Tandem Cycling - Stick a "fork" in it?

240990

Hi.

After reading threads regarding old tandem forks I grew concerned about the current setup on our '92 Ellison Aluminum Bike Co. Tandem. I rebuilt this baby last Spring and retained the Tange Switchblade fork with a 1-inch steerer. After visually inspecting the fork, I had it powder-coated and then had it installed by my LBS. I've had no problems to-date, but I'm feeling uneasy now thinking that a 20-year old fork, particularly a one-inch steerer, may be ready for retirement. So, I'm reaching out for some guidance - as I would feel far more comfortable installing a new fork. Apart from a Wound Up carbon, are there other more modestly priced options available in the one-inch, tandem-rated category?

Weight is not a huge factor. Do you have any recommendations?

Check the photos and measurements below.

Trail = 41mm / Wheel Flop = 10mm / Mechanical Trail = 39mm / Head Angle 75 degrees

Our weight is ~350# (captain + stoker). While the Switchblade is disc brake compatible, we run Shimano Deore LX cantilever brakes.

Thanks!

Just want to confirm that this is the fork you have:
http://equusbicycle.com/bike/tange/tangecat97/pdf/20tangecat1997.pdf

The failure point will be in the crown. You could have an x-ray done to look for cracks if you very worried.

If you choose to go with a replacement for, I recommend Cr-Mo such as this Surly: http://www.amazon.com/Surly-Cross-Fork-1-Black/dp/B001CK0C7S/ref=sr_1_6?s=cycling&ie=UTF8&qid=1331554756&sr=1-6

On a steel fork I would recommend Magnetic Particle Inspection to look for cracks. Look for Non Destructive Testing labs in the local phone book.

240990

Hi.

After reading threads regarding old tandem forks I grew concerned about the current setup on our '92 Ellison Aluminum Bike Co. Tandem. I rebuilt this baby last Spring and retained the Tange Switchblade fork with a 1-inch steerer. After visually inspecting the fork, I had it powder-coated and then had it installed by my LBS. I've had no problems to-date, but I'm feeling uneasy now thinking that a 20-year old fork, particularly a one-inch steerer, may be ready for retirement. So, I'm reaching out for some guidance - as I would feel far more comfortable installing a new fork. Apart from a Wound Up carbon, are there other more modestly priced options available in the one-inch, tandem-rated category?

Weight is not a huge factor. Do you have any recommendations?

Check the photos and measurements below.

Trail = 41mm / Wheel Flop = 10mm / Mechanical Trail = 39mm / Head Angle 75 degrees

Our weight is ~350# (captain + stoker). While the Switchblade is disc brake compatible, we run Shimano Deore LX cantilever brakes.

Thanks!

Wheel flop of 10 sounds nice.

It has been mentioned on this forum that Santana sells replacement 1" forks for its old tandems. You could give them a call and see if they could fix up something for you. I believe the rake on their forks is usually 55mm.

Wayne

Just a data point for consideration.

The steel brazed frame and fork on my fixed gear bike were manufactured in the 1960's.

When I bought the bike about 10 years ago, I had it refurbished by CycleArt. Their inspection readily noted expansion of the steerer tube caused by overzealous tightening of a quill stem, but no other issues.

They replaced the steerer tube, repainted the frame and fork and I continue to ride it to this day.

Magnetic particle examination of the steel components, as has been suggested by other posters, is a cheap and easy method for detection of cracks on the outer surfaces of the fork. To properly examine the fork, removal of the powdercoating would be necessary.

Magnetic particle inspection, properly done, will easily find surface cracks whether painted or not, subsurface concerns if they are able to induce a magnetic N/S pole setting.

A qualified NDI technician should be able to accomplish the inspection 100% via a "coil shot", meaning no physical contact with the machines coil, and no electrical current is passed through the part.

Ideally, they will use a wet fluorescent method as opposed to a dry powder method. The defects that can be found with mag particle when done properly is sometimes amazing at how much is seen and can show with repeatable results.

Not sure where you live, but you also consider aircraft engine overhaul shops, aircraft propeller shops, and as mentioned NDT specific shops. I would avoid a machine shop that uses a yoke and dry powder since the shape is not conducive to a good inspection.

PK

Magnetic particle inspection, properly done, will easily find surface cracks whether painted or not

Actually magnetic particle sensitivity is poor for non-conductive coatings over 0.003 inch thick.

Depending on the type of powdercoat, the OP's fork may or may not fall over that limit.

If you choose to go with a replacement fork, I recommend Cr-Mo such as this Surly: http://www.amazon.com/Surly-Cross-Fork-1-Black/dp/B001CK0C7S/ref=sr_1_6?s=cycling&ie=UTF8&qid=1331554756&sr=1-6

Unfortunately Surly does not rate the Surly Cross Check fork for tandem use. The only fork they rate for tandems is the Instigator (http://surlybikes.com/parts/instigator_fork/) which is 1 1/8".

Not many choices for those of us with 1" steer tubed tandems. You can keep riding the old one, you can buy the Santana replacement for $300, you can roll the dice with a non-tandem rated fork, or you can get a custom fork made for >$300.

trayraynor, if you like your current fork, and know the history of it, and the bike has had fairly moderate usage then it's probably pretty safe. On the other hand if the bike has been ridden hard, lots of miles, fast descents, rough roads, etc then older forks can fail. See the thread by uspspro (http://www.bikeforums.net/showthread.php/535601-Tandem-Fork?p=8812452) for an example of one such failure. My impression is that uspspro and stoker put a lot of good hard miles on that tandem before the failure.

