BSA C10 C11 C12

BSA C10 C11 C12 Forum => Technical Section => Topic started by: Donald on February 13, 2019, 08:46:46 pm

Title: c11g rear wheel offsett
Post by: Donald on February 13, 2019, 08:46:46 pm
Hi all,
Trying to get an accurate offsett measure ,rear wheel C11G 19 inch WN1 rim ,,
am getting 0.41" to ,0.45" measured across brake I am thinking it should
be 0.43"
Anybody Know for sure?
And will a 3.5 tyre fit ok ? as I have a good 3.5 tyre on front.
Title: Re: c11g rear wheel offsett
Post by: camman3 on February 13, 2019, 10:09:40 pm
I dont know about the offset Donald, but i do know you can fit a 3.5 tyre..just...or at least you can in a c12 with about 3mm clearance of chainguard when wheels aligned.
Having said that, you need to be aware,  not all 3.5 tyres are actually the same overall width.
Title: Re: c11g rear wheel offsett
Post by: Ginge on February 14, 2019, 06:10:59 am
I'd mount the rim and hub without tyre, true the sprocket to the gearbox sprocket and then start measuring rim to a reference point on the frame.  Run the axle hard into the axle slots without the chain tensioners.

If it's a freshly spoked wheel I'd not be finally truing it until I knew the sprockets were aligned and the spacers in the hub were going to allow the wheel to sit where it should for good wheel alignment.  Include the speedo drive in the exercise.

Once in place you can start truing it to the frame rails.  Then you will know what your clearance to frame will be for tyre fitment.

It's a fiddly process but important and satisfying.
Title: Re: c11g rear wheel offsett
Post by: timsdad on February 14, 2019, 07:11:26 am
From memory, the last one I did was an offset of 1/2", which is a very good starting point. As Ginge noted, the wheel can then be finally trued up in the frame because it takes very little tweaking of the nipples to pull the rim across 1/4" either way. However, I would true the two wheels together with a couple of parallel straight-edges for a perfect alignment because that's my method and it works for me. I always did that on race bikes where it can make a difference but a humble C will be fine with less accuracy. Just get it in line with the centre of the frame, check alignment with the front wheel and all will be well.

There is no point in fitting a bigger tyre than a 300, it's only cosmetic. I would be very surprised if any 350 went into a C plunger frame because I could only get a 325 Dunlop into my plunger C11G by running it on the piss to clear the chain guard until I got a new 300 to put in. I know different makes of tyres are different widths but there's little point in going up a size of two because there's not enough power to gain anything and it puts alignment out when you lean the thing on different width tyres front and back.

It's illegal to run a bigger tyre on the front as the largest tyre(s), if they're mixed sizes, has to be on the back of any vehicle. In a nutshell, I'd fit a pair of 300-19 tyres on the bike, pressures 28 psi frt, 30 psi rear,  - it will improve the sharpness of the handling no end. However, it's your bike so do whatever you like with it, Donald!

Title: Re: c11g rear wheel offsett
Post by: Donald on February 14, 2019, 11:53:01 am
Hi all
Thanks Ray, In the box of bits there is a usable front wheel with ok chrome and a new but old 3.50 tyre .the rear wheel is solid but rusty and a 3.50 tyre that looks like a sidecar tyre. When they are fitted to bike ,the rear chain lines up and so do the wheels.The rear tyre  marked 3.50 , measure's 3.25.
I am going to rebuild rear with new rim ,and I think will replace tyres with 3.00 . The rim has a slight wobble so I was going for the middle of my measurements for the offset.
Title: Re: c11g rear wheel offsett
Post by: timsdad on February 14, 2019, 12:19:24 pm
I just wear up old 350 and 325 tyres that I find on my daily-ride bikes. The older the better, as long as they look sound, as they'll last longer than modern namby-pamby soft rubber!

Old tyres just need a couple of hundred miles to scrub them in again and they're as good as gold, wet or dry. I've just replaced an old Michelin on the back of my Thunderbird that I fitted last year. This part-worn Michelin came off the rear wheel of an MV Agusta 250 that I bought in Turin in the mid-80s and it's now worn right up. It handled just fine apart from a bit of white-lining towards the end of its life.