Wobbly Wheels

[Eric7]

A dealer was quoted saying that in the industry, the Radrunner's front brake mounting is known to be unsafe. I don't understand.

Thanks for your tips in your full email.

I don't take a position on the lawsuit - just my thoughts on this sentence.

I think when the brake is behind the front axle, ●when you apply the front brake going forward●, it tends to pull the front axle away from the fork. The front axle may be loose because of user error or the neighborhood kid decided to play a bad joke on you. Bad things happen when you lose the front wheel. Conversely, ● when you apply the brakes going backwards● it tends to wedge the front axle deeper into the fork.  In other words, even if the neighborhood kids completely loosen the front wheel bolts, if you brake going backwards, the wheel is not coming off the bike.  This situation would occur say you are going uphill and stopped and the bike wants to slide downhill backwards.

<<Please don't ride with loose axle bolts.  I am just saying as an example - a hypothetical.>>

Therefore, according to some way of thinking, it would be safer putting the brake pads in front of the front axle because when you brake going forward, which is most of the time, the axle would be pushed up into the fork and you don't have to rely on the front axle bolts to work.

<<Side story.  It is an interesting design in cars because it has been used for an anti-dive system.  If the brake pad is behind the car, the harder the car brakes, the harder the front would be pushed up, countering some of the front-diving tendencies of a braking car. This does not apply to bicycles because of the simple fork design.>>

Many bikes have brakes like Rad. My guess is that it is a design decision for simplicity - which may be a safety feature in itself.

Putting the brake pads in front would increase the chance of damage (e.g., in a crash) and possibly make the cables longer and make the design heavier, and complications increase the risk of failure due to damage or bad maintenance.

Just my guess of the answer.  I don't know if this is a good argument and it is easier to say after the fact.  For example, having a welded on non adjustable seat and handlebar is probably safer too. Getting rid of all bike front racks and backracks would make the bike safer.  It goes on and on.

[handlebar]

A dealer was quoted saying that in the industry, the Radrunner's front brake mounting is known to be unsafe. I don't understand.

Thanks for your tips in your full email.

...
<<Please don't ride with loose axle bolts.  I am just saying as an example - a hypothetical.>>
...

I like your theory about the crash. I didn't go into oscillations with underinflated tires, so I can't say for sure it could have happened.

I believe quick-release front wheels were developed for racers, whose very light front wheels were often damaged. A standard English bike came with a bag hanging on the back of the saddle. It was big enough for a lunch or garment. It came with a sheet-metal wrench, maybe 3mm thick, with holes for the various hex fasteners on the bike. Boxing instead of spanning would prevent rounding off fasteners. You could count on having it because there was only one piece to avoid losing, and it wasn't much good for other applications. That wrench made wheel removal quick and convenient.

I think quick-release axles are a disservice to most riders in terms of convenience as well as safety. Adjustment requires trial and error and may still not be as secure as using a conveniently small wrench. Both ends clamp simultaneously, and I can't be certain that both were fully seated at that instant. I wish it were feasible to retrofit front axles with nuts, like rear axles.

[Eric7]

I think quick-release axles are a disservice to most riders in terms of convenience as well as safety. Adjustment requires trial and error and may still not be as secure as using a conveniently small wrench. Both ends clamp simultaneously, and I can't be certain that both were fully seated at that instant. I wish it were feasible to retrofit front axles with nuts, like rear axles.

I agree with you.  Thank you for your insight.

Just adding a qualifier.  I took 2 years of physics in college and got good grades.  I apologize if I over simplify below but it makes the discussion shorter.

When quick release was first introduced, the brakes were at the rim, at the top.  When the brakes were applied, the wheel axle were pulled ●backwards●, roughly 90 degrees to the fork opening which was pointed down.  So some problem but not much even if you forgot to use the quick release - I know from experience by being stupid as a kid. <<please don't try this, you will get hurt>>

When the disc brake pads were put behind the front wheel axle, the axle were pulled ●down● during braking in the same direction as the fork opening (down), causing problems as I described. So the rules changed. If you forgot to tighten the front axle you will hurt yourself.

A further problem is the disc brake pads were so close to the axle and cause a force multiplier effect.  If the braking was 100 pounds say, where the rubber meets the road, the braking force on a rim sidepull brake would be say 110 pounds and the force on the front axle would be about 110 pounds because the rim is in the interior of the wheel.  With modern disc brakes, the brake pad may be only 1/3 of the diameter of the wheel or maybe 1/4 so the force is multiplied 3 to 4 times.  Once again, if the force was 100 pounds where the rubber meets the road, the force on the disc brake may be 300 to 400 pounds and the pulling force on the front axle would be also 300 to 400 pounds down in the direction of the opening causing great demand on the integrity of the quick release lever.  About 3 to 4 times the demand of a traditional quick release.  And if the bike is 70 pounds and loaded with a passenger, maybe 5-10 times the demand of a traditional quick release on a racing bike.

