billh92109

I have Shimano 105 grouping compact double with an 11-28 in the back. I would like to get a replacement for the big chainring to go from my 50 to perhaps something in the 60-70 tooth range. It looks like there *might* be some dura-ace rings up to 56T -

Is that as high as I can go?

Is this a machine shop project or is there a ring I can purchase from somewhere that I can just swap out with mine?

(btw - if it *is* a machine shop project then what metal to use? What alloy?)

(dont get into the why - ;p)

Thanks.

canopus 

I've never seen one and don't really want to. You would need to determine the amount of force on the ring because on a compact crank and the diameter you are talking about there would be a lot of flex in the ring and arms of that setup due to the small diameter of the chain ring bolts. Also if you were planing on using the front derailleur you would have to make a new custom one since a stock one would not handle that diameter and shift from small to large. Also that shift, if you could make, it certainly won't be quick.

So there is a reason people ask why. It is because, depending on the application, there might be a better solution to your problem than a 60t or 70t front chain ring that has a whole host of other problems that come along with it and that is usually why they are not made.

FBinNY 

Above 56t or 57t you're in the world of custom machined rings made one up for motor paced world speed record attempts.

I don't know if you're considering such an application, but if not consider that if you could turn a 53/11 combination at a cadence of 100rpm, that would have you moving along at a 38mph clip. Even at the low cadence of 50rpm it's still 19mph.

IMO you're thinking about gearing the wrong way. Bigger gearing doesn't mean more speed, because it requires greater torque to turn, and like a truck grinding up a hill in too high a gear you'll run out of torque and slow down rather than going faster.

Focus your effort on building your ability to maintain decent cadence against load, and you'll find you become faster using human type gear ratios.

Imagine yourself as a horse, what would rather be? A thoroughbred race horse, or the much stronger, more powerful, but far slower Clydesdale?

(oops, sorry I got into the why, feel free to disregard)

If you do wish to go forward as a machine shop project, expect to spend dough. You can use a 2000, or 6000 series aluminum both of which are commonly available in plate form. Also if going super large, you'll need to use a thicker blank, and leave some of the thickness out near the perimeter to improve rigidity as is done for track chainrings. Good luck.

prathmann

My Bike Friday came with Shimano 105 components and a 60 tooth large chainring. Originally it was combined with a 50 tooth small ring but I changed that over to a 42 tooth for wider range gearing. The front derailleur (unmodified 105) has worked fine with both sets of chainrings. Note that due to the smaller wheel size, the gearing is equivalent to having 44/31 teeth chainrings on a bike with 700c wheels. I'm not sure of the make of the large chainring, but would suggest checking with Green Gear (Bike Friday) to find out their source.

PS:
Found this source for 63, 73, and 80 teeth chainrings:
https://www.greenspeed.com.au/gsparts.html
[look under 'Brakes']

djb

I was on an organized 6 day tour the other week and a couple in their 50s had a pair of Bike Fridays, neat looking bikes. They told me that there are two wheel sizes and that they had a larger than normal size, so they had a spare tire or two with them. Seem nicely made. Had only seen them in photos before.

good idea for the chainring source.

fietsbob

Specialty shop in UK https://www.highpath.net/ make what you wish , in Ergal.
and there are big rings from TA, and Schlumpf , in France and Switzerland.

Plus, Herr Schlumpf's speed/High speed drive planetary overdrive cranks make the existing ring 1.6 or 2.5 X larger.

BCRider

Smaller wheeled speed recumbents are one area where large chainrings are used. They provide "normal" gear-inch combos in conjunction with the small wheels. That may be the "why" but he may not want to spill the beans.... That's also the "why" that the Bike Fridays use the bigger rings.

billh92109

Thanks - Quite likely I wont really be just 'swapping out' the ring anyway - more like building a whole bike around it ;p

DiabloScott

One more caveat - if you have a braze-on front derailleur mount on a standard bike you won't be able to raise it high enough for anything bigger than about 55t.

canopus 

Found it.

Just kidding....but it is interesting.

https://forums.roadbikereview.com/showthread.php?t=77348

or this

https://www.fleettrikes.com/tth8.htm

DannoXYZ 

Why such tall gearing? You certainly won't go faster.

