Dual disc hub – anything like this around?
I am looking at running a dual disc set up on the front wheel for a project with some custom forks to match.
I am having issues finding a hub that has two for the front wheel, the closest I have come is finding a disc/fixed rear hub and then a disc adaptor for the fixed side, a fixed/fixed track hub and use two adaptors OR a disc front hub and use an “over the top” disc adaptor that uses the spokes to maintain lateral tension (it fits over the top of your flange and acts as a new flange).
Any ideas where I could find a dual disc hub? standards are not a huge issue but =>100mm would be beneficial, would be fitting around a set of custom dual crown (the crowns from a set of 888’s) rigids. A larger axle would be a bonus but by no means essential.Posted 4 years agorOcKeTdOgSubscriber
There was a guy in Cheltenham making them back at the turn of the century, can’t remember his namePosted 4 years ago
Yeah, someone in the 90s did them – was it middleburn?
Your fixed hub idea is probably the closest to being practical.
Though unlikely as I suspect it will be, it could be worth a word with Hope – they manufacture in house and setting up the CAD for this wouldn’t be a big job (assuming that they have some CNC set aside for test pieces rather than all being tied up for production) and they might be willing to help on a project of interest (particularly if it was academic in some way).
So out of interest, why the need for double disk?Posted 4 years ago
CA – I see it has been done, hence the interest
Stoner – Not a bad idea actually.. I like it.
Clubber – I doubt hope would be up for it but once I’ve done some cad there cant be any harm in asking I suppose. The project will involve a pair of 36″ wheels each weighing in at around 5kg each, I would quite like to stop at some point so dual 180’s on the front (with bb7’s) and a 180 on the rear (4pot zee) should give me ample stopping power, someone has done custom dual disc with 210 rotors either side and nearly snapped their stem by grabbing too much brake so 180 would be ample.Posted 4 years ago
Do you *really* need double disc for that? People manage ok on 160s with 26″ so assuming that the nominal wheel size is approximately right, 36/26 x 160mm = 220mm. You can certainly get 220mm discs.
The 5lb wheels aren’t much of an issue really given that’s a small weight compared to most riders and the bigger wheels obviously turn slower than smaller ones.
EDIT – just noticed it’s 5kg – I’m still not convinced you really need double discs or at least not considering the associated hassle.Posted 4 years ago
clubber – based on what ive read its either double disc, 4 pot w/ 210 rotor or 2 pot with custom rotor and mount. Considering the tyres weight 1.6kg, the rims weight 1.1kg and thats the rotating mass, its a lot to try to stop with one rotor, I would definately risk overheating riding downhill, even rotor warping at that kind of temp.Posted 4 years ago
I don’t agree. How much do you weigh? Very heavy riders cope with reasonable sized discs unless they’re riding the Alps (and brake dragging 🙂 ) and the wheel weight isn’t that big an issue – as I said, it’s rotating weight but it will rotate slower to the same degree as the size increase.
Anyone know the weight of a set of DH wheels and tyres?Posted 4 years ago
But the wheel weight will matter, especially that far from the hub, I could get the same force at the tyre with a 220 rotor but that wouldn’t slow me down as quickly because my wheels and bike (~20kg estimate) are that much heavier, at the same speed as a 26″ I would have more energy to get rid of so I would brake significantly slower for the same tyre force. Even though it will have a lower rotating speed if its a pig to get up to speed it will be a pig to slow.
I weight 85kg on a good day.
TL – Ill give them a look, might be worth it, if not Ill just have to make my own.
Jamie – absolutely, but this will take actual designing and not geometry robbing like my current 29er project.Posted 4 years ago
Just FYI, rotating mass effectively doubles the weight from a linear momentum point of view (assuming the mass is all at right at the outside of the tyre, of course in reality, it’s less as the rim, etc are a bit closer in).
So, your 10kg 36″ wheels compared to say 4kg 26″ wheels are only making 12kg difference as far as the discs are concerned (for heat management purposes, the larger rotor will account for the leverage difference) – that’s a bit under 2 stone. That really isn’t critical. Or at least, not to the point of needing dual discs.
All IMO, of course.Posted 4 years ago
but that would be front and rear, so I would have a stone extra to stop and slow (I think your forgetting how awesome it would look as well 😀 ), but based on the trouble it looks like I am going to have to go with a large rotor and some massive 4 pot calipers.Posted 4 years ago
two 36″ wheels = 10kg, right? so that’s effectively 20kg linear mass
two 26″ wheels = 4kg = 8kg linear mass
so total differnce for the bike is 12kg = 2 stone.
You’re saying that a rider changing weight by 2 stone would require dual/different rotors. I’m saying that you might choose to do so but it is far from necessary, particularly given the hassle required. In fact my weight has varied by more than 2 stone over the years but my rotors remain the same size and I haven’t died/turned my rotors molten yet.Posted 4 years agochris_nMember
Phil Wood make an ISO track hub – a double sided fixed hub for 6-bolt cogs. 120 mm OLN so a little wider than a normal front.Posted 4 years ago
maximusmountain – Member
clubber – based on what ive read its either double disc, 4 pot w/ 210 rotor or 2 pot with custom rotor and mount. Considering the tyres weight 1.6kg, the rims weight 1.1kg and thats the rotating mass
When you pull the brake on there’s 60-100kg of you to stop also, with its CoG centred way more distant from the front hub.
EDIT the CoG isn’t actually relevant.Posted 4 years agoThe PinksterSubscriber
It’s all very well having stupendous stopping power but don’t forget the thing that actually stops you is the grip between the tyre & ground.
If the tyre/surface interface isn’t good enough it’s not going to matter how good the brakes are, you still won’t stop well.
I’m circa 95-100kg at he moment in my stockinged feet, go out well kitted up on a bike probably weighing around 16kg (possibly more) and find 205 front & 180 rear discs using Hayes Strokers more than enough stopping power when pointing downhill.Posted 4 years agoAndy RSubscriber
nedrapier – Member
Have a look at trials motorcycles:
1 diddy disc up front. Probably down to competition rules than anything else, but they work.
There’s no maximum permitted size for brake rotors but bigger = heavier of course, so it’s down to the smallest that will do the job.Posted 4 years agoir_banditoSubscriber
There was a run of production z1’s (can’t remember what year) with double disc mounts.
I had a pair!Posted 4 years ago
Z1 Alloy, imported from Supergo in california in 1998.
Had “Formula” mounts on both legs – similar to IS, but slightly smaller bolt spacing, meant could only run a (single) Hope C2 as that was they only brake available with optional mounts.
After some quick calculations I have found that actually I have ~250% more energy to lose with 36″ wheels (5% increase with a rider on in linear terms at 20mph), so I think my requirement for dual discs isn’t un-sensible when I could run dual 180’s to dissipate the heat and reaction forces more evenly, and less funny things happening on the stanchions. The traction at the wheel isn’t a concern considering the expected contact patch and weight transfer.Posted 4 years agobencooperMember
Oh, some basic physics – you don’t have more energy to dissipate with a larger wheel, but the leverage ratio is worse – so to get the same braking force as a 180mm rotor on 26″, you need a 250mm rotor on 36″.
Might be a lot easier to use a custom Hope rotor and a fork with disc mounts higher up.Posted 4 years ago
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