jimmyl Posted September 20, 2009 Report Share Posted September 20, 2009 I have a TLR 200 and 4rt and being an inquisitive engineering type have cast a tape over various dimensions. Most notably is that the engine is much further forward in the 4rt and obviously the steering is much sharper. I have a project to fit a 315 swing arm into the TLR (with lugs welded on for 2 shocks) but as the 315 swing arm is longer I need to shorten the front end of the s/arm which is no problem. But as I have the longer swing arm and before I cut off 2"s I was wondering what would be the effects of pushing the engine forward to mimic 4rt dimensions (especially if combined with sharpening up the head angle) Would be interested to hear peoples opinions -is there any mileage in trying to get geometry similar to a 4rt so a tlr would to steer and feel like a 4rt (with a lot less power) or will it make it a dog. Opinions and views welcome Quote Link to comment Share on other sites More sharing options...
andy m Posted September 20, 2009 Report Share Posted September 20, 2009 I can't answer your question but I can say I was observing at a trial today and I was talking to one of the Tlr200 riders and he has his geometry set to the same dimensions as a Montesa 315r. Quote Link to comment Share on other sites More sharing options...
grahamjayzee Posted September 21, 2009 Report Share Posted September 21, 2009 Interesting project, and discussion for us engineering types! As I understand it, there are many benefits of a longer swinging arm (more grip, suspension less affected by chain pull) and moving the engine forward is the way to achieve this. It's not that the swinging arm is made longer to accomodate the forward engine position. However, there are loads of knock-on effects by any one of these changes. I'm guessing you will be limitted by the 'packaging', but I would have thought getting the motor forward and increasing the swinging arm length will improve the rideability, and obviously steepening the steering angle to maintain the wheelbase will go along with this. What are you planning to do with the footrest position? All the above changes will have a big effect on weight distribution and I suspect you may need to re-position the other moveable mass centre (your good self)! I shall watch with interset! Good Luck Graham Quote Link to comment Share on other sites More sharing options...
bobtlr Posted September 21, 2009 Report Share Posted September 21, 2009 hello, a longer swingarm is a good thing on those tlr's (250 needs it more) the front of the tlr is very light and using a longer swingarm helps here on the 200 you could move the footrests back a bit but you should lower them at the same time (balance will improve ) on a 250 you better don't move the pegs back. I wil be doing this to my own 250 during the winter. regards bob Quote Link to comment Share on other sites More sharing options...
farjazz Posted September 21, 2009 Report Share Posted September 21, 2009 my tlr 200 has had the head angle altered footrest position lowered ,moved back .It is a 250 frame with alloy swing arm and now has same dimensions as a 4rt cannot say if it feels like a 4rt to ride as ride a beta but certainly feels very modern now and very light in sections Quote Link to comment Share on other sites More sharing options...
jimmyl Posted September 21, 2009 Author Report Share Posted September 21, 2009 Just been doing some measuring and weighing. 4rt has 50 50 weight distribution 39.5 kgs each on front wheel/back wheel. TLR weighs 50.3 kg back wheel and 39.9 front Tends to show shoving weight forward would be good. Centre point of head stock on TLR is about 20mm back from a 4rt. Engine is 45mm further back on tlr. I think push whole bike forward by 20mm by tightening head angle to 4rt spec then use the longer swingarm to get wheel base back to 52.5". Adjust footrest position afterwards to something like 4rt. One thing I have noticed is the yokes on tlr have smaller offset fork centres to head stock centre line - 15mm approx. 4rt has 35mm offset.Tis pushes forks further away from centre line of steering axis - what effects does this have?? All part of camber, caster and rake etc but don't know the theory Farjazz do you know what dimensins where changed from/to on your tlr Quote Link to comment Share on other sites More sharing options...
alan Posted September 21, 2009 Report Share Posted September 21, 2009 One thing I have noticed is the yokes on tlr have smaller offset fork centres to head stock centre line - 15mm approx. 4rt has 35mm offset.Tis pushes forks further away from centre line of steering axis - what effects does this have?? All part of camber, caster and rake etc but don't know the theory the bigger the offset reduces the trail and makes it easier to steer and more difficult to keep it going straight. Offset used to be acheived by having a leading axle, this has the advantage that it reduces the inertia caused by offsetting the weight of the forks and wheel. i guess with modern forks being lighter this is less critical, and sharper head angles means that both fork offset and leading axles are required to reduce the trial. Quote Link to comment Share on other sites More sharing options...
bigmike1961 Posted September 25, 2009 Report Share Posted September 25, 2009 One thing I have noticed is the yokes on tlr have smaller offset fork centres to head stock centre line - 15mm approx. 4rt has 35mm offset.Tis pushes forks further away from centre line of steering axis - what effects does this have?? All part of camber, caster and rake etc but don't know the theory the bigger the offset reduces the trail and makes it easier to steer and more difficult to keep it going straight. I too am rather interested in this steering geometry black art as I'm sitting looking at a TL 125 frame just aquired from Ebay, an XL185 engine. a complete TL 125 and my Scorpa SY250.I was wondering if it would be possible to make the TL steer more like the Scorpa. The second hand frame was obtained to modify to but have an origional untouched frame incase things went horribly wrong in the modification process. Quote Link to comment Share on other sites More sharing options...
