Small frame with long stem & seat post to compensate

rocky.raccoon

A more technical question..

I've been riding a 58 cm frame which I find a bit stretchy due to its long top tube length. The seat and knee to pedal alignment are perfect.

I think 2 to 3 cm less/shorter on the total top tube (55 or 56) would be ideal.

After a lot of research and reading I believe that it is possible to ride a smaller frame as long as the other dimensions are the same or closer to the ones of the bigger frame, and use stem & seat to compensate the difference.

So lets say, two bikes from different manufacturers.

Bike 1 is a 58 cm or X-Large according to its manufacturer


Horizontal Top tube c-c (cm) = 58
Stem length (cm) = 8
total reach 58+8 = 66

Seat tube c-t (cm) = 54
Seat tube angle (°) = 73

Head tube angle (°) = 73.5
Head tube (mm) = 205


Bike 2 is a 54 cm or Medium according to its manufacturer

Horizontal Top tube c-c (cm) = 55
Stem length (cm) = 8
total reach 55+8 = 63 ideal

Seat tube c-t (cm) = 54
Seat tube angle (°) = 73.5

Head tube angle (°) = 73.5
Head tube (mm) = 135

Would anyone agree that it might be possible?

What I don't understand is how the head tube length can affect this set up? One is 205 and the other is 135 mm.

on-yer-bike

Smaller HT means larger vertical distance from seat to bars. So if you are tall, with proportionally long legs and you want to ride a small frame with a long stem be prepared for a very racy, uncomfortable position.
8 cm stem is way too short on a frame with a 58 TT. Its the length of stem normally used on an extra small frame. Its even short for a M frame. If you have a bike fit you will be armed with the frame measurements ideal for you, then its just a case of finding a frame closest to those measurements. Look here: http://www.tour-magazin.de/services/qtr ... x.html#/70

letap73

on-yer-bike wrote:

Smaller HT means larger vertical distance from seat to bars. So if you are tall, with proportionally long legs and you want to ride a small frame with a long stem be prepared for a very racy, uncomfortable position.
8 cm stem is way too short on a frame with a 58 TT. Its the length of stem normally used on an extra small frame. Its even short for a M frame. If you have a bike fit you will be armed with the frame measurements ideal for you, then its just a case of finding a frame closest to those measurements. Look here: http://www.tour-magazin.de/services/qtr ... x.html#/70

+1 excellent advice.

Op - you are comparing two completely different bikes - the 58 is akin to a Giant defy, the 54 is akin to a Caad 10.

IrishMac

I've had the same sorta problems with a 58, can't get comfy on the front end, I should've went with a 56cm bike
A 54 would be too much full stop
I'm currently looking at getting a 100/90mm stem, not ideal, a 110/120 stem looks better IMO
Although you also have to look at the reach of the handlebars, which is quite long on my bike.

Either way, steer clear of buying online (my real mistake) you can't beat swinging your leg over a bike before buying

rocky.raccoon

Interesting stuff..

on-yer-bike wrote:

Smaller HT means larger vertical distance from seat to bars. So if you are tall, with proportionally long legs and you want to ride a small frame with a long stem be prepared for a very racy, uncomfortable position...

What about replacing the stem with one that has a greater angle to reduce the vertical distance from seat to bars and maybe adding more spacers under it? Since both frames have the same steer angle, would it work?

letap73 wrote:

Op - you are comparing two completely different bikes - the 58 is akin to a Giant defy, the 54 is akin to a Caad 10.

That is the idea! Manufacturer size their frames differently...

Crashs2k

I've done something similar and went from frame with a 58.5cm top tube to a 57cm. As others have said you also need to pay attention to the seat - bar drop. If it is too much you will most likely end up with lower back pain and seat / perineal pain which won't be solved easily.

The previous owner of my bike slammed the stem and chopped the steerer so I have a drop of about 11cm which is proving to be too much. Only option left for me is to fit a new fork and add spacers as I've already tried flipping the stem and lots of different seats.

Nothing wrong with that apart from the appearance and 'kudos' of not having that pro look of no spacers under the stem and a huge seat to bar drop. Personally I'd rather have a bike that is comfortable and which I can enjoy my rides on as nothing is worse than an ill-fitting bike that causes you pain!

