Cycling UK Forum

I have a very similar thing on my commute. Thankfully it's not too busy when I use it although it can often be tricky getting into the RH lane. Unfortunate thing is it's a 3% up hill, less than a minute from my front door on the way into work so dare not push it as I'm not warmed up.

I too go for the left of the RH lane, but I don't switch over till a little further up from where the cars do.

hubgearfreak wrote:here's a car being driven outrageously on the public road.
from what you say i guess that it must be a saxo?

Ooh ouch that was bellow the belt!

Kinda proves my point!

Ahh, we have at least one other closet aircooled VW (or at least former) fan, this is the business end of the one I was reffering too, you may appreciate it Si!



...and for those worried about the temptations of driving a vehicle with 225bhp / ton not to worry he gets his kicks from run what you brung sessions at Santa Pod.

Wow that is a mighty tight clearances! Looks good for it too.

Mick F wrote:My chainstay length is 16 3/4 inches.

Got exactly the same on my 26" MTB. Do you have 700 or 26" wheels on you bike?

tatanab wrote:Why would the chainstay length change?

I wasn't saying I thought it should change, but I was confused over why it was the only thing that didn't change, when every thing else did change, including things like seat and head tube angle.

Cheers for the explanation on the chain stay, the chain has a maximum +/- angle that it can be diverted from perfectly inline with the current chain ring. Any closer and either the mud guards wouldn't fit, or the amount of gears you can select from one chain ring would be reduced.

...also I really like the look of he Kona Sutra, a fast Tourer but I can't understand why the Seat and Head Tube angle change, whilst maintaining the chain stay length over the different frame sizes:

Kona Sutra Link

I always thought that aside from the wheels the larger frames where just incrementally scaled up, without altering the frame angles.

Edit: - So far found these sites:
Wikipedia Bicycle Geometry
Wikipedia Bicycle Dynamics

I'm I along the right tracks with what I said?
Any good books or websites to read more?
Assuming the same tyre design, materials, and wheel design can be used for both smaller and 700 wheels why use 700?
If a MTB has a 73 degree seat tube and is being compared to a road racer with the same angle is the higher average speed (assuming neither run out of gears) of the racer accounted for purely by aerodynamics?

The more I get into cycling the more the 'hidden' technicalities become fascinating! Mick F and CJ where discussing one of the what seems to be critical measurements in "No Hands!" and I'd like to understand the others, or indeed be pointed towards a good book or site to look through. Unfortunately my quick searches just came up with lots of frame sizing and geometry charts, rather than technical details. Right then, bare with me...



The diagram shows:
Black ground line
Line 1: - Parallel to the ground from the spindle to spindle of the wheels.
Line 2: - Rear spindle, directly down to the centre of the rear tyre contact patch.
Line 3: - Front spindle, directly down to the centre of the rear tyre contact patch.
Line 4: - Along the centre of the seat tube.
Line 5: - Along the centre of the head tube (steering axis)
Line 6: - Effective top tube length (from centre of top headset to line 4.)
Measure 1: - Frame size (Centre of BB to centre of seat clamp)
Measure 2: - BB ground clearance. (Centre of BB to the ground)
Measure 3: - Trail (Centre of front tyre contact to intersection of Line 5 and ground.)

Missing:
Seat Tube Angle: - between line 1 and 4
Head Tube Angle: - between line 1 and 5
Wheelbase: - Center of front tyre contact patch to centre of rear tyre contact

So firstly and most important is the bike fits and beyond that the changes effect the bike handling:

For the same steering angle input on the handlebars a longer wheelbase bike will have a greater turning circle than a short wheelbase bike.

The greater the trail of the bike the greater the tenancy for the steering to self centre. To make an analogy with driving a car if the steering wheel is released while turning and the car steering wheel returns to the centre quickly then this would be the equivalent to a bike with a large trail. A longer trail bike would require less steering input as the steering would tend to self centre after small bumps, whereas a short trail bike would not self correct. Conversely the larger the tendency to self-correct the heavier the steering. Moving weight forward would reduce the tendancy for the bike to self correct.

Greater seat tube angle moves the rider so more of their weight is supported by the pedals and and handlebars, rather than the saddle. Seat tube angles of around 73 tend to be for speed orientated bikes. Lower angles give a more upright relaxed riding style where the riders weight is supported by the saddle.

