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Discussion Starter #1
Hey,
I'm sorry to start another suspension thread, but I've looked everywhere and can't find an anwer to my doubts.

I own a 2007 YZ450F (yamaha) SuMo. I race it in my country on a say "rookie" level. (This is my 4th year racing on SM, 3 years road racing before that).

My problem is that when I come into the corner fast, trail brake and just start accelerating my front tire loses traction.
Also what I noticed is that my front tire wears out about 2-3 times faster than the rear. And it's easy to break traction on the rear end coming out of the corner.

Maybe the wear of the front is normal and loosing the front is the result of my poor technique (maybe I use the throttle to little, or use wrong body balance, etc.)

My other theory is that I have too much weight on the front wheel. But other than loosing the front the bike handles great.

Last session I tried raising the front (forks down by 5mm in the clamps). First thing I noticed was the worse steering - it was simple harder to turn.
I was riding with caution (read: slow) and since the front problem only appeared when going really fast it seemed to be gone. Then when I started to feel more comfortable and safe with this setup I started to go faster ... and this is when I lost the front end again, big time (including crash), just before the end of the long trail brake (so still on the brakes).

This is when I got confused. I took weight off the front (thinking it was overweighted) and then it gives up under braking... ? Doesn't make sense to me.

Maybe you can help me understand what happened and how to set my bike correctly - what to try first.

Thanks,
--
Luke
 

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what springs are you running? valving? it doesnt sound to me like you are loading too heavy on the front. sounds more like the front is pushing back at you and just sweeping out... more info will be needed.
 

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Discussion Starter #3
The springs are theoretically good for my weight (187 lbs). No idea about the valving since I bought the bike already set up as Supermoto. All I know is that the suspension was set up by profesionals (the original was sent and rebuilt for sumo). The previous owner did it - he was my weight. What else do you want to know?
Remember that the problem appears just after I finish braking and start accelerating. Thanks.
 

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When getting on the gas and losing grip on front tire says the rear of bike is squatting too much and taking weight off front tire. Adding a little preload to shock could do the trick to keep the rear from squatting too much, add a little and see what happens. Put a mark on lower ring with a sharpie for reference point. In most cases, from middle of corner to exit the shock should be looked at.
 

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Discussion Starter #5
When getting on the gas and losing grip on front tire says the rear of bike is squatting too much and taking weight off front tire. Adding a little preload to shock could do the trick to keep the rear from squatting too much, add a little and see what happens. Put a mark on lower ring with a sharpie for reference point. In most cases, from middle of corner to exit the shock should be looked at.
So what you're saying is that the front is underweighted? Becasue adding preload to the rear would raise it. It would also change the sag I have set up.
 

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It's also possible the rear has too much pre-load already, that will lead to the front wanting to tuck as well as the rapid front tire wear as the bike would have too much front end bias. As mentioned above, mark the pre-load adjuster ring before making any changes. My bike was doing the same thing at one point, I took two full turns of pre-load out, and it was rock solid.
 

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Will have to excuse me, I am still in sport bike tuning mode. Just started working with supermoto set up over the past few months myself, still have a lot to learn about these bikes.
 

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Will have to excuse me, I am still in sport bike tuning mode. Just started working with supermoto set up over the past few months myself, still have a lot to learn about these bikes.
I would think the basic concepts would be the same, but I don't know, I learned what little I know here. I think your advice would be dead on it if was plowing the front under power. The tire wear, and fact it's under braking are what I'm going off of, but hell I may be wrong too. Suspension is a mysterious art, and everyone like their bike to feel a certain way. I can do basic stuff, the rest I take to an expert and let him do it.
 

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If the problem starts just as applying throttle with the front tire losing traction it kind of points at the shock and weight coming off front tire. Could be damping issue or not enough preload I would think.
 

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Discussion Starter #10
Ok, my theory, correct me if it's probable: Just as I finish braking I start applying the throtle and push the bike further down, make the lean angle steeper. This theoretically would be ok, because accelerating makes the bike stand up, so I have more ground clearance and can lean further. The theory is that I accelerate too lazy... and the bike is pushed down more by the extra lean than it is pushed up by the throttle -> the front pushes....
After a few years of racing I'm banging my head against the wall of my limits and this makes me reinvent even the simplest theories in search for better laptimes. So please be patient with me and don't be shy to tell me I'm doing it all wrong :)
 

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Discussion Starter #12

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A guy in front of me crashed once and in the pits another, much more experienced guy walks up to him and asks "do you know why you crashed"? "You didn't load the front tire enough so it skid out from under you trail braking, you have to get over the handlebars and load it up".

Coming from road racing I can see how it's easy to be doing that. Where's your ass on the seat when you get into the corner - way back or in the middle? Also did you try to find out how much travel are you using on the forks? Race sag front/rear?
 

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Discussion Starter #14
Last weekend was the racing weekend for me. Weather conditions were ugly - dumpy cold in the morning (mud all over the track) to sunny and hot in the afternoon. Anyway I crashed twice becasue of the front giving up under trail braking.
This + the dave moss movie showing tire use makes me thing the tire is either underweighted or it has too much air in it.

Riding on the muddy track obviously made me ride smoother and brake lighter. This + blowing 24 psi (I was using 26 before) into the tube made the tire "heal itself".

Seems this is it, but I will know for sure in a week or two when my body heales itself after those crashes...

If you think it maybe useful I can post photos of the front tire before the weekend and now.
 
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