I'm doing my homework to swap my stock 796 forks out with 848 forks, and I seem to have all the gear I need. My question is on technique, specifically with regards to suspension geometry.
Here are a couple different options I'm considering for how high to set up the 848 forks in my triple tree:
1) With the bike on a lift and front wheel off the ground/forks unweighted, measure the distance on the stock fork from bottom of lower triple to center of axle. Then just set up the 848 forks to the exact same distance from bottom of lower triple to middle of axle while front end unweighted. I saw this approach elsewhere on the forum as one option somebody used.
2) With bike on ground and suspension WEIGHTED WITHOUT RIDER, measure distance from bottom triple to center of axle, and then set up the 848 fork to the same distance weighted without rider.
3) With bike on ground and suspension WEIGHTED WITH RIDER, measure distance from bottom triple to center of axle and then set up the 848 fork to the same distance weighted weighted with rider.
I think I'm leaning towards Option 2 with the 848 forks set to the stock factory settings as far as rebound, preload, and compression -- I'm not sure, but this seems to equalize the approaches by accounting for the different characteristics of the forks to put the front end at the right height -- front end weight of the bike loading the different springs, for instance.
At least one forum member has made a case for the first option though, and I would guess someone could make a case for the third option.
Can someone smarter than me on suspension setup school me? I need to have a game plan going into the swap this weekend so I can take measurements first as needed.
Number 1 !
That's the way to get 'correct' geometry (which you can later change IF you need/want)
Number 2 and 3 mix suspension adjustments with geometry = fail.
your 796 forks probably have a heap of sag, which should be fixed. so fitting anything with the correct sag will raise the front to some extent. and keep it higher for much of the travel.
you're getting caught up in what you think is 'correct process'. who said the stock geometry is good?
#1, fit springs as required to suit you, set the sag, adjust fork position as required from there to make it do what you want it to.
are you fixing the rear as well?
So #1 is in the lead. Makes sense that #2 and #3 are incorporating suspension adjustments into the setup, I guess I was just too focused on front end height and losing the forest for the trees.
I will be adjusting the rear, but right now I'm not planning on swapping anything out on the rear. When I get everything put together and I get into the adjustment process, I'll decide from there if I need a different rear spring (my weight without gear is about 185 lbs).
The ultimate goal is to make this bike a decent track machine -- I'm not out to race, but I want something that I can push my limits on on the track. The idea is that if the bike handles well enough maybe it will hold off my insatiable want for putting another bike in the garage.
I'll add another vote for #1.
I don't recall what the OEM rear spring setup is in a 796.
IIRC the 696 and 1100 were fitted with springs originally intended for logging trucks.
I'll wager after you get the forks on and even only partly sorted, you'll be going after the rear to fix it.
Quote from: Speeddog on May 05, 2014, 06:29:37 PM
I'll add another vote for #1.
I don't recall what the OEM rear spring setup is in a 796.
IIRC the 696 and 1100 were fitted with springs originally intended for logging trucks.
I'll wager after you get the forks on and even only partly sorted, you'll be going after the rear to fix it.
;D That's funny!
Before buying mine, I rode the demo thoroughly and made a mod list for set-up prior to buying mine. On that ride, the forks, tires and overall handling were quite nice..., BUT the rear wasn't really doing much other than keeping things settled. The Sach was pitched for a "cheap" Ohlins from NC with spring matched to my weight. Three years later I still have no complaint about the fork other than the improvement a better quality oil would undoubtedly make.
I'd suggest this shock swap to the OP prior to going beserk on SBK forks. Just my $0.02...
And Speed, thanks again to you, Carlos and Dexter for the specs on the rear axle. Made the tire swap go very smoothly!
+1 for #1
Same steering head, same frame, same triple, same offset, same rear shock height = one remaining variable for rake and trail (fork length).
You are right on and then can tweak by .25-.5 increments once on the track based upon riding style, body position with respect to clip-on rise and any adjustable rearsets.
I probably missed something, so others please chime in.
I would say, any of the 3 methods will work as long as you keep track of what you are doing, and take a careful test ride.
#1 is a good starting point, assuming spring rates, sag etc. are set to sensible values.
If spring rates and sag are the same, #1 and #3 amounts to pretty much the same thing.
I would check sag with the stock set-up, then with the 848 forks, and make an eductated (?) guess based on #1 and the respective sag values, since that is the easiest method. Then, test ride and go from there.
