Search found 727 matches

by NetworkMan
10 Apr 2022, 8:45pm
Forum: Bikes & Bits – Technical section
Topic: Beware! Shimano short cage RD has less capacity than claimed
Replies: 10
Views: 630

Re: Beware! Shimano short cage RD has less capacity than claimed

Yes I added two links after measuring big-big. It's a bit annoying because I thought I might swap the 28T sprocket for 26T or even 24T but that may not now be an option. Guess I may have to revert to the mountain bike RD. I don't usually bother too much about aesthetics but it did look neater with the shorter cage.

IIRC I looked at some other short cage RDs from other groupsets and they quoted less capacity so I suspect it's just a publication error.
by NetworkMan
10 Apr 2022, 7:14pm
Forum: Bikes & Bits – Technical section
Topic: Beware! Shimano short cage RD has less capacity than claimed
Replies: 10
Views: 630

Re: Beware! Shimano short cage RD has less capacity than claimed

Actually there has been much discuussion on line about the effect of max front difference on capacity. The general consensus was that it cannot make any difference on its own. The front difference is taken into account in the capacity calculation anyway. It is actually impossible for this RD to wrap 37T of chain; the cage is just too short. I suspect it is no coincidence that the 16T front difference is that of a road bike with a 50-34 compact double which probably has a wider range casette than my 12-27!

Anyone on here got any idea how the wrap capacity of an RD is affected by anything other that total (front plus rear) difference?
by NetworkMan
10 Apr 2022, 5:25pm
Forum: Bikes & Bits – Technical section
Topic: Beware! Shimano short cage RD has less capacity than claimed
Replies: 10
Views: 630

Beware! Shimano short cage RD has less capacity than claimed

My Spa Audax bike has a 9 speed 12-27 casette and a 48-38-28 chainset. I had been using an old Shimano LX mountain bike mech but the changes didn't seem as snappy as I'd like. I suspected that the slant angle of this RD is is intended for a wide range mountain bike casette, rather than a close ratio one like my 12-27. Could I use a road type RD I wondered?

The spec for the Shimano RD-3000-SS quotes a capacity of 37T:-
https://bike.shimano.com/en-EU/product/ ... 00-SS.html
...and I need only (48-28)+(27-12) = 35T so I bought one at a good price from Rose Bokes just before Brexit stopped such things.

After fitting it I was surprised to see that it is only just adequate for small-small and some investigation shows that the capacity is indeed less than claimed - more like 35T or even a bit less; the cage is just too short.

What's more I'm not sure that the slant angle is actually any less my old Deore LX!
by NetworkMan
10 Apr 2022, 4:53pm
Forum: Bikes & Bits – Technical section
Topic: Chain length - is my maths right?
Replies: 7
Views: 551

Re: Chain length - is my maths right?

As Slowster says there is a simple way and a hard way. The simple way assumes that the chain will wrap around half of the chainring and half of the sprocket but as the relative sizes become larger this assumption becomes less true. As long as you make sure that you can shift big-big wihout strain then the simple calculator should be good enough I would think.
by NetworkMan
2 Mar 2022, 4:22pm
Forum: Bikes & Bits – Technical section
Topic: Is it possible to swap cantilever brakes for v-brakes
Replies: 11
Views: 2572

Re: Is it possible to swap cantilever brakes for v-brakes

It might be an easy swap but if the bike is old the bosses may be too close together. My 1993 Dawes Horizon is one such. You can measure between the bosses and compare with a new bike which has v-brakes.
by NetworkMan
17 Feb 2022, 4:32pm
Forum: Bikes & Bits – Technical section
Topic: Balancing NiMH batteries
Replies: 48
Views: 2441

Re: Balancing NiMH batteries

Hello Sweep,

My Garmin Etrex has the two cells in series. This is almost always the case and if you look at the metal contacts you should be able to see that at one end there is a solid metal strip joining + on one cell to - on the other. This is always a sure sign of series connection.
Even if you start off with two cells nominally the same you are sure to find that eventually one develops lower capacity than the other. When this happens the voltage of the lower capacity one will drop far lower than the other as they discharge and the series sum of the two voltages will then be too low for the Etrex to carry on working. It's just an unfortunate fact of life. I just fit a pair and keep them together, accepting the fact that one will inevitably wind up with lower capacity than the other. When they get too old I just replace the pair. I use Lidl low leakage ones ones which are pretty inexpensive.

