Triumphrat

Slinky · 04-26-2006

I am planning to lower my T-bird, the plan is to use progressive springs on the front with shortened (maybe 1" or so) preload spacers.

There seem to be a few different brands about, which of them ( if any) use a spacer? And is there any difference in fork oil level with the different springs? Thanks.

I plan to balance things up by using Legend drop links on the rear. THis is partly for looks, partly to lower the centre of gravity- I'm nt sure that it will make any significant difference to the latter.

jimmyj900 · 04-26-2006

I put Progressive Suspension 11-1144 springs (with 5-13/16" PVC spacers) in my forks and it works fine, so that's a baseline for you.

I'd really suggest that you lower the front end by pulling the fork tubes through the clamps as much as possible rather than taking all the distance off the spacers. You'll be throwing away your suspension preload by shortening the spacers.

I'd also suggest you go to 20 weight fork oil (Yamaha fork and shock oil is good) since you're going to reduce your suspension travel.

Jim

MickMaguire · 04-26-2006

Ditto what Jimmy says on lowering the forks rather than the preload. If you lower the preload you will end up with a squishy suspension with way too much sag. dropping the trees down the forks will maintain stiffness while still lowering the bike. Oil level wise you shoudl keep it the same no matter what the springs etc. Its actually all about the airspace above the oil not the quantity of oil in there.

As Jimmy hints it would be a good idea to stiffen the suspension if you drop it to a point where bottoming might cause impact problems - persoanlly I would do this via increasing preload rather than thicker oil, (but then I would also fit cartridge emulators)

Slinky · 04-26-2006

Thanks Jimmy & Mick,

I was hoping that progressive springs would stiffen up the forks to compensate for less preload via spacers. The other thing I am trying to accomplish is less dive under braking, because my wife complains about it when she rides pillion.

It does make more sense to raise the tubes, I will give that a go.

Saigon5 · 04-26-2006

If you fell that you have dive now, you will have the feeling of more if you take out preload. More or less preload will not change the rate of your springs. There is only one remedy for dive and that is stiffer spring. The stock spring in the TBird are progressive but too soft. I prefer linear rate but that is only me.

At the moment I am using Race Tech springs .95 in my TBS and I weight 160 pounds. I could go a little lower since I can not reach the normally accepted level of sag but at least the dive is not a problem. I made the mistake of using the same rate of springs as I have in my Sprint but the valving was redone and it is stiffer than my Sprint. Basically put, great under hard braking but a bit harsh and jumpy.

Keep in mind that if you work on the front end, the back will come at you. Suspension normally works in balance and affecting this balance will bring your attention to the other end.

jimmyj900 · 04-27-2006

Quote:

I was hoping that progressive springs would stiffen up the forks to compensate for less preload via spacers. The other thing I am trying to accomplish is less dive under braking, because my wife complains about it when she rides pillion.

The progressive springs will cure the braking dive very nicely with the setup I gave above, but you definately need some preload on the spring -- both to control the initial sag and to set up the response of the front suspension under compression.

The spacer I mentioned gives about 3/4" of preload and you can adjust that upwards by adding some fender washers from the local hardware store. To adjust the preload downwards you'll need to shorten the spacer.

If you're going racing then by all means go for a complete Race Tech type system with fixed rate springs and emulators but if you're running a street bike then I think the progressive springs are a better setup.

On a race track you don't have to worry about potholes, railroad tracks or seams in the blacktop so the fixed rate springs are best for the application.

On the street you've got every kind of bump and dip known to mankind and that's where the progressive springs shine. You get a smooth, fairly soft ride on good surfaces and the suspension stiffens up as the bumps get harsher so you don't bottom.

To put it in a nutshell: constant rates for constant conditions and variable rates for variable conditions. Please note that that's my personal opinion and you can expect disagreement. :wink:

Jim

MickMaguire · 04-27-2006

The cartdige emulators are designed to better cope with bumps, not the other way around as you suggest Jimmy. They actually improve the handling dramticly on bumpy roads - I can highly recommend them - they are certainly not just for "racing use".

Quote:

From Race Tech: Old fashioned damping rods while inexpensive to manufacture have major limitations. To create compression damping, oil is shoved through a hole or holes. Shoving oil through holes creates very little resistance to flow at low vertical wheel velocities as when hitting a dip or gully or applying the front brakes. This allows the forks to shoot through the travel fairly easily, diving or bottomming in these situations. On the other hand when the wheel hits something square edge, especially at speed, it needs a lot of oil to pass through the damping holes very quickly. Unfortunately the nature of shoving oil through holes is that as the wheel velocity increases the damping force increases with the square of the velocity. In other words if you double the velocity you get four times the force. This means the hole basically "hydraulic locks" resulting in a harsh spike. Damping rods give the worst of both worlds, they are both too mushy and too harsh at the same time.

what others have to say (I happened to still have some of the links from when I was researching the idea of using them):

Fitted to a sprint

in a v-max

they fit em for off road they are good too

Installed in cruisers for a "plush ride"

The Tiger guys like them too

[ This message was edited by: MickMaguire on 2006-04-27 06:31 ]

MickMaguire · 04-27-2006

Slinky, the best mod - better than fitting race tech springs and emulators that I made was a the swap to the ZRX forks - a lot of work but SIGNIFICANTLY improved over even the upgraded stock items. OK I did ad race tech springs to my ZRX forks but the cartridges are stock.

As an aside Spooner has done the ZRX conversion and "gone the whole hog" with gold valves in his cartridges. I would seriously love to try that out, but unfortuantely my forks are a later design where the cartridges are sealed. At this point I am pretty sure we are into noise level compared to the mods above.

jimmyj900 · 04-27-2006

Well, this thread got way off track.... :-D

Slinky, a concern you expressed was reducing braking dive with your wife riding pillion. Installing the Progressive Suspension (PS) front springs will do that quite nicely and keep the ride smooth and comfortable. I suggested adding 20W fork oil to that since the combination works well with the progressive springs and gives a bit more road feel, but it's not a necessity.

I've ridden my bikes with stock and PS setups, and I've ridden a couple race-prepped bikes and I feel that the PS springs are the best setup for a street bike. You get to keep *most* of the smoothness of a stock bike without the braking dive and you avoid the harshness of the race setup -- but you have to be aware that every bike modification involves some sort of tradeoff.

Cost is another issue. To do the PS setup here in the US would cost around $100. That's $75.99 for the springs from Dennis Kirk (expensive but in stock), shipping, 3 pints of 20W fork oil from the local Yamaha dealer and a couple feet of schedule 40 PVC from the local hardware. Ask the RT fans what their setup costs: I don't know personally and haven't looked at the pricing in years.

The real question here is what you want. If you're just cruising with the wife and want to end the braking dive then the PS springs are the way to go. If you're occasionally pushing the bike to your limits and need extended capability then by all means go for the RT setup.

Jim

jimmyj900 · 04-27-2006

Quote:

The cartdige emulators are designed to better cope with bumps, not the other way around as you suggest Jimmy.

Quote:

On a race track you don't have to worry about potholes, railroad tracks or seams in the blacktop so the fixed rate springs are best for the application.

I was talking about the springs, not the emulators. That's not an 'issue' from my end, OK?

Jim