How Stiff Do You Want It?

[Phatmike]

I'm after feedback from those who believe they can properly comment on the 'feel' of a frame - I'm looking at people like Matt Burrows, Ali C, Tarty Ad and Stedman etc; guys that really think about the products they're using when riding.

In the mtb & road world, guys talk about the feel of frames, just as much as they do weight, geometry & size.

What I'm asking is your opinions on how frames feel when they're ridden. Koxx talk a lot about the stiffness of their frames, which makes sense for things like optimum power transmission and a sharp ride. Is there a flip side to this (such as Ali C's global Ti, and the Triton frames) that can be discussed in any more detail than 'they just feel better'?

Do you think frames should be designed to be as stiff as possible to the upmost? Or can flex benefit?

Thanks in advance for your thoughts..

[trialsrider101]

Do you think frames should be designed to be as stiff as possible to the upmost? Or can flex benefit?

I know Im probably not what you would call an experianced rider but here goes;

In my opinion stiff frames would (sorry to use the phrase) feel better for most moves in trials, due to It reacting quicker but there are alot of streety moves that i dont think i could peform on a stiff frame eg 360's 180's stuff like that, but on the other hand i suppose there would have to be a small amount of flex in any frame because would'nt no flex= snap happy?

Edited December 10, 2010 by trialsrider101

[dirt jumper jake]

I know Im probably not what you would call an experianced rider but here goes;

In my opinion stiff frames would (sorry to use the phrase) feel better for most moves in trials, due to It reacting quicker but there are alot of streety moves that i dont think i could peform on a stiff frame eg 360's 180's stuff like that, but on the other hand i suppose there would have to be a small amount of flex in any frame because would'nt no flex= snap happy?

I would want a frame thats decently stiff in the rear brake area (seatstays) yet flexy enough to not snap or crack.

[Phatmike]

I'm taking cracking and breaking out of the equation here Jake. Purely about the feel of the frame when it's still alive.

[Nick Manning]

Mike, I rode Jack Meek's Koxx recently and personally didn't like the feel of how it ride. It is a lot stiffer than my Zoo Piranha. You could feel this while hopping the rear wheel, there was just no give anywhere, it didn't feel nice. But then Jack loves it, so I think a lot of how a frame feels to a rider depends on the individual.

I think you want some flex in a frame as it'll have more flow and will like it'll do anything, where as a stiff frame just feels likes it's designed to go in a straight line and nothing more.

[dirt jumper jake]

I'm taking cracking and breaking out of the equation here Jake. Purely about the feel of the frame when it's still alive.

In that case, as i said before really, minimal flex as possible on the seat stays but yet enough flex in other areas as so not to break your knees doing a 10ft drop

[Matt Vandart]

Flex will lead to snappage eventually also with aluminum.

I think mods feel better when stiffer, rather than stocks, but then I have never really had a very stiff stock.

Talking to Kerr the other night he was saying that he had a go on a koxx frame the other day and that it was very stiff.

This was said in a positive way.

One thing I really liked about my Skull frame was that it was very stiff as was the zoo Lynx.

Edited December 10, 2010 by Matt Vandart

[Mikee]

Going back to my ashton justice after a few months on a different frame, I noticed that everything on the ashton (being flexier), feels smoother but putting power down wasn't as responsive.

[Greetings]

It's a tough one. I remember being very impressed with the stiffness of the Levelboss 1030 when it came out. It felt like it was an extension of your spine, a kind of precision tool. Before that, all we had were Montys.

On the other hand, I rode a Triton for almost 2 years and got very used to the springyness of the frame. It really did make a difference.

I sold the frame on last year and had the chance to ride it this year when I met it's new owner. Getting on it after riding a Gu Le BB40 for a few months was a sensational experience. Despite my GU weighing in at 8.6kg and that Triton build being around 9.5, it felt as if I got a massive boost of energy. It's really difficult to describe but every little hop on that frame felt light.

