Slowman's Top Tube Length

Mar 29, 06 12:56

Post #1 of 27 (5786 views)

I was re-reading Dan's old tribike fit article and came across this paragraph:
"Should you desire a steeper-angled bike, you can either choose a bike that is already sufficiently steep, or a shallower one might work if it's also long in the cockpit. I, for example, like my bikes steep, like 80 or 81 degrees. I also like them low in front, and short in the cockpit, like 55cm or 56cm of top tube (my road race bikes have 60cm of top tube). I can make a 76- or 77-degree bike work, however, if it's got 58cm or 59cm of top tube. Certain QR and Felt bikes are good for me in this respect. By the time I move the saddle forward (by any number of means) the bike is both steep and short enough for my liking."

Doesn't this seem like the handling would be poor? Is this the reason for the forks with a larger rake? I was just told a 55cm p3 would be too short for me in the top tube but this makes me think it would be ideal. I ride a 56cm road bike and my measurements are:
Height: 186.5
Inseam: 85
Torso:152.5

Thanks,
Dan
www.aiatriathlon.com

http://www.aiatriathlon.com

Re: Slowman's Top Tube Length [dtreeps] [ In reply to ]

Mar 29, 06 13:16

Post #2 of 27 (5730 views)

"Doesn't this seem like the handling would be poor? Is this the reason for the forks with a larger rake?"

I would think that a slacker head tube angle woulld help with the handling too. Increased fork rake would help compensate for the increased trail created by the slacker head tube, it would also help lengthen out the wheelbase. Comfy and predicta-ma-ble.

Re: Slowman's Top Tube Length [dtreeps] [ In reply to ]

Mar 29, 06 14:07

Post #3 of 27 (5614 views)

"Doesn't this seem like the handling would be poor?'"

in this PARTICULAR case, the case you noted, handling is not affected. if i take an overlong top tube and overshallow seat angle and alter both by moving the saddle forward, i've made a "standard" (for me) seat angle and a standard (for me) top tube. in other words, a 78� seat angle bike with a 58cm top tube is essentially the same thing as an 80� bike with a 56cm top tube (in a bike my size). same bike. no difference.

now, since then i've altered my thinking a bit, and i'm now happier with a bike that has 1cm to 2cm more top tube, and that same amount decrease in stem length. but that's a separate issue than what you wrote about.

Dan Empfield
aka Slowman

Re: Slowman's Top Tube Length [Slowman] [ In reply to ]

Mar 29, 06 14:16

Post #4 of 27 (5587 views)

Thanks Dan, that makes sense. Is there any type of multiplier (akin to the .885 or .883 for seat tube length approximation) to determine rough top tube length?

Thanks again,
Dan
www.aiatriathlon.com

http://www.aiatriathlon.com

Re: Slowman's Top Tube Length [dtreeps] [ In reply to ]

Mar 29, 06 14:47

Post #5 of 27 (5538 views)

"Is there any type of multiplier (akin to the .885 or .883 for seat tube length approximation) to determine rough top tube length? "

i don't have one. but i don't think it would be that hard to make one. the problem is, it's going to vary based on torso length, not seat tube length or inseam or anything. so, if anything, it would be something like height - inseam x the multiplier.

Dan Empfield
aka Slowman

Re: Slowman's Top Tube Length [dtreeps] [ In reply to ]

Mar 29, 06 14:53

Post #6 of 27 (5516 views)

"Is there any type of multiplier"

okay, here's a quickie, it more less works for me:

(overall height - saddle height) x .61 = top tube + stem

i have no idea how well that might work for others.

Dan Empfield
aka Slowman

Re: Slowman's Top Tube Length [Slowman] [ In reply to ]

Mar 29, 06 14:56

Post #7 of 27 (5503 views)

But as you go lower in front isn't the length of your aerobars going to have to decrease (and stem/tt increase) to avoid hitting your knees on the pads?

When sitting more upright this isn't an issue, so you can ride more bars and less tt/stem.

Re: Slowman's Top Tube Length [Slowman] [ In reply to ]

Mar 29, 06 15:16

Post #8 of 27 (5471 views)

for your equation, I am assuming saddle height refers to center of BB to top of saddle and not the saddle height from the floor.

