Question about changes to road bike fit...

jjpptt2
jjpptt2 Posts: 5,609 Member
I have 2 bikes - one is a racier 54, the other is a slightly more relaxed 56. The 54 fits/feels great, so I'm trying to adjust the 56 to fit/feel more like the 54.

Since I can't change things like ST angle or HT angle, I'm looking mostly at TT length, reach, and stem length. Should I be looking at any other measurements?

The better feeling 54" bike has a shorter TT length (15mm shorter)... but a longer reach (6mm). That tells me that the first adjustment should be a more forward saddle. If I understand this correctly, that will shorten the effective TT length while not impacting the reach.

Do you agree?
Is there any reason I shouldn't do this? Obviously I'll be sure to have a small allen with me to make adjustments during the first couple of rides in case there are any unexpected side effects... but am I missing anything big here?

Replies

  • NorthCascades
    NorthCascades Posts: 10,893 Member
    I would try to position the saddle in the same place on both bikes relative to the BB.

    That's obviously going to affect what stem you go with. You probably already know this, but different bars give you different reach as well, so the stem isn't your only lever to pull.
  • jjpptt2
    jjpptt2 Posts: 5,609 Member
    Thanks, I think you succinctly put what I was trying to get at conceptually. Unfortunately, the bikes are about 3,000 miles apart, so I can't stand them side-by-side and line all the parts up. That would be way too easy.

    So looking at the numbers...
    TT length - reach = ST to BB distance, right?
    If I can make that distance on the 56 match the distance on the 54, that should be a good starting point for improved fit, right? Or am I just way over complicating things?
  • NorthCascades
    NorthCascades Posts: 10,893 Member
    I'm going to start off by saying that fit is one of the areas I know the least about, about cycling. So if anything sounds off, it probably is.

    I think what your saying about top tube minus reach should get you seat tube to bottom bracket distance would work, except that you said they're at two different angles? You could probably do the math based on the angles, I wouldn't trust that personally, but I'm kind of neurotic.

    The reason you'd want to keep the saddle in the same place over the BB is for your knees. You can probably achieve the right position even if it isn't exactly the same by using a plumbe line. (That's with the assumption that there's a range that works for you.)
  • awinner_au
    awinner_au Posts: 249 Member
    edited July 2019
    I agree with NorthCascades re bb, measure saddle height, drop a plumb from the front of the seat and measure distance behind bb, measure distance from front of seat to middle of handlebar, measure the saddle to bar drop, measure seat angle. Replicate this on the other other bike.

    edit: https://www.youtube.com/watch?v=psbu9OH69sI
  • jjpptt2
    jjpptt2 Posts: 5,609 Member
    Unfortunately, I can't. The other bike is 3000 miles away. All I have to go off of is geometry numbers on the Cannondale website.
  • BrianSharpe
    BrianSharpe Posts: 9,148 Member
    jjpptt2 wrote: »
    Unfortunately, I can't. The other bike is 3000 miles away. All I have to go off of is geometry numbers on the Cannondale website.

    Take the measurements that NorthCascades suggested, write them down and then replicate them on bike #2. If there's a significant difference in reach you may need to replace your stem to get them to match (or get closer)
  • jjpptt2
    jjpptt2 Posts: 5,609 Member
    Slid the saddle forward about .5"

    Early impressions are good... need a couple longer rides to see if there are any unintended consequences...
  • jjpptt2
    jjpptt2 Posts: 5,609 Member
    Got in a nice 30 miles the other day...

    Made a slight tweak to the saddle angle to adjust for the more forward position... no issues there.
    No lower back soreness or fatigue...
    Reduced upper back tension (main reason why I was/am adjusting fit)
    Increased hand numbness.

    Made a couple slight adjustments to my cockpit (handlebar rotation and break lever positioning) in an attempt have a better feel/angle in the drops while still being a bit more upright/relaxed on the hoods.

    Stay tuned...
  • jjpptt2
    jjpptt2 Posts: 5,609 Member
    Getting better with each little adjustment...

    peta6ezwnfbs.jpg
  • lorrpb
    lorrpb Posts: 11,465 Member
    jjpptt2 wrote: »
    Got in a nice 30 miles the other day...

    Made a slight tweak to the saddle angle to adjust for the more forward position... no issues there.
    No lower back soreness or fatigue...
    Reduced upper back tension (main reason why I was/am adjusting fit)
    Increased hand numbness.

    Made a couple slight adjustments to my cockpit (handlebar rotation and break lever positioning) in an attempt have a better feel/angle in the drops while still being a bit more upright/relaxed on the hoods.

    Stay tuned...

    Yeh, I’ve been making a lot of similar tweaks, mainly for shoulder/hand pain & numbness. There are also exercises you can do for the hands that help release/decompress the nerve. It’s a very common cycling problem. You can Google ulnar deviation or ulnar flossing.
  • NorthCascades
    NorthCascades Posts: 10,893 Member
    Not related to the topic, but I'm always impressed by photos like that, where it looks like the bike is balancing itself. Whenever I go to shoot one, I get nervous about a gust of wind.
  • jjpptt2
    jjpptt2 Posts: 5,609 Member
    Not related to the topic, but I'm always impressed by photos like that, where it looks like the bike is balancing itself. Whenever I go to shoot one, I get nervous about a gust of wind.

    As well you should be (I've seen your bike)! But this bike has been though a lot... tipping over won't even phase it at this point.
  • jjpptt2
    jjpptt2 Posts: 5,609 Member
    39 miles and 4700' of climbing today... bike felt pretty good.
  • NorthCascades
    NorthCascades Posts: 10,893 Member
    Holy crap!! Well done!