Nice, thanks to all for the inputs. As for coffin reservoir spacers, anyone think I'm going to need them with zero-rise renthal clip-ons over the top triple? I'll find out soon enough as I start piecing this all together, but if someone knows either way it might save me some headache/time.
Coffin masters only clear the *bar* by 2 or 3 RCH.
If there's a bit over 10" of bar outboard of the clamp, they'll fit.
Just measured, and the Renthal bars only leave about 9 3/4 in outboard of the clamp. So it sounds like there's a good chance I'll need the spacers.
So when I put the 1098/1198 forks on my 796, I measured the distance from the bottom of the lower triple to the center of the axle with the bike on a triple lift stand. (Front end unweighted.) I took my Ohlins in to be resealed and resprung as well as having the damping adjusted. My suspension tech reminded me that because the geometry of the two bikes is different (weight bias, rake angle, etc) the setup (spring rate, damping set points) aren't going to be the same either. It will definitely take some test and tune work. Have you addressed your triple tree plan yet? IMA makes a great bolt on product. Also remember that with SBK forks you need an SBK front axle along with 5 bolt 15 mm offset rotors (999R I believe is what I used.). No matter what, with a triple that gives you 796 rake angle, the SBK forks will be much taller above the triple than the 796 forks are. So you have plenty of fork tube to set your ride height with.
Hope this helps, I probably shod have finished the updates on my fork swap thread and saved you some research.
Quote from: freeclimbmtb on May 10, 2014, 11:44:04 AM
So when I put the 1098/1198 forks on my 796, I measured the distance from the bottom of the lower triple to the center of the axle with the bike on a triple lift stand. (Front end unweighted.) I took my Ohlins in to be resealed and resprung as well as having the damping adjusted. My suspension tech reminded me that because the geometry of the two bikes is different (weight bias, rake angle, etc) the setup (spring rate, damping set points) aren't going to be the same either. It will definitely take some test and tune work. Have you addressed your triple tree plan yet? IMA makes a great bolt on product. Also remember that with SBK forks you need an SBK front axle along with 5 bolt 15 mm offset rotors (999R I believe is what I used.). No matter what, with a triple that gives you 796 rake angle, the SBK forks will be much taller above the triple than the 796 forks are. So you have plenty of fork tube to set your ride height with.
Hope this helps, I probably shod have finished the updates on my fork swap thread and saved you some research.
Gonna get my stock top triple bored out to 53 and just shim my lower triple, I already got the Corse Dynamics shims. I got the SBK front axle, and I got the 5 mm rotor shims also. As you can see with my other post here, I'm currently having difficulties getting the rotors off. An impact driver isn't even turning these bolts off. How naive of me to think this would be easy!
Quote from: Speeddog on May 05, 2014, 06:29:37 PM
I'll add another vote for #1.
I don't recall what the OEM rear spring setup is in a 796.
IIRC the 696 and 1100 were fitted with springs originally intended for logging trucks.
I'll wager after you get the forks on and even only partly sorted, you'll be going after the rear to fix it.
Speed, do you know if an 848 shock fits on a 796? Just not sure about that reservoir sticking out the side. I found a stock 848 shock for $75, which seems like it would be a low cost solution to the issues associated with the 796 shock, but only if it fits.
Quote from: aftriathlete on May 10, 2014, 07:43:12 PM
Gonna get my stock top triple bored out to 53 and just shim my lower triple, I already got the Corse Dynamics shims. I got the SBK front axle, and I got the 5 mm rotor shims also. As you can see with my other post here, I'm currently having difficulties getting the rotors off. An impact driver isn't even turning these bolts off. How naive of me to think this would be easy!
the rotor screws are loctited in. loctite requires some subtleness, not impact. heat is your friend.
i found out yesterday that mts1200 front rotors are 5 bolt, but shallow offset. might be of use to some when doing an sbk swap. put them on a ms4rs and you can't get the calipers holes to line up. kind of obvious at that point.
I had to use a fluted nut remover to get one of my rotor bolts out. Craftsman sells them as a kit for removing rounded bolts/nuts. As for the rear shock, no. The 796 and 848 use completely different rear end setups and the shock with the external reservoir will NOT fit the 796. The options are (from Ohlins at least) the DU737 or having a TTX shock built for you...ugh.
Copy, thanks. I emailed Dan@kyleracing yesterday too, and he basically said the same thing -- no-go on a 848 shock on my bike.
Update on my progress: going to attempt to prime and paint my top triple tonight while I'm waiting for my new rotor bolts to come in on Friday. I'll post pics.