FF: Forks Modified Steering Stem

[Martyn Goodwin]

Mr Hulstone took my Comet for a run today - with a back to back compare with his std comet setup. I had a set of the supplied 30 lb springs in my comet with the modofied headstem including the Greg Brillus roller bearing kit, for the exercise. Initial sag, bike stationary with rider just tippy toe was around 50%. Out on the road the ride was reported as very supple though the front may have 'bottomed' out on large bumps.

Have just now replaced ONE of the 30 Lb springs with a David Dunfrey 'White" 130 Lb/In. spring. Here is a photo of the front shock showing static sag with rider astride. Position of bump stop rubber shows the sag point - still looks a tad excessive to me. In the photo the suspension is 'topped out' so the sag, as indicated by the position of the bump stop, is around 40% Opinions??? BTW - Front shock is a Thornton unit.

Next step open to me is to replace the second 30 lb spring with a DD 'Red" 75 lb/in spring.

Mr Hulstone will be posting his impressions of the suspension setup (with the 30 lb/in springs) later today.

Last bit of data for now - I tip the scales at 90 Kg and Mr Hulstone is at least 15 Kg lighter.

 

[Martyn Goodwin]

Just swaped out the second 30 Lb/in spring. Now have a set of DD springs in place, one white and one red. Initial sag - measued same methos as earlier appears to be around 30%. Bouncing the front it seems a bit stiffer with less apparent tendance to go to the compression limit of the shock. More road testing required - but it seems to be getting better and better.

Here it is at static sag with the pair of DD springs installed.

 

[Harry Hulstone]

Hello all, Mr Hulstone the crash test Dummy here, fresh back from test riding Martyn modified Comet.

First impression were the front suspension compresses when I sit on the bike, it doesn't on mine.

Second impression was, "he's left something loose here!" when I bumped down off the pavement onto the road. The headlight coming up towards me.

Initially I thought there is a lot of movement going on here, it was taking my concentration to be honest, strange bike etc. When I actually started concentrating on riding I realised my wrists weren't coping a hiding and things were quite smooth.
I've ridden a lot of Vincent's in my time and unless everyone of them had stiction, none of them could have felt like this. The girdraulics were moving a lot.

Back in Martyn's shed we noticed the front Thornton shocker had been bottoming out and as I weigh 15kg less than the big man he's clearly going to have to do something here. Sounds like he already has.

I will be doing this mod to my Comet and as I'm not made of money or do I like getting my hands dirty, that says it all really. I didn't notice the difference in the new stroke because of the altered head stem angle on such a short ride.

Well done boys, I'm impressed.

 

[greg brillus]

Ok the first thing to say is, a big thank you for testing Martyn's bike ..........Yes the front end does and will move a lot more than you would be used to, for several reasons. But now the big question arises........There are two approaches to the spring equation........This example is based on using a pretty week spring rate but with about 3 inches of preload on assembly of the spring box's. The two examples I have up here, not including the race bike which is a "Special" is that I have stronger springs in these two bikes but with less preload. Basically the springs were at 40 lb.'s rate but were too long, so we have chopped about 50 mm off the springs that went into Neal's Comet, and these ended up about 15 mm longer than David's springs, and on my Rapide, I cut off about 75 mm off each spring which gave me about 40 mm of preload. Now because we cut the springs down, the spring rate goes up .....and I'm guessing that the springs in my Rapide are close to 50 lb.'s. At that set up, I am not far off being completely happy with my bike and I still need to try a pair of the 36 Lb. springs from Norman when they arrive soon. So we are getting close to some useable springs, though I feel we will need perhaps 3 different springs to suit different riders and bikes, which is a similar result to what David came up with. The bearing upgrade is like a new kind of "Fast food" once a couple got the taste for it, now everyone wants it. It certainly allows the forks a new freedom of movement, and it is way easier to set up and nil maintenance thereafter, all good.

