willum44 

I just replaced a set of [mavic cxp30's with mavic hubs and Maxxis Fuse 25c tires] with a set of [campy sciroccos with older axial pro 23c tires]. The Sciroccos feel much faster than my older mavic wheelset.
I also purchased a pair of nos Axial pro's 25c which I plan to put on the new wheels. My question is:
1. What is your opinion of Axial pros 25c?
2. Should I consider keeping both 25c tires for the rear and buying a 23c or smaller tire for the front. Say a new Michelin light, or something else?
Thanks for your help in this.
Cheers all
Bill

Al1943

I'm still running an Axial Pro along with several Pro Race tires, the replacement. The Pro Race tires feel a bit softer, could be the compound or just that the Axials are older. The Pro Race tires seem to show some small weather cracks sooner, but I still get plenty of miles out of them, 1500 to 2000 on rears and 3000+ on fronts.
If it was me I'd run the 25's on the rear and put 23's on the front. But tires do harden some with age whether you ride them or not. For time trials I run 23's on the rear and 20's on the front.

Al

operator

Unless you're riding on smooth panes of glass, 25/23 will have lower rolling resistance than smaller tires.

Of the aero benefits will outweigh the rolling resistance as you go faster. Then you want to go down in size.

willum44 

thanks Al. Both my old 23c pros do have weather cracks and one has a damaged sidewall. I am leaning towards using the new 25c's for the rear only. What do you think is the fastest 23c tire out there. I only weigh 126lbs and I'm 61 so I'm not too hard on equipment!!

operator

If you're going to mismatch the tire sizes, the big one should be up front. But also realize that the rear tire wears out much faster like this. If you aren't time trialing, not much point in putting a 23 in the rear.

willum44 

Thanks operator, but I do not comprehend why the larger tire should be in front. I thought the larger should be in the rear,
as it is behind the seat tube and sheltered; plus the tire with less wind resistance would be in front.

curt in denver

What's the range of tire size a 700cc rim will accomodate?

spinerguy

I depends on the rim width & break cleareance. Usually a typical road max out at 28 & about 40 on cyclocross bikes.


At 126# you are borderline anorexic

huhenio

Small torax and shoulders, thin bones, the aero pink panther.

Boy ... I was 146 once and pretty healty ... but 126 ...

rmfnla

It shouldn't. Most of your weight is on the rear so you want the additional air cushion there.
(I'm not sure that 2mm of width on a rotating object will make any aerodynamic difference.)

I think the larger-tire-in-the-front thing is a holdover from BMX and MTB riding, where you want the larger contact patch up front for cornering traction in the dirt.

Wake up, guys; this is road.

juicemouse

Are you saying a larger contact patch up front won't improve cornering grip on the road?

And if a narrower tire does not have a (small) aerodynamic benefit, why do the pro's usually resort to 23mm widths? It has been demonstrated that wider tires can have both more grip and less rolling resistance.

jo5iah

i really dig my schwalbe fat albert 29ers - 700 x 60.
oh wait... i thought it was fattest tires...
they do go fast downhill...
in a hurricane.

willum44 

SPINERGUY:
Im also 5' 3" so with no access fat 126lbs-130lbs is okay. I eat a lot. Just do not eat junk or hi glycemic food when I'm not about to exercise. Lots of organic vegitables and nuts etc. I'm also a land surveyor so spend very little time sitting at a desk.

sngltrackdufus

the fastest tires would be 99% of who be on top of them driving them..

AnthonyG

I was going to make a simmilar comment however the guy say's he's 6'1". That bit makes me wonder.OK ignore this because I misread the posts. 126 lbs is not that light for 5'3". I'm overweight at 130 lbs and 5'1"

EDIT: OK back on subject the best advice I've seen say's to run the larger tire on the rear because that's where the weight is and only if you insist you can run a smaller tire on the front for the aerodynamic advantage but at the cost of grip.

Regards, Anthony

juicemouse

The OP says he's 5'3", and 61 years old.

DannoXYZ 

Larger contact patch is only a function of pressure, not tyre size. You do get better grip with larger tyres because you can run them at lower-pressures. Tyre size and pressure are independent factors. Although the rounder shape of the wider contact patch does provide slightly more grip than the long narrow shape of a small tyre at the same pressure and contact-patch size. But that's not as great as the difference of a larger contact patch from less pressure.

In the context of the OP's question on rolling-resistance, while splitting hairs is fun, you might as well do it the best you can. In which case, you want to minimize tire-compression. That means you should customize the size for the load its carrying. The larger tyre in the rear will sink and compress less compared to the narrower one when the rider hops on, leading to less rolling-resistance. Of the two possible configurations, bigger in back/smaller in front will be faster (and longer lasting).

juicemouse

I agree completely. Here's a link with more info for you hair-splitting types: https://www.cyclingnews.com/tech/?id=...res/conti_tech

My strategy:

My tires are also slicks for road use, which increase grip (wet and dry) and aerodynamics and decrease rolling resistance. I prefer clinchers for convenience, though tubulars offer less rolling resistance and lower weight.

rmfnla

DannoXYZ 

Hmm.. interesting.... I'd think you'd want to adjust pressure based upon the amount of tyre-compression/deflectionn. You'd use pressure to balance load vs. contact-patch vs. compression. The numbers that's been posted is a 15% sink-rate, you might want to use 10% if you want even less rolling-resistance and sacrifice some cornering ability. In any case, you'll find that the rear-tyre will end up with more pressure than the front if they're both the same size. In the case of a 25/23mm rear/front combo, they may end up at the same pressure. However, a low-pressure, narrow tyre is just asking for flats and high rolling-resistance.

juicemouse

Aerodynamic resistance, not rolling resistance, is dominant at road racing speeds. Anything smaller than 28c or so in width is going to be able to run a high enough pressure that rolling resistance won't be a huge factor anyway. At lower speeds (such as when climbing) lighter tires are an obvious advantage.

Grip is extremely important on road bikes, especially when the conditions are bad due to wet roads, debris, etc. That's why some racers elect to use wider tires than the typical 19c width for time trials under these conditions (so they can run lower pressures to make the contact patch bigger, without risking flats/blowouts).

But for the recreational rider, the performance differences are slim enough that none of this is nearly as relevant as comfort.

juicemouse

Yeah, I haven't gotten nearly that "scientific" about it. I just adjust the pressure so that there's some visible deflection of my front tire under load.



I'm not talking ultra-low-pressure here, just something like 80-90 psi front and 110-120 rear. I don't weigh very much (140 lbs.) so I've never had a problem with flats and I haven't noticed any increased rolling resistance.