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Clydesdales/Athenas (200+ lb / 91+ kg) Looking to lose that spare tire? Ideal weight 200+? Frustrated being a large cyclist in a sport geared for the ultra-light? Learn about the bikes and parts that can take the abuse of a heavier cyclist, how to keep your body going while losing the weight, and get support from others who've been successful.

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Old 10-31-09, 11:26 AM   #1
yrrej
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Lower Tire Pressure equals lower speed?

My stats over the last month have started trending down. ie lower cadence, lower avg speed.

I have a specialized sequoia comp with 700x25 tires which I had been running at 120~125 psi.
My weight has been 205+-4 pounds all spring and summer.

This last month I tried dropping the pressure to 110~115 psi.

The lower pressure has certainly helped smooth the ride.

On the other hand this this has been the coolest Oct in quite a while. Most of the
month I have been wearing a windbreaker and knee warmers. ( It also has been
a bit windier than during the summer.)

This has been my first year of riding. I got the bike last November and have put
on about 900 miles since june.

On yet another hand I had my seventy first b'day this last August...

So...Does Fall bring on a slow down (in general) or should I go back to higher
inflation pressures?

Jerry
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Old 10-31-09, 11:42 AM   #2
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I've used 25s @ your wt. (my wt.) and prefer 28s; 25s are ok though and you've not had problems in many miles. I've always maxed my tire pressure, you haven't, again no problems. I DID have more flats if I didn't keep 'em high. They ride faster too from what I've noticed.
High summer temps. DO lead to higher pressure in the tire ("same" amt. air)
When it's VERY cold, I find that the tires need more air to mantain a high pressure.
It's only a significant difference with extreme temp. chages.
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Old 10-31-09, 12:11 PM   #3
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In "general" terms lower pressures will result in higher rolling resistances but it really depends on the tire design. Some tires are designed for lower pressures and actually have lower rolling resistances at these pressures. 10-15psi in 25mm tires isn't going to make that huge of a difference. There is probably some other variable or combination of variables affecting your performance. I would guess that it's probably the temps that are causing your drop. It takes longer to warm up and you generally ride slower when it is really cold and/or really hot.
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Old 10-31-09, 05:00 PM   #4
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Originally Posted by yrrej View Post
( It also has been a bit windier than during the summer.)
TAH-DAAAAAH! There ya go!..............Homey is way of on lots of things he posts here, but in this case, there may br some truth to what he says!


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There is probably some other variable or combination of variables affecting your performance. I would guess that it's probably the temps that are causing your drop. It takes longer to warm up and you generally ride slower when it is really cold and/or really hot.
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Old 10-31-09, 07:04 PM   #5
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TAH-DAAAAAH! There ya go!..............Homey is way of on lots of things he posts here, but in this case, there may br some truth to what he says!
Yep.

10-15psi won't make much difference. I guess you could say it could be measured (the amount of increase in rolling resistance), but I doubt you or I could notice it.
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Old 10-31-09, 08:07 PM   #6
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TAH-DAAAAAH! There ya go!..............Homey is way of on lots of things he posts here, but in this case, there may br some truth to what he says!

No Mr. Beanz, I'm not off on a lot of things, I'm just off...
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Old 10-31-09, 08:16 PM   #7
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No Mr. Beanz, I'm not off on a lot of things, I'm just off...

I know, I was just being nice!

But for reals, I can feel and see a difference just going form hot to cold. Cold air seems dense and thick, harder to penetrate. Warm air seems thin and ez to slice for speed....I think most people on the road are going slower this time of year.
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Old 10-31-09, 08:56 PM   #8
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Here is the flip side. Colder air is denser, it contains more oxegen per breath.

Personally, I seem to be able to make a faster pace at 40 degrees than 90 degrees.

Also the pressures in your tires will be lower at lower tempretures. So if you topped off at 90 degrees, and it is now 40 degrees, and there is no loss of air, you will have lower pressure.
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