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-   -   Trying to true rear wheel. (https://www.bikeforums.net/bicycle-mechanics/938135-trying-true-rear-wheel.html)

Gary3 03-13-14 06:38 PM

Trying to true rear wheel.
 
:bang:Newbie here, trying to true the rear wheel on my 30 year old road bike. I can get it pretty true laterally OR radially not both at the same time. I've watched several tutorials on wheel truing. No one has mentioned this problem. How do I overcome this?

Wheels are Araya 700c red labels.


Best Regards
Gary

koolerb 03-13-14 06:54 PM

I just took an old wheel set apart over the winter to clean really good. Also so I could try building them back up. It took a few tries to get them right. I ended up buying a spoke tensioner, that helped. There are a lot of good tutorials on-line. The logic is, get them round first, then get them true laterally.

lopek77 03-13-14 06:59 PM

Good topic. I was experimenting with that...did well considering it was a true figure 8 /not even kidding/,5 minutes in to my learning experiment. I fixed that, it was pretty true, but it ended up with a little hump. Maybe not a huge deal, but imagine that wheel on a wet surface while cornering :cry:
This is one of a few things I'm looking forward to learn about, including wheel building.

cny-bikeman 03-13-14 07:02 PM

A rim that is physically bent will prevent you from achieving both round and true, because to pull it over you have to crank too much on on the spokes on one side, pulling the rim down as well as over. if you are tightening and loosening in pairs but having to choose round or true that is likely the problem. Easiest way to tell if the rim is bent is without spokes - laying it on a flat surface, but basically if you can't true it without loose spokes on one side and very tight ones on the other that means the rim is bent. Spokes don't really straighten a wheel very much, they just provide the force necessary to have it run straight in relationship to the hub.

hueyhoolihan 03-14-14 12:40 AM

as mentioned above, sometimes it's a no win situation, but all is not lost.

recently i had to toss my old bent Araya Red Label rims. i hated doing it, but i can't ride on an untrue wheel. i tried fixing them, but it proved to be impossible, for me anyway. so i bought some fairly inexpensive Sun ME13II (polished). they are dead ringers for my old Araya Red Labels. they even come in a 630mm version.

dabac 03-14-14 01:04 AM


Originally Posted by lopek77 (Post 16575776)
it was a true figure 8 .

Sounds like it taco-ed. Too high spoke tension will do that, or a wicked side impact. If yours was from unsuccessful trueing, then you need to back down on spoke tension all over, and then take it back to round and true.

Depending on the degree of taco, the rim may have taken a permanent set, which will make it difficult/impossible to achieve the triple target of tension, true and round.

Sometimes it's possible to unlace bend the rim back manually and then build up a functioning wheel.


Originally Posted by lopek77 (Post 16575776)
.. it ended up with a little hump. Maybe not a huge deal, but imagine that wheel on a wet surface while cornering

Humps are humps. For control, it doesn't matter if it's the ride surface moving up/down, or if it's the rim/tire moving up/down.

Myosmith 03-14-14 06:05 AM

I just rebuilt wheelset and used a Park spoke tension gauge throughout the process. The gauge was one of my best investments ever. I've used one before at the bike co-op to spot check my finished work but I've never had access to one during the build until now. My target was 21 to 21.5 on the gauge (= 105Kgf to 111Kgf) which was the high end recommended by the rim manufacturer. I started in the typical way, counting turns of the nipples to bring the wheel to a low tension and relatively true both radially and laterally. I took out the gauge and brought both sides of the front and the drive side to 15. I then alternated making half turns on all the nipples, checking rough true, then correcting any variances in tension. After about three times around the wheel I was at 20+ and fairly true. A couple more times with finer adjustments and I hit 21. I finished off with fine truing and a couple of minor tension adjustments. The whole process including the assembly took a good long afternoon (I wasn't rushing and did a lot of note taking and a bit of trial and error) but it was a blast. Things went smoother than on my first couple of wheel rebuild attempts and I was more confident in the finished product.

The final result is that the tension on both wheels is very even (much closer than the results of the spot checks I had done on previous efforts). The front wheel is very true both radially and laterally. The back wheel is true laterally but still has a mm or so of hop. I rode them 30 miles yesterday and am pleased. I plan on rechecking true and tension after a couple hundred miles and may try to get that last bit of hop out of the back wheel (I can't notice it when riding and would normally accept it, but I just want the practice to see how close I can get to perfect).

Bottom line, IMHO, if you can get a spoke tension gauge during your build, it is well worth it. OP, it might be worth detensioning or even disassembling the entire wheel and starting from scratch. I'm new to wheel building, but have a couple years experience truing and repairing wheels at the bike co-op, so take my opinions for what they are worth.

Gary3 03-14-14 06:16 AM

When it is close to round, it is easily 1/8" out of true, about half that the other way around. My best chance to save the wheel is to unlace and try to manually flatten the wheel (laterally), then rebuild the wheel? Seems a complete newb (like me) could do more harm than good.

Alternatively, could I pull the wheel round, then try to manually flatten it? Or should I try to find someone who knows what they are doing?

Regards
Gary

Gary3 03-14-14 07:13 AM

The tire also has some radial run out. the witness line is consistent against the rim, maybe I can use that to my advantage?

cny-bikeman 03-14-14 07:31 AM

You can't manually flatten the rim unless the spokes are loose at least in that area, and it can be challenging to get right. If you are only 1/8 out of round solving the problem depends on what the spoke tension is in the out of round area. TENSION is the most critical variable on a wheel, so what we need to know is what the tension is in the area(s) where there is a problem. The pattern of tension on a fairly true wheel is an indicator of where problems exist in the rim itself.

Truing is not a matter of memorizing what to do when but rather understanding the physics of a wheel. As I noted before, all the spokes do on a straight, round rim is hold it in position in relation to the hub. They can fix only minor deficiencies without causing tension problems, and of course they can only pull, not push. That means that if a rim has a flat spot from impact the spokes cannot correct it, and if the rim is bent to one side the spokes on only one side can pull it back to center, they will pull down more than to the side, and the other spokes will have to be loosened below normal tension to even allow that to happen. So a bent rim on a "true" wheel will have a low area and uneven side-to-side tension, or OK roundness but very loose spokes on one side.

Looigi 03-14-14 07:40 AM

My experience: With rear wheels with a lot of dish (most), the DS spokes have much more influence on radial truing and the NDS much more influence on lateral truing due to their different bracing angles. My process is to start with all spokes slack, then bring up to tension only the DS and radial true using only the DS with the NDS spokes slack. Once the DS is tensioned and the rim radially true, I dish and laterally true using only the NDS spokes. Dishing the rim with the NDS spoke only slightly increases DS tension. Once there, it's a matter of stressing the spokes, equalizing tensions and fine tuning the trueness recognizing that the DS still has greater influence over radial and the NDS greater influence over lateral.

Gary3 03-16-14 05:26 PM

I slacked all the spokes and flattened the wheel laterally by bending over the edge of the bathtub, took lots of tries, but definitely got it flatter, then I pulled as round as I could using the drive side spokes, (there is still a small flat spot in it), then I trued it laterally with the non drive side spokes, then increased the tension a 1/4 turn all the way around, then trued again . It is much better! the tension throughout the wheel is MUCH more even.

Thanks for all the replies!

cny-bikeman 03-17-14 06:21 AM

Great to hear. The moral of the story is that a bit of logic goes a longer way that a tension meter.


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