TY175 swingarm lengthening

[David Lahey]

Had some workshop fun last weekend - just another page in the endless "fiddling with my TY175" story

[Reinald]

Hi Dave,
Is this due to other frame modifications or just for stability up hill?

[David Lahey]

The standard TY175 frame is short and has slow steering. I find the standard combination is pretty good except for uphill turns. The first set of frame mods made the steering lighter in turns so is a bit easier to control when going very slowly with a lot of load on the front. It also moved the bars forwards, which improved the ergonomics but uphill turns were still tricky. The motor mods made the motor much more snappy which exaggerated the instability in uphill turns. The swingarm mod has put noticably more weight on the front end and it now turns uphill much better. The steering is still nice and light even when loaded. The swingarm lenthening has also softened the rear suspension a bit, due to the increased wheel travel.
I rode the modified TY175/205 back to back today with the 250 Majesty and the handling and steering is very similar, but the TY175/205 is lighter-feeling overall.

[Reinald]

Was this the bike that you cut a piece out of the frame to shorten the "backbone"?
If you can get to handle like the Majesty then that would be worth the mods.

[David Lahey]

Ah yes - from a man who has ridden the Majesty. The TY175 might now handle like the Majesty, but what more do I have to do to it to make it handle like an SWM TL320 hey??
The frame mod was to lengthen the top tube frame tube. That moved the bars forward and steepened the head angle.
I've just put a better story and more photos on the Trials Central Yamaha forum by request
David

[Tee-Why]

Nice productive work David, I always enjoy the reasoning behind the mods too. I know how much thought it is before one cuts and welds, measure twice-cut once is the plan. As with the final results, it can be a bit of budge with something else to alleviate like the brake rod items etc. (from experience with making a lift kit for a 4x4, there was another added task attached with each step!)

I have been looking at my own TY175 for similar reasons, more power has made the front end plow in tight turns. So far I have managed to keep the bottom end tractable enough. I made new footpegs plates fitted new wider footpegs lower, not back. This lowered the rider weight without loading the rear any further, and less tendency to feel poor on uphills. But I want to weight the forks by moving the controls forward to load the front end with bar offsets. This will basically mean no frame mods. But the rear springs are standard length, and could really be the longer ones to achieve a bit more forward bias. As always, never finished looking outside of the box for improvements!

[Guy53]

Super nice job on the swingarm. My question is not on that job but on the front end, I finaly laid my and on a ty250A frame that I intend to torture, I will lay shock mount '' A LA Majesty '' try to raise the motor an inch but what realy interest me is to play around with the fork rake, it seem's to me that I should '' close '' the angle. Did you ever tried and if so what was the result?

Guy

[David Lahey]

I like the standard steering angle on the TY250 twinshock so have not tried changing it. I have fiddled with a TY250 frame though, to raise the motor by shortening the frame uprights.
Raising the motor by relocating the shock mounts does give more ground clearance under the motor but also raises the bike's centre of gravity. The first Majestys were made using modified Yamaha frames that had the frame uprights shortened, as well as relocating the top shock mount to soften the action of the rear end.
If you raise the bike by raising the rear end you will get a steeper steering angle without having to do frame cuts.

[Guy53]

That was my first intention but I tought it would alter the overall balance of the byke. Footrest mod made such an improvement ( 1 3/8 inch lower and back ) my idea was that increasing the lenght of the shock more than 340 mm would pin down the front end without giving me quicker steering.

[Greg Harding]

Hi Everyone,

Interesting, I assume all of you realize that there are purists who only beleive in concourse del elegance and the manufacturer got it perfect in every way!

Thankfully most people are more realistic, ever since the beginning of time we have been improving things and why not?

All of the modifications discussed here could have been acheived in that era and I have no problem with them at all.

Personally, (hypothetically speaking) A 35mm longer swingarm with axle slots 10mm lower mounted to a standard frame improves the overall handling. What about the chain hitting the swingarm pivot you say? Good question, 60 tooth sprocket and 340mm between centres shock absorbers gives enough squat under power. Plus more ground clearance and steering which is both responsive and stable. Yes it does raise the centre of gravity a little but the improvements in the way it puts down power up hill makes it worth it. Always more than a couple of things to consider.

