

Thanks Brucey - useful app.
Is this the Spa chainset you mentioned: https://www.spacycles.co.uk/m2b0s109p2016/SPA-CYCLES-XD-2-Touring-Double-Chainset-with-custom-TA-chainrings

[Brucey]

this is the one I was thinking of, which accepts smaller inner chainrings

https://www.spacycles.co.uk/m2b0s109p3383/SPA-CYCLES-TD-2-Super-Compact-Chainset-with-Zicral-Rings

as I mentioned earlier it is really a modified triple. BTW 46,28T chainrings are possible but is not one of the standard combinations but 46,30T is.

cheers

[halhorner]

An update for anyone who may be interested...
Finally got round to doing this and went for Brucey's reccomendation of the Spa 'super compact' chainset 46-30t option.
So far I am really pleased with it, the chainset is really nice quality and the range It gives with my existing 12-28t cassette seems much more suitable for me. I used it properly for the first time on Saturday on a fairly undulating 200km audax and found I was able to find the 'right' gear much more often, and never once found myself wishing for a bigger gear at the top end.
Thanks Bruce for the excellent advice - at £80 for the chainset and BB I feel like I've got a lot of bang for my buck in terms of improved ride enjoyment!
Cheers!

[sojournermike]

Sounds like a good result!