Barchettaman

I need to drop the rear wheel very slightly to fit a 700/28 tyre. It very nearly fits but fouls slightly in the brake bridge.

I've removed as much aluminium from the Underside of the brake bridge as I dare, so now need to get some room the other end.

There is at least 2mm to be gained by mounting the wheel slightly lower in the vertical dropout but I think I need a plastic spacer in the there (or something similar) to stop the axle shifting back up in the dropout on bumps.

Who makes such a thing?

I have searched, honest.

Thanks all
Simon

Sixty Fiver

The solution is to run a tyre that fits your bicycle... assuming here that you are probably on a road bike with tight clearances that only has enough room for a 700:25 slick at best.

dddd

Making a shim to fit in the dropout will be easy, but it should be much less than 180 degrees or will wedge in between the axle and dropout, and may not allow the axle to settle in equally on both ends.

The bigger problem will be how to keep the shim from falling out the first time you remove the wheel.

Some vertical dropouts have a set screw for adjusting the depth of the axle in the dropout, unfortunately it sounds like yours do not.

Perhaps a different caliper could be found with more clearance below the centerbolt?

And, mounting your caliper in front of the seatstays might also gain some clearance.

FBinNY 

I've done this to improve fork clearance for street use on my track bike. You won't find a spacer or any kind, and cannot use a flat strip formed into a U since you only want to fill the bottom, without narrowing the sides.

I did it as follows. I cut a few bits from a spoke, (you can also use a bearing ball) and used that as reinforcement (and as a gauge) then did the job with body filler. That was 40 years ago, and I still use that fork without having to do anything else.

Kimmo

Really? I've never seen such a thing.

bobotech

Do you have a picture or even a drawing to show what you mean? I'm curious about it.

fietsbob

you, probably.. may be a JB Weld use..

Barchettaman

Thanks all for the reasoned responses.

The rear triangle has plenty of room at the chainstays & seat tube for a bigger tyre, but for some reason the brake bridge is a massively meaty piece of aluminium that wouldn't look out of place on an oil rig, and the tyre fouls there.

A 700c 25 now fits fine, and in the absence of a U shaped plastic thingyamyjig I suppose I'll use them. I do prefer a 28 though as they go a bit better on the gravel/farm tracks in the countryside here, and I do like to mix up the riding with a bit of light trail action.

Thanks all once again, and hope you're all enjoying spring.

Kimmo

I've seen FB talk about this before; the idea is to cut short bits of spoke as long as the dropout is thick, and glue a couple of them in place in the dropout above the axle. Car bog completes the job of holding them in place.

ksisler

OP; Nothing off the shelf likely. Just find or pick up a piece of small diameter aluminum or steel tubing with about the right wall thickness and a hacksaw with metal blade. Use the saw to split the tube down the middle about a half inch and then cut the two half moon spacers off the tube to match the width of your drop outs. If the resultant spacer is a bit to big or too small to slide into the dropout and stay in place, just tweak them a bit with a hammer to change the radius as needed. You want a tight fit. 10 minute job at worse.

After you are reassembled, give it a ride at your top speed....as I don't really know if bike tires grow in diameter at speed like a car tire... if so, you may need to add a second spacer.

HTH; /K

Barchettaman

I was actually thinking of getting creative with some nylon washers from the hardware store.

FBinNY 

I could draw a sketch, but don't know how to upload it to a post.

Anyway it's fairly simple. Draw a U. You want to raise the bottom (upside down for explanation purposes) without narrowing the sides, so you can't do something like putting a bushing on the axle. You could just use body filler, or solder or whatever to do the job but need a control so that both sides are the same. So find something of the thickness desired (in my case a spoke for 2mm) and glue it to the bottom of the U. Then fill in and contour with body filler, and finish by forming (when half hard) of filing (when hard) the correct semi circle until the shim is just visible.

In use the shim will handle any loads as the wheel is fitted, until it's tightened.

Reynolds 

'91 GT Karakoram (the adjusting screw is removed here):

Sixty Fiver

What kind of bike is this ? If the max tyre is a 700:25 it is probably not designed for light trail action or gravel although that has never stopped me from hitting the trails on my road bike.

Kimmo

It's pretty easy, you see the five colourful formatting icons above the text entry field? The second one from the right (the little tree) is meant to represent a picture... click it, and a dialog box pops up with a couple of tabbed pages. The first page is labelled 'From Computer' with a 'Select Files' button. Hit that and browse to your image.

