Date sent: Sat, 23 Dec 2000 16:55:33 -0800 Send reply to: mc-chassis-design@micapeak.com From: "Michael Moore" To: MC-CHASSIS-DESIGN Mailing List Subject: Re: CHASSIS LL fork stuff - very long Hello Bryan, > more understandable for a beginner. And it can be fitted to a > conventional frame - my old Guzzi for instance. So I'm avidly and > gratefully reading this thread. The need for a different front end on my V50 Guzzi LSR bike is one of the things that has made me think more about LL-Fs. I've got several different sets of 35mm clamps and telefork legs, but they'll all need stems made and probably caliper hangers etc, as well as fitting with Race Tech Emulators or other damping fiddling. Tony's Aermacchi fork uses a single damper, and the external mounting means that you can fit a nice quality and tuneable Ohlins/WP etc without struggling with fitting the larger springs into the stanchions. I think too that the straight stanchions, without an added on pivot carrier box, will end up lighter than the heavyweight LL-F parts.. I can see ways in which a more conventional (like Craig's and Tony's big bike forks) LL-F lmight be easier to engineer (if you have a milling machine handy), but the lightweight fork has got me thinking about ways and means. *************** I want to now try and work out some numbers for a typical modern RSU sporting telefork, and then similar numbers for LL-F. The new Suzuki GXSR-600 has a 45mm/1.77" OD RSU Showa telefork (reputed in RRW to be the best conventional production street fork). I don't have any modern teleforks, but I just measured a stanchion from a set of 35mm Marzocchi MX forks (which are quite a bit thinner than a set of 36mm Maico stanchions, and less prone to bending too) at >.100"/2.5mm wall thickness. I will presume the Suzuki fork has the same wall thickness for the stanchion tube. The area of various tubes would be: Showa fork = .525 sq inches. 2" x 16g = .380 sq inches or 72% of the Showa 2.25" x 16g = .433 sq inches or 82.5% of the Showa 2.25" x 18g = .339 sq inches or 64.6% of the Showa If I plugged these properly into Tony's second moment of area formula then: Suzuki is .218 2.o " x 16g = .196, approx 90% of the Showa figure. 2.25" x 16g = .282, approx 129% of the Showa figure 2.25" x 18g = .219, approx equal to the Showa figure So the 2" x 16g tube, when compared to the telefork, has 90% of the second moment and 72% of the weight. A 2.25" tube of .065 wall gives a second moment 1.3x larger than the Suzuki and is still only 82% of the weight. Going to .049" wall would make the second moment of the 2.25" tube basically the same as for the Suzuki tube, but with approximately 2/3 the weight. I have no idea how long the Suzuki stanchion tube is, but I'll guesstimate it at 24", which is about what it looks like the 38mm Ceriani is on my Laverda. With a straight tube as on Tony's Aermacchi fork you could have the stanchion be about 28 or 29" - I'll round it to 30" just to be generous to the Showa fork (and to have a round number to work with). That gives a weight per stanchion on the Suzuki of whatever 12.61 cubic inches works out to be, and LL-F stanchion (let's use the 2.25" x 16g to be generous) is 12.885cubic inches. I just looked and found that carbon steel weighs about .284 lbf/cubic inch, which would give the Suzuki tube set at 7.16 lbf and the LL-F 2.25" x 16g tube set at 7.32 lbf, or .16 lbf heavier (roughly 2.5 oz). That difference could be offset by shortening the top of the LL-F stanchion tube and using a dropped upper clamp, but I'll just let it stand for now at the 7.32 lbf figure. The Marzocchi 35mm fork slider and damper rod assy weighs 2.5 lbf per side, and I'd expect the Suzuki sliders to be heavier being as they have a 10mm bigger ID with presumably somewhat similar wall thickness (and some caliper lugs etc). But I'll just use 5 lbf for a pair of Suzuki sliders and damper assys. I just weighed a pair of fork springs from a set of 35mm Ceriani RR fork at 2.5 lbf. I'm going to assume the GSXR fork springs will be larger in OD and somewhat longer overall, and bump the weight to 2.75 lbf for this exercise. That gives a dry weight of 14.9 lbf per pair of 45mm RSU Suzuki fork legs. If they take roughly 200cc of oil each side then that sounds like about .75 lbf for oil, or round it all off at 15.75 lbf for the wet fork leg assys. One of Craig's links (2x1.5x16g, 