Layback Seatpost

[Anthony]

I agree with Rody that the choice of seatpost and saddle position should be governed by the individual's riding posture, which classically has to do with the length of your femur or some such - and not whether the bike is the wrong size for you.

The difference in top tube length between sizes of Kona is half an inch per size, so basically a size 16 with a layback post and saddle as far back on the rails as it will go is in effect the same length as a size 20 with a straight post and mid position for the saddle. So anybody who has the frame size even anywhere near right shouldn't need to mess up their seating posture to square their circle.

BITD one of Kona's selling points was that the frames had an 'aggressive' and 'racy' 74 degree seat tube angle. So it always seemed odd to me that people who would tell you with some pride about their 74 degree seat tube would fit a post and saddle that effectively put the saddle in a 70 degree position, which is quite a passive and weak position from which to pedal (unless you happen to have an exceptionally long thigh bone).

But then maths is boring, I guess.

 

[Wold Ranger]

Lay back

I have a long back and short legs. so need some layback or feel too "over the top" I always found that in line posts regardless of TT length or stem length just feel "not right" somehow and prefer to be well behind the crank axle. I have been notching up the bike miles for 40 years plus and have never suffered with my knees, despite in addition, 30 years of clocking up 40 to 140 miles road running per week too.

 

[FairfaxPat]

layback post

The layback post is a good way to get more room on top if the top tube isn't long enough but the seat tube is just right. Manufacturers differ in their ratio of top tube length to seat tube length. Early Fishers, for example, have longish top tubes per frame size because that was what fit Gary Fisher best and the frames were made to suit him. One drawback, as Rody suggested, is that your center of gravity moves backward, making the front end lighter and more wheelie prone.

 

[Wold Ranger]

Wheelies

I found that bar height and stem length, by far and away affects the tendency for a bikes front to lift, not seat position which is virtually non existant. 2 inch plus riser bars being horrendous for this! and a short (100mm or less) stem.
Strangely modern bikes are now touting 65mm or less stems and lowish riser bars, but the advocation of 150mm plus fork travel is for making very high front ends, with the huge swing to trail centres complete with lifts! Ordinary trail and XC riding is definitely fading into oblivion.

 

[Wold Ranger]

Frame sizes

The biggest problem with most MTB bike designs is that they are just all badly designed and So sooo wrong. Kona/Klein got it right with the long top tube, short seat tube format. U need at least 4 inches and preferably 6 under your nuts when stood flat on the floor to allow for getting a foot down on lary terrain. Many bikes in order to get the right top tube length result in way too much standover height! Based on my height, and an average under bb height of 12.5 inch I need an 11 or 12 inch frame! diamond frame. Length wise I need a 21.5 ctc top tube. How many do you see that size made? The answer is a layback post on a small frame!

 

[Anthony]

Re: Frame sizes

The biggest problem with most MTB bike designs is that they are just all badly designed and So sooo wrong. Kona/Klein got it right with the long top tube, short seat tube format. U need at least 4 inches and preferably 6 under your nuts when stood flat on the floor to allow for getting a foot down on lary terrain. Many bikes in order to get the right top tube length result in way too much standover height! Based on my height, and an average under bb height of 12.5 inch I need an 11 or 12 inch frame! diamond frame. Length wise I need a 21.5 ctc top tube. How many do you see that size made? The answer is a layback post on a small frame!

OK, but if the layback post gives you a weak pedalling position, it doesn't sound like a very good solution to me.

You sound like you need a Rody frame, but if Kona is ok why not try a size 16 Cotic Soul? bb height 12, c-c seat tube 13, c-c top tube 21.75, head tube 4, like a Kona size 16 but half an inch longer.

I like sloping top tubes as well, but I don't think we can seriously say that a bike like a Yo Eddy is badly designed - there's lots of people on here with long legs who find a Yo Eddy just perfect.

 

[Wold Ranger]

Cotic

No got plenty of small old bikes, 14 inch Merlin 631, 12.5 in GT with dropped top tube, XS Klein. 15.5 Orange etc. Weak pedalling position? No comfortable and bein a trials rider for 40 years plus, I stand up a lot! All hills of ny grade will be tackled stood up. The Cotics are over priced and over hyped for what they are really too. On ones and Rock Lobsters much better value as are the Sirius.

 

[Huntso]

Been reading this thread with some interest, having short legs for my height I also need a smallish frame for a bit of meat and two veg clearance.
Use a Thomson layback on a M5 Sworks which has a fairly long top tube/low bb clearance and it puts me in a more comfortable pedalling position, so not sure of the maths, but if it ain't broke etc etc

I also agree that those Cotics seem very pricy for a mass produced Taiwanese made frame, still good luck to the bloke if he can flog them. Not for me though,which ain't surprising seeing as I prefer alu frames anyway

 

[Wold Ranger]

Frames

On the Yo bit, yes they are a totally bad design and rust at a pretty amazing rate of knots. Leg length is only relative to standover at the end of the day. Pootling about posing on OK, but tackling a rock/root garden off camber, no thanks.

 

[FairfaxPat]

What you say makes sense on a conventional diamond back frame, Wold Ranger-that is why there are all those modified diamond frames on the market with a sharpish downward slope towards the seatpost tube to provide standover room.