bward1028

ordered a thompson straight post online and was sent a setback post instead. before i decide whether to return it or not, what's the real difference? how big of a change am i going to notice between the two?
is it going to be aesthetic more than anything?
is there any point to asking this without trying it out first?

currently riding a bianchi giro with a setback post and 90mm stem.

bdcheung

If you ordered a non-setback without any good reason, then you might as well try the setback.

bac

The question really is - do you need setback? I would begin by using the KOPS (do a search if you don't know what that is) method to determine if a setback post is necessary. Remember that KOPS is just a start. You will want to adjust to your riding style and feel.

Good luck! BTW, good choice on the Thomson! (no "p", btw)

... Brad

bward1028

that's what i figured. the only reason i went with the straight post was b/c when i got fitted (on a bigger bike) the guy told me to go no setback. i've since sold that bike and gotten another one. guess i'll give it a try.

merlinextraligh

The point is you want to get your self positioned in the right position over the pedals. There is only so much adjustment you can make by sliding the seat back and forth on it's rails. Whether you need a seatpost with setback is going to depend on the bike's geometry, size, and how it relates to your anatomy.

If your current seatpost has setback, and the bike fits you correctly, it may be that you couldn't get the proper set up with a seatpost without setback.


Edit, with a different bike, all bets are off. No setback may have been what you needed to get the last bike fit correctly. But the new bike is a new story if it has different geometry. It maybe that you still need no setback, but you can't tell that without trying.

Take a look at the fitting threads. Particularly the ones discuss KOP

teterider

Almost all people need setback posts with road bikes especially with angles around 73 degrees. Only very few body types should use straight posts for proper setup. If you've been fitted to a straight post, and your new Bianchi has the same seat tube angle, you will again need a straight post. A 0.5 degree difference can likely be adjusted in the saddle rails. And the knee over pedal spindle thing is complete BS, so as said, it can be a place to start adjustments though. It is also common to have saddle pain by being too far forward in relation to the bottom bracket. A lot of riders try saddle after saddle and post after post on BF to fix saddle pain, when their problem is entirely from their saddle too far forward placing more pressure on the pubic bone.

wanders

I have a longish torso relative to my legs, so in order to get the correct reach, I went with a longer stem and a setback seatpost. This was to compensate being sold a bike/frame based entirely on standover height. D'oh.

Camilo

I hope you set the seat correctly to the pedals before you adjusted the reach with the stem. Seat to pedals position first, then stem to adjust reach.

A lot of people use the seat adjustment (setback post and/or sliding on the rails) to adjust reach, but that isn't the way to do it.

But you make an excellent point about standover. Yes, it is important to know (up to a point), but the top tube is usually more important.

wanders

I paid for a fitting at a shop 60 miles from where I live(not the one that sold me the bike). He did all of the measurements and was the one who set up the stem, seatpost and saddle for me. Having that done was easily the best spent money for me thus far.
Mavic Ksyriums are a distant second.

euro trash

if your current position on the bike feels correct, I would overlay the Thomson and old post to see how close the heads are for reference. if they look similar, you might need the setback after all.

bward1028

thanks all. i did just that, and they were more similar than not, so i'll take what i got shipped, not what i ordered

theopowers

Yeah, keep in mind that a Thomson setback post looks like it's really set waaaay back because of the freaky angle, but in fact because of the "on-top" design of the clamp it is actually set back less than your average "set back" post.

ezee

Depends on your thigh length.

If they're relatively shorter than "average", then non set-back post will give you a KOPS without having to jam your seat WAY forward realtive to the post.

If you have longish femurs, set-back post are the way to go.

Either may work if you have average proportioned thighs (relative to total leg length / torso).

Road Fan

If the two bikes (the one that fits, and the one you are setting up) are going to use the same or very similar saddles, you can use measurement. On the one that fits, use a plumb line and a ruiler to see the distance between the nose of your saddle and the BB. See if you can position the saddle at that position on the new bike, with correct saddle height. This will tell you if you really need setback or not on the new bike.

The two bikes could have different seat tube angles, but this technique sidesteps that issue and directly checks the butt/pedal/BB relationship. The key to finding the best startign point is to get your contact points into the same positions on both bikes. I've found this strategy to work with my 4 bikes.

Road Fan

mx_599

do i recall reading once somewhere that the setback on a thomson is about 10mm?

ezee

Wouldn't saddle too far forward put less pressure on your pubic bone?

I think a saddle too far back +/or a rider too forward (riding on the tip), +/or combined with riding with hands in drops will usually cause increased pubic bone pressure.

WheresWaldo

I think its 16mm

https://www.lhthomson.com/docs/Elite_sketch.pdf

Murrays

If your saddle is too far forward, it will actually cause you to slide forward on your saddle (actually, fall forward) meaning you have to a) put more weight on your hands and b) push yourself into the saddle to maintain your position.

I think Peter White does a good job explaining it: https://www.peterwhitecycles.com/fitting.htm

-murray