Geo / Position experts - Comments pls.

[BdaGhisallo]

Here are a couple of pics of my bike and position. I feel pretty comfy on it position wise but I have a feeling something is a little off with the front end handling.

I love the stability at speed but slow speed manouvering can be tricky at times, feeling like the wheel flops around doing u-turns at very slow speeds.

The more I look at the geo of the frame the more odd it seems. 73deg is a shallow sta for a 54cm frame, giving a relatively short effective top tube ( what's left of the t tube length once you subtract out the setback - or the amount of top tube that is forward of the bb). I am using a thomson no setback post with the aliante all the way back on the rails.

The schematic shows a 50mm rake fork. That has since been changed to a 45mm rake, lowering the front center a touch from the 582mm shown. It feels as I described above.

This started as a frame based on a fitting from a serotta tech. Since that time, I increased the top tube to 54cm as shown, lowered the stem about 3cm and lengthened it 2cm, and went with the 8cm bb drop.

The stem is a newton 82 in a 110mm length with no spacers under it. The bars are the newton shallow.

Is there anything obvious I could do to design this geo better? I have been looking at some of geos of the more prominent prod builders, like Merckx, Pegoretti, Pinarello and the like and this has really tuned in the oddness of my geo. Their frames with a similar toptube length have steeper sta's in the region of 74deg.

The 72 deg hta and 50 mm rake was originally done to reduce toe overlap.

Talk to me boys. What do you think?


Edit

Due to the site problems, I think, I am having real troubles uploading the pics. So let me summarize the geo I have:

54cm st 54cm tt 73deg sta 72deg hta 45mm rake 41.0cm chstays
97.85cm whbase 58.2cm fr center 8cm bbdrop

[Peter]

The photos are missing but I don't think they're needed to diagnose your problem.

Your wheel IS probably flopping around on slow speed turns because the contact patch of the front wheel is changing location versus the amount of turning. Riding straight, the contact patch is directly underneath the axle. What you're experiencing is the contact patch shifting to either forward or rearward of the axle as you turn the fork. This either applies a leverage to the front wheel, making it turn more, or causes the front end to rise/fall as the fork is turned. I'd say you went in the wrong direction in changing the fork rake. You should have gone to a 55mm. With a 23mm tire, you'd have 56mm of trail, which is in the range many framebuilders shoot for.

Don't worry about the seat tube angle or the top tube length; I don't think they're that critical, you can adjust to them pretty readily. It's the fork...

[BdaGhisallo]

I suppose I could put the 50mm fork back on and give it a whirl.

I am still working on getting those pics up.

[William]

Diagnoses: Your stem is too short.

That will be $75.00 please.



William JD ;)

[BdaGhisallo]

Now that the picture upload is working I thought I would give it a bump up the ladder.

Any more input?

Thanks.

[e-RICHIE]

lower your saddle.
raise your h'bar.
lengthen the front center.

[manet]

relax your elbows

[OilyFish]

Are you sure those brifters are positioned in an optimal manner? Further round / forward would slow the steering surely?

[Fixed]

lower your saddle.
raise your h'bar.
lengthen the front center.bro listen you got lucky cheers :beer:

[shaq-d]

lower your saddle.
raise your h'bar.
lengthen the front center.

what riches said. altho lowering ur saddle would effectvely raise the h-bar anyway. lower that saddle...

sd

[soulspinner]

Nice to know that you can get advice from one of the greatest ever at his craft. I also thought his saddle looked high(leg overextended) but didnt notice the front center. Nice bike. I love my Strong. A best buy frame until I can afford a Sachs or Spectrum lugged steel.

[BdaGhisallo]

"lower your saddle.
raise your h'bar.
lengthen the front center."

Hey E-Richie, thanks for the quick and pointed advice. Does the front center need to be lengthened from what it is now - 45mm rake so f/c shorter than 58.2cm shown on diagram - or what is on the diagram, ie 50mm rake with f/c of 58.2cm?

Also regarding the saddle height. I should have been more conscious of it when the pic was snapped, but my leg is not that extended when I pedal. I pedal quite toes down, but I guess just sitting on the bike at a standstill my ankle dropped a good bit. But I will check it out.

The stem will be raised!

Thanks all. Amazing what a few pics can do. This thread died a quick death when I couldn't post them.

Geoff

[manet]

Amazing what a few pics can do. This thread died a quick death when I couldn't post them.

Geoff

http://www.hrc.utexas.edu/exhibitions/online/ddd/includes/images/475/032.jpg

[Smiley]

Peter covered the fork rake thing as when you shortened you added trail which why its stable at high speed but goosey at low speed . Richie says it right that in my eye too the saddle is too high , wish there was a shot of you on the brifters . Best of luck .