So for the bike pictured above the seat tube angle is 73, giving a quick ride. The head tube angle is 70. Is this for the benefit of the suspension in this case? The angle of the head tube effects the trail, and wheelbase, steeper angles giving more trail than required that then has to be corrected by fork offset. However the wheel base can't be corrected without compromising the top tube length. This results in the bike seeming less responsive to steering input.

Now back to the Front suspension MTB vs Road Bike geometry. Due to the shallower head tube angle the MTB will feel less responsive. The greater weight (granted not geometry related) will make the bike accelerate slower, whether or not this is perceivable when your going from a rider bike combination of 12 & 84kg to 8 & 84kg is up to debate. The front suspension if locked up will waste energy, if not then it's just added weight. The MTB may feel less responsive due to the longer wheelbase, but otherwise cruise speed should be unaffected by the geometry, so long as it is compared to a road bike with similar seat tube angle.

Any other effects of the headtube angle other than trail and wheelbase? Is the effect of a short chain stay similar to that of a closer to vertical head tube? I'm guessing longer wheelbase plus a slight shift proportionally of rider weight towards the front wheel.

With regards to the wheel size debate I'm struggling to see the benefits of a larger wheel. If anything the larger wheels seem to impose limitations on the frame designer as the it has a direct effect on the wheelbase. Over rough terrain the larger wheel may roll easier, but I'm mainly talking about road bikes. The gearing issue isn't that great and weight could be saved by using larger rings rather than larger wheels. Also to get a 700 wheel as stiff as a similar (ie same materials used for both) smaller wheel on the same size hub must mean more material. The one thing I can see going against the use of smaller than 700 wheels is the lack of road tyre choice.

So to conclude I ask am I along the right lines with what I've said above, and if so are the narrower drop handlebars forcing a more aerodynamic rider shape really the main cause of the higher cruise speed of a road racer / fast tourer assuming the mountain bike is running 26"*1.125 slicks and the other on similar width tyres? Any one tried putting a fairly wide set of drops on an MTB (with all the brakes etc mounted on the horizontal section)? Does most of the benifit come from the reduced width of the rider bike combo (in which case I'll just get flat bars and narrow them!) or would a lot be gained from keeping the height down too by using the drops?

Edit - Looking at my bike I think a narrow XC bar with clip on tri-bars could be the way to go. I think the drops would be too low for my bike!

How can you possibly be against modification to suspension, engine, and exterior but against Hot Rodding? Hot Rodding is the modification of vehicles, typically American with large capacity engines for linear speed and acceleration, ie road legal drag cars. Taking the driver out of the equation these cars would be more tricky to drive, and more dangerous on tight and twisty roads than the cars (/ owners) you are trying to outlaw!

Cars come from the factory setup with very specific goals based on market research and the intended life and economy of the vehicle. People who modify their vehicles are doing so to gain new driving characteristics rather than just buying a new car. Modifying a car for more power could actually be more environmentally friendly than just buying a car that is set up from the factory with more power due to the vast amount of emissions created during manufacture of the new vehicle.

From a purely emissions standpoint (roughly speaking is directly linked to economy) modifying for power, particularly older vehicles can result in either no reduction in economy, or even gains. Take my chosen toy the VW Beetle for example. Alas I'm having to sell mine due to lack of money and space, but I was aiming for going from 50bhp, up to about 80, with an increase in economy. While my friend has taken his right through to 150 even before the engine has run in and has probably lost less than 5 mpg on cruise.

However, all that said I think you mean something different, you want a crack down on irresponsible driving, and show boating on public rights of way that are often linked to boy racers and there airfix/halfords atrocities! Granted, it seems a high proportion of people driving saxos and such with huge air brakes fitted on the tailgates drive badly, any government effort (/money) spent on driving standards would be more effectively spend on research into and adoption of automatic detection of bad driving in general. Lets face it, detection of speed is very easy, and so is a popular method to detect bad driving. However people who speed may be less likely to have an accident than those who regularly tailgate, undertake, jump red lights, stick in the middle lane, overtake badly, etc... If these systems where implemented with reasonable safety guards (such as videos of the occurance and a few 10s of seconds either side) in place I honestly don't think there would be a public outcry in the same way as there is for speed camaras.

