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20C vs 23C tyres(7 posts)

20C vs 23C tyresNoam
May 22, 2002 11:24 PM
Hi there

Time to get new tyres. I always fitted the 20C mainly because they look slimmer and faster. Now I hear that it was all-wrong and that the 23C are faster. Could any Guru out there give me some physical explanations (aerodynamic, friction),or is only an unquantifiable "comfort" that makes 23C more popular. I know that in off road vehicles slimmer tyres are more suitable because of the weight per sqcm (or sqinch your units) is higher. Consequently better grip onto the surface driven on. How this relates to road cycling wheels and tyres. Lets get scientific. Prove it.

Anyone there experienced riding on Vredstein Fortezza


Down Under
what ive readishmael
May 23, 2002 9:11 AM
is the contact patch of a 23 tire gives less rolling resistance. Instead of a longer patch its rounder and shorter...why this shaped contact patch would give less rolling resistance i cant figure out. Just the opposite makes sense to me. If the size of the contact patch is the same it seems to me that longer would be better similarly to a long boat not being as affected by waves
what ive readgrzy
May 23, 2002 3:02 PM
All other things being equal, at 120 psi you need less tire deflection with a 23 mm tire to develop the same contact patch area required to support a given load. If you can increase the pressure as the tire become smaller then things would change. The other factor is that since a 20 mm tire has to deflect more there is the stiffness and work of the casing structure to consider. These are frictional losses and once they're gone you don't get them back. the counter arguement is that a more narrow tire presents less frontal area and lower aerodynamic drag. In the final analysis the devil is in the details and the numbers really do matter and many of the relationships are non-linear. Also, with a 20mm tire you're more likely to dent a rim or get a snake bite flat if you wack something. Then there's the added enjoyment of trying to change a 20 mm w/out the use of tools. Realize also that the 20 mm tire doesn't tend to corner as well.
re: 20C vs 23C tyrescyclequip
May 24, 2002 2:02 AM
All tyres flex at the contact patch with the road surface. The deformation caused at the contact patch springs back to shape once the patch moves, but this isn't 100% efficient. This flex amounts to a loss of energy as the flex is converted to heat. Feel your car's tyres after a fast journey - they will be warm if not hot! This is caused by the tyre flexing - with a smaller amount of friction thrown in adding to the temperature. Modern bicycle tyres hardly get hot - unlike car tyres - but the flex still robs the tyre of its 100% energy transmission capability. We can lessen this loss by using a higher tyre pressure - this lessens flex which in turn lessens energy loss - so the manufacturer's maximum recommended tyre pressure is always the best one to use. But there are other ways of lessening flex that work as well! Another option is to go to wider tyres. This is because a tyre's contact patch is determined not by tyre width, but by pressure and the weight the tyre supports. (Contact Area = Weight divided by Tyre pressure. So a tyre at 100 psi supporting 100 pounds has a contact patch of 1 square inch). Width has nothing to do with this, but tyre width will influence the shape of that patch. Simply put, a narrower tyre needs a longer patch to make up the 1 square inch, a wider tyre needs a shorter length of patch. The problem comes because long patches flatten more of the tyre casing sidewall than short patches. This leads unavoidably to a greater energy loss since more tyre gets flexed per contact patch. The wider tyre with the shorter patch flexes less and hence consumes less rolling energy. In addition the wider tyre corners better than the narrower one since it presents a better, more stable contact patch profile when leaned over. Even with MTB tyres, the wider rubber provides more traction than the thinner tyres.
I ride Fortezza all the time - great tyre, but then so are most top-end products.
re: 20C vs 23C tyresNoam
May 25, 2002 5:34 AM
Following these arguments, how about a 20C front and a 23C rear like the motobikes. Do you see any advantage(s)using this setup?

re: 20C vs 23C tyresWoof the dog
May 25, 2002 8:33 AM
from control point of view, you want wider tire in the front for more grip. The back wheel slide you can save but not the front one i guess. So, i am not sure about the motorbikes. The downside of wider in the front is less aerodynamic leading edge basically. So, it depends on the event. For JRA I'd use 23c.

I wish bikes were like motorcycles - taking corners at 45+ mph, scraping your pegs and your exhaust and still staying up.

Rock out

Woof the radiodog
20 is faster, they sayWoof the dog
May 24, 2002 10:09 PM

Granted, 23c will be more comfortable, maybe safer for a heavier person, will corner safer, and will square off slower.

Vredestein Fortezzas are the greatest tires ever. Axial Pros are good too though.