The nature of the springyness of Tritons (at least mine) was that it felt very rigid but delivered a small kick out of nowhere. A sensational feeling if you're not used to it and also difficult to describe.

On that basis I'm a big fan of springy frames but it's got to be done right. A 221 X-Lite I had in the past where the seat tube broke off the BB might have had a good 20mm of travel under hard preload but wasn't the kind of springyness one was looking for.

[monkeyseemonkeydo]

I'd say it depends on the sort of riding. A stiff frame is ideal for technical comp riding and gives you full confidence in wheel placement and instant power transmission but won't necessarily be overly 'comfortable'- it would be a sharp tool, built for a purpose. However, for a more rounded frame for use on streets and just general trials riding, I think a degree of flex is both forgiving (to components and the body) and also more 'comfortable'. Obviously you don't want it being so flexy so as to be unstable but a little 'give' in certain directions wouldn't be bad.

I guess that's part of the reasoning behind curvy tubes- a very stiff rear end for instant power transmission and confidence on the back wheel but flex and a little 'give' up front.

[dirt jumper jake]

I guess that's part of the reasoning behind curvy tubes- a very stiff rear end for instant power transmission and confidence on the back wheel but flex and a little 'give' up front.

As in physically bent tubing or hydro formed?

[monkeyseemonkeydo]

As in physically bent tubing or hydro formed?

Physically bent. In theory hydroforming will increase the stiffness of a given tube compared to a plain tube.

[Mark W]

I hate the feeling of anything flexy pretty much anywhere on my bike. Ever since the old Slinger/T-Master proto frame I rode for Onza yeeeeears ago, I've always loved really stiff frames/setups. I usually overtighten my headset for that reason, and run really high spoke tension too (as well as using paper-thin grips and thin pedals). Flexy wheels are the absolute worst - it's amazing how much 5 minutes with a spoke key can transform how your bike rides...

Sticking with frames though, I'm much more of a fan of having them as stiff as possible. I like to be able to feel what's going on when I'm riding, and feel what my actions are doing to my bike, so having a frame that flexes too much just kills that totally. I like the feeling of control you have when you know that the input you give is going to have the reaction you'd expect, in much the same way I 100% prefer riding hardtails compared to full sus bikes because you can use pumping and movement of your body much more.

[forteh]

Im with inur on this one, after riding the triton for the last two years or so and getting the setup dialled to how I like it, I now cant ride anyone elses bike because they just feel heavy and dead

On the last brum ride I was on I had a go on max-T's piranaha and I hated it, felt like it weighed 15kg (obviously it doesnt) and it didnt seem to have any life to the frame; got back on the triton and it feels like a feather because it springs and flicks about so easily. Again that could be alot down to personal setup.

When heavier or powerful riders (thinking bigman heavy here!) have had a go on my bike they complain about the flex, I could see it bending under adam from 20 foot away though!

However for my weight and its just about right.

I think everyone who has ridden my bike (tunnicliffe, swindlehurst, burrows, brady, max to name a few) has said how light and flicky it feels.

[Nick Manning]

I think the problem with opinions of frames being stiff or flexy is that everyone likes things differently. You could have 2 of the same frame spec'd differently and they would feel differently on stiffness, and then again different people would find them feeling stiffer than what other people do.

[JD™]

I like it as stiff as possible at the rear end.

[sstein]

Flex will lead to snappage eventually also with aluminum.

I would like to question this statement. a metal will have the same breaking point irrespective of it's rigidity, for example if you were to take the same amount of alloy and make a solid rod rather than a hollow tube it would have the same tensile strength yet the tube would be much stiffer because of it's overall diameter. If anything flexy frames are less likely to snap because they will reduce the momentum caused by impact rather than stopping it in a single go, thus there will be a slower acceleration and less force actually put through the frame. 

In my opinion the best frames are sufficiently rigid not to feel flexy yet have enough movement to make the ride more comfortable, that is why steel frames feel great because they are stiff yet allow a certain amount of flex

[Phatmike]

Flex will lead to snappage eventually also with aluminum.

