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PostPosted: Mon Jul 11, 2011 12:22 am 
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Joined: Sat May 12, 2007 3:40 am
Posts: 412
Location: Triange, NC
For the past two years I've been running Conti 4000 in 25 and pumped to 80#. I weigh 180# and no pinch flats. In fact I've only had two flats in two years and both times it was the valve stem/tube interface. And my bike rides sublime. I never intend on going back to 23s except maybe for time trials.


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Posted: Mon Jul 11, 2011 12:22 am 


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PostPosted: Tue Jul 12, 2011 2:07 am 
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Joined: Mon Feb 02, 2009 7:24 pm
Posts: 23
Location: Northern VA, USA
In addition to a general lowering of tire pressure, what sort
of pressure difference are folks using between the front and
rear tires? I weigh 170 lbs, and use 95 in the front and 110
in the rear of my 25mm Vittoria's, and have been thinking
about lowering both.

Thanks in advance.


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PostPosted: Tue Jul 12, 2011 4:54 am 
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Joined: Thu Sep 30, 2010 5:50 am
Posts: 315
+1

I am 160lbs and am running the Conti 4000S 25C at 95 front and 105 rear. I'd be interested in hearing what others are running.

I was working on a bike and was installing a michelin cheapy tire (25c) and it's sidewall said max pressure was 102 psi :shock:


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PostPosted: Tue Jul 12, 2011 6:02 am 
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Joined: Sat Jun 04, 2011 3:05 am
Posts: 43
I had been meaning to post about this.

Original tires - Continental Ultra Race 700x23c
"New" tires - Continental Grand Prix 4000s 700x25c

I got the 25c's to see if I could run lower tire pressures while avoiding pinch flats ultimately so I could descend on bumpy technical roads with more confidence. The 23c's at the old tire pressure of 95-100psi were skipping over bumps mid corner which wasn't a good feeling. Then I lowered them a little too much - felt great over bumps but managed to double flat on a nasty pot hole that others ran over and didn't affect them.

Now I have the 23c's at what I think is a good tire pressures that don't feel like they're so low as to bottom out hitting bumps or feel too hard and skip over bumps in turns. I'm currently running 87f/91r. I'm pretty happy with the setup but if I could get more comfort over bumps that would be a bonus.

I experimented with the 25c's and right away they felt so much more comfortable. On bumpy descents the bike felt rock solid and didn't have any troubles with mid corner bumps.

There's a nearby paved bike path that I always wanted to ride. I found that it's a bit old and beat up but basically flat. The 25c's handled the bumps great! There's a 15mph speed limit and I noticed that it was taking more effort to maintain that speed then usual. I also noticed they didn't accelerate as well. I swapped tires the next day and sure enough the 23c's felt effortless albeit much harsher.

I thought maybe I had the 25c's too low and experimented adding 5psi at a time. I eventually pumped them up to 105psi. Between 95-105psi they felt better, more like the 23c's but there was still a bit of sluggishness. It didn't make any sense to me that I should have to put more air into the 25c's than the 23c's - it should be less.

So I tried 25c on the front and 23c on the back. That was better still but overall lacked the feeling of effortlessness having 23c's all around gave me.

I've gone back to 23c's all around. To me the lower resistance is more important than the added comfort.

I guess the other difference other than size is the tires themselves. I would've thought the GPs would have lower rolling resistance than the Ultra Race but maybe that's not the case?


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PostPosted: Tue Jul 12, 2011 7:35 am 
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Location: Los Angeles / Glendale, California
With motorcycles, it is common that the front tire is less wide than the rear.
Similarly, a few racers on one of my teams run 23c up front, 25c on the rear. Not sure about what pressure though.

Similarly to that, Continental's set of Attack/Force vary between front and rear widths. Intentionally.


Thoughts?

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PostPosted: Tue Jul 12, 2011 6:40 pm 
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chaos888 wrote:

I've gone back to 23c's all around. To me the lower resistance is more important than the added comfort.



Just to get this straight, it seems to be accepted that (at the same pressures) 25c tyres will have less rolling resistance than 23c simply because they suffer less sidewall deflection.

I ride both but really prefer 25c which I discovered maybe three years ago. I'm currently running the Michelin Pro Optimum which are front and rear specific. The front weighs 210g. The rear 254g. The durability is superb as is the ride. I'll happily take the extra little bit of weight for the ability to descend at previously uncomfortable pace.


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PostPosted: Tue Jul 12, 2011 7:41 pm 
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Joined: Sat Jun 04, 2011 3:05 am
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airwise wrote:
chaos888 wrote:

I've gone back to 23c's all around. To me the lower resistance is more important than the added comfort.



Just to get this straight, it seems to be accepted that (at the same pressures) 25c tyres will have less rolling resistance than 23c simply because they suffer less sidewall deflection.

I ride both but really prefer 25c which I discovered maybe three years ago. I'm currently running the Michelin Pro Optimum which are front and rear specific. The front weighs 210g. The rear 254g. The durability is superb as is the ride. I'll happily take the extra little bit of weight for the ability to descend at previously uncomfortable pace.


That is the conventional wisdom so I really don't know what was going on. I've changed tires so many times trying different combos and retesting over and over again. I would love to get a set of Ultra Race 25c's to see if it's the tire but I don't want to throw more money at this just to experiment.


