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Wheel alignment

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Wheel alignment

Posted by George Phillips at Wednesday 19:37
If both wheels are correctly aligned why should the bike head off to the left (on a flat road) when I let go the bars (on a private road of course!)? I have to lean to the right to maintain a straight line. George

Re: Wheel alignment

Posted by Barry Carson. at Wednesday 22:51

George, how do you align your wheels i run a string around to check mine.

Barry

Re: Wheel alignment

Posted by Dan Field at Wednesday 22:58

Are the forks twisted?

Re: Wheel alignment

Posted by George Phillips at Wednesday 23:30
I use a length of angle iron. How do I check for twisted forks?

Re: Wheel alignment

Posted by Barry Carson. at Thursday 00:43

Re: Wheel alignment

Posted by Dan Field at Thursday 07:32

Re: Wheel alignment

Posted by Kevin Bell at Thursday 09:59
Previously George Phillips wrote:
If both wheels are correctly aligned why should the bike head off to the left (on a flat road) when I let go the bars (on a private road of course!)? I have to lean to the right to maintain a straight line. George
Camber of the road? Most of my bikes have drifted left with no steering input. I suppose if the steering damper was screwed down, it would hold it straight? Kevin

Re: Wheel alignment

Posted by Dan Field at Thursday 10:30

The rear wheel not being centralised in the swing arm can cause that, if you make sure the forks are straight (see above) and the rear wheel is central then you can  run a line or laser (or angle iron!) along both wheels the line should just touch both edges of both wheels, allowing perhaps for a fatter tyre at the back. The other possibility is a bent frame. But how bad is the pulling, can you feel it when you riding along?

As said it might just be the camber, have you tried another road?

Re: Wheel alignment

Posted by Dan Field at Thursday 22:47

How'd you get on George?

Re: Wheel alignment

Posted by Tony Ripley at Thursday 22:56

I would say the real difficulty here is checking the rear wheel is central to the frame, not actually central to the swinging arm as the arm is not symmetrical as far as I remember. so where would you measure ?

If the wheel is offset to one side, you will still be able to use the straight edge method to get the wheels in line but it will still not be in line with the frame.  The 'not straight ahead' of the handlebars would be difficult to see unless it was really bad.

So how do you check the wheel is central to the frame ? There are methods to do it but I think it involves complete strip down and slate beds !

Anyone got any suggestions ?

By the way, I have ALWAYS had to lean slightly to one side to keep the bike straight when hands off.

Tony

 

Re: Wheel alignment

Posted by les_howard at Saturday 10:17

Previously George Phillips wrote:

If both wheels are correctly aligned why should the bike head off to the left (on a flat road) when I let go the bars (on a private road of course!)? I have to lean to the right to maintain a straight line. George


The answer is simple...It is caused by the CASTER ANGLE on the head-stock of the front fork. If we assume the frame is straight and the head-stock is undamaged the weight of the bike pushing down on the front will want to turn and keep the front forks pointing EXACTLY forwards and dead in line with the frame. ....However, when the rear wheel is NOT dead centre caused by incorrect offset or a bent swinging arm you will STILL be able to line up the rear and front wheels by canting over the rear wheel to point towards the front wheel but to fully achieve this pseudo alignment it will necessitate that the front wheel and forks are turned slightly from the dead ahead position to line up with the rear wheel being aimed at it. When on the move however, the caster angle will always be trying to return to the dead ahead position and when you release the handlebars grip it will do so and result in the non alignment re-occurring and steering the bike away from the dead ahead course.

It is also easy to check the rear wheels alignment but you will have to remove the rear mudguard. When done, stand the bike absolutely vertical by checking with a spirit level across the rear frames top tubes. Then set a straight bar across these tubes from one side to the other above the centre of the tyre. You will then need to find the centre of this bar either by running a line or laser down the frames top tube or measure the centre if the frame is a duplex Featherbed type. Then drop a short plumb line down to meet the tyre or better still the wheel rim without tyre fitted. The difference from the wheels centre gives the correction measurement (if needed) noting that you will halve this distance to true the wheel. Doing this will ensure the bike tracks straight hands free, assuming the steering head is not twisted sideways from the vertical plane.....Les

Re: Wheel alignment

Posted by David Cooper at Saturday 16:06

Surely if the objective is to track straight, by far the easiest method is to pull over and adjust one side forwards and backwards a bit and  a time until it's what you want?

Re: Wheel alignment

Posted by les_howard at Saturday 18:30

Hi David..this is fine if you want a bike that "crabs" and I have seen many when following them on ride outs....

