Hi all
Does anyone know what the rim offset should be on the rear wheel (QD wheel with crinkle hub). There is much talk on forums of what people THINK it should be but I cant find anything actually definitive. The genuine BSA workshop manuals all say the rim should be central between the spoke flanges of the QD hub but I've built the wheel like this and the rim is a whole INCH off the centre line of the bike. Central Wheel Components advise that with a WM2 rim the edge of the rim should be flush with the spoke flange on the splined side (which puts the rim centre 1/4" off centre of the hub) - this will help bring the rim closer to the centre line but it wont be anywhere close to the centre line of the bike.
Lots of wheels must have been built so someone out there must know the answer to this. Maybe the wheel is not even supposed to be on the centre line ??? (I used to own a BMW that was intentially off line). Please help if you can.
Thanks
Derek
Hi again
Well, I thought I would update this post with what I've found out and where I am now - maybe, just maybe, it will help someone in the future - or maybe it wont !
Information I've got:-
Central wheel components (who I bought the rims and spokes from and who have provided excellent service) advise that the rim offset for the rear (edge of rim flush with the spoke flange on the splined end with WM2 rim) is what they have been using for years and they must have built 1000 wheels like that.
SRM advise a dimension taken from the end of the splined bit but it boils down to exactly the same as the CWC advice - note that I got this from another forum posting and not direct from SRM.
The statement made in the BSA workshop manuals of the period that the rim should be central to the spoke flanges puts the rim centre so far off the centre line of the bike that its rediculous.
Using the CWC / SRM dimensions puts the centre line of the rim 1/4" off the centre line of the frame and swinging arm (the sprocket lines up with the engine sprocket though as the brake drum assembly is effectively a separate unit and locates directly on the left hand side of the swing arm - but you all know that anyway.) To get the rim on the centre line of the frame would need it going 1/4" over towards the drive side.
On the basis that CWC have been building wheels like this for many years I've now got mine to their specification - though it goes against the grain to have the wheel not on the centre line and also not in line with the front wheel (see below).
As for the front wheel CWC advise an offset of 9/16" from the edge of the drum to the edge of the rim (WM2 rim). This matches the figure given in the BSA manual of 1 15/16" from the brake drum edge to the centre line of the rim - and it puts the rim smack in the middle of the fork legs and therefore bob on the centre line of the frame.
So, thats where I am. Doesnt seem right but it looks like many bikes are running around like this.
If anyone out there can shed any more light on this then I'd love to hear it.
It will be a long time yet before the bike is finished and on the road so I can see how it rides. Worst case scenario is that I need to adjust the rear offset so its not the end of the world.
Derek
Hi Derek,
Wheel offset and being off centre is an anomaly in the design of the frames. If you do a search of this Forum you find a good discussion and explanation as to why the A65 wheels are not central or indeed line up very well.
Dave.
Hi Derek oh what a familiar conundrum! Rebuilding 67 hornet which arrived in several boxes. The wheels were a complete basket case,hence the research began! I searched for original rims etc even used Hoffman bearings from just up the road and i also took it as gospel as per BSA manual! Well i consulted several of my local and very well renowned experts one of whom raced goldstars etc with great success! Over many years. They all have differing views but if you believed half then how did they ever acheive a mass produced road bike? But you know what? Im glad they did-its fascinating. Good luck. DAVE
Thanks to the two Daves who have posted replies. I am guessing the post you refer to (Dave Brady) is the one you started about the 1deg angle of the front wheel ? Very interesting that one. My forks are what I think are refered to as the push through spindle variety (pushes through from the left side and screws into the right leg). Both my legs / sliders are the same length so no 1deg angle on these. Interestingly though I did some trigonometry (first time since leaving school !!!!) and worked out that a 1deg angle with the top of the rim central in between the fork legs gives an approximate distance off centre at the tyre contact point with the road, of 10mm - which is close enough to the off centre distance I've got on my rear wheel. So it all makes sense.
One further bit of info I forgot to mention first time around - In the book 'BSA Twins A50 & A65 Gold Portfolio 1962 - 1973' there is a reprint of a March 1967 'Cycle' road test of a 650 Lightning. In it (page 97) is reference to changes made by Doug Hele to improve handling - "A touch more 'rake' in the steering, and a change in the front wheel did the trick. The front wheel is laced to bring the tire over under the bikes centre of gravity, which is slightly offset with regard to the chassis centreline." Unfortunately for us now, it doesnt say which way over it was moved or by how much - sad that as it would have helped a lot.
Derek
Hi,
The wheels were originally designed to be 3/8" out of line to get the secondary chain to run true. On the later forks the front wheel 1 degree variation was added, putting the wheels in line and improving steering characteristics.
Best wishes...
The 1966 type forks were modified during that season with the offset drilling and each leg marked with an A on the mudguard bracket. See the service sheets below.
This is what the modified 1966 type look like, lease excuse the dreadful blue paint.
You can just see the stamped "A" on the mudguard bracket.
Thanks Bess and JulianS for your input - its all making sense now. My fork legs are powder coated so no chance of seeing if they have the 'A' stamped on them but comparing them with the photos posted I think I have the earlier pre-modified legs.
Can anyone think of a good reason why I shouldnt just modify the lacing of the FRONT rim to bring it over to the right by 1/4" which would put it in line with the back rim ? I know I would need to check there was sufficient clearance for the edge of the tyre against the leg and/or mudguard and that may limit how far over it could go. Maybe it was this clearance issue that led BSA down the strange route of canting the wheel over by 1deg ? By the way, I intend fitting Avon Roadriders as I have these on my other classics and they are great.
Derek
I have a fully restored 1966 A65L and, to be honest, I didn't notice at the time that the front wheel was tilted over by 1 deg and the back wheel was displaced 1/4" off the centre line of the bike. My A65L does have the modified fork legs but I have no idea why this mod was done.
In terms of the question asked:
When I restored my A65L, I would have aligned the two wheels with a straight edge - having done this, I don't remember there being a clearance problem with the back wheel; for example, rubbing on the chain guard or swinging arm. So, if my memory is correct (10 years ago), I'm not sure there is a reason for offsetting the front to match the offset of the back wheel.
The other consideration is that offsetting the front wheel from the centre of the forks will be very noticeable to the eye especially in respect of the front mud guard when you stand in front of the bike. My front wheel is definitely centred although I can't remember whether I rebuilt it or got CWC to do it.
Hi Derek,
The engine has such a big primary its fitted in the frame so the drive sprocket is 3/8" further over hence the back wheel doesn't line up with the front. The reason for tilting the front wheel is to line the wheels up to improve steering so the bike will go in a straight line.
Both our family's A65's are made with Triumph sliders which are of equal length and the front wheel is upright. On one I notice a steering problem and consciously hold the bike in a straight line, I notice it more after riding the A10.
To answer your question I wouldn't bother with a modification, ride it first and see if its an issue for you (your frame might be slightly bent or twisted anyway).
Best wishes...
Thanks for your input Spaceman and Bess - all info much appreciated as it helps get a clear understanding of how things were / are. If I've understood things correctly from other posts, the 1deg angle on the front wheel put the tyre contact patch on the road in line with the rear wheel contact patch - hence lining up the front and rear wheels with a straight edge at the bottom of the wheels shows evrything to be correctly in line. With my forks (no 1deg angle) the front and rear wheels can never line up and also be true to the centre line of the frame (not necessarily the same as being ON the centre line). But thats how BSA built them at the time it seems.