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carlo_sg
07-31-2014, 04:23 AM
Hi,

I recently traded my SXV550 for a DD1200 and I was going through the exercise of lowering the bike. I contacted a suspension specialist and they confirmed they can shorten the stock shock by shortening the shock’s body (cylinder).

I measured the geometry of the bike and plotted it in a CAD programme.
I found the forks can be raised in the triples by a maximum of about 35mm.
The stock shock length is 325mm and has 20mm of thread for reducing preload – effectively the maximum amount the shock can be shortened by and maintain the same preload.

So to maintain the stock geometry and lower the saddle:
I raised the forks by the maximum 35mm, then shortened the shock by 12mm. (therefore using the same spring, the locknut would be unwound by 12mm– to keep the same preload)
This arrangement maintains the stock bike’s rake of 27.3degrees. But the wheelbase is shortened by 12mm
The seat is effectively dropped by 31mm

http://i290.photobucket.com/albums/ll253/carlo_sg/01_zps3ed57ee1.jpg (http://s290.photobucket.com/user/carlo_sg/media/01_zps3ed57ee1.jpg.html)

For the maximum drop in seat height:
I raised the forks by the maximum 35mm, then shortened the shock by 20mm. (therefore using the same spring, the locknut would be unwound by 20mm– to keep the same preload)
This arrangement increases the bike’s rake to 28.1 degrees and the wheelbase is shortened by 10mm over stock
The seat is effectively dropped by 45mm

http://i290.photobucket.com/albums/ll253/carlo_sg/02_zps003f88d7.jpg (http://s290.photobucket.com/user/carlo_sg/media/02_zps003f88d7.jpg.html)

My question is, has anyone dropped their bike and how is the handling. I’m worried the increase in rake will slow the steering.

Nito
07-31-2014, 07:22 AM
I'm not generally on this part of the forum, but this thread caught my eye on the frontpage.

All I can tell you is that when I bought my Tuono, it had been lowered 5mm at the rear and front. The handling was atrocious. After looking into it, it is to do with chain pull when the swingarm passes horizontal and you end up with pro squat as a result of the geometry of the swingarm, chain, sprocket, centre of gravity etc. Google anti squat. Here's one but there are loads of articles http://www.sportrider.com/more-fun-geometry

258912

Rectifying the rear shock solved the issue. I would say this would play a far larger part in your calculations than purely rake. I've also messed with the front forks, lowering them 5mm in the yoke and yes it increases steering speed at the expense of stability. That'll come down to preference or you will soon get used to the revised characteristics. But squatting is awful as the slightest bit of throttle has the bike rearing up on corner exit and means you can't place the bike where you want in a corner, slightest bit of throttle has the bike running wide.

HTH
Nito

carlo_sg
07-31-2014, 07:48 AM
A bit of a side topic but…
Most sport orientated bikes are set up according to your pics as – “Anti-squat”.
This can be seen when you run a bike on a dyno, the rear of the bike lifts up (with the front strapped down).
The reality on the road (where the front is not strapped down) is the bike feels as though the rear squats under acceleration and you run wide. This is because the torque is lifting the front and the rear is not stiff enough to resist it.
When you look at race bikes on the gas the bike sits tall, this is a combination of the front wanting to lift from the torque and the rear lifting from an “anti-squat” swingarm.

Thanks for the comments though

Nito
07-31-2014, 09:22 AM
A bit of a side topic but…
Most sport orientated bikes are set up according to yourpics as – “Anti-squat”.
The reality on the road (where the front is not strappeddown) is the bike feels as though the rear squats under acceleration and yourun wide. This is because the torque is lifting the front and the rear is notstiff enough to resist it.

Thanks for the comments though

I think we're at cross purposes. What I'm saying is the Tuono, as an example, handles like shit when lowered. Mine was virtually unrideable. We're talking 5mm here (at the shock which also translated to 5mm at ride height). By lowering your bike, the effect at the rear could be far more of an issue than rake. That said the Dorsoduro has much more travel so it might not be effected anywhere near as much. I'm not talking a soft rear end, and the adjustment was not done on the preload either in my case. My bike was wheelieing in third gear with small throttle applications. It's to do with the chain pull and top of rear sprocket to top of front sprocket alignment which pulls the swingarm into the bike once you go over the tipping point, which has a massive effect on handling.

wrx_02
07-31-2014, 10:06 AM
Increasing the rake will slow the steering.
Shortening the wheelbase will help with turn in and make the bike more nimble but will also make it less stable in a straight line.
Lowering the bike overall will lessen your lean angle, but ay not be an issue unless you are dragging knee right now.

Also just moving your body forward a little will greatly change the geometry. I dropped my handle bars 5mm once and it made a huge difference on the brakes cause it made me stay lower on the bike.

sdk187
07-31-2014, 12:13 PM
I don't want to get into a debate about all this. I just want to let you know that if you want to shorten a shock, you should consider having the suspension company install a spacer below the shim stack base plate which prevents the shock from opening up all of the way. Doing it this way allows the shock to be returned to its stock setup should you wish to revert. There are no permanent modifications needed to be done to the shock body. This has been done in MX for years. I can't get the picture attachment to work. but if you go here: http://www.lt-racing.com/html/suspension_topics.html near the bottom of the page it shows a picture of a shock with the spacer installed.

Locky
09-19-2014, 09:55 PM
When I first got my 1200 I looked at getting a custom shock from Penske to lower the bike but in the end I settled for dropping the forks to the last line and two extra turns of compression to stop the bike from squatting so much.It seems to make the bike set up and hold it's line better. The Dunlop Qualifiers I find to hard and to my eye the profile of the front tire is to round.