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Help with helping client buy new tri bike
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Hello,

Please help! I have a client who wants to use my fit data to purchase a new tri bike. I have been using the fantastic calculators on this website but I am not sure if I am doing it correctly so want you FIST guys or girls to verify or correct my error(s) before I get back to my client.

I performed a retro fit on a Trek 1200 56cm 2004 road bike with Profile Design T2 Wing 42cm base-bar and Profile Design T3+ Carbon aero-bar with 15mm of riser.

Serotta XY co-ordinates: 448/630 (X/Y)
Head tube angle 73
Stem length: 70mm
Stem angle: +6
Stem Clamp height: 40mm
Spacer Height: 30mm
Headset topcap: 10mm (this is an estimate as forgot to take the measurement: external bearing headset was in use)
Effective seat tube angle: 73.7

Now using the F.I.S.T Bar to Head Tube Calculator I get a Stack and Reach of 545/401

I then understand that as the effective seat tube angle is shallower than on a tri bike and therefore the reach needs to be extended to compensate:

I calculate this to be adding an additional 22mm for a 76 STA to make Stack and Reach of 545/423 - - Is this correct?
(calculation using ST 560mm. I have also used the shallower of the typical tri STA on the basis it is cheaper to buy a longer stem than a new bike)

Using the Stack and Reach Database I am getting a close sizing for:

Trek SC in Large (541/426)
Dimond in Medium (540/425)
Cervelo P3 or P5 56cm (540/425)
Cannondale Slice 57cm (547/420)

Are these the bikes I should be recommending or am I overlooking any factors that will influence the right bike such as the stem length used on the stock bike etc? My understanding is Stack and Reach means that I can ignore these other parameters.

Again your help in this matter would be very much appreciated.

Alexander
PS: And yes I know I should do the FIST course but can't afford it at the moment.

Serotta Advanced and Advanced Triathlon
Retul Certified in 2011
Qualified sports massage therapists
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Re: Help with helping client buy new tri bike [SteelAl] [ In reply to ]
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Serotta XY is handlebar XY right?
Pad XY would be more useful (to back/top of the pads). T3 aerobar means that you can't have the pads set back too much as it has the J4 clamp but it can cause problems if you use an aerobar with a lot of pad offset and then only calculate to the bar centre. Plus bar xy meaningless on the Speed Concept.

I'm not sure why you would need that reach correction unless you're planning to transpose the position to a steeper STA.

Speedtheory | ST Interview
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Re: Help with helping client buy new tri bike [cyclenutnz] [ In reply to ]
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Yes that right Serrota is handlebar XY.

I don't have Pad XY coordinates and wouldn't know how to calculate stack and reach from such a measurement. I do have measurement for tip of saddle to pads, pad drop, tip of saddle to extension tip, tip drop etc. What I am needing to know is what is the best frame size my client and I believe the stack and reach given above is how I should determine this though I have my doubts because obviously tri bike don't come with external bearing races and 30mm of headset spacing.
So if I gave my client the above info and he went out and bought one of the bikes would he be able to get the pads in the right height (most important consideration for him) or will it be too low.

Yes, the reach correction is for using a steeper STA.

Serotta Advanced and Advanced Triathlon
Retul Certified in 2011
Qualified sports massage therapists
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Re: Help with helping client buy new tri bike [SteelAl] [ In reply to ]
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If you're wanting to rotate the position forward you need to factor in the increased drop as well.

The reason pad XY is useful is demonstrated below (using your measured Bar XY)



The Cannondale can just barely get there with a flipped stem. The Felt would get there more easily as it has a little more stack. But you wouldn't need to flip the stem as the stock aerobars come with a lot of pad stackers and the pads are able to be offset a long way behind the bar.


Because the Slice comes with terrible bars they would need to be changed and the right selection could remove the need for flipped stem there too.
Speed Concept could almost certainly hit that position as it has huge adjustment, though would likely need the Giraffe Stem.


Aerobars are a really important part of the calculation. Attachment shows a different tool (from the one above) that demonstrates balancing stem/spacer and aerobar specs to deal with differences in Frame XY.


Speedtheory | ST Interview
Last edited by: cyclenutnz: Jun 8, 15 2:53
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Re: Help with helping client buy new tri bike [cyclenutnz] [ In reply to ]
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Hi cyclenutz,

Those images comes from an specific software? can you give me the name?

