Some advice on tire pressure and rear wheel alignment needed

Hi folks,
Just getting ready to gas up my 75 mk3 after a pile of work to various systems.
I've got two main concerns at this point. Tire pressure first, Avon 19" 100s I believe. Nice looking sticky tires although I'm not crazy about the modern looking tread I am hoping on better feel and grip. Anyone have a recommendation on a starting pressure? I'm in the Northeast with temps around 80's.

Second question is on tire alignment in the swing arm. I have new oem adjusters installed but am haveing a real hard time finding a good point of reference since the rear fender is a bit out of center and on my life I'm having a hard time "feeling" a spatial difference between the tire and swing arm. Is the swing arm symmetrical? I have seen some that are not thus this gap measurement is not always correct.

Would a measurement on the rear adjusters (bolt head to adjuster) be close? Any tips are greatly appreciated.

Re: Some advice on tire pressure and rear wheel alignment ne

Rusty bucket said:

Tire pressure first, Avon 19" 100s I believe.

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Do you mean the Avon 100/90-19 Roadrider universal?

If so, the Avon recommended pressures are 29 front, 32 rear: http://www.avon-tyres.co.uk/motorbike/8 ... r-commando

Rusty bucket said:

Second question is on tire alignment in the swing arm. I have new oem adjusters installed but am haveing a real hard time finding a good point of reference since the rear fender is a bit out of center and on my life I'm having a hard time "feeling" a spatial difference between the tire and swing arm.

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Your point of reference should be the front wheel/tyre. If the bike is propped up so the centre stand can be raised out of the way then either a straight edge or string line can be used to line up the wheels.

Rusty bucket said:

Is the swing arm symmetrical?

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No.

Rusty bucket said:

Would a measurement on the rear adjusters (bolt head to adjuster) be close?

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Not accurate enough in my opinion.

Re: Some advice on tire pressure and rear wheel alignment ne

Thanks LAB! Yes the string might just work! Yes I'm running the RoadRiders. I had the front on properly after swapping it then I reversed the forks and brought the caliper back to the left side as the PreMk3 bikes. I never liked the look of the caliper on the left side, so know I've got to swap it back again.... I'm going to run it as is for a few miles as I'm out of patience and need a damn ride!

Re: Some advice on tire pressure and rear wheel alignment ne

I think Hobot's method of keeping the rim to rear swing arm distance the same on both sides is pretty cool and simple. I used the string line method etc before, but is comes back to the Hobot method all the time unless your bikes been biffed.
Dereck

Re: Some advice on tire pressure and rear wheel alignment ne

The straight edge method is the best way to align the wheels. Neither the swingarm nor the chain are necessarily true to the centerline of the wheels.

Re: Some advice on tire pressure and rear wheel alignment ne

Here's a good method given to me by a frame builder and straightener...

The rear axle must be parallel to the swingarm spindle. Since the swingarm spindle is hard to get to on Nortons, I measure from the axle to the rear isolastic spindle. If both sides are equal then the rear wheel is in line with the frame. I use a large pair of dividers I found in a yard sale but they are available on ebay pretty reasonable.

Re: Some advice on tire pressure and rear wheel alignment ne

The spindles can be perfectly parallel but the wheels can be off-set and therefore out of line. I go along with LAB use a straight edge, or string. It's what Norton advised.

Cash

Re: Some advice on tire pressure and rear wheel alignment ne

+1 on all the above, but check your tyre is fitted correctly in the first instance, concentric and to the same depth on both sides on the rim, this will ensure that it is not fitted across the rim.

Re: Some advice on tire pressure and rear wheel alignment ne

Madnorton said:

+1 on all the above, but check your tyre is fitted correctly in the first instance, concentric and to the same depth on both sides on the rim, this will ensure that it is not fitted across the rim.

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+1 and don't forget to check for correct wheel offset on both wheels. Straight edge works fine as long as everything else is in order.

Pete

Re: Some advice on tire pressure and rear wheel alignment ne

I could never tell if the string method was aligned properly, so came up with cheap straight edges - the almost 8 foot long florescent light tubes. They have their own set of issues, but for me they work better than string.
Bill

Re: Some advice on tire pressure and rear wheel alignment ne

There are multiple issues to alignment...

How flat are the bike's rims? If there is rim wobble, then the angle measurement changes as you rotate the tires, so the rims need to be true

How much play is there in the swingarm, swingarm tube, and isolastics? Obviously side loading the isolastics deflects the alignment of the rear tire. A lot of play in the swingarm negates the point of adjustment.