It's all a matter of training and tuning your body to achieve maximum-power or maximum steady-state power (FTP). Even if you manage to generate a sustained 400-watt output for around 25-27mph, that power can only generated at a high RPM of around 90-100rpms at the crank. If you use higher gearing than that, you get less power and end up going slower.

HillRider

Yes, Bike Fridays do come with 60T large chainrings but they are mounted on standard road (130 mm bcd) cranks and the OP has a compact (110 mm bcd) so a change of cranks would also be needed.

Note to djb: Bike Fridays are available with two different "20" wheels" depending on the model. The smaller of the two is ISO 406 and it's the same size used on most children's and BMX bikes. The larger is ISO 451 and it's far more uncommon so the couple was carrying the spare tire since even most bike shops won't have them. 406's are available in any bike shop, Wal-Mart, etc.

Jeff Wills

As noted, recumbent suppliers often have large chainrings for small-wheel bikes and trikes. Hostel Shoppe is one supplier- they list 60-tooth rings in 110mm and 130mm bolt pattern:
https://hostelshoppe.com/cgi-bin/read...sory=990633343
https://hostelshoppe.com/cgi-bin/read...ory=1016049820
and larger rings (up to 73 teeth) from a variety of companies:
https://hostelshoppe.com/cgi-bin/read...ory=1155076891

Bikewer

As FBinNY says.... such large gears are normally the realm of motor-paced record attempts. Such machines are normally towed up to a sufficient starting speed as it's not possible for normal humans to start in a gear "development" which may be in the realm of hundreds of inches...

Very few elite cyclists can "spin" standard road 52 x 11 or 12 gearing even on a level road.

zzyzx_xyzzy

People in this thread are assuming a lot. Maybe the OP is just setting up a small wheeled bike.

AEO

If you go the machine shop route, then the material choice should be a 6000 or 7000 series aluminum alloy.
But if you don't care about the weight penalty, then you can easily go for some cro-moly or hi-ten steel material.

but a 60T with 20" wheels should give similar gearing range to a standard 53T on a 700c wheel.
Another thing to consider is the possibility of ground strike, if the chainring becomes very large.

djb

tks, I knew they mentioned the details but I forgot what they said, seeing your answer made me recall that they mentioned what you just said. I should have taken a photo, they had neat little high pressure looking tires. Never saw them on the road, would have been neat to ride along with them to see how they were while going along.

deep_sky

I suddenly got flashbacks of NEUROSPORT as soon as I read the OP....

prathmann

No, you'd need about a 72T ring to get the same gearing as a 53T on a 700c wheel. As mentioned above, the 60T ring I have on my Bike Friday (using the larger '20"' wheel) is similar to a 44T ring on my 700c bikes. You have to get up to much larger ring sizes before there's any danger of hitting the ground.

HillRider

My son-in-law has a Bike Friday with the ISO 451 wheels. There are a couple of makers that supply slick, high pressure tires in this size but they are a specialty item. My LBS does carry them but most don't.

I've ridden his bike a few times and it does take a few minutes to adapt to the different handling charactreristics of the small wheels but after a short time the bike feels quite natural.

Garthr

You gotta remember too, the larger the chainring, on the smaller of BCD ..... any imperfections in the spider will be even greater. If you have a small amount of lateral movement of your 50t ring, in a 60t the movement will be even greater. This is what made the TA Cyclotourist crank for instance, so unstable. Big , weak rings on a tiny BCD.

davidad

https://www.thethirdhand.com/index.cg...d=264055311835

JanMM

https://www.thethirdhand.com/index.cg...d=264055311835

I put one of these on my first recumbent, which had dual 20"/406 wheels. The stock ring was 63T.

LarDasse74

Please tell us the 'why.'

scandalej@gmail

I ride a Moulton Am-7 (converted to an AM-1 with fixed-gear) and it has 17" wheels. So with a home-made 72T chainring I have no trouble getting adequate gearing with 14 or 15 tooth rear cogs. The chainring is made by Doug Milliken, the local Moulton expert and with the straight chainline that a fixed gear setup gives me, there is no chainring flex and no problems. I commute to work on this bike and use an 88-inch gear.