 

[timetraveller]

Very good! This is just the kind of feedback I need. On their way to Greg are two 33 lbs/inch springs and some 36 lbs/inch springs. Chris Launders has been using the 36s ever since he did this mod with complete satisfaction on a twin so they should be at least strong enough on a single. However, when Chris changed from Oilite bushes in the rear of the lower link to needle rollers he found that a lot more movement is taking place and he is currently experimenting with different damper settings. If that proves not to sort out the problem then he has a cunning plan to fit a cut down 'C' inner spring inside the 36s. The idea here is that the cut down spring will be short enough that it is not doing anything with the bike stationary and the forks will have to have compressed by about one and a half inches before the lighter spring comes into action. The ideas is that over small bumps one will have the comfort of the 36 lb springs while, once one is half way through the total movement the rate will suddenly become 46 lbs/inch.
For the tests taking place in Oz my recommendation would be to try two 33s as the next step. If that is not enough then one 33 and one 36 and finally if that is not enough two 36s. There is absolutely no problem getting stronger springs made but the idea here is to combine the handling provided by the JE geometry with softer springs and better damping.
There is one thing to note. When pumped by hand the Thornton springs are much easier to move in and out than the AVOs. The AVOs can hardly be moved and yet under real road use they seem to be superb. Hadronuk has already told us that altering the damping on the AVOs alters the rebound damping much more than the compression damping and that a damper set up for the rear of a Vin would have stronger initial compression damping. I freely admit that with the damping I am out of my depth. How a damper which is really difficult to move by hand can work as well or better than one which moves easily I don't pretend to understand but that is what we are finding. Before we all rush off to fit stronger springs it is possible that stiffer damping needs to be tried. Is anyone going to volunteer to try a 'rear' AVO or do I have to buy one and lend it to someone?

 

[Harry Hulstone]

Test dummy here. I too am no expert on damping, especially when it comes to girdraulics, but I know from the Ducatis we ride that we have all found a light spring and a bloody good adjustable damper, usually Ohlins, is most favourable. It did appear today riding Martyn's Comet that the Thornton unadjustable damper was having a hard time controlling the 'lively' springs. I ordered a front AVO recently because I like the idea of adjustability, but the bloke sent me a rear instead for some reason, which didn't fit, so I haven't tried one. It looked like it was off a 4WD if I'm honest.

 

[timetraveller]

Hi Harry, it sounds like they might have sent you a rear coil over damper. If so you might find that useful in the future. What Chris Launders has found is that with the new set up at the front, the rear is starting to show its shortcomings. Thanks for doing the testing.

 

[greg brillus]

Don't fall for the trap of changing loads of things hoping to arrive at a good result, look at one item at a time. Remember when I did Neal's Comet before Christmas, we were still using an original Koni set on it's softest setting, and this felt great to me. Only change was that Neal felt a slightly softer spring would be worth a try. I feel you need to get the basics right first, meaning if the bike bottom's out quite easily then it is obvious that the springs are not strong enough. A shock absorbers main function is to keep the wheel in constant contact with the road surface, it is not designed to assist with taking any weight of the bike/rider, but to absorb oscillations of the spring. The reason the 30 lb springs were possibly ok on the twin racer at Goodwood is because the track surface is much kinder than the open roads. Plus his front brakes were probably close to stock, given their rules. I think on my racer that under very hard front braking (230 mm Four leading shoe Ceriani), there probably isn't much front travel left, and I have a single 180 Lb spring up front not unlike that on the stock Brampton's.

 

[timetraveller]

The Goodwood racer had 8" front brakes which had uprated linings fitted, still single leading shoe though.

 

[greg brillus]

The problem with racing, and I mean flat out......... not just a track day........Is that you really have very little time to analyze everything with total certainty. That is, unless you have had some extra run time to assess how the bike is performing. Generally you are so busy just making sure you get around the track quickly without getting hit, and the bike operating with some level of reliability. Anyway, the trick here is having enough spares to play with and swap things around until you get the bike where the front end performs nicely, doesn't top out or bottom out. We are getting closer day by day.