Centrix cruiser by Jamis

[horsefarmer]

Centrix cruiser by Jamis. My late brother Barry - known here as "Yooperman" built it up from a bare frame for the first Unofficial March shootout in 2019... https://ratrodbikes.com/threads/unofficial-march-shootout.108241/page-2

After inheriting the bike I have started modifying it to fit me better. Mods include different seat and longer seat post. I also ditchted the semi-knobbie tires for smooth street treads and alloy ball bearing flat pedals for the original plastic ones.

Gearing seems "off" to me as in way to low. 3rd gear on the 6 speed seems just about as low as I would need after a couple of test-hops. Also gearing seems to low on flat or slight downhills so I will swap the factory 44t chainring for a 48t model.

Shimano 6-speed 14t - 16 - 18 - 21 - 24 - 28 t freewheel
From this:
Calculated the gear inches using stock 44 t front sprocket
1st gear 28 t = 41 gear inches
2nd gear 24 t = 48 gear inches<- useful low gear
3rd gear 21 t = 54 gear inches
4th gear 18 t = 63 gear inches
5th gear 16 t = 71 gear inches
6th gear 14 t = 82 gear inches <- too low high gear

To this:
Calculated the gear inches using 48 t front sprocket
1st gear 28 t = 45 gear inches <- useful low gear
2nd gear 24 t = 52 gear inches
3rd gear 21 t = 59 gear inches
4th gear 18 t = 69 gear inches
5th gear 16 t = 78 gear inches
6th gear 14 t = 89 gear inches<- about 10% taller than standard high gear

This will give me one more gear choice and 10% higher top gear.

It's probably an inexact science, but I will make the chain longer when changing the front sprocket as the chain seems too tight in low gear and sometimes it's reluctant to stay in low.

 

[horsefarmer]

Surprised that bottom bracket was lubricated but adjusted way too tight and would not turn freely. Adjusted it and added 48t chainring and alloy 175mm crank arms. Stockers were maybe 165mm cast iron or steel construction. Just have to add some extra chain links and ready for a another test ride.

 

[Wildcat]

That bike looks fast.
The calculator I use on BikeCalc.com shows your numbers are pretty close to theirs. I entered 26 x 2.125 for tire size.
Gear Inches for this wheel in these gears.

Ring Cog	44	45	46	47	48	Ring Cog
14	82.46	84.29	86.39	88.23	90.07	14
15	76.94	78.78	80.62	82.19	84.03	15
16	72.21	73.79	75.63	77.20	78.78	16
17	68.01	69.59	71.16	72.48	74.05	17
18	64.07	65.65	67.23	68.54	70.11	18
19	60.92	62.24	63.55	64.86	66.44	19
20	57.77	59.08	60.40	61.71	63.02	20
21	55.15	56.20	57.51	58.82	60.14	21
22	52.52	53.83	54.88	56.20	57.25	22
23	50.16	51.47	52.52	53.57	54.88	23
24	48.06	49.37	50.42	51.47	52.52	24

 

[horsefarmer]

Thanks Wildcat! Weather turning more blustery and more snow coming here - ugh.
Surprised, I thought I'd would have to lengthen the chain but it popped right on and shifted great down the driveway!

 

[horsefarmer]

Couple days ago, nice sunny day temp mid 40's F and enough headwinds to make it a workout.
Bike did outstanding. Lower couple gears handled the hills and my favorite long downhill stretch with headwind kept me out of top gear so gearing perfect for me!