veggiedog Posted December 4, 2009 Report Share Posted December 4, 2009 I too am rather interested in this steering geometry black art as I'm sitting looking at a TL 125 frame just aquired from Ebay, an XL185 engine. a complete TL 125 and my Scorpa SY250.I was wondering if it would be possible to make the TL steer more like the Scorpa. The second hand frame was obtained to modify to but have an origional untouched frame incase things went horribly wrong in the modification process. Funny, I too have both an SY250 (2004) and a TL125 (1974). The Scorpa head rake is 5 deg steeper than the Honda. I calculated that pulling the bottom of the steering neck on the Honda back 0.7 inches will result in the rake matching the SY250, and that translates to about 5" raise at the rear axle to have a similar effect on steering geometry, so I went into the drive, perched the Honda's rear wheel on a 5" rock (handily stuck in the middle of my drive for trials practicing), and I balanced out. Very intuitive feel for balancing the bike, similar to Scorpa. I feel very compelled to pull the bottom of the steering neck back on the Honda. I plan on upgrading the rear shocks, if I go longer, or I raise the rear of the bike by relocating the bottom shock mount higher (welded tab), I can pull the neck back a little less so that the end result is still similar to the Scorpa's rake. Will I still be able to compete vintage? If I update the front forks with dampening cartridges (I have a lathe and CNC mill), will that violate the spirit of vintage competition? Quote Link to comment Share on other sites More sharing options...
b40rt Posted December 5, 2009 Report Share Posted December 5, 2009 Funny, I too have both an SY250 (2004) and a TL125 (1974). The Scorpa head rake is 5 deg steeper than the Honda. I calculated that pulling the bottom of the steering neck on the Honda back 0.7 inches will result in the rake matching the SY250, and that translates to about 5" raise at the rear axle to have a similar effect on steering geometry, so I went into the drive, perched the Honda's rear wheel on a 5" rock (handily stuck in the middle of my drive for trials practicing), and I balanced out. Very intuitive feel for balancing the bike, similar to Scorpa. I feel very compelled to pull the bottom of the steering neck back on the Honda. I plan on upgrading the rear shocks, if I go longer, or I raise the rear of the bike by relocating the bottom shock mount higher (welded tab), I can pull the neck back a little less so that the end result is still similar to the Scorpa's rake.Will I still be able to compete vintage? If I update the front forks with dampening cartridges (I have a lathe and CNC mill), will that violate the spirit of vintage competition? Most genuine pre-65 frames have had this type of mod, so if you know anybody that runs one, they should be able to give you first hand experience. Quote Link to comment Share on other sites More sharing options...
n714ag Posted December 5, 2009 Report Share Posted December 5, 2009 In ITSA competition, those mods would move you from "Historic Twinshock" into "Modern Twinshock"... In "Modern Twinshock" "anything goes" as long as it has twin shocks, air cooled engine and drum brakes... Murray Quote Link to comment Share on other sites More sharing options...
pat Posted December 5, 2009 Report Share Posted December 5, 2009 (edited) Not just a Honda but chassie geomtr improvements seems to be nice from looking at pics: TLR http://www.flickr.com/photos/70366351@N00/2880053056/ Fantic 240 Special http://www.thetwinshockshop.co.uk/bikes.php Puma Racing Sherpa http://www.flickr.com/photos/70366351@N00/2910344640/ http://www.flickr.com/photos/70366351@N00/2880043228/ Montesa 247 de Jose Luis Rodriguez (Mr Puma Racing) http://www.flickr.com/photos/70366351@N00/3654146615/ Bultaco & Ossa at the middle of this page, bikes of the year in my opinoin http://montesakingscorpion.blogspot.com/20...ores-en-el.htmlB Bultaco alone http://www.flickr.com/photos/70366351@N00/3654145849/ Sorry for answering on this OT posting, but postings about "std trials bikes status as bought from a dealer" are due to non issues as I see it -its motorsport competition equipment and rider status stands for 80-85% of final results. Murray, Definatley odd to set up those kind of rules now because; nationals or WTC have never had regs against bike improvements..regarding weight red, chassie geomtr, susp- or brakes improv, NOT TODAY or not 35y ago..(for classic trials comp, manufacturing year of replacement parts is easy to define and accept or not) Collectors eg a Norton Manx in the living room is an other topic.. Yes its big difference today in matter what can be accomplished by skilled workshops/engineering and is available for lot more people, nothing is impossible to manufactor/improve. note: inovative solutions for motorsport in general is in fact not a new thing, google around and search for RoadRacing engineering from late 50`mid 60 Edited December 6, 2009 by Pat Quote Link to comment Share on other sites More sharing options...
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