Custom chainring is on-board…Tiso CR Series 51t

8 09 2010

Previously I wrote of some options to consider concerning the compact crankset I’m racing. Here’s the shortcut to that article: http://wp.me/pJ7ub-9Z. I recently acquired a “custom” chainring which has 51t on a 110mm bolt-center-diameter (BCD). Here, I comment on what I’ve found after riding with it on my Trek Madone 5.2. Most of the topics below deal with questions or concerns contained from the previous article above.

Picture of Tiso chainrings

The Front Derailleur

Capacity– The Shimano specifications state that the capacity of my FD-6600 derailleur is 15 teeth. In this case, a 51t chainring less a 34t chainring is 17. This would seem to present a problem but so far I’ve had no issues.

Outer-cage edge/curvature– Again, no problems here. The lower (forward) edge of the outer cage is about 1.3mm away from the top of the chainring teeth.

Adjustment– I raised the derailleur to clear the teeth with the above gap. The low and high limit screws were checked to allow the proper clearance from the closest chain link. The cage is generally parallel with the chainrings and specifically a bit “tail-out” to follow the chain angle when in the 51t/11t gear.

The Chainring

Fit & finish– The chainring mounting points were very tight when first positioned against the Ultegra spider. I almost thought it wasn’t going to fit. However, after I started to tighten the chainring bolts, the mounting points came together without any difficulty.

The chainring is painted black overall with what appears to be a silver-white powder-coat lettering application for the company logo. Very stylish IMO.

I expected a closer fit between the chain and the chainring, but maybe this is non-consequential at this point.

Shift points— There are six pins positioned in pairs around the chainring diameter.

Material– This chainring is completely CNC milled from 7075-T6 alloy stock. T6 temper has an ultimate tensile strength of 510 – 538 MPa and yield strength of at least 434-476 MPa. It has a failure elongation of 5-8%.

Gear inches– Largest 26.3 inches x 51/11= ~122, smallest 26.3 inches x 51/25 = ~54.

Component integration– I’m running an brand-new Ultegra 11t-25t cassette,  a brand-new Ultegra chain, Ultegra front and rear derailleurs, and Ultegra SL cranks.

Performance

Shifting–  The shifts are solid and quick. I’ve noticed no hesitation, chattering or delayed shifting. I have noticed an intermittent ringing harmonic sound when pedaling in various gear combinations. Also a “ching” sound when shifting into the big ring as the chain reaches its resting position. None of these are detrimental, but rather pleasing in nature.

Flex– I’ve noticed no flexing of the chainring when sprinting out-of-the-saddle or at any other time.

Wear– This is a brand-new chainring. I will have to delay discussion on this point until I’ve accrued sufficient mileage. (Let’s say 1300 to 1500 miles).

Opinion

Thus far I have a very positive regard for this chainring. It reduces my RPM in the higher gear combinations for the same power output, and allows “more” gears when pedaling in a pack, especially in downhill situations.

The recent club ride demonstrates this condition as when chasing-down a break or when the pace-line increases to higher speeds. I’m a sprinter so the lesser teeth (51t) as compared to a 52t or more allows me to reach my terminal speed quicker. (This remains to be further tested.)

I’ll report on the durability at a later time.

Picture of the test chainring--Tiso 51t 110BCD

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