Speeding downhill
-
- Posts: 42
- Joined: Thu Dec 29, 2011 1:15 pm
- Location: Brisbane
Speeding downhill
Postby Sauce » Wed Feb 13, 2013 7:23 pm
My opinion is that it is physically impossible to descend the mountain under the speed limit without dismounting and walking. Having heard all the horror stories of tyres puncturing due to overheating rim brakes, I'm led to believe that if you were to coast the brakes the whole way down, you would more than likely end up in a ditch on the side of the road before you even made it half way. I do my best to manage my speed during the descent so I am in less of a hurry to brake for the intersection at the bottom of the hill, but I still end up sitting above 60km/h for most of the descent.
I feel that Queensland Police have failed to recognise the fact that the road is a one-way single-lane configuration, with significant room to maneuver around the corners, and a very wide separation from oncoming traffic.
Regardless of this latest campaign, I would like to continue to ride Mt Coot-tha but suspect doing so would result in a hefty fine, which I would very much like to avoid.
As road cyclists, what are our options? Disc brakes? Won't these warp under continuous braking and then jam the caliper, resulting in skid / somersault over the handlebars?
-
- Posts: 9810
- Joined: Tue Dec 01, 2009 11:48 am
Re: Speeding downhill
Postby human909 » Wed Feb 13, 2013 7:46 pm
- RonK
- Posts: 11508
- Joined: Mon Aug 24, 2009 2:08 pm
- Location: If you need to know, ask me
- Contact:
Re: Speeding downhill
Postby RonK » Wed Feb 13, 2013 7:54 pm
- London Boy
- Posts: 818
- Joined: Fri Nov 19, 2010 3:43 pm
Re: Speeding downhill
Postby London Boy » Wed Feb 13, 2013 8:02 pm
I'd have to say that the last time I rode a laden touring bike was around Ireland 20 years ago, with simple cantilever brakes. Whatever the gradient, I do remember that braking was no problem at all. And Ireland is far from the flattest country on the planet.RonK wrote:Rubbish. I have no difficulty controlling the speed of a heavily laden touring bike on longer and steeper descents than Mt Coot-Tha, using only cantilever brakes.
This was with tent, cooking kit, water, clothing and everything else I needed. No credit card touring for me back then...
- jonbays
- Posts: 417
- Joined: Mon Sep 03, 2007 8:14 pm
- Location: Sydney
Re: Speeding downhill
Postby jonbays » Wed Feb 13, 2013 8:42 pm
- Lukeyboy
- Posts: 3621
- Joined: Tue May 29, 2012 2:38 am
Re: Speeding downhill
Postby Lukeyboy » Wed Feb 13, 2013 9:52 pm
I solved a similar problem a long time ago.jonbays wrote:Of course it is damn hard to read the cateye with my chin on the bars!
-
- Posts: 23
- Joined: Fri Feb 10, 2012 10:08 pm
Re: Speeding downhill
Postby Chillibones » Wed Feb 13, 2013 9:58 pm
- il padrone
- Posts: 22931
- Joined: Mon Apr 07, 2008 11:57 pm
- Location: Heading for home.
Re: Speeding downhill
Postby il padrone » Wed Feb 13, 2013 11:13 pm
"An unjustified and unethical imposition on a healthy activity."
- Lukeyboy
- Posts: 3621
- Joined: Tue May 29, 2012 2:38 am
Re: Speeding downhill
Postby Lukeyboy » Wed Feb 13, 2013 11:53 pm
- il padrone
- Posts: 22931
- Joined: Mon Apr 07, 2008 11:57 pm
- Location: Heading for home.
Re: Speeding downhill
Postby il padrone » Thu Feb 14, 2013 12:03 am
But if I recall, 45-50kmh should be enough speed to ventilate your rims enough to avoid a blow-out, even if you're on the brakes the whole time.
"An unjustified and unethical imposition on a healthy activity."
- Lukeyboy
- Posts: 3621
- Joined: Tue May 29, 2012 2:38 am
Re: Speeding downhill
Postby Lukeyboy » Thu Feb 14, 2013 12:39 am
- il padrone
- Posts: 22931
- Joined: Mon Apr 07, 2008 11:57 pm
- Location: Heading for home.
Re: Speeding downhill
Postby il padrone » Thu Feb 14, 2013 12:57 am
Don't they use hob-nailed gloves for breaking anyway ??
"An unjustified and unethical imposition on a healthy activity."
-
- Posts: 9810
- Joined: Tue Dec 01, 2009 11:48 am
Re: Speeding downhill
Postby human909 » Thu Feb 14, 2013 1:08 am
I believe it is less about simple ventilation and more about the power (heat) going into the rims. At high speeds a greater percentage of the potential energy is lost in wind resistance and so brake overheating does not occur. At very low speeds (say 15kph or less) the power (heat) input into the rims remains low. At moderate speeds (30km-45km) the heat input into the rims is high enough to cause run away temperature increases.il padrone wrote:But if I recall, 45-50kmh should be enough speed to ventilate your rims enough to avoid a blow-out, even if you're on the brakes the whole time.
