3rd chainring

James_Russell

Hi guys,
I've just rebuilt my bike from scratch with lots of shiney new bits, I've just got a quick question to ask:
I replaced my second and third chainrings, but because I'd previoulsy upgraded them to 48-36-26 rather than 44-36-26, there was only one replacement chainring online so I ordered it. Its fitted now and working beautifully, but I notice it is machined rather than pressed aluminium. Does this mean its better for what I'm doing (road use and commuting) or worse than the old pressed item? I spend probably over 60% of the time on my bike on the third chainwheel as I'm a big lad and tend to fatigue less when I use more torque, less speed (hence the upgrade)
-James

Shadowduck

If it's machined the chances are it's better quality than a pressed item, more accurately made etc. I imagine it'll be stronger and harder wearing as a consequence but I doubt you'll notice any improvement in performance / shifting unless there was a problem with the old one (bent or worn out).

I could, of course, be wrong.

James_Russell

Yeah the old one was starting to get hooked, and this one feels better. It is noticably thicker than the old 48t chainring, and feels somehow more solid, although that could have something to do with the new BB too!
I think upgrading the gear ratios is probably my favourite mod on my bike, top speed from last summer was 44.9mph (wicked downhill) and I think it'll be even faster since the rebuild now it has lighter wheels which are nice and true, and I've got fitter. Final ratio in top gear is 1:4.4
Thanks for the reply shadowduck!
-James

gtr mart

Hi there

yes totally agree about the machined chain ring being better than the pressed one. The material properties of billet made stuff over pressed or cast items is better and parts more likely to be accurate.

really interested in the mods you have done. I have a specilized rockhopper disk which I normally ride off road. I am doing a charity cycle ride (140 miles) and have been doing some training rides. All generally road based.

I have made some changes to the bike, like slicks, to make it better on the road and am now looking at the possibility of changing the gears.

I couldnt find any rear cassettes that went lower than the 11 teeth my current 9th gear has and as I want to keep the bike suitable for off road riding have looked at changing the biggest chain ring on the front.

I have so far only been able to find a 48 tooth ring which is 'only' 4 teeth bigger than the standard 44 tooth one. How much differece is this going to make? Road chain rings have more than 56 teeth!

Cheers
Mart

James_Russell

Okay, I was rather hoping the machined one was better!
the external diameter of an MTB freehub won't allow for any fewer than eleven teeth unfortunately (ruling out a nice cheap gear mod!)
44t front and 11t rear means that for every revolution of the crankset you get four revolutions at the wheels. with 48t you'd get 4.4. I did all the maths at the time (I've lost all my scribbles) but by taking my top speed before the gear change, translating that into maximum crank rpm (about 120 I think), and then substituting that maximum rpm into my upgraded gears and figuring out how many wheel revoultions and therefore my mph. Off the top of my head, I think my THEORETICAL increase in top speed was 3.9mph, which turned out to be pretty accurate actually. Its only theoretical though as the higher the speed the higher air and surface resistance, so logic would dictate that the increase wouldn't be as much as that.
Your chainset is geared exactly how mine was before the mod, so all that waffle above is relevant.
The main difference is that you never trully max the top gear out unless your really going for it or the gradient is with you. This just felt better to me because I hated the feeling of terminal velocity on my bike, and I spent a lot of time on flat roads trying to pedal frantically to up my speed. I find my endurance is much better now, and both my mates (both fitter than me and both geared 44-11) noticed it too. I'm a heavy, powerful rider but I fatigue quickly when pedalling that fast. I find my bike much more stable at high speed and on the hole more enjoyable to ride.
It sounds like the nature of your riding is very simular to mine as well. Remember that a lot of road bikes (particularly those with 56t front sprockets) have more than eleven teeth at the back, typically 12 or 13. Some single gear racing bikes have higher gearing, but these are only ever any good on indoor tracks were there is no wind, gradients etc.
Remember that fitting a larger chainwheel will reduce the ground clearance from the chainwheel to the floor, so it might comprimise you off road slightly (but barely)
Finally, its not a cheap mod. I required a new BB, cranks and crankset to do it, but I was very lucky on it. I put the bike in for a service, and had an informal chat with the guy about fitting a larger chainwheel. I asked him to do the service and phone me to tell me how much the chainwheel upgrade would cost. I got a phone call about ten days later from the guy saying my bike was finished and it had cost £164 something. I told him I hadn't told him to do the work and I only wanted a quote, and as a result got free labour and 25% off the parts, so the upgrade ands the service came to under £120!
sorry for the essay, I hope some of it is useful.
-James

