Problem with Disk position after deepening of the fork

Kittenrainbow · Jul 1, 2015

Hey Guys

I opened some other threads here and was nearly already set for a small front hub set for my citybike. (With a "Cute"-Series Motor: Q100).
But then I read that it would be nescesary to deepen the dropouts on the front fork.

One question:
I have disk brakes. If I deepen the dropouts of the fork, wouldn't then the position of the disk brake in relation to the brake saddle be wrong (The disk beeing to "high")?
How do you deal with this "problem"?

Regards
Me

bowlofsalad · Jul 1, 2015

Have you considered getting a new fork and/or glue, solder, braze or weld on some doctorbass torque arms. https://www.endless-sphere.com/forums/viewtopic.php?f=31&t=29129 If all you did was add these torque arms, it's very likely you wouldn't need to change anything else.

Are you familiar with torque arms?

Drunkskunk · Jul 1, 2015

What fork? You only need to deepen the dropouts if they aren't deep enough. it's not an automatic need.

yes, if you deepen the drop outs you will also very likely need to adjust the disk brake. You can add a few washers under the bolts and get the clearance you need, if you need it.

teklektik · Jul 1, 2015

The original shaft was probably 10mm so the shaft center was 5mm from the bottom of the dropout.

The motor shaft is 12mm or 14mm. The center of the shaft is 6mm or 7mm from the bottom of the dropout - or 1mm-2mm further out than the original.

Minimally you will want to file the bottom of the dropout to the 12/14mm shaft radius - instead of the existing 10mm. This allows the shaft to seat properly and actually rest on the bottom of the slot. This does not deepen the dropout - it just squares it up a bit -- it will still be curved but squarish and meet the flat dropout sides with a hard angle.
Having the shaft center 1-2mm further out than the original will not materially affect the brakes. If you wish, you can file the dropout 1-2mm deeper for a better shaft seat and to re-center the shaft - but as DS pointed out - this isn't an automatic requirement. If you do this, be aware that even slightly different dropout depths will cock the wheel to one side -- so BEFORE you file the slot deeper, drop in a wheel and measure the rim-to-fork offset. AFTER you file the slots deeper, repeat and ensure the rim offset is unchanged - otherwise adjust one slot depth to properly restore the proper offset. That PITA should be enough to discourage you from unnecessarily deepening the dropouts.

John in CR · Jul 1, 2015

Are you talking about an aluminum fork? If so, then modifying the dropouts is putting your life at serious risk. Even unmodified requires special torque arm considerations to transfer the twisting force caused by the motor to a much greater radius. Picture the motor causing the front wheel to disconnect from the bike at the worst moment, leaving you in a faceplant with oncoming traffic. Bicycle forks are not designed to take any twisting force at the axle, and even a low power geared hubbie puts thousands of pounds of force at the 5-6mm radius of those axle flats.

d8veh · Jul 2, 2015

The idea of deepening the drop-outs is to re-centralise the axle so that the disc is in its original position, otherwise it will be approximately 2.5mm lower. The other problem it solves is getting the anti-rotation washers' tab into the drop-out.

Make sure that you use at least one properly anchored torque arm.

dogman dan · Jul 2, 2015

Exactly. File so that your axle center on the motor is exactly where it was with the non motor wheel.

For a 12mm axle, file 1 mm deeper. For a 14 mm axle, file 2mm deeper.

But especially with 12mm, if your dropout is not too shallow in the first place, 1mm less pad touching the rotor is not that huge a deal. So it might be optional really, to file.

John in CR · Jul 2, 2015

I wonder how many forum members have died from inadequately installed front hubbies. With so many thousands of members it's gotta be greater than 0, though it's unlikely that we would ever hear about it. Some years ago I remember hearing about one member very seriously injured in a faceplant accident from a front hubbie. I personally was very lucky my dual torque arms kept the wheel on the fork in the first 10ft of my first hubmotor ride where both slightly modified AL dropouts snapped right off.

neptronix · Jul 2, 2015

Front hub is a terrible idea for many reasons, safety, handling, etc. I don't know why they still make them.. get a rear motor if you haven't ordered already. You won't regret it.

d8veh · Jul 2, 2015

It's not a problem for a low-powered motor like a Q100. I don't know why you're all getting so hystetical about it. About half the OEM electric bikes sold in Europe have 250w front hub-motors.

amigafan2003 · Jul 3, 2015

neptronix said:
Front hub is a terrible idea for many reasons, safety, handling, etc. I don't know why they still make them.. get a rear motor if you haven't ordered already. You won't regret it.

I commuted 14000 miles on a front hubbed Q100 - I'm still alive.

neptronix · Jul 3, 2015

My statement mainly applies to more powerful motors.

I ran a wimpy front hubbie on a bike once. But i was giving it 450w nominal, 800w peak. I saw the solid steel fork i had bend a little under power and was amazed at how so little power could do that though. :shock:

I ran a 900W peak front MAC an another bike and experienced front wheel slip whenever it'd hit sand. Noticeable fork bend too. It also had weird, unsafe feeling steering characteristics ( felt like torque steer )

So yeah, i'm a bit biased. I've never ran 250-350w actual on a front. Still think it's a bad idea if it means hacking away at a fork though..

But that's just like, my opinion, man.

dogman dan · Jul 3, 2015

I spend all day on the chat at work telling folks, Noooo, you don't want a front hub motor. It's not easier to install.

That's despite 10,000 miles of trouble free commuting with a front hub, and racing with 4000w to a frontie. But 99% of riders won't grab throttle in a wet corner, so other than breaking forks from a shitty install, a front hub can work fine for many, particularly a low power ride.

The main reasons to run front hub are.

No brakes at all if you remove a coaster brake rear wheel

Internal geared hub in back

Delta trike, that cannot use a rear hub.

Hill climber, dual motors.

You are an ebike manufacturer, but don't know shit from shinola.

beast775 · Jul 3, 2015

Agree with john in cr...Filing front fork dropouts will weaken them, the legs,especially if you file the radius where the flats meet it [round part at the top].

Problem with Disk position after deepening of the fork

Kittenrainbow

10 mW

bowlofsalad

100 kW

Drunkskunk

100 GW

teklektik

100 MW

John in CR

100 TW

d8veh

1 GW

dogman dan

1 PW

John in CR

100 TW

neptronix

Administrator

d8veh

1 GW

amigafan2003

1 kW

neptronix

Administrator

dogman dan

1 PW

beast775

100 kW

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