Thanks!
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Re: Help with helping client buy new tri bike [cyclenutnz] [ In reply to ]
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Cheers Cyclenutnz for providing such as detailed response.

I now get why XY pad is important however they are measurement I don't have. Also I don't have access to the awesome bike sizing tools you do. A wee bit jealous!

You say I need to factor in increased drop as well. I understand this means you have to increase stack height to compensate for this drop hence why the Felt is a better fit? I assume this is due to everything being rotated around the bottom bracket. How can I calculate the new stack height if I do not access to software like you do? Does Slowtwitch.com have anything about this? Sorry for asking so many questions.

Alexander

Serotta Advanced and Advanced Triathlon
Retul Certified in 2011
Qualified sports massage therapists
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Re: Help with helping client buy new tri bike [SteelAl] [ In reply to ]
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Having these tools is easy - devote half your adult life and a large amount of $ to developing them yourself. Background in Maths and an understanding wife also useful.

Sometimes I'll have a client get in touch for whom I previously had modded a road bike to use aerobars in a respectable fashion - now wanting a tri bike. To give them options to consider (before travelling to see me again) I'll calculate shifting the saddle forward by an appropriate amount (ie whatever it takes to get to 78-79deg STA from where they were) and increase the drop by 3/4 that amount. That's generally a safe rule for keeping angles the same while rotating around the BB to give a starting point for using a tri bike.

This means you will be increasing pad X and reducing Pad Y (as whole position moves forward). The Felt is a good option because the bars have so much adjustability. Ultimately that is the most useful thing for a first tri bike - allows tweaking the position later with less hassle.

I don't think any of the ST calculators handle this.

Work out the effective seat angle of the numbers you have. Then calculate the forward movement based on going to 78deg (that is the shallow side of most good tri fits). Increase Bar X by a corresponding amount. Multiply that number by 0.75 - subtract this from Bar Y. Then you have a rough starting point that assumes using the same bars as in the fit. From there the ST calculators can help, or I should be able to make it much easier in the next couple of days (hint - I didn't spend all that time and money on the tools to keep them to myself).

Speedtheory | ST Interview
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Re: Help with helping client buy new tri bike [cyclenutnz] [ In reply to ]
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Kudos to you for spending the time, effort and money to develop such software; Some independent software is much needed as I am not sure how impartial such software is from the likes of Guru, Retul and Purley being owned/developed by bike manufacturers who have a vested interested in selling more of their own bikes and not the competitions. Anyway I digress.

OK, being a rookie I need some clarification on a few points. In the last post you said I would also have to reduce stack height to compensate for an increase in STA and very kindly gave me figures to calculate this.
  • This makes sense but, the Felt as a higher stack height. Is this because you were calculating to my original Bar XY where as if STA was increase bar XY would be longer and shorter? In other words my client would have his bars lower than current with a steeper STA?
I have recalculated* using your figures and got a Bar X/Y of 482/612 - then used ST calculator to get a new stack and reach of 529/428, which is almost bang on with a Felt B16 56cm.


*Not sure if I did my calculations right: OLD = Effective STA 73.7 (STA = 73.8) and Saddle Height (SH) of 793mm. This give a horizontal distance from the centre of the saddle to the centre of the BB of 222.5mm . New = ESTA of 76 and SH of 799mm (6mm compensation for more forward saddle position) - new horizontal dist. = 193mm. Difference is 29.5mm which I added to my measured Bar X of 453 to get New Bar X 482 rounded down. Then 0.75 x 29.5 = 22mm rounded down subtracted from old Bar Y of 634 to give New Bar Y of 612. Then this was put through ST calculator for S&R.

Serotta Advanced and Advanced Triathlon
Retul Certified in 2011
Qualified sports massage therapists
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Re: Help with helping client buy new tri bike [SteelAl] [ In reply to ]
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Nothing wrong with your calculations.

In the numbers I gave I'd shown how the Cannondale would get to target BarXY but only put the Felt beside it to compare frame numbers. Because the Felt has much more adjustable aerobars it's not necessary to flip the stem for that original position.

Your original numbers are based on an aerobar with pad stack of 75mm. The Felt bars can go somewhat higher than that (maybe as high as 120mm, I've not had to build one to the max height to know). So you don't necessarily need to have as many spacers under the stem as you've assumed in the ST calculator.



