ModeratedUser150120149

How much clearance must there be between the rear tire tread and the sculpted portion of the frame where the seat post and the two chain stays intersect on a carbon fiber road bike?

One LBS says any clearance is enough. Tire tread is smooth so it won't pick up things. As long as the wheel rotates freely all is well.

A second LBS says it isn't safe to have less than 3mm or so clearance.

The first LBS put 700x28 tires on the bike. The second used 700x25 tires, saying the 28s gave too little clearance.

I've ridden the bike with 28s. Seems to work OK. But I've not really tested it under all circumstances.

I respect the people at both shops. But, ultimately it is my decision.

Help

cyclist2000

I prefer to have a little space between the tire and the stays, this is incase the wheel becomes untrue while riding or breaking a spoke. I will just open the quick release on the caliper brakes and I can continue the ride until I get home to fix the spoke.

FBinNY 

There's no set answer. It depends on where you're riding and what you might pick up. t also depends on the shape of the narrow clearance. Is it a tapering wedge where a stome might get carried in and jammed, or more like the typical brake bridge where a stone might get pushed in and end up getting pinged back out. (remember the tires have give.

Lastly, safe for who? You or the frame. Tight clearances might mean some extra wear and tear on the frame, but are unlikely to cause you any injury. In any case, rear wheels getting jammed because something was caught (excluding spokes) are a very rare occurrence.

As pointed out above, the real issue with limited clearance is limited room for error such as crash or pothole damaged wheels. OK for racing, not so OK for riding solo far from home.

dabac

It's partially dependent on rider alertness and ability to abort a ride. If the wheel would go out of true, wheel rub can damage a CF frame quite fast. But if the rider reacts to that in time, and sorts it out, then it's not a problem with tight tolerances.

Panthers007

The closer the distance of wheel/seat-tube, the more quickly the bike will react to turning. They will have a rather unforgiving feel to them in the corners. With a longer wheelbase the bike will still be fast - if it's so designed - but it will have a more relaxed character. With my Puch road-bike, which has a long wheelbase, just an autonomic 'twitch' of my intent to turn and the bike gracefully obliges and you're there in a flash. With the tighter clearance frames it feels more as though I was thrown around the turn.

To each his own.

bradtx

HawkOwl, Both are correct, after all clearance of any width is enough. In your case I would prefer to have a little extra clearance because wheels don't always return from a ride as true as when the ride began.

Brad

Andrew R Stewart 

The trend to reduce clearances to as little as can be is a fool's goal. On pro bikes (those actually used in sponsered racing, not by the many more dreamers) where wheels are kept in well trued condition, your support vehicle has spare wheels if there's a wobble during the ride, the roads the race is on are most always clean and smooth, the tires are usually narrow, and any resulting damage from a stone or rub is not going to cost the rider any $ these tight clearances are fine.

But for the masses who buy their own equipment, can't keep their only wheel set true, want to use tires with better ride charictorists, ride on rougher roads, don't know how to use their hands to rub off stones while riding, ride carbon frames these tight clearances are senseless (stupid IMO).

But soo many bikes are sold with the dreamer's ego in mind and not the real day to day riding that they actually do. I have little sympathy for those who chose a bike with real tight clearances that do nothing for to make the bike faster (except as it flys off the sales floor). Andy.

fietsbob

May have designed the frame around 23mm tires /sew-ups and users fitted fatter tires.

Cross OTOH is about Mud clearance..

jowilson

I have a quick question here. How does <3mm clearance pose a safety risk? My good friend's road bike can't fit a tire larger than a 700x23c on the rear, otherwise it'll rub against the front derailleur clamp. (Just to visualize the clearances on this frame, or lack thereof). He's a hefty guy, weighing in at about 215 pounds, so 23's aren't comfortable for him, which could pose medical risks (numbness?), but doesn't pose a real safety risk, as he's mentioned a few times.

Second, how could tight clearance more wear and tear on a frame? Does the frame material have anything to do with this?

Josh

FBinNY 

I don't know why you're asking me about the safety issue. I thought I was fairly clear that I didn't believe there was one, unless there was a unique taper wedge shape that could actually jam a stone and lock the wheel (never saw one, but who knows).

As for frame wear, tires do carry abrasive grit and small stones which can cause wear in tight clearances. The top of my track fork (2mm clearance) is polished through the chrome and undergoes constant rust/polish cycles over time. The material is important because the wear rate of carbon would be fairly high compared to steel. OTOH is the lowest clearance spot was in a less critical area it wouldn't matter.

I don't think 1mm is serious, but the OP should be aware of the implications.

My track bike ridden on streets has clearance of 2mm or so under the fork, but only about 0.5mm (if that) under the brake, and I constantly hear small stones get pinged out from there like out of a slingshot.

jowilson

I was just curious. I don't think 1mm is serious either, but you may have to keep the wheels in better condition and more frequently than if you had more clearance. I personally prefer more clearance, as I've dealt with clearances of ~2mm and found myself using ratchets to tighten things down, because of the very small amount of hand room available.

