Home Made Bikes

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flag smalltownboycustoms
Posted: Jan 1, 2020 at 9:53 Quote
Homemade carbon fibre frame update:

Homemade carbon frame

After riding for over 2 years in the above setup I decided it was time for the geometry to be updated. So decided to make a new steel front triangle utilising the original homemade swing arm - I've always liked the idea of a carbon fibre/steel mix.

The last frame of 2019 A new Steel front triangle for the homemade carbon fibre frame. After riding it for over 2 years the geometry needed a bit of updating.

Updated geometry:
HA: 63º
STA: 76º
CS: 430mm
Reach: 450mm
Travel (f/r): 160/140mm
flag TheGnome
Posted: Jan 1, 2020 at 11:22 Quote
wow that looks amazing Salute Helmet
flag dirtysanchez44
Posted: Jan 2, 2020 at 8:41 Quote
A question which I thought of when looking at the Field Test 13 Bikes Hucked to Flat video the other day... Do any of you home builders consider the effect of tyre rate in your suspension spring rate calculations?

Additionally, what level of structural analysis do you carry out for your frames, or is it a case of rule of thumb and experience?
flag R-M-R
Posted: Jan 2, 2020 at 8:55 Quote
I'm a design consultant, not a home builder. To address the question of tire/tyre rate on suspension spring calculations: no, it's not explicitly considered during chassis design. It rarely, if ever, changes the decision on shock spec. The customer may want to adjust the dampers a click or two for high-volume tires.
flag cedric-eveleigh
O+
Posted: Jan 2, 2020 at 11:01 Quote
That's an interesting question about if and how frame design and suspension setup should be adjusted for tire volume and pressure. Whether tire inserts are present and what tire inserts are present should probably also be considerations.
flag R-M-R
Posted: Jan 2, 2020 at 11:48 Quote
cedrico wrote:
That's an interesting question about if and how frame design and suspension setup should be adjusted for tire volume and pressure. Whether tire inserts are present and what tire inserts are present should probably also be considerations.

You're overestimating the precision with which the chassis and dampers can be tuned, let alone the precision with which they are tuned.
flag aks2017
Posted: Jan 2, 2020 at 14:39 Quote
cedrico wrote:
That's an interesting question about if and how frame design and suspension setup should be adjusted for tire volume and pressure. Whether tire inserts are present and what tire inserts are present should probably also be considerations.
I would doubt you see frames tuned for tires based on the amount of variance described above

If someone builds a frame around a 2.2” Ground Control, and the rider throws on a 2.4” Minion, then that would negate the additional frame tuning.

And that’s if you could do that level of tuning at all...
flag dirtysanchez44
Posted: Jan 2, 2020 at 15:03 Quote
I agree, there are too many variables to do it for the open market, but for a one-off homemade bike which you will be riding, I would have thought it would be easier to integrate the calculation into the design. Afterall, the tyre is acting in series with the suspension, allbeit with very little damping but it does have a spring rate...

I'm guessing that the calculations are good for getting a starting point, but it really boils down to how the bike feels on the trails and making changes based off that!
flag R-M-R
Posted: Jan 2, 2020 at 17:03 Quote
jgmu97 wrote:
I agree, there are too many variables to do it for the open market, but for a one-off homemade bike which you will be riding, I would have thought it would be easier to integrate the calculation into the design. Afterall, the tyre is acting in series with the suspension, allbeit with very little damping but it does have a spring rate...

I'm guessing that the calculations are good for getting a starting point, but it really boils down to how the bike feels on the trails and making changes based off that!

You're overestimating the precision with which the chassis and dampers can be tuned, let alone the precision a home builder can realistically attain, especially without dozens of iterations.
flag dirtysanchez44
Posted: Jan 3, 2020 at 1:27 Quote
R-M-R wrote:
jgmu97 wrote:
I agree, there are too many variables to do it for the open market, but for a one-off homemade bike which you will be riding, I would have thought it would be easier to integrate the calculation into the design. Afterall, the tyre is acting in series with the suspension, allbeit with very little damping but it does have a spring rate...

I'm guessing that the calculations are good for getting a starting point, but it really boils down to how the bike feels on the trails and making changes based off that!

You're overestimating the precision with which the chassis and dampers can be tuned, let alone the precision a home builder can realistically attain, especially without dozens of iterations.

That was why I also asked about how deeply builders analyse the structural performance of their frames. Yes FE analysis would give you an idea of frame stiffness and you could optimise stiffness with tube profiles etc, but there’s still going to be compliance in the system and the likelyhood is most frame builders won’t have access to that level of computer program anyway.

