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Fit question, changing bikes.
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I am swapping from a Large Shiv to a Medium Dimond Marquise and I wasn't sure what fit numbers would be the same since the geometry of the bikes are a bit different. While I do plan to get a more turned in fit, I'd like to get the dimond setup as close to possible then go for changes from that position.


Can anyone help?
  • are my stack/reach numbers just transferable?
  • what about saddle height and offset from the BB center?
  • any thing else that I need to consider?


Fit numbers:
  • Stack: 650
  • Reach: 510
  • Crank Arm length: 165mm
  • Saddle Height from BB center to saddle center: 78.5cm
  • Saddle tip set back: 3cm
  • The seat tube angle on the Shiv is 77 degrees vs. 79 degrees on the dimond.

Thanks in advance for the help!
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Re: Fit question, changing bikes. [palmdoggSAE] [ In reply to ]
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Your fit numbers are your fit numbers.

If you are comfortable, there is no need to change anything.
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Re: Fit question, changing bikes. [palmdoggSAE] [ In reply to ]
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it's a little unclear what you're asking.

the answer to most of that it seems like you are asking is "it depends." the reach should be easy, the medium marquise's frame reach is 425. the stack will depend on your bar setup, as the frame stack on the marquise is 540, so you'll have to add, effectively 11cm to that to get your armpads to where they need to be.

saddle height is definitely transferable, probably. will depend on whether you're buying a new or a used marquise.

saddle offset depends on type of saddle you have, but should be transferable.

if you are happy with your fit, you'll make it work. given that you are on a large shiv (which is generally only a good fit for very tall, very long limbed people) and going to a medium marquise i'm guessing you are buying used.
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Re: Fit question, changing bikes. [jkhayc] [ In reply to ]
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I've been told I probably should have bought a medium shiv vs. large a few times in the past. I am just ready to move on to a new bike and I got the large probably from a LBS that has no business selling tri-bikes but they do anyway - I was new into the sport and my position wasn't great to start, they just set me up and I said, this feels ok (lesson learned there was get a bike fit before you buy a bike).

I assume my stack/reach don't need to change and I can get those dialed in pretty easily., but given the seat tube angles are not the same - keeping the length from the saddle center to the BB center the same will mess with my hip/knee angles, right?

If the Shiv seat tube angle = 77 and my length from the BB to the seat is 78.5cm, then I can calculate the effective vertical height of my saddle above the BB center.

If the seat tube angle is now 79, the same 78.5cm length to my saddle is effectively longer since the angle is steeper. So I'd expect I need to drop my saddle a bit to keep the vertical height the same. It also would move my saddle forward as the angle is steeper. So I'd assume I need to not only drop my saddle a bit, but also increase the saddle setback vs the BB center to find the same effective vertical height and offset I had with a flatter seat tube angle?

This would all just be some trig math that I can do, but I wasn't sure if that is the right path to go down or if I am over thinking it?
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Re: Fit question, changing bikes. [palmdoggSAE] [ In reply to ]
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"(lesson learned there was get a bike fit before you buy a bike)"

Are your fit numbers that you state from a new bike fit or are these taken from the position that you have evolved to on your Shiv?
If the numbers are from a new bike fit then you just need to look at ways to make the new bike meet those parameters.
If however these are numbers you are taking from your position on the Shiv I would say take your own advice and "get a bike fit before you buy a bike".
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Re: Fit question, changing bikes. [palmdoggSAE] [ In reply to ]
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"given the seat tube angles are not the same - keeping the length from the saddle center to the BB center the same will mess with my hip/knee angles, right? "


No.
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Re: Fit question, changing bikes. [jimatbeyond] [ In reply to ]
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Can you explain why the answer is "no". maybe the answer is that the changes are too small to matter?

I can just use the same offset from my saddle tip as before, but the angle still makes the effective height longer, so I need to drop the seat...probably 0.5cm or so. Maybe that is to small to matter...I don't change my seat height and it doesn't move so I wouldn't know if that would cause issues in other areas.
Last edited by: palmdoggSAE: Jan 18, 19 12:23
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Re: Fit question, changing bikes. [palmdoggSAE] [ In reply to ]
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you have your nose setback, keep it and bb distance the same and it will be....the same
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Re: Fit question, changing bikes. [palmdoggSAE] [ In reply to ]
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palmdoggSAE wrote:
Can you explain why the answer is "no". The math doesn't agree. But maybe the answer is that the changes are too small to matter?