The exact speeds where it is dangerous would be very dependent on gradient however.
-
- Posts: 94
- Joined: Wed May 09, 2012 8:18 pm
Re: Speeding downhill
Postby GH » Thu Feb 14, 2013 1:31 am
There are no points associated with bicycle speeding, and I think the fine is not too bad either, just as an aside.
- VRE
- Posts: 582
- Joined: Fri Aug 24, 2012 9:14 am
- Location: Ringwood North, VIC, Australia
Re: Speeding downhill
Postby VRE » Thu Feb 14, 2013 7:28 am
That was my thought, although I'm unfamiliar with Mt Coot-Tha. I've descended Mt Baw Baw east of Melbourne, and just used pulse braking, keeping my average descending speed probably at about 40km/h. Some might think that's too slow, but you have to ride to the conditions, because we don't have a God-given right to descend hills at the speed limit.il padrone wrote:What is the speed limit for the road? What is the gradient of the descent? Is it not feasible to control your speed with simple pulse braking?
-
- Posts: 3056
- Joined: Tue Jan 05, 2010 2:54 pm
Re: Speeding downhill
Postby zero » Thu Feb 14, 2013 8:54 am
Cantilevers don't impact heat generation over long periods of braking.RonK wrote:Rubbish. I have no difficulty controlling the speed of a heavily laden touring bike on longer and steeper descents than Mt Coot-Tha, using only cantilever brakes.
Loaded tourer typically won't blow a tire off because it has larger tires and heavier rims which take considerably more energy input to raise the temperature (and thus raise the pressure), and are lower pressure so they start further away from the pressure required to blow a clincher off (not convinced thats linear but it is favourable to larger tires), and the loads are usually relatively unaerodynamic compared to the stored potential in their mass.
- RonK
- Posts: 11508
- Joined: Mon Aug 24, 2009 2:08 pm
- Location: If you need to know, ask me
- Contact:
Re: Speeding downhill
Postby RonK » Thu Feb 14, 2013 9:17 am
Rubbish! It doesn't matter what type of rim brake, the heat generated by braking forces will be the same.zero wrote:Cantilevers don't impact heat generation over long periods of braking.RonK wrote:Rubbish. I have no difficulty controlling the speed of a heavily laden touring bike on longer and steeper descents than Mt Coot-Tha, using only cantilever brakes.
Loaded tourer typically won't blow a tire off because it has larger tires and heavier rims which take considerably more energy input to raise the temperature (and thus raise the pressure), and are lower pressure so they start further away from the pressure required to blow a clincher off (not convinced thats linear but it is favourable to larger tires), and the loads are usually relatively unaerodynamic compared to the stored potential in their mass.
My 15kg touring bike with 20kgs of luggage and me sitting on it will generate far more braking heat than my 7.5 kg CF road bike. And with tyre pressures at 80psi they are not much different either.
And to rubbish again, I regular ride my road bike on Mt Coot-tha. It's not unusual to see a speed trap near the Legacy Way tunnel workers car park, and it's not at all difficult to stick to the speed limit.
-
- Posts: 479
- Joined: Fri Jul 04, 2008 8:33 am
- Location: Maribyrnong,Victoria
Re: Speeding downhill
Postby william » Thu Feb 14, 2013 9:24 am
How do truckies manage it?
-
- Posts: 9810
- Joined: Tue Dec 01, 2009 11:48 am
Re: Speeding downhill
Postby human909 » Thu Feb 14, 2013 9:55 am
Engine breaking and a radiator to dissipate the heat. On long steep hills cars will have the same problem. Though in Australia we don't have too many of them.william wrote:How do truckies manage it?
Personally I haven't had any problems with overheating bike brakes but then the only big hills I have ridden is the 450m down into Lorne. I didn't really brake much until the bottom.
-
- Posts: 42
- Joined: Thu Dec 29, 2011 1:15 pm
- Location: Brisbane
Re: Speeding downhill
Postby Sauce » Thu Feb 14, 2013 10:17 am
- il padrone
- Posts: 22931
- Joined: Mon Apr 07, 2008 11:57 pm
- Location: Heading for home.
Re: Speeding downhill
Postby il padrone » Thu Feb 14, 2013 10:21 am
Riding up the lower reaches of Dead Horse Gap, the smell from burning brake pads from the descending cars was overpowering. Lots of people driving automatic transmission cars know nothing about use of gears to slow the car - they just hang on the brakes and overheat them
Descending into Lorne is just a gentle roll. On the bike Mt Baw Baw was one of the most extreme descents I've done under brakes. In 6kms you descend about 800m. On a light road bike I was forced to sit on the brakes continuously to hold the speed. After about 1 km I blew out the front tyre. I walked a good bit after that. Gradient is about 12-15%.
If you want another road to ride fully-loaded for some very challenging descents (and climbs) do the Western Explorer through the Tarkine in NW Tasmania. Sheer hard graft - but some beautiful country.
"An unjustified and unethical imposition on a healthy activity."