How well aligned are the yokes and the fork legs?


Once all that is measured as good, my method was to make 2 straight edges out of some 1/4 inch plywood (on my tablesaw which has an 11'6" sliding table) and scribe out those straight edges where parts of the bike frame contacted it so I could raise them up and get the longest contact between both the tires and the straight edges. After I made the rear wheel adjustment, I measured the distances from the lugs on each side of the swingarm that the adjusters fasten into and noted that the length of both adjusters were exactly the same,.... SO, now I just use the lug measurement on each side since it's been proven to be accurate to align the rear wheel.

I've always run 19inch K-81's front and rear. I try to keep them over 35lbs and they feel precise. Last week my rear tire was down the 25lbs and it felt noticably sloppier to me and when I got home I checked the pressure and sure enough it was low. I always wanted to try a softer tire and a less triangular tire as well, but I'm a cheapskate so I have stuck with the K-81's...

Re: Some advice on tire pressure and rear wheel alignment ne

I use a string line to align the wheels and loop it around the rear of the tyre are rim on the rear wheel and the front of the tyre and rim on the front wheel, and tie it off to one of the spokes. Because the rear tyre and rim of the rear wheel it bigger than that on the front. I use two equal sized matchboxes tucked between the string line and the rear of each side at the rear of the rear rim.
Then you find that when you turn the front wheel, the string line is spaced slightly out from the sides tyre at the rear of the front wheel. Also when you adjust the rear wheel there is a gap between the sides of the tyre at the front of the rear wheel. If you get the gaps equal at each side of the front of the rear tyre while the gaps are equal at each side of the tyre at the rear of the front wheel - you have the wheels in line. You might need to turn the steering while you adjust the rear wheel adjusters.
If you don't use the two matchboxes as spacers each side of the rim at the back of the back wheel, you end up with a bend in the string line each side at the front of the rear wheel, and you will never get it right. If you stretch the string line tightly, it all becomes easy. You should be able to do the job in 5 minutes. You need the bike off the stand and on its wheels with someone else holding it upright.

The worst situation is when there is a twist in the swing arm or the frame. The easiest way to pick that up is to get someone else to ride the bike while you follow along behind. You can sometimes see it if it is there. Alternatively have a look from behind, when you have the engine and gearbox out of the frame. You can still get the wheels in line at one suspension load if there is a twist, however handling is better without it.

Re: Some advice on tire pressure and rear wheel alignment ne

Thanks for posting your matchbox method with string, it sounds good. Next time I need to align wheels I will give it a try, and probably retire those florescent tubes.
Bill

Re: Some advice on tire pressure and rear wheel alignment ne

It works well with the matchboxes. If you have bends in the string where it crosses the sides of the tyre at the front of the rear wheel, you can't tell where you are. With the matchboxes in place, I simply turn the front wheel and adjust the rear wheel until the four gaps between the string and the tyres are correct . - It is very easy.
One thing I forgot to mention. The guy who had my Seeley frame before I did, fitted a different threaded stud to one of the chain adjusters. It means when adjusting the chain, you can't pull the rear wheel back by counting the number of turns on the spanner each side to keep the pull equal. I bought another piece of allthread to get both adjusters with the same thread, however now I find I don't have the right tap, and the thread is something I don't usually use so I'm too lousy to buy the right tap. It's only minor, but a bloody nuisance.

Re: Some advice on tire pressure and rear wheel alignment ne

I've used string and a 5' straight edge. Lately I've just been laying prone behind the bike and sighting down the rear tire toward the front.

Imagine the rear edge of the rear tire was the rear sight of a gun, the front edge of the rear tire was the front sight, and the edge of the front tire was the target. It works about as well as the other methods for me and requires no tools. I was shown this technique by Phil Radford. After you get the wheel aligned you just make sure to turn each adjuster the same number of flats when you adjust the chain.

Re: Some advice on tire pressure and rear wheel alignment ne

As a cabinetmaker, I have worked to a string line on a few occasions, scribing radiator covers between columns on the outside walls of big skyscrapers in NYC. It's the best way to make sure all the heights of each individual run of cabinets are all the same plane... We do the same matchbox trick with a thickness of wood, so you can measure the offset in different places along the string. Anywhere that the string is the same distance from your work as the thickness of your "matchbox", you are measuring your alignment as good! Cool to see that same method applied to a motorcycle's wheels...