Mike Plumb, TriPower MultiSports
Professional Running, Cycling and Multisport Coaching, F.I.S.T. Certified
http://www.tripower.org

Re: Slowman's Top Tube Length [caleb] [ In reply to ]

Mar 29, 06 15:19

Post #9 of 27 (5463 views)

" But as you go lower in front isn't the length of your aerobars going to have to decrease (and stem/tt increase) to avoid hitting your knees on the pads?"

yes, that's true theoretically, but i'm not assuming there is a lot of upsy-downsy in the aerobar height. according to me, there is one's *correct* height, and there's only about 3cm of total range up or down. so, that's not much of a floating number.

Dan Empfield
aka Slowman

Re: Slowman's Top Tube Length [Slowman] [ In reply to ]

Mar 29, 06 15:22

Post #10 of 27 (5459 views)

hmm. very interesting. This would be a good formula to have b/c it seems the simplistic way to get the right size is based on seat tube whereas a top tube approach might be better.

according to this I would need a 58cm p3 with an 12cm stem.
(186.5-75).61=68.01

Thanks,
Dan
www.aiatriathlon.com

http://www.aiatriathlon.com

Re: Slowman's Top Tube Length [Mike Plumb] [ In reply to ]

Mar 29, 06 15:35

Post #11 of 27 (5424 views)

"center of BB to top of saddle and not the saddle height from the floor."

yes, to the middle (fore/aft) of the saddle.

Dan Empfield
aka Slowman

Re: Slowman's Top Tube Length [ In reply to ]

Mar 29, 06 15:42

Post #12 of 27 (5400 views)

Yes, my fit falls exactly on that equation. Guru set me up on a 54 top tube and 10cm stem.

(182.88-78)X0.61= 63.98

I have always looked at top tube length. I learned the hard way with uncomfortable bikes from un-knowledgeable salesmen that if I went on seat tube I would be on a bike 2 sizes to big.

Re: Slowman's Top Tube Length [Slowman] [ In reply to ]

Mar 29, 06 15:45

Post #13 of 27 (5394 views)

works pretty close for me then. It shows that my set up should be 64.66cm and it's actually 63cm.

Mike Plumb, TriPower MultiSports
Professional Running, Cycling and Multisport Coaching, F.I.S.T. Certified
http://www.tripower.org

Re: Slowman's Top Tube Length [dtreeps] [ In reply to ]

Mar 29, 06 15:46

Post #14 of 27 (5390 views)

"according to this I would need a 58cm p3 with an 12cm stem.
(186.5-75).61=68.01"

this might work out, if you ride the P3 steep and assuming i understand you correctly. you're 6' 1 1/2" and you have a saddle height of only 75cm? that's short. that either means you're measuring the saddle in a different way than i am, or else you're short-legged, with a long torso. which means that you'd ride the same length bike as i do, if you'd ride that cervelo steep, as do i.

Dan Empfield
aka Slowman

Re: Slowman's Top Tube Length [Slowman] [ In reply to ]

Mar 29, 06 16:01

Post #15 of 27 (5362 views)

Also works for me:

(171-72)*0.61=60.39

S700 lucero (50.5) + 10cm stem

Ale Martinez
www.amtriathlon.com

Re: Slowman's Top Tube Length [Slowman] [ In reply to ]

Mar 29, 06 16:06

Post #16 of 27 (5356 views)

Yes, you're reading me correctly. I'm about six one and a half inches tall. My inseam measurement with feet 8 inches apart and a book in the crotch is 85cm. Am I a genetic abnormality?

Thanks for the help,
Dan
www.aiatriathlon.com

http://www.aiatriathlon.com

Re: Slowman's Top Tube Length [dtreeps] [ In reply to ]

Mar 29, 06 16:20

Post #17 of 27 (5338 views)

"My inseam measurement with feet 8 inches apart and a book in the crotch is 85cm. Am I a genetic abnormality?"

i'm not really good at judging inseam. i'm much better versed in seat height, as long as that's correctly positioned. as to your place along the gradient of long-to-short-legged, consider the other guy posting here, 3cm shorter than you with a saddle height 3cm taller than yours. he's got just about my seat height, and he's probably 5cm shorter or so. he's maybe the other end of the spectrum.