David and Chippy, maybe this will distract your attention away from my heavy duty tie down points?

[Tee-Why]

Hi Everyone,

Interesting, I assume all of you realize that there are purists who only beleive in concourse del elegance and the manufacturer got it perfect in every way!

I dont know what the Yamaha engineers or Mick Andrews (still a legend anyway) were thinking when they made and endorsed the TY175, but the biggest fundamental flaw in the swingarm design in my opinion is the axis or pivot point of the location of the swingarm bolt. Having it rear set of the bottom frame loops and close to the footpegs allows no progressive leverage. They inset mounted the swingarm on the TY250 and all the DT's also, when there is just enough room to do this mod carefully anyway. This would lengthen the swingarm somewhat also, and would need stiffer springs. Also having the countershaft spocket closer to the pivot is usually the norm on most bikes anyway to lessen chain loading and wear.
Just look at a modern bike to compare how far back the pegs are to the pivot point,but then the linkages in the shock are progressive also.

I did a comparison with a DT175 swingarm to the TY175, its way too long, heavy and shock mounts wrong. Nothing like it could not have been an achieved mod back in the era, using like available era parts??

[David Lahey]

Why manufacturers make bikes the way they do is a fascinating subject. Here are some ideas I had for the swingarm pivot location:
Maybe the motor is hard to get into the frame (with cylinder attached as it would have been in the factory) with the swingarm pivot any further forwards?
Maybe it is something to do with the TY175 motor being so short front-to-rear and Yamaha wanting to keep the swingarm length similar to the other trials bikes of the era?
Maybe it was because the TY175 was based on a slapped-together prototype? (as was the small-wheel TY80).

[Guy53]

I was working for a Yamaha/Bultaco dealer in 74, I was riding a trialised Alpina 350 and practicing EVEREADY and I repeat EVEREADY day 300 feet behind the dealership, many owners or owners to be of ( in the time ) called '' off road motorcycle '' where watching me and 3 or 4 riders who where, in our area just tring to learm what '' trial '' was, and we ( I ) where pretty good. I can tell you that we sold more than 25 TY250A that year ( price was I remember $980.00 cnd dollars including taxes ), I dont think that 15% of those bykes where actualy use for real trial, most guy's used them as low seat very '' gentle '' t r a i l byke ( compared with DT's Susuki RL and other of that kind they where fun to ride ) and installed knobby tires on them. Yamaha , Kawasaki, Suzuki and other companies realised before they whent into production that most buyers wouldn't use there trial moto for real trial but for casual trail riding. So I think that, at least in North America ( specialy in Canada ), Yamaha and other's didn't develop a real TY 175 or 250 but a general public close to trial moto. Maybe that's why we are today asking us why they did not made and sell them as would Mick, Sammy or other legend of the time would have. Maybe I am wrong but that doesn't change a thing, I am still locking for ways to improve my 250A and that job on the swingarm is a super job.

Guy

[David Lahey]

Guy it was the same here in Australia. For every ten TYs sold, only one would ever see a trials section. The KT250 was especially popular for trail riding and almost never seen at trials competitions.
Sounds like the chicken or the egg question to me. Did the Jap trials bikes make gentle/mountainous terrain trail riding popular, or did the Japs make their trials bikes to be good for that sort of trail riding?
I remember plenty of magazine tests of the time saying how this or that Jap trials bike fitted the requirements of the Bultaco Alpina/OSSA Explorer rider but was probably going to be less hassle to own and maintain than the Spanish bikes.
I do know that the TY250A is a very close copy of the prototype bike that Mick Andrews rode in the 1973 SSDT, so that makes me think that when Yamaha made the TY250A, they were pretty serious about making a bike that was good for trials competition. Not sure about the TY175 and TY80 though.

[David Lahey]

Hey Guy. You were talking about your trialised 350 Alpina. Here is mine in a photo taken in 1975. Mine was the first model 325 Alpina fitted with a big rear sprocket and trials tyres.
Hagsta, you can see those black Inter-Am solid alloy bars in this photo - that's why yours are going on my current Alpina.

