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38.2 mm seatpost clamp with rack eyelets ?

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38.2 mm seatpost clamp with rack eyelets ?

Old 04-22-23, 01:36 PM
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38.2 mm seatpost clamp with rack eyelets ?

I am looking for a seatpost clamp for my Stromer ST1 with eyelets for hooking rear rack brackets to. I measurement my seat post and the caliper reads 38.2mm. and I really can't find any products that fit these requirements. Eyelet clamps seem to stop at 35-36mm....I hope I am wrong here but would appreciate insights.

Some background info in case someone has encountered the exact problem and found a solution :

I love my Stromer ST1 but ever since I wanted to mount child bike seats on it to take my twins riding with me I have sort of started hating it. Pretty no bike seat that I have tried is compatible with the Stromer without requiring adapters or modifications. Overall an extremely frustrating experience.

I finally managed to mount Thule Yepp mini to the front (this has been the one with the least issues ) and now trying to mount the Maxi as my rear child seat and I have been stuck without a solution so far. I thought I was close to one with the Topeak rear rack but I cant find eyelet clamps that fit my bike..this is the last piece of the puzzle that is proving elusive
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Old 04-22-23, 03:02 PM
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When looking for a seatpost clamp do not measure the seatpost. Measure the seat tube. If your seat post measures 38mm ... wow. Either you are measuring wrong or ... I don't know. But I do know that this will fit your bike and you can keep your existing seat clamp.
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Old 04-22-23, 06:57 PM
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One possible option might be keeping your existing clamp, and securing the rack using a longer QR or nut and bolt arrangement through the clamp's eyes.

Essentially, it's the same hardware to hold the rack and tighten the clamp.
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Old 04-22-23, 07:09 PM
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Originally Posted by psychoanalyst
I am looking for a seatpost clamp for my Stromer ST1 with eyelets for hooking rear rack brackets to. I measurement my seat post and the caliper reads 38.2mm. and I really can't find any products that fit these requirements. Eyelet clamps seem to stop at 35-36mm....I hope I am wrong here but would appreciate insights.

Some background info in case someone has encountered the exact problem and found a solution :

I love my Stromer ST1 but ever since I wanted to mount child bike seats on it to take my twins riding with me I have sort of started hating it. Pretty no bike seat that I have tried is compatible with the Stromer without requiring adapters or modifications. Overall an extremely frustrating experience.

I finally managed to mount Thule Yepp mini to the front (this has been the one with the least issues ) and now trying to mount the Maxi as my rear child seat and I have been stuck without a solution so far. I thought I was close to one with the Topeak rear rack but I cant find eyelet clamps that fit my bike..this is the last piece of the puzzle that is proving elusive
There are two ways to go about this. One is get a seat post clamp with eyelets and the other is a seat post collar assembly with eyelets which replaces your existing seatpost clamp. You will need to know your seatpost diameter as well as your seatpost collar diameter and see what is available out there. Once you have those dimensions Google is your friend.
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Old 04-23-23, 12:32 PM
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Seat post measurement

Seat tube measurement

Mwave seatpost clamp with eyelets (34.8mm)
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Old 04-23-23, 12:36 PM
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Originally Posted by Leisesturm
When looking for a seatpost clamp do not measure the seatpost. Measure the seat tube. If your seat post measures 38mm ... wow. Either you are measuring wrong or ... I don't know. But I do know that this will fit your bike and you can keep your existing seat clamp.
I have attached some pics that hopefully clarify my measurements.

The seat tube measures 36mm + ( I got lazy and measured the inner diameter of the seat post clamp). The seat post measures close to 32mm.

So essentially the eyelet clamps that I found on Amazon all are too small. I bought the widest available clamp (34.9 mm) and obviously that does not fit since the seat tube is bigger.

Thanks for the option you pointed out! That would be perfect and I think the only solution that would work I think
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Old 04-23-23, 12:52 PM
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31.6 mm is one of the standard mtn seat post diameters. I don't know of any that are wider. Either your caliper is out of adjustment, or you have it at a non 90° angle.

I think what you need is the Salsa Rack-Lock Seatpost Collar in the largest size, 35.4mm. You can pry it apart slightly to get it to go on your 36mm OD seat tube (which is probably slightly smaller in diameter, given what your calipers read for the 31.6mm post).

Last edited by Polaris OBark; 04-23-23 at 12:59 PM.
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Old 04-23-23, 12:55 PM
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Originally Posted by FBinNY
One possible option might be keeping your existing clamp, and securing the rack using a longer QR or nut and bolt arrangement through the clamp's eyes.

Essentially, it's the same hardware to hold the rack and tighten the clamp.
This is a very interesting idea....might be the least invasive
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Old 04-23-23, 12:58 PM
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Originally Posted by Leisesturm
When looking for a seatpost clamp do not measure the seatpost. Measure the seat tube. If your seat post measures 38mm ... wow. Either you are measuring wrong or ... I don't know. But I do know that this will fit your bike and you can keep your existing seat clamp.
I checked out the adapter you pointed to but looks like it might be too small
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Old 04-23-23, 01:09 PM
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Originally Posted by Polaris OBark
31.6 mm is one of the standard mtn seat post diameters. I don't know of any that are wider. Either your caliper is out of adjustment, or you have it at a non 90° angle.

