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| USD forks, altering front geometry??? http://ducatipaso.org/forum/viewtopic.php?f=3&t=4565 |
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| Author: | 900streetfighter [ Fri Jan 28, 2011 11:11 am ] |
| Post subject: | USD forks, altering front geometry??? |
Hi all, as mentioned in a prev post Im trying to fit a SSie front end. Im getting bits together and will be trying them in a few months, The legs are 60mm shorter, I can get back 30mm with a modded top yoke, drop them in the yokes a further 5-10mm so the fronts dropped by 25mm max. The USD's have less travel so I shouldnt be hitting the rad with the wheel. Overall this should quicken the steering, no bad thing. The yokes have a longer offset putting the legs further forward by a few mm, this is handy as the legs and yokes should clear the tank, but what will this do to the handling?? cheers, Keith. |
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| Author: | Tamburinifan [ Fri Jan 28, 2011 11:15 am ] |
| Post subject: | Re: USD forks, altering front geometry??? |
Have you calculated rake & trail? Would give a hint on rideability. 25mm f sure sounds like a lot... |
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| Author: | 900streetfighter [ Fri Jan 28, 2011 11:51 am ] |
| Post subject: | Re: USD forks, altering front geometry??? |
Ive ridden 907 with 20mm lower forks and it was fine apart from rad/tyre contact under hard braking. The offset difference is about 5-10mm but I dont think the wheelbase will alter much as the shorter legs will counteract the offset but with steeper steering angle. K. |
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| Author: | 907pasonut [ Fri Jan 28, 2011 11:55 am ] |
| Post subject: | Re: USD forks, altering front geometry??? |
I dont have any engineering qualifications in steering geometry  ...but in my opinion the handling would change a little and possibly for the better, and at the same time inherit a more sportier (lower front 25mm) riding position  then there is...the individuality factor  ...GO FOR IT KEITH 
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| Author: | paso750 [ Fri Jan 28, 2011 12:18 pm ] |
| Post subject: | Re: USD forks, altering front geometry??? |
the lower the front and the quicker the steering, the easier you get front wheel wobble at high speeds and you also put more pressure on the wrists. Most forks can be lengthened by 10-20mm by inserting a spacer at the bottom or in case of an USD fork on top of the tube. If it´s a nonadjustible you can also have higher endcaps machined. Many full adjustible forks can also be lenghtened I heard, but that is probably a bit more complicated. G. |
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| Author: | 900streetfighter [ Sun Jan 30, 2011 6:23 pm ] |
| Post subject: | Re: USD forks, altering front geometry??? |
Thanks for replys and encouragement, I'm passed the point of no return now having bought a few more parts to go ahead. I'm trying to do this on a budget and use as many excess parts as I have in my garage. The adjustable SSie legs and yokes were in stock and a pair of 65mm calipers were too cheap on ebay to pass on. That leaves a wheel, discs and spindle to find, although I can rob these from my SS for a trial. I'll modify a top yoke to lower the legs over the next month or so and put it all together in spring. Ive got a selection of clip ons that i can try and I intend to mount them above the top yoke. Ive spent a lot of time thinking about how its going to ride, and have convinced myself it'll be OK. The yoke offset is +4mm, which'll move the front wheel 2-3mm forward. The forks will be 25mm shorter, that'll steepen the steering by maybe a 1/2 degree and bring the F wheel back again by a couple of mm perhaps, giving bigger weight bias to the front. I dont understand much about rake and trail but I think this will give it more front end feel. I dont think anything drastic is going to happen, to me the steering on 907's round town is a bit vague, with luck this will improve. I dont think high speed stability will suffer as they're a long heavy bike. The new forks are about 10 kg heavier, which is a bummer but the new wheel will be a bit lighter. I'll learn to post piccys and show you how it turns out. Cheers Keith. |
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| Author: | ducbertus [ Sun Jan 30, 2011 6:38 pm ] |
| Post subject: | Re: USD forks, altering front geometry??? |
Hi Keith, what about the with of the lower yoke. has it sufficient room to move in the fairing? there is not mucht space between the leg and coolant reservoir or electronix on the left side. Bertus |
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| Author: | higgy [ Sun Jan 30, 2011 6:56 pm ] |
| Post subject: | Re: USD forks, altering front geometry??? |
The basics of Fork geometry |
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| Author: | 900streetfighter [ Sun Jan 30, 2011 7:24 pm ] |
| Post subject: | Re: USD forks, altering front geometry??? |
[quote="ducbertus"]Hi Keith, what about the with of the lower yoke. has it sufficient room to move in the fairing? there is not mucht space between the leg and coolant reservoir or electronix on the left side. Hi Bertus, I havent looked further below at clearance but the showa yokes back edge is the same as the marzocchi from the stem, so hopefully wont foul anything. |
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| Author: | paso750 [ Sun Jan 30, 2011 8:11 pm ] |
| Post subject: | Re: USD forks, altering front geometry??? |
| Author: | 900streetfighter [ Sun Jan 30, 2011 9:11 pm ] |
| Post subject: | Re: USD forks, altering front geometry??? |
[quote="paso750"]I`m curious to see some pictures or drawings. As the fork is already a bit shorter I don`t understand how it would be possible to mount clip ons above the upper triple tree. To do that you would have to lower the whole front even more. I have a cunning plan, Im going to have some leg clamps(cut from a st yoke) welded below the top yoke that will hold the fork legs below the yoke. The empty upper clamps can hold a 60mm high piece of 50mm dia tube, to which I fit the bars. |
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| Author: | 907pasonut [ Mon Jan 31, 2011 9:23 am ] |
| Post subject: | Re: USD forks, altering front geometry??? |
| Author: | 900streetfighter [ Mon Jan 31, 2011 10:05 am ] |
| Post subject: | Re: USD forks, altering front geometry??? |
| Author: | paso750 [ Mon Jan 31, 2011 10:27 am ] |
| Post subject: | Re: USD forks, altering front geometry??? |
| Author: | 907pasonut [ Mon Jan 31, 2011 11:58 am ] |
| Post subject: | Re: USD forks, altering front geometry??? |
Keith...I know you're the one skinning this cat...and good on you for having a go G's idea with the tube extension makes a lot of sense, and if you have the joint in the centre of the top triple tee you can gain at least 10mm without loosing metal strengh...then fit the clip ons on top... PS: make sure the top extension does not spin around when stressed by the clip ons ie R/H side during emergency braking and L/H side by quick accelleration...as this may have dire consequences |
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