Shock length racing

[bendik]

I am changing my forks and wanted to know what peoples experiences was w different length rear shocks for track use?
Does everybody run the std length?
On my SS900 and Pantahs I am running slightly longer shock to quicken up the steering, have anybody tried that on the singles and what are the experiences?

[LaceyDucati]

Bendik
It depends on the forks used, if using standard Mk3/desmo Marzocchi, I've used 310mm. Some customers have used up to 330mm, but you will probably need a nylon pad on the swingarm to avoid wear. That said I mostly raced Narrowcases so my personal experience is limited with racing Widecases. Nigel Palmer always used 310mm shocks on his 450. Eldert should have some thought on this matter.

Nigel

[bendik]

I am actually using a NSR125 fork. I will double check the length agsinst the 31.5 fork
This is also a NC

[Eldert]

Hi Bendik

the tripple clamps or yokes also make a lot of differance in the steering .what is de offset of the yokes ?

invest in some books so you can calculate your trail.

i use John Bradley's book the racing motorcycle . sadly no longer available .

Eldert

[LaceyDucati]

Hi Bendik

Sorry I forget you had a narrowcase! I only ever used 300mm in conjunction with Metal Profile forks (similar offset yokes to the Marzocchi W/C yokes but shorter). I will look up the trail I used. With the set up I used 310mm shocks tipped the edge of instability. As Eldert said fork and yoke dimensions make a lot of difference, so does the rolling diameter of the tyre. Another book for chassis set up is, Motorcycle Chassis Design: Practice and Theory, by Tony Foale and Vic Willoughby. Not as detailed as John Bradley's books but good all the same. Also not in print, but you can often pick up a used copy.

Regards Nigel

[LaceyDucati]

Bendik

I had a look for the info on my old race bike, but I couldn't find any reference to the trail, If I recall correctly I think it was something like 3.25" (82.5mm). The Metal profile fork legs were recorded at 27" (785mm) from spindle to top of stanchion. I think as original they were shorter, similar to Ceriani GP legs, but I had long steel top nuts to extend the stanchion slightly. The off set of the yokes was about 60mm with a shallow drop top yoke. The extension to the legs was because I moved from a 90/90 Avon to a 2.75/3.75 Dunlop KR825 which had a smaller rolling diameter. The longer legs maintained the trail. Much of this is probably not relevant, Probably best measure the trail with your present set up and see where you are.

Regards Nigel

[bendik]

Thanks to both of You!
The offset on the new fork is quite a bit less than the original at 40mm. The top crown is also flat do measuring the fork leg length wont help me much, but measuring from the bottom of the frame to the axle, it looks like the new set up is about 30mm higher. But I can slide the legs thru the crown.
Also the Hagon shocks fitted is 220mm length and the swing is almost hitting the footrest holders on the frame
So I think I need to put the front wheel on to measure up the trail and see where I am at before deciding on shock length

[graeme]

Hello Bendik,

A racer in Italy uses Honda NSR125 forks and triple clamp.
He uses 320mm rear shocks.
It's obviously a wide case frame not narrow case
The frame has 24 degree rake.
graeme

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[Eldert]

the NSR 125 forks are nice 35 mm items with bushings to eliminate stick slip .

the JC20 uses a Marzocchi fork and those bushings are no longer avialable new

the never JC22 NSR uses a Showa fork and those are still available

Eldert