You can see that the Felt B2 (incl B12, B14 and is higher than B16) fits quite nicely with the aerobar specs you've based the calc on. As an example of using high stack bars to good effect - a P2 could fit well if you had bars with 15mm more stack than you were using on the Felt (something like Profile Aeria Alloy)

Speedtheory | ST Interview
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Re: Help with helping client buy new tri bike [SteelAl] [ In reply to ]
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Hello Alexander my name is Colby Marple, marketing manager at GURU. Our company has developed a software solution called Bike Discovery which takes 4 measurements off of an existing bike or stationary fit bike to generate complete bike solutions for any bike manufacturer.

The measurements that we use are slightly different than those that you provided in your post. Let me know if you are able to measure the following:

Saddle Height = center of BB to top of middle of saddle (measure along seat tube)
Setback = nose of saddle to vertical center line of BB (measurement taken horizontally)
Reach = nose of saddle to end of aero extension
Drop = middle of saddle to floor MINUS middle of pad to floor

In addition, please send the following equipment information:

Saddle length = middle of rails to nose
Saddle thickness = middle of rails to top of saddle (middle)
Pad stack = center of basebar to top of pad (middle)
Pad offset = middle of pad to back of pad
Extension length = middle of basebar to end of extension


With this information, we will be able to provide your customer with recommended bike configurations from Cannondale, Felt and more than 100 other brands.

I can send you measurement guides for each of the points listed let me know if you have any questions. You can also learn more about Bike Discovery here and download a free 10-day trial: http://www.gurusports.net/software


Regards, Colby
Last edited by: GURU_GURU: Jun 16, 15 14:31
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Re: Help with helping client buy new tri bike [cyclenutnz] [ In reply to ]
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Phew, pleased to know my maths is up to scratch.

Thanks for the clarification. However your post has thrown up one issue regarding the ST calculator, and I think I may be using it incorrectly.

In your post you stated
Quote:
So you don't necessarily need to have as many spacers under the stem as you've assumed in the ST calculator.

As you spotted I have put in spacer height of 30mm. I used 30mm of spacing as this is what the bike I did the fitting with had. Now I know with tri bikes, the less spacers the better. Therefore should I be applying in the ST calculators with the intended headset spacer amount stem angle etc e.g.: 10mm, -6 etc to get the stack and each to work off?

I have done a ST calculation using stem length 70mm, stem angle -6, spacer height 10mm and headset top cap 0 (integrated) - and got a

Stack and reach of 570/422. Inputing this through your frame comparison and using ST Stack and reach database I got the Blue Triad SL to come in with a bar XY of 483/612 with a stem of 60mm, -6 and 5mm of spacers. This is only 1 mm off on the reach!

Basically what I am trying to say in a long winded way is: Does having less height set spacers better when determining frame size for tri/TT bikes?

Serotta Advanced and Advanced Triathlon
Retul Certified in 2011
Qualified sports massage therapists
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Re: Help with helping client buy new tri bike [GURU_GURU] [ In reply to ]
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Hi Colby,

Thank you for the reply. I am aware of your software but do not use most of the measuring protocols you do. I also feel that to take all these additional measurement would be far to time consuming during a fit session as I already take 32 measurements. It might be the case I need to revise measurements for tri bikes and include pad stack height and extension length for example.

I would be interested to know why you measure saddle length from
Quote:
middle of rails to nose
, and clarify the pad offset which part of me thinks is an error as I can't see how
Quote:
middle of pad to back of pad
is going to vary unless you use a different type/make of pad.

Cheers,

Alexander

Serotta Advanced and Advanced Triathlon
Retul Certified in 2011
Qualified sports massage therapists
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Re: Help with helping client buy new tri bike [SteelAl] [ In reply to ]
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Hi Alexander,

Pad stack height and aero extension length measurements are critical in determining how to configure a position on a new or existing Tri bike. These are the biggest determining factors when it comes to figuring out frame size (based on stack/reach), stem length and bar positioning.