The other page is 'From URL' - click that tab to enter an image address. If you check the 'Retrieve remote file and reference locally' box, it'll make a copy on the BF servers so the pic doesn't ever disappear and posts a clickable thumbnail, or if you uncheck it, it just embeds the full-sized image, loading it from wherever you found it.

Well blow me down. That's a bit odd.

FBinNY 

Cool, now I need a drawing pad, or I can use pen and paper and scan it in. At least I'm half way there.

BTW- I always wanted a "draw on screen" application or pad, this is one more step motivating me to go ahead. As it is I hate adding programs or updating, because it always takes me time to unimprove all the changes I never wanted in the first place.

Kimmo

A tablet would be handy... I have one here for PS3 that came with some crap bundled game, but I can't find any PC drivers for the damn thing. Bloody rubbish...

Also, if you don't have a scanner, you could just take a photo.

dddd

That was a very good solution using the spoke lengths.

I also thought JBWeld would be well suited, but anything really tough would last maybe forever.

I had a RockShox Paris-Roubaix road-suspension fork that needed a millimeter or two extra height (tire clearance) at the bridge, and coincidentally found that there was a tiny hole cast or drilled in the lower leg up from the curve of the slot!
I slid a small, flat-head nail into each fork slot's hole, secured with silicon glue. This lifted the fork up from the axle, and gained the needed space atop the tire for a skinny cyclocross tire.
Of course I didn't go anywhere near mud with such scant clearance above the tread!

And BTW, I don't recommend drilling any holes in the OP's dropouts.

FBinNY 

Thanks. 40 years ago when I did this, Bondo was handy and I figured the spoke would take the load. I also wanted something that I could easily ping out in one clean shot with a hammer and punch, or at least file out with a dull file to restore the original geometry.

So far It's still there, but if I ever change my mind I still can.

dddd

I remember putting a fatter, Armadillo tire on my friend's Raleigh Technium, and the 26mm tire was a fatty.

I took my leather dress belt, layed it along the top of the tire, with a strip of coarse, stiff belt-sander paper atop the leather.

I inflated the tire incrementally, then moved the tire/belt/sandpaper back and forth under the DiaCompe caliper.
I achieved the ideal of only removing enough metal exactly where the tire's path wanted to be, and assumed that tread wear would keep pace with any increase in the tire's inflated girth over time. I tried first loosening the caliper and lifting up while re-tightening the mounting bolt.
I can't remember what I did with axle positioning or even what kind of dropouts the bike had, but that big tire lasted him for many years.

FBinNY 

Watch out, the boobirds will lecture you on the deathly implications of removing material from the underside of brake arms.

I did the same on the front brake of my track bike, simply eyeballing and filing freehand. It wasn't enough so I filed the back of the center bolt at an angle and bent the mounting bolt so the brake rises at about 5° leaving the face of the fork.

That solved the tire clearance issue, but I had to braze tabs to steel shoes to raise them above the top of the slot on the shortest brake I could find.

xenologer

a less kludgy solution might be to convert wheelsize to 650b

dddd

I actually came across some vintage brake pads with offset bolts, above or below the pad.
I didn't know what fitment was intended, but it occurred to me that the braking force might spin the pad loose from it's nut.
But we're talking a very much shorter offset here I assume.

I've had to extend pad slots in a few alloy brake arms, even occasionally filing off some bolt threads(!), with no ill effects to date.
I actually had to do all this on my 1979 Peugeot UO-9 SuperSport, just so the stock Weinmann caliper's pads could fully align with the normal-size 27" rim (as apparently they favored using the short-reach version of this caliper in front, and/or didn't want anyone to even think about using a 700c rim).

FBinNY 

I don't know which you found, but the offset mount shoes I've seen were also offset at an angle, and were intended for brake which strike under the rim as the old "Bobby" bikes brakes did.

Anyway, seem to be from the same school of wrenching as I am, the do what's necessary to make it work school.

One nice feature of the zero clearance fork on my street track bike is hat it's a built in tire saver which does a great job of flicking stones, flints and glass shards out of my front tire. To tell you how close it is, I hear tire rub on top with hard bumps.

Dilberto

Get any amount of front or rear tire clearance, without ever having to adhere or bond spacing material inside dropouts:


Reversed tabs create the spacing - easily removable, so you can mount on roof rack too: