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Tri bike rear dropout mod for tire size options

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Tri bike rear dropout mod for tire size options

Old 03-09-21, 10:00 AM
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treebound 
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Tri bike rear dropout mod for tire size options

Iíve got a Trek Equinox 7 from around 2008, and even though it was specíd with 23mm wide tires when new, modern 23mm tires wonít clear the seat tube so I had to find a 700x20mm tire and 20mm tires are virtually non-existant these days.

So I think my options are to convert the bike to 650b (I really donít want to go this route), or modify the rear dropouts, or have the rear dropouts replaced.

Right now Iím thinking it might be viable to machine or file a horizontal slot rearward in the vertical slot thereby turning the dropout into a pseudo-horizontal dropout. I havenít done any careful measurements yet to determine how far rearward I would need to extend the slot nor have I verified if this is even feasible. Iím kind of thinking just an axle diameter might be enough to provide clearance to the seat tube.

I donít want to convert to tubular rims, so if I damage or wear out the current tires then the bike is basically parts.

I have attached a marginal photo of the rear of the bike along with a quick and dirty CAD sketch showing what Iím considering. And of course if I cut too far rearward then durability becomes a factor.

I figured the framebuilders section might be the best place to post this. I donít know how long Iíll keep this bike so just looking for input right now.

thanks for any advice or opinions.



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Old 03-09-21, 01:25 PM
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unterhausen
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I feel like you're out of luck. I didn't see what kind of aluminum this is made out of, but generally replacing aluminum dropouts isn't a great idea.
I think the dropout will break if you mill the slot.
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Old 03-09-21, 04:05 PM
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Thanks for the input, kind of the conclusion that I'm coming to.
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Old 03-09-21, 07:09 PM
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How wide are the rims, are they OEM spec still? (We've had more then one older bike that when "up graded" to current trendy wider rims end up not having much/any tire clearance with the older tires). I assume the bike has seen a number of different skinny (23?) tires in the search. I say this because the labels are not the actual dimensions and playing with tires "suggested" widths is an age old marketing device to drive sales. When things get tight or close there's no method like actual trying to be sure. Bummer that the bike is so restrictive but I guess that's part of the untold cost to buying on the ragged edge. Andy
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Old 03-10-21, 05:52 AM
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The rims are narrow. The problem is the height of the tire which rubs against the rear side of the seat tube.

I think I still have an pair of dried out 700x23 tires that are shorter than the 20’s currently on the bike.

I might have to just stop at one of the local bike stores and bring some calipers with me and start measuring tire heights.
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Old 03-10-21, 06:51 AM
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This is why I'd never own a vertical dropout tri/TT bike. Sorry that doesn't help the situation. But I wouldn't do what you have listed.

You could perhaps experiment with running wider wheels like an HED. 23's site shorter on those than narrower wheels. You'd just have to measure your chainstay width. If your rims are really narrow now, even the older HED "c2" width wheels might be wide enough to fit that 23 tire. Maybe find a local who owns a set of said wheels and meetup just to test fit.

Used HED's go for reasonable used prices if they aren't the newer 25mm wide ones. The 23mm wide ones go for pretty reasonable.
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Old 03-10-21, 10:06 AM
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I’m going to check the rim widths of my road bike wheels, and if wider then I will begin some tire swapping checks.
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