What tires and tubes are you using? Some tires are much stiffer than others, plus latex tubes are much smoother rolling than butyl. Luckily, low crr tires are the smoothest rolling, so you get a better ride and go faster as well.

Chad

I'm using Michelin Pro 3 Race, but with butyl tube.

I noticed as much difference switching to latex tubes as I did swapping out the conti tires for the PR 2's. When I first started using that combo I would air it up to 105 and it would still feel soft. Out on the road it felt really smooth and it was definately faster than anything I had used previously.

Chad

bump...

Try to get some more opinions. Thanks.

I don't think opinions have changed since April, 80-100 psi depending on rider weight. I have a lot of respect for what Psycholist has to say and he's about your weight, so I'd say 90 psi for you. Yes, I know this link is your previous thread, it may help someone else reading this for suggestions. I've been playing around a bit with pressures 95-105, but I'm about 25 lb heavier than you.

http://forum.slowtwitch.com/...h_string=c2;#2308701

Have you tried another pump or the ever-so-accurate thumb test? I can't believe you feel beaten up at 80psi. Is there any chance your gauge is off? If you're riding "regular" road wheels at 120 psi, how can anything feel harsh at 80?

Thanks for the props QRNub.

Actually, some of the thinking may actually HAVE changed since April. I believe Tom A. and AFM have played around with the C2s a bit and found some really nice Crr results at pressures in the 125 psi neighborhood. I hope they'll chime in and elaborate.

That said, my purpose in buying C2 wheels was for a couple of long course events I do that have really crappy chip and seal pavement for long stretches. One race, in particular, I've done each year for about the last 5 now. Last year on the C2s I beat my previous best time by 3 minutes (HIM) and I attribute that mostly to the fact that I wasn't beat to death by the road surface. I was still fresh over the final 15 miles where the pavement had really taken its toll in prior years. Tom A. argued with me at the time that it wasn't the C2 concept so much as merely running a more appropriate tire pressure. But I argued back that 80 to 85 lbs feels really squishy and squirrely on a 19mm rim and doesn't feel nearly so squirrely on a 23 mm rim.

Bottom line. The way I'm using the wheels now is, for a TT, I'm going with around 125 psi. For a long-course event, I'm going with 85 psi or something in that neighborhood. Does that mean that's the best way for the OP to go? Who the heck knows.

I must add ... I'm also about 150 pounds and I race and train on some of the crappiest roads on the planet. I can't understand how the OP can regard the ride of PR2s at 80 psi on C2 rims as too harsh.
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Bob C.

The "science" on any matter can never be settled until every possible variable is taken into account.

if 80psi on that tire is too stiff and bouncy for you I would suggest either a beam bike or perhaps a sport involving large boats instead of bikes

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

perhaps his pump is reading half pressure

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

I tested both a VF Record and Bonty RXL Pro clincher with latex tube on a Zipp 404 (narrow), Velocity Aerohead (medium width), and a C2 Jet 9 (?) (wide) rimmed wheel. Didn't find any significant difference in Crr at 120 psig but didn't run any lower pressures. The measured tire width was greater by ~ 2 mm for each tire on the C2 compared to the 404. Bob - not sure if you have the Jet C2 which of course is a spoked wheel which I think would be more comfortable than a more rigid "solid" disc.

Maybe it's 80 bar. I think that would be rather harsh. :-)

on advise from hed i run apx 90-95 psi
however i cant understand the logic of running lower psi due to it being a wider area, surely pressure is pressure irrelevant of width and contact between rider and ground is bike-wheel-tube/air-tyre-ground goin by this 90 psi is 90psi ,120 is 120 irrelevant of witdh or volume of air
maybe somebody can explain if i am wrong

My 140 pound friend rides his C2 Jet 60's at 120psi, and he's fast as hell. Not very scientific, but according to his bike splits, I'd say it works for him.

maybe somebody can explain if i am wrong

You're wrong!

Just kidding.

I don't think you're wrong, but I shouldn't be your final authority. I think that, for any given pressure, once you're on a tire mounted to a wider rim you're going to have widened out the contact patch (and theoretically shortened it's length in the direction of travel ... which I think is the relevant concept). As AFM pointed out in his post above, testing would seem to indicate that the 2mm difference relative to the contact patch has no discernable effect on rolling resistance. As you say ... going with lower PSI wouldn't seem to accomplish anything except enlarging the contact patch.

