TT250 / TT350 Rear Spring Rate

[Colin Jay]

I would like to setup the rear suspension of the 1988 TT250 that I have recently built up for reliability trials to suit my weigh (about 125kg ready to ride) a bit better as the suspension sags just a bit too much when I am on the bike.

The bike is currently fitted with the std rear shock and spring. I know that the shock is probably past its best (which probably wasn't the best to start with), but it feel ok having reasonable damping and appears to still have it gas charge. If I decide to keep the bike long term, I will invest in a better rear shock, but for now I would just like to sort out the spring rate to better suit my weight.

So some questions;

1. What is the spring rate of the std TT250 rear spring?

2. Is the rear spring rate on the TT350 the same / different? If different, what is the spring rate? (I have a 1990 TT350 that has a shock that feels ok doing a "bump test" and If the spring is heavier I will give it a try)

3. I also have a rear shock from a XT350, does anyone know what rate spring was fitted to this model? (spring has fewer turns and the spring is thicker, which to me means it is a higher (heavier) spring rate.)

4. Any suggestions of other Yamaha models that have springs that might be suitable?

Thanks in advance,

CJ

[80-85 husky]

if your shock is still intact, not leaking oil etc it should be fine to rebuild. I tried twice to rebuild a mates shocker (cocky from the bush) but it had gone up and down 1 too many times without oil and had damaged the seal / upper body just enough to become unfixable..it lasted a month after the first rebuild then the second time a week and the whole seal head failed somehow and Mr Mc Hanic showed me the body was out of round.

I would think that the stock damping on max with new oil and gas should be capable of working for you with the right spring...plenty of suspension experts about..they should get you sorted. may even be good upgrades for that unit I don't know...

[Tomthesparky]

The 250 and 350 shock is the same. Had shock treatment rebuild mine with new spring and damping to suit my weight and could not be happier with it. Well worth every cent.

[80-85 husky]

there ya go "shimples"

[Colin Jay]

I had a bit of a play with the springs yesterday evening. I set up a set of bathroom scales in my press and did some compression tests on the springs by seeing how much weight was recorded on the scales for 10mm of compression of the springs.

The std TT250 spring took 60kg to compress it 10mm so I would say the spring rate is 6kg/mm.

The XT350 spring took 65kg to compress it 10mm so I would say the spring rate is 6.5kg/mm.

Even though the spring XT350 spring is slightly bigger in diameter and a faction shorter than the std TT250 spring, I fitted it onto the TT shock and fitted it into the bike. With a bit of preload adjustment, the static sag was much better, and loaded up (my fat arse on the seat) the loaded sag was a whole lot less than with the std spring.

Out of interest I also took the spring off of a TT600 Ohlin shock that I have and tested it. It took 60kg to compress the 10mm so must be the same rate as the 250 shock at 6kg/mm. It is a real shame that it is about 25mm shorter than the 250 shock, otherwise I would I would give it a try.

I will take the bike out for a test ride somewhwere in the next couple of weeks and see how thing are with the XT350 spring fitted before going any further with "development".

[Wasp]

Just back from up your way , Col . Went for nice ride with the triple , If I knew you needed a hand , I could have called in for a warm drink and annoyed you bit . I think you are on the right track anyway . 

[80-85 husky]

sounds like the xt spring on the ohlins would be worth a try

[Colin Jay]

Just back from up your way , Col . Went for nice ride with the triple , If I knew you needed a hand , I could have called in for a warm drink and annoyed you bit . I think you are on the right track anyway .

I was down in Adelaide for most of the day, plus I presume you were up at Clare so we weren't going to meet up, plus I now live up at Stirling North (no where near Stirling in the Hills, but just out of Port Augusta).

I was going to give you a call today to ask about checking spring rates, but decided to have a bit of a play once I got home from Adelaide and have got thinks sort of sorted for now. I will catch up with you later about whether anything can be done with the TT600 Ohlin shock.