Best would be to either get a bike fit done where they will suggest your optimal contact points and then you can choose a frame with the right stem / reach / drop or get a decent 2 hour test ride on if you already know what they should be.

I've got an appointment with the Bike Whisperer next month with a view of getting a custom bike made for next year.

rocky.raccoon

The recommendations from manufacturers and users/riders are only a guideline, not mandatory.

A more leisurely riding style will ask for a slightly larger frame therefore less drop from the saddle to the handlebars.

My main problem is that a larger frame will have a longer top tube and that is what I'm trying to avoid.

So ideal frame for me it'd be one with a shorter top tube and a longer head tube. Does it exist?

holiver

What frame is it? Do you know the stack and reach measurements?

These are all affected by tube lengths and angles. Different manufacturers use different measurements for each of these which means that two 56 frames could be pretty different.

on-yer-bike

rocky.raccoon wrote:

The recommendations from manufacturers and users/riders are only a guideline, not mandatory.

A more leisurely riding style will ask for a slightly larger frame therefore less drop from the saddle to the handlebars.

My main problem is that a larger frame will have a longer top tube and that is what I'm trying to avoid.

So ideal frame for me it'd be one with a shorter top tube and a longer head tube. Does it exist?

Frames they call sportive frames like the Specialized Roubaix are more like this.

rocky.raccoon

holiver wrote:

What frame is it? Do you know the stack and reach measurements?

These are all affected by tube lengths and angles. Different manufacturers use different measurements for each of these which means that two 56 frames could be pretty different.

I appreciate the effort into replying to my post. I intentionally refrained from describing my height and bike details such as brand and model as I didn't want it to influence the interpretation of geometry


Bike 1 (I find the top tube reach too big for me)
Reach 401.58 mm
Stack 605.65 mm

Bike 2
Reach 390 mm
Stack 540 mm

ollie51

rocky.raccoon wrote:

What I don't understand is how the head tube length can affect this set up? One is 205 and the other is 135 mm.

That's a colossal difference. Probably going to be unworkable. What's you current saddle height, bar drop and spacer/stem arrangement?

rocky.raccoon

My current one
Saddle height is 74.5 from centre bb to top of saddle
The bar drop is 0.5 cm almost leveled with bars
25 mm spacers under stem plus another 20mm the bit from the top head tube to the first spacer I'm not sure whether it counts
Stem 80 mm +6 degree

ollie51

rocky.raccoon wrote:

My current one
Saddle height is 74.5 from centre bb to top of saddle
The bar drop is 0.5 cm almost leveled with bars
25 mm spacers under stem plus another 20mm the bit from the top head tube to the first spacer I'm not sure whether it counts
Stem 80 mm +6 degree

Is it intentional that you have 25mm spacers on top? Because if it is, you're not going to cope with a Bike that has a headtube 7cm shorter. On a bike with 135mm headtube and a saddle heigh of 74.5cm even with the stem poiniting upwards and 3cm of spacers below you're still looking at increasing your drop by a good few cm. I think you should probably look at an 'endurance' frame, i.e. long head tube, relative to top tube.

itsnotarace

ollie51 wrote:

rocky.raccoon wrote:

My current one
Saddle height is 74.5 from centre bb to top of saddle
The bar drop is 0.5 cm almost leveled with bars
25 mm spacers under stem plus another 20mm the bit from the top head tube to the first spacer I'm not sure whether it counts
Stem 80 mm +6 degree

Is it intentional that you have 25mm spacers on top? Because if it is, you're not going to cope with a Bike that has a headtube 7cm shorter. On a bike with 135mm headtube and a saddle heigh of 74.5cm even with the stem poiniting upwards and 3cm of spacers below you're still looking at increasing your drop by a good few cm. I think you should probably look at an 'endurance' frame, i.e. long head tube, relative to top tube.

+1

if you compare the stack of the two frames listed there is 65mm difference so to get the same bar height on the 54cm frame you would need 45mm (your current spacers and bearing cap) + 65mm = 110mm of spacers. I don't know of any manufacturers that allow for 110mm of spacers on a fork steerer.

ai_1

205mm is a pretty long head tube even on a large frame size. Since you're using this with spacers and a positive stem angle, I think it's going to be difficult to change to a smaller frame and keep a similar saddle to bar drop. However you've chosen a bike with a head tube of only 135mm which is at the other end of the spectrum. That's a shortish head tube for a bike with a 550mm top tube. There will be plenty frames with top tubes around 550mm and head tubes around 140-170mm and I'm sure there are some with longer head tubes that might work for you but your choice will be limited.

