bbeasley

For no other reason than reading on the Internet, I bought a set of Conti GP 4000s IIs in the 25mm width. I put them on at the same 100 psi I ride my 23s (Conti GP 4000s) at. Off I go on my usual Wed ride. This is a fast group, for me, and I'm where I can hang on mid pack, a bit of pulling at the front but not able to do my fare share yet.

On this ride it felt like I was dragging a dead body behind me. Folks who I can usually beat to our first rallying point are passing me up and asking if I'm OK? At the stop I get off the bike and check to see if the brakes are dragging. Seriously it was that bad. Saturday is attempt #2 , same group, same results. At 110 psi I'm thinking a hub is seizing and I get spit off the back and end up finishing the ride with a slower group.

Today my new Flo 30 wheels came in. They're 24mm wide and while built and tested for 23mm tires I thought they might be a better fit for the new tires. Mounted up and same results, my bike won't get up and go. It feels like I'm riding into a 15 MPH headwind. I rip off the offending tires and mount up my 23s - it's like someone put an electric motor on the bike and with every pedal stroke I get a 50w boost. It feels light, responsive and very fast.

I don't know why my experience was so bad and different than other folks. The 25s are a plush ride and the Conti compound has that same killer grip in the corners I expect, however for me it's 23s, I'm done testing.

MattFoley

The physics of rolling resistance disagree...

Tech FAQ: Again, bigger tires roll faster! - VeloNews.com

chaadster

I can feel ya. 25s on my Velocity Aeroheat (or Aerohead, I can never remember which!) felt slower than 23s; I never had a group ride fail on your level, but the 25s certainly never felt fast, and I don't recall setting any PRs on 'em either. Plus, I could feel sidewall flex when cornering or hard out of the saddle on the Michelin Pro3 Optimums. They're now relegated to winter/spring rides, and I'm otherwise 23s on a wide rim (mostly) or on standard Mavic 19mm rims.

chaadster

Not really...there's more to rolling than Crr. Rim/tire aero cost plenty; Zinn said above some speed it costs MORE than Crr gain. We don't know how fast the OP was riding.

Sullalto

I'd check your brakes again. Mine have needed adjusting every time I changed tire width.

achoo

It's just one ride. Without a powermeter to measure what you were putting out, there's no way to tell what the cause was.

MattFoley

True, but either way the difference is at most a couple of watts, down to fractions of a watt, depending on conditions. Maybe a big deal for a pro trying to gain a second on a TT, but I doubt you'd ever be able to tell the difference under any conditions other than a high-level racing.

bbeasley

Articles like this is why I tried.

bbeasley

These rides average 19.7 to 20.5 MPH. If I remember correctly the industry standard for wind tunnel testing of wheels is 30 MPH.

bbeasley

I fully understand how something can "feel" fast or slow and not necessarily be. My racer buddy proved to me, using a PM, that I was just as fast at 100 psi as the 120 psi I was hooked on. Of course the ride was much better at 100 psi and over time nothing changed regarding my number of flats.

With the 25mm tire issue I was so disappointed I checked everything. I verified, via Strava, the group didn't speed up. I checked wind speed and direction. On the second ride I was very careful with nutrition and sleep. The wider tires just sucked, not sure why. Now even if proved it was laser beams from space monkeys, mentally I'm a none believer when it comes to wider tires. I'll take a placebo that works over science that doesn't anytime

cb400bill

I find your post interesting as I set a PR tonight on a club ride using 25mm Conti GP4000S tires.

I had the 23's on previously.

brawlo

There is something wrong here that is not the tyres. I would definitely be checking your fork clearance on the front and also checking the clearance on the rear both in between the wheel and the seat tube and in between the chainstays.

I would go back to 25mm tyres in a heartbeat if I could run them on my Felt '12 F4. I was running 25mm GP4000 tyres on A23s on my old bike and they were definitely not any slower than my 23mm tyres. When I was looking at a new bike I had a look at the Cervelo R3. It ended up being too small, but one came into the LBS for repair so I curiously tried putting my 25mm tyred wheels on it. This is supposedly a cobblestone style of bike, made for riding rough roads, on which you would of course run wider tyres??? The front wheel wouldn't turn, the tyre was wedged to the top of the fork and the rear had less than 1mm to the seat tube! So that was the R3, but now onto my F4. I carried over my A23 wheels with 25mm Contis from my old bike. After riding less than 200km, I took the rear wheel off to change the cassette for a 11-28. I noticed the tyres had been rubbing the chainstays. There is only about 1mm of clearance either side of the tyre. If I hadn't noticed this so early in the piece, I could be looking at an expensive repair, replacement or even worse.

