Back end bouncing / Front end understeering

[Cabot]

I have a problem. :think:

First of, heres the details.
Me- 135-140 pounds w/o gear, 5'9ish
Bike- 05 Honda CRF250
Suspension = stock. Race sag set in rear, and I've been playing with the clickers a little bit + or - 2 clicks from stock setting. Last time I was out I had 1 click in on both compression and rebound on the forks, and the back end was stock.

Whenever I go through soft sand where it hasn't been groomed in a while and big hard acceleration bumps have formed, my back end is bouncing like crazy. I'll be going hard in third gear, and my back end will be bouncing off the jumps, not gaining speed cus more then half the time the back tire is in the air, and the engine is bouncing off the rev limiter. :bang:

Also, when riding the low, steep, sandy rut/banks that form in real sandy tracks my front end will understeer, pushing my back end out so I won't track straight out of the corner. And the front tire does NOT want to follow the ruts coming out of the corners. I tried sitting back farther on the seat, which helped alot with understeeringm but not completely, still doesn't want to follow the ruts. Maybe its not the suspension, just me, I don't know.

I hope I explained this good enough, and I know I would prosper much from getting the suspension revalved for me, but theres not enough time before this weekend to do that.

Also, I'm looking for a good book to purchase explaining how modern motocross suspension works (in much detail), and how to tune it well based on conditions, etc. If anyone has any titles or authors for me, that would be great.

thanks! :cool:

 

[whenfoxforks-ruled]

Your shock sounds like the rebound is to fast, slow it down. Like jetting, make 1 adjustment at a time. What is your static sag, and what exactly is the sag set at? If the rebound does not slow it down, the shock is blown. Do nothing to the front until the back is sorted out. I really recommend MX Tech. Some of the best people on the planet. Fast turn around. You get every bit you pay for, and then some. http://www.mx-tech.com/

 

[_JOE_]

Im with Wffr on the rebound. The front could be simply a tire issue. Mine doesn't like to bite up front either. I will be switching to the d742fa when I do the tires this summer.

 

[Cabot]

Thanks for the help! I'll try it out in a couple days.

I forget the exact numbers, but I set the race sag at 100mm +/-5mm, and the static sag was around 25ish mm, where it should be according to the guide that I used. This should be right, right?

I was looking at either mx-tech, or pro action for the rear shock.
And I've heard good things about Race Tech Gold Valve kits for the forks. And I could do the forks myself, saving $. Which I don't have much of, lol.

 

[_JOE_]

Does the bike have alot of hours on it?

 

[whenfoxforks-ruled]

The rear shock directly effects the front. It may not be why the front wants to knife, but, you fix and set the back first. The forks can be to high in the clamps. Race tech is blasphemy, MX TECH, no compromise. He has magic valves also!

 

[Cabot]

I was running the back rebound 12 clicks out from full in, and by the time I was done with it I'm at 6 clicks from full in.
BIG difference.
Not only is the back end staying down in the bigger sandy acceleration whoops, its bouncing alot less in the small harsher breaking bumps. Feels alot more progressive in the corners, if you know what I'm trying to say, and its tracking straighter coming out of them.

All that from 6 clicks, dang! Thanks!!

Now i just need some new tires...

 

[whenfoxforks-ruled]

No more issues with the front?

 

[Cabot]

Well, the front was going where I wanted it to go, but the track I was at didn't have the 6 inch deep ruts in the semi-hard dirt that I was really having a problem with earlier. But in the soft sand it wasn't understeering like I explained earlier.