You definitely need to do a bit more research or get a bike fit to be in with a good chance of picking the appropriate frame style and size. Also don't forget that the bar reach and alignment and position of the hoods on the bar effect the reach and drop too. You may have some adjustment available here on your existing bike?

racingcondor

As said 'Endurance' frames will have a much better chance of fitting you if you're moving to a smaller frame but need to avoid dropping the front end. My 54 Condor Squadra for instance has an effective Top Tube of 550mm and a 173mm head tube so might work out here, that 135mm Head Tube just won't unless your current position is completely wrong for you.

You are suggesting using an 80mm stem on the smaller frame though which is a bot of a worry as that's still pretty short.

rocky.raccoon

racingcondor wrote:

As said 'Endurance' frames will have a much better chance of fitting you if you're moving to a smaller frame but need to avoid dropping the front end. My 54 Condor Squadra for instance has an effective Top Tube of 550mm and a 173mm head tube so might work out here, that 135mm Head Tube just won't unless your current position is completely wrong for you...

I wouldn't say my current position is completely wrong but something is not right. I'm not trying to avoid the drop because I still don't know what works. Maybe a bit more drop might not make any difference.

Ai_1 wrote:

... There will be plenty frames with top tubes around 550mm and head tubes around 140-170mm and I'm sure there are some with longer head tubes that might work for you but your choice will be limited... You may have some adjustment available here on your existing bike?

You're right! Unfortunately, I run out of options in reducing the reach. Stem is already the shortest. Top tube is still "on my way"...

ollie51 wrote:

Is it intentional that you have 25mm spacers on top? ...

No intention at all! I bought it like that, found the reach too long and replaced the stem for 80mm one. I had only realised I had 25 mm spacers when I recently started looking into reach/stack. Not sure I need them.

itsnotarace wrote:

...if you compare the stack of the two frames listed there is 65mm difference so to get the same bar height on the 54cm frame you would need 45mm (your current spacers and bearing cap) + 65mm = 110mm of spacers. I don't know of any manufacturers that allow for 110mm of spacers on a fork steerer.

At the moment saddle to bar drop is just 5mm. I believe drop is a matter of personal flexability and comfort. I'm still young.. might be able to adapt myself to a bigger drop.

The idea was to use 35mm spacers and a 120mm stem +17degrees. Therefore the stack difference would only be 12.3mm. I'm not sure it would work, my calculations are right or whether 12 mm drop is too much.

letap73

If you are contemplating a change from a 58 - with a giant defy type geometry to a 54 with Caad 10 geometry then you are looking at a big change. Your current setup has a very small drop, moving to a more aggressive geo will result in a significant drop which personally for me makes a big difference. Putting lots of spacers and an upturned stem would defeat the purpose of having an aggressive geo bike. You would probably be better of with a less aggressive geo circa a Defy or Secteur.

I have a 56 Defy - slammed stem with a drop of 10 cm and a 54 Supersix evo with lots of spacers with a drop of 16 cm, and I can safely there is a big difference.

ollie51

The idea was to use 35mm spacers and a 120mm stem +17degrees. Therefore the stack difference would only be 12.3mm. I'm not sure it would work, my calculations are right or whether 12 mm drop is too much.

That sounds like a massive compromise to me! I.e. you need a different frame to the one you want.

ollie51

letap73 wrote:

If you are contemplating a change from a 58 - with a giant defy type geometry to a 54 with Caad 10 geometry then you are looking at a big change. Your current setup has a very small drop, moving to a more aggressive geo will result in a significant drop which personally for me makes a big difference. Putting lots of spacers and an upturned stem would defeat the purpose of having an aggressive geo bike. You would probably be better of with a less aggressive geo circa a Defy or Secteur.

I have a 56 Defy - slammed stem with a drop of 10 cm and a 54 Supersix evo with lots of spacers with a drop of 16 cm, and I can safely there is a big difference.

16cm is huge. How tall are you?