Finding grip & longer swingarms

[jc2]

Can anyone tell me the theory/reasons why longer swingarms are said to give more grip?

[feetupfun]

I think that it isn't really the length of the swingarm per se that is important, but that the relationship between the upper run of the chain and the location of the swingarm pivot is important.

Changing swingarm length on a bike can affect the geometry of the chain run, and it also changes the fore/aft weight distribution of the bike+rider.

[old trials fanatic]

Depending on the shock mounts positioning, usually better to lengthen between the shock mount and the rear wheel spindle as a general rule of thumb, it can give a longer suspension travel at the rear wheel which in theory should give softer longer suspension movement improving traction. However the trade off is a longer wheelbase which makes tight turns more difficult. when you "modify" a bike the first thing you should do is decide what it is you want to achieve and where you are havin difficulties. Dont be a sheep analize what you are doing. Decide on a course of action and accept there will always be a trade off.

somebody is bound to disagree though

[ham2]

I realise that there are so many factors involved in trying to make a trials bike grip but I was also very curious about that question a few years ago.

So...

I had a 2001,2002,2003 290 Sherco available for a bit of back-to-back testing (on the same slope)and the one with the worst grip was the 2002...the one with the longest swing-arm?!

[baldilocks]

This is my theory so dont kill me for it but a polite correction is perfectly acceptable.

I think grip is related to weight distribution and keeping the wheel on the ground. If the shock was adjusted to compensate for a change in swinging arm length then I think a shorter swinging arm should grip better as the rider and engine are closer to the rear tyre ??

[audimess]

Thats because you need a shorter swinging arm for more grip and a longer swinging arm for directional stability. As always its a compromise.

If you want more grip, never ever (in the UK especially in winter) run your chain adjusters any where near their maximum extension, use a half link and keep the wheel as far forward as poss.

[jon v8]

Just to confuse even more,surely standing on the footpegs on the balls of your feet,(Rather than the instep) will transfer your body weight further back to obtain better grip in a poor traction situation.I know this is tiring,but for a short time in a section might help.

Now I know I've stirred it up.

[sir dabs alot]

With Mt bikes, shorter chain stays equal more traction. Reason being that the rear wheel is more directly under the weight of your body. If chain stays are long, the rear wheel bites pretty well until you lean forward to keep the front end from coming up then the rear wheel will loose traction and spin so a good balance of front to rear weighting keeps things optimal for traction as well as stability (keeping the front end on the ground).

I recently bought a Cota 242 from a guy who also had a Cota 200. The 200 turned noticably better than the 242. My initial thought was that the head angle was steeper on the 200. He told me it the 200's head angle was actually slacker than the 242 and that a shorter swing arm on the 200 was the reason for the better turning traits. He said the only downside of the short swing arm on the 200 was that it had a tendency to wheelie out from under him on steep uphills. After riding both bikes back to back, I have to agree with him. I noticed in a trial I rode with him that he had a time keeping the front end down and he is a VERY accomplished rider.

Edited December 1, 2010 by Trialsin1

[htrdoug]

So why is it my 2003 TXT Gasgas has loads more grip than my 1984 240 Fantic? The Gasgas swing arm is several inches longer,plus the Gasgas will turn inside the fantic anywhere.fantic has a almost new sharp edged rear tire,gasgas rear tire is almost worn out. They have virtually the same wheelbase,engine and footpegs are farther forward on the gasgas.My 309 Fantic has close to the same layout as the Gasgas and it also hooks and turns better than the 240.

[sir dabs alot]

Could it be the quality and functionality difference of rear shocks??????

I have measured peg to rear axle, peg to front axle and wheelbases on different bikes before trying to set one up to react like the other.

Even though the swing arm is longer on the Gas Gas is the rear axle closer to the pegs????

I'm just throwing things out there because this is an interesting topic to me and I have had the same questions before.

I've read articles on older bikes and the comment about long swingarms was that the bike stayed on line better and the front wheel stayed down instead of having to fight it to keep it on line and planted for steering.

