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Proper sizing?(15 posts)

Proper sizing?ShawnD
Feb 14, 2002 8:12 AM
I am going to buy a cyclocross bike this year. I am planning on using it for commuting, road rides and some mild single track. I have never owned a road bike. I am having a hard time figuring out how to properly size it. Should I go with the road bike formulas or something more related to cyclocross. I am 5'9" in case that makes any difference to anyone. Any help would be great.
Proper sizing replybuffalosorrow
Feb 14, 2002 10:05 AM
I am 5' 7 1/2" without shoes and have a 33" inseam/ stand over (crotch to floor w/o shoes, although I wear a 30" inseam pant)

The two cyclocross bikes I have are 50cm center to center and
52cm center to top, both have a standover of around 78cm/
30 5/8"

The top tube sizes are 54cm and 54.5cm, I use straight seatposts and a 110mm and 120mm stems, I could cut off a cm and push the seat all the way back. Or opt for a 53cm top tube length.

In my opinion the same size roughly should work, if your height includes shoes, if not perhaps a 52cm. I would run around to local shops and check out end of season deals on bikes, try them on, dont let the salesman/ woman push you into a size larger, if it does not feel right, go with you instincts. Don't buy a uncomfortable sized bike on sale.

Most of the 52cm cyclcoross frames and a squinch too large for me.
HmmmmCT1
Feb 14, 2002 3:34 PM
Do you suggest a smaller cross frame than a standard road frame? Seems like it from your own sizing.

I'm 5' 8" with a 32" inseam. My road bikes are all 53-54cm CT with 54.5 cm TT's. These bikes fit perfecto with 12 CM stems. I would normally just order a 54cm Dream cross which has an actual CT of 53cm but I want to understand this cross specific sizing a bit better before placing the order.

Do all cross bikes have high BB's??? I could see how a high BB might goof standard geometry considerations.

Thanks in advance.
JohnG
yes... slightly smallerbuffalosorrow
Feb 14, 2002 8:26 PM
Seems that we ride the same size frame.
I do have a road frame but it is and older japanese w/ suntour, fun to ride. The TT is 55cm and ST is 52cm CT. The cyclocross frame are a .5 - 2cm shorter. The TT would be if I were to purchase another new road frame 1- 2cm increase.

I did notice that the bottom bracket height with 27c cross tyres on the colnago is 26cm and my SS cyclocross with mich's sprints is 27cm. Vaires on the tyre you ride. To answer your question, yes most cross frames have high BB's.

I have the 54cm (ST CT), 53cm TT colnago dream cross, with a 12cm stem and straight seatpost. I must give the bike 5 stars in handeling and speed.

The custom SS cyclocross is modeled after the Independent Fabrication longer TT 54.5. I was trying to eliminate toe over lap, since I ride fix. I did not work out.

The idea behind a smaller fitted frame is that, you can dismount easier, and that with the shorter TT length plus a wider bar you have tighter control.
wowCT1
Feb 14, 2002 8:52 PM
So the geometry of the Dream cross is different than the Dream+! Never would have figured that. That seems like a very short TT. ??? Wow.... so much to learn.

Don't you feel "cramped" with a 53cm TT???

Thanks again!!
JohnG
wowDream plus
Feb 15, 2002 8:47 AM
I ride a 54cm Dream Plus road bike. I've never ridden a Dream Cross, but I've been comfortable on a Redline 52cm Cross bike which has a 53.25cm tt , 78cm standover. Of course geometry plays a part, but i would order a slightly smaller cross frame. In cross it's not unusual to ride more upright and a shorter top tube allows you to do that.
Oh-oh....CT1
Feb 15, 2002 11:01 AM
The trialtir usa web site has the dream cross and standard geometry tables. Interestingly, these tables show that the cross frame is nearly identical to the standard in terms of sizing. According to these tables the cross frames have a tiny bit slacker seat tube angle with a corresponding tiny bit longer TT length. I.e. the effective TT length looks to be the same. Hmmmm.... ???? Does your 54cm (ST CT) really have a 53cm TT?? This doesn't match the table. Their showing the cross frame as a 54X54.2. ARGH..... I wish this was simpler. ;)

I may still up for the 1cm smaller frameset than "normal" as I'm not at all cramped with the 54cm Nago that I've got. Also, adding an additional 1cm spacer under the stem shouldn't be a problem since the frame uses a steel steerer tubed fork. I'd probably still use 2cm of spacers which isn't excessive. The one cm smaller frame might be good since the tires will be a fair bit taller on this bike.

