G12 ride height

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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duncanamps
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Joined: Thu Aug 06, 2015 4:23 pm
Location: Essex, England

G12 ride height

Post by duncanamps »

Hello :) I've always had the feeling that my G12 sits too low down, this causes issues with the side stand leaving the bike too upright and the centre stand is difficult to engage.

I've taken a few measurements with the bike on the side stand. Could a kind soul with a G12 / AJS model 31 check these over for me? Trying to find out if it's too low at the back, front, or both.
  • The front distance between the centre of the wheel spindle and the underside of the top yoke is approximately 700mm
    The rear distance between the centres of the lower and upper shock absorber securing bolts is approximately 300mm.
Are either or both of these out ? Grateful for any advice :) There's a picture of the locations here: https://www.dropbox.com/s/zhszdj9zc1ysw ... s.jpg?dl=0
Image

Regards,
Duncan
Groily
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Re: G12 ride height

Post by Groily »

Quick check on my Mod 31, 1961, off the stands, shows 28" or 711mm from wheel spindle centre to underside of top yoke, and the centres of the rear unit mounting bolts are a foot apart, or 305mm. Your yellow circles equivalent. Girlings, near new - but can't remember what setting they're on.
I have no idea if this is 'correct' or not, if figures are available even, but it looks about right to my eyes. The centre stand works fine (haven't had to replace it with a Rob Swift upgrade yet), and side stand is OK, at a fair angle of lean in fact.
So in round numbers I have best part of half an inch more than you at the front, and 1/4" more at the rear. Which I guess could or might make the difference ref the stands?
As to jacking things up a bit . . . rear damper settings maybe? Tired fork springs, and / or are the damper rods a tad short perhaps at the front?
Andy G
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Re: G12 ride height

Post by Andy G »

705mm and 315mm for me. (Rear shocks on lowest setting)
Bombling contentedly around rural Aberdeenshire
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dave16mct
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Re: G12 ride height

Post by dave16mct »

2 bikes: 722 and 310mm, 725 and 312mm. Both rears on lowest setting.
Dave.
duncanamps
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Joined: Thu Aug 06, 2015 4:23 pm
Location: Essex, England

Re: G12 ride height

Post by duncanamps »

Thanks for the feedback, much appreciated.

It sounds like I may have a problem front and back so I need to investigate both. Looks like the spanners (and the credit card) are going to have to come out!

Regards,
Duncan
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spitfire
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Re: G12 ride height

Post by spitfire »

Have you got the right size wheels? Should be 19" wheels on a G12 if they are 18" this would lower the bike quite a bit.
Andy G
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Re: G12 ride height

Post by Andy G »

duncanamps wrote: Thu Apr 29, 2021 7:15 pm Thanks for the feedback, much appreciated.

It sounds like I may have a problem front and back so I need to investigate both. Looks like the spanners (and the credit card) are going to have to come out!

Regards,
Duncan
Are you sure you want to react to those estimates without a little more scientific checking? I mean my measurements were empty tank and on side stand. Grolly said off stands, and I'm sure if I bounced the suspension I could probably get +/-5mm change each time it settled!
Maybe adjust rear settings first and see what happens. As long as it won't fall off the side stand, the most important thing is that it rides comfortably?
Bombling contentedly around rural Aberdeenshire
duncanamps
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Joined: Thu Aug 06, 2015 4:23 pm
Location: Essex, England

Re: G12 ride height

Post by duncanamps »

Andy G wrote: Thu Apr 29, 2021 9:29 pm Are you sure you want to react to those estimates without a little more scientific checking? I mean my measurements were empty tank and on side stand. Grolly said off stands, and I'm sure if I bounced the suspension I could probably get +/-5mm change each time it settled!
Maybe adjust rear settings first and see what happens. As long as it won't fall off the side stand, the most important thing is that it rides comfortably?
Indeed - it's not an exact science due to the number of possible variations, although to be fair my shocks were measured on the highest of the three settings, completely empty tank, and are still shorter than the measurements on here with the lowest of the settings. There was a consistent pattern in the answers, and that in itself was enough for me to go and order another pair through the club earlier today. If it turns out they are not much different, I can sell them on or retain as spares.

The ride is fairly comfortable and the handling seems OK.

The side stand is a cause for concern; it's already rolled off it and taken out a headlight rim+glass and clutch lever. I believe there's two problems with the side stand (1) the bike doesn't tip over to the left very much; this may be caused by the bike being a little lower than I would expect. (2) It doesn't go over-centre very much in the fore and aft direction, maybe 5 degrees tops. Parking on even the mildest downhill will cause it to come off the stand. This may well be an alignment problem, I've looked at a few pictures this evening of G12s on side stands and they seem to lock out on a bigger angle than that.

Spitfire wrote: Have you got the right size wheels? Should be 19" wheels on a G12 if they are 18" this would lower the bike quite a bit.

Good point, have checked and the bike is running on 19" rims and what I believe to be the correct profile tyres (3.25F / 3.50R).

Regards,
Duncan
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clive
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Re: G12 ride height

Post by clive »

I have two bikes a 58 G11CS and a 67 G15 mk2. The stand on the G15 was similar to yours allowing the bike to stay too upright and the one on the G11 allowed the bike to lean over too far. Relatively easy solution for me as I swopped them over but in doing so I checked the length and angle of both stands and they seemed to be the same. So why the difference?
From your description of the fact the stand does not seem to come as far forward as others. Perhaps the difference between my stands is the stop point where the stand hits the frame. If you ground yours back a little you might get a better angle.
Incidentally I would never park my bike on the side stand on even a mild downhill slope without either turning it so that it faces uphill, or if left pointing downhill leaving it in gear with the bars on full lock.
clive
if it ain't broke don't fix
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