Caculating the right seat height

Samvan77

Hi all,

I have recently started road cycling on my new Giant 56cm(55.5cm) bike - I am 5 foot 9 and I am feeling strain in back if I am riding for longer than 40 minutes at a time. I am pretty confident the bike frame is the right size so I am thinking seat height is the problem.

According to this site there are few different ways of calculating the correct ride height. http://www.bikeradar.com/fitness/articl ... ght-14608/

I will be experimenting with these to see which works, but was curious if any of you have any thoughts, experience or recommendations on this?

Gizmodo

There are hundreds of systems out there and as many YouTube videos, for example http://youtu.be/FAl_5e7bIHk

In my personal opinion you can't beat a professional bike fit from a reputable and experienced pro. You really need a turbo trainer and an experienced 2nd person.

lotus49

Fitting a bike is a dark art but there are some reasonable rules of thumb when it comes to seat height. Generally speaking, new cyclists tend to have their seat too low but I have no way of knowing in your case.

You should have the seat high enough so that your leg doesn't quite straighten out (25-35 degrees out from straight should be right for most riders) when your foot is at the bottom of the stroke. How high that is will depend on several factors such as leg length, frame size, foot position (ie do you tend to pedal with your toes down or flat) etc. You should be able to tell if you have it too high if your hips start to rock as you are pedalling.

Some of these things are difficult to judge for yourself while you are on the bike so it would definitely help if you could find an experienced cyclist to watch you while you ride. Gizmodo's suggestion of using a turbo is a good one if you or a friend have one to use.

Seat height is probably the most important factor in fitting a bike but you won't know whether that is the cause of your backache until you can get it right and see how that affects you. My guess is that it is more likely to be that you just aren't used to leaning forward in the way that you usually do on a road bike. If your back ache doesn't disappear once you have your seat properly adjusted you can turn your attention to the height of your handlebars and the length and angle of your stem. Alternatively, you may just find that you will get used to it with more km under your belt.

defycomp2

I have a nasty feeling that your Giant might be too large. You are 5'9" on a M/L frame whilst I am 5'11" on a M. Overall you need to be measured; height, torso, thigh etc as the combination will lead to a good fit. I have long legs relative to my back so I need a short reach and so a M giant fits a treat.

MichaelW

Check the reach and assess your riding position. Are you trying to ride in an aerodynamic racing position with a horizontal back? Are you riding on the drops or the brake hoods?
New riders should start with a more conservative touring style position with the back at about 45 degrees. Over the next year or so, your body will adapt and you can lengthen and lower your stem as required.

lotus49

DefyComp2 wrote:

I have a nasty feeling that your Giant might be too large. You are 5'9" on a M/L frame whilst I am 5'11" on a M.

5'9" is at the bottom end of the height range quoted by Giant for the M/L but of course body shape will play a big part in determining which size is correct. The larger sizes will have a longer top tube meaning you are stretched out more and therefore more likely to get back ache. If you have relatively short legs and a long torso, the M/L may be the right size but if you have long legs for your height, you might not have the right size bike.

Samvan77 wrote:

I am pretty confident the bike frame is the right size so I am thinking seat height is the problem.

Can you explain what the basis for this confidence is? I'm not saying you are wrong but if it is based simply on looking at a sizing chart that only takes height into account, your confidence may well be misplaced.

cyberknight

I find this works..
http://www.jimlangley.net/crank/bikefit.html
http://bikedynamics.co.uk/guidelines.htm
http://bikedynamics.co.uk/achesandpains.htm
As for calculating seat height by a formula i find a modified lemond method of .889 x inside leg works for me and come out close enough to the heel on pedal method. Both measurements come about 1 cm over the holmes method that i personally find to low .

Samvan77

lotus49 wrote:

Samvan77 wrote:

I am pretty confident the bike frame is the right size so I am thinking seat height is the problem.

Can you explain what the basis for this confidence is? I'm not saying you are wrong but if it is based simply on looking at a sizing chart that only takes height into account, your confidence may well be misplaced.

Hi all thanks for the input. Apologies for the typing error in my original post - my height is actually 5 foot and 11 inches(and not 5 foot 9) I was advised my LBS to go for a 56cm frame when I fitted a Specialized Allez, I however changed my mind about the Allez when I saw the Giant elsewhere and consulted their website about the sizing before purchasing the bike.

I have tried the 109 % method and raised my saddle which seems a bit better (when I went for a run this morning)but not quite there yet. I suppose it will be trial and error. I am currently riding with my hands on the hoods until and I suspect it will probable take some time to adjust to the riding positioning

styxd

Got any pictures of how the bike is setup at the moment?

lotus49

It may be worth alternating between riding on the hoods and the tops to see whether that helps as being on the tops will mean you aren't leaning forward quite so far. Don't forget that you cannot brake from the tops though - crashing will be a lot more uncomfortable than mild back ache .

Pross

Don't bother trying to calculate it you are better off getting an experienced bike shop or cycling coach to have a look at you on the bike and make any necessary adjustments. Total guesswork without a photo but a bad back is likely to result from either a bigger saddle to bar drop than your flexibility can cope with or the stem / top tube combination is too long.

Samvan77

Went for another ride today and my back is feeling much better, so it look like to 109% method might be paying some dividends.