I’m guessing for dampers you’d need to get a custom tune where the damper could be run on a dyno which is again out of reach for most one-off builds?

Seems like the best approach is experimenting out on the trail with fork/damper settings and tyre pressures.
flag faul
Posted: Jan 3, 2020 at 3:40 Quote
cedrico wrote:
how frame design and suspension setup should be adjusted for tire volume and pressure.
You are adjusting your tire/tire pressure to fit your frame and suspensions, not the other way around.
And after that your riding style will smooth all the technical details.
flag R-M-R
Posted: Jan 3, 2020 at 7:13 Quote
jgmu97 wrote:
That was why I also asked about how deeply builders analyse the structural performance of their frames. Yes FE analysis would give you an idea of frame stiffness and you could optimise stiffness with tube profiles etc, but there’s still going to be compliance in the system and the likelyhood is most frame builders won’t have access to that level of computer program anyway.

I’m guessing for dampers you’d need to get a custom tune where the damper could be run on a dyno which is again out of reach for most one-off builds?

Seems like the best approach is experimenting out on the trail with fork/damper settings and tyre pressures.

Standard practice for designers is to just do the surfacing of the bike, often with little to no FE, and let the factory handle the lay-up and wall thickness. A particularly low-effort design firm once told me "we just draw whatever looks good and the factory sorts it out with lay-up". This firm has done only road bikes for the past decade, where the double-diamond shape and rigid frames are nearly impossible to thoroughly screw up; when tasked with doing a mountain bike, their incompetence forced me to take over the detail work and dimensions of the design, which I normally don't do.

Although this represents the lower end of the spectrum of competence, it's not completely unusual and illustrates the extent to which the industry is just guessing. Marketers create an image of teams of top gun engineers doing countless FE simulations to perfectly tune their precision machines. This is marketing, not truth. As an example, look at the weights of frames within a category and you'll find frames with comparable materials that differ in weight by pounds, yet the failure rates are completely independent of weight. Bikes are nowhere near as refined or optimized as they're made out to be.

At best, a modest amount of FE is done, and many companies do none. Those that do, rarely have a specific target in mind; they're just looking to smooth out the stress profile by reducing the worst hot spots, not unify the flex profile and tune it to achieve some known, ideal value.

A bit of CFD may be done for high-end road bikes, but again, some of these accomplish about as much as an F1 aerodynamics team could do over a lunch break.
flag dirtysanchez44
Posted: Jan 3, 2020 at 7:55 Quote
R-M-R wrote:
jgmu97 wrote:
That was why I also asked about how deeply builders analyse the structural performance of their frames. Yes FE analysis would give you an idea of frame stiffness and you could optimise stiffness with tube profiles etc, but there’s still going to be compliance in the system and the likelyhood is most frame builders won’t have access to that level of computer program anyway.

I’m guessing for dampers you’d need to get a custom tune where the damper could be run on a dyno which is again out of reach for most one-off builds?

Seems like the best approach is experimenting out on the trail with fork/damper settings and tyre pressures.

Standard practice for designers is to just do the surfacing of the bike, often with little to no FE, and let the factory handle the lay-up and wall thickness. A particularly low-effort design firm once told me "we just draw whatever looks good and the factory sorts it out with lay-up". This firm has done only road bikes for the past decade, where the double-diamond shape and rigid frames are nearly impossible to thoroughly screw up; when tasked with doing a mountain bike, their incompetence forced me to take over the detail work and dimensions of the design, which I normally don't do.

Although this represents the lower end of the spectrum of competence, it's not completely unusual and illustrates the extent to which the industry is just guessing. Marketers create an image of teams of top gun engineers doing countless FE simulations to perfectly tune their precision machines. This is marketing, not truth. As an example, look at the weights of frames within a category and you'll find frames with comparable materials that differ in weight by pounds, yet the failure rates are completely independent of weight. Bikes are nowhere near as refined or optimized as they're made out to be.

At best, a modest amount of FE is done, and many companies do none. Those that do, rarely have a specific target in mind; they're just looking to smooth out the stress profile by reducing the worst hot spots, not unify the flex profile and tune it to achieve some known, ideal value.

A bit of CFD may be done for high-end road bikes, but again, some of these accomplish about as much as an F1 aerodynamics team could do over a lunch break.

That's quite shocking then when you consider some of the marketing claims you read/see...

Thank you for some great industry insight!!
flag DanAlmberg
O+
Posted: Jan 4, 2020 at 3:44 Quote
Build me a new front triangle Smile
new front build up

 


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