Dan Empfield
aka Slowman

Re: Slowman's Top Tube Length [dtreeps] [ In reply to ]

Mar 29, 06 16:29

Post #18 of 27 (5307 views)

<< I'm about six one and a half inches tall. My inseam measurement with feet 8 inches apart and a book in the crotch is 85cm. Am I a genetic abnormality?

I'd say that your legs are a bit short for your height. I'm 5'9" and inseam measured the same way you did with the book is 87cm. You're 4 inches taller and inseam is almost an inch shorter. Not meant to be a negative, it just points out how everyone is porportioned differently and why it is important to fit a bike not just by height alone.

Mike Plumb, TriPower MultiSports
Professional Running, Cycling and Multisport Coaching, F.I.S.T. Certified
http://www.tripower.org

Re: Slowman's Top Tube Length [Slowman] [ In reply to ]

Mar 29, 06 16:47

Post #19 of 27 (5269 views)

Are you referring to my post Dan? I am 6ft tall and my fit measured inseam was 85cm, two of the guys I ride with are very close in height to me but one is at 81 cm saddle height the other is 82cm. My knee angle is a bit shallow at 149 degrees, but I tend to have my heels level or a bit up. I always felt my torso was a bit long in relation to inseam as it relates to bike builders. I was FIST fitted and am quite comfortable, or at least as comfortable as one can expect on such a bike. Maybe dtreeps rides heel down, and my heel up makes up for that 3cm. I might just have to pony up for fist fitting from a different shop to compare results.

On the other hand if I came down a cm or two my knee might be at a better angle, possibly 152-153 degrees and I may ride with a bit more power. I guess I need to get on a computrainer of other power device and check this out.

Re: Slowman's Top Tube Length [Race4LV] [ In reply to ]

Mar 29, 06 17:21

Post #20 of 27 (5235 views)

"My knee angle is a bit shallow at 149 degrees"

i'd say that's pretty spot on. 150� is ideal or as close as you can get. you're 6' even and i'm 6'2", so i'm 5cm taller than you, yet i ride a tri bike with a saddle only 1cm taller than yours. i think i'm pretty evenly proportioned, which makes me think you're long-legged, or else my torso is a bit on the long side perhaps.

Dan Empfield
aka Slowman

Re: Slowman's Top Tube Length [Slowman] [ In reply to ]

Mar 29, 06 17:34

Post #21 of 27 (5214 views)

Would this formula work for a traditional road bike set-up as well?

Re: Slowman's Top Tube Length [archistu] [ In reply to ]

Mar 29, 06 17:54

Post #22 of 27 (5184 views)

"Would this formula work for a traditional road bike set-up as well?"

no

Dan Empfield
aka Slowman

Re: Slowman's Top Tube Length [Slowman] [ In reply to ]

Mar 29, 06 18:23

Post #23 of 27 (5143 views)

Another yes vote for the equation.

(181cm - 75cm) x .61 = 64.66

Cannondale 56cm (54tt) with Carbon X 100mm stem

Re: Slowman's Top Tube Length [Slowman] [ In reply to ]

Mar 29, 06 18:42

Post #24 of 27 (5122 views)

Dumb question, but how would I go about measuring the top tube length on my Titanflex?

I have it set up the same as my old P3 at what I think is around 79 degrees. The Cervelo table for my old bike says 51 cm. I measure in the obvious way on the Titanflex and I get an absurd 45.5 cm.

Re: Slowman's Top Tube Length [Slowman] [ In reply to ]

Mar 29, 06 19:38

Post #25 of 27 (1812 views)

Spot on for me as well:

Size L Lucero (56.5) + 100mm stem = 66.5.

Dan's equation gives me 66.1.

That's pretty awesome...

"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @jordanrapp

Our Partners

transition-DOT-area-AT-slowtwitch-DOT-com

Advertise with us

©1999-2024 Slowtwitch, Inc., and Slowtwitch.com
Reproduction of material from any Slowtwitch.com page
without written permission is strictly prohibited.