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Trek seat mast too short: Solutions??

Old 09-28-18, 06:05 PM
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DarrinNYC
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Trek seat mast too short: Solutions??

I LOVE my two Trek bikes (2016 Madone and 2018 Domane). Trek decided some time ago that a seat mast cap that slides over a mast is the way to go when it comes to setting saddle height. Well, I just went through a thorough bike fit today (Tim Dougherty out of Cycle Craft in NJ), and I need to raise my saddle A LOT. The challenge? I ran out of mast and cap length to get enough height.

Has ANYONE seen or heard of a workaround to this problem?

I do have Trek's longest seat mast cap, btw.

Thx.
Darrin
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Old 09-28-18, 06:35 PM
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How did this predicament arise if the cap was in hindsight too small at the outset-- bike too small or did you go to shorter cranks?
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Old 09-28-18, 07:06 PM
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I would say there's a conflict between whoever chose the Trek's frame size and your current bike fitter. On face value I'd say you are now on the wrong frame size, IF the new fit is actually the better one.

Trek has had a frame replacement program for a number of years. Usually motivated by out of warranty things (like a too small frame??). This is one option.

Finding someone to fabricate a custom seat mast is another option. Who? I have little idea but there are a number of custom carbon builders out there. Maybe one of them can help. For that mater the mast likely doesn't need to be carbon, or have the frustrating Trek seat rail clamp design.

Going to longer crank arms or finding the classic Shimano DID arms/pedals system to drop your feet further is another unlikely option.

You have some pretty well designed bikes. Do they all match fairly close in stack/reach? Have you changed their seat height (and any other fit specs that this new guy has told you to do)? Have you put many miles in differing conditions with the new fit spec? How were these other bikes chosen WRT the fit? Have you changed in your abilities/flexibility/strength/riding style since they were bought?

We see people coming in often enough with bikes that we feel are the wrong size, usually due more to reach and not seat height though. We do the best we can with what they have already paid for and give them our advice for the next bike if they ask. Andy (who really dislikes the brand specific frame/fit designs that are all the rage these days
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Old 09-28-18, 08:35 PM
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How much too short, in mm?
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Old 09-29-18, 10:50 AM
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My brother has a friend who is a machinist! They feel they can take a titanium or aluminum hollow tube and mill it to fit into the frame-integrated seat mast... effectively making it taller. The outside diameter of the titanium tube that sticks above the seat mast will match the outside diameter of the existing, frame-integrated seat mast. Simply, I can slide the Trek seat mast cap over the titanium extension we design and create. We are thinking a 75mm insertion into the seat mast and a 100mm extension above the top of the current seat mast so the seat mast cap can then be SAFELY and SECURELY extended.

The plan is to create tolerances that will be secure with the friction between the carbon and titanium tubes, some carbon paste, and the Trek factory seat collar on the Trek cap tube.

The goal is to gain 25mm of saddle height ABOVE Trek's recommended safety line.