8" OC) weighs 1.5 lbf with a pair of 3/4"ID Timken taper roller bearings - another 1/4 lbf is added for the .75" OD x .39" ID x 2.2" long (shank and threads) AN bolt and aluminum nut that Craig used for the pivot spindle. That's a .180" wall, and I think that size spindle/bearing set may be larger than is needed in this application. Keep in mind that these were basically prototypes and Craig wasn't taking any chances on things breaking. I think Tony has mentioned using 10mm pivot bolts and a pair of correspondingly smaller sealed ball bearings in some of his LL-Fs, which could knock off about .2 lbf per bearing/pin set (.4 lbf for the fork). In any event, using Craig's links (designed for 25mm axle with lots of clamp so no rear loop was used) gives a pair of link assys weighing 3.5 lbf. With a pair of LL-F straight stanchion tubes we are up to 7.32+3.5 or 10.87 lbf vs an approx 15.75 for the Suzuki forks. A typical Hagon spring/damper assy is 3 lbf, and the Works Performance aluminum-body spring/damper assy for an EX250 Ninja is 4 lbf. The Works spring is going to be a lot heavier than anything you'd need for a fork, so I'll deduct .5 lbf, which gives a single damper mass of 3.5 lbf or a conventional dual damper w/springs mass of 6 lbf. When adding up the LL-F stuff we were at 10.9 lbf. Adding the different dampers possibilities gives a total leg assys mass of approx 14.5-16.9 lbf, or roughly plus or minus 1.25 lbf (depending on single/dual damper) when compared to the Suzuki fork. Smaller bearings/pins in the LL-F could reduce the overall weight by .4 lbf, which would make the LL-F +.85 or - 1.65 lbf when compared to the Showa fork. Don't forget this LL- F stanchion tube is 1.3x on the second moment of area vs the Showa.. The 100x18 Dunlop 591 on the front of my Laverda is roughly 12.5" radius. If we use a 1.25" OD loop-type of link assy with an inside width measurement of 6" (my V65 Guzzi twin disc front is about 5.5" wide at the discs) and 3/4" clearance to the back of the tire we'd need about 33.5" of tubing. 1.25" OD x 18g is .616 lbf/ft, or roughly about 1.7 lbf of tubing. If we use the LL-F stanchion pair weight of 7.32 lbf, the loop link of 1.7 lbf, and 1 lbf for a pair of bearings and spindles we have 10 lbf - round that up to 10.25 lbf for misc sheet metal bracketry. With damper(s) we'd then have 13.75-16.25 lbf for the LL-F less triple clamps. That would be +.5 or - 2.0 lbf when compared to the Showa, possibly a bit less depending on bearing selection. Triple clamps for both kinds of forks would be, if made the same way, roughly equal in weight. I think welded up yokes on the LL-F can end up lighter and stiffer than the cast aluminum clamps on the Showa fork. So from the above it appears that we could end up at roughly the same weight, or 12% less, and with a significantly stiffer assy, than a current good quality production telefork (presuming the figures didn't get away from me somewhere in the process). I'll let someone else figure out the unsprung weight of the LL-F vs the Showa - I need a rest! cheers, Michael ******************************** Ceriani 35mm forks 5" inside width at axle 4" CL radius U bends: 1.25" = 6.75" inside tube 1.375"/35mm = 6.625" inside tube 1.5"/38mm = 6.5" inside tube 1.5" may have a 3" CLR which would be 4.5" inside Headers by Ed 1.25" OD 2.5" CLR, 9", 15" x .049 - 3.75" inside 1.375" OD x .049" 3" CLR 6" and 6" - 4.625" inside 3" CLR 12 and 20" 4" 6 and 6 - 6.625" inside 1.5" OD x .049 3" x 9 and 15 - 4.5" inside 3" x 12 and 20 4" x 9 and 15 - 6.5" inside 6" x 12 and 12 13 June 2015: Jan 1977 Cycle World Maico 400WR 23/30 lb/in spring in 9.0" stroke, 28 degree, 4.9" trail 47/53 @ 256lbf 1/2 wet Aug 1977 CW 370 Pursang 9" leading axle 18 lb/in curb weight 232 lbf 43.4/54.5 FR June 1976 CW 35mm l/axle Marz for 125 from DG 7.5" travel 19/22 progressive Jan 1977 CW Husqvarna 360WR (enduro) 8" 20 lbf/in MX3 CanAm 175 7.5" Betor 23 lbf/in 217lbf curb weight RaceTech 36mm Maico stock .54kg/mm RT 74 CR400 Husky 35mm says stock is way too soft, recommends FRSP 2838 .4, .44, .48kg/mm recommend for me .457kg/mm 4mm preload which is 25.6 lbf/in or 4.48 N/mm Bultaco 35mm Betor also FRSP 2838 or FESP 911 X 40 y 729 166% rise X 35 Y 728 174% X 45 Y 731 159% X 50 Y 732.5 151% 164mm vertical X 55 Y 733.5 145% peak at 156mm then drops 144-143% X 60 Y 734.5 139% peak at 150mm then drops to 137%