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PostPosted: Wed Jul 13, 2011 2:05 am 
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Joined: Fri Nov 17, 2006 12:04 am
Posts: 66
I was running the conti attack (22)/force(23) on my Lynskey then switched to vittoria open pav'es(24) with vitt latex tubes. My rides generally range 25 to 50 miles. I feel more sure of myself riding the pav'es and notice no decrease in overall performance. It feels plush, yet no lack of feed back. I weigh 180 lbs. and use 105psi in front and 110 in rear. I really like this set up. :)


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PostPosted: Wed Jul 13, 2011 7:46 am 
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Formerly known as wassertreter

Joined: Tue Apr 12, 2011 8:08 am
Posts: 1946
Location: Pedal Square
prendrefeu wrote:
With motorcycles, it is common that the front tire is less wide than the rear.
Similarly, a few racers on one of my teams run 23c up front, 25c on the rear. Not sure about what pressure though.

Similarly to that, Continental's set of Attack/Force vary between front and rear widths. Intentionally.

Thoughts?


I used to run 23mm Schwalbe Duranos at 8bar, now moved to Attack/Force at 7. Feels very nice but since I also changed the bike I can't compare directly. Definitely would like to try 25mm ones around 6bar front / 6.5 rear. Streets are very smooth here. Rider weight is around 75kg.

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PostPosted: Wed Jul 13, 2011 1:38 pm 
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Joined: Wed Jul 13, 2011 1:21 pm
Posts: 12
I think that in general 700x23 tires are more aerodynamic (obviously this depends on the brand of tire, and rim, but speaking in broad generalities I think this is true). While 700x25 tire tend to have less rolling resistance when comparing the same tire in 23's and 25's. This is why a narrower in front where aerodynamics matter more and a wider tire in the rear for lower rolling resistance makes sense to me. I'm currently running 20's in front and 23's in back, only because I got them at a discount, I had 23/25 before. As an added bonus the wider tire in rear tends to absorb more of the jarring bumps that would otherwise be transmitted to your bum.
Joe

As an aside I've never seen any hard numbers for when the power saving of an aerodynamic front tire overtake the watts saved from the lower rolling resistance of the wider tire. So I don't know what speed this might occur at... anybody have any insight into this?


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PostPosted: Wed Jul 13, 2011 2:01 pm 
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Quote:
+1

I am 160lbs and am running the Conti 4000S 25C at 95 front and 105 rear. I'd be interested in hearing what others are running.

Another +1 on that.
I am actually using 23 right now, but I have just come off some 25s and I really liked them.
One problem I have is frame clearance. a 25 just barely fits.....and I mean barely.


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PostPosted: Wed Jul 13, 2011 3:38 pm 
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Joined: Thu Feb 03, 2011 2:28 pm
Posts: 380
I'd like to try a 25mm on the rear.

My favourite clinchers are Conti Supersonics or Veloflex Corsas, but the widest size they're available in are 23mm and 22mm respectively. Does anyone have any suggestions for a 25mm with a nice light supple casing?

I was completely unimpressed with the Schwalbe Ultremos I tried recently, so won't be using them again.

I see that the only high-end Vittorias that are available in anything bigger than 23mm are the Corsa Evo CX.

Anyone have any experience with them? Other options I should consider?


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PostPosted: Wed Jul 13, 2011 3:47 pm 
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Joined: Tue Jul 27, 2010 8:31 pm
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josephjcole wrote:
As an aside I've never seen any hard numbers for when the power saving of an aerodynamic front tire overtake the watts saved from the lower rolling resistance of the wider tire. So I don't know what speed this might occur at... anybody have any insight into this?


I'd love to see that! I wonder if the choice of fork (and it's clearance) would impact any results? I'd also love the aero brains on WW to explain why (if there is an advantage in 23mm tyres) I consistently go noticeably quicker downhill on 25's :wink: On my list of priorities aero comes somewhere just below spoke colour.


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PostPosted: Thu Jul 14, 2011 4:53 pm 
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Joined: Fri Dec 15, 2006 7:45 pm
Posts: 3321
Location: Natovi Landing
prendrefeu wrote:
With motorcycles, it is common that the front tire is less wide than the rear.
Similarly, a few racers on one of my teams run 23c up front, 25c on the rear. Not sure about what pressure though.

Similarly to that, Continental's set of Attack/Force vary between front and rear widths. Intentionally.


Thoughts?


In December, Jan and Feb I ran Conti Force (24mm) front and rear and really rated it. Longevity wasn't great but in all other respects a very good clincher. Weight was low - 199g IIRC. Comfort increase over 23mm is noticeable.

I personally find the front tyre has a bigger bearing on comfort than the rear and if you're doing rougher roads having wider up-front makes sense as long as the aero penalty is bearable. Given the choice, for example, of 23F and 25R or 25F and 23R to ride pave, I'd choose the latter.


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PostPosted: Thu Jul 14, 2011 4:55 pm 
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Joined: Fri Dec 15, 2006 7:45 pm
Posts: 3321
Location: Natovi Landing
airwise wrote:
josephjcole wrote:
As an aside I've never seen any hard numbers for when the power saving of an aerodynamic front tire overtake the watts saved from the lower rolling resistance of the wider tire. So I don't know what speed this might occur at... anybody have any insight into this?


I'd love to see that! I wonder if the choice of fork (and it's clearance) would impact any results? I'd also love the aero brains on WW to explain why (if there is an advantage in 23mm tyres) I consistently go noticeably quicker downhill on 25's :wink: On my list of priorities aero comes somewhere just below spoke colour.


Think of the air hitting the wheel rim and then stalling on a bulging 25mm tyre, or the air hitting the wheel rim and flowing smoothly over a 21mm tyre that does not bulge wider than the rim.

You should re-order your priorities!


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Posted: Thu Jul 14, 2011 4:55 pm 


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