Wheels, forks and frames and their steering geometry MUST ALL have their centres coincide perfectly in a straight line and in the vertical plane. If any one of these aspects is out, the bike will handle with a bias and no mucking about with the rear wheels chain tension adjusters will fix it. Obviously some riders will accept this and the way the bike needs constant correction by handlebar pressure or by body weight to offset a left or right steering bias even if it does make them wonder what is wrong and even be moved to ask a question on this forum why.....Les

Re: Wheel alignment

Posted by john_holmes at Saturday 19:35

My MK2A Commando used to drift hands off to the left, I accepted it as,

1. With hands on the handlebars I did not notice

2. It was seen as being a problem with the disc brake which was cured on the MK3 by swapping the fork legs so the disc was on the other side. ref NOC notes page 29.

I fitted a new rear tyre, checked and adjusted the rear to front tyre alignment and checked and adjusted the iso's gaps.

Then I thought I would check the result  and one, two or all of these cured the drift and I can now take my hands off and it steers straight on a flat uncambered road. As I never tested between each adjustment I cannot tell which one or combination made the difference.

Now the question is why does my bike not drift to the left like it should ;)

And no its staying as it is.

Re: Wheel alignment

Posted by robert_tuck at Saturday 20:38

Not sure it was Read or Hailwood who complained that the 650 ss would not go in a straight line and needed weight put on a footrest. It was decided that there was a weight bias and so the wheels were moved accross off center to counter this.Are you riding like them??!!.

Re: Wheel alignment

Posted by richard_payne at Saturday 20:39

Les is spot-on here. It is very easy to let the the steering turn slightly and then align the the rear wheel with that.  If front and rear rims or tyres are not the same width then it's even easier to be misled.

 

Some people have an inherrent ability to sit on any mis-aligned bicycle, make corrections automatically and effectively be happy with the handling of a camel. I rather envy them actually.

Re: Wheel alignment

Posted by George Phillips at Sunday 22:32
Apols for the long silence guys but I've been driving round the south of England for the last day or two. Thanks for all your inputs. The slight drift to the left is not noticeable when riding normally, only when "hands off" (and on a flat road as I noted first off). I've got no intention of stripping it all down to get to the bottom of it but am very interested in the reasons given. Another project for next winter!

Re: Wheel alignment

Posted by John Shorter at Monday 09:32

Why would anyone want to ride "Hands Off" in the first place?  For a start, it is a traffic offence, just as eating, while driving a car. 

Re: Wheel alignment

Posted by les_howard at Monday 09:43

This is an interesting subject George so thanks for airing it. I once owned a bought new Commando Roadster that pulled fairly strongly to the left if the grip on the bar was released and I was always baffled as to why it did this knowing that I had the rear wheel dead in line with the front one.. It's only in recent years the penny dropped when a Matchless G80 short stroke I own seems to have something very much out of line and even dishing the wheel over hasn't corrected it so I've given the subject quite some thought. In this case though I reckon the swinging arm is bent and hopefully it is rather than the frame.

By the way, the info I gave as regards correcting the wheel offset is wrong....I said halve the error distance of the centre measurement on the rim. Indeed, if you are dropping the plumb line to a KNOWN dead centre on the rim or tyre this measured difference is the TOTAL measurement that the wheel needs to be pulled across (assuming the frame and swing arm is all OK). However, If you are comparing rim EDGES to each other from the centre line the difference is in this case DOES have to be halved for your new correction of the rim position....Les

PS...You might want to correct the rear rim the following way. If you can get someone to hold the front wheel absolutely dead straight ahead (I know this is not easy but you can lock it there by using the damper knob if fitted) then using your straight edge adjust the rear wheel so that the edge is PARALLEL to the front wheel on both sides. You will probably notice that one side is perhaps bigger than the other which is the error on the rear wheels alignment as regards the centre line of the frame. So as said, halve this distance when correcting the rear rim. I would say if the bike pulls to the left the rear wheel for whatever reason is over to the left...REASON: If you have aligned your wheels perfectly to the the front you will be riding with the bar slightly to the right to get the front wheel to line up with the rear. As explained above, when you release the bars the wheel will return to the straight ahead position due to its caster action and this will now be turned to the left in relation to the previous alignment thus steering the bike to the left. Bare in mind these correction movements are tiny but enough to exert a small bias on where the bike wants to head for....

The problem with this method is getting the front wheel in an absolute front ahead position in relation to the frame which is why I favour the previous method where the rear mudguard has to be removed to get an accurate centre line through the bike from the headstock....Worth a try though I reckon....Les

PPS:  Please note everything I have suggested is assuming the FRONT wheel IS DEAD CENTRE....well it is so easy to get this right no-one should have any excuse not to have it that way...IE: same gap either side of the rim to the forks sliders or tubes....

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