I think what you need is the Salsa Rack-Lock Seatpost Collar in the largest size, 35.4mm. You can pry it apart slightly to get it to go on your 36mm OD seat tube (which is probably slightly smaller in diameter, given what your calipers read for the 31.6mm post).
Yeah....the seat post is indeed 31.6mm and my calipers are out of calibration.
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Old 04-23-23, 01:29 PM
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There is also a second kind that clamps to the seat POST directly (and you can keep your current collar).

https://www.salsacycles.com/gear/post-lock

If you get the 31.6 size (the largest) you will know it will work, and it is very high quality.
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Old 04-23-23, 03:52 PM
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The seatpost measurement is irrelevant. Seat clamps are sized by the diameter of the frame’s seat tube. Given how far off your seatpost measurement was, I suspect that your seat tube is actually 35mm or, more likely, 34.9mm which is the common size. Measure the seat tube (or inside the seat clamp) again. Jenson has the 34.9mm clamp from Problem Solvers for about $12. This place has an Axiom one for $8. You can even get an uber fancy titanium one on Ebay.

Edit: Just noticed that the collar you have is 34.8mm. How close is it to fitting on the frame? Can you spread it a little to make it fit or is it way off?
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Old 04-23-23, 09:35 PM
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Originally Posted by cyccommute
Edit: Just noticed that the collar you have is 34.8mm. How close is it to fitting on the frame? Can you spread it a little to make it fit or is it way off?
I am going to try that...but for sure the 34.9mm clamp I got is smaller than the one currently on my bike. I can take a side by side pic to show that....so I am not too sure that it will work.
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Old 04-23-23, 10:30 PM
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Originally Posted by psychoanalyst
This is a very interesting idea....might be the least invasive
I see this mostly working....I looked at the current clamp closely and the quick release has a partially threaded M5 rod which easily screws out. I just need to replace that with something longer and I can then use the clamo as my rack support as well. I am going to hit a couple of hardware stores to locate the M5 threaded scress.
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Old 04-23-23, 11:14 PM
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Originally Posted by psychoanalyst
Yeah....the seat post is indeed 31.6mm and my calipers are out of calibration.
Digital caliper of this type need to be zeroed EVERY TIME you use them.

My preferred way to do that is to close them on a dollar bill. Then slide the bill while applying some pressure to wipe the jaws clean. Now, close fully and reset.

Note, if they've ever been dropped the tips may be bent so they can't close flat.

Take a moment to close and hold to the light to confirm.

Last edited by FBinNY; 04-23-23 at 11:19 PM.
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Old 04-23-23, 11:23 PM
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Originally Posted by psychoanalyst
This is a very interesting idea....might be the least invasive
A variation on this theme is to buy a collar that fits the post.

Now, the original clamp can be used as is, and the new clamp can be used with a through bolt to hold the rack ro the post.
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Old 04-24-23, 02:30 AM
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Originally Posted by Polaris OBark
There is also a second kind that clamps to the seat POST directly (and you can keep your current collar).

https://www.salsacycles.com/gear/post-lock

If you get the 31.6 size (the largest) you will know it will work, and it is very high quality.
Or if you don't need that high a quality, there is this Sunlite clamp:

I had this on my son's bike and it was very sturdy.
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Old 04-24-23, 10:53 AM
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Originally Posted by FBinNY
A variation on this theme is to buy a collar that fits the post.

Now, the original clamp can be used as is, and the new clamp can be used with a through bolt to hold the rack ro the post.
This is the perfect solution! Modifying the existing clamp etc. would work but there are subtleties that make it non ideal. Also saves me a trip to the hardware store hunting for the right M5 threaded screw.
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Old 04-24-23, 10:55 AM
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Originally Posted by icemilkcoffee
Or if you don't need that high a quality, there is this Sunlite clamp:

I had this on my son's bike and it was very sturdy.
This is also a great solution, except just looking at the descriptions, it won't fit my seatpost. I think I am going to go with a eyeleted seat clamp, but mount it to the seatpost (and leave my current clamp as is).
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Old 04-24-23, 12:37 PM
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Originally Posted by psychoanalyst
There are several common seat post diameter standards, some of them differing by less than 1mm. You're using the caliper incorrectly. This is how to use a caliper properly. The caliper goes on the outside of the object. Your caliper is above the object and you're trying to eyeball it. It's never going to work. https://www.thegeekpub.com/wp-conten...ipers-0004.jpg

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Old 04-24-23, 01:43 PM
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Originally Posted by psychoanalyst
I checked out the adapter you pointed to but looks like it might be too small
It is not too small. First, it comes in two sizes. I bought the larger one and it is much too big and I have a tandem which uses the largest size seatpost collar that they make. You would put it around the seatpost, right above your existing seatcollar. If you get a longer bolt for your existing seat collar the mounting points for your rack will be too close together! Here is how you properly measure your seat clamp collar if you have unreliable calipers or no calipers at all: obtain a tape measure with metric markings on the opposite side, most do. Carefully measure the circumfirence of your seat tube. Not your seat post. Remove the seat collar if there isn't enough clear seat tube below it to get a good wrap of your measuring tape (I get 35mm which tracks with a 34.9 standard seat collar) Bob's your uncle.

Edit: after writing the above I realized there was an even easier way since the o.p. bike model was known. Several sources confirm the ST1 as having a 34.9 seat collar circumfierence. Interesting that Stromerbikes.com assiduously avoid supplying this information. However, I couldn't help but notice in the o.p. that they want to carry twins on the ST1. Seriously? I think that would get you pulled over in my city. I'm out after suggesting the o.p. look into a cargobike if they want to take passengers on a bike.
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Old 04-29-23, 02:02 PM
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Originally Posted by Polaris OBark
There is also a second kind that clamps to the seat POST directly (and you can keep your current collar).

https://www.salsacycles.com/gear/post-lock

If you get the 31.6 size (the largest) you will know it will work, and it is very high quality.
Thank you for this. A little pricey, but its just the biscuit for the problem I'm trying to solve.
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Old 04-29-23, 05:49 PM
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Originally Posted by Leisesturm
a cargobike if they want to take passengers on a bike.
Or a Burley bike trailer for 2 kids. We had one. It is arguably the safest way.
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