2/15/14 8:38 AM

so i have this retro-ish steel racing bike from the mid '90s. brand doesnt matter. bottom line: it handles like a pig. feels dead and unresponsive. when riding no-handed, the normal little subtle steering shifts in my hips that work on every other steel bike i've ever owned dont have the same effect. this one seems to take more deliberate weight shifts to steer no-handed and bring the wheel to whatever direction you want it to go. riding with hands, it just feels dead and unresponsive.

that was riding 23mm tires. when i went to 30m tires, the handling changed for the better. still not what i'm used to, but it feels more lively and responsive. that got me thinking, maybe i can just get a new fork built with "better" specs to bring the handling into my personal sweet-spot.

i did some google-fu and used a <a href="http://yojimg.net/bike/web_tools/trailcalc.php" target="_blank">trail calculator</a> to figure out the effect of various changes, starting with simply increasing tire cross-section/diameter on handling and then testing out offset changes as well. in my mind i would have figured that i'd need to reduce the trail to improve the handling and make it more lively/responsive. HOWEVER, increasing tire cross-section/diameter actually increased trail -- the opposite of what i would have expected based on how the handling changed!

now i'm confused and am looking for some counsel on trying to interpret these geometry numbers vs. actual handling i'm experiencing. if i can have confidence in what changes i need to make to yield a desired result, maybe i'll have a new fork made to liven this thing up w/ my normal 23 section tires.

for the sake of simplicity, i'm assuming a baseline 74 HTA, 45mm offset, and 700C tires. +2mm trail is the approximate change spit out by the calculator going from 23 to 30 tires -- that small magnitude of change seems in line with the modest improvement in handling. however, the direction is completely opposite to what i was expecting.

any input from the forum would be appreciated!

Last edited by walter on 2/15/14 12:06 PM; edited 2 times in total

2/15/14 9:19 AM

I typed a bunch of stuff but none of it makes sense. I would try to measure the fork axle-crown, raske, and try to measure the herad tube angle. Something is amiss. I assume the headset is smooth?

2/15/14 9:40 AM

brand new king, HT has been faced.

getting a measure of the HTA shouldnt matter when i just want to change the handling based on the things that i can change (i.e., fork and wheel/tire). the HTA is pretty much fixed and the calculator takes into account the tiny angle changes due to differing wheel/tire diameter.

2/15/14 9:53 AM

Sounds like a stable stage racing machine to me. Bikes of the era were designed to be steady and hold a line. That stability is related to the caster.

If it has the original fork and 23s it is riding as designed.

If you want it to be quicker try a carbon Kestrel EMS fork of the era with a 45mm rake, I used one on a Klein for years, it was freaky fast handling and good for crits but a bear to ride with no hands. It was twitchy like an F1 car.

2/15/14 11:19 AM

Sounds like 2" of rake. You also did not mention if 700c or 27". I think these older race frames had a lot of trail.

The old Franken-CX-Trek with 25c instead of 35c Pasellas steered a lot faster and neutral.

And as mentioned, the axle/crown height is at issue. Seems like older frames really are more than the 365-70mm that got to be the norm? So a shorter fork with less rake to quicken up? Although it seems you like the feel w/bigger tires, which should have slowed things, no? Shorter fork of course has the effect of steeper HTA. See chart at bottom of post I've found that useful when toying about.

My 1972 Paramount has 5CM rake. I'd love less to try it. I am unaware of a Nervex crown/lugged silver soldered fork that matches being in existence or I would be looking for it.

I do get used to that feel pretty quick, and don't ride it that much really. It's neutral steering seems to be a speed specific sweet spot. The 84 Colnago OTOH is less of that feel.

2/15/14 11:28 AM

...simply switching to a fork with the same rake but a different material will have no effect on the geometry or inherent handling. The increased fork stiffness will make the bike feel different, but it will handle the same.

As Walter has discovered, increasing the fork rake will reduce trail and result in more responsive handling. However, if the frame actually has a 74 degree head angle, 45mm would be considered a pretty large amount of rake already. I'm not aware of any aftermarket forks with more rake, which is probably why Walter is talking about having a fork built. That is likely the only avenue for a new fork.

