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Bike Sizing

post #1 of 26
Thread Starter 
I know comfort and personal pref has a lot to do with choosing the right bike, but is there any helpful hints in bike sizing? I'm 5'8 and fairly aggressive. Looking for a CC or FS setup. Currently looking at the GT I-Drive, Trek Fuel 98, Giant NRS, and maybe throw Cannondale in there. I know this is two diff topics, but any thoughts out there?
post #2 of 26
Some of the folks here will tell you all about geometry, and maybe even throw formulas around. But I found that your best bet is to just demo different sizes of each brand, or each different frame that each brand offers, and see what feels comfortable. Think about being on it for hours on end, and going up and down steep hills. Originally, I liked the way I fit in my frame, but found that after an hour and a half to two hours, my ribs started feeling compressed. So I added riser bars, and love the way it feels now, even after a 4 hour ride. hink about how your rear is situated on the seat, how comfortable the distance of the bars is, how high they are, how long of a leg stroke you get on the pedals, etc. In general, you would use a smaller MTB frame than road frame, and you probably don't want to be laying quite as flat on a MTN bike as a road bike. You'll need to be able to get your arse behind the seat while holding the bars and breaking, for really steep decents, and be able to get your chest up over the bars for climbing, without having your knees slamming into your bars.

As for those specific brands of bikes, I'm even less help. I've briefly demoed a Cannandale lefty and a GT I-Drive, as well as some others (most notably a Schwinn Rocket 88, which I liked), but have no recollection of my thoughts on them. I ended up with a K2 Proflex 4000.
post #3 of 26
Thread Starter 
Thanks John and Gonzo, exact info I was looking for. I was hoping not to get all the geometries going. Would look like one of the Ski Technique posts Was mainly looking seat angle, head angle and the right positioning. My current bike is old and prob never fit right in the first place. Thanks again and anyone else, please, still chime in with other advice.
post #4 of 26

Is that 15-20 degree knee bend Mountain Bike specific. For years I was a roadie and have always put my seat just short of lock out. When went to Mtn. I kept that same seat lenght unitl recently. I have been slowly lowering it to find my comfort zone for downhill technical.

My problem is that I have to ride long flat intervals to get to any climbing and downhills. After your comments even though my seat is lower than its has ever been it could probably be lower.


post #5 of 26
Thread Starter 
Gonz, unfortunately I ride like I ski. I love the blistering downhills, but prefer tight single track. I love the technical stuff like rock climbs, drops, logs, etc. I guess I'm looking for a solid all around bike that will last a while. Been looking for a Santa Cruz superlight X to demo, but no luck around here. Others I'm looking at are Giant NRS, trek Fuel 90 or 98, GT I-Drive 1 or 2, and maybe throw a cannondale Jekyll in there. Any opinions on these? Trying to keep it as close to (or less) $2k as possible. Don't mind going up a bit if it has the components and is worth it.
post #6 of 26

Although I'm not much of a roadie, I would guess that yes, for road riding your legs should be straighter when the pedal is down. The straighter your leg is, the stronger it is. For MTB riding, you should probably have more bend and a lower seat for a couple reasons. One is safety. You can get your feet on the ground, and your balls off the top tube when necessary. Another reason would be so that you can get your butt behind the seat for steep downhills. And yet, another reason, would be so that you can get out of the saddle for when things get really bumpy, or you are landing. The bigger air you get, the more room you need. If you're flying down some singletrack, and you launch off a root, you could get quite a bit of air. And I don't like to land with my butt on the seat. Rocky sections are the same way. Not just because of possible pain, but because the bike can get squirrley as rocks shift, so you want to be out of the saddle, and prepared to put a foot down if necessary.
post #7 of 26
Best method of determining seat height I've found is to place your heel on the pedal with your leg completely straight. Once your seat is adjusted to allow this, when you clip in or place the ball of your foot on the pedal you'll automatically have the proper amount of bend in your leg. Now get a marker and make a small mark on the seat post, so you'll be able to easily know the proper height setting.

