brooklyn_bike

i have a friend out in socal who recently dimpled the inside of a steel fork of a mid level bridgestone about 1-2mm per fork blade to gain enough clearance to go a up a tire size. frame already had enough space on the chainstays. i'm curious to ask any frame builders : do you think this would have any adverse effect or since it's steel and the dimple was 1-2mm it not really an issue? not sure i'd be open to doing something like this in the future but it is interesting. he went from 1.8" width tires to 2.3". i've seen people dimple chainstays but i hadn't heard of fork blades - thanks for you feedback !

merziac

Standing by.

brooklyn_bike

@ merziac : i'm always impressed with your bike knowledge when i read your comments / posts - i'd be curious your opinion on fork blade dimpling

merziac

Uhh, well Tx but I'm not sure, seems plausible to me but we need to wait and see if our very own true experts weigh in.

oneclick 

a) which way did the dimple run - the clamp shows 90, but obviously rotates; just curious, because
b) I wouldn't ride it either way

Trakhak

To the OP: click on the red "!" button at bottom left in one of your posts in this thread---you'll then be able to write a message to the moderators asking for this thread to be moved to the Framebuilders subforum.

In over 50 years of paying attention to bicycle topics, I've never heard of a framebuilder dimpling a fork blade, which probably means it's a very bad idea.

brooklyn_bike

will do thank you for your feedback !

juvela

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dimpled blades for tyre clearnance were a common thing at OEM for decades

one manufacturer who continued to use them after most others had ceased was Puch/Steyr of Graz Austria

often wondered if maybe their buyer had gotten a great deal on them at some point BITD and so they continued to use them until all gone...


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Trakhak

The question is whether it's a bad idea to dimple the top of fork blades in the heat-affected zone, I think. The fork blades for the manufacturer(s) you referenced undoubtedly dimpled the blades before brazing them into the crown.

TenGrainBread 

Given your tire width references in inches, sounds like a Bridgestone mountain bike? If so it might be ok. You want to make sure the blades are of a thick enough gage to handle the crimping without fracture.

The other consideration is the fork crown. You should be cautious not to distort the blade at the joint. TIG welded unicrown will probably be least risky since the joint is furthest from the crimp area compared to crowned forks, and TIG joints are very strong.

This query reminded me of something I saw recently on tontonvelo. Handmade "muletier" by Jacques Busset, ~1980. Not 100% sure the fork blade bends were done originally by Busset but it is likely. If original to the bike, no doubt the bends were made before brazing. He has other early "VTT" bikes he made with wide tandem fork crowns, maybe this was an attempt to save weight. Bike also has a sloping top tube and some other "mountain riding" features.


tontonvelo link

dddd

Steyr's lower-level Clubman and "Sears 10 Speed" models used wider crowns so needed no clearance crimps.
They needed the dimples however with their earlier bi-plane style of fork crown having very narrowly-spaced sockets (as used on the fancier Ted Williams Racer and Burgmeister).

The fork blades are slender fore-to-aft, but made of heavy-walled tubing.
Fork weight on this un-cut OEM example is a stout 1060g or 2.33lb

brooklyn_bike

thanks for the feedback everybody . the consensus from info here and the Framebuilders sounds like crimping your own bike could be considered but not a bike being passed on to someone else. some bikes with thicker tubing it's been done at the manufacturer and is prob ok. and dimpling steel before brazing is less risky than after bike is complete

chain_whipped

Early Schwinn's such as the 'World Tourist' had crimped forks. Heavier stock though the crimp was approximate third distance down from the top.