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scot taco

Comerfords 199B

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I just finished reading a good interview with Yrjo Vesterinen on another site(don,t know if I can  name it without causing trouble).In it he states that he knew there was a problem in 79 with the rear suspension on the Buls.

 In 82,working with Comerfords they had modified it to a point that it was working better.So my questions are to you guys that have the modified Comerfords bikes.

 

Is it a noticeable difference to the average rider?

 

Which modification achieved the improvement?

 

Just curious and trying to learn more about the history.I would love to try and duplicate one,but just plain old 199 models are hard to come by over here and I,m not about to ruin my A model by "trying " to duplicate one. 

 

Thanks,Scott

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I've read the article mentioned. Vesty has never exactly said why they were trying different swing arm and rear suspension. But the point he is trying to get across is that the amount of " anti squat " that was present with the Bultacos was unacceptable for him. " on the rear suspension swing arm angle and chain forces combine to cause stiffening or softening of the rear spring rate during acceleration and deceleration. The effective stiffening is called anti squat as it " holds up" the rear of the motorcycle during acceleration keeping it from squatting." The chain pulls on the rear sprocket and causes the rear suspension to actually extend. This extension causes a momentary lack of grip on with the rear wheel. Woody if you're reading this , this may be why you have said many times that the Bultaco rear suspension feels "dead " Think of a dragster in slow motion pulling away from the start of a 1/4 mile strip. Throttle is applied the rear wheels and suspension actually raise up considerably before forward momentum is gained. This lack of grip obviously can be unwanted. The idea of moving the swing arm forward and up as close to the countershaft sprocket ( main shaft on Bultaco) tends to alleviate the anti squat issue. In theory it makes perfect sense. Look closely at all motorcycles today and you'll note that the swimg arm pivot is almost always as close as possible to the front sprocket. Its been mentioned on this forum that with tire technology being what it is these days the swing arm mod is not something that is necessary for most riding situations. i happen to agree, modern tires are a big step forward from what used to be available. The best advice is to take your time and set up your bike properly. Good quality front and rear suspension set for your weight. Good quality tires Properly adjusted carburetion and no air leaks. Properly adjusted ignition timing. Proper clutch set up. And updates for brakes. All of the above and you'll have a fine weapon for trials !!!

Pleas note that anything in the above post in quotations was not written by me but by Paul thied from the book motorcycle suspension. I've only used it here to describe the issue that vesty wanted to overcome

Steve

Edited by stevem75
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The changes are massive if it's a full replica you're looking at. Airbox and exhaust need complete redesign to fit. And they weren't a pretty bike either...

 

With modern tyres and rear dampers I'd guess it's really not worth the trouble, the rear end on the later Sherpas works as well as anything else really, Fantics and Hondas aside which work better, particularly in light of the sections they're ridden over now.

 

I know a few people who rode Vesty's last bike in trials after he finished with it and to them there was no real noticeable advantage to what had been done

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I had one done by reg at the time for the basic swinging arm and othermods and as stated above it wasnt drastically different in either handling or otherwise.

The bike Woody refers to the ugly one is probably the 3rd 0r 4th generation of moving positions. The rear ward setting of footrests on the 198 probably has more effect on average rider.

However as with all these things there is a trade off. My 340 has more movement at the back wheel which allows for a better suspension set up this also causes a slightly steeper angle at the front and the chain run is much better as pivot is closer the gearbox sprocket.

Yes i think it grips better too.

Is it worth it? I think it depends on what you want from a bike tbh.

I rode vestys bike in a Falcon series in wales and i did think it good although at that stage poorly set up and maintained it was definately the best Bulto id ridden.

Whether the more recent pumas are any good i dont know, vazquez i rode wasnt great tbh.

Edited by nigel dabster
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I just finished reading a good interview with Yrjo Vesterinen on another site(don,t know if I can  name it without causing trouble).In it he states that he knew there was a problem in 79 with the rear suspension on the Buls.

 In 82,working with Comerfords they had modified it to a point that it was working better.So my questions are to you guys that have the modified Comerfords bikes.

 

Is it a noticeable difference to the average rider?

 

Which modification achieved the improvement?

 

Just curious and trying to learn more about the history.I would love to try and duplicate one,but just plain old 199 models are hard to come by over here and I,m not about to ruin my A model by "trying " to duplicate one. 

 

Thanks,Scott

I'm happy to find out more from the 'man himself' if you like?

 

Big John

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Moving the axle of the swing arm as much as possible towards the front sprockets will - as already stated - reduce load sequencing reaction a lot.The distance between the front sprocket and the swing arm of a Sherpa is quite impressing so I think that effect (which hardens the the rear suspension will be much less noticable). In my experience bikes with "short" swing arms do too have the tendency to have a more nervous rear when rolling over "bumpy" obstacles like a field of bigger stones for example.

 

That's one of the reason why the Majesty TY had got an about 30mm lengthened swing arm.

 

Looking forward to any pic's in this matter.

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Stevem75,    I have an Ossa gripper, when I was in my garage at home if my rear tyre was past its best I would sometimes have a bit of fun and  put the bike in forth gear max the revs and dump the clutch and spin the rear tyre out of the garage (dragster style) and the odd thing was the rear of the bike would rise.

I always  thought it was an Ossa thing? And wondered if it made it grip more (pushing the tyre into the ground?)

 

                                               Steve.

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Thanks for all of the replies.

 

Big John and Nigel,that would be great! Pictures and more info from the man himself.

 

Larry and I were taliking the other day after watching some videos(1978 experts in Alabama and the 1982 British experts) about the same topic that Woody brought up.It was amazing what those guys were riding up and with todays tires and suspension our bikes are probably better other than maybe tuning.

 

Steve,that does make sense and I,m sure that is what they where trying to achieve.I hadn,t thought about that because it,s been so long,but I raced a 1979 Maico 400 for some time.The countershaft sprocket on it is right next to the swingarm pivot and when you came out of a corner and got on it hard it would squat,hook up and go.

 

Cheers,Scott

Edited by scot taco
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Thanks for all of the replies.

 

Big John and Nigel,that would be great! Pictures and more info from the man himself.

 

 

Consider it done, but I don't post photos on TC and haven't done so for two years.

 

Big John

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You'd think the tire being pushed into the ground would hook up. But the reality is the suspension is unweighted and that's where the loss of grip comes from.

Steve

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