You can do a thought experiment to see this is true.  If you are trying to stop a spinning tire on a stand with no brakes, it is much easier to put your hand on the rubber.  It will take 3-4 times the effort/hand strength/pressure to try to stop the wheel by rubbing against the disc brake only.

[handlebar]

I think quick-release axles are a disservice to most riders in terms of convenience as well as safety. Adjustment requires trial and error and may still not be as secure as using a conveniently small wrench. Both ends clamp simultaneously, and I can't be certain that both were fully seated at that instant. I wish it were feasible to retrofit front axles with nuts, like rear axles.

I agree with you.  Thank you for your insight.

Just adding a qualifier.  I took 2 years of physics in college and got good grades.  I apologize if I over simplify below but it makes the discussion shorter.

When quick release was first introduced, the brakes were at the rim, at the top.  When the brakes were applied, the wheel axle were pulled ●backwards●, roughly 90 degrees to the fork opening which was pointed down.  So some problem but not much even if you forgot to use the quick release - I know from experience by being stupid as a kid. <<please don't try this, you will get hurt>>

Ah, rim brakes! I think it was in 1919 that cars in America became as popular as bicycles. In the preceding 20 years, bicycle periodicals urged riders to get brakes, which a lot of riders eschewed. On this side of the ocean, brakes were coaster brakes. They could fail on hills. When Schwinn eventually came out with something that looked like an English bike, it had only a coaster brake. Swept-back bars were the fashion offered by American companies, and maybe that would have made a front brake dangerous.

As a teen, I lived at the bottom of a thousand-foot, 10% hill on US 4, with a traffic light at the bottom. Coming down that hill in pouring rain, I'd pull the levers very hard, knowing that eventually the rubber pads would dissipate the film of water and take hold.

I took physics in 11th grade. The teacher told my father I was brilliant. That was a feather in my father's cap, but to me it was weird. How could I be brilliant at was essentially grade-school math? There were several boys in my class whom I found just as capable.

That class was one of my few chances to associate with kids not in my designated group. In grade school, all the boys my age had been friends. The only worthwhile part of school was the playground:after breakfast, after lunch, and two recesses each day. They say Facebook is bad for mental health and I agree. As in a classroom, a remark you make to somebody is really putting on a show for the audience. On a school playground, you could chat freely. Playground segregation meant we didn't know the girls well. Starting in 7th grade, we were segregated into 6 classes. I didn't know any of my classmates, and without a playground, we couldn't bond as kids had in grade school.

Without Physics, I would never have met Doug, the only other kid in the school who could be seen on a bike. (I didn't blame the others for never riding. They owned Schwinns.) He sometimes rode his Huffy 4 miles to school. He had to climb 1100 feet to get home. At the end of the school year, we rode on an overnight camping trip. Looking back, I don't know how we managed to schedule it. "Lord of the Flies, which the author said misrepresented what boys were like, was treated like required reading. Parents and teachers considered boys a bad influence on each other, so home visits were discouraged, and we were overloaded with homework, organized activities, and employment.

During those 24 hours, we didn't talk or act differently from at school, but the absence of an audience made a big difference. Big Brother wasn't watching. A friend is someone with whom you can be at ease, and we were at ease.

[Roverdrive]

Speaking of physics, another problem with disk brakes that I don't see discussed much is they can be way harder on spokes and rims than rim brakes.  When the brakes grab the disk, the breaking force has to be transmitted through tension in the spokes out to the rim and tire.  Rim brakes do stress the spokes some but nowhere near as much.  I have seen several rear disk rims where fatigue cracks have grown out of the holes on both the drive and non-drive side of the rim.  With rim brakes, the only fatigue cracks I have seen in the rims have only been on the drive side. 

[handlebar]

Speaking of physics, another problem with disk brakes that I don't see discussed much is they can be way harder on spokes and rims than rim brakes.  When the brakes grab the disk, the breaking force has to be transmitted through tension in the spokes out to the rim and tire.  Rim brakes do stress the spokes some but nowhere near as much.  I have seen several rear disk rims where fatigue cracks have grown out of the holes on both the drive and non-drive side of the rim.  With rim brakes, the only fatigue cracks I have seen in the rims have only been on the drive side.

