What gearing - ?

[ColinJ]

I was just thinking that it would be handy if someone invented a fixed hub with a clutch to turn it into a freehub for fast downhills. Then I thought that...

1. Somebody has probably already done it.
2. It could be bloody lethal if the clutch failed and the transmission suddenly re-engaged when the bike was going really fast!

 

[TheDoctor]

The fix-free has indeed Bindun. I've been unable to find a link for it, but I do remember it from about 30 years back.
A singlespeed is well worth having IMHO. Mine is 39/17 for about 61" on a 700C wheel, on a 401Ti Dynatech frame with horizontal dropouts. It's not the best for hills, but I have been touring on it.

 

[12boy]

I could be wrong but I am talking about sensitivity to the wheel beginning to lose traction which when there are no jockey wheels or chain tensioner seems more apparent. My hills are too steep to enjoy fixed descents, so i went SS so as to coast down hill, but I rarely used my brakes. Slowing by resisting the pedals and accelerating by pushing them allows for modulating effort in very small increments of adjustment which I found useful on snow and ice. Of course, I could be simply mistaken.

 

[12boy]

She is a beauty, Doctor

 

[Chris S]

but a fixed gear bike seems much better sensiing traction loss than about anvthing else I've ridden.

How so? As a practical person of medium intelligence, how is it different to spin out a tyre fixed v freewheel?

If you lose traction then you can immediately feel if through the pedals.

 

[Ming the Merciless]

I was just thinking that it would be handy if someone invented a fixed hub with a clutch to turn it into a freehub for fast downhills. Then I thought that...

1. Somebody has probably already done it.
2. It could be bloody lethal if the clutch failed and the transmission suddenly re-engaged when the bike was going really fast!

It’s called single speed!

 

[ColinJ]

It’s called single speed!

No it's not - I've got one of those and it doesn't work like that!

The problem with singlespeed is going up steep hills. The cranks are going round so slowly that I struggle to get each one up over the top 'dead spot'. I have watched people do it on fixed and the chain forces the chainring round through that difficult part of the pedal stroke. I want that advantage, but I don't want the resulting crazy cadence on descents. I would sometimes have to hit 250 rpm on some of my local ones or brake, but even then I could be doing 150+ rpm.

 

[I like Skol]

If you lose traction then you can immediately feel if through the pedals.

Same as a freewheel/hub then, if you are pedalling, which if we are talking about traction then we must be? Grip is a different kettle of fish and if you are cornering or braking at the limit of adhesion then I would imagine that any additional forces applied through a fixed drivetrain could be the difference between maintaining or losing grip. Fixed gear drivetrains might give a lot of 'feed & feedback' but this comes at the risk of sliding more when compared to freewheel systems?

 

[Deleted member 1258]

Same as a freewheel/hub then, if you are pedalling, which if we are talking about traction then we must be? Grip is a different kettle of fish and if you are cornering or braking at the limit of adhesion then I would imagine that any additional forces applied through a fixed drivetrain could be the difference between maintaining or losing grip. Fixed gear drivetrains might give a lot of 'feed & feedback' but this comes at the risk of sliding more when compared to freewheel systems?

How do you think that works? There's no more risk of sliding on fixed than on a free wheel, in slippery conditions a fixed is at an advantage, on my fixed I can lean against the rising pedal to use the fixed to control my speed rather than use my brakes.

 

[T4tomo]

How do you think that works? There's no more risk of sliding on fixed than on a free wheel, in slippery conditions a fixed is at an advantage, on my fixed I can lean against the rising pedal to use the fixed to control my speed rather than use my brakes.

agree, its like slowing a car down by shifting into a lower gear, vs braking, and I know which 'd rather do on snow etc

 

[T4tomo]

I'm debating whether to get a 'fun' bike with a flip flop rear hub to enjoy when I retire in a couple of years or so, but haven't rode single speed for may a year; said previous bikes being general purpose rather than sporty. I'm now 67 and with my knees being a bit worn , am riding lower gear ratios than in the past. Any recommendations as to suitable gearing for proposed chromoly framed bike please - ?

I was going to say daft idea unless its quite flat - then saw location Norwich - so crack on. when I commuted into London I used to use a SS for the London end of the commute, which was an ideal tool for the job. Its now hanging up unused in the bike shed.

 

[Chris S]

Same as a freewheel/hub then, if you are pedalling, which if we are talking about traction then we must be? Grip is a different kettle of fish and if you are cornering or braking at the limit of adhesion then I would imagine that any additional forces applied through a fixed drivetrain could be the difference between maintaining or losing grip. Fixed gear drivetrains might give a lot of 'feed & feedback' but this comes at the risk of sliding more when compared to freewheel systems?

Sorry, what's the difference between traction and grip?

 

[Ian H]

Another 67yr old who still rides his fixed-wheel. Devon hills are fine on 63". For flatter or longer rides I can turn the wheel round for a 67" gear. I discovered the other day that I can still spin at 180rpm. I could get over 200 a couple of decades back.

 

[12boy]

I would say traction refers to friction with the ground. Grip to me implies a grab.

 

[I like Skol]

I could be wrong, but for me traction implies a driving force for propulsion while grip is required for turning and braking. Both require friction between the tyre and the road and this is limited by the contact area, the weight applied and the friction coefficient. The nett total of the tractive force and any force required for braking and/or cornering must not exceed the friction between the tyre and the road or else the tyre will slip.
Cornering hard while freewheeling will allow all of the available friction to be used for cornering. If you are riding fixed gear and applying a positive or trailing force to the drivetrain then you may just add enough force to the equation to exceed the available friction resulting in a loss of grip that would not have happened on a freewheeling drivetrain.