My next bike which I have already started researching for will be as stiff as the F4, but I want clearance to run 25mm tyres again. I'm heavily limited with what's on the market due to my size, and the top contender I can't even get here in Oz. So I have some time to find a way to get one here... Canyon!

Dunbar

Something is amiss. The 25's would have slightly less rolling resistance at the same pressure. The aero difference is 1-4w at 30mph which I doubt you'd feel. Maybe the tires were rubbing the brake caliper or frame?

FLO Cycling

Can I ask what frame you are riding?

Thanks,

TrojanHorse

well, it should be glaringly obvious that you did SOMETHING wrong. I'll assume you know how to check for frame and brake rub but clearly something was interfering somewhere, you just didn't see it.

There is no way 1mm on either side would make that big of a difference otherwise. I've used plenty of 23 and 25mm tires and the only real difference for me is that I can inflate the 25 tires a little lower. Other than that, no drag, no electric motors, none of that.

Astrozombie

.08'' of a difference, I find that hard to believe. Try 10 rides on one and 10 rides on the others....

youcoming

Ride what you like, end of story no expaination or voodoo science required....lol I'm stuck on my Conti Comps with a 22 on the front and a 25 on the back. Fiance went from 23's to 25's this year and she will never see a23 again. My son races and about 60% of the field including him run on 25's, I'm no expert but I would argue in 5 years 23's will have gone the way of 19's.

Mark Stone

Sounds like the "scientific method" was correctly used here - however I don't understand why this small of a width difference would make that much of a difference. So I'm going to add another thought: Bad tires. Maybe the construction of the tires is off? Just a thought . . .

bbeasley

Okay guys, I've got my dunce cap on and am sitting in the corner. After posting this thread, I remounted my rear 25mm tire as it was the closest to rubbing. With the bike on the stand it has minimal clearance between arch of the rear brake and center of the tire. With me, lard ass, on the bike it rubs ever so slightly. Close inspection reveals the rear significantly worn compared to the front.

I built my bike, buying first a frame set and then swapping components over from a previous bike. Live and learn. I'm really glad you guys weighed in on how ridicules this all sounded, otherwise I would not have figured it out. I guess my options are 1. ride 23s, 2. get a rear brake with more drop? Higher clearance or whatever it's called.

brawlo

Sounds like you'll just have to ride 23s. Your rear brake will be limited by the pivot point rather than the reach of the caliper arms, which is what a long reach brake gives. There may be some different brakes that have less material at the underside of the pivot that may allow you to run 25s.

Or of course you could just go and buy a new bike..... Yeah you need a new bike. Thinking about it, it's the only obvious solution!

TrojanHorse

That would be a pretty hard thing to notice, especially if it requires your butt on the seat. Don't feel bad. It's possible that there are other brakes out there with more clearance between the pivot and the bottom of the arms, but who knows. If 23s don't bother you, ride them in good health.

You could probably get a pretty long thread going on the dumb shade-tree mechanic mistakes the rest of us have made...

bbeasley

Yeah, I'm a dufus. The way I caught it was by jumping on the rollers with the resistance set at zero. If there's something wrong you'll know it quick, sometimes after a quick trip to the garage floor.

baron von trail 

I figured something was indeed rubbing. Glad you located it.

sstorkel

You might measure the tire and see how wide it actually is. When I bought my Cervelo RS, the shop told me the fork would clear 25mm tires. Swapped in the wheels from my old bike... and the front wheel would rub the fork. Thought maybe it was a fork issue, so the shop swapped forks. Front wheel was still rubbing the top of the fork. Brought the wheel and the fork to the shop, they measured the tire, and even though labelled 25mm it was actually about 26.5mm!

If it turns out that your tire is a bit over 25mm, it might be possible that there are other brands that run more true to size...

jimxyz

I thought it was your tire rubbing on the chain stays - i had that happen to me as well. My bike is about 4 years old and the clearance is just not quite wide enough for the wider tires (some anyway. Depending on the wheel and tire choice it seems that some tires are wider when inflated than other). I'm looking at new bikes and I am checking the geometry carefully as I want to run wider tires if possible.