Josh

Al1943

My son once had a major brand road frame that had so little clearance that the rear wheel could not be mounted without deflating the 23 mm tire.

FBinNY 

Yes, like so much else about bikes, wheelbase was subject to fashion. I also remember when this went crazy, while horizontal dropouts were still in use. It reached the point that you had to deflate tires, or if it wasn't too extreme, give the rear wheel a sharp shove forward against the tire and have it pop past the lower front of the dropout.

A friend had one of these, and asked me to help since he raced and fast wheel swap was paramount. I ended up filing off almost 1/4" off the lower front of the dropout, and filing hat I left to a wedge. To install a wheel with full tire, he'd position the wheel, an shove the frame down hard popping the wheel around the dropout.

It was near the end of this short wheelbase era (curved, notched or interrupted seat tubes) that we started seeing more vertical dropouts.

Al1943

Interesting, but my son's frame had a vertical dropout, built about 10 years ago.

FBinNY 

I'm surprised that this is a problem with verticals. Since the point of nearest pass is above the dropout, the wheel should get closer as it slides into the dropout, and reach the nearest position when home.

That's unless the dropout is tilted so the wheel slides back slightly as it seats. (semi vertical).

Sounds like someone wasn't thinking.

gregf83 

I don't think it's abnormal. I had the same issue on a Bianchi. If I mounted 25mm tires they were fine when mounted but when taking them off they rubbed. I just looked at my Tarmac frame and I think larger tires might rub on the chainstay cross brace.

Al1943

We no longer have the bike around and the manufacturer (Specialized) no longer makes this model. There was more wheel clearance when the wheel was fully seated in the dropouts. As I recall, the tight spot was where the chain stays met the seat tube, and once above that spot there was enough clearance for pumping up the tire. The dropouts appeared to be vertical.

FBinNY 

I don't doubt you, b ut it shows that someone wasn't thinking. The beauty of vertical dropouts is that the entry slot can be made exactly perpendicular (or even at an obtuse angle) to the nearest point of close clearance. There's absolutely no reason that the wheel should be closer then slide back on entry.

OTOH, checking the angles, and attaching dropouts at the right angle is a minor detail that requires thought. It falls into the category of sweating details and some are better at it than others. Unfortunately, with the high rate that models change, and the focus on innovating and/or having a certain cool factor, sweating details gets pushed to the side.

Bike companies used to beta test by sending stuff to a corps of friendly PIA sticklers in the dealer network. Nowadays there's not time for that, or they just don't care and let their consumers do the beta testing.

Camilo

Yea, my 80s Sannino has the same issue mounting the rear wheel. I can sometimes pop it in, but it's much easier to deflate the tire.

The bike is very quick turning - I'm still trying to decide, but so far don't like that aspect of it. I've only got about 1,000 miles on it though. I think I'll move the rear wheel as far back in the dropout as I can to see if it mellows out the handling a little. It won't help the wheel installation issue though. I was actually thinking of doing what you did (remove some of the dropout making it shorter). It's quite a long dropout, but I'm reluctant to do something like this to an old frame that's in pretty darn good shape. I did spread the rear spacing, so it's not like I'm keeping it original.

Eric S.

I've been running 700x28 tires on my 2004 LeMond Buenos Aires for quite awhile now. Haven't had any problems so far.

ModeratedUser150120149

Interesting how those wheelbase posts crept in. Anyway I've now had a chance to physically see and ride both bikes and talk face to face with the people at both shops. On one 700x28 tires will mount and spin just fine. On the other they will not. The tire tread touches the frame at the junction of the seat stay and the chain stays. Lateral clearance is fine on both.There seems to be some difference of opinion on How Much Clearance Is Enough. But there is precious little analytical information.

The unsafe comment came from one shop thinking I was going to ride a bike where the tires were rubbing. He did not realize that the larger tires did have some tread clearance on the bike at the other shop. Once we were face to face we got mutual understanding.

The key people in both shops agree that on a road bike any clearance between smooth tire tread and the frame is enough. Some bikes have sheet-of-paper clearance and some have more. There are theoretical advantages to all. Practically, except for certain specialized situations it probably doesn't matter.

The Why the Difference question remains. They are the same make and model bike but two different production years. So, probably there is a slight difference in the dropouts.

Body

I got just my ti frame from the builder but was surprised about the distance between seat tube and 25 mm tire, see picture. I have send back the frame and hope they will fix it.

Will be 3 mm minimal distance enough??

HillRider

Did you tell the builder you planned to use 25 mm tires when you ordered the frame?

Body

Unfortunately not.
Now we have to look for a solution. The chain stay is 406 like my old bike, I used all the measurements of my old frame, thats why I was surprised. Anyway, shall a chain stay of 408 suits better?

HillRider

Even if the chain stay length is the same as your older bike, the seat tube diameter may be larger and that would reduce clearance., Also not every "25 mm" tire is the same and some are larger than others. A 408 (2 mm longer) chain stay would improve the situation but I'd try to go still longer if possible. Why limit yourself when you have the opportunity to improve the versatility? Unless this is a crit bike, short chain stays offer no advantage.