It's "no" because what matters is that the saddle position is the same relative to the bottom bracket. If the saddle height relative to the BB is the same, and the setback of the saddle nose relative to the BB is the same, then the saddle position is the same.

These two fits are the same, even though the seat tube angle is very different. The setback from the saddle nose tip to the BB is the same for both:


Last edited by: HTupolev: Jan 18, 19 12:29
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Re: Fit question, changing bikes. [palmdoggSAE] [ In reply to ]
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The center of your saddle doesn't depend on the seat tube angle. With your saddle at the correct height, you should be able to move your saddle fore/aft to get the proper offset from the BB.

Strava
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Re: Fit question, changing bikes. [HTupolev] [ In reply to ]
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yes, I get that. I probably just went in a full circle in my head but I understand and I was probably just over thinking it, which is what I thought when I first posted. Appreciate all the replies and the help.
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Re: Fit question, changing bikes. [palmdoggSAE] [ In reply to ]
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Okay, hold on. Let's take this one step at a time.

I'm not 100% sure if you believe in (are happy with) your current fit on your old bike, but let's pretend you love it and you want to duplicate that on the new bike.

Saddle first and in two ways (and use existing saddle, if you go to a new saddle that can change things dramatically):
1) get the new bike set up with the same seat height 785mm. Dimond geometry page says that'll work.
2) get the new bike set up with the same set back. For now ignore seat angle, the new bike has lots of room for the seat clamp to slide fore and aft - just duplicate the set back. If you want advice on how to measure that get back to use here.

Then you'll want to position the front end. The large Shiv had a Stack and Reach (and I'm using those terms accurately to mean to the top of the head tube) of 565 & 425. The new bike in a medium has a Stack and Reach of 540 & 425.

If your goal is to recreate the same exact cockpit distance, pad width, extension length etc. Then you are most likely going to tweak some stuff. That might include different stem, spacer position under the stem, pad fore-aft, etc. Based on the Stack and Reach the Shiv is 25mm taller stack than the Dimond so you're gonna need to build up a bit to make up for that missing 25mm of space - does the Dimond come spec'd with 3T bars? Those pads sit ~50mm above the base bar - that will be a factor to compare to the bars that are on the Shiv. The reach is identical so that should be easier to duplicate.

Ian

Ian Murray
http://www.TriathlonTrainingSeries.com
I like the pursuit of mastery
Twitter - @TriCoachIan
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Re: Fit question, changing bikes. [ianpeace] [ In reply to ]
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Thanks! The bars are alpha X slammed on the shiv, the lowest I can go without an undermount setup and I tilt the extensions so undermount isn’t ideal.

I’m on a dash strike, no desire to change - love it unless it’s another dash.

I’ll have plenty of ability to get to the same stack/reach on the dimond with even more room to go lower/forward which will be nice as I continue to work on my position.

I can ride my position mostly in aero for long periods of the time, long enough for IM racing as needed so I’m not looking to substaintly change it for comfort reasons, but make some minor tweaks along the way if it could be faster, yes. I’m not sure what you mean by 100% on my fit though. I’ve riden some respectable times with it when comparing my time to others with watts/kg in consideration, so it can’t be a horrible one.. some meat on the bone for cda - most likely yes.
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Re: Fit question, changing bikes. [palmdoggSAE] [ In reply to ]
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Quote:
I’m not sure what you mean by 100% on my fit though

Sorry for the confusion, what I meant was....I couldn't tell from your OP if you are loving your position on the Shiv and wanted to replicate that on the Dimond or if you were looking for a new position on the new bike. Now you've expanded on that so I understand now.

Good that you're loving that saddle. I think it'll be helpful to put the Diamon on a trainer with a wheel block and get it level before you start the replication. It's easy to get a lot of "noise" in the numbers so be diligent on the seat height and set back first. Getting that accurate is a must for power and from that you can then measure off of the saddle to position the pads et al.

Ian

Ian Murray
http://www.TriathlonTrainingSeries.com
I like the pursuit of mastery
Twitter - @TriCoachIan
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