shmuelyosef

I have been riding the same two roadbikes for 40 years (yes...literally); both Miyatas: one is a Team Pro frame (from the 1980 Olympic builds) with extremely tight and rigid geometry, the other is a more slack (still more 'tight' than most modern bikes) Miyata 710. These have been updated with modern builds every 1-1.5 years (both were Shimano Ultegra 3x9 until a month ago when I turned the 710 into a 2x9 hill climber (30/46 with 11-34T cassette). Both bikes are nominally what used to be measured as 54cm bikes, which meant I had 13-14cm extension at the seat and short 50-60mm stems. As I look to get into a more slack geometry (I'm seriously considering a Cannondale Topstone) I'm befuddled about the geometry. As I'm an analytical sort, I've been looking at geometries to consider whether to buy:


- The small size which would require a seatpost capable of 24cm extension (Thomson makes up to 44cm posts that are fine) and possibly needing to deal with a rise on stem (particularly if they have cut the fork short to 'look cool' rather than leaving it to be fitted


OR....

- Get the medium size and use a short stem and compact handlebars (which I like anyways). I would have to probably replace the cranks in this case as they serve up 172.5 cranks with the medium and 170 (which I'm used to) for the small frame.


I could probably make either choice work (although I'm worried about the fork post on the small)


I have attached the meaningful measures of my existing bikes and the two Cannondale size choices to simplify a conversation.

Road Fan

I'm also an analytical sort but I don't just look at the dimensions, I try to look at the human factors, at least how I can see them affecting my riding. For me the most important part of the change would be the shallower seat tube angle, which moves the saddle back about 1 cm per degree. For your Team Pro that would be a very significant change for me! This alone increases the effective top tube of the slacker bikes relative to the old friends.

Why do you want a slacker geometry? I like it because it reduces weight on my hands and ability to lift off the saddle as I approach a bump. I have a few bikes with 75 degree seat tubes and they place my weight just too far forward without extreme seatpost/saddle measures (Nitto S-84 seatpost with Selle Anatomica saddle). Too bad, one is a 1980 Masi and the other a similar vintage Mondonico, great rides in every other respect! But I think it matters why you want to make this change.

As far as TT comparisons, the modern Reach measurement is good but it's not the whole story. It accurately represents the distance from a plumb line dropped to the BB axis to a plumb line dropped from the steering axis at the top of the head tube. It does not give you anything related to where your sit bones are. For me true reach is the distance, in my riding position, from my sit bone primary pressure points (points of biggest pressure forward to the front of the brake hoods where I rest my hands. When reach is a little too much as it is on my 650b, I feel my hands tending to slide back away from the front end of the brake hood. To correct this I need to shorten the reach at the cockpit by a few cm, so I'm looking for a compact handlebar to suit me on the bike - right now I'm using a Compass Randonneur style. To give you the full picture of how reaching will compare between two bikes and how fore/aft balance will compare, you need to look at the position of the saddle due to seat tube angle, seat post setback (i.e. zero mm for a straight Thomson and about 15 mm for a bent Thomson, about 30 or 35 mm for the Nitto S-84).

Iride01 

You have to decide whether you want a more aero position or a less aero position. Once you know that, You'll be able to eliminate bikes. More aero, lower stack heights. Less aero, more stack height. Sure the rest of the geometry might come into play, But likely not for the bikes you are looking at.

Regardless, all the math in the world isn't going to fit you to a bike that isn't custom built for you. So try them out and see what you think.

shmuelyosef

I'm looking for a slacker geometry because a lot of the backroads I ride in the hills south of San Francisco are in disrepair. In addition to the Team Pro geometry, I can barely squeeze a 25mm tire in (I can get a 28mm in on the 710), and at 70 years old, I'm just getting beaten up...so looking for slack geometry and ability to run at 32-40mm tires...this is what has got me looking at gravel bike geometries

With my length (inseam-->height) peculiarity, I have always struggled with these choices, and that's what has always driven me to short wheelbase bikes with parallel HeadTube-SeatTube geometries, which I no longer want. My real question, given that there are no "perfect" bikes for me out there, is "what might be the tradeoff between, and possibly in addition to, the two approaches I outlined below to customize an imperfect frame geometry to my satisfaction.

Regarding "So try them out and see what you think"...I would love to do that, but none of my LBS (on the SF peninsula) have any bikes on their showroom floor, so my choices require buying from warehouses or mail-order from bike shops in more distal settings. The local warehouses will let me return a bike in the first 30 days, and I may just take them up on that although inventory is spotty.

Iride01 

Just find frames that have a similar geometry and try them out. Then you'll get a better idea. Even if it's just to sit on it in the store and not ride it. Though I'd ride it if they let you.

My bike wasn't on the showroom floor either. But the shop was more than willing to let me ride the two lower tier models for more than 10 miles each so I could make up my mind. Though I did let them order the bike for me.

And I do realize that some stores haven't go a lot of inventory of anything at the moment. So I might consider a trip to one that does in another city.

