Mountain Bike Reviews Forum banner
1 - 11 of 11 Posts

·
Registered
Joined
·
264 Posts
Discussion Starter · #1 ·
I recently got an '09 Sir9 which replaced my '08 Sir9 XL frame, and I had everything transfered over, including the Fox 29er fork set at 100mm, a 110mm stem, and 180mm cranks, and same tires/wheels.

I have noticed that the front end seems to be higher and lighter. This is especially noticable when going downhill. The bike currently feels as though the front end is going to wash out sometimes, especially on gravel/non-tacky trail surfaces...almost as if the front is hydroplaning (yikes!). I would also note that I'm used to shifting my weight behind my seat because I use a bolt-on seat post clamp. However, the thing is, I used that on the '08 bike and didn't experience any issues.

I noticed that the front-center spec on the '09 frame is 1/2 inch longer and the seat tube angle is also 1/2 degree slacker. Would anyone care to chime in if you think the changes in the geometry would make the bike feel washy like I am describing? What do you think the best way is to get it back to normal? I've thought about moving my seat forward, but then I'd need a longer stem and it also shortens the distance between the bottom bracket and the point of contact on the seat. Also, I tried reducing my head tube stack by 15mm, and it did help bring the bars down, but the front end still feels light.

Geometry:
XL Frame NEW '09 / OLD '08
Standover: 32.8" / 32.7"
Seat tube angle: 73° / 73.5"
Head tube angle: 72° / SAME
Head tube length: 5.1" / 4.7"
BB drop: 2.8" / 2.75"
Wheelbase: 44.3" / 43.7" / SAME
ETT: 25.25" / SAME
Seat tube length: 21.5" / SAME
Chain stay length: 17.3" / SAME
Front center: 27.3" / 26.8"
 

·
Registered
Joined
·
1,179 Posts
I am experiencing the same thing on my Jet with an old Reba at 100mm. I just flipped the stem and hope for a difference on the next ride.
 

·
Registered
Joined
·
264 Posts
Discussion Starter · #4 ·
letsgo said:
zip tie some lead weights to the fork right around the hub. Should solve your problem :thumbsup:
Should balance out the oversteer just perfectly :cool:
 

·
Registered
Joined
·
494 Posts
I notice the the changes too, and love them. I was getting ready to try a lay back seatpost and a shorter stem. The 09 is exactly what I was hoping it would be (I've had an 07, an 08 and now an 09 Sir9, the 09 is my favorite.
c
 

·
Banned
Joined
·
7,930 Posts
I say just ride it, and adapt.... in a month or so, you won't notice the difference and will have adapted your riding style to the frame.
 

·
Registered
Joined
·
264 Posts
Discussion Starter · #7 ·
I am trying to adapt, but I am slow at doing so! I am going to try running a few different sets of front tires and see if that helps. I'll keep you guys updated on my progress.
 

·
Registered
Joined
·
1,179 Posts
Bar Height...

made more of a difference than tire choice on my Jet. Flipping the stem and moving spacers around until I had just the right amount and not to much weight on the bars did the trick. As little as one spacer makes a difference. With a 100mm fork, I have my 6 degree/90mm stem flipped with one spacer underneath it and flat bars on a medium frame. The bars are slightly lower than the saddle. I think the 100 fork made this setup necessary.
 

·
Underskilled
Joined
·
4,751 Posts
slide the seat slightly further forwards that'l help a bit.
 

·
Registered
Joined
·
1,875 Posts
I've thought about moving my seat forward, but then I'd need a longer stem and it also shortens the distance between the bottom bracket and the point of contact on the seat.
No. And yes.

No, you wouldn't need a longer stem. Consider getting wider bars. What width are you running now?

I can't fathom a 110 stem and I'm 6'3" with long arms. 70 mm stem and 700 mm bars is what i run on a bike w/ similar geo to your SIR9.

And yes, you might need to fine tune the seat height but shouldn't require much change.
 

·
Registered
Joined
·
264 Posts
Discussion Starter · #11 ·
Update:

So I had my LBS drop my fork from 100mm to 80mm. Wow, what a difference! I did a 32 mile ride yesterday, connecting all of my local trails (mostly lose/dusty stuff), and I gained a lot of confidence back that I previously lost. The bike felt like it was back on rails, I could still roll big stuff. I'm going to ride some gravely granite/bearing-sized lose terrain later this week and I'm hoping I'll have the same experience.

frorider,

110m stem for some reason works perfect. I've got pretty long arms. Running 27" wide bars = 685mm.
 

Attachments

1 - 11 of 11 Posts
Top