As for doing technical downhills, buy a quick release seat post clamp and drop your saddle LOW. This makes a big difference when descending the nasty stuff. Once you're down the nasty stuff, just readjust the saddle to it's previous height.
post #8 of 26
Check your stand-over height on the bikes too. For a mtn bike for off road use you should have at least 3 inches of clearance from the top tube to your crotch when stradling the bike. Pending on the type of terrain and the type of riding will also help determine what size you want. The more aggressive, technical, riding you do a slightly smaller frame can be benificial. Since it is a smaller mass the bike is more easily manipulated, plus with the added standover you can move around the bike easier. A slightly larger frame is better for distance or long XC logging road type riding. Stretches you out and provides more comfort. If you go too small you'll end up too compacted causing fatigue, too big and you will not be able to get any weight on the front end to control the bike. For technical riding a bit small would be the lesser of two evils since you'll probably be out of the saddle most the time and you can transfer your weight accordingly.

Also on fore/aft saddle position. The cranks should be at 3 & 9, with your tibial tubrosity (front of the knee/spelling?) directly over the pedals spindle (of your forward leg).

Saddle height? In general, sitting on the saddle, pedal @ 6, place your heel on the pedal and you should have almost full extension. That is what you do for road. That is where to start on your mtn bike. Get that placement set up and then mark your post. It is not uncommon to raise your saddle for long climbs, then drop it down a bit for the decent. With the saddle raised you get better power transfer and a more effecient pedal stroke. The more technical the riding you do the lower saddle height you will want. Ever try to take a big drop, go to move over the back of the saddle and have your shorts hang up? Not a pretty picture.
post #9 of 26
I have a slight caveat to Argus' stand-over height. It doesn't work if you don't have a traditional, horizontal top tube. A lot of full squishy bikes don't. The top tube tends to tail towards the... (damn! need another T word!) (oh, got one!) Thingy*!

*"Thingy" would be the rear gear set, so that it has a better angle to make the bike stronger.

**Due to the power shortage, the light at the end of the tunnel will be turned off indefinitely.
post #10 of 26
Thread Starter 
Let me ask this as well...anyone have experience/knowledge on Rocky Mountain bikes? Read some great things on the Slayer and found a dealer around here.
post #11 of 26
The Slayer is a great bike as are most of the Rocky bikes. It is heavy though (30-32 pounds). If you're not into freeriding and all the crazy drop offs and jumps involved, I'd say it's a waste.

All the Rocky FS bikes are a little less plush than some other four bar designs (Specialized, Ellsworth, Titus, etc.) due to the rear pivot being located on the seat stay instead of the chain stay.
post #12 of 26
speaking of geometry and bikes that fit. Yesterday, after riding my old, cheap hardtail home, I hopped on my K2 to take the dog for a run. MAN what a difference. I've never really ridden one for a while, then jumped on the other. They both weigh the same, but the K2 just feels beefier, rides better, and fits me soooo much better. The seat on my hardtail is a gel seat, but the seat on my K2 is actually more comfortable because I'm sitting on it properly. I feel like I'm in a more comfortable, upright positon, but yet, like I also am able to apply a lot more power to the pedals. It was kind of a cool feeling.

**Due to the power shortage, the light at the end of the tunnel will be turned off indefinitely.
post #13 of 26
Thread Starter 
Gonzo, Once again a huge thanks. More info I was looking for but unclear exactly what to ask. The FS 'light' I'll call it is more the way I was looking. Go with something that has more travel and set it up to do possible XC rides. Will be looking into the Specialized Enduro and Hopefully the RM Slayer in next day or two. Thanks again.
post #14 of 26
My two cents on degree of bend in the leg after having several bike fits done: about 10 degrees, whether road or mtn.

Try walking up steps without fully extending your legs. It hurts. If you are too low on either a road or mtn bike you don't get good power transfer and you could cause knee damage.

To me 20-30 degree bend in the knee is very old school. Look at how low road racers were prior to the advent of science in cyclng prior to the 80's. Look at pro mt & road bikers now, they have very straight legs at 6 o'clock.