Road Fan

I have two REEAAALLLYY vintage bikes which I think are nearly perfect for that kind of riding. Both have 70 degree seat angles, 73 degree head angles and fork offset around 65 mm, and forks whose blades really flex on a good old midwestern dirt road. The Peug also takes corners as it on rails, but clearly not a ballet dancer! They also both take 27x1 ¼ tires and have 45 or more cm chainstays. One is a Peugeot UO-8 from about 1970 or before, and one is a Rudge Aero Special from 1952!! On the Peugeot I plan to install 700 x 35 mm at least, and for the Rudge I plan to stay with 27x 1 ¼ - it's more historic and it has narrower frame clearances than the Peug. This Rudge and its twin the Raleigh Super Lenton, were Raleigh's top model for the aspiring time trialer or Lands' End to John O'Groats rider of the day - similar to us buying full up rando bikes today. The Peug has Peugeot proprietary steel, whatever it was, and the Raleigh uses Reynolds 531 throughout, but it is straight gauge. Any case, the Rudge frame is designed match its standard tires pretty closely and don't allow much extra room for added tire width - a purpose-built machine back in 1952. I'm near 70 and this bike is just a little bit older than I am.

One of the reasons I like these both for dirt roads, is that the 70 degree seat tube lets me set the saddle back far enough that my body center of gravity is centered over the BB shell. Then it's very easy to just lift my butt off the saddle a little bit so the bike can move over bumps without clouting me with the saddle. I also don't have to grasp the bars tightly at the same time, so I'm pretty well isolated from shock and vibration, except for my feet. But, the knees stay bent and serves as a spring suspension. So my feeling is you are correct to look for a more laid back seat tube. The questions are, how far back to you need to go, and can you move the cockpit back to keep your hands in the right place on the bars?

cyclezen

OK, so you and I are very similar in Dims, age and maybe bike dim considerations...
I 72 yrs , 58 as a dedicated rider/road racer - 5' 9", 150 lbs 34 1/2" inseam flr to crotch, 33 3/4" arm lght, cervical prominens to wrist. Long legs, v-short torso, long arms/hands.
I tend to prefer a more laidout/forward torso position for 'road', 56 cm bike size these days - 11 cm stem, 7.5 to 8 cm seat setback on a 73 deg ST, 42 bar width, 94.25 seat top from top of pedal spindle extension, 45 - US 11 shoe size.
so, given the dims you have for the Topstone....
The Head and seat angles seem very middle road for current gravel bikes. TT length is less of a concern on these
The 2 dims I personally would work with are the Reach and Stack.
Reach shows a diff. of 7mm - a nominal difference easily compensated by stem. and numbers are very middle road.
STACK however, is a marked difference ! 30mm lower for the SM = 549 which, even for me liking 'low', is quite low limit.
MD stack at 579 is much more workable... Why? Even with a 17 deg 11 cm stem in 'up' position gives only 2 cm higher stack on the SM, so you'd need to go 30 degree stem to go above the MD base 'stack'
Consider the stack on your Miyatas - are you willing to go 'Lower' than they are? Or do you want to go a bit Higher?
Wheelbase is a none issue... since echainstay lengths are identical. This means just a slightly longer Front/center, which assures less chance of 'toe overlap', which could be a consideration depending tire Dim (wider spec 700c or 650b means longer diameter...) Toe overlap is always a consideration in tight turns, like switchbacks, turns where bike lean is limited.
I would quickly rule out the SM - for me.
And Yes, I tired modding my Roubaix with larger width CX tires, but could only fit 28mm measured CX tires... works ok... but my gravel bike is way better...
My Gravel bike has 367 stack and 383 reach - 11 cm stem at +7 angle, a tad higher and shorter reach than I normal ride - but I may go with a longer stem, also +7.
So, if you want to 'position' a bit higher, the MD stack seems way better than the SM...
crank length - ride the 172.5 for a while - you prolly will adapt/like them just fine. A 2.5mm crank length difference is more considered for short leg ride - usually not an issue for us with long legs.
I rode/raced 170 for 20 yrs before going up to 172.5 and even 175 is an easy adaptation without any realized issues of any kind. Bike has cranks? I'll ride it... LOL!
Ride On
Yuri
EDIT: Santa Barbara Valley has some serious bad tarmac and rough offroad/dirt/gravel... I'm very much enjoying the wider, lower PSI tires !!!

tangerineowl

https://forums.thepaceline.net/showthread.php?t=279796

Am 5'9.5 with 34. Wingspan same as height.
Have found a low 360mm frame reach, with around 380mm+ frame stack works best for me.
Those kind of numbers, you can run a normal 90mm+ stem length, rather than a super short.
Ideally you'd be on a frame that has a decent seat tube length to suit this inseam height.
Like the custom AR 650b above [362/580], with the close? to horizontal top tube.
Seat tube angle on that frame looks around 72deg or so; a good fit for a longer femur.

Most production frame bikes these days though have somewhat 'compact' frame triangle, but if you get something with around a 51cm+ seat tube, then that would be fine.
On a 363/578 gravel frame at the moment, with 90mm stem.

https://www.lfgss.com/conversations/359004/
Another [custom frame] Elephant NFE 'monstercross' steel example, at 364/595.

One carbon gravel bike model that would be a good fit is the Argon18 gravel bike.
One of their '3D+' fit mod frame sizes would achieve similar low-360 / approx 580.

Calsun

At this time my first choice would be one of the Trek Domane in size 54cm or 56ccm. The geometry is excellent for riding long distances and they have good gearing and rims and tires. The Trek charts put me at 5'9" on a 56 but in the past my non-touring bikes have been 54cm ones. The 56cm has a 1.5" longer top tube which allows one to stretch out more but it may be too much. I would want to try out a size 54 and a size 56 before deciding which one to buy.