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Tires - how much faster is skinnier?(9 posts)

Tires - how much faster is skinnier?rockbender
Feb 4, 2003 11:31 AM
In a few months I have a local multisport race that I participate in doing the bike leg. The course is about 25 miles long and mostly downhill or flat (one short climb).

My question is, what little things can I do to go a little faster, next to getting a TT bike?

Will x20 tires be noticibly faster than x23's?

Running k's for wheels - should I try to find a disc cover for the rear?

I've already got tall gears and aero bars.

thanks!
re: Tires - how much faster is skinnier?ClydeTri
Feb 4, 2003 12:04 PM
many many factors play into this evaluation. Your weight makes a difference, the condition of the road. The smoother a road is, the more less rolling friction a smaller tire generates. If you are heavy, you could cause a smaller tyre to be less in its "normal" shape, just increasing rolling friction. There is no easy answer. A compromise might be a 77x20 up front, and a 700x23 in back. A larger tyre also increases your comfort, which can lead to faster bike splits and better runs as you are not as worn out coming off the bike.

Aero wheels do make a difference..if you bike in the middle 20s in mph, it can add approx a 1/2 mile per hour over a 40km course, which is significant. If you can only have one aero wheel, go with the front as it effectively leads the rear (i.e. the rear wheel drafts the front). Also, you might consider a forward seat post if you are on a traditional geometry bike. YOu need to practice with this one in advance and get your positioning down first though.

Tri ON!
re: Tires - how much faster is skinnier?jeff27
Feb 4, 2003 12:44 PM
I wondered about this too. I don't have
any hard and fast answers ;-) but check this link
out, it is interesting, that's for sure.

http://sheldonbrown.com/tires.html#rolling
23c is fastercxer
Feb 4, 2003 12:55 PM
23's have lower rolling resistance, grips better and is more comfortable.
Wrong! 20 c is fasterWoof the dog
Feb 5, 2003 8:17 AM
20 c is faster because less drag generated by a thinner tire profile more than makes up for a slight increase in rolling resistance. We've been through that too many times, come on!

Sincerely

Woof the dog.
re: Tires - how much faster is skinnier?No_sprint
Feb 4, 2003 12:57 PM
How much faster? Un-noticeable if any faster at all. If the course is as you say, mostly downhill and 25 miles, you can do this section in significantly under an hour. If you're dealing with any side type winds, a rear disc can hurt you. Disc cover? Man, how heavy are those things? I wouldn't even be concerned. Tall gears are good, however, I don't know that I've even spun out my 53x11. If you need any more than that, you'll be doing over 50mph and on one helluva descent. Doubt it.

What can you do to help? Scope the course, increase your power at LT. Depending upon the course makeup, investigate just how far above your LT you can sustain for the entire course. Ride smart, don't pop early. Gage your effort. If you've got legs to win, you won't even need a TT bike. My team's best TT'r can beat our 2nd, TT bike or no. Doesn't matter.
thanks!rockbender
Feb 4, 2003 2:25 PM
Thanks for the info.

I've done the race before, and you typically average 30+ mph, and in years past I have ran 60x11 and mashed past those who had spun out or were just coasting on a few of the downhill sections.

Now that I think about it, the course must be about 22 miles or so, because I put in a sub-40 minute effort one year.

I think the best tips for sure are to train and plan appropriatly, but I always like to get any extra edge I can!

The best part about the race is that we have a company team that does it (and quite competitively!) together, so our boss is very supportive and insistant on getting our training in... even if it means taking off an hour here and an hour there.

cheers!
30 mph average? Holy smokes, turbo!!seyboro
Feb 4, 2003 3:33 PM
Either you're a beast or I have to sign up for the world's only constant-25 mph-tailwind-always-downhil-time-trial...
It IS mostly downhill...rockbender
Feb 4, 2003 4:56 PM
The course has a decent amount of elevation drop to it (like 2000 feet!), so that certaintly helps contribute to the 30mph average, but you still really have to crank to overcome the wind drag. Too bad drafting isn't allowed!