Gallery
DISC WHEELS
The extra weight makes very little difference on a flat course.
Aerodynamic drag is the largest resistance when cycling on flat roads.
For disc wheels
In side winds you can gain speed due to the lift force.
The drag of wheels can vary from 10% to 16% of the total amount of drag while cycling.
An improvement in being aerodynamic form 36 spoke wheels to deep section wheels to a disc wheel.
One with a fitted power meter is the best to allow you to evenly distribute your power throughout the whole time trial.
Don’t forget that drag on the rear wheel can be reducing dup to 25% by the seat tube.
Improving the drag by using a disc wheel can save up to 25% of the existing wheel drag and this will only be saving from 2.5% to 4% of the total drag
Time saving
Expect to save from 2% for slower cyclist to 3% for fast cyclist. This is due not to the time taken but the extra drag created by going faster. So if you travel at 40km an hour a disc wheel will help the quicker rider much more.
Hills
Once the cyclist slows to below 9 mph the effort is to go against gravity than aerodynamics.
Against disc wheels
Side winds or large Lorries that drive by can cause the air to push against the disc
Gusty winds can make it hard to ride in a straight line especially for riders who weigh less than 65kg.
Riding in a one gear less you can have more control during parts of the course that has a cross wind.
Once damaged they are hard or costly to repair. Can be easily damaged from side impacts.
Can feel harsher to ride so avoid pumping the tyre up rock solid.
Spoked wheels compared to a disc wheel
Manufacturers claim that disc wheels can be form 4 minutes to 10 minutes quicker over 112 miles (180km) than a 36 spoke wheel.
Remember that in The Ironman we have to run a marathon after.
I have found personally that the fly wheel effect can actually help as it wants to keep going. I also like the whirring nose it can make.
Disc wheel tips
Look for gaps in the hedge or buildings where the cross winds can be stronger
Braking
Don’t forget that for carbon rims you will need to fit carbon brake pads for better stopping power and avoid wearing down the carbon