Any experts in bike geometry here?

Shaun @ Tru6 · 05-02-2018, 03:50 PM

I need a new bike. Looked at a few and just rode a 54cm BMC 18 Team Machine with 105. Fit me like a glove. Loved it.

But I also know of a Felt F2 frame and fork that is exquisite. I would have to build it up with Ultegra.

Here are the geometries of both bikes. What can you tell about them? Anything? Can seat tube height and stem length compensate to match the Felt to the BMCs fit-like-a-glove feel? Most numbers are very close but some have a reasonable delta.

I want to avoid getting the Felt and finding out that it doesn't fit in the same way the BMC does.

Shaun @ Tru6 · 05-02-2018, 03:52 PM

look 171 · 05-02-2018, 04:01 PM

Shaun, the BMC is just a slightly bigger bike with a taller head tube compared to the Felt which is shorter tighter with a shorter wheelbase. That's what you feel the most, the quickness and responsiveness. IMO, the BMC is a bit lazier therefore you feel more at ease or comfortable especially with the taller tube tube, when you are hunched over or a deeper reach.

look 171 · 05-02-2018, 04:05 PM

Describe the fit like a glove to me. What type of riding will you be doing? General sports riding, get out and hammer for two hours and come home or ride to enjoy the day and stop by the coffee shop and take it easy home? The set up makes a difference on the type of riding you do. For example, sitting in the cockpit of an F1 car is no fun if you have to go to the market or even go out for a drive in the canyons. Set up your bike based on the type of riding you are after.

Shaun @ Tru6 · 05-02-2018, 04:16 PM

Thanks Jeff, that's exactly what I wanted to know.

I will be doing all the types of riding you outlined adding in inner city sprints. My sense is the Felt's agility will be a lot of fun in the city. The majority of time will be 20-30 mile rides not so much hammering but working. Then there's riding to Walden Pond stopping by the Dairy Joy along the way. City fun and of course biking to Harvard Square for a slice of Otto's pizza and watch the world go by at least once a week this summer.

The fit like a glove meant we adjusted the seat height and I got on and rode around the block and the bike just felt natural. It didn't feel particularly fast but it was very comfortable.

So here's my big question. Can the right stem get the Felt closer to the BMC? Honestly, if the BMC felt faster I wouldn't even be posting. I want something with a little more edge. Does the Felt have too much edge? I like quick, agile bikes so the wheelbase doesn't bother me.

Shaun @ Tru6 · 05-02-2018, 04:21 PM

Quick note to say that I used to be in love with Cannondales and loved aluminum. Then I got a Kestrel and then a Trek OCLV and never looked back. I did also test ride a Felt Z85 recently which is Al with carbon fork and wow was that a disappointing ride.

look 171 · 04:47 PM

I raced on a Cannondale and absolutely loved it. It was quick and stiff. This was a time when most bikes were steel and had a little flex built into them. Our racing was super smooth roads around the block so not too many tooth fillings were lost. I have a Torelli that's alum with carbon stays. I like it but its no comparison to the new higher end carbon bikes out there today. Kestrel and Trek's OCLV (I had two) took all the buzz out of the road compared to alum. frames. Today, I rather not take an alum bike for more then 30 mile ride. Hammer fest OK, but not a longer training ride.

The felt will be fine. Make sure you have enough space on the steer tube for a couple of spacer to get the stem high (er) enough so you are not bend over sitting on your balls on the nose of the saddle. For hammer fest, that's fine, but riding to the coffee house or a leisurely ride, that's no fun. Part of hammering is that the pressure from your legs to the pedals are actually hold your body up off the saddle just ever so slightly, taking the weight off from the saddle whereas if you are going slow, you are actually sitting on the saddle with all your weight. This causes all type of issues from tired shoulders and a sore ass or the soft area between your balls and your anus. If you are 30 miles away from home and those areas are hurting you, that's gonna to be a long day in the saddle.

A 10mm shorter stem may work out better for you. I noticed the top tube is only 5mm shorter. I really think you will get used to it but getting the stem up higher will make a big difference. I would take the Felt only because its smaller so its faster and handling is general sharper. Faster out of a corner for sure. That's all racing talk.

stuartj · 05:01 PM

Ive just changed bikes, and was concerned about the same thing. I'd had my old bike fitted to me by a bike whisperer. I have found that the key measurements are:

centre of crank>centre seat (st), then
centre seat>to centre of bar at the stem (tt)

I made this easy by using the exact same saddle, and took these measurements to the new bike. Had to change the stem. Ive done 3000 kms now and haven't had to touch the new bike since set up. So IMHO as long as you can achieve these measurements on each frame, you could be happy on either. By the way, if you planning on serious miles, thoroughly recommend having your new bike fitted to you.

