Bicycle Mechanics - True a tire?
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09-12-12, 12:53 AM
my back tire has a wobble. how do i true the tire?
09-12-12, 01:24 AM
Is it the tire or the rim?
Remove the tire from the rim, this will identify where the issue is, if it's the rim, see here for how too's http://www.parktool.com/blog/repair-help/categories/wheel-and-rim-service
If it's the ire, unless it was not seated correctly, it will probably need to be replaced.
09-12-12, 06:48 AM
If the rim is true and remounting the tire (it may take a couple of tries to get it straight) doesn't help you will either have to live with it or replace the tire. No tire is prefectly round and concentric, there will always be some irregularities. If the tire is grossly distorted (bulged or twisted) it may have damaged plies and of course should be replaced. The same if it affects the ride or induces too much OCD.
09-12-12, 06:52 AM
if the rim is ok and is effectively a problem in the tire then you cant. With tubulars you can work that out, with clincher tires you cant.
Assuming your rim's straight, there are three reasons why the tyre wouldn't be.
A) It's cheap crap.
B) It's not seated properly; to ensure it's seated properly, deflate the tyre and squeeze the bead together around the tyre to unstick it from the rim. Pump it up to say, 20psi and then give it a spin. If it looks good, keep pumping, If not, grab the tyre near the valve with the wheel side-on to you, and haul back and forth on the tyre around the wheel, dislodging and returning the bead to its seat. Spin, rinse and repeat if it's still not good.
C) If the tyre was once good but has been left too long improperly seated, it may become impossible to seat properly.
Oh yeah, there should be a line moulded into the tyre just above the rim for you to gauge the seating.
Assuming it is the tire, make sure the rim strip is seated properly. Also you can put soapy water on the bead and inflate to max psi with a compressor. This will help to seat the tire.
09-12-12, 12:07 PM
I just went through this with some Bontrager Lite tires (new tires/new cr-18 rims. There seems to be two issues to be aware of. First, some tires have a habit of turning in the wheel channel, so when you inflate the tire one side is barely seated in the hook and the other side is riding up high. To fix this, deflate the tire and work the bead of the tire into bead in one side (don't worry about the other side). Once you have done this the tire should be fairly centered. Second is sometimes the tire will not be evenly tensioned on the rim. This means, if you look at the tire standing up in front there is a slightly more tire at the top then bottom. This will show up as hump on the side (because the tire tension is less) and a tight spot on the other side. What you need to do is deflate the tire, put your toes on the end of rim where there is a hump, grab the the tire, one hand on each side and pull on the tire, once below center, once center and once top of center. Then as I said before, seat one side in the tire bead and inflate. This may take some trial and error (one tire with a wire bead took me several hours to get where I wanted it but you will get it centered. BTW, in 40 years of riding this is the second time I have experienced this, but it is an issue with some tires.
09-12-12, 01:28 PM
Bicycle tires have the bead seats standardized, but they also usually have little rubber lips molded onto the outside edge at the bead. The purpose of these is supposed to help guide the tire into seating concentric.
Problem here is, the rim lips and the rubber tire lips dimensions aren't standardized (at least, not that I have been able to find). So you can get a tire+rim combination where the rubber lip interferes with the tire seating properly.
Inflating the tire with the wheel lying flat (horizontal) is one trick to try to get it to seat concentric, but you may still end up with low spots or high spots.
It is possible to shave a tiny amount of the tire's rubber lip off all the way around (on both sides), and often that helps the issue significantly. This is risky though because if you cut into any of the casing threads, now you have a significantly-weaker spot on the tire. A lower-pressure tire may still be usable, but for a high-pressure tire that means it is probably ruined.
If you've got no other use for the tire, it's worth trying though. Use a new razor blade and try to cut a very-thin strip off the raised lip's top--like, 1/2mm or so.
Seeing that you just posted in another thread about the LBS replacing your back wheel instead of repairing (2) broken spokes, I think you should just bring this wheel back in to the LBS since it appears they either:
Sold you a wheel with too few spokes for your 240 lb weight.
Sold you an adequate wheel, but did not have proper tension on the spokes.
Sold you a piece of junk wheel instead of repairing your old one.
Either way, since the wheel seems to be fairly new, the LBS should address this.
Oh yeah, one last piece of advice if you want useful answers, you should give everyone a complete picture and background and not a one sentence question. You should not expect people to have to look up your old posts to figure out why you are asking your question.
I suspect that most of the responders have never been in an urban bike shop.
Often when people come in and ask about truing a tire, they mean the wheel. If that are talking about a wheel w/o tire -- that's a rim.
You need an urban bike shop dictionary to work through these questions.
To the OP, if you're talking about the entire wheel wobbling, between the brake shoes, you true that by tightening and loosening the spokes to pull it back into alignment. You can search aligning (or truing) a bicycle wheel on the internet for some basic tutorials.
09-12-12, 07:33 PM
i took the whole wheel to a different shop the rim was slightly out of true. it was the tire causing the problem.so 48 bucks later i have a new tire and no wobble
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