BTW in 60+ years messing with battery operated appliances I don't think I've ever encountered one with the cells in parallel.
by NetworkMan
23 Jan 2022, 11:26am
Forum: Bikes & Bits – Technical section
Topic: More Schwalbe Marathon Woes
Replies: 35
Views: 2878

Re: More Schwalbe Marathon Woes

simonhill wrote: 21 Jan 2022, 9:32am I reiterate my point.

It often seems that those who have failures have multiple failures. Whereas plenty have no failures.

Statistically this is rather odd.
Not so odd really. This is not a random sample of the population. Perehaps people with just one failure find that unremarkable and don't mention it. People with many failures are rightly annoyed and have commented here. People with no failures are so amazed by the horror stories that they feel motivated to comment. I myself had a Schwalbe One delivered with a sidewall fault but Bikes24 replaced it with little bother and I've not reported it on this thread until now. I also have Marathon Greenguard and have had no trouble with them.
by NetworkMan
14 Jan 2022, 2:51pm
Forum: Bikes & Bits – Technical section
Topic: Triple chainring spacing.
Replies: 21
Views: 1764

Re: Triple chainring spacing.

I've done this sort of thing twice myself and never had a problem.
In each case I went from 48/38/38 to 48/38/24 - both 7/8 speed.

I agree that 48/38 is the smallest you can go with a 130 mm BCD road chainset.

On my Spa Audax I'm about to go from 48/38/28 to 48/38/24 again, this time 9 speed. I wondered about 26T but it's just 7.7% lower - only about 1/2 a gear in my book whereas 28->24 is 17% lower and well worth having.

On another bike I went from (IIRC) 52/42/30 to 48/38/28 using the same FD after reading that it's a good idea to maintain the same spacing between the two largest rings though if you go from 12T spacing to 10T you will probably be OK and you can drop the FD a little.

If you are gong to lower the FD you need to be sure that the bottom of the cage will clear the chainstay. You can estimate this by allowing 2 mm per tooth, so if you go down 2 teeth you need 4 mm clearance etc.

You can generally use anything you like for the small chainring; chainging down you just knock the chain off and it lands on the small ring. Changing up you just press the chain against the middle ring. It's the change between the two big rings that's the tricky one.
There is a chance the chain could rub the bottom of the cage when on small front and small(ish) rear. You can check, again using the 2 mm rule.

Of course you need to be sure you have enough capacity in the RD or the chain may go slack in the smal/small(ish) gears. Of course that may not be a problem if you never use those gears anyway

Good luck!
by NetworkMan
3 Jan 2022, 11:27am
Forum: Bikes & Bits – Technical section
Topic: Wheels!
Replies: 6
Views: 743

Re: Wheels!

Any half-decent wheel will roll as well as any other, it's the tyres that make the difference.
How fast do you ride? You probably need to be going pretty to fast to notice any aero difference due to wheels.
Most aero effects come from the rider, their position and the clothes they wear.
by NetworkMan
3 Jan 2022, 11:20am
Forum: Bikes & Bits – Technical section
Topic: Derailleur idler gear assembly.
Replies: 8
Views: 540

Re: Derailleur idler gear assembly.