Bill Verburg · Bill Verburg's Garage

JMO, but like cars no one is going to be really good at everything

I've narrowed it down to 3 fot most uses

1) custom Ti, w/ semi compact ultra gearing. Great for really fast group rides where you are really hammering. very edgy race geometry. Great in the mountains and on fast windy roads. Almost all of my PR's were set on this bike. Fit and light weight and gearing are everything.

2) Cannondale Synapse all carbon from wheels to the bars to the seat, Di2, really nice for more relaxed rides not as fast or edgy but you can go forever w/o any issues., Hate the deep wheels in cross winds, love them everywhere else.

3)Fugi Absolute, al frame, 28mm tires, platform pedals, flat bars, 105 group set. Not fast, not comfy for long rides but fine for shorter rides in sloppy and/or cooler weather

LEAKYSEALS951 · 05:16 PM

I own A BMC pro machine from the same era.

The geometry is all different from regular bikes. I need to look this up when I have more brainpower, but BMC geometry is different. I bought a 51 frame (or was it a 52?) (which in TT and ST lenths is identical to a 54 frame, however the wheelbase is shorter, which wasn't listed. Also HT lengths are all different on BMC's compared to regular bikes.. Like Look said HT lengths on BMC's are longer.. I think... that' the lay of the land.

I would almost say- if you ride a 54 BMC, buy a 54 regular bike and don't think a minute more on this- but let me think about this tomorrow A.M.

Dont take my word on it right now. Life is too complex, however, finding a right size frame is important.

LEAKYSEALS951 · 05:33 PM

bmc 911 bike porn here:

Basically, I spent much needed brainpower dedicated to achieving a similar HT,ST, and DT as my 54 equivalent, and giving me as much exposed seat post as possible (for cool points) and comfort as well as long stem length 130?

What I got was a good bike, great climber, but twitchy as speed on mtn downhill. I ride my specialized 54 tarmac plain jane over the BMC most days. I just feel better on it. Don't ask me why.

look 171 · 05-02-2018, 05:41 PM

Leak, some bikes are just built differently even if the frame geometry is identical. For example, my Time is an exceptionally great frame flying down a mountain side and inspire true confidence but I have other bikes are just not as stable even through they are almost identical. The way they go over bumps at speed in the turns is where some of the higher end frames shine like a bright star.

LEAKYSEALS951 · 05-02-2018, 05:47 PM

Quote:

Originally Posted by look 171

Leak, some bikes are just built differently even if the frame geometry is identical. For example, my Time is an exceptionally great frame flying down a mountain side and inspire true confidence but I have other bikes are just not as stable even through they are almost identical. The way they go over bumps at speed in the turns is where some of the higher end frames shine like a bright star.

I guess that is what I am trying to get my head around- The numbers should work, but the overall experience doesn't make sense, and I don't know how to make a prediction based on it.

For example- the only real difference between my BMC and Tarmac is the wheelbase, yet, I cannot sprint on the BMC with any power, which seems counterintuitive.

LEAKYSEALS951 · 05-02-2018, 05:49 PM

Quote:

Originally Posted by look 171

Leak, some bikes are just built differently even if the frame geometry is identical. For example, my Time is an exceptionally great frame flying down a mountain side and inspire true confidence but I have other bikes are just not as stable even through they are almost identical. The way they go over bumps at speed in the turns is where some of the higher end frames shine like a bright star.

I guess that is what I am trying to get my head around- The numbers should work, but the overall experience doesn't make sense, and I don't know how to make a prediction based on it.

For example- the only real difference between my BMC and Tarmac is the wheelbase, yet, I cannot sprint on the BMC with any power, which seems counterintuitive. I would think with a tighter triangle and stiffer build- it would be opposite.

Shaun @ Tru6 · 05-02-2018, 05:50 PM

Quote:

Originally Posted by stuartj

Ive just changed bikes, and was concerned about the same thing. I'd had my old bike fitted to me by a bike whisperer. I have found that the key measurements are:

centre of crank>centre seat (st), then
centre seat>to centre of bar at the stem (tt)

I made this easy by using the exact same saddle, and took these measurements to the new bike. Had to change the stem. Ive done 3000 kms now and haven't had to touch the new bike since set up. So IMHO as long as you can achieve these measurements on each frame, you could be happy on either. By the way, if you planning on serious miles, thoroughly recommend having your new bike fitted to you.

Good advice and definitely doing this.

