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View Full Version : Measuring a clincher rim...... ?



Steve Swan
03-21-2016, 02:07 AM
Which part (or area) of the clincher rim does one measure to determine the size (diameter) of the rim ?

the o.d. of the rim (center of bead edge to center of bead edge) is approximately 21". (closer to 20-7/8")

the i.d. of the rim is exactly 20" (where the base of the tire bead lays against the inside of rim.)

the tire diameter measured from "V" to "V" of the clincher bead is exactly 20". The i.d. of tire (inner base of bead) of tire is 19". (these are 3.85x20 Coker tires)

do these rim measurements sound right for a 3.85x20 tire ?

i have the inflated tube inside the tire with zip ties 3" apart the circumference of the tire, so the bead is pretty much the shape it will form to when mounted on the rim.

i'm confused and paranoid i got wrong rims because the distance the tires have to stretch over the rims appears at least 2".

i am going with these nasty clincher tire like massive rubber band bastards actually have to stretch that that 2" distance. Part of the insurance policy the tires stay on the rim, i ass.u.me.........

Sucks when i don't know what i am doing and brute force and a hot sunny day is the recommended prescription. don't wanna scratch my paint, dammit anyway........ !@#$%^&*()(*&^%$#$%*()&*&$%!!!!!

Thanks in advance.

exeric
03-21-2016, 09:20 AM
Steve, the last set of 3.85x20 tires I installed were the all white Cokers that I put on a Series 20 Excelsior. I don't believe they sell them anymore as I understand they wore very fast, and were a much softer compound. I feel bad for you, and I certainly didn't want to imply that you aren't doing something properly. Perhaps you should contact Coker and ask them for advice. If they suggest you hire a gorilla, or the Incredible Hulk to put them on, then maybe you should go with drop centers.

harleytoprock
03-21-2016, 09:38 AM
The rim measurements seem correct but the tire Id seems on the small side. Are the tire sides flat ? That might make the id smaller and the od larger. Put tubes in the tires with a little air and re-measure.. Last clinchers I put on were a set of 3.85 x 20 Firestones and a set of Goodyears. All from Coker and they went on with no hassles.

Steve Swan
03-21-2016, 09:41 AM
oh heavens no Eric ! never ever never even took it 'wrong' way !!!

i was only asking questions and just want to make sure the tire and particularly the rim size are the right ones before i go mono e mono. just a little humor of mine....... i will get this done.

will call Coker as i hope think they would know rim size that goes with their 3.85x20 tires, but i wanted to ask on the forum before i made the call.......

and will take pics of how i have the one tire set up with inner tube in it slightly inflated and zip ties around.

tfburke3
03-21-2016, 09:48 AM
Which part (or area) of the clincher rim does one measure to determine the size (diameter) of the rim ?

the o.d. of the rim (center of bead edge to center of bead edge) is approximately 21". (closer to 20-7/8")

the i.d. of the rim is exactly 20" (where the base of the tire bead lays against the inside of rim.)

the tire diameter measured from "V" to "V" of the clincher bead is exactly 20". The i.d. of tire (inner base of bead) of tire is 19". (these are 3.85x20 Coker tires)

do these rim measurements sound right for a 3.85x20 tire ?

i have the inflated tube inside the tire with zip ties 3" apart the circumference of the tire, so the bead is pretty much the shape it will form to when mounted on the rim.

i'm confused and paranoid i got wrong rims because the distance the tires have to stretch over the rims appears at least 2".

i am going with these nasty clincher tire like massive rubber band bastards actually have to stretch that that 2" distance. Part of the insurance policy the tires stay on the rim, i ass.u.me.........

Sucks when i don't know what i am doing and brute force and a hot sunny day is the recommended prescription. don't wanna scratch my paint, dammit anyway........ !@#$%^&*()(*&^%$#$%*()&*&$%!!!!!

Thanks in advance.
I am not familiar with clinchers but like any repro part I would pay close attention to the tires compared to an original example.
For instance the Coker classics 5.00x16 in my opinion are not an accurate reproduction.If you take a close look at the tire bead seating surface they are not nearly as deep a scallop to seat the rim properly as an original.You can spot this from ten feet away with the rim edge sticking out about a 1/4 inch outside the sidewall.Even on their web pics you can see the poor fit.They may function ok but they are different than original.The Beck copies are a better fit.
Tom

Steve Swan
03-21-2016, 11:36 AM
I'll call Al McRoberts for some clarification. i bought the rims from Al. if i recall correctly, when i spoke to Al before i bought the rims, we discussed the 28x3 sizing in Rider's Handbook translates to 20x3.85

have been searching for a tire/rim sizing chart..... no luck so far.

don't want to beat this topic or a dead horse to death, i just want to understand. or know...

AFJ
03-21-2016, 08:32 PM
I'll call Al McRoberts for some clarification. i bought the rims from Al. if i recall correctly, when i spoke to Al before i bought the rims, we discussed the 28x3 sizing in Rider's Handbook translates to 20x3.85

have been searching for a tire/rim sizing chart..... no luck so far.

don't want to beat this topic or a dead horse to death, i just want to understand. or know...

Steve,
In the old days tyres were labeled as to their outside diameter and width. A 27 x 4 was what we call these days a 19 x 4 - since it fits a 19" rim.
The clincher tyres on my 1927 Levis 2 stroke are 24 x 2.25 size and the rim is 19.5" in diameter. Get it?

On a 20" rim a 3.85 tyre will have an outside diameter of 20" + 3.85 + 3.85 or 27.7" (and would have been called a 28 x 3.85 tyre)

Correctly sized clincher tyres should go on with just tire-mounting fluid or French chalk and a warmed tyre. Gentle use of tire irons padded with thin cardboard to protect a painted rim might be needed.

AFJ

Steve Swan
03-22-2016, 01:22 AM
Thanks AFJ, i get the math. Thank you. it's helpful for me to understand how tire sizing translates to rim sizing.