[sir dabs alot]

So why is it my 2003 TXT Gasgas has loads more grip than my 1984 240 Fantic? The Gasgas swing arm is several inches longer,plus the Gasgas will turn inside the fantic anywhere.fantic has a almost new sharp edged rear tire,gasgas rear tire is almost worn out. They have virtually the same wheelbase,engine and footpegs are farther forward on the gasgas.My 309 Fantic has close to the same layout as the Gasgas and it also hooks and turns better than the 240.

I've never measured them but my Beta swing arm looks several inches longer than my KT or Cota and grips better by a long shot than either of those bikes.

[old trials fanatic]

So why is it my 2003 TXT Gasgas has loads more grip than my 1984 240 Fantic? The Gasgas swing arm is several inches longer,plus the Gasgas will turn inside the fantic anywhere.fantic has a almost new sharp edged rear tire,gasgas rear tire is almost worn out. They have virtually the same wheelbase,engine and footpegs are farther forward on the gasgas.My 309 Fantic has close to the same layout as the Gasgas and it also hooks and turns better than the 240.

Youre trying to compare monoshocks to twinshocks and there is no comparison. I go back to my earlier statement about suspension travel or to be more accurate rear wheel travel. The main reason for going mono was to get a longer and smoother rear wheel movement. That is what a longer swing arm does, simple physics really. As for tighter turning well i did also say in my original posting that there is always a trade off and a longer swingarm means a longer wheelbase which means slower turning all other peramiters staying the same. Of course a shorter swing arm gives grip at the expense of looping over on climbs but a longer arm gives better grip on climbs and absorbs rocks, steps etc maintaining grip and traction. To maintain the length of the wheelbase and get the bike to turn tighter you would have to steepen the head angle and the trade off for that is the bike will tend to "tuck under" on tight turns over rocks especially.

Why does everbody never look at the big picture? If it was that simple everybody would do it. If you decide to modify from the "compromise" that the manufacturer thought would suit the vast majority of their customers you have to decide 1. What do i actually want to achieve and 2. What downside am i willing to accept?

[sir dabs alot]

Youre trying to compare monoshocks to twinshocks and there is no comparison. I go back to my earlier statement about suspension travel or to be more accurate rear wheel travel. The main reason for going mono was to get a longer and smoother rear wheel movement. That is what a longer swing arm does, simple physics really. As for tighter turning well i did also say in my original posting that there is always a trade off and a longer swingarm means a longer wheelbase which means slower turning all other peramiters staying the same. Of course a shorter swing arm gives grip at the expense of looping over on climbs but a longer arm gives better grip on climbs and absorbs rocks, steps etc maintaining grip and traction. To maintain the length of the wheelbase and get the bike to turn tighter you would have to steepen the head angle and the trade off for that is the bike will tend to "tuck under" on tight turns over rocks especially.

Why does everbody never look at the big picture? If it was that simple everybody would do it. If you decide to modify from the "compromise" that the manufacturer thought would suit the vast majority of their customers you have to decide 1. What do i actually want to achieve and 2. What downside am i willing to accept?

Good point! I guess it really takes more than plug in wheelbase x, heangle x and swingarm x and ride. Offset and rake for forks, fork length, motor position fore and aft, peg position and on and on make it hard to put in a neat nice package for all.

[baldilocks]

also power delivery is a factor here. If you put the 240 fantic engine in the Gas Gas frame it wouldnt grip the same as with the Gas Gas engine.

I had a 240 fantic as a kid, rocky trials were great, muddy trials stay at home.

[jimmyl]

52 inch wheel base has been the optimum for a long time. Older bikes had larger head angles to give stability for no stop riding. The modern riding style (use of clutch, stop start, improved fitness, lighter bikes etc) and improved rear suspension has tightened head angles and pushed engines forward allowing longer swing arms.

I think you need to determine how you ride and what characteristics the bike has before you can determine what effect the swing arm will have.

I have tweaked a tlr head angle in to help steering but find front end lighter now, will lengthen swing arm to get back to 52 inch wheel base to restore balance.

21" front wheel, 18" rear wheel, 6" suspension travel front and back and 52" wheel base leaves few major things to play with