90S front-rear attitude

[Abstruse1]

I just finished upgrading the forks on my '76 90S with RaceTech springs and emulators (and Toaster Tan's top triple clamp). I also replaced the rear shocks with a pair that has adjustable damping (compression and rebound together) My reason for doing this was that in ordinary riding, the forks compressed almost all their 8.1" of travel, and I wanted to improve the handling.

The bike rides fine now, for the most part, but it does have a tendency to "float" a bit at highway speeds. This isn't like it's starting to wobble -- if I bump the bars to induce a bit of wobble, it straightens out nicely. Maybe these old bikes always rode like this.

Like a moron, I failed to measure the bike's attitude -- fore and aft ride heights -- before doing this (altho that may not have been very instructive if the springs were fatigued). As it is set up now, hard bumps cause a bit less that 4" of travel from the unloaded position, and the sag is ~1" (with me on the bike). Ride is plenty comfortable.

So, I'm wondering if I changed the bike's attitude, e.g. by lowering the front end an inch or two, how that would affect the at-speed handling.

Bike has new tires and I'm running abt. 32/36 psi F/R.

Your thoughts appreciated. Thanx.

[bbelk]

Too tight on the steering bearings can cause a weave. Not as dramatic as a wobble, but still unnearving.

[Mal S7]

Racetech springs are a lot stiffer than stock so your forks are most likely sitting higher rather than lower. Stock they sag quite a bit when loaded. I fitted Sonic springs and emulators, the front definitely sits higher, stiffer springs limit the maximum 'sag' you can set. Sitting higher at the front will slow the steering a bit (think of a chopper as an extreme example) and give you a bit more ground clearance. Mine feels very stable on sweepers, hairpins are challenging. It shouldn't make the bike feel 'floaty' though. Sounds like maybe its lack of damping? What oil and pre-load on the emulators are you using? Tyres and pressures maybe? As Bbelk said, steering head bearings, if they are damaged or too tight that will do it.

The only other thing I know about "front-rear" attitude, I had a bike (chook chaser) where the front end would slide out on corners in dirt roads, it was unnerving! A top enduro rider told me to drop the forks through the clamps to lower the front end. Sure enough it made all the difference. Not sure if that puts more weight over the front wheel or what but it worked.
Sadly the design of the 70s airhead front end means you can't drop the forks through to try this, except maybe with a toaster tan top brace you can?

[Major Softie]

If you are saying that the total sag is 1" from topped out with you on the bike, then that is VERY little sag. That means either the springs are much too strong, or there's way too much preload.

If you mean that there is 1" more sag when you get on the bike, that's probably about right.

These bikes are very susceptible to problems from stiction, so having the forks perfectly aligned is very important and could be contributing to your issue, but tires and tire pressure can do it too.

[ME 109]

My reason for doing this was that in ordinary riding, the forks compressed almost all their 8.1" of travel, and I wanted to improve the handling.

If you mean that under your average riding conditions that at times the forks would compress that much, then you're not far from the mark.

If you mean that the front end constantly wallowed about near the bottom of its range, then springs are too soft.
Lets not forget rider weight in the pursuit of the ultimate goal, an airhead that handles.

[khittner1]

Lets not forget rider weight in the pursuit of the ultimate goal, an airhead that handles.

Whoa, there, ME,---now you're hitting below the belt---or, in my case, almost anywhere above the belt . . .

[Abstruse1]

Okay, here are a few more details.

With the front wheel off the ground (on center stand) as 0, the sag with me onboard is 3/4". If I hold the front brake and bounce the bike up and down, the total movement is 2-1/8". After a ride hitting modest bumps, the total travel is 2-3/8".

My riding weight (with helmet, etc) is ~190 lbs.

We drilled out the damper tube as suggested in the Race Tech instructions (I think that's where I read this), as I remember with two, 1/4" holes. I'm using 15 wt fork oil.

I don't remember emulator settings, but we would have dome what RaceTech suggested.

I'll check the steering head drag again.

Without the springs in place, and no oil, but with the fork brace and Toaster Tan top clamp installed, the fork sliding movement didn't feel tight, but there was -- of course -- some stiction (yes, new seals). As best we could determine, the stanchions were parallel in both planes.

I also ride a 2015 KTM 690 Duke. Of course it handles differently, esp. with the steering damper I installed. So maybe I'm just being unrealistic about what I can expect.

Remember -- my original question was, could my situation be due to the bike's attitude.

Thanx, guys.

[Mal S7]

Remember -- my original question was, could my situation be due to the bike's attitude.

Thanx, guys.

Umm hard to say as 'floaty' is a subjective experience. If you aren't used to riding airheads it might be just how they feel to a KTM rider. A ducati riding friend was horrified after a ride on my bike, he said he has never been on a bike where the handlebars felt so disconnected from the front wheel.

3/4 inch laden sag is hardly anything at all. I checked my notes, started at 1.5 inch laden sag but I recall increased it some more by reducing the preload (I have had that front-end apart a dozen times now trying to get it where I want it). My weight is something over 200lbs. Sonic Springs are softer than Racetech, but stiffer than stock.

Remember that sag isn't just for ride height. The suspension needs to work in both directions to keep that wheel in bumps and dips. I'd be very cautious on bumpy bends til you know how it will react. Roads here in NSW are often rough so we get lots of practice on bumpy corners. Maybe you don't have them there?

Sounds like you have the stock set-up for the emulators. I'd love to take it for a ride to see how that feels. Dallas is a bit out of the way though. I went back to 7wt oil as 15wt was seriously overdamped on rebound with my set-up, you probably need it though with the stiffer springs. After lots of fiddling with settings I am happy with the front end now.

Your emulators have a little spring that can be adjusted for pre-load. You can get different springs for more adjustment. It changes the compression damping curve. Stock setting is a blue spring with two-turns of pre-load ... I will stop now as its not answering your question but you have to rule out all the possibilities. I don't think the forks sitting so high would make it feel 'floaty' but it may not be optimal for other reasons.

[Abstruse1]

Thanx, Mal S7 (and others). I'll spend more time on the bike, trying to understand better just what the phenomenon I'm feeling is.

Altho the Toaster Tan triple clamp will allow doing so, I can't push the stanchions up in the clamps more than maybe 1/2" without changing the handlebar mounts. An easier step would be to cut down the PVC spacers that RT calls for.

Stay tuned.

[ME 109]

I'll take a guess that "floating" is resulting from too tight steering head bearings.

With your bike on the c/stand, and front axle nut and pinch bolts loose, are you able to rotate the axle easily with your fingers?

I'll also take a punt at too stiff springs.

Changing attitude by sliding stanchions up should not be necessary and will have increasingly adverse effects.

Did you use a known flat piece of glass to assess stanchion alignment?

How did you assess the fit, and effect of tightening the bolts on lower fork brace? (where the fender mounts)