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Discussion Starter · #1 ·
Hey I just read another thread that was asking about 20mm axles and why people need em.
This got me to thinking about flex from the rear of the bike. I know that when my front wheel deflects off of a rock or an off-camber section my bike goes in that direction. Is this the same for the rear wheel? To me it seems like flex in the rear would not be as noticeable and wouldn't have the same dire consequences as front end flex. So how big a deal is frame flex for aggressive rock strewn type riding, the type that benefits from a 20 mm axle up front.

To help illustrate where my confusion comes from; I ride an Al HT which has zero flex but I have an older fully rigid steel bike that I use on a fluid trainer. The steel bike flexes while I am pedaling but on the trail I can't notice any negatives to this flex. It tracks straight through rock gardens and around corners. If I use a fat tire I can make it rub around fast corners but that seems to be the only thing I can notice.

Also could someone correct me on this related question, wouldn't frame flex help with highspeed cornering? If the bike flexed there would be more of an arc to the wheelpaths and wouldn't that bring the bike through the corner better?
 

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well i would think that frame flex would be somewhat of a big deal, though on a very miniscule level. as you mentioned, the qualities of steel allow it to flex more, giving a plusher ride, but also giving it greater strength as it can absorb more impact. a full suspension frame is at its very basic core a frame that will flex a LOT vertically. so i guess frame flex is a pretty big deal.

I don't think that frame flex would help with cornering much, no. it just doesn't seem to make sense in my mind, but it's late and i could be totally talkin out of my arse.
 

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It hurts cornering and riding off camber stuff mostly. Flex is a completely undamped spring action. That's not good because it's like having a shock with no rebound.
 

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my bodyboard flexes to throw me off big lips and off the bottom of gapping pits , but it drives me crazy when HT flexs when I put the pedal down with a lot of torque. I am a clyde and I pretty sure my bike doesn't handle my weight well. A bodyboard is desinged to have a spring action to it like the rebound on shock/fork. I don't fel that positive springing action from the rear of my AI HT.
 

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Well, I think that you have to consider the whole bike flex (not just frame). I think that a laterally rigid bike is better for heavier riders (I'm 230 lbs plus gear) riding on rougher terrains. Probably for more XC riding by lighter riders it wouldn't be noticed. And somewhere in between it would depend on riding styles, rider weight and terrain.

My frame is a very strong frame, but I had some Mavic Crosslands, which I thought were good, until I tried a XT/819 wheel set, which has 32 spokes vs 24 on the Crosslands. This just makes for a completely different, more confident fell.

For me, I would think it is very important for a bike to be stiff.
 

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I ride 4 different aluminum hardtails that all have varying degrees of flex. The lightest frame wants to squirm and whip me around in babyheads but takes an edge off some impacts which is nice on longer rides.
If you ride a beefy overbuilt frame you usually have big arse tires to cush things up so take that into consideration .
I have had a uberflexy FS bike (AMP) bend so much it was scary and dangerous and some old steel frames ghostshift from hammering on the peddals, Not fun!
 

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Discussion Starter · #9 ·
Thanks for the input. I was referring to lateral flex, sorry that I didn't make that clear. Looking back my talk about my hardtails would make it seem like I was talking about vertical flex. My steel hardtail flexes laterally when I stand and hammer cause I tip the bike to the side with each pedal stroke (this is on top of the tires and crank arms moving).

So the overall consensus seems to be that off camber is the place where flex affects you the most, is that right? For those who find they have issues with flex, could you elaborate a bit for me. Does it make it harder to track straight like a flexy fork does and comparatively how big a deal is it. What I am hoping to get out of this is a good guess of how stiff a full susser I would need when I get a new frame. I now my minimum level of stiffness for a fork so if someone could maybe draw a parallel for me that would be greatly appreciated.

Forks that I found to be too flexy-bomber z5, RS psylo, RS sid.
Fork that I found to be at the minimum level of stiffness-Manitou sherman firefly, but I would of preferred that fork with a 20mm through axle because I still get a some flex at high speed and through rock gardens.
So if you have experience with these forks or similar ones and would like to comment on what would be a comparable full susser, I would really appreciate it.
 
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