Bike fit question- weight balance on bike

I seem to be struggling to get my mass in the right spot on the bike and would appreciate any advice from the crowd. My intention has been to get a proper fitting but at this point I’m waiting to be fully vaccinated and hoping to solve at least the scariest problem sooner than that.
My problems are the following:

  1. Often I find myself sliding forward on the saddle. I’ve played around a little bit with the saddle fore/aft position but to no avail.
  2. When I’m out of the saddle sprinting I occasionally lift the back wheel enough to lose traction.
  3. Terrifyingly, 2 days ago while descending a hill at 40mph a bump made my weight “adjust” the handlebars down 1/4". I was on the hoods at the time, not the drops. I use torque wrenches and the stem bolts are torques to spec so I’m thinking I just have lots of weight forward on the bike and the unavoidable bump just added enough force?

For filling in the details, I’m 5’10" (178cm) and 150 lbs (68kg). The bike is a 54cm tarmac SL5, stem is 90mm.

Thanks!

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  • Why do you think you are coming forward?
  • Sometimes a saddle at the wrong angle will lead to this movement, or you may be trying to overcome another fit issue with this shift.
  • This is a problem sometimes, if you have insufficient weight on the rear tire, from leaning too far forward and/or not enough upper body control.
  • What material are the bars and stem?
  • If either or both are carbon, are you using a friction paste between the parts?
  • Yes, with weight on the hoods, this is about the worst case loading with respect to the bar to stem clamp control. In the drops, your weight actually reverses the loading on this joint in most cases, so a slip would be far less likely under a sharp loading like you describe.
  • 90mm might be considered “short” for this frame size and your height. But without knowing your inseam, it’s not certain since you may have different body proportions or other reasons to use a stem on the shorter side of what might be considered “typical”.

  • Along with reach/length, the drop from the saddle is another important factor in weight distribution.

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I appreciate the feedback.
The bars are carbon, stem aluminum. I did not use any paste, should I? Or maybe just dial it back a bit on the crap roads I’m on?
As far as saddle, I have to physically shift myself back periodically to feel like I’m not out on the nose.
Could easily be that it’s a result of other fit issues, tough to say. I can measure myself all day long but never feel like I’m getting accurate info. I really need to see a pro but am hesitant until vaccinated.
Sprinting: it’s possible my upper body control is off, but I didn’t have this problem on my previous bike (caad12) and I love to be super low in the front while sprinting.
I think my inseam is 32" or so but I really don’t feel like I can get a reliable measurement, seems to be a little different every time I measure!
There is definitely a drop between saddle and bars, but the bars aren’t slammed.

Yes absolutely use carbon paste. Finish Line - Bicycle Lubricants and Care Products - Fiber Grip™

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The perils of being an underexperienced home mechanic! I will descend slowly until I can get some carbon paste delivered!

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  • YES, 100% you MUST use friction paste with that carbon interface (bar/stem). This is why your bars slipped, even with the proper torque on the screws.

  • The ONLY exception that I personally skip the paste is for a stem onto the carbon steer tube of the fork. This is a low force application and I don’t see it as critical. Slipping of this connection generally only happens in a fall, and not in the process of riding.

  • Watch this: https://youtu.be/r7Ug37tNuYI

Generally speaking, you need to get seen by a fitter to fully review and address the issues here.

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I was alway coached to go in the drops for fast descents - hitting a bump at speed on the hoods can easily knock a hand off, brake control and leverage is reduced, and steering control is also reduced.

Notwithstanding the comments regarding using paste in the mounting interface, positioning is also a potential issue.

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What’s weird is that I feel like I have better brake control when I’m on the hoods. Which is why I was on them when the bars shifted as I was anticipating a stop at the bottom of the hill.
I think this is good advice though and I need to get more comfortable braking in the drops. Thank you.
Realistically I have no business enjoying the descending speed as much as I do. I should probably just chill the f out a bit!

I have ordered some friction paste and I will schedule a fitter, thanks for educating me!
Feeling lucky that my bars didn’t drop further and pitch me over at speed in traffic.

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Cleats position can cause not balanced weight distribution. And also core strength and saddle heigth/position/angle/type… it is not that easy to fingerpoint it. Do you have hands fatique?

No hands fatigue. My core is pretty good, I struggle sometimes with hip flexor tightness.
Im pretty sure my cleat position is not right, but it’s probably one of many things with my fit. I tried to measure my sitbones and order appropriate type/size saddle but honestly I’m not sure it’s located correctly or that my legs are same length.
Was hoping for a fix to hold me over for a while but I’m getting clear message that I need a fit asap!

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I’d suggest buying this DIY guide to fit from Bike Dynamics UK.
I used it recently to update the position on my trainer bike and gravel bike (new 6 degree stem, reward cleats, added pedal spacers)

I followed the guide and did the incremental adjustments on my trainer setup, then measured them over to my gravel bike.

Totally worth it.
https://bikedynamics.co.uk/shop.htm

I also used Bike Fast Fit to capture some of the measurements:

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I’ve used that pdf as well - it’s a good resource. Do set aside a couple of hours, though, and make sure you have a willing helper. My Mrs got fed up after 45 minutes and it nearly caused a domestic :man_facepalming:t2:

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Cannot imagine getting buy in from my partner on this effort, but perhaps its worth a read anyway!

Hard to say from the photo, to me it looks like your saddle is angled nose down.

Sometimes saddle designs also end up having to sit slightly more nose up than you’d expect to feel neutral. At least my WTB saddles are like that.

Perhaps try and get the middle/sit bone area neutral to help with sliding forwards. Ignore the tip and it shouldn’t take much angle change.

Probably a good idea, I will dial it back a touch tomorrow and see if it stops some of my squirming around.

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It sounds like something is not right with your bar/stem/torque wrench. The bars should not rotate under any circumstances, even without grip paste. Especially if you only weigh 68kg…

Maybe put some calipers on the clamp section of your bars and make sure they aren’t undersize. See if you can check your torque wrench against another one also. I recently threw out one of my preset torque wrenches because it wasn’t clicking at the same pressure as my other ones. The torque didn’t feel right so I checked it against a couple of others. Sure enough it was way too high.

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That reminds me of another thing, on a four-bolt bar clamp, make sure you tighten the bolts gradually and in a cross-shaped pattern (ie upper left and lower right, then the opposite), an not just whack each bolt in to full torque individually. Otherwise it’s possible for the plate to go on slightly askew, and effectively only be clamped correctly on one side.

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Measured the bars with a digital caliper, they seem the right size for sure. I am familiar with the alternating bolt tightening pattern so I don’t think that’s the case.
Even after the incident when they shifted, I was unable to move them with just my own (really weak) effort. I think it was more a case of a crazy amount of force then a fundamental problem with stem/bars. I did get and apply the friction paste (stuff seems like someone mixed sand and petroleum jelly and sold it for 100x) and that will hopefully help.
Other than that I’m going to schedule a fit…is retul the way to go or should I be trying to find a long time bike fitter? I have a retul fitter near me but its maybe 30% more costly than the other option (BG certified fit, not sure what that means).

BG is the “Body Geometry” fit that was done by Specialized up to the point that they bought Retul and adopted that name for their fitting process.

Any system can give good or poor results. What matters most is a fitter which knowledge and experience, good listening skills, and the ability to focus their experience to give you what YOU need.

It’s hard without interviewing the fitter a while and maybe talking to past clients. But you want to avoid fitters who are dogmatic to the point of squeezing you into their system, even if it’s not best for you.

Retul process and tools are great, but can be a crutch or a distraction in some cases. Tech matters far less than the fitter.

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