Thoughts on all this?
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Old 09-29-18, 10:55 AM
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What is your crank length and how tall are you? For example, if you add 5 mm to the crank length you can lower the saddle 5 mm.
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Old 09-29-18, 11:08 AM
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Originally Posted by McBTC
What is your crank length and how tall are you? For example, if you add 5 mm to the crank length you can lower the saddle 5 mm.
REALLLLLY tall! 6'4" -- 37" inseam when I buy jeans --- 175mm cranks --- My concern with going to longer cranks as a compensation is that my knee bend at the top of the pedal stroke would increase even more than it already does.
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Old 09-29-18, 08:26 PM
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Originally Posted by DarrinNYC
REALLLLLY tall! 6'4" -- 37" inseam when I buy jeans --- 175mm cranks --- My concern with going to longer cranks as a compensation is that my knee bend at the top of the pedal stroke would increase even more than it already does.
I wouldn't go to larger cranks either. You're dilemma with this bike rings a bell with me... I like my current rig but as it's happened before over the years I came across a new Trek Domane in a bike ship not long ago and was pretty interested in it as coming across large bikes sort of turns bike-buying into a treasure hunt and is especially fun if you can get a good deal on something you really like. This one was a size 62 which is unusual since 61 is usually tops and, I think it's be perfect for me and maybe you too but I passed on it because the seat post arrangement -- like what you have -- it sort of scared me off because, If I'd bought I'd have wanted 165 cranks and I wasn't sure how high the seat could be raised... especially being CF. I may be stuck with my alloy frame and an alloy seat post that'll go far higher than I'll ever need.
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Old 12-13-21, 06:47 PM
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Bump! anyone know any other solutions i have the same problem
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Old 12-15-21, 07:00 AM
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The seat mast cap comes in two different lengths.
I'm not a fitter but if you need more than 175mm your frame is probably too small.
Here the link
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Old 12-15-21, 09:12 AM
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OP, you should ask your bike fitter if your bike is just too small before investing in any seatpost solutions. If you already have the longest mast head and it's still way too short you would have to have an extremely long set of legs in relation to your torso to make this work with your current frame. You also have to consider that your handlebar height may not be able to extend far enough upwards for you too.
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Old 12-15-21, 05:31 PM
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Does it really make sense for someone 6'4" to be on 175mm cranks? HTFU and get some 185mm, or even longer! Problem solved. But unless the o.p. has T. rex genes in their DNA ... their frame may be too small.
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Old 12-16-21, 02:21 PM
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You could try to get a custom seat mast made. Some custom frame builders create their own. Speedvagen comes to mind.
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Old 05-28-22, 02:05 PM
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I have the opposite problem. Just bought a secondhand Trek Madone SL7 52cm frame. I'm 5ft 8 and TOO SHORT for the lowest seat post position! The mast won't physically go any lower within the seatpost, Also, the lower bolt you tighten it up with is nearly buried below the access slot. I need another cm or two lower but if this were achievalble, the lower bolt would be inaccessible. When I tried the bike, the saddle was pointing slightly upwards so its rear end was a tad llower - it felt OK. For longer rides, I need the saddle more horizontal.
Something odd here as according to Trek's size chart, I should be slightly too tall. I prefer the smaller frame size because of reach. The seat mast is not very long, less than 30cm.
Any ideas how I can get round this?
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Old 05-28-22, 02:36 PM
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Originally Posted by Davehut
I have the opposite problem. Just bought a secondhand Trek Madone SL7 52cm frame. I'm 5ft 8 and TOO SHORT for the lowest seat post position! The mast won't physically go any lower within the seatpost, Also, the lower bolt you tighten it up with is nearly buried below the access slot. I need another cm or two lower but if this were achievalble, the lower bolt would be inaccessible. When I tried the bike, the saddle was pointing slightly upwards so its rear end was a tad llower - it felt OK. For longer rides, I need the saddle more horizontal.
Something odd here as according to Trek's size chart, I should be slightly too tall. I prefer the smaller frame size because of reach. The seat mast is not very long, less than 30cm.
Any ideas how I can get round this?
No idea how you "get round this". However, 5'8" should, in fact, fit on a 54cm frame so Occam's Razor says your assertion of being "TOO SHORT" is ... wrong. What length stem comes on the 54cm frame? If it was 20mm shorter could you be comfortable? We need pictures and/or more information. "There are no mysteries, only insufficient information" -Leisesturm
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Old 05-28-22, 02:42 PM
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Originally Posted by Davehut
I have the opposite problem. Just bought a secondhand Trek Madone SL7 52cm frame. I'm 5ft 8 and TOO SHORT for the lowest seat post position! The mast won't physically go any lower within the seatpost, Also, the lower bolt you tighten it up with is nearly buried below the access slot. I need another cm or two lower but if this were achievalble, the lower bolt would be inaccessible. When I tried the bike, the saddle was pointing slightly upwards so its rear end was a tad llower - it felt OK. For longer rides, I need the saddle more horizontal.
Something odd here as according to Trek's size chart, I should be slightly too tall. I prefer the smaller frame size because of reach. The seat mast is not very long, less than 30cm.
Any ideas how I can get round this?
Do you have the long mast cap? It's 175mm, the short is 135mm.
ETA: What's your saddle height?

Last edited by cxwrench; 05-28-22 at 02:46 PM.
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Old 05-28-22, 05:00 PM
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Total body height reference tables are just so lacking in help for many. I have a friend who is 8" taller than I am but their standover and seat heights are only about 2" more than my 5'6" body has. I also have a pair of friends that has him about an inch taller then her but her seat height is near an inch taller. Then there's a friend who has lost 3ish inches, over the last 15 years, from her torso due to health issues... There's a reason why custom frames are still being made. Andy
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Old 07-21-23, 06:48 PM
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trek seatmast too high

Hello did you find a solution? i also have a trek seat mast that is too tall and i'd like to bring it down. are the bikes designed to cut the carbon fiber?