John Rogers · 05-02-2018, 07:19 PM

Back in the 1970's and 1980's when I was racing I had 4 bikes. One was a track bike, no brakes, etc. One was the training bike with long wheelbase, shallow seat angle and head tube angle so it rode very smooth since many roads in the San Diego area were rough and riding 500 miles a week you want smoothness. My road racing bike was almost the same geometry as some road races were on rough roads or your part of the road in a pack might not be smooth. Lastly my criterium bike was shorter and stiffer and it could turn/maneuver very fast. All had the same dimensions so when the crank arm was at the bottom of the stroke, my knee was bent 10 degrees and my heel was upward at 10 degrees also. The road bike and criterium bike had long enough top tubes so that my back was flat when my hands were in the curve of the bars. All of them had a bit longer seat tube and shorter seat height above the top tube.

Back then all were steel tube and mine were made in Italy except the track bike that was made by Benotto in Mexico City. I finally bought an aluminum framed Vitus bike in 1984 and used it in criteriums mostly. The first carbon bikes were failing because of poor resin and curing.

look 171 · 05-02-2018, 07:38 PM

Quote:

Originally Posted by Shaun @ Tru6

Good advice and definitely doing this.

Maybe you can save a few bucks and fit yourself. I standby my traditional European road race fit and tighten up or let loose from there to dial in precise fit for a particular riding style.

Once you find the saddle height (sit on the saddle and put your heels on the pedals and pedal backwards without rocking motion from your hip. I like to add 1/2" to that), the general rule of thumb is to have your elbow to the nose of the saddle and try to touch your handlebars with your middle finger. My finger is about 1' form the handle bar. Then go ride the bike with your hands on the hood, the top (flat part) of the bar should cover the hub. My hub is in the back of the handlebar because I like to stretched a bit to achieve a flat back. Raise or lower your stem from there. I would start high then move it no more then 1/4" each time and ride the bike for some time before you lower another 1/4". I like to lower as much as I can for fast riding. That's not comfortable for most. For sure not comfortable for a regular ride to the coffee shop. The rest of just playing around with all the settings at no more then 1/4" at a time.

I have help many people set up their bikes that way and I always find out the type of riding they are likely to do so I make sure there's no slammed stem even through most learn quickly that that's best looking, the long slammed stem with huge seat post showing.

look 171 · 05-02-2018, 07:45 PM

Quote:

Originally Posted by John Rogers

Back in the 1970's and 1980's when I was racing I had 4 bikes. One was a track bike, no brakes, etc. One was the training bike with long wheelbase, shallow seat angle and head tube angle so it rode very smooth since many roads in the San Diego area were rough and riding 500 miles a week you want smoothness. My road racing bike was almost the same geometry as some road races were on rough roads or your part of the road in a pack might not be smooth. Lastly my criterium bike was shorter and stiffer and it could turn/maneuver very fast. All had the same dimensions so when the crank arm was at the bottom of the stroke, my knee was bent 10 degrees and my heel was upward at 10 degrees also. The road bike and criterium bike had long enough top tubes so that my back was flat when my hands were in the curve of the bars. All of them had a bit longer seat tube and shorter seat height above the top tube.

Back then all were steel tube and mine were made in Italy except the track bike that was made by Benotto in Mexico City. I finally bought an aluminum framed Vitus bike in 1984 and used it in criteriums mostly. The first carbon bikes were failing because of poor resin and curing.

Ha, I had a Benotto from Mexico. I can't kill that thing. It was a road bike.

Many of the off the shelf frames were made to the typical stage race geometry. Some of the American frames had higher BB and tighter wheelbase due to the around the block racing we did. I had a Gios that I crashed into the back of a car on a race course and destroyed. I love that thing as it was a faster bike due to the slightly higher BB and shorter Wheel base. I found the French frame of the time, compared to Italians, they has a longer top tube. Still, today, my Time has a top tube that's 5mm longer then most bike out there. I am spoiled, for a steel frame it has to be Italian. I had a Medici Track bike. I sucked at the track. I am smaller, so the bigger guys have huge muscles that can really turn an angry pedal. Plus those bastards leaned on me too much. Around the mid to late 80s, the Rainer brothers (Mark,I think its Matt) are from SD and they raise hell up here at the Encino track. Fast mofos.

John Rogers · 05-02-2018, 08:12 PM

Those names are familiar. We had a club named the LaJolla Cycling Club and had some pretty fair track riders mainly Mark Gorski who won the sprint gold medal! Most of the road riders were on the power house 7/11 cycling team. At the end of 1984 the team members had a big garage sale as the team was going to break up and I bought Davis Phinney's wheels and a bunch of Campy parts like pedals and wheel hubs. Sold all that a few years back as I can't ride now days.

look 171 · 05-02-2018, 09:51 PM

Gorski was fast and pure world class act too. I saw him in 83 at the 7-11 velodrome riding against then world champ Sergi Kopylov. Oh yeah, Mark beat him. Then there's Lutz Heslich.

Team break up? I thought they went on to Europe or did they break up to turn pro and ride for the 7-11 pro team. The 7-11 started in 82 I think?