Shadowduck

gtr mart wrote:

Road chain rings have more than 56 teeth!

<nitpick>

A "standard" double road chainset is 39/53, while a compact is usually 34/50. You can get bigger of course, but they're not normal.

</nitpick>

James_Russell

wow, I didn't realise that. I suppose a lot of the 'gearing up' is done by the extra rolling circumference of bigger wheels.
-James

gtr mart

thats great info. good post.

I am riding on slicks which have reduced the OD of the rear wheel. This in itself has reduced the gearing as its now easier to turn once than it was with a mountain bike tyre on. similar to changing the final drive on a car I guess.

I was kind of hoping that I would be able to fit a replacement big chainring without changing cranks etc. I have LX kit at the mo and have seen a 48 ring deore replacement for c. £20

I have emailed chain reaction cycles about this and the benefit it could bring and will consequently check the bolt positions of the two. They are certainly both 4 hole and since they are both shimano and similar level (ie LX and deore) hopefully it will be ok.... (famous last words...)

re the size of road chain rings, it seemed that replacement chain rings available on chain reaction were mostly 56 teeth. I did see that there were some that were smaller though so can believe what your saying.

gtr mart

one other thing - I was riding next to a road bike and asked about the size of their wheels and they claimed they were only 26" like mine.

Will Snow

gtr mart wrote:

I am riding on slicks which have reduced the OD of the rear wheel. This in itself has reduced the gearing as its now easier to turn once than it was with a mountain bike tyre on. similar to changing the final drive on a car I guess.

are you sure it isnt the lower rolling resistance of the tyres that make the wheel easier to spin??? youve prob only lost half an inch of diameter, id say it was more likely you were feeling the benefits of slicks.

supersonic

There is less inertia with a smaller wheel, so it acclerates quicker - but at constant speed, assuming rolling resistances are the same, the energy required to keep at that speed is the same.

RE pressed chainrings - isn't this akin to forging? This strengthens the metal.

Shadowduck

gtr mart wrote:

one other thing - I was riding next to a road bike and asked about the size of their wheels and they claimed they were only 26" like mine.

Most road bikes have 700C wheels, but I think some tourers are built with 26" as it's easier to get spares in remote areas. There may also be others I don't know about!

supersonic wrote:

RE pressed chainrings - isn't this akin to forging? This strengthens the metal.

As I understand it, pressed parts are simply stamped from a sheet using a die - this results in a cheap but not particularly high quality part. Forging can also be done using a press, but is (in spirit at least) more akin to the way a traditional blacksmith would have formed metal with a hammer. A forge is one name for a blacksmith's workshop (also called a smithy), hence the name.

supersonic

26" wheels can be made a little more sturdy - thats why you never see 700c wheels on offroad tandems! Also see them on triathlon bikes, as allows a more aero position.

gtr mart

If the rings are stamped or pressed out then billet will be better. if they are genuinly forged then the forged parts would be stronger. Thinking about the profile of a chain ring, I think it does actually have bits that stick out. This suggests that the parts are actually forged.

I would presume a machined ring will be steel so it shouldnt matter too much as it will still be adequatly strong.

What's 700 in old money? 28"?

Will Snow

bout that yeh

Will Snow

wait no 29