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Old 06-13-10, 01:43 PM   #1
EDDIE1963
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700x25 tires

I change my tires on my 2010 Specialized Sirrus base model from 700 x32 to 700x 25. What a difference. I rode 25 miles today and I was able for the first time keep speeds between 15 and 18 MPH.
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Old 06-13-10, 05:47 PM   #2
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Yeah they do make a nice difference as do the weight and stifness of your wheels.
I changed from 700x35c crosstyres to 700x23c race tyres and found my average speed to increase from 18,5m/h to 22m/h on the first run
I have two wheelsets now so I can choose between equiping for purely roads or for versatility of roads & cross-country.
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Old 06-13-10, 07:59 PM   #3
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My 2009 Sirrus came with 28c tires, and I have thought about ordering some Michelin Krylion 700x25c tires to put on it. I feel its too slow, and I only ride pavement. When i had a road bike (with Krylion 23c tires) I could average 16mph on my slightly hilly 13mile route...now getting 13.9mph is an achievement! 23c would be too small unless I bought a carbon fork to suck up the vibrations...I think.
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Old 06-14-10, 08:26 AM   #4
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Have you thought about increasing the pressure in the OEM tires, beyond max listed, to improve the roll - usually, an additional 5-10# makes a big difference, with larger tires.

Even my 35s and 40s, running at 90-92 PSI (85# tires) makes a huge difference in roll.
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Old 06-14-10, 09:42 AM   #5
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I am running my Specialized All Condition tires at 115psi now (max on tire) I used to run my 700x23c Michelin Krylion Carbon's at 115/120psi, IIRC.

I do believe that Michelin designs better tires though. I am sure my current All Condition tires are great if your going to ride in rain or slicker roads, but for my needs I could use a full slick design, with a harder rubber. Guess I will have to save some pennies
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Old 06-15-10, 11:10 AM   #6
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Do the 23's flaten out on so much on the hybrid rims to make even more tire touch the road then with say the 25s or 28s?

I just stopped at the bike shop and picked up a set of 23's for my Trek 730. I'm wondering if maybe I would have been better off picking up a set of 25's or even 28's. I am currently riding ... 35's...I think, not at home at the moment.
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Old 06-15-10, 11:43 AM   #7
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Just a head's up - make sure your rims are narrow enough for a 23 - 25mm tire. A wheel meant for 35mm tires may be too wide. Also be sure to recalibrate your computer for the smaller tire or you will fool yourself as to speed.
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Old 06-15-10, 12:24 PM   #8
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Just a head's up - make sure your rims are narrow enough for a 23 - 25mm tire. A wheel meant for 35mm tires may be too wide. Also be sure to recalibrate your computer for the smaller tire or you will fool yourself as to speed.
Yeah, looks like from Sheldon's chart that I to be at least in the "teens" inside width wise to run a 23mm tire. I have no idea what the inside width of my rims are. I'd guess 20 or better however.

I'll check them out when I get home.
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Old 06-15-10, 12:37 PM   #9
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Quote:
Originally Posted by Shepp30 View Post
Do the 23's flaten out on so much on the hybrid rims to make even more tire touch the road then with say the 25s or 28s?

I just stopped at the bike shop and picked up a set of 23's for my Trek 730. I'm wondering if maybe I would have been better off picking up a set of 25's or even 28's. I am currently riding ... 35's...I think, not at home at the moment.
At any given pressure, the contact patch will be the same, for whatever tire you put on there.

Example, two tires carrying the same load, at 100 PSI - say the load is 200#. Each tire will have a contact patch of 1 square inch.. The size of the tire makes no difference - the only change will be the "pattern" of the contact patch. A wider tire will have a wider contact patch, and a skinnier tire will have a longer contact patch.

The air inside the tire, is what holds you up, and the contact patch is determined by the air pressure, and the amount of weight on it.

Another example: assuming everything is the same as the first example, except the PSI in the tire, which is now 50 PSI, the contact patch will be 2 square inches per tire.

It's all just basic math, once you know the variables.
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Old 06-16-10, 05:51 AM   #10
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Yeah, looks like from Sheldon's chart that I to be at least in the "teens" inside width wise to run a 23mm tire. I have no idea what the inside width of my rims are. I'd guess 20 or better however.

I'll check them out when I get home.
My Trek 730 still has the stock 36 hole Matrix Journey Rims, I measured them before I attempted to install the 23mm tires and to my surprise they were only like 16 to 18mm wide (inside width). There were no issues installing the 23's, they did not flatten out accross the rim and I like them. I can tell no difference in the comfort between a 35mm or 23mm on a 20 or 25 mile ride even at 125lbs. of pressure.

I would imagine one negative aspect is durability, but the speed and time savings is worth it in my opinion.
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