TIA
JohnG
Don't get flusteredbuffalosorrow
Feb 15, 2002 5:15 PM
Colnago measures ST CT ie my 54cm has a 53cm TT.

Trialtir might measure CT TT the 54cm now is a 55cm with the 54.2 TT.

Can I confuse you more?

On my custom SS cyclocross I have 2cm worth of spacers, some argue that the head tube should have an extension, to each is own. I don't mind.

Colnago dream cross geo, the ST have more of an angle, the BB is raised, throwing off the ST sizing by a cm or two.

On my Colnago I have a 12cm stem, I could either center the seat on the straight post or push it back and use a 110mm stem.
"can I confuse you more" ......... ;)CT1
Feb 17, 2002 6:58 AM
Gotta say that was a pretty confusing post. .

I've got the Trialtir geo charts and the 54cm is listed as a 54X54.2 That's virtually identical to my 54X54 CT1. I've got a fair bit of standover clearance with my CT1 so I'm strongly leaning toward the 54cm CX frameset.

Colnago measures the Dream frames to the bottom of the seat tube clamp. I.e. a listed 54cm frame will actually have a 53cm CT (top of TT) measurement. My CT1 is just a tad different than the Dream in that the TT is a little closer (0.2cm) to the seat tube clamp.

*** The really odd thing about Colnago's sizing is that the effective TT length is nearly constant for sizes smaller than 53cm. Bummer for women!

JohnG
re: Proper sizing?jrm
Feb 14, 2002 12:32 PM
Im one inch shorter than you. i ride a 53cm roadie but am riding a 52cm cross bike. The difference being a higher BB thus less standover then the roadie.
re: Proper sizing?KenS
Feb 14, 2002 2:06 PM
There are two sizing systems, Center to Center [CC] between bottom bracket and seat tube and Center to Top [CT] from bottom bracket center to top of seat tube. Bottom bracket height will vary and this will change the size of the seat tube also. Pay more attention to standover height and go with whatever frame size corresponds for that manufacturer.

I am about 5' 9 1/2" and I looked for a 78-79 cm standover height. In CC sizing, this was about a 50-51 cm and in CT sizing this was about a 52-53 cm, depending on the bike.

www.coloradocyclist.com describes how to measure yourself for standover height.
re: Proper sizing?Mike the Snake
Feb 14, 2002 4:21 PM
Be careful with using the C-T measurement as a guidline. In the old days, all bikes had level top tubes, so this made sense. What you really want is the vertical distance from the center of the BB to the top of the steerer tube. Some manufacturers list this as "virtual length", but some do not. IMHO the top tube length is more important, because you can always raise or lower your seat, and get a different rise stem without greatly affecting the handling of the bike. Going longer or shorter on the stem, though, can make a huge difference, especially off-road. Best to go to the dealer, ride a few bikes till you find one that fits, and write those measurements down. Better yet, find a "fit-bike" and get the distances from that. Happy trails.
alsojs
Feb 15, 2002 10:35 AM
to top of what? used to be top tube, sometimes seat lug, now I've seen some measure to top of bigass protruding top of seat tube.
re: Proper sizing?mackgoo
Feb 15, 2002 7:23 AM
I just set up my first cross bike. My own experience suggests go with basic road measurements the only consideration I have found is any cross tire ads significantly to the stand over height of the bike so you need to take that into consideration. My bike in particular has a much shorter T/T than my road bike. In the future I would measure total length T/T and stem for the road bike and then go for that same total length for the cross perhaps shorter by 10mm or so, but I think the road setup for me would work fine.
Thanks for all the input!ShawnD
Feb 15, 2002 9:49 PM
Thanks for all your help. I have found very interesting and informative. Made things alot clearer.