I found an article about the choice between rim and disk brakes. It said disk brakes have more stopping power. I wondered why, since my disk brake operate on 1/3 the rim radius.

In stopping power, I think the rim brake's Achille's heel is the distance between the pads and the hinge bolt. The distance may be reasonable on a road bike, but an ebike will probably have bigger tires, entailing longer arms and more leverage to bend arms or hinge pins. Ebikes may have more weight and speed, but rim brakes would have to be designed for less braking force.

[Roverdrive]

I think the smaller diameter of the disk rotor is offset by how much force the pads can exert on the breaking surface.  Most road bike rims are relatively thin, and all of the higher end ones are aluminum (or even carbon).  They tend to use only mildly abrasive pads to reduce wear as thinning of the breaking surface can mean rim failure.  If rim brakes used similar pad materials and forces as disk brakes, rim life would be severely compromised.  I worked with a guy that used to "ride" his brakes all the time and he seemed to go through a rim a year!

[Dlennard]

Well this post has gone off topic quite a bit.

My RadCity 5 Plus StepThru still has a low speed wobble that can initiate a whole-bike shimmy. It is not headset looseness, fork softness, spoke tightness, tire pressure or tire bead location. It has been to 2 bikeshops and 2 bike mechanics. All agree it is a combination of front for bridge and headset angle : in other words it is baked into the very geometry of the bike itself. My partner and I have each fallen off it twice in traffic and will no longer ride it. This is a dangerous bike.

[DrSmile]

As I stated in the link I posted previously, my Step-through Radcity 5's wobbles were cured by replacing the OEM tires. I have ridden it at 40mph downhill since then without issue. It is quite stable at speed as long as you don't mind the coefficient of drag close to 1... it feels like I have a parachute on compared to my road bikes. I don't think it's possible to exceed 40mph unless you throw it off a cliff.

[Ddaybc]

DrSmile, I remember that post and that's a good reminder. If your bike has a wobble, vibration etc and everything checks out then perhaps change the tires. Purchase good quality tires as it's potentially the last thing to look at and not overly expensive. It may solve the problem as it did for you.

[Mooree]

If the wheel is not true, meaning it's not perfectly straight and round, your bike wheel may wobble. This can result from a bent rim or loose spokes. Inspect the wheel for visible deformities and have it trued by a professional if necessary.

[Altema]

Wow, lots going on in this thread! Most of the wobble in bikes is due to loose tolerances or improper assembly, but this bike has been apparently reassembled by pros. The most likely suspect is the front suspension fork, and I've seen this on other brands as well. A quick check is to hold the handlebars in the normal riding position with your feet on the ground, hold the front brake only, and rock the bike back and forth. A suspension fork with loose tolerances internally will look ok on the outside, but the sloppy movements on the inside will contribute to wheel or frame oscillation at certain speeds. If your front fork seems loose in this test, take it back to the shop to have them confirm, then they may recommend a replacement fork.

Regarding tire pressure, there's low pressure compared to normal tires, then there's low pressure that's far away from the recommended pressure for that specific tire. The K-Rad tire Kenda makes for a lot of Rad bikes is made for 30 PSI and it's printed right on the tire. 10 PSI is way out of range. 16 is the extreme minimum, and that should only be used in extenuating circumstances like ice. On bare pavement at 16 PSI, handling and safety will be affected. The minimum pressure I will use on pavement is 18 PSI, and my normal pressure is 20 to 22 PSI because of the horrendous sidewalk cracks and tree root issues where I often ride. It should be noted that K-Rad tires, even at 20 PSI, are stable up to 40mph, so I don't think there is a safety issue with Rad tires that would cause a crash... unless the tires are underinflated due to a leak, ignorance, or lack of maintenance. All bikes are unsafe if the tire pressure is too low.

The front brake issue does not apply to Rad bikes, and was a "try anything" attempt by the lawyers to place blame. When disc brakes were first went into use on bicycles, the quick release lever had enough travel to actually get caught in the brake rotor, causing serious crashes. This is impossible with Rad's design, and the most obvious way to demonstrate it is to bring a rad fork and wheel into the courtroom and have ANYONE replicate the lever/rotor interference issue. It just can't happen. I feel sorry for the loss of a child, but responsible parents would not have let them ride a powered vehicle they were not old enough for, especially if it was not in proper working order. One of my kids got a used pedal bike last week, and we spent an hour making adjustments and corrections before I let her get on it.