[Guy53]

Oh God, I don't like to see that picture : low front fender, trial bars, and big sprocket. Where you set up with an 11 tooth front sprocket ( out of a 1972 125cc Pursang ) ? It was a lot of fun to ride. Mine was serial # 116000295 imagine I still remember that number by heart !!! Would you beleve I went to buy tire at Motosport GL in Bedford ( Quebec ) and the frame of that Alpina was lying in the back yard.

Guy

[David Lahey]

Personally, (hypothetically speaking) A 35mm longer swingarm with axle slots 10mm lower mounted to a standard frame improves the overall handling. What about the chain hitting the swingarm pivot you say? Good question, 60 tooth sprocket and 340mm between centres shock absorbers gives enough squat under power. Plus more ground clearance and steering which is both responsive and stable. Yes it does raise the centre of gravity a little but the improvements in the way it puts down power up hill makes it worth it. Always more than a couple of things to consider.

David and Chippy, maybe this will distract your attention away from my heavy duty tie down points?

Greg, You have just made me very interested in having a close look at your "hypothetical" swingarm mods.

I don't think I need to check out the "tie down points" too much because I reckon I already know what is going on there. Another hypothetical person who makes hypothetical changes to 1970s bikes needed some fork tubes for a hypothetical TY175. They hypothetically used the tubes from an early 1980s CR80 Honda MX bike. At least they hypothetically shortened the tubes back to TY175 length in the lathe first.

[Greg Harding]

Hi Everyone,

Interesting, _____________________________________________________some one let the cat out of the bag!

Roger (Subanator), according to Mick Andrews, both the TY175 and TY80 were developed without the bosses consent. If you compare TY250 and TY175 swingarms, they are very similar and share components. So I am thinking the location of swingarm pivot on the TY175 has more to do with using existing components rather than making it work better. Although I agree with your opinion, you are missing a major point about the length of a swingarm, generally the longer it is improves the way the bike puts down power especially up hill by reducing the tendency to wheelstand.

David, I can confirm one of your hypothetical questions, the HEAVY DUTY tie down points came to me as is on a TY175C. The previous owner told me they were CR 80 tubes with TY175 sliders, all I have done is change to lighter oil and play with the preload to suit my liking. Hypothetically speaking, longer tubes and longer springs may equal a more progressive action!

[David Lahey]

Seeing we were on the subject of swingarm length, I thought a few swingarm lengths from popular old trials bikes might start a bit of discussion.

Here is what I could reach with a tape measure last night in the shed. I measured wherever the axle was at the time rather than the middle of the adjustment slot.

I have put them in order of when the model was first sold because there seemed to be a rough correlation between swingarm length and year of bike release:

Bultaco M49 series 1 (1968) 385mm
OSSA MAR (1972) 390mm
TY250 (1973) 380mm
TY175 (1975) 385mm
KT250 (1975) 420mm
Cota 348 (1976) 430mm
Bultaco M198 (1977) 410mm
SWM TL320 (1980) 455mm

[David Lahey]

After the swingarm lengthening went so well I decided to keep fiddling. The next thing I thought of was that the rear suspension was not moving enough. A few weeks ago I watched the new Mick Andrews DVD and he has a lot to say about suspension settings so after mulling it over, I fitted 40 pound springs instead of the 50 pound springs. At the same time I tested a couple of different types of bottoming cushions and ended up very happy with the rear end. After that I rode a practice session that had lots of rocks and decided that the forks were not using enough of their travel. The forks were TY250B with less preload than standard and otherwise standard. They were just right as far as preload goes, just returning the forks to the top with no rider aboard, but they seemed harsh compared with the same forks on a TY250 (probably due to the weight difference between the bikes). As an experiment I removed the preload spacers and fitted short sections of fork spring instead, effectively reducing the overall spring rate.
The forks are now much more supple. The fork setup change and the rear end changes have made the bike more relaxing to ride in general and much better in rocks.