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Cannondale 'Fatty' fork failure

Stephen Carson2025-09-30 19:59:42

Hi everyone, 

I was changing my disc pads and rotor this evening and noticed a stress fracture to my Cannondale fatty fork. There appears to be a crack spreading bilaterally from the upper edge of the IS disc mount involving about 180 degrees of the tube. I'm visually impaired but fortunately this was quite evident to touch which is how I noticed it. The front brake had developed a screach and judder, I was going to change the pads and rotor but I am guessing this is  more likely the cause of the problem.

It's definitely terminal, I've included pictures and explanation mainly for people's interest. 

Basic question is - I want to replace the fork , but what with?

I can easily buy a replacement tandem fork from someone like JD, quite inexpensive but weighs two kilograms.  I would prefer something closer to the original. I could consider a Landescape fork - not too worried about the £500 if it is the right way to go, I'm just not really aware of other options in the UK. I would appreciate people's thoughts and advice. Thanks in advance, Steve

 
Stephen Carson2025-09-30 20:21:59
From the other side
Stuart Hunter2025-09-30 20:30:15

you need a fork built for a tandem and a tandem with a disk. So unfortunately, it will be heavy, stopping a Tandem with a disk Brake puts a lot of stress on the lower part of fork around the area you have the crack. 

 

Stephen Carson2025-09-30 20:53:38
Thanks Stuart, but what are my options, what else is it there?
Stephen Carson2025-09-30 21:17:47

Any thoughts on these? 

https://ebay.us/m/qhKHma

Stuart Hunter2025-09-30 21:54:56
Well, personally, I wouldn't trust them, have you talked to JD Tandems or Pete Bird? I had a cracked fork on my co motion, Pete Bird said he could replace them for I think £400, or you could have some made for you, ArgoS Cycles would probably do it. JD Tandems sold me a pair in the end, I didn't need disk forks though. if all else fails you could give up the disk and convert to v brake front forks. They'd be a bit lighter.
Stephen Gray2025-09-30 22:23:37

At least one tandem specialist refuses to fit disk brakes on the front of a tandem (Thorn).

The force generated by the weight of two people,"the bending moment" I believe it is called is considerable and will do exactly what you have seen to a fork that isn't sufficiently robust. Some may think there is no fork that isn't sufficiently robust (Thorn).Obviously JD Tandems fit disc brakes to their Orbits. i am told that they have never had a problem so far. When I asked specifically if the fork had been designed for a tandem with disk brakes I didn't get a convincing answer, so I decided to go with a rear disk brake and a V brake at the front initially. Would like to go to disk but waiting to see how reliable the forks are over the long term. 

Stephen Carson2025-10-01 06:34:01

Thorn must have changed their opinion

https://www.sjscycles.co.uk/thorn-tandem-replacement-forks/

Robert Lyon2025-10-01 09:48:30

it sounds like the landescape fork is the way you want to go. I'm not sure what its made off but for me personally i'd take the weight penalty and go with steel. But then i value the safety and durability over performance, at least it gave a warning it was going.

Out of interest how long/how many miles did you get out of the Cannondale fork. If you got the same fork and life expectancy out of it would you buy the same again?

Neil Plant2025-10-01 10:47:02

When we had a new tandem built about 4 years ago, we ordered a fork from Co-Motion (via The Tandem Shop) as we wanted something proven on tandems.  I recall it being around £500.

Neil.

Neil Plant2025-10-01 10:47:02

When we had a new tandem built about 4 years ago, we ordered a fork from Co-Motion (via The Tandem Shop) as we wanted something proven on tandems.  I recall it being around £500.

Neil.

Ruth Hargreaves2025-10-01 12:02:37

There seems to be some incorrect information on this thread regarding our disc brake forks, which are designed and manufactured for tandem use, and weigh 1.4kg, available in 2 different axle to crown lengths.

We have supplied them to at least 2 customers with Cannondale fatty forks that have cracked in the same place as above.

Regards Ruth

JD Tandems

 

Stephen Carson2025-10-01 20:01:43

My apologies Ruth, I was commenting on a fork I'd had the opportunity to weigh.

Robert - the Landescape fork is alloy, produced by Duratech. I like that it is a thru-axle design. Whether or not it would fit the Cannondale I'm not sure - I have a suspicion it may be a tapered steerer.

The Cannondale fork is from a 2010 made in USA model, very much unmarked frame and fork, second hand so I cannot be accurate on use history. I would likely buy the same fork again if available but I do note Ruth's comments.

Neil, anyone who mentioned Tandems by Design - thanks for the Co-Motion advice / advice to discuss requirements with Pete Bird - I will do. 

Carbon Fibre - interestingly Co-Motion offer a carbon fork on a tandem, I'm not saying this as fact BUT Co-Motion cite developing their carbon fork with a carbon specialist - from what I could find on the internet this seems to be Wound Up (please correct me if I am wrong).

Wound Up specifically state their Duo2 disk fork is Tandem specific (there must be some confidence in that this is specificity developed for tandems), quote from Wound Up website 'Amazingly light, yet plenty strong enough for the demands placed on it by two adult riders taking a steep downhill corner. Plenty strong for the torsional forces that it experiences when you brake sharply while it carries four hundred and fifty pounds. We know, because, in our testing, we make sure that it will handle way more than you’ll ever throw at it in its intended use'

Disk Brakes - we need and want disk brakes, we live and ride in the Pennines with most rides involving thousands of feet of climbing and descending in at times appalling weather conditions. Disks offer powerful, safe and predictable breaking.  Disks front and rear are widely specified by multiple respected tandem manufacturers. 

Lightness - I do value strength over weight so read light as 'lighter if possible'. Strong, light, cheap - choose only 2, I'd go with strong + 'lighter' (if reassured safe).

I'm not a materials or tandem expert, I am a life long cyclist with years of experience of riding and maintaining bikes who has developed a very keen interest in cycling and associated tech.  I've been riding tandem for several years, Tandems (and Zwift) have allowed me to continue my passion for riding bikes. 

I'm genuinely looking for knowledgeable advice and experience, all comments welcomed and appreciated - thanks