23mm or 20mm tyre for time trials?

kevin_stephens

Clinchers, 10 mile ususally, not particularly fast at present but training ambitously

Any comments / pros and cons?

I need to order some and could do with some guidance overwhich box to tick

Thanks

ddraver

I have 20mm on the front on my commuter (by mistake)

They have less rolling resistance and when pumped up hard (i'm a big boy) they havenever punctured

preumably your not concerned about comfort, and if its gonna be dry (!!!)then i'd go for it

Monty Dog

Please search for previous posts, it's been covered so many times but in two words, don't bother.

kevin_stephens

Monty Dog
Thanks for the search tip Fraser; lots of useful info. I'm really enjoying the bike and have started to look forward to the pain of my local wednesday evening 10 every week,

The 25mm tyre rubs on the chainstay so I was going to go for 20mmm to give some extra clearence unless there is a particular reason why the 23 option would be better. I'm ordering the 20mm.

Kevin

knedlicky

I used to ride 20 mm but about 6 years ago changed to 23 mm, partly because I read a report in a cyling magazine (I forget which) which concluded that the rolling resistance with a 20 mm tyre was greater than with a 23 mm tyre, so the common perception that 20 mm have less rolling resistance was false.

About the same time, a bike shop guy told me that that was the reason professional riders mainly use 23 mm nowadays.

When I told him that riding on 23 mm after having been on 20 mm felt like I was on a bouncy castle, he suggested that 20 mm in front would make little difference but I should definitely stay with 23 mm at the rear.

Dorian Gray

knedlicky wrote:

I used to ride 20 mm but about 6 years ago changed to 23 mm, partly because I read a report in a cyling magazine (I forget which) which concluded that the rolling resistance with a 20 mm tyre was greater than with a 23 mm tyre, so the common perception that 20 mm have less rolling resistance was false.

This is absolutely true, though as you say, commonly misunderstood. All things being equal, fatter tyres have lower rolling resistance. This is because rolling resistance is created by elastic hysteresis in the tyre wall caused by flexing, and narrow tyres deform more than wider tyres because they have a narrower contact patch with the road.

Generally speaking, tyres with thinner, more flexible walls will have lower rolling resistance, but be more prone to punctures. It's usually a trade-off.

That said, rolling resistance absorbs a small amount of your energy compared to aerodynamic drag at TT speeds. Using narrower tyres will reduce drag more than they will increase rolling resistance, which is why no-one is doing time trials on 28 mm tyres. But the best tyre width will depend on your speed and weight. I don't know the speed at which a 20 mm tyre would become faster than a 23 mm tyre, but I would guess it would be very high, maybe around 28 or 30 mph. And the difference wouldn't be very much.

I'd say stick with 23 mm tyres unless you have a strong reason to believe you'd be faster on 20 mm tyres. 23 mm tyres will also be a bit more comfortable and offer more grip, so better to err in that direction if in doubt.

aracer

Dorian Gray wrote:

All things being equal, fatter tyres have lower rolling resistance.

"All things" does include tyre pressure though, and you can generally pump a narrower tyre up to higher pressure (in fact it's usually recommended). That really depends on your road surfaces - if they are smooth, then a narrow tyre pumped up harder may be better, if rough then probably the wider tyre.

A good compromise though is to use a 20 on the front for decreased air resistance and a 23 on the back for better rolling.