There is nothing significantly wrong with adding additional internal springs to the Petteford springs, I did this years ago in attempt to stop bottoming out when fully sprung and fully loaded, and that was using A Koni rear damper, and like yours, not satisfied with one additional spring I also tried an additional 3rd spring using a cut down air rifle spring, but that proved to be a step to far, the first inner spring by the way was a cut down girdraulic fork spring. If done correctly it should not stress the damper, the secondary springs can be shorter than the primary spring, and only come into effect after the primary spring has compressed, say 25%, or subject to experimentation, I did ditch the rifle spring as it was deemed unnecessary.
Bear in mind when the Thornton suspension kit was available, they also supplied a couple of secondary internal springs of different lengths so you could experiment to find the level of suspension spring strengths that suited your requirements, just take a look at the next Vincent gathering you attend, you will see a solo bike being ridden by lithe fit guy of possibly 10-11 stone (as I was once, sadly no longer) and you will possibly see two very large individuals heave themselves onto a heavily loaded Vincent, that is probably why you have discovered what you have, one suspension set up cannot cater for this.
I have to ask why you have purchased new springs at all, I would have tried the your original springs without the additional inners, by the looks of it they are probably of better quality than what you have been supplied, maybe the length disparity has little detrimental effect, if any, but as an engineering friend constantly informs me "If its not right, its wrong!"
Bear in mind when the Thornton suspension kit was available, they also supplied a couple of secondary internal springs of different lengths so you could experiment to find the level of suspension spring strengths that suited your requirements, just take a look at the next Vincent gathering you attend, you will see a solo bike being ridden by lithe fit guy of possibly 10-11 stone (as I was once, sadly no longer) and you will possibly see two very large individuals heave themselves onto a heavily loaded Vincent, that is probably why you have discovered what you have, one suspension set up cannot cater for this.
I have to ask why you have purchased new springs at all, I would have tried the your original springs without the additional inners, by the looks of it they are probably of better quality than what you have been supplied, maybe the length disparity has little detrimental effect, if any, but as an engineering friend constantly informs me "If its not right, its wrong!"
Last edited:
