Swing Arm Extensions For '74 Ty250?

[thats_a_five]

I have a '74 TY250 and it seems like the back end is a bit skittish. I saw someone had posted in one of the forums about modifying the rear suspension to match the dimensions of a Honda TLR200. I checked the measurements and it looks like the swingarm on the TLR is about 1.56 to 2 inches longer that the TY. I have seen a set of weld on extensions for the TY250 on eBay.

Anyone have any inputs on this? Anyone extended theirs? How did it work out?

Note, I am in the USA so no problems with scrutineers. The TY250 is mostly a buddy bike and occasional play bike, not a serious competition machine.

Thanks.

[goudrons]

I extended my 175 like this

Cut up under the shock mount (but not all the way through), than out backwards. Welded a piece in of around an inch.

This way is just brings the slots for the spindle back just over an inch, but you haven't cut all the way through or had to alter the shock angle or mounts.

The 175 is a little short, wheelbase wise and it can make the front end a bit flighty on climbs, also the tyre is very tight against the front of the arm and likes to collect mud, so much so it can jam the wheel. (lots of wet mud over here!)

So far it's worked well, it allows the mud to pass, keeps the front end down a little better on climbs and helps with the feel of the rear suspension.

One thing, you need to lengthen the brake torque arm by the same amount.

I just made another longer one out of a bit of alloy bar.

[mattylad]

In my opinion the TY 250 is perfectly OK with a standard swing arm.

I would move the pegs back 1".

The TY175 however does need to be lengthened 2" is about right on a standard frame

[old trials fanatic]

Miller always used to say 51.5" is the best compromise wheelbase. Seems to work for me too

[thats_a_five]

Nice clean looking TY175 Goudrons. I do expect I will need to extend the brake rod and chain if I do this. And we get plenty of mud here in the US Pacific Northwest - climate similar to the UK.

Matty - not sure I want to move the pegs back. The bike is already pretty front end light, in fact I was thinking the longer swing arm might take it down a little for steep uphills.

[old trials fanatic]

Being able to easily lift the front is not a bad thing and is very useful much better than a heavy front end. If you are having problems on climbs it's more about the riders weight distribution than the bike. Learn to bend your knees and keep the body perpendicular. In the same way that you put your bum as far back as possible on steep downhills the bars come right up to your chest on steep climbs. An extra inch or two on the swing arm will never compensate for poor body positioning.

Sorry if thats not what you wanted to hear but it's a fact.

[b40rt]

Miller always used to say 51.5" is the best compromise wheelbase. Seems to work for me too

Hi Paul

How much of a noticeable difference would an inch either way make ?

Ross

[old trials fanatic]

Hi Paul

How much of a noticeable difference would an inch either way make ?

Ross

You should ask the wife LOL

OK tried lengthening the swing arm by about 1" on the OSSA to be honest all it did was make the bike a pain on tight nadgery stuff. Didnt make any difference on climbs, see my previous comment, so i changed it back and put the old mark 1 swing arm in as i prefer the shorter wheelbase on the tight stuff.

Not saying it wont make a difference but not as much as correct body positioning.

Edited December 5, 2012 by old trials fanatic

[thats_a_five]

I appreciate the discussion so far. Let me get back to my original post. Here is some background.

I normally ride a ’94 Gas Gas. I picked up the TY250 mostly as a buddy bike that would be easy for new riders or friends who had not ridden in a long time to ride. My Gasser was out of service and I was helping set up a trial so used the TY250. I was able to keep up with my buddies on the trails and was really impressed with how well the old girl worked. The main thing I noticed was the back end seemed “skittish.” By that I mean the back end wanted to go sideways almost as much as forward. FYI, I am using modern competition tires.

In reading one of the forums here (maybe Yamaha, maybe Twin shock) I saw a post comparing TY250 and Honda TLR200 rear suspensions and the feeling was the TLR is better. I also happen to own a TLR200. I lined up the Gasser, the TLR and the TY and it became immediately obvious that the TY swingarm was much shorter. I don’t remember the measurements but I think it was 1.5” shorter than the other bikes. Then I saw a listing on eBay for some swingarm extensions for the TY250 built in the UK that add about 1.5 inches in length. My ball bearing sized brain said “Aha!” then went back to sleep.

Hence my post. I do like to tinker so may give them a try but didn’t want to waste my time if everyone told me it makes the TY turn like some Harley chopper or drag bike with wheelie bars.

So, I am still open for input.

To Old Trials Fanatic – The TY is actually a little more front end happy (which I like) than my Gasser. I agree completely on your comments about body position. Now if I could just get my old, fat body to stop flopping around like a cork in a bathtub. . . Cheers mate.

[feetupfun]

The TY250 swingarm is shorter than the TLR swingarm mainly because the TY motor is longer. The most important dimensions for handling are the distance from the rear axle to the footpegs and from the rear axle to the front axle. Yes a longer swingarm will improve the action of the suspension, but the practical upper limit for swingarm length is that the swingarm pivot needs to be behind the motor (for ease of manufacture). The TY250 wheelbase is a bit shorter than most other trials bikes (TLR included) so some people add a bit of wheelbase to get them to be more like other bikes to ride. If you do extend the swingarm, I recommend moving the pegs rearwards to correct the resulting fore-aft weight distribution change, and to add any extra length to the rear of the lower shock mount. You can safely add 25mm to the standard TY250 swingarm and it will still be one of the best turning twinshocks around.

[b40rt]

Interested to know what the standard wheelbase for TY175 & 250 actually is.

feetupfun, you mention the distance between footrests & rear axel & wheelbase as being important, any figures ?

Ross

Edited December 6, 2012 by b40rt

[feetupfun]

My theory is that its the ratio that is important rather than the actual distance ie a longer wheelbase needs the footpegs further forwards in absolute terms than a bike with a shorter wheelbase, but the ideal ratio (for trials) of those distances will be independent of wheelbase. The ratio I'm on about is footpegs to rear axle/front axle to rear axle. I plan to do some measuring on the weekend to see what my various bikes have as that ratio.

I just measured some bike wheelbases that were easy to get to tonight:

Standard TY250 twinshock 50.25 inches

Standard Cota 348 50.75 inches

Standard Godden Majesty 250 52.5 inches

Standard M49 Sherpa T 53 inches

sorry my only standard TY175 is in pieces - my memory is saying 48.5 inches for that one

[jc2]

David, I'm of that theory too, tho expressed as a percentage rather than ratio. I read years ago (in twinshock era) that footpeg-to-rear-axle should be 29% of wheelbase. Thats what I work on as a starting point.

(Tho the modern trend I'd imagine would be different.)

[feetupfun]

OK so I measured some bikes and here are the wheelbases and footpeg loaction ratios expressed as percentages (100xfootpeg to rear axle/wheelbase)

Cota 348 50.75" 28%

TY250A 50.5" 28.7%

Godden Majesty 250 52" 27.4%

M49 Sherpa T 53" 29.7%

OSSA MAR 51.5" 26.2%

KT250 51.5" 28.2%

TY80 41" 30.7%

GasGas50 (2011) 39.25" 33.1%

[b40rt]

That's fantastic, I will add some more when I get a chance, hopefully later today

I take it the higher the percentage the further forward the footrests are ?

I'm really surprised how short the 348 is, somehow I imagined it would be one of the longest.

Ross.