#35 Sprocket Sizing and Gearing

When customers choose #35 pitch gearing (which we highly recommend for projects due to the 2-piece split sprockets and removable link chains – see our chain guide for more information) we’re often asked the question “What is the inside diameter of your split sprocket?” and “What is the outside diameter of an x tooth sprocket” so we’ve decided to write this informative but straight-forward guide focussed on explaining what needs to be done to fit our standard race kart sprockets and gearing your project.

Generally, when gearing your project, you have 3 problems to overcome.

1.       Fitting the sprocket to your axle

2.       Ensuring the overall sprocket size does not foul on the ground or chassis

3.       Selecting a practical starting gear ratio

This guide will run you through the decision making process as well as provide technical details on the products so that you can decide if #35 race kart gearing is suitable for your project.  I’ll run through these three sections quickly but informatively in the hope I don’t bore you, but that you have easy access to the information needed to get it right the first time.

PART 1 – Fitting the sprocket to your axle

Our #35 sprockets are a split sprocket which is ideal in situations where the sprocket is driven ‘inboard’ on the axle (ie: between the axle bearings).   They are easy to remove and install making gearing a breeze to get correct, or to change out a worn sprocket.

You can find our full range here: /product-category/sprockets-chains/sprockets-chains35-pitch-sprockets/

The centre bore size A is 116mm.

The PCD Diameter(B) is (6x) 132mm (centre of 6mm holes on opposite sides of sprocket)

All standard race-kart sprocket hubs will accept our sprockets.  We can supply sprocket hubs to fit most metric shaft sizes – 25mm, 30mm, 35mm, 40mm.

You can find sprocket hubs to suit here (Click your axle size and keyway width to find your hub):

25mm/6mm, 30mm/6mm, 30mm/8mm, 40mm/8mm

The hubs will accept the sprocket perfectly.  All you need to do is slide it onto your shaft.  Select the correct size shaft version of the sprocket.  If you have an imperial size shaft, we cannot offer a solution, but some people have successfully adapted the metric hubs to an imperial shaft.

PART 2 – Ensuring the overall sprocket size does not foul on the ground or chassis

Your new #35 sprocket will differ in sizing depending on the number of teeth you have chosen.  Circumference will determine the number of teeth you will have.  The reason the size differs is because the pitch of the chain determines the length required for one full link or tooth.

For those uninterested in the math, please skip this paragraph.  #35 pitch is 9.525mm, so for every tooth, the circumference must be increased by 9.525mm.  In addition, the height of each tooth is about 5mm so we need to add approximately 2.5mm extra from the centreline of each tooth (or approximately 5mm to the diameter)   This means we have a formula #TEETH x 9.525mm = Pi x Diameter.  Or we could write it as #teeth x 9.525mm divided by Pi = Diameter plus 5mm.  Translating back to diameter, our smallest sprocket (53T) has a diameter of   53 x 9.525 / Pi (3.141592) = 166mm. 

Your chain will sit around 3mm proud of the tip of each tooth, so you’ll need to add approximately 6mm to the diameter of the sprocket to get the correct clearance amount.

Here’s a table of diameters:

#Teeth	Dia mm	Dia w/chain mm
53	166	172
54	169	175
55	172	178
56	175	181
57	178	184
58	181	187
59	184	190
60	187	193
61	190	196
62	193	199
63	196	202
64	199	205
65	202	208
66	205	211
67	208	214
68	211	217
69	214	220
70	217	223
71	220	226
72	223	229
73	226	232
74	229	235
75	232	238
76	235	241
77	238	244
78	241	247
79	244	250
80	247	253
81	250	256
82	253	259
83	256	262
84	259	265
85	262	268

PART 3 – Selecting a practical gear ratio

Once you’ve determined your limitations in relation to ground and chassis clearances, the next step is to determine the best gear ratio.  There are several things to consider, including:

–          Desired Acceleration

–          Desired Top Speed

–          Minimum operating speed

o   One of the most important considerations is the minimum ‘fully engaged’ clutch speed.  Most stock clutches engage around 2000rpm.  With a governed 4-stroke engine, that means you have a working range of somewhere between 2000 and 3500rpm.  If you select too tall gearing, and you constantly operate the kart at speeds which bring the motor close to or below the 2000rpm engagement point, you will encounter clutch problems as the clutch is continually slipping.