-
- Posts: 1494
- Joined: Thu Apr 29, 2010 8:10 pm
- Contact:
Re: Speeding downhill
Postby high_tea » Thu Feb 14, 2013 10:40 am
Shrug. Coot-tha isn't that long or steep. Pulse brake, as il padrone said, or alternate front and rear if you're concerned. Plus sit up as high as possible to maximise frontal area. This assumes metal rims - carbon might be another matter, I don't know. But still, 2.5k on, what, 8% average or so is something that any decent bike should handle.Sauce wrote:Dont mistake this thread not looking to have the speed limit changed, simply wondering what we can actually do to make our bikes "roadworthy" in this aspect. I simply dont trust rim brakes to do the job safely.
-
- Posts: 3056
- Joined: Tue Jan 05, 2010 2:54 pm
Re: Speeding downhill
Postby zero » Thu Feb 14, 2013 11:25 am
Can't see how that differs materially from what I said. Not sure where the Rubbish! is coming from.RonK wrote:Rubbish! It doesn't matter what type of rim brake, the heat generated by braking forces will be the same.zero wrote:
Cantilevers don't impact heat generation over long periods of braking.
its undoubtedly more upright as well, and with load it has considerably more frontal area and thus drag. For me, adding 27kgs of weight would increase the stored energy in the bike at the top of the hill by 25%, and increase the drag considerably as well. ie (with my weight) the brakes probably have to dissipate at most 20% more energy to maintain the same descending speeds. Making the bike 3x as heavy doesn't make the system 3x as heavy.
My 15kg touring bike with 20kgs of luggage and me sitting on it will generate far more braking heat than my 7.5 kg CF road bike. And with tyre pressures at 80psi they are not much different either.
I agree, but not starting at 120psi is a big factor in how far you can drag the brakes before blowing the tire off - ie you pretty much have to burn the tube (180 deg c might not even do it).
And to rubbish again, I regular ride my road bike on Mt Coot-tha. It's not unusual to see a speed trap near the Legacy Way tunnel workers car park, and it's not at all difficult to stick to the speed limit.
- InTheWoods
- Posts: 1900
- Joined: Sun Jul 31, 2011 2:34 pm
- Location: Brisbane
Re: Speeding downhill
Postby InTheWoods » Fri Feb 15, 2013 2:22 pm
If anything I think the back of cootha is worse. But again pulse braking, front and rear, and its no issue. My rims are about lukewarm by the time I get to the bottom.
At the end of the day, if your gear can't safely keep you under the speed limit, then you shouldn't be riding there - the problem is yours, not the road's. What would happen, if, gasp, you had to slow right down or even stop to avoid an obstruction! Maybe even your frame would melt from the heat radiating from your red hot rims
- elantra
- Posts: 3181
- Joined: Tue Jan 13, 2009 6:01 am
- Location: NSW and QLD
Re: Speeding downhill
Postby elantra » Fri Feb 15, 2013 3:18 pm
There is the back way and the front way, it is a circuit several kilometres in length.
Most cyclists ascend the back and descend the front, for no better reason than that the back descent is more dangerous.
Descending the front is a lot of fun, and i generally reach a speed of 70 km/hr, but not for very long.
I have been doing this for over 30 years, and i will probably continue to do this.
The current publicity about bikes speed is appropriate as a general reminder to exercise care, but i don't use a speedo.
So i am not going to get too neurotic about controlling my speed if it seems appropriate (depending on conditions) to go a bit over 50 km/hr.
BTW, in the last few years there have been 2 car accidents up there resulting in driver fatalities.
As far as i know, there has been one cyclist fatality.
Return to “General Cycling Discussion”
- General Australian Cycling Topics
- Info / announcements
- Buying a bike / parts
- General Cycling Discussion
- The Bike Shed
- Cycling Health
- Cycling Safety and Advocacy
- Women's Cycling
- Bike & Gear Reviews
- Cycling Trade
- Stolen Bikes
- Bicycle FAQs
- The Market Place
- Member to Member Bike and Gear Sales
- Want to Buy, Group Buy, Swap
- My Bikes or Gear Elsewhere
- Serious Biking
- Audax / Randonneuring
- Retro biking
- Commuting
- MTB
- Recumbents
- Fixed Gear/ Single Speed
- Track
- Electric Bicycles
- Cyclocross and Gravel Grinding
- Dragsters / Lowriders / Cruisers
- Children's Bikes
- Cargo Bikes and Utility Cycling
- Road Racing
- Road Biking
- Training
- Time Trial
- Triathlon
- International and National Tours and Events
- Cycle Touring
- Touring Australia
- Touring Overseas
- Touring Bikes and Equipment
- Australia
- Western Australia
- New South Wales
- Queensland
- South Australia
- Victoria
- ACT
- Tasmania
- Northern Territory
- Country & Regional
Who is online
Users browsing this forum: Amazon [Bot], mikesbytes
- All times are UTC+10:00
- Top
- Delete cookies
About the Australian Cycling Forums
The Australian Cycling Forums is a welcoming community where you can ask questions and talk about the type of bikes and cycling topics you like.
Bicycles Network Australia
Forum Information
Connect with BNA
This website uses affiliate links to retail platforms including ebay, amazon, proviz and ribble.