So what's the point of running a C2 and running it at 80 or 85 psi? To repeat what I said earlier, I think the point is secure handling and comfort at a lower psi without the risk of puncture that you'd have running the same psi in the same tire on a 19 mm rim. I don't have research to demonstrate that, but I do have a year of riding and racing on C2 wheels. If I try to run even as low as 90 psi in tires on my 19mm wheels, they're more prone to pinch flats, they feel squishy and they don't corner well. On a C2 rim, 90 psi is a higher volume of air in the same tire and the sidewall shape is different. The result is a less-squishy feel, but still comfortable (unless you're the OP, I suppose), it's not as prone to pinch flats and the handling is simply superb.

Over the years I've acquired an arsenal of wheels. If I'm racing long-course and/or I know there's going to be a significant amount of dicey pavement (common in my area), The C2s are my wheel of choice. I don't think they're any faster and they may, in fact, be a bit slower in terms of pure speed. In terms of how they influence wear and tear on your body and how that influences your speed over the closing miles of a long-course event ... there's the key benefit.

sorry i dont understand :-) only kiddin
i agree running a lower psi may well be better for comfortablity and loss nothing in terms of rr
however what my point would be we dont need to be on c2 rims to avail of this and
what do we gain by running c2 rims
by they way i do have a c2 jet disc and like it but apart from the whole "lightbulb" effect on the tyre
to me lower psi is not relevant to c2's and are we just be sold it as a red herrin

I am a little heavier than you (167 lbs) I currently run 90 - 95 lbs in my Jet C2's. I am running PR3 tires with butyl tubes.

Given that I choose a 23mm tire before anything else loosing the light bulb is going to be more aero. A by-product of loosing the light bulb (given my original choice to run 23mm and therefore the need for a wider rim in order to loose that light bulb) is a little wider tire contact patch that may or may not be faster in terms of Crr. And now that I am wider I am probably more comfortable given the new lower pressure requirements. Others would say why not just run 19's on your old rim and I would say I want to be more comfortable on my 23's so I run a rim that is optimized to my 23mm tire choice. This doesn't necessarily mean that my choice is faster than a system optimized to a 19mm tire though. It is just faster for me.

to be honest you don't know which is faster for you, really.

switching from 23mm PR3s to 19mm bontrager aero TT had no noticeable comfort change for me, for what its worth.

but then, some people here seem to be extremely sensitive to comfort issues =)

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

Yes I do notice a comfort difference when running different tire pressures and widths. I think more people would agree than not. And given that I choose 23mm I do know what is faster for me once I have made that choice. Do I need to say it a third time?

You can say it as many times as you want but unless you have done some controlled power meter testing you don't know which is faster for you. I don't imagine it makes much difference either way really

=)

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

I can see from your above posted switch to the 19mm bontrager aero TT tire that you too probably believe that rim/tire interface is important. I am looking for the same thing as you just in a 23mm tire as I do feel the ride difference. I guess my "butt-o-meter" is more sensitive.

i agree we get to run 23mm with less aero loss and possible better rr but i still dont get it why it is the c2 rim that allows to run lower psi
surely a set psi is the presure in tyre irrelevant of witdh of tyre
why is it the c2 rim makes any differnence to this????people advise 115ish but if c2 rim 95ish????? why

Because Pressure=Force/Area, as area decreases pressure increases and vice versa.

OK ... HERE'S WHY (as explained to me by a HED representative). It's very simple.

Same tire and tube on a 23 mm wide rim will hold a higher volume of air than it does on a 19 mm wide rim. Somehow this is supposed to allow you to run lower pressure and get away with it.

Don't shoot me. I'm just the messenger. As I think I've quite clearly stated in several previous posts, I use the C2s for long course 'cuz I'm comfortable on them at lower pressures and this saves me from a lot of pounding on the crappy roads around here that wears me down. I know the esteemed Jackmott seems to imply that such comfort concerns aren't legitimate. I invite him to come to where I live and do a few training rides ... and to come do the HIM I'll be doing in early October. That one has 20 miles of road that'll rearrange the fillings in your teeth. I invite him to come back and try it after he's reached his 50th birthday and see how much more fun it is then.

im at around 190 and have been riding the JET60 C2 for 18 months now. i just upgraded my tires to the paired combo (22 front/24 rear) and found that 100psi front / 110psi rear works good for me with limited bounce and enough grip to hug the road around fast corners (even in the wet).

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