Truing Rim

I am swapping the rear 19 inch rim for an 18 inch rim and installing a 120/90/18 tire.
I am in the middle of lacing/spoking the wheel.
The 18 inch rim is not running smooth at the welded joint.
The two flanged sides of the rim are pulled in: the rim measures 3.18 wide (OD), except at the welded joint where it measure 3.13.
Most of that 0.05 difference is on one side. I know this is a small number, but it looks like hell when I spin it, and there is no way to pull it out with spoke tension.

Question 1: Has anybody had any luck moving a rim with force?
I am thinking of setting the rim up on blocks of wood and thumping the flange with another block of wood.
Alternatively, I could bump the rim using wood on top of a heavy rubber mat.
Or should I just live with it? Thoughts?

Question 2: Should I change the offset to get better clearance from the swingarm and chainguard?
I know this tire size is tight and wonder if the best fit requires a different offset from stock.

Thanks for your thoughts.

Stephen Hill

Steel rim? Alloy? 37 years in metal industry is inclined to leave it as is, you're the only one who'll know it's there.

1. can beat that part of rim that much outward no problemo, in stages checking.
2. can fit 120 w/o altering anything as the tightness to fit is just getting it past the fender/drum/swingarm squeeze puzzle with some force then all clear once mounted and chained.
3. unless you have distinctly more than 50 hp and willing to use it so lean traction loss on 110 or 4.10 upsets your thrills, a 120 is better mileage tire but detectably more sluggish to change direction fast on ordinary Cdo power but it unnoticed if behaving mostly legally.

My hot rod Peel would trip out too easy on 110 and use them up in 2000 miles - 1/2 month but same 18x120 tire on my ordinary factory Combat Trixie it felt like running in construction boot so removed it even though plenty of meat left.

concours said:

...inclined to leave it as is, you're the only one who'll know it's there.

Click to expand...

Agreed. It might show up heeled-over in a hard sweeper when running against other bikes (as in, a sanctioned race), but I highly doubt you'll ever notice it in street mode. That's the same set-up on my '74, and it has a similar bump.

Nathan

Every new rim I've gotten has had a small flat/pulled in spot at the weld, I've been told that anything from Central Wheel has it. Enough of them out there that I don't think it's a problem. Once laced and trued with a tire on it's not noticeable.

The rim is stainless steel. I tried moving the rim with blocks of wood and a sledge. Nothing!
Guess I live with it.

Stephen

Best to ignore the weld and the areas two or three inches each side of it. Every wheel I have ever laced or dialed in is out in this area. Even my expensive Buchanan's Sun rims are out at the weld, though they are a little closer than those from Central or Devon.
If you are able to get the rest of the rim running true within 10 thou each way, that is , within five thou +- of the zero, then you have done slightly better than Buchanan's who state that they get rims "within 15 thou, ignoring the weld area"
The real trick is to be able to do this and keep the spoke torques all in a close range. Most rims, even many professionally done have greatly differing tensions on the spokes. Also, a lot of wheels are left with spoke tension that is maybe half of what it should be for full strength.
A spoke torque wrench is a big help. Again, Buchanan's use these even though they have tradesman working who do nothing but lace wheels all day long , every day.


Glen

I tried this swap. This tire will hit your chainguard and make tire installation a real challenge. Don't recommend it. Need a thinner tire here.

i have read-asked pretty deep into rim defects for a few years to agree this common little defect is cosmetic even to racers as tires are not that prefect and deform way more anyway. Just as long as bead seats with its indicator line even all around good to go. I was able to fit same 18 steel rim 120 tire into 2 Combats w/o chain guard on any rubbing issues once I working past the mudguard, which is reason enough not to bother. I was a bit surprised I did not like in on plain ole Trixie which I like 110 front 4.10 rear after various combo not as good mileage or grip security for me.

Still annoyance every time ya try not to think about it so maybe a thermal method might help, ice the sides of the area and heat the center while straining and counter relieving spokes helped out by large crescent wrench bending as hammering is pretty useless.

Job is done. Reasonably true rim if you blink when the weld comes around. The tire just fits into the "hole". The chain guard has about 1/8 of an inch clearance against the wheel. The swing arm on the right side (looking forward) has over a quarter. If I needed to I could claim that difference with offset. It is worth noting that it you are mounting an 18 inch rim to take this tire, bias the offset to the right a little less than an 1/8 of an inch.

Not sure how different it will feel. Unfortunately I just removed a very old and very worn Avon Supervenom so my base line is a little skewed. Sure looks cool though!

Stephen

Hi Stephen.
I have that size tyre on my 18" rim and it fits squarely to the swingarm without rubbing (same offset as the 19" rim to ensure the centreline is constant). I had to drop tyre pressure for the 18" compared to the 19" to retain cornering (otherwise it felt like I needed to 'help' the bike into the corner).
Ta.

If the ride height is different at the rear, the handling might change due to the difference in steering geometry ( head angle). I think that with most road bikes the difference is probably non-critical. With something such as those old water-bottle GT750 Suzukis which already have poor handling, might be a problem. It sometimes only takes a fraction of a degree.

Diameter of a 120/90/18 is calculated at 26.5 inches.
Diameter of 100/90/19 is calculated at 26.1 inches.

Generally considered to be similar enough not to affect ride height.
However, the contact area, mass, and width are also changed, which can also affect how the bike turns.
For the Commando, the consensus (is there such a thing?) seems to be thinner tire, faster turning.

Needing, what tire pressure do you use on the 18 inch rear? You mentioned you had to lower the pressure to retain cornering.

Stephen

Stephen Hill said:

Diameter of a 120/90/18 is calculated at 26.5 inches.
Diameter of 100/90/19 is calculated at 26.1 inches.

Generally considered to be similar enough not to affect ride height.
However, the contact area, mass, and width are also changed, which can also affect how the bike turns.
For the Commando, the consensus (is there such a thing?) seems to be thinner tire, faster turning.

Needing, what tire pressure do you use on the 18 inch rear? You mentioned you had to lower the pressure to retain cornering.

Stephen

Click to expand...

Hi Stephen.
19" = 28psi
18" = 26psi.
Ta.