But, I also know some folks want to be lower to the ground for safety/peace of mind, and DH bikes have low saddles...but they aren't ridng them uphill for hours at a time, which is what I tend to do so I favor a straighter leg.

post #15 of 26

I certainly don't know the answer or have videos, but to give Chimp some credit, we DO walk with our legs fully extended (actually hyper extended), and skiing is an open-chain activity, while riding is closed-chain. I could see that some riders would go for full (or nearly full) extension. Our joints work the same as a screw jack, in that they get stronger as they get more extended, because they gain more leverage. Try to do a 1 legged deep knee bend. If you can do it (which you shouldn't because it's really bad for yur knees), it's hard as hell. But with your leg at 5 degrees of bend, you could probably lift double your body weight. So the real advantage to getting as far away from the pedal as possible, comes just as your foot passes over 12:00, and you are trying to power the pedal as much as you can, with as much leg bend as you're going to get. The less bend you have, the more powerful the top of the stroke, which is the power part of the stroke, and the most fatiging.

Not to say that either of you are right ot wrong, because I know about as much about road racing as I do about needlepoint.

**Due to the power shortage, the light at the end of the tunnel will be turned off indefinitely.

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[This message has been edited by JohnH (edited May 17, 2001).]</FONT>
post #16 of 26
Thread Starter 
Hey Gonzo, since you have all the info (and since I can only find a few bikes in the area)I'm mainly comparing the Enduro Expert and the Giant NRS 1. I can get the Enduro for around $1700 vs 1999 for the NRS. Whats your take on these 2? Thanks as always
post #17 of 26

I never thought about the hip sway. I woudn't think that you would actually want to ride with full extension. I was just stating the fact that the leg is stronger, the more it is extended. You said to watch someone pedal at 100rpm or higher. Just curious, but what do most road racers ride at? I know that I had heard that they train to ride a specific rpm, and try to maintain that rpm rate all the time, because it helps their endurance on those long-ass rides. Do racers usually ride all day at 100+rpms? I just can't imaging going for 8-10 hours at 100+ rpms! I'd die in about 10 minutes! But then, I couldn't run 5 minute miles for 2 miles, much less 26, like top marathon runners do, either.
post #18 of 26

I have noticed, that when I put my head down, stare at my feet, and concentrate on spinning a circle, I can get them to spin faster, with less effort, and it's way smoother. However, it's just a tad less *safe*! But it seems like, whenever I pick my head up and look where I'm going, I fall back into the up-down stuff again. And I can't, for the life of me, spin circles when I'm out of the saddle. I guess it's just something I'll get used to, and get better at, as I ride more.

90 to 110, huh? I guess you're saying it's better for long rides to spin faster with lower resistance, then to go to a higher gear? Since I had started riding as compensation for not being able to ski, I tended to think of riding as ski training. So I have always gone for lower rpms with higher resistance (higher gears), since it's closer to the way you use muscles when skiing. I may have over-trained myself this way, because I find it intensly fatiguing to spin at high speeds, and much less so, to run in higher gears. I noticed this, quite dramatically, when riding with Gill last week. He'd be spinning away, and I'd be limbering along in a much higher gear, and thinking it would kill me to spin that fast.
post #19 of 26
Hey guys,

Thanks for the input on seat height. Sorry have not gotten back sooner but I was out of town for a couple days. I am going for a quick release seat post. I can out spin 97% of my buds but my downhills suck. I'm going lower!!

JohnH, I had to edit my post here to give my two cents. When trying to achieve higher RPMs be careful not to over rev. I can almost never maintian my cadence at max gear I fatigue out and end up dropping back. Spinning, cadence and RPM maitenance is about balance. I can spin on flat single track in 22nd or 23rd gear for long periods of time. But I am never over revving.

I may be way off here but this is how I found my balance. Get on flat paved area and ride in your top gear at about 90-95 rpms. Watch your speed. If you are like me you will burn out and have to drop back a gear. Find the gear that allows to increase RPMs but stay close to that speed you had in top gear.

On that problem you have with losing the "shape" of your pedalling. When you have your head up think about your leg from the hip to the knee, the thigh, as it comes up. Concentrate on keeping these movements even and smooth. I don't think about my feet going around in circle. This may be wrong I don't know, these are only my personal observations. I think about the major muscle groups. I would love to hear Lisamarie's take on this subject.