Phew! I though my balance was getting worse!

Started riding very small distances again and got a new bike about 4 years ago, after not riding for about eight years. I've since started doing more miles and on occation tried riding no hands but found my Rockhopper really twitchy. I can do it but it's not exactly possible for a relaxed stretch!

...I'll have to get my tape measure out now!

I guess that was being written while I was editing!

Yeah the fibres arn't the issue, it's more the binder that could cause the issues.

...and there are other ways of fooling bone using foams and lattice structures.

eileithyia wrote:Clearly I've missed out only have good ole stainless steel in my shoulder, never thought to ask for carbon, and no it does not campag or shimano on it apparently.

I believe carbon fibre is not bio compatible. Implants have a completely different set of problems, not least of which is the the way in which the bones adapt to loading (hense the recent article in one of the cycling mags about cyclists low bone mass), and can reject foreign, non compatible material.

Stiffness and stress shielding is a huge concern in implants, but designers don't really want for example a hip replacement stem to be as stiff as possible as this gives reduces the loading on the bone in places around the stem (stress shielding) which leads to the body re-absorbing bone that is not required, thining the bone around the implant which leads to the implan needing replacement.

I don't thing you really want repeat surgery!

Edit: Carbon composites are currently making their way into rabbits! However this will be a very different material as the epoxy binder will have been picked to be bio compatible. EIther way the design chalanges in implant design are very different. Still a lighter implant would feel more natural in the case of a knee replacement where you are swining the weight around while moving.

Lawrie9 wrote:I would suggest that a steel bike would perform better in windy conditions and being slightly heavier may reduce vibration.

Vibration in the frame is down to the hysteresis of the material and frame design.

Hysteresis can be demonstrated with a rubber band. Stretch it and release it many time really quickly then hold the rubber band over your skin, it will be warm. To create this warmth took energy. Some of the energy you where putting into the rubber band was used warming it up as it stretched and was not returned when you moved your hands together. A material which has a high degree of hysteresis is good for damping - ie polymers / elastomers / rubbers. A material that has a lower degree of hysteresis is good for a spring - spring steel is an example of this. In general metals are more springy than polymers and composites, but that is a huge generalisation. Carbons can be designed to be springy - hense the bloke who ran on carbon false legs (/springs) being banned from competing with abled bodied athletes. His leg replacments returned more energy than human legs do during running.

Design geometry can also effect vibration. Natural frequency is the frequency that something will naturally vibrate if it bent then released. For example flick a ruler which you've held against your desk at one end and it will vibrate (and really irritate others ), if you have less hanging of the desk it will vibrate faster. Equally if you flick a ruler that is stiffer it will vibrate at a higher frequency, even if it was made of the same material. If all the parts of the frame have a natural frequency which is the same, the bike could feel uncomfortable under certain circumstances. If different bits of the frame have different natural frequencies then it can effectively dampen itself. Adding curves and not using constant diameter tubing with constant wall thickness if designed appropriately can add stiffness raising the natural frequency to a level that is rarely triggered, or felt by the user.

Carbon fibre is easier to make into these elaborate geometries and so is stiffer so the frames would naturally have higher natural frequencies. But equally where necessary the designers can design in springy sections potentially making the frame much more comfortable.

Plenty of low gears is one thing, but not being able to make advantage of even slight down hills would be irritating and I think it would lead to the bike feeling excessively slow.

Sorry I didn't mean I could hold 20 as an average! However, given a decent anything from flat to slightly down hill (1 to 2% ish) gradually building up the speed to around 20 would not be difficult. The bike would require more power to accelerate at a give rate, but doubt it would differ much in terms of power required to sustain a given speed when compared to a similar, but shorter flat bar bike.

hubgearfreak wrote:

hubgearfreak wrote:the kona ute is aluminium. hardly utility in my mind.

i know i shouldn't mention the gears so i won't

...or lack of! 26, 36 and bash guard if memory serves me right! Are they worried about it going fast? You'd struggle to get a sustainable speed above 20 on that gearing!

Like the bike, but don't fancy cleaning that chain! Think the bike is around £550.