I have been doing a lot of searching on chassis geometry numbers. I have had my suspension revalved, but being a broke mofo I will be getting the geometry in better shape myself. I have a good handle on how to arrive at the numbers I need, but want some advice on the numbers themselves. I understand that there are no magic numbers even for a specific bike and that they can be pretty subjective. For trail figures I have heard from the high 80's up to near 100mm. I am comfortable with a bike on the twitchy side and have a Scotts. Any recommendations for a starting point? Also swingarm angle. I have heard 15*, is this as measured from the center of the front sprocket to the rear axle? Or from the swingarm pivot? Pivot to axle I am seeing about 12* with my Ohlins jacked up pretty far.. This will be used on a 2002 R1 Thanks alot for any info!
Also, in the manual for my OHlins shock, it says the the max height has the jam nut just revealing a groove in the threads. There does not seem to be any visable groove in the threads. I have 3.5mm of threads engaged into the shock body right now. Once the jam nut is secured it should effectively be part of the shock also. Does that sound like enough?
After cleaning them up I can now see the groove, which sits quite low. Having it just visable would mean you can only raise the shock about 5mm from full bottom. If I'm not mistaken, to match stock length, it wasn't bottomed out. Has anyone pushed this boundry? At the recommended max height, there is about 10mm of threads engaged into the shock plus another 5mm for the jam nut. For something that sees no side loading, only compression, it seems exessive. My digital angle finder will be here tommorow. Someone has to have good ballpark trail and swingarm angle numbers!!!
Okay, still no replies With my Ohlins shock jacked up to the "safe" max and then some, the forks 8mm through the trees, and 39mm static sag, I am getting 24.3* of rake. Figuring a 25mm offset fro the stock clamps, and 292mm ground to axle height, that gives me 104.4mm of trail. One more mm than the stock claimed. :down: Right now a set of 208 GPs (180 rear) are on there. I realize that going back up to the 190 slick, I will gain some steeper inclination of the front. The swingarm angle axle to sprocket is 10.3* and axle to pivot 11.4*. These also seem small from what I have read. Does anyone make an extended eyelet bolt for the rear shock? Come one guys, help me out!
Have you measured the offset of the stock triples? 25mm doesn't sound right to me . With R1's it is very important not to run the shock too long, because a situation can arise where the shock eye hits the suspension link arm at full top out and bends it. The worse case scenario here is that the link arm breaks and a BIG crash results. I seem to recall people running shorter link arms to gain ride height rather than lengthening the shock. The pivot to rear axle angle is the one you should be concerned with, 11.4 degrees should be fine. 15 degrees will be too much. The shock should not be run past the Ohlins recommended maximum length. These things work in compression and extension.... think about when the back wheel is off the ground under brakes. Another thing........ 39mm static sag where? Front, I'm guessing. Would that be static sag without rider?
Whoops 39mm was a typo. Static front is 31mm, with rider 43mm. Rear static is about 15mm, with rider 32mm. Yeah I have heard about the eyelet clearance issue so I think I will machine myself a new shorter dogbone, since I'm not paying $130+ for a piece of aluminum with two holes in it. Actually there really isn't any way I can see for the bottom shock mount to be put into tension, but that doesn't really matter anyway. From what I hear shortening the dogbone will also add some progression to the linkage which apparently this bike is short on. I haven't personally measured the offset, but 25mm seems to be the consensus. To start I am going to shoot for about 22.7* rake, which would give me 97.6mm of trail. Sound good? Side note: After going out for a test ride, I came back in and rechecked measurements. I found that the warmed up front tire (re: increased pressure) raised the radius 6mm to 298mm. That alone changes the trail almost 3mm. You've got to be on top of this stuff!
