Rocking the forks

[Scud]

Chris - is because you just want it to be "correct" or because you can tell the difference when riding?

Phil is saying that pretty large offsets have worked fine on race bikes. I would assume it less important on the street. The fine adjustment seems Much Ado About Nothing.

[Chris Wilson]

Years ago I did the original 'Stay Upright' defensive riding course here in Australia and it included a vertible circus of low speed tight turns that vexed even the most experienced rider.

I noticed that tip in differed when doing tight figure 8's and that's when I made an alignment board to check that both wheels were indeed tracking one behind the other.

So although at the speed of death race conditions (where I don't ride) it may not be noticed but I can tell in a lot of carpark situations. And once noticed it hard to forget.

So both answers are right, I want to be correct and I can feel the error.

Chris.

[Lucky Phil]

33 minutes ago, Scud said:

Chris - is because you just want it to be "correct" or because you can tell the difference when riding?

Phil is saying that pretty large offsets have worked fine on race bikes. I would assume it less important on the street. The fine adjustment seems Much Ado About Nothing.

To add to that, the vertical alignment of the wheel is more important then the track within reason. If your chasing a mm or 2 track alignment on a road bike you're insane. Most alignment issues are either a design compromise or manufacturing tolerances unless the bikes been crashed badly. There is a limit to how much you can use spoke wheel offset and hub shimming to correct track misalignment and it would be my view that any slight alterations you could achieve within the sensible range of that wouldn't be worth the effort. 

Ciao

 

[Chris Wilson]

Thanks guys, the alignment board trick is more to prove than chain adjustment marks on the rear of the swing arm can be WAY off.

[po18guy]

On 12/8/2021 at 8:13 PM, Lucky Phil said:

So whats the plan when you find it's out of alignment?

Ciao

Either crash just right or hydraulically bend. We have to trust the Italian frame jigs and the worker's willingness to seat everything properly at welding time.

Suddenly I don't feel quite so confident...

Actually riding interstate with one hand as I do causes more misalignment than I could ever correct for - if there was any adjustment, that is. Only time and tread wear tell the tale.

[docc]

6 hours ago, Lucky Phil said:

To add to that, the vertical alignment of the wheel is more important then the track within reason. If you're chasing a mm or 2 track alignment on a road bike you're insane. Most alignment issues are either a design compromise or manufacturing tolerances unless the bikes been crashed badly. There is a limit to how much you can use spoke wheel offset and hub shimming to correct track misalignment and it would be my view that any slight alterations you could achieve within the sensible range of that wouldn't be worth the effort. 

Ciao

 

At least we know why I'm insane. Some people are insane and nobody knows why . . .

[Chris Wilson]

I don't know how many here have actually had a frame made for them that is guaranteed 100% straight.

 I watched engineers make me one on a lathe bed and informing me of what was going on and the importance of it .

First task is to use a datum line that represents wheel track and everything else is spawned from that.

The reason of the importance of getting the track as accurate as possible is that errors multiply from that.

If the track datum line is not as accurate as humanly possible then the projected steering head will radiate exponentially to the wrong spot.

When I first rode the completed bike I was sincerely amazed at how nuetral it steered.

Just my experiences, add salt to taste.

Chris.

[Lucky Phil]

38 minutes ago, Chris Wilson said:

I don't know how many here have actually had a frame made for them that is guaranteed 100% straight.

 I watched engineers make me one on a lathe bed and informing me of what was going on and the importance of it .

First task is to use a datum line that represents wheel track and everything else is spawned from that.

The reason of the importance of getting the track as accurate as possible is that errors multiply from that.

If the track datum line is not as accurate as humanly possible then the projected steering head will radiate exponentially to the wrong spot.

When I first ride the completed bike I was sincerely amazed at how nuetral it steered.

Just my experiences , add salt to taste.

Chris.

Yea I've had a few but they were Italian frame builders so the guarantee was an Italian one. A bespoke frame you'll aim to get it spot on of course but the reality of mass production is another matter. Even Casey Stoner liked the carbon box framed Ducati MotoGP bike better than the trellis framed bikes because he said every trellis bike felt different due to manufacturing variability. I'm no Casey Stoner.  

Ciao 

[Lucky Phil]

2 hours ago, docc said:

At least we know why I'm insane. Some people are insane and nobody knows why . . .

Welcome aboard docc. Brothers for different reason but still brothers 

Ciao

[bbolesaz]

Just FYI. Wheels don't have to track. BMW Airheads have a built in wheel offset to counterbalance the offset weight of the transmission.  Same for many Harleys. 

I just darksided my BMW K1600 so not only is the tire square but it is also offset from the centerline of the bike by about 3/4".  Doesn't bother anything.

 

[Lucky Phil]

25 minutes ago, bbolesaz said:

Just FYI. Wheels don't have to track. BMW Airheads have a built in wheel offset to counterbalance the offset weight of the transmission.  Same for many Harleys. 

I just darksided my BMW K1600 so not only is the tire square but it is also offset from the centerline of the bike by about 3/4".  Doesn't bother anything.

 

Yea, I had a feeling there were quite a few makes out there that were offset for one reason or another. Harleys don't surprise me as handling doesn't seem to be on top of their agenda. It's better to be aligned of course but within reason it's not an issue. It's also worth remembering that the track difference when measuring from the side of the rims as a differential is twice the actual centreline offset so say a 5mm side to side difference is only 2.5mm centreline offset which doesn't seem as bad.

 

Ciao

[Chris Wilson]

If the vehicle is asymmetrically weighted then surely the track is best kept parallel and simply moved over under the CG.

[Chris Wilson]

On 12/14/2021 at 9:27 AM, Lucky Phil said:

It's also worth remembering that the track difference when measuring from the side of the rims as a differential is twice the actual centreline offset so say a 5mm side to side difference is only 2.5mm centreline offset which doesn't seem as bad.

 

Ciao

Not understanding the above Phil.

Surely if the tyre is manufactured symmetrical a 5mm side offset equates  to a 5mm centreline offset?

Chris. 

[Lucky Phil]

27 minutes ago, Chris Wilson said:

Not understanding the above Phil.

Surely if the tyre is manufactured symmetrical a 5mm side offset equates  to a 5mm centreline offset?

Chris. 

Forget the tyre's, tyres are variable. So you place a pair of straight edges on each side of the rear rim and they run forward past the front rim so you can measure the gap differences on each side of the front rim aft and fwd. Lets assume the frame is perfectly straight the measured gap between the sides of the front rim aft and fwd will be exactly the same. Now lets assume you move the "centre line"  of the front wheel one way by 5mm the measured gap between the sides of the front wheel to the straight edges will now be a 10mm "difference" in measurement. So the measured "difference" between the sides is twice the actual centreline track offset.  

Ciao

[Chris Wilson]

I don't agree.

For example if both wheels  are the same width and on track then the straight line will tell that if you move the track of one 5mm then the other is obviously the same 5mm out.

I think that you are missing that if you move 5mm right then you lose 5mm left between the straight edges (plural) and the 'gap' remains constant..

My head hurts.