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Frame Differences ?


b40rt
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Hi Ross!

I looked up the old bike test from Trialsport, when the yellow Guanaco came out the frame geometrie and the steering angle was changed stated in the bike test from 1980.

When SWM changed the fork from Marzocchi to Betor and cutted away the mudguard loop (which was in 1981 / 82) these were the "only" differences statet back then in a short message in Trialsport (As I found so far), likewise the change to the blue color scheme this was only mentioned once as a favor due to Pernod which was their main sponser !!!

Then again with the Jumbo the complete frame was new developed and also the steereing angle altered, (a story bout the development of the engine and frame in Trialsport of September 1982, issue 78), the foot pegs were placed 5cm to the rear and the complete center of gravity was also placed 2,5cm to the rear, the front therefor feels much lighter on these later bikes.

Anyway with the fork swap from Marzocchi to Betor the complete steering angle was too changed as the dimension and also the overrun is much different between these Fork models.

As I figured out even between Betor forks for Bultaco and SWM.

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Hi Ross!

I looked up the old bike test from Trialsport, when the yellow Guanaco came out the frame geometrie and the steering angle was changed stated in the bike test from 1980.

When SWM changed the fork from Marzocchi to Betor and cutted away the mudguard loop (which was in 1981 / 82) these were the "only" differences statet back then in a short message in Trialsport (As I found so far), likewise the change to the blue color scheme this was only mentioned once as a favor due to Pernod which was their main sponser !!!

Then again with the Jumbo the complete frame was new developed and also the steereing angle altered, (a story bout the development of the engine and frame in Trialsport of September 1982, issue 78), the foot pegs were placed 5cm to the rear and the complete center of gravity was also placed 2,5cm to the rear, the front therefor feels much lighter on these later bikes.

Anyway with the fork swap from Marzocchi to Betor the complete steering angle was too changed as the dimension and also the overrun is much different between these Fork models.

As I figured out even between Betor forks for Bultaco and SWM.

Thanks Patrik, in the last paragraph you say the steering angle was changed with the betor forks, do you mean the design of the forks themselves caused the change ?

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Yes,

the fork set up in geometry between the Marzocchi and the Betor is much different, beginning with the yokes then the length of the forks itself, (Marzocchies are around 30mm longer) and the distance between the axis of the fork and the front wheel axle differs too. I made some measurements and compared the forks but I don't know in which pile I have left the notice. Here some photos:

Marzocchi SWM TL.NW 1980 - Betor Bultaco (lightend) - Betor SWM

WP_20140705_002.jpg

Yokes Bultaco - Yokes SWM:

Yokes.jpg

Distance axis fork to front axle: Marzocci - Betor Bultaco - Betor SWM:

fork+02.jpg

Fork and overrun, as any change in forkangle, fork length, distance fork axis steering steam ... changes the overrun to the fork :

Gabel+03.1.jpgGabel+04.1.jpg

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The difference between the Jumbo type frame (350 or 240 version as the frame is the same) and the previous blue frame is quite noticeable when riding, even just standing on the bike. It's much tighter on the Jumbo and the steering is much quicker. As mentioned above, it's lighter on the front and more maneouverable. The SWM with the Jumbo frame is a very capable bike.

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No, sorry, don't know any figures but the head angle is very similar to modern bikes. Footrest position is personal taste really depending how tall you are, I'd say there was nothing wrong with it for average height riders. I lowered the pegs on mine a bit but didn't move them back

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Cheers Woody. On my bike I have moved my footrests down and back, lengthened the shocks to 395mm and dropped the forks 10mm. Steering is pretty good,as it now stands.

I have just picked up a new frame and plan to steepen the head angle, any pointers would be gratefully received.

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Mmmh ... The hole package counts, even different shock length or rear swing arm length have an influence to the steering geometry.

If I would have an SWM frame - suspension unit left and want to have the unit transformed in something special ... I would take the geometrical specs from a more modern bike and compare them to the geometry of the SWM unit. I would then transform the spec's from the modern bike to the SWM frame. I guess a later Aprillia or end nineties Gas-Gas

(As mentioned IF I would have a spare frame AND would like to some kind of practical RESEARCH.)

There was a very good series about modern trials frames and suspensions and the geometry of the steering, too discussing the possibilities and geometrical spec's. Issued in Trialsport a couple of years ago, I have too look up the numbers.

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Cheers Woody. On my bike I have moved my footrests down and back, lengthened the shocks to 395mm and dropped the forks 10mm. Steering is pretty good,as it now stands.

I have just picked up a new frame and plan to steepen the head angle, any pointers would be gratefully received.

Sorry, can't help with steepening head angles, I wouldn't have a clue how much to do it by. However, having ridden a mate's black frame 280 recently I thought what a nice bike it was and wonder whether the small gain you'd get from altering the steering is worth all the effort. If I owned that black frame bike I definitely wouldn't bother, it didn't feel as though it needed it when riding.

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The other area to consider is the swing arm. The distance between the swing arm spindle and bottom shock mount on the steel units is longer than on the later alloy Jumbo type.

Various differences on the stock footrest positions, I will try and take some photos later in the week when I get back

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