Gear

Technical Q&A with Lennard Zinn – Grinding gears and a slight oversight

Avoiding the grindDear Lennard,I'm having a problem with my 13-39 X 53/39 Campy Chorus (2003) set-up.When it is on the 39 ring and in the 26 or 29 cog, the space between thecog and the upper roller/jockey of the derailleur is so close that thechain is rubbed/grinded in between. I have tried turning the screw on thederailleur cage but to no avail. It appears that the chain is too longeven if I followed the somewhat confusing instruction of the Campy manual.Can you please share any other tip to determine proper chain length? I'vesearched the VeloNews archives for your feature on this asI

By Lennard Zinn

Avoiding the grind
Dear Lennard,
I’m having a problem with my 13-39 X 53/39 Campy Chorus (2003) set-up.When it is on the 39 ring and in the 26 or 29 cog, the space between thecog and the upper roller/jockey of the derailleur is so close that thechain is rubbed/grinded in between. I have tried turning the screw on thederailleur cage but to no avail. It appears that the chain is too longeven if I followed the somewhat confusing instruction of the Campy manual.Can you please share any other tip to determine proper chain length? I’vesearched the VeloNews archives for your feature on this asI remember coming across the subject at one time but can’t find it. I e-mailedCampagnolo but they stuck to the reliability of their manual and advisedme to check if I used compatible parts. My derailleur has a medium cageand their manual says this is appropriate for the 13-29 cogset.
Ron

Dear Ron,
The best way I know for a road bike double is to put the chain on thelarge chainring and the smallest cog. The derailleur cage should be vertical.Then adjust the b-screw on the back of the derailleur hanger so that thejockey wheels track as close as possible to the cogs without pinching thechain between and making noise.
Lennard

Dear Lennard,
After you sent that response, I decided to approach my problem regardingchain length with a compromise. I took off a couple of links from my chain.This resulted in a set-up wherein it exceeds the 10-15 mm between the chainas it wrapped around the lower jockey wheel (as recommended in the Campyinstruction sheet) although the derailleur cage is not quite vertical whenthe chain is on the large chainring and the smallest cog. I then turnedthe b-screw counter-clockwise until it fell out, screwed it back in untilit bit in far enough so it won’t drop out.

It works great. Shifting is smooth and no grinding noise.

Thank you very much for the tip. At the very least, you pointed outhow short the chain can go.
Ron

DOH!
Dear Lennard,
I had some old wheels with Campy Record hubs and I wanted to cleanup the hubs and get rid of the old rims. I inadvertently removed the spokesfrom a rear wheel before I removed the freewheel (actually, about 6 – 8inches of cut-off spokes remain). Is there any way to remove the freewheelor is it too late? The freewheel is probably on pretty snug as these arefrom when I lived in California close to the beach.
Charles

Dear Charles,
You will have to build another rim onto that hub (just using the leftside should be enough) so that you can twist the hub hard enough to unscrewthe freewheel.
Lennard

How bad is that rack?
Dear Lennard,
The tech question on carbon forks compatibility with roof racks awhileback was very interesting. However none of the manufacturers addressedthe potential of vibration loosening of the glue caused byWind buffeting the bike while on the roof rackVibration transferred from car to bike via contact points i.e. fork dropouts.Have fork manufacturers done any vibration and or resonance testing of the forks under simulated conditions to establish if these phenomena haveany effect?
Tim

Response from True Temper:This is a good question. Fatigue failures occur very differentlythan high load failures and therefore must be tested appropriately. Infact most of our product testing addresses the fatigue failure mode becausethis is the loading that the products will encounter during many yearsof use. Wind buffeting, cornering and vibration loads (from racks as wellas riding your bike) are very small in comparison to the testing I wroteabout in the Nov.4th, 2003 tech Q&A and are covered by industry standard testingwritten by the International Organization for Standardization (ISO).

To put things in perspective, a 10 Kg (22 lb. mass) bicycle with a centerof gravity 380mm (15 inches) above the tray – wind load and cornering load:

Wind load- John Cobb has done wind tunnel testing on the effect of sidewinds on frames and wheels. According to his data, a 30mph cross wind willpush your bike with about 8 Kg (18 lb. force) using race wheels like theZipp 440. This force depends greatly on the type of bicycle. Aero wheelsand frames catch more air from the side than standard equipment. John measureda disc wheel at 16 Kg (36 lb. force) in this 30mph side wind. SO, on afork mount rack the race bike applies a 30 N*m moment at the fork mount.This is only 13 percent of the TUV load standard. (See Nov.4th, 2003 tech Q&A).

Cornering load – A 1G lateral acceleration (only top sports cars canachieve this) generates a 37 N*m moment at the fork mount. This is only16 percent of the TUV load standard. These calculations assume that a standardstrap mount is used on the rear wheel.

The fatigue test for forks is defined by ISO 4210:1996(E) section4.6.3:

A fully-reversed, dynamic force shall be applied in the plane ofthe wheel and perpendicular to the stem tube to a loading attachment andswivel on an axle located in the axle-slots of the blades. A force of+/-600N(135 lb. force) shall be applied for 50,000 test cycles. The maximum frequencyshall be 25Hz.

The ISO spec is used throughout the industry. At True Temper Sports,we test all Alpha Q products at a higher force and for more cycles. Ourminimum spec is 750N (170 lb. force) for 250,000 cycles for every modelof fork.

A much more severe in-house test that we have developed involves anincrementally increasing force starting at 800N (180 lb. force) and increasing200 N every 5000 cycles. In this more severe test, every fork will eventuallyfail when the loads get large enough. Our forks are designed to fail firstin the dense crown area, manifest by increased deflection (soft feel) andevident by cracks visible in the paint and outer layers of carbon fiber.A failed fork could be ridden home and replaced. It is not acceptable tofail in the blades or dropouts, as this could cause an accident. We callthis a catastrophic failure, and this is avoided by proper design. We usea special epoxy developed by 3M which is more ductile (less brittle) whichoptimizes performance when subject to a vibrating load. 3M tells us thatsome other USA bike component companies are now using this same product,but they won’t tell me which companies, which I respect.

The abuse of daily use, as well as transportation on roof racks is wellsimulated by industry standard testing defined by the ISO 4210:1996(E)Standard. Some manufacturers do additional testing beyond minimum requirements.Dropouts debonding should be covered under warranty
unless the fork has been used in a way not approved by the manufacturer,wrecked, etc.
Bert Hull
Program Manager, Bicycle Products
True Temper Sports Inc


Technical writer Lennard Zinn is a frame builder (www.zinncycles.com), a former U.S. national team rider and author of several books on bikes and bike maintenance including the pair of successful maintenance guides “ Zinn & the Art of Mountain Bike Maintenance” and “Zinn & the Art of Road Bike Maintenance.”Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn. Zinn’s column appears here each Tuesday.