Not necessarily, see below,

I would like to question this statement. a metal will have the same breaking point irrespective of it's rigidity,

Flex does usually play a part in the strength of a material, but the main issue with frames is fatigue. Aluminium is very poor compared to steel, which is worse than Ti.

To put numbers on it you could bend a piece of alu once, bend it back and it would snap. Steel would last 20 bends and Ti around 1000! That's what makes Steel & Ti such tough materials. Have you seen the dents put in Stedman's steel bikes over the years? I remember when we'd throw massive rocks at each others bikes trying to dent them! I wouldn't imagine a Sky being so tough, even if it was much heavier.

Stress is a measure of internal stresses in a deformable body (thanks wiki), "internal forces are distributed continuously within the volume of the material body". That is to say that an optimum design would really distribute stress evenly throughout a frame rather than let stress areas build up. Even if we ignore stress risers such as welds or design flaws (which just make an area more likely to break) then flex won't always lead to snappage, even repeated, cyclic stress.

Providing the stresses that are cyclically applied don't exceed the endurance limit then theoretically the part will never break. The endurance limit is the level of stress that can be applied cyclically, indefinitely before a part breaks - essentially a type of elastic limit. A factor of safety could even be calculated and built in for big moves and crashes - as in the graph above the uts is 4 times the endurance limit.

If you wanted to be really technical you could measure the forces put on a bike and their frequency. Over a set time the stresses could be used to calculate exactly how long a part would last given an individual rider's usual riding! Seriously geeky stuff

The bottom of the curve would be close to the endurance limit. (In this case around 70Mpa for an alu of 320Mpa Ultimate Tensile Strength)

So if you want flex and spring and you can calculate it, where would it be? Up and down in the back end, but not torsional?

Edit: Hmm, this all sounds very german. I'll try and keep the visuals a bit more organic at least!

[isitafox]

Are all these threads requesting pics and opinions leading to something Mike? Your not planning on bringing out a Phatframe are you???

[eskimo]

I noticed a huge stiffness increase moving from my Monty PR to my Triton. But the Triton runs a harder 20" tyre, 4 more spokes, stiffer forks, a faced headtube, a big front and rear triangle (like a bmx), and generally better components. So it's not surprising it's going to feel stiffer. But i've not had anyone say that my bike is at all flexy when they had a go, but neither did i ask. Though i know 2 people with steel 24" bikes with large triangles also, those feel stiffer than mine. But it's not something you would or even could compare in my eyes. Does this help, probably not

[Scotty Evil1]

He uses big words and a graph! I believe everything he says!

[dirt jumper jake]

i understand most of what mike said, yet this is beyond me haha

[PaRtZ]

I see a frame in the pipeline

I do like stiff frames, but I do prefer slightly flexy ones more. Cant explain why, but flexy frames just feel more fun and less 'dead'. Stiff frames are great for natural and stuff like that, but id rather have a little flex in the frame that I ride

Assuming ofcourse you can overcome the brake setup problems...

[Phatmike]

Are all these threads requesting pics and opinions leading to something Mike? Your not planning on bringing out a Phatframe are you???

Dave, they sure are leading somewhere. It's got to be done right, so I'm taking my time.

We should be seeing phase frame prototypes early next year, most of the design spec got written up at a meeting several months ago. I'm working on themes independent to mad and will be able to spend much more time on the Phrame . I'd like to collate as much rider opinion as possible, though that's got to be filtered through to get anything tangible!

[Al_Fel]

Dave, they sure are leading somewhere. It's got to be done right, so I'm taking my time.

We should be seeing phase frame prototypes early next year, most of the design spec got written up at a meeting several months ago. I'm working on themes independent to mad and will be able to spend much more time on the Phrame . I'd like to collate as much rider opinion as possible, though that's got to be filtered through to get anything tangible!

That right there make me instantly not want to buy one.