[BdaGhisallo]

Here's a couple more shots to help. I think the main reason my saddle is where it is, is that my thighs bump into my gut at the top of the stroke if I get much lower. I guess the plan is lower the saddle and lower the circumference of my gut!!!

Many thanks.

[Smiley]

OK , it it was my fit I'd change the bars to a short reach POCO type bar so you can lower the brifters on the bends to smooth out the transition to the flat hood or if you like them that way just shorten the stem to a 10 cm stem. I personally don't like to see brifters pointing skywards as I think it artifically shortens your reach . My 2 cents and free advise is just that worthless since it FREE after all .

[Dave]

I agree that the saddle looks to be on the high side, if your leg is fully extended and the foot is horizontal. Whether it's too high depends entirely on your "normal" foot angle while pedaling. If you pedal with a significant heels up, toes down foot angle, then it might be OK. It's way to high if you pedal with the foot horizontal.

How low are the bars relative to the saddle? I couldn't say that there's anything wrong without this info. An 8-10cm height difference would be common. Also, what's your saddle height?

The frame has a pretty short TT for the vertical size. I'd measure the front to rear weight balance with your hands in the drops, fingers in reach of the brake levers and the upper back lower. Unless the front has over 46% of the weight, lengthening the front center would not be wise, IMO. Since you only use a 110mm stem, it's a simple matter of getting a longer stem to see what more reach feels like. To me, you look kind of cramped.

As for the steering geometry, it's doesn't seem too far off to me. My 51cm c-c LOOK frames have a shorter front center (57.1-57.5cm), but the the same 72 degree HTA and only 43mm of rake. I have no low speed or high speed steering problems. I spend a lot of time riding up a mountain at 7-14 mph and a lot going down at 35-50 mph. A stock LOOK 481 in a 54cm c-c size would have a 58.3cm front-center, the same 72 degree HTA and and a 43mm rake.

Hopefully the frame was built for the fork length that you have. It's common to overlook fork length. The wrong length could cancel out a change in fork rake or increase the intended change in trail, depending on the direction of the error.

Changing the position of your brake hoods won't slow the steering by any significant amount. This is a common misconception. Even a large change in the stem length from an 80 to a 120mm only changes the length of the "steering arm" by 15%.

[BdaGhisallo]

Appreciate the feedback.

Dave, the frame was built around the reynolds fork. The 50mm rake was a reynolds so no problems with the length of it.

Smiley, the bars have been rotated down a smidge since then. These pics were taken soon after I put on that stem and hadn't ridden on the road yet. Two miles and I knew the shifters were a touch high. As for the bar, I do quite like the newton shallow - 135mm drop and 80mm reach. I do have an easton ec90 equipe bar with 130mm drop and 75mm reach. I may give that a go.

Thanks.

[BdaGhisallo]

Let me throw another option in the mix.

I also have an older Strong frame built to the blueprint here, the difference being a top tube 1.25cm shorter and with a 7cm bb drop.

Handling-wise might I be better off going back to that frame and compensating for length with a longer stem? That would certainly get more weight over the front wheel.

What do you think?

[Peter]

After looking at the photos, here's what I can add:

You look "stuffed" between the seat and bars. If you like your fore/aft position, then get a longer stem. Personally, I'm not crazy for zero offset seatposts and I'm also not a big believer of "knee-over-the-pedal" theories, so my solution would be to switch to an offset post and slide the seat back. After, if you still have those gut interference problems, you can raise the stem. In your case, I see you have some steerer tube left to do that, and you can also get a stem with more rise.

I don't think your STA is shallow for your frame size; my custom built commuter (54cm) and my stock ATB (fits someone who would ride a 54 on the road) both have 73 degree seat angles and fit this 5'6"/32" inseam fine. Don't begin to think Carl Strong did something wrong; I'd have faith in the geometry he chose.

I wouldn't have noticed the seat height until e-richie mentioned it, but he's right though you did have an explanation for it. Otherwise yeah; lower it.

And I'll repeat my initial response-Put the 50mm fork back on. Report back to us on whether it gives you back your handling qualities.

TIP: I noticed the reflective tape on the rims. Rather than have the pieces equally spaced about the rim, try placing the same number of pieces ADJACENT to each other. The brain doesn't respond quickly enough to the amount of light being seen by the eye as the wheel rotates. Placing the pieces adjacent to each other means the flash of reflected light will last a longer period of time as the wheel rotates, sending a longer CONTINUOUS pulse of light towards drivers-it will thus APPEAR brighter. Experiment by taping the pieces to the rim first. I use five pieces, and it works tremendously.

[Ti Designs]

I think the color of the bike is all wrong. As for the fit, I can't tell a damn thing from that picture.