The beauty of using Bike Discovery is that you only have to take 4 measurements off of the bike to figure out a complete bike solution. These measurements are very easy to record - and in the case of the fit data measurements, they do not require an XY tool. In the case of Tri bikes, you need to add cockpit configuration data as previously specified - but beyond that, our software only requires 4 points in space to deliver a complete bike solution. If you haven't done so already, I would recommend trying our 10-day trial version - which you can download here: http://www.gurusports.net/software

In regards to why we measure saddle length in the manner specified below, our setback and reach measurements (using fit data method as opposed to the XY method) are calculated from the nose of the saddle. Therefore, Bike Discovery needs to account for how far forward the saddle is located relative to the middle of the seatpost. Our software's bike configurations are derived from XY data - and the saddle XY measurements are all taken from the middle of the rails on the seatpost clamp.

The pad offset instructions provided are correct - this measurement is taken from the middle of the pad to the back of the pad. Pad offset is required for our software to deliver a complete bike solution for Tri bikes because the horizontal pad position is the number one determining factor when it comes to the reach of a given position. Therefore, pad offset is required in order to determine the best frame size/configuration to obtain that pad position - as individual pad dimensions will yield varying frame size/stem length options. It is critical that the pad configuration used during a fit session aligns with the pad configuration on the customer's actual bike. If there is a variance between the equipment used during your fit session and what is actually installed on the customer's bike, there will be a discrepancy in positions between your fit sessions and the client's actual setup


Regards, Colby
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Re: Help with helping client buy new tri bike [SteelAl] [ In reply to ]
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Hello,
I really don't mean this to sound obnoxious, arrogant, etc., but what you are trying to do, which if I understand correctly is taking fit data from a road bike, to help your client buy a tri bike, is not a good idea.
You will get half baked results at best since your assumption that you can rotate forward and leave everything the same is a very big assumption.
You also have to consider differing aero bar geometries and a whole lot of other things.

If you want to serve your client best, it would be best if you suggest that he/she go so someone with a fitting bicycle so that a proper tri bike fit can be executed.

Best,
Jonathan

Jonathan Blyer,
ACME Bicycle Co., Brooklyn, NY
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Re: Help with helping client buy new tri bike [jonblyer] [ In reply to ]
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Hi Jonathan,

I appreciate your point of view and agree that the use of a sizing bike would be preferable (and easier) to using than an existing road bike. However I don't believe it necessary for establishing what would be the most appropriate frame geometry for an off-the-peg tri bike purchase.

I also believe there is a fundamental difference between a bike sizing, which is what I was doing, and a bike fit. I therefore disagree that I will end up with half baked results in determining the correct frame geometry for a tri bike using an existing road and apply the appropriate calculations to accommodate the differences in design of the two types of bikes. Also since other experienced bike fitters have posted here without expressing any reservations to my objectives and have provide advice on how to successfully make the calculations I can only conclude that this method is viable, does produce positive outcomes for my client, but is obviously not as neat and straightforward as using sizing bike.

Finally what I am doing has to be put in context with the fact that the vast majority of people in the UK are still buying their tri bikes based on price, recommendations by friends and reviews in the cycling press and not on what is the best size and geometry frame for them. Because of this I believe I have saved by client over 3000 as I advised him not to purchase the bike he wanted based on the results of my bike sizing, and to go for a tall and short geometry that is more in keeping with his functional abilities.

Cheers,
Alexander

Serotta Advanced and Advanced Triathlon
Retul Certified in 2011
Qualified sports massage therapists
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Re: Help with helping client buy new tri bike [SteelAl] [ In reply to ]
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Hi Alexander,

You post yourself as Serotta Advanced and Advanced Triathlon as well Retul Certified and you don t own a fit bike?? In my opinion that is the most important tool a fitter can have apart from knowledge and experience if you really want to give your client and Advanced and solid advise. As a triathlon specialist fitter i totally agree with Jon.

Besides that, even if the vast majority in the UK are buying their tri bikes price based or for one of the other reasons you write that is no excuse to give half baked fit advise.

Jeroen

Owner at TRIPRO, The Netherlands
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Re: Help with helping client buy new tri bike [tri-run] [ In reply to ]
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Hi Jeroen,

No I don't own one. Lucky for those who can afford to buy a fit bike: we are not all in a privileged position to do so.

Secondly my advise is not half baked; it is based on calculations and advise given by other highly experience bike fitters.

Serotta Advanced and Advanced Triathlon
Retul Certified in 2011
Qualified sports massage therapists
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