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Two-up


Slowpup's picture

By Slowpup - Posted on 10 June 2014

The Ventandem in full fun mode.

4.5
hawkeye's picture

Smiling

Simon's picture

A mate of a mate scared himself massively on a home made one.

Two up means way more heat to dump for the brakes on a big fast track. Turned their brakes to vapour.

Slowpup's picture

Simon, even the Hope V4s with 8" rotors both ends arent up to the full duty of an overloaded tandem. http://nobmob.com/node/46967 John suggested twin front rotors. I've been trying to engineer a solution, but get stuck with the caliper mounts on the RH leg.

You'll notice in the photo that we aren't even carrying camelbaks. Just 3 bottles of water, a pump, trail tool and tube in an effort to keep the weight down. Total rig weight was somewhere north of 180 kg for this ride.

Andy Bloot's picture

Are you in a race
or you just keep the plate on to let everyone one know you're always on race pace Sticking out tongue
edit: Oh Convict 100
great photo

Rob's picture

You've seen this, right? It appears these guys overcome the mounting problem by using a motorbike fork?

http://www.bikerumor.com/2011/09/24/gatorbrake-e...

Although there are some in this thread that are certainly MTB:

http://www.bikeradar.com/forums/viewtopic.php?f=...

hawkeye's picture

... what pressure you ran in the fork and rear shock?

Slowpup's picture

The fork has a real spring in one leg. Made of actual metal. So I only ran 100 psi to tune the fork preload.

The poor old Fox CTD was pumped up fit to burst at about 300 psi. Smooth travel, reasonable damping, though we do need to increase rebound a few notches, and the platform performs as it says on the box.

Tyre pressures were more amazing. I usually run 2.4" RaRas at 19/21 psi tubeless on my singles. Ran an Ardent up front and a RaRa out the back, with tubes both ends at 40/42 psi. No pinches, no wallowing or rolling tyres. The tandem just rails turns IFF both Captain and stoker commit fully and lean with the bike. If the stoker gets cold feet it becomes understeer city and you wash the front away.

I hadn't seen the Gatorbrakes Rob. I really only have one option to fit brakes to the RH fork stanchion. Replace the fork leg, or end piece with a LH leg. Doing that means I'd lose the damper, negative pressure canister etc.

I could knock out a prototype dual disk hub in about half a day at work. We've already looked at the requirements to set up billet bike parts. Competing on cost is no hope though, so I'd only do it as a one off because what I want isn't available.

The alternative is to fit two brakes to the LH side of the wheel. Two calipers on one disk can't give the heat rejection required, but the calipers could cheaply be stagger mounted on a custom adapter. It would need two rotors and two calipers to be effective, or ...... I might just have had an idea worthy of investigation.....

At the end of the day though, the cheapest option is to take a break from the brakes every so often. Next cheapest is fitting a water cooler to the front brakes, and lastly get the stoker some kevlar undies, and force them to sit on the rear tyre when the brakes overheat.

Rob's picture

You could always get a rim hydro brake and run that too? Ugly-ass solution, but I'll bet it would work!

Running two rotors on the same side? Don't see how you could fit them both in, even if one was smaller than the other. Not unless you can find some ridiculously thin calipers.

I notice Hope make vented discs, thought about those? At first I thought they were simply describing the standard 'venting' holes all discs have, but then found this picture (there is no side shot on the Hope site):

Just don't look at the price... http://www.chainreactioncycles.com/au/en/hope-v2... Sad

BTW... don't forget to join this club - the things you stumble across doing random research Eye-winkhttp://app.strava.com/clubs/tandems

kitttheknightrider's picture

Rob posted earlier mentioned that gator brake already does a dual 6 bolt flange hub.

As for mounts, could you not fabricate a "sleeve" with post mount stubs that encompassed the whole of the lower section of the right side lower, kind of a beefed up, longer version of what the "DH Beast" has pictured in this thread http://singletrackworld.com/forum/topic/dual-dis...

You have the technology

hawkeye's picture

Another option - perhaps equally ugly from an engineering point of view, as it would require a modified, widened caliper - is to run two floating discs side by side with pads sandwiched in between. The dual rotor would dissipate the heat better but probably not as optimal for keeping heat out of the calipers as the Gatorbrake solution.

We used to do that with the nitro R/C cars when I raced them way back when. The "brake sandwich" ran "pad-disc-pad-pad-disc-pad", if that makes sense. It was the only way we could get the necessary braking power in the messy oily environment without burning out servos (which we didn't always succeed at).

If you can fabricate, it might be a cheaper solution?

Rob's picture

pad-disc-pad-pad-disc-pad? Likey! Smiling

Although, this would ideally be hydropot-pad-disc-pad-hydropot-pad-disc-pad-hydropot. Otherwise the discs would end up bending inward more and more as the inner pads wore out. I can't really see that being workable though Sad

Slowpup's picture

Would you lot be quiet please? Someone's working on an idea and is "hope"ful of being able to make a buck.

That ...disc-pad-pad-disc... bit has hair on it, and so does the other option with the middle cylinder. The secret lies in rotors that are lighter than water Eye-wink

hawkeye's picture

Flexing rotors is a non issue I reckon. Rotors flex in most mechanical calipers anyway, as the clamping force is driven from one side by a cam, and from memory the Hayes So1e hydros were driven from one side too. The outside (left) pad bends the rotor over to meet the inner pad before any braking force is applied.

So long as the rotor is all stainless there should be no fatigue cracking. Alternatively, you allow the rotors to float a little side to side, and learn to live with intermittent rotor rub noises.

Rob's picture
Slowpup's picture

Though on a fatty don't you only need stop pedalling to come to a halt?

It's a moot discussion from my perspective now as the tandem is available for other like minded souls to purchase.

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