Anyway, spinning for me is a medatative state. Zen almost. I have a very quiet and relaxed upper body. I concentrate on the function of the major leg muscle and find a breathing rhythm.

Rambling . . must stop rambling ..



Ed<FONT size="1">

[This message has been edited by Powdigger (edited May 18, 2001).]</FONT><FONT size="1">

[This message has been edited by Powdigger (edited May 18, 2001).]</FONT>
post #20 of 26
all this talk about spinning has my head spinning. time for some wine...
post #21 of 26
JohnH - Try to concerate on "pulling" your foot back through the bottom transition. Pretend you have someting on the bottom of your shoe and are wiping it off on a welcome mat or something. This image helped me learn to pedal in more of a circle. Keep in mind that I'm still on platform pedals (I just don't like clipless for how and where I ride). If I can spin on flats, you can easily do it on clipless.

Oh, and by the way, you were far from limbering or lumbering along. You're pretty darn fast on that bike!

We need to get that weekday, post-work ride going. I can probably scrounge up a few others as well. Thursday nights would work best for me.
post #22 of 26
Thread Starter 
Ok, since I got the new bike, should I look more for a computer that registers rpm? current is really only milage/speed/avg spd. I never really thought of how I ride as spinning, but after the descriptions, that sounds like how I ride. Very quiet upper body with power concentrated throughout circle. I do find the pumping action on some steeper climbs. However, never thought of sticking to a rpm. I know what the majority seems to think here, so how about some advice on decent computer.
post #23 of 26

What I meant was that my feet were lumbering along. Yeah, I was easily able to keep up. I think that after all these years of skiing, my muscles have gone slow-twitch, where as you seem to like to spin lower gears at higher rpms than me. I have this sickness of wanting to keep up with people, so I tend to ride too close. Especially when I'm in unfamiliar territory. I liked riding Avalon by myself because I could go at high speed and only stop when I needed to, and only for short periods. When I rode with that group of 10, I got sort of bored of waiting for the whole group to get together, then decide where to go. I really enjoyed riding with the 2 other guys that showed up late, but the half hour wait for them was torture.

Yeah, we can start riding weknights as soon as the weather clears up. Thursays are probably good. I don't care how many people we gather up. I'll ask other if they are interested, too. But if it end up just the 2 of us most days, that's fine. We can get some wind in the face for an hour or so, and maybe search out some new trails.

As I've been driving up Rt15 toward Frederick, I've noticed some nice looking hills just off to the west of 15 (maybe a mile or two. On the map, there seems to be a road that goes along the ridge of these small mountains (maybe 600-700 vert and a ridge line that's a couple miles long). I'd love to see if there are any trails back there, or any potential for some. It'd probably take a half hour or less to get there. I'd probably need to do some research and see if there are any land owners there that I'd need to get permission from.
post #24 of 26
JohnH - That sounds great! I'm always up for exploring/bushwacking. I've never checked out the hills off of route 15, but who knows - they could hold a bonanza of MTB stuff.

I agree that waiting was a pain, but I felt bad that we left them in the parking lot. I realize they didn't let me know they were coming, but I hate leaving folks behind.

That second out and back ride to Lake Fairfax Park was my favorite part of the ride. I love blasting along at top speed and don't usually push myself that hard when riding alone.
post #25 of 26
Last night I had a bike fit to get m new road bike set up properly. I had thought, maybe from reading some book ears ago, that the bend in the knee ought to be around 10 degrees. I asked the guy checking that angle on my legs and he told me they want it around 30 degrees. I stand corrected. Gonzo was right when he said that. Shows what I know.

The bike is way cool if I say so myself.
post #26 of 26
Yeah, Sorry.

You are most likely MORE wacked than you think you are. I figure this is a good starting point for my own realty.

I thought about this info and remember seeing a photo in a book on cycling from the dark ages before Lemond and some science came into things. The photo showed a very good time trialist taking a right turn. His left leg was extended and nearly straight. See the 10 degree bend, the caption must have read. Of course, he was weighting that leg to control the turn.

Maybe I'll just take up spewing all kinds of hearsay, misinformation and off-kilter gizmo lingo...purely to entertain of course.
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