crazyravr

Basically feels like I am going over a bump. This happens on smooth road. Any ideas?

alcjphil

Tire not seated properly?

Iride01 

Or you have too large a tube and it's folded over on itself. In which case the tire won't be inflated properly in that area.

Possibly a blister between the tire tread and casing. But I haven't ever had that on a bike tire. I have on a car tire.... long long ago when tire technology wasn't as good and when I couldn't afford new tires and bought used tires.

FBinNY 

Hang or hold the bike with either wheel off the floor. Put a finger just above the top of the tire, spin the wheel, and look for a high or low spot. Investigate if you find one. Repeat with the other wheel.

KLiNCK

Over-tensioned spokes can be a possible cause for a rim to "ovalize" or develop a "hop"...
More information/background required to make an educated guess.
There are many "possible" causes.

Unca_Sam

I'll agree with FBinNY . It seems like you have a flat spot on one of your wheels. You can use the tail of a zip tie or a straight edge across the fork or seat stays to check significant deviation from average, or just watch the sidewall of the rim vs a fixed reference point, like your brake pads if you use rim brakes. If the sidewall doesn't deviate more than 1/8" it's likely the tubes and tires.

From experience, a feeling like a bump every rotation indicates a low spot, you feel the bump as the trailing edge of the dip rotates against the pavement.

zedda

I experienced recently a defective (poor quality) new tyre which was initially round and symmetric, but bump it somewhere along the way and it just goes 'out of center', developing a spot where it even visually looks narrower. Tube was fine, it didn't have anything with it. I had to remount the tyre to make it round again, but for how long would it stand round before something similar occurs agains? So I just switched it to a better quality tyre. It was a cheap Bontrager 25x700C with wire. It's wire diameter was a bit too wide and I suspect this is what made something such possible.

JohnDThompson 

Either a poorly seated tire or a damaged rim can do this. Watch the wheel as it rotates. If the tire seems to hop in one place, but the rim itself does not (watching the rotation as it passes through the brake pads can be a useful indicator), then the tire is not fully seated or too deeply seated at the hop. The fix is to deflate the tire and re-seat it. Sometimes, a hop can be caused by tire casing failure; in this case the tire width changes at the hop, as casing fibers pull apart and allow the tube to expand more. If you find this, you will need a new tire.

OTOH, if you see the rim itself hop as it passes by the brake pads, the rim is not radially trued, or it is damaged. Damage is more likely in my experience, as radial truing problems are seldom abrupt enough to create a perceptible hop while riding. If you find this, take the wheel to a bike shop to see if it can be fixed, and be prepared to buy a new wheel or pay to have the existing wheel rebuilt.

KerryIrons

Echoing the other posters and quoting Yogi Berra: "You can observe a lot by watching." Slowly spin the wheel and look at what is happening. There is a small rib on the side of the tire that should be evenly spaced from the rim. If the tire is not seated properly, you will see this rib "dip" at some point. If there is a hop but the tire is seated properly then you should be able to see the rim moving up and down relative to some reference point on the frame (like a brake pad)..

crazyravr

Thank you guys. I will investigate and report back. I will start with with the simple, tire check, tube check and then see if the wheel somehow got damaged. Never had such an issue before. Could be after my recent flat tire / tube replacement. Maybe I did not get the tire on properly.

FBinNY 

You nailed it, as did post 2.

You would have gotten more on point answers all around if you'd mentioned the tire change to start with.

Spin the wheel slowly, eyeballing the tire's molded reference line just above the rim.

davidad

I doubt that that is the case. If the spokes are too tight for the rim it will taco.

Schweinhund

Well dang, if it tacos can we eat it?
Jokes aside, I have never, ever seen a rim taco from over tensioned spokes. Lots of cracks around spoke holes, some pulled through the rim, but not one single taco. I'm not saying it's impossible, just implausible

FBinNY 

Not counting those folded in a crash, the new wheel taco is best understood by imagining a ball cradled at th Ed top of an M. It stays put because it has to go uphill in either direction before it can fall off.

Likewise, a built wheel is stable because moving the rim to either side would increase the tension of spokes on the opposite side. Once past the point of no return it will taco, because that condition has the lowest total spoke tension.

However a highly dished wheel is like that ball balanced on an M with a low side. So, comparatively less force is needed to push the rim past the right flange and cause a taco. Not high tension, but uneven tension can leave an area not well braced, and prone to taco.

IME, I've seen this happen when builders get carried away stress relieving newly built wheels, but never without some help to start the process.

davidad

Read Jobst Brandt's book The Bicycle Wheel.

KLiNCK

LOL! EXACTLY! I find an open mind is invaluable when trying to evaluate very vague diagnostic symptoms.

FBinNY 

I haven't read more than a few snippets, but based on 50+ years of experience, I'm willing to bet some imported beers that if you progressively and uniformly add tension to a built wheel it will not taco until either a spoke snaps or tears out of the hub or rim.

Once that happens the unbalanced load may (depending on spoke gauge and rim rigidity) pull the rim over far enough to taco.

It's like the ball on the M - which must go uphill before it can go down.

cyccommute 

Does your tire look anything like this? It will have kind of a “S” shape to it…a bit like a snake moving along the ground. If so, you likely have broken one of the cords in the tire which means the tire can’t hold its shape. This is more of a problem on low thread count tires because the each thread is doing more work than on higher thread count tires.



In extreme cases, the tire can split. You can see in this picture that the cords aren’t sitting close to each other and in a regular pattern like they should. You can see the snake belly “S” at the top of the picture.



These cords are completely broken and have worked their way out of the tire casing. This was not a blow out and, in fact, the tire held air quite nicely. It rode like crap but it held air.

crazyravr

Thank you all that helped. The tire was not seated properly. This was a first for me and I have swapped tires and replaced flats 100s of times. Live and learn.

ClydeClydeson

Having overtight and massively imbalanced spokes absolutely can cause the wheel to taco - I have seen it happen when a less experienced tech was working on his friend's wheel in the shop truing stand. HE was truing a wheel, which normally would not be that complicated of a job. Then I started hearing the telltale sound of spokes being brought up to very high tension...
'squreaaak...... squreeakk....... squreeeeeaaakkkk... SQUREEEEEEAAAAAAAKKKKK....'
then...
'SPROING!!!!' and the wheel suddenly jumped from being somewhat straight to a complete taco.

It is not super common but it happens. I suspect my colleague was tightening all the spokes on one side and not touching the other side, which led to a huge L/R imbalance in tension.

It is also possible that, if one were tightening L and R spokes in one area of the rim, it would pull the rim into a 'flat spot'. However, a rim flat spot would have to be quite extreme to be able to feel it - the tire naturally wants to be round so it will usually make up for any minor to medium rim problems. When the tire is not seated properly or the casing is damaged, it is no longer round, and that can almost always be felt when riding. Notsomuch the rim.