REVIEWS DEALS BIKESHOPS TRAILS

FAO Dave Turner

2317 Views 16 Replies 11 Participants Last post by matsoki, Jan 14, 2010

Dibbs_

Discussion Starter · Jan 13, 2010

You had better stop the production run of your DHR. A chap called JohnB on singletrackworld has some structural engineering advice for you

http://www.singletrackworld.com/2010/01/spy-shots-new-turner-dhr-prototype/#comments

Comment 4, classic internerd comment

1 - 17 of 17 Posts

moosehead

· #2 · Jan 13, 2010

Noticed that The Lecht Rocks also has another newsworthy troll. Shocker. I bet a jackson Dieter's either stalking Turner, or he's on Nicolai commissions.

Imagine the contortions folks will go through when the RFX hits? Uh, speaking of which, any spy proto's, pre-announcements, teasers?

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Renegade

· #3 · Jan 13, 2010

Commenter #4, John Beard, knows all about bike frame construction, as he is an infamous custom car creator:
http://www.beardmorebros.co.uk/
who is currently looking for employment:

I am currently looking for employment in engineering.

My skills are varied and I am very adaptable but my main areas of expertise are mechanical problem solving with design, in a hands on role. As you can see from the cars I have built I have extensive practical fabrication skills.

I have worked in a test and development role developing automotive vehicle safety, including conducting full crash tests. In this job I played a leading role in a team to update a model to cope with an increase of crash test speed from 48kph to 80kph. This included analysing FEA, analysing crashed vehicles, designing and conducting component tests, assisting designing components, working with mechanics to prepare crash test cars and presenting to the management of the model..

I am hard working, very organised, with a very high attention to detail.

Able to start immediatly.

Willing to relocate."

Mabey DT can give him a job designing the rfx.

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RAPIT

· #4 · Jan 13, 2010

Everything is relative and arguable but..... JohnB's comment is [email protected] right

SCUBAPRO

· #5 · Jan 13, 2010 (Edited)

RAPIT said:
Everything is relative and arguable but..... JohnB's comment is [email protected] right

How do you know that? Please explain. Thanks.

turnerbikes

· #6 · Jan 13, 2010

DownTube

Yes that shock pressing into the down tube used to look suspect to me as well, and since I am not an engineer I have had 2 looking at every part of this bike for months. I will go with my peoples expertise on this. Something that John does not know is how thick the tube is or how big in diameter or how large the loads are. As anyone that has followed the proto frame knows, the 'seat tube' used to curve to the down tube to give it structure, but that added more weight than was needed. We have run the FEA on the frame extensively and it is as strong as it needs to be. We chose to do it with a butted tube instead of adding a full length seat tube and corner gusset like the proto, this is lighter and plenty strong.

DT

big-ted

· #7 · Jan 13, 2010

From an Engineering point of view, yes, he's right, but there's no such thing as a perfect system. What would be the alternatives? Re-design shock placement so that loads are transferred elsewhere? Given the restrictions based on desired wheelpath, weight-placement and shock curve I would think that would be difficult. Nicolai have a strange brace running to the seattube to carry similar loads on one of their bikes. I'm sure DT just settled on ensuring the area in question was suitably reinforced. He's hardly a novice at this game...

Edit: Damnit. Sniped by the man himself!

Renegade

· #8 · Jan 13, 2010

I'm sure JohnB fed the solidworks picture of the bike into his E-FEA program and did a complete analysis....

This is his version of the DHR:

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RAPIT

· #9 · Jan 14, 2010

turnerbikes said:
Yes that shock pressing into the down tube used to look suspect to me as well, and since I am not an engineer I have had 2 looking at every part of this bike for months. I will go with my peoples expertise on this. Something that John does not know is how thick the tube is or how big in diameter or how large the loads are. As anyone that has followed the proto frame knows, the 'seat tube' used to curve to the down tube to give it structure, but that added more weight than was needed. We have run the FEA on the frame extensively and it is as strong as it needs to be. We chose to do it with a butted tube instead of adding a full length seat tube and corner gusset like the proto, this is lighter and plenty strong.

DT

hum, everything is relative and arguable, in frame design and..... in life, I suposse

(and I can only say I admire you)

However the fact that the impact energy of the rear when suspension bottoms up hits the middle area of the down tube is not a very good idea structuraly-wise opposite being closer to or on top to a tube joint area. Since: a) requires more material locally in the shock mount area (being the middle area of any tube the optimal for thinner material) for impact ressistance creating the first weight penalty and b) requires more material at both ends of the mentioned tube to withstand the Moment the bottoming produces, again a weight penalty.

This pure structural physics concept, and it is only this, not the whole thing. The whole package needs to be studied since other compromised may have been taken that get into a well balanced system before the frame can be judged.

A more accurate study could determine whether these weight penalties can be absorved in other areas where less material is required due to stress being on top tube, but I would disagree at first thought.

There would no need for me to write these comments unless some fanatics judged JohnB as a nerd without any sort of technical background which puts me off big time. I cannot stand it.