The following table gives approximate speeds for gearing.  It is recommended not to use gearing in the orange sections, and red sections will almost certainly result in mechanical failure. 

 Tall gearing (lower ratios) may struggle to gain rpm if the power of the engine is not enough to overcome the torque of the axle.  This is more pronounced the larger the wheels are, so bear this in mind. 

What if I have very large wheels in excess of 400mm and still can’t get a short enough ratio for the ratio needed?  

It’s ok, don’t panic – there are a couple of options – you can consider a Torque Converter (CLICK HERE TO READ ABOUT TORQUE CONVERTERS) and in addition we’ve got a brand new 2:1 reduction kit available in stock to suit #35 sprockets (there’s one due for 420P shortly too!) so you can run up to 800mm rear wheels and tyres!  Awesome right?  This little kt goes in-line between your torque converter or dry clutch to reduce the ratio by another 2 times – meaning you can run about a 6:1 reduction using a torque converter, allowing for the use of really big wheels.  CLICK HERE TO FIND OUR 2:1 REDUCTION KITS

Always select the shortest gearing (highest ratio) first and work your way down with rear sprocket sizing to ensure you do not damage your clutch and that you can ensure your project will get mobile initially.

For the tables below, use the following legend:

Not Recommended 
(either gearing too tall, or sprocket diameter too close to ground)

Certain damage to drivetrain (too tall gearing or sprocket fouls)