As above. On all the 1/2 dozen or so Shimano ones I've taken apart the upper pulley had a metal bush in the centre; the lower one doesn't. Are you sure the shoulder isn't just compacted grunge?!!
by NetworkMan
6 Dec 2021, 3:27pm
Forum: Bikes & Bits – Technical section
Topic: Dawes Galaxy refurbish - old Brifters - 105 FD
Replies: 27
Views: 1070

Re: Dawes Galaxy refurbish - old Brifters - 105 FD

Yes, looks like it - 105 should be. You now need to check that you have a road chainline. Do you have the number of the chainset (or was it upthread)? Does it look as if the curvature of the big rig matches that on the outer cage plate on the FD? What rings do you have? Are they (say) 48-38-28 like my Horizon had or larger like a road bike may well have had?
by NetworkMan
6 Dec 2021, 2:31pm
Forum: Bikes & Bits – Technical section
Topic: Dawes Galaxy refurbish - old Brifters - 105 FD
Replies: 27
Views: 1070

Re: Dawes Galaxy refurbish - old Brifters - 105 FD

Dawes Galaxys from the 1990s use a mountain bike FD, as does my Horizon, and a mountain bike chainset too. These FDs don't work with road brifters because they need more cable pull. They work fine with road downtube shifters which have no indexing. I don't know the vintage of your Galaxy though if it had a cup and cone BB it sounds older than my Horizon. You can reduce the length of the lever arm on some of these FDs by attaching the cable to the other side of the cable anchor bolt and thus get more travel though the downside is more resistance and more force on the brifter lever. Your FD may well be old - I have replacement rings, wheels, RD and brakes etc. on the Horizon but same chainset and FD.
by NetworkMan
20 Nov 2019, 5:58pm
Forum: Bikes & Bits – Technical section
Topic: A collation of dynamo/generator drag/efficiency data
Replies: 32
Views: 2147

Re: A collation of dynamo/generator drag/efficiency data

Brucey wrote:the standard StVZO test is to drive a purely resistive 12 ohm load. This means that if you see a test output (with a 12 ohm load) expressed in Volts, then the power (in Watts) is related simply by

Power x 2 = Voltage
cheers

Power = V*V/12 for a 12 ohm load

P = I * V
I = V / R
Therefore P = V squared / R

I remember when my father gave me my Miller dynamo set in about 1960 he bemoaned the fact that his 6 volt S A dynohub was only IIRC about 1.5 watts versus the 3 watt Miller.

He said that the prewar SA was 12 volts and of much higher power output. Does that make sense?
by NetworkMan
11 Nov 2019, 9:14pm
Forum: Does anyone know … ?
Topic: Trek Domane Al 3 vs Pinnacle Laterite 3 - which to buy tomorrow?
Replies: 7
Views: 869

Re: Trek Domane Al 3 vs Pinnacle Laterite 3 - which to buy tomorrow?

Are you sure the gears go low enough? Many people on here buy bikes with compact double 50/34 chainsets only to find the gears are too high for hills. This may be a significant issue if you have knee problems.
by NetworkMan
6 Nov 2019, 11:16am
Forum: Bikes & Bits – Technical section
Topic: The elasticity of mismatched Shimano drivetraims
Replies: 11
Views: 1055

Re: The elasticity of mismatched Shimano drivetraims

Sooooo,in a fit of 'nowt to do on a wet afternoon' I wondered if the MTB Acera 22/32/42 triple on the Vaya would work with the Ultegra mech and if the Deore MTB shifter could operate across the three rings.
You know what?
I works like a dream.
One snag though,that's if it is a snag,there's and 8mm gap between out ring and outer cage plate and I can't lower the mech down the seatube coz the rear of the cage will foul the chainstay.

I'd be inclined to retitle it as .... elasticity and unpredictability of .....
My guess would have been that with such a large gap between cage and big ring that there would also be a large gap between cage and middle ring. In turn that would mean trouble getting the chain to derail from the middle ring especially when shifting down under load with the rear already on the big sprocket. That's what you need when you run out of gears and the hill is getting steeper. I remember having a FD with the lower limit screw too far out and that shift failed. I stalled, couldn't get enough momentum to restart, and had to walk the rest of the way up the hill!