All angles measured with the bike in "static sag". just the weight of the machine, nothing more, nothing less. Then shimmed plumb with jack stands.
that os why your numbers are way off to the others that you have heard being floated around. Places like GMD Computrack measure the bike with jackstand under the pegs and engine, this way changes in spring rates wont effect the geometry of the bike. yes it changes when you are in a corner but it's just the way they do it
So they measure the geometry with both wheels in the air? Are the tires both exactly the same distance from the ground? They would have to be I guess, to get accurate angles. That seems weird not to take spring rate/sag/etc. into your measurements. Because the reality is that spring rates DO effect the geometry.
IF you are getting these rider sag numbers I think your spring rates need attention. I have liked 30mm front, 25mm rear with rider on several bikes. What do you be weighing and what spring rates do you have now? Also, what sort of pace are you expecting to run, Pro, Expert, Novice etc? I would advise that you check the offset yourself, to be sure. 97mm trail sounds good but I don't know how you are going to get 22.7 degrees without jacking up the rear a LOT. If you get the swingarm too steep you can end up with other issues like too much anti squat, but that probably needs its own thread. Hope this is helping.
I have had the stock forks and Ohlins revalved by GMD. They put in .90's in my forks, and I believe the rear spring is a touch softer. I weight about 157lb + gear. Before the shock work I was barely getting any sag on the shock, so they installed a drop preload collar to relax the spring a bit. Now I have the hyd. maxed out to get that number. Ohlins says 25-40mm sag with rider. The front forks when I got them back were giving me only 25mm static, 30mm with rider, so I was sagging the front only 5mm. The bike was running wide everywhere. The preload adjusters were backed all the way out. I had them cut the spacers down 7mm. Ohlins says 35-50mm front rider sag. My preloads are still backed out, so I can dial that down if need be. I am running expert class and run a pretty quick pace. I dominated the half season of AM I ran last year on stock suspension and ran as high as 5th place into the experts (combined grid). I have only managed to finish about half pack since the suspension work. But from my measurements, it looks like I had about 26* rake and 117mm+ trail. Doh! I will check the offset but I am quite sure it is 25mm. Plugging in the stock figures of 293mm front radius, 24* rake, and 103mm trail leaves you with a 25mm offset. Thanks for the input...
it sounds like you are looking for numbers that do not exist. measurements like sag, swingarm angle, trail and others are mearly starting points. you accelerate in a very different way than someone else on the exact same bike. this changes your rear end set up considerably. you break in a very different way than someone with the exact same bike. this changes your front set up considerably. this is just the beggining of the problems with using anybody elses numbers. they really have to be yours. a street rider in mountains will use lots more trail than a track rider in the desert. get the picture. 3 things will get you to your goal. testing, testing, and testing.
Yeah thanks for the news flash. If you had actually read my posts you might have caught this: "I understand that there are no magic numbers even for a specific bike and that they can be pretty subjective." There are in fact good ballpark numbers to start from for an expert pace racer. If you have anything constructive to add, please do.
Okay, I made a shorter dogbone to get the extra height I needed in the back. My numbers: Rake: 23.3* Trail: 100.25mm SA angle to pivot: 12* Does this sound like a good starting point to tune from? Thanks again!
Also, now with the dropped spring perch that GMD installed and my hydraulic adjuster maxed out I am getting 16mm free sag and 38mm with rider. This struck me as too much, but after talking to GMD I was told that they like to run 16-18mm free sag on Ohlins shocks. It just seems like 38mm is excessive. My understanding: Adding more preload would drop both the sag figures, while putting a stiffer spring on and leaving the preload as is. would help preserve the free sag while reducing the rider sag. Any thoughts?
+1 here. I recall that you weigh 157 plus gear, correct? Free sag can change from track to track, depending on a lot of things. 16-18mm free sag sounds like lots. Different springs with different preloads can give the bike different characteristics, whilst maintaining the same rider sag.
Work a coupla extra days(12 hr days) a week for about a month, save the cash in a cookie jar......go to Jennings sometime when Thermosman is going to be there, work with him for one day and you will leave going faster feeling more comfortable and with less chance for failure (crashing due to incorrect application of erroneous information). **You may insert the name of any competent suspension guy, I just used Thermosman because that is who works with my son, and that is who, in my "Opinion" is the best.**