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moosehead

· #10 · Jan 14, 2010

RAPIT said:
hum, everything is relative and arguable, in frame design and..... in life, I suposse

(and I can only say I admire you)

However the fact that the impact energy of the rear when suspension bottoms up hits the middle area of the down tube is not a very good idea structuraly-wise opposite being closer to or on top to a tube joint area. Since: a) requires more material locally in the shock mount area (being the middle area of any tube the optimal for thinner material) for impact ressistance creating the first weight penalty and b) requires more material at both ends of the mentioned tube to withstand the Moment the bottoming produces, again a weight penalty.

This pure structural physics concept, and it is only this, not the whole thing. The whole package needs to be studied since other compromised may have been taken that get into a well balanced system before the frame can be judged.

A more accurate study could determine whether these weight penalties can be absorved in other areas where less material is required due to stress being on top tube, but I would disagree at first thought.

There would no need for me to write these comments unless some fanatics judged JohnB as a nerd without any sort of technical background which puts me off big time. I cannot stand it.

Rapit, I believe we are all saying the same things, and a lot of us here are nerds FWIW. The call out on John B was related to his overt presumption that all of these items were ignored and that the outcome was the worst compromise. This is in essense not giving DT, his engineers, or many test riders the same benefit of the doubt you are asking for on JB's behalf.

Per DT's post, not only is that shock mount area reinforced properly (as are many other DH rigs with downtube mounts), but it appears that there are less than direct forces applied to that area due to the leverage and loads taken by the dual links. As you indicate, DT also gets big credit for building durable bikes that he stands behind in the event they have issues.

Peace.

SCUBAPRO

· #11 · Jan 14, 2010

RAPIT said:
The whole package needs to be studied since other compromised may have been taken that get into a well balanced system...

Isn't that what DT said his engineers have done?

RAPIT

· #12 · Jan 14, 2010

moosehead said:
Rapit, I believe we are all saying the same things, and a lot of us here are nerds FWIW. The call out on John B was related to his overt presumption that all of these items were ignored and that the outcome was the worst compromise. This is in essense not giving DT, his engineers, or many test riders the same benefit of the doubt you are asking for on JB's behalf.

Agreed, although i do not consider myself a nerd in this subject, but the benefit of doubt of JB had been already been taken out when I first worte on this post when 4 of the 6 entries were to trying to ridicule JB without a single technical argument

Per DT's post, not only is that shock mount area reinforced properly (as are many other DH rigs with downtube mounts), but it appears that there are less than direct forces applied to that area due to the leverage and loads taken by the dual links. As you indicate, DT also gets big credit for building durable bikes that he stands behind in the event they have issues.

I have to disagree here. The energy of the impact is pretty much fully transmited to the shock mount regardless of how the linkage looks like. I agree with JB that having the shock mount there is inefficient structurally wise. DT hints that the tube is thicker in that area, hence proving JB valid. DT comments are right once you take into account the defined shock position, which is exaclty the only thing JB is criticising.

Peace.

Peace2

RAPIT

· #13 · Jan 14, 2010

big-ted said:
From an Engineering point of view, yes, he's right, but there's no such thing as a perfect system. What would be the alternatives? Re-design shock placement so that loads are transferred elsewhere? Given the restrictions based on desired wheelpath, weight-placement and shock curve I would think that would be difficult. Nicolai have a strange brace running to the seattube to carry similar loads on one of their bikes. I'm sure DT just settled on ensuring the area in question was suitably reinforced. He's hardly a novice at this game...

Edit: Damnit. Sniped by the man himself!

Just thinking on DT considering on taking an idea from his friend Nicolai made me smile mouth wide open.

lidarman

· #14 · Jan 14, 2010

Great thread.

Oh yes, did you know when you push the middle of a stretched thread, it takes very little force to deflect it and really amplifies the tension?

Mtn. Biker123

· #15 · Jan 14, 2010

lidarman said:
Great thread.

Oh yes, did you know when you push the middle of a stretched thread, it takes very little force to deflect it and really amplifies the tension?

I hope his racers are smooth

JWB

· #16 · Jan 14, 2010

I didnt realise my comments would produce such discussion...................

Most design is a compromise and it would appear that rear suspension function (in particular coil over damper position) has taken priority over structural effeciency. As the bike is a downhill machine then weight is less of an issue and suspension function more of an issue, that is the designers choice.

Loads into the middle of a tube can (and obviously do) work very well but the tube has to be bigger to take the loads.

There is no doubt in my mind that the bike is structurally solid and will last a long time.

John

PS The pic above is of my brothers first attempt at chassis design. His skill is bodywork.

Mine

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matsoki

· #17 · Jan 14, 2010

JWB said:
I didnt realise my comments would produce such discussion...................

Most design is a compromise and it would appear that rear suspension function (in particular coil over damper position) has taken priority over structural effeciency. As the bike is a downhill machine then weight is less of an issue and suspension function more of an issue, that is the designers choice.

Loads into the middle of a tube can (and obviously do) work very well but the tube has to be bigger to take the loads.

There is no doubt in my mind that the bike is structurally solid and will last a long time.

John

PS The pic above is of my brothers first attempt at chassis design. His skill is bodywork.

Mine

OMG what a mess...............

John dont give up your day job, and leave DT too his.

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