Originally Posted by Davehut
I have the opposite problem. Just bought a secondhand Trek Madone SL7 52cm frame. I'm 5ft 8 and TOO SHORT for the lowest seat post position! The mast won't physically go any lower within the seatpost, Also, the lower bolt you tighten it up with is nearly buried below the access slot. I need another cm or two lower but if this were achievalble, the lower bolt would be inaccessible. When I tried the bike, the saddle was pointing slightly upwards so its rear end was a tad llower - it felt OK. For longer rides, I need the saddle more horizontal.
Something odd here as according to Trek's size chart, I should be slightly too tall. I prefer the smaller frame size because of reach. The seat mast is not very long, less than 30cm.
Any ideas how I can get round this?
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Old 07-22-23, 08:41 AM
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Originally Posted by DarrinNYC
My brother has a friend who is a machinist! They feel they can take a titanium or aluminum hollow tube and mill it to fit into the frame-integrated seat mast... effectively making it taller. The outside diameter of the titanium tube that sticks above the seat mast will match the outside diameter of the existing, frame-integrated seat mast. Simply, I can slide the Trek seat mast cap over the titanium extension we design and create. We are thinking a 75mm insertion into the seat mast and a 100mm extension above the top of the current seat mast so the seat mast cap can then be SAFELY and SECURELY extended.

The plan is to create tolerances that will be secure with the friction between the carbon and titanium tubes, some carbon paste, and the Trek factory seat collar on the Trek cap tube.

The goal is to gain 25mm of saddle height ABOVE Trek's recommended safety line.

Thoughts on all this?
Ok, I'm an engineer. I suggest being careful about this. The original seat post was designed to accommodate a maximum lever arm. Extending the post adds to the lever arm. This could put a higher than normal stress on the post at its base. Probably no big deal if you weigh 150lbs, but likely a problem if you weigh 250lbs.
If I understand the idea, you'll take a thick wall tube and bore out the ID on half the tube length to fit the post on the bike, and then you'll turn down the other half to accommodate your seatpost. Suggest ensuring that you leave some distance of tube in the middle where the tube is left unbored and full diameter to avoid creating a stress riser. Even if you don't, the general approach limits how far down you can put the seatpost. It may end up being too long! You will need some form of clamping for the bottom of the Ti tube. I would not use loose collars or hoseclamps. Best practice would be welded on ears, drilled and countersunk and hose lamps. If you use Ti screws (hint: don't) make sure that you gob on antisieze. By the time you buy the correct tube, and cut, bore, turn, weld, post-weld heat treat, and drill it, it may be cheaper to find a larger frame on ebay, and sell your smaller one. It will almost certainly be more flexible than is desirable. I have a Trek Domane (bought it from the racer Neco Mullaly, after he switched to another sponsor) and the high end Trek cf frames are great. But I don't like the proprietary seat posts, nor the direct to CF bottom brackets.
On edit, I see that you are 6'7" with a 37inch inseam. This suggests that you are 200# plus. I'm only 6'2" but stillness have trouble getting stuff my size, so I understand your frustration in getting big enough bikes. When I worked in a bike shop eons ago, we sold a bike ro the NBA star Jim Chones. 26 inch frame (Paramount) with a long post. I don't think think we were able to get a long version of the Campagnolo post. But that tube extended into the frame for some distance. If you already have the largest frame, you could try the Ti extender idea. Or as Andy suggests, get a larger frame. Possibly find a make of CF bikes that come in a size compatible with a 37" inseam. But maybe no one makes these? (!) I suspect that you have to have a King sizened - and that you sleep diagonally!
You might call up Zinn cycles. Lennard Zinn is a tall former bike racer (he was 6'6" when on the US National Team) who makes bikes for tall folks. He may be able to give you some advice. Look up some interviews in Velo online on why extending smaller bikes for tall people is suboptimal.

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Old 07-24-23, 10:24 AM
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Originally Posted by DarrinNYC
Has ANYONE seen or heard of a workaround to this problem?

I do have Trek's longest seat mast cap, btw.

Thx.
Darrin
Get a bigger bike.
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