Magnetic particle inspection will NOT work on the crown of this fork if it is the one in the link http://equusbicycle.com/bike/tange/t...ngecat1997.pdf (http://equusbicycle.com/bike/tange/tangecat97/pdf/20tangecat1997.pdf) of my post above - the crown is ALUMINUM - magnetic particle inspection does NOT work on aluminum.

Given you are a relatively light team - I stand be the Surly suggestion.

Well the aforementioned Wound-Up will make a fork with a steel or carbon steerer for you, but it isn't exactly cheap. You can get a custom fork made to your specs. I once talked to Waltworks about making me a custom fork (our tandem has a 1" steerer too). His custom forks are amazing, but he could obviously make a unicrown overbuilt fork if needed.

I would think any custom builder could make the fork. I'd focus on strength not weight, as peace of mind when descending is much more important than grams when it comes to 1" forks.

Just want to confirm that this is the fork you have:
http://equusbicycle.com/bike/tange/tangecat97/pdf/20tangecat1997.pdf

The failure point will be in the crown. You could have an x-ray done to look for cracks if you very worried.

If you choose to go with a replacement for, I recommend Cr-Mo such as this Surly: http://www.amazon.com/Surly-Cross-Fork-1-Black/dp/B001CK0C7S/ref=sr_1_6?s=cycling&ie=UTF8&qid=1331554756&sr=1-6

Hi nfmisso: Yes, the Tange Switchblade shown in the URL you provided is the fork I presently have, it has an aluminum crown.

Just want to confirm that this is the fork you have:
http://equusbicycle.com/bike/tange/tangecat97/pdf/20tangecat1997.pdf

The failure point will be in the crown. You could have an x-ray done to look for cracks if you very worried.

If you choose to go with a replacement for, I recommend Cr-Mo such as this Surly: http://www.amazon.com/Surly-Cross-Fork-1-Black/dp/B001CK0C7S/ref=sr_1_6?s=cycling&ie=UTF8&qid=1331554756&sr=1-6

Nigel, the Surly fork you recommend, do you know if it is tandem-rated?

Magnetic particle inspection will NOT work on the crown of this fork if it is the one in the link http://equusbicycle.com/bike/tange/t...ngecat1997.pdf (http://equusbicycle.com/bike/tange/tangecat97/pdf/20tangecat1997.pdf) of my post above - the crown is ALUMINUM - magnetic particle inspection does NOT work on aluminum.

I should have picked up on this, but forgot that "light alloy" is bike industry speak for aluminum.

The rest of us metallurgy types just ask "light alloy" WHAT, exactly?

Nigel, the Surly fork you recommend, do you know if it is tandem-rated?

Someone above mentioned that it is not tandem rated; but given your team's weight; I would not expect any issues.

We are a 500+ lbs team.

I overlooked the entire Switchblade description. Stupid me I have a friend that has one on his urban bike and know it is a multi piece fork.

My focus was primarily on the steer tube and the ability to inspect that by MT methods.

Even though powder coated, that fork should be able to be disassembled. Have the steer tube inspected and the left and right legs inspected where they clamp. Although the powder coat may exceed the .003" spec I would believe that a wet fluorescent inspection on a part with such a great L/D ratio would show indications.

The crown being aluminum, you wanted that inspected, eddy current testing would work for a major portion without removal of the powder coat.

PK

I overlooked the entire Switchblade description. Stupid me I have a friend that has one on his urban bike and know it is a multi piece fork.

My focus was primarily on the steer tube and the ability to inspect that by MT methods.

Even though powder coated, that fork should be able to be disassembled. Have the steer tube inspected and the left and right legs inspected where they clamp. Although the powder coat may exceed the .003" spec I would believe that a wet fluorescent inspection on a part with such a great L/D ratio would show indications.

The crown being aluminum, you wanted that inspected, eddy current testing would work for a major portion without removal of the powder coat.

PK

I contacted a local metallurgy testing service here in San Diego. For a cost of $90 they'll test the steer tube, crown and blades; they say the powder coating does not matter and that they can test w/o disturbing the finish. I'm wondering if I can have the unit tested w/o attempting to remove the blades from the crown?

And, there's the economics, do I spend $90 to test the existing 20-yr old fork, or, should spend ~$90 to get the Surly 1-inch fork suggested by nfmisso, which is not tandem rated? Any final suggestions?

I'm wondering if I can have the unit tested w/o attempting to remove the blades from the crown?

They wouldn't be able to detect a crack at the fork blade/crown interface if you don't disassemble it, as the mechanical interface will mask it.

Your call.

Magnetic particle inspection will NOT work on the crown of this fork if it is the one in the link http://equusbicycle.com/bike/tange/t...ngecat1997.pdf (http://equusbicycle.com/bike/tange/tangecat97/pdf/20tangecat1997.pdf) of my post above - the crown is ALUMINUM - magnetic particle inspection does NOT work on aluminum.

Given you are a relatively light team - I stand be the Surly suggestion.

Oops! I mistakenly looked at the wrong fork. Sorry for any confusion. Mag Particle is for steel and x-ray is for aluminum.

Since I live in Seattle my first call would be to R&E Cycles--home to Dennis Bushnell for a recommendation.