Gents,
I've been giving some tho't to some of the handling vagaries of TS/TM250s since I picked up a 72/3 TS 250 frame & swingarm to go w my 76 motor w the tho't of a Vinduro mount. Seems to me the frame design, construction & geometry are half-decent, but the swingarm is lacking considerably.
At only 32mm OD & 18-19" long, its rather long & slender (to put it mildly) to be resisiting much flex. See 1st pic below. (Ignore the date)
Also, the cross-bracing near the pivot is minimal compared to any decent handling bike of the day, esp euro bikes. See 2nd pic (in subsequent post) along side Ossa Phantom swingarm (whose OD is 36mm). I could have put a Maico, Mon, Cooper or Bul swingarm there as the comparison is similar.
Suz improved things themselves on later TSs. Compare 3rd pic alongside later TS250 swingarm (in 3rd post). Larger OD & better cross-bracing.
Add to that the poor quality of Japanese steel of the day & you have a recipe for a flexy-flier of sorts.
I'm lead to believe that the TS/TM400 swingarms are little/no larger in OD than the 250s 32mm (tho they are apx 1" shorter), which may also help explain some of their infamous handling traits.
As we all know, accessory Cro-Mo swingarms provided a fix back in the day, but where do you find them (at reasonable cost) these days?
It seems to me that a gusset (apx 20x3mm) welded in the vertical plane along the underside of each arm would stiffen it considerably & reduce much of the flex. Bending stresses are highest at the cross-brace, so the gussets should be max height/depth there, then could be tapered down, which would also look better (less obtrusive). Obviously you’d need to check chain clearance too, esp at max suspension travel.
Thats what I plan to do on mine, but its a long way from being completed yet.
I'm not suggesting this would fix all the handling issues & its hardly original, but it is simple & cheap & might just help considerably.
The cross-brace could do w improving also, but thats a bit more involved.
