bencohen

I have a vintage KHS road bike from the 90's (I think) and I am looking to replace the front small chain ring with something smaller. Though after a lot of research I cannot find one that matches the dimensions I have. The BCD is 76mm and the bolt holes are 8mm. The small chain ring is currently a 42 tooth so I am looking for anything smaller, preferably 30-34 tooth. If anyone could help me that would be much appreciated!

shelbyfv

That sounds like an unusual crank. Maybe from a MTB? Common road cranks from that era would be 130 BCD with a small ring of 42 or 39; I think 38T was the smallest possible. You might have better luck getting a complete new "compact" crank with 50/34 or similar.

bencohen

yes agreed I thought it was a very odd measurement and I measured it multiple times. It is all stock parts from the original bike I believe.

BoraxKid

I can't post a link, but the first result of googling "76 mm BCD chainring" brought up exactly what you need from a site called thebikesmiths. Watch out when selecting your new chainring because a lot of the option I saw were oval-shaped. And hopefully you've considered what size tooth-jump your front derailleur can handle, as well as the effect changing a chainring size will have on chain wrap for your rear derailleur. Good Luck!

bencohen

I should have mentioned in the original post but I need one with a 5 bolt pattern not a 4 bolt pattern. Though I did not consider the length of chain that’s a good point

BoraxKid

Well that does sound unusual. According to Sheldon brown (dot com slash) cribsheet-bcd (dot) html, the only 5-bolt chainrings that meet your description were 74 mm BCD. You can find plenty of sites selling those chainrings if you google "5 bolt 74 mm BCD chainring".

Are you certain your measurement is not off by 2 mm? If you trust your measurement, then it's possible that your bike had a proprietary crankset spec. In that case, replacing the crankset would be the easiest way to accomplish what you're after. Alternatives to replacing the crankset would include things like searching ebay for your specific part, or looking for a custom bicycle shop that could machine or modify a chainring for you. Good Luck!

Unca_Sam

Keep in mind most bike measurements are made from the center of the circle or cylinder. 2mm sounds most like a measuring error.

bencohen

yes normally I would agree with you that it’s measurement error but I am 99% sure it’s 76. I would attach a photo of my measurement but it won’t let me.

BoraxKid

An inexpensive test would be to purchase a 74 mm BCD chainring and attempt to mount it. If it doesn't work, you can always return it. If you can buy it from Amazon, their returns are stupidly simple nowadays. I returned a U-lock I didn't like by just dropping it off at a UPS store and letting them scan a barcode from my phone; I paid zero money for that return and got a full refund.

seypat

Take a picture of the crank with the model number/name and post it. We need that info to really solve the problem.

bencohen

I like this idea cause I have also returned stuff through amazon and it’s super easy. I went ahead and ordered 74 mm BCD 30t chainring. Fingers crossed it will work!