As for the change in trail with the fatter 30mm tires, it's due to the fact that they raise the entire bike off the ground by an additional 3.5mm vs. the 23mm tires (assuming these dimensions are accurate). There are two related effects that come to mind, which may explain the improvement in handling:

1 - The contact patch is shorter and wider, which should make it easier to turn the front wheel. This would make the bike more responsive to subtle inputs.

2 - The center of gravity is higher, which makes the bike less stable.

Apparently, these changes are enough to overcome the effect of increased trail. Restoring the trail by increasing the fork rake should further quicken the handling with the fat tires or maintain it with skinny tires.

FWIW, in light of the advantages of wider tires, I can't think of any good reason to go narrower than 25mm, unless they simply won't fit. Here's a related article that I received yesterday (how fortuitous!):
http://www.competitivecyclist.com/learn/25-vs-23?cmp_id=EM_CC_1067215_S1&mv_pc=r105

2/15/14 12:14 PM

Taking the thread into the direction of the wider rim/tire, I will say this.

Since I have gone with A23s and 25-8c tires at lower pressures my flatting seems improved greatly. Lower pressures perhaps? When I took my tubulars out on the first Paramount ride @ 120lb, guess what happened. Just built up a HED C2 Belgium wheel-set too, in the interest of using all wide rims. Going to try 23C 4Ks on these. Been pulling a lot of Open Pros off wheels in the last year.

Running GP4Ks 25C on 23mm wide rims @ 85/90lb, been doing well. The All Seasons I am a bit less nervous than the 4Ks when encountering glass debris fields I try to pick a line through. But both the All Seasons an lighter tires @ these lower pressures I have not flatted yet. A bit nicer of a ride too!

Even the Atom Comp 23s on the Scott on 19mm rims @ 90 and 95lb have been un-punctured yet and them are light tires @ 175 or so grams.

I think I used to run too high pressures for the previous 14 years.

2/15/14 2:01 PM

I missed the rake he posted. Bryan you are totally correct. I have to question how a 74 degree head tube and 45 rake would be a slow handling bike.

2/15/14 2:26 PM

i just used those as my baseline, cuz those values are within normal for a bike in my size. regardless of the actual specs, they are what they are and the bike handles like a pig.

i'm trying to understand what i can effect to liven things up. like i said, HTA is basically fixed. all i have to work with is the fork. i can measure my offset as best i can, then do some what-if to see how the trail changes with +/- tweaks to offset.

2/15/14 2:29 PM

"I have to question how a 74 degree head tube and 45 rake would be a slow handling bike."

"HTA is basically fixed."

Is it? ;) The crown to axle spec and issues come into play.

74^ HTA with a 420mm VS 385mm Axle/Crown slows/lessens the HTA and changes the trail due to angle as well as the rake changing the trail. Where is the window that he prefers?

I get friends all the time that have a MTB frame asking me why the 650 road fork when they tried to roadify the bike handles like shit. Sometimes the HTA and BB height go in the right direction enough, but never saw it really work out worth riding.

Beyond tire choices issues etc. yada

2/15/14 2:47 PM

that HTA cannot be changed directly w/o tearing up the frame.

of course you can do other stuff that <i>affects HTA indirectly</i> and any single change affect a couple other things at the same time, but the only way i can <i>change HTA directly</i> is by having someone tear this frame apart and re-braze with a new HTA -- something that will not be happening!

Last edited by walter on 2/15/14 4:20 PM; edited 1 time in total

2/15/14 2:52 PM

Question is "can you make it change enough" indirectly I guess?


"I typed a bunch of stuff but none of it makes sense"

Like that ever happens?? ;)


Good point on the headset BTW, if too tight or binding you are in for wonky steering big time.


Also, if these changes in HTA and resulting trail are at the edge of a window, way more effect to be noticed ?

