Auction Frame Size -- Help

[va rider]

You all did a great job analyzing whether an auction frame would fit a rider, so I was hoping that somebody could give me a little help.

The auction frame is compact geometry on a 57cm frame as follows:
ST: 50 SA: 72.5 TT: 54.4 HA: 72 TT Slope: 7deg.

I am 5'11", Inseam 87.5 cm Torso 59 cm, arm length 66.5cm
Saddle Pedal Start 93 cm to 96 cm. (maybe a little more).

Basically, I am long in the leg, short in the upper body and I don't have a ton of flexion in my lower back.

The above measurements are from about 3 weeks ago when a LBS fit kit me. I was riding a 59cm frame with a 57.5 cm tt, which was way too long up top. I could barely ride on the hoods and never in the drops. According to the fit kit, I should be riding a 56.6 cm seat tube and 55.4 cm tt with a 110 cm stem.

Frankly, I have no idea if this frame will fit me. My biggest concern is that even is the tt will fit, the amount of drop will be way too much.

Help!

[Needs Help]

From the "geometry head scratcher" thread,

virtual top tube length / sin 100.5 = 54.4 / sin 72.5

vttl = (sin 100.5) (54.4/sin 72.5)
= 56.08 cm

seat tube add on / sin 7 = 54.4 / sin 72.5

stao = (sin 7)(54.4/sin 72.5)
= 6.95 cm ==> seat tube length = 6.95 + 50 = 56.95 cm

So, by my calculations, the equivalent frame with traditional geometry would have a TT measurement of 56.08 cm and a ST measurement of 56.95 cm measured C-C.

[Needs Help]

nm

[va rider]

thanks, that makes it pretty close. the tt may be 1 cm more than ideal, but I think it is within my tolerable zone with maybe a 100 cm stem.

[Smiley]

why don't you see a good Serotta fitter and have them throw you on their size cycle for a couple of bucks and check the exact fit of this bike. Its really that easy and then you can bid with confidence that the fit will work or not. The 72.5 degree seat angle is a little relaxed but you can check your KOP with a non off-set or off-set seat posts and bring your current saddle and pedals to make the fit just right.

[djg]

I'm probably overlooking it, but I don't see anything on the auction site saying whether they are reporting the actual or virtual top tube length. My recollection is that they used to report the "virtual" tt on their geometry chart, and at least some of the frames listed seem to be (or seem as if they ought to be) reporting virtual tt on sloping tts.

[va rider]

Smiley -

are you the mobile fitter for Serotta in the D.C. area? I thought I saw that posted on Serott'a website. Or, if you are, is it for a particular LBS?

Good point, I am going to my LBS tomorrow to pick up a Serotta to test ride, I will have him set up this compact frame on the Serotta cycle to see if it works. It is kind of a wierd frame size. It is compact, but has a relaxed seat tube. But, I guess I need to figure out if the tt is virtual or actual.

thanks for your help.

[Needs Help]

I would think there would be some indication on the specs if the virtual top tube were listed. However, the fact there is even a doubt means they should list the number as "actual top tube" or "virtual top tube". I would think that if Serotta wants to sell the frames, they should at least let the customer know what they are bidding on.

[Peter]

I used the simple formula in Lennard Zinn's book for the top tube length and, using your body measurements, came up with:

Seat tube: 58.3cm (2/3 inseam)

Top tube: 61.18-59cm

Stem: 11-14cm (more "aggressive" riders lean towards longer stems)

The top tube length is wildly different from what you seem to think you want, which is okay but raises some red flags.

Check your numbers, using some of the on-line fitting systems available; if you don't know where to look just ask and we'll give you some web addresses, and be sure someone ELSE measures you; don't try to measure yourself.

[Smiley]

I can't believe that the fine folks at Serotta would not have meant Virtual TT length as the actual TT length is MEANINGLESS in a compact design. Va Rider check your mail .

[Kevin]

Smiley,

I sent an e-mail to Serotta asking about the measurements on a compact frame (actual vs. virtual). When I get a response I will let you know.

Kevin

[Needs Help]

I can't believe that the fine folks at Serotta would not have meant Virtual TT length as the actual TT length is MEANINGLESS in a compact design.

Same for the seat tube, right?

[va rider]

Zinn's numbers are interesting.

The numbers I posted are from a recent fit kit from a small lbs in my area. I was riding a ti Eddy Merckx 59 cm (c-t) with a 57.5 tt (cc)/110 stem (c-c). And, I can tell you, I have never, I mean never, rode in the drops. Also, even riding on the hoods was a stretch. My arms would have to be locked out. I recently tested a 56 cm IF with a 56 cm tt/120 cm stem. And, even that was too long. And, to boot, my at 39 yrs old, my lower back is not too great.

My UBM is 125.5 cm, as well. So, basically I have pretty long legs, monkey like arms (66.5 cm) and though not related, a pretty big nose. But, hey, I am great at a party!

Anyway, after getting fit at a lbs, who sells the IF, I realized it was time to get a bike that fits. Though I am not in any of your leagues, I love to ride, get in about 2500 miles a year, ride some centuries, some faster club rides and even commute to work. I also teach spinning.

Tomorrow, I will ask the lbs who sells Serotta to set up the auction sizing on the Serotta cycling. I am picking up a Fierte to see how I like the Serotta steel and a 55 cm top tube.

But, the sizing of this Ottrott is pretty unique, I think. But, I just do not know enough to know if given the compact geometry if the numbers were accurate. The angles are funky and though I may be able to get it for a good price, If it don't fit, It is a waste.

[Needs Help]

Some LBS's have the Serotta proprietary spreadsheet on their computers, so they can plug in the numbers to verify what the traditional geometry would be. If not, you can call Serotta directly or email them and ask about the actual size.

tel: 1-518-584-1221
email: info@serotta.com

[va rider]

Good call Needs Help. I will give Serotta a call, if my LBS does not have the Serotta spreadsheet.

But,the more I talk to people with experience, the more I think that although the auction frame looks good, I am difficult enough to fit that I really need the time and attention of a good fitter. I am not sure the HA of 72 is ideal for a non-racer like myself.

I am going to check it out with my lbs, but I am thinking a CIII with a good fitting is the ticket.

Thanks for all of the very good advice. It is well taken.

[Kevin]

Smiley,

I heard back from Serotta, the TT lengths are virtual measurements.

Kevin

[soulspinner]

Spoke with someone a couple of weeks ago and he indicated that bikes with sloping top tubes are listed with effective top tubes, not actual.

[jpw]

"virtual", "effective", "actual", goodness, i'm confused. :confused:

[Needs Help]

Then....that means to calculate the traditional seat tube for a Serotta compact, you need to take the listed top tube length and multiply it by the ratio:

sin(TT slope) / sin(180 - ST angle - TT slope)

and add that to the listed ST length. In the case of the bike va rider was interested in,

virtual TT = 54.4 cm
TT slope = 7*
ST angle = 72.5*

So,

ST add on = 54.4(sin 7)/(sin 100.5)
= 6.74 cm

and

listed ST + ST add on = 50 + 6.74
= 56.74 cm

[soulspinner]

Thus the 57 cm frame size listing in the first post. The headtube length on a sloping frame determines the virtual or effective size of the frame. The frame in question is undersquare in that the effective or virtual( if it was a level top tube bike) top tube is shorter than than the seat tube (frame size of level top tube equivalent). Ive effectively confused myself...or is it virtually confused myself..anyway this frame fits me but since I have a Strong with less than 400 miles on it and my wife would evict me, I cant bid on it.