shorter top tube - set back seatpost?

ajb72

I'm looking at a possible new frame, a Wilier Izoard. Looking at the geometry chart my current set up, which I think is spot on for me, sits somewhere between a large and XL Wilier.

My thought is to go for the large Wilier size, as the seattube and headtube are closest to current frame, whereas the XL Wilier is very different in these areas. The chief difference is the toptube, which would be 15mm shorter on the Wilier. My quesiton is, rather than buy a new stem (as I have only recently done this) could I buy a seatpost with a setback in order to compensate for the shorter toptube and achieve the same position? Is this too simplistic and is there something else I should be taking into account?

I would hope the seatpost would be the answer, as I would need to buy one anyway due to the smaler diameter tubing than my current frame.

redddraggon

You could try more seatback, but it may not feel right, but it's worth a try.

ajb72

Yes, that is my fear, that by effectively pushing the seat back it might feel a bit wierd on the bike, more weight over the rear wheel etc. I don't want to be puling wheelies on climbs!

redddraggon

ajb72 wrote:

I don't want to be puling wheelies on climbs!

I do that already on a 74deg seattube + non setback post on 20+%ers

pontarlier_pete

Messing around with saddle setback can be very dangerous for your knees, so if I were you i'd spend the money on a new stem and put the old one on ebay to try to recover some expense.

maddog 2

you can only compare top tube lengths if you know the seat angle too.

in other words, the Willier is shorter but if it has a slacker seat angle too then it's even shorter

But all other things being equal, you should set the seat position relative to the cranks, not the bars.

What length is your current stem?

ajb72

Current stem length is 120mm.

I shoud just be content with what I have, but those Wiliers look so nice...............

keef66

@ mr dragon: you're climbing 20% hills while seated? I doff my cap to you sir.

ajb72

keef66 wrote:

@ mr dragon: you're climbing 20% hills while seated? I doff my cap to you sir.

My current stem length of 120mm is perfect for pushing the bike up a 20% climb

redddraggon

keef66 wrote:

@ mr dragon: you're climbing 20% hills while seated? I doff my cap to you sir.

Said bike has a 53/39/30 triple with 13-29 cassette. I can't climb standing up for long though, so I normally stay seated as long as I can even on my bikes with steeper gearing.

keef66

I suppose 30 x 29 would allow you to sit down for longer. My lowest gear is 30 x 25 which would see me standing all the way up a 20% hill, should I ever encounter such a thing.

Daimler

Why not try it.....a new post is cheaper than a new frame.

My SL3 has a set back post (15mm IIRC) as standard and on a 52cm frame. I run a 90mm stem.
I'm 5'8" inside leg 30 and I always go for 535-540 top tube.
I've just ordered the CAAD9 in a 52cm as well as I am happy to run a 100mm stem or even a 110mm if needed plus the set back post that comes with it.

For me, I like to fit onto the smallest frame possible without sacrificng speed/comfort.
I never suffer aches and pains so I must be getting it right.

greasedscotsman

ajb72 wrote:

Current stem length is 120mm.

I shoud just be content with what I have, but those Wiliers look so nice...............

I would be wary of putting a huge stem on it as well. Maybe it's just not the bike for you

ajb72

I am talking myself into this purchase (with a bit of help from you guys!)

Anyone ridden a Wilier Izoard? I need to find a demo bike to ride asap!

huuregeil

ajb72,

maddog2 has it right, you need to sit down with a couple of sheets of paper, a ruler and a calculator. Dust off your geometry from school.

Your arse needs to be in the same position relative to the bottom bracket. This is easiest measured by measuring the horizontal distance from the nose of your saddle to the bottom bracket using a plumb line. Measure back to the centreline of your seatpost clamp. Considering the amount of lattitude your saddle gives you moving fore and aft, you're in a position to work out whether the seat angles on your new frame permit your arse to be in the same position. (This needs some trigonometry). If not, stop there. If so, then proceed.

You need to do the same thing with your handlebars. Easiest way, again, is to use the nose of the saddle to handlebar distance, together with the drop of the bars (best measured relative to the floor, e.g. measure saddle vertical off the floor, subtract handlebar vertical off the floor). Using such things like headtube angle, stem angle, allowable spacers, does your new frame (givenyour arse in the same position) permit your handlebars to be in the same position. And, if so, what are the resulting requirements for your stem and spacers.

Seat-tube angle is critical to this whole calculation, it's not just about top-tube length. If your arse is too far back, you'll knack your knees.If it's too far forward, you'll be uncomfortable on your hands/shoulders. Assuming your current fit is good, it's simply a matter a calculating the relative positions of your contact points in space. In other words, don't just buy a new frame, whack the saddle back and hope for the best. A new stem is only, what £20-40, and you can ebay your old one. Compared to the cost of the frame, this is peanuts!

Bingo!

ajb72

huuregeil wrote:

ajb72,

maddog2 has it right, you need to sit down with a couple of sheets of paper, a ruler and a calculator. Dust off your geometry from school.

Your ars* needs to be in the same position relative to the bottom bracket. This is easiest measured by measuring the horizontal distance from the nose of your saddle to the bottom bracket using a plumb line. Measure back to the centreline of your seatpost clamp. Considering the amount of lattitude your saddle gives you moving fore and aft, you're in a position to work out whether the seat angles on your new frame permit your ars* to be in the same position. (This needs some trigonometry). If not, stop there. If so, then proceed.

You need to do the same thing with your handlebars. Easiest way, again, is to use the nose of the saddle to handlebar distance, together with the drop of the bars (best measured relative to the floor, e.g. measure saddle vertical off the floor, subtract handlebar vertical off the floor). Using such things like headtube angle, stem angle, allowable spacers, does your new frame (givenyour ars* in the same position) permit your handlebars to be in the same position. And, if so, what are the resulting requirements for your stem and spacers.

Seat-tube angle is critical to this whole calculation, it's not just about top-tube length. If your ars* is too far back, you'll knack your knees.If it's too far forward, you'll be uncomfortable on your hands/shoulders. Assuming your current fit is good, it's simply a matter a calculating the relative positions of your contact points in space. In other words, don't just buy a new frame, whack the saddle back and hope for the best. A new stem is only, what £20-40, and you can ebay your old one. Compared to the cost of the frame, this is peanuts!

Bingo!

Thanks for such a thorough reply, much appreciated. I know you are right about a new stem, in the scheme of it all its a smallish expense.

I have spoken to Adriam Timmins about a fitting session, so will see what he has to say first and then try and replicate that position