2/16/14 12:14 AM

You could try 650b wheels with 32mm tyres. The smaller wheel will make the steering quicker, as will the slightly reduced trail from the smaller wheel size. Both Panaracer and Hutchinson make 32mm 650b tyres.

I did that conversion with my old road race Litespeed - not to change the handling but to be able to fit a larger tyre than the 25mm max that I could shoehorn in there with 700c wheels. As well as the 650b wheels I also needed some longer reach brakes (Tektro R556).

<img src="http://www.users.on.net/~njpayne/bikestuff/litespeed_650b.jpg" width="1024">

2/16/14 8:14 AM

I know aguy- that faced 1 cm off the bottom of a headtube, to quicken things up. Alas, the seat tube also steepens at the same rate.

My Calfee, with a 74 head angle, was spec'd with a 40mm rake fork. You cannot call it a slow handling bike.

2/16/14 1:12 PM

...you'll most commonly see fork rakes in the 38-42mm range. I suspect that the HTA on Walter's frame is more likely to be around 73 degrees.

2/16/14 6:15 PM

"I suspect that the HTA on Walter's frame is more likely to be around 73 degrees."

Walter is tall! his size frame should be a 74^ HTA and possibly some years big race frame saw almost 75^ HTAs.

So I have little doubt it is 74^ myself, although anything is possible.

2/16/14 9:13 PM

a mid '90s merckx. i've done some google-fu but unable to locate a merckx geo chart that shows HTA. but eyeballing with respect to all my other frames, it certainly looks 74-ish to me.

edit: just did an angle-measure with GIMP...the HTA looks on the steep side. GIMP showed it at 76 deg, but let's stick with 74 deg.



<a href="http://brown-snout.com/cycling/bikes/merckx_corsa-os/walter_merckx_corsa-os_v2.jpg" target="_blank">original image</a>

Last edited by walter on 2/17/14 10:01 AM; edited 5 times in total

2/16/14 9:19 PM

Get rid of it! ;)


Or at least put some Merckx deep drop non ergo bars on it! ;)

2/17/14 10:16 AM

...about their HTA's for some weird reason. They use something like 73.2 degrees, though that likely varies with the frame size.

If you want to measure the HTA, you need two things:

1- a level surface to set the bike on
2- an angle finder, like those used for setting up tools (table saw blades, jointer fences, etc.)

I've used two types of angle finders, one that's a mechanical protractor with a free swinging arrow that points to the angle and an electronic one. Both have magnetic bases, which is handy since you have a steel frame. The mechanical ones are pretty cheap, but not as accurate. Here's an example of one:

2/17/14 10:26 AM

?GIMP showed it at 76 deg, but let's stick with 74"

Honestly 74-5^ is in league with the time/brand I think. 76^ OTOH is out of the park, but still possible.

I do not know what the HTA on the 90s Merckx EX Ti frame I had circa 2000-2. But there was something about how it did some things that was a little spooky and I never liked frankly. Talking braking at speed and high speed bumps, which a very steep HTA kind of supports in theory.

2/17/14 10:27 AM

unbelievably inaccurate. i'd much rather just work with an image file -- it's certainly no less accurate an approach.

starting to think its just *really* stable stage-race geometry, like erik said.

i have a ciocc which handles somewhat similarly, more deliberate in cornering. -- although not to the same extent as this merckx

2/17/14 11:17 AM

I had an MX Leader, and I didn't notice anything odd about the handling. Like the idiot I am, I sold it.

2/17/14 11:30 AM

"MX Leader"


Did you donate it to the county to use for a bridge truss?

2/17/14 11:32 AM

Isn't that what Merckx has always made? There are plenty of charts of Merckx "century" geometry which for a 60 c-c frame show a 72 seat tube angle and 43 rake (as Brian said, they don't show the head tube angle). They are advertised as bikes you can ride all day. I'd just ride it.

2/17/14 11:42 AM

BTW Walter, did you put a level on the floor and the top tube. How are making sure the top tube is absolutely parallel to the floor? If it is not by even the slightest, knowing the angle in relation to the top tube does not net the HTA.