Senior rear rims & slicks 11×7.10-5 265mm dia
Clutch Sprocket	Rear (Axle) Sprocket	Final Drive Ratio	2000rpm (min) KPH	3500rpm KPH	7000rpm KPH
12	53	4.42	23	40	79
12	54	4.50	22	39	78
12	55	4.58	22	38	76
12	56	4.67	21	37	75
12	57	4.75	21	37	74
12	58	4.83	21	36	72
12	59	4.92	20	36	71
12	60	5.00	20	35	70
12	61	5.08	20	34	69
12	62	5.17	19	34	68
12	63	5.25	19	33	67
12	64	5.33	19	33	66
12	65	5.42	18	32	65
12	66	5.50	18	32	64
12	67	5.58	18	31	63
12	68	5.67	18	31	62
12	69	5.75	17	30	61
12	70	5.83	17	30	60
12	71	5.92	17	30	59
12	72	6.00	17	29	58
12	73	6.08	16	29	57
12	74	6.17	16	28	57
12	75	6.25	16	28	56
12	76	6.33	16	28	55
12	77	6.42	16	27	54
12	78	6.50	15	27	54
12	79	6.58	15	27	53
12	80	6.67	15	26	52
12	81	6.75	15	26	52
12	82	6.83	15	26	51
12	83	6.92	14	25	51
12	84	7.00	14	25	50
12	85	7.08	14	25	49
Clutch Sprocket	Rear (Axle) Sprocket	Final Drive Ratio	2000rpm (min) KPH	3500rpm KPH	7000rpm KPH
13	53	4.08	25	43	86
13	54	4.15	24	42	84
13	55	4.23	24	41	83
13	56	4.31	23	41	81
13	57	4.38	23	40	80
13	58	4.46	22	39	78
13	59	4.54	22	39	77
13	60	4.62	22	38	76
13	61	4.69	21	37	75
13	62	4.77	21	37	73
13	63	4.85	21	36	72
13	64	4.92	20	36	71
13	65	5.00	20	35	70
13	66	5.08	20	34	69
13	67	5.15	19	34	68
13	68	5.23	19	33	67
13	69	5.31	19	33	66
13	70	5.38	19	32	65
13	71	5.46	18	32	64
13	72	5.54	18	32	63
13	73	5.62	18	31	62
13	74	5.69	18	31	61
13	75	5.77	17	30	61
13	76	5.85	17	30	60
13	77	5.92	17	30	59
13	78	6.00	17	29	58
13	79	6.08	16	29	58
13	80	6.15	16	28	57
13	81	6.23	16	28	56
13	82	6.31	16	28	55
13	83	6.38	16	27	55
13	84	6.46	15	27	54
13	85	6.54	15	27	53
18	53	2.94	34	59	119
18	54	3.00	33	58	117
18	55	3.06	33	57	114
18	56	3.11	32	56	112
18	57	3.17	32	55	110
18	58	3.22	31	54	109
18	59	3.28	30	53	107
18	60	3.33	30	52	105
18	61	3.39	29	52	103
18	62	3.44	29	51	102
18	63	3.50	29	50	100
18	64	3.56	28	49	98
18	65	3.61	28	48	97
18	66	3.67	27	48	95
18	67	3.72	27	47	94
18	68	3.78	26	46	93
18	69	3.83	26	46	91
18	70	3.89	26	45	90
18	71	3.94	25	44	89
18	72	4.00	25	44	87
18	73	4.06	25	43	86
18	74	4.11	24	43	85
18	75	4.17	24	42	84
18	76	4.22	24	41	83
18	77	4.28	23	41	82
18	78	4.33	23	40	81
18	79	4.39	23	40	80
18	80	4.44	22	39	79
18	81	4.50	22	39	78
18	82	4.56	22	38	77
18	83	4.61	22	38	76
18	84	4.67	21	37	75
18	85	4.72	21	37	74
Not Recommended  (either gearing too tall, or sprocket diameter too close to ground)
Certain damage to drivetrain (too tall gearing or sprocket fouls)
13″ Off-Road wheels 13×5.00-6 290mm dia
Sprocket	Sprocket	Final	2000	3500	7000
Clutch	Rear	Ratio	Min	Max	Max
12	53	4.42	25	43	87
12	54	4.50	24	43	85
12	55	4.58	24	42	83
12	56	4.67	23	41	82
12	57	4.75	23	40	81
12	58	4.83	23	40	79
12	59	4.92	22	39	78
12	60	5.00	22	38	77
12	61	5.08	22	38	75
12	62	5.17	21	37	74
12	63	5.25	21	36	73
12	64	5.33	20	36	72
12	65	5.42	20	35	71
12	66	5.50	20	35	70
12	67	5.58	20	34	69
12	68	5.67	19	34	68
12	69	5.75	19	33	67
12	70	5.83	19	33	66
12	71	5.92	18	32	65
12	72	6.00	18	32	64
12	73	6.08	18	31	63
12	74	6.17	18	31	62
12	75	6.25	17	31	61
12	76	6.33	17	30	60
12	77	6.42	17	30	60
12	78	6.50	17	29	59
12	79	6.58	17	29	58
12	80	6.67	16	29	57
12	81	6.75	16	28	57
12	82	6.83	16	28	56
12	83	6.92	16	28	55
12	84	7.00	16	27	55
12	85	7.08	15	27	54
13	53	4.08	27	47	94
13	54	4.15	26	46	92
13	55	4.23	26	45	90
13	56	4.31	25	44	89
13	57	4.38	25	44	87
13	58	4.46	25	43	86
13	59	4.54	24	42	84
13	60	4.62	24	41	83
13	61	4.69	23	41	82
13	62	4.77	23	40	80
13	63	4.85	23	39	79
13	64	4.92	22	39	78
13	65	5.00	22	38	77
13	66	5.08	22	38	75
13	67	5.15	21	37	74
13	68	5.23	21	37	73
13	69	5.31	21	36	72
13	70	5.38	20	36	71
13	71	5.46	20	35	70
13	72	5.54	20	35	69
13	73	5.62	19	34	68
13	74	5.69	19	34	67
13	75	5.77	19	33	66
13	76	5.85	19	33	65
13	77	5.92	18	32	65
13	78	6.00	18	32	64
13	79	6.08	18	31	63
13	80	6.15	18	31	62
13	81	6.23	18	31	61
13	82	6.31	17	30	61
13	83	6.38	17	30	60
13	84	6.46	17	30	59
13	85	6.54	17	29	59
18	53	2.94	37	65	130
18	54	3.00	36	64	128
18	55	3.06	36	63	125
18	56	3.11	35	61	123
18	57	3.17	35	60	121
18	58	3.22	34	59	119
18	59	3.28	33	58	117
18	60	3.33	33	57	115
18	61	3.39	32	56	113
18	62	3.44	32	56	111
18	63	3.50	31	55	109
18	64	3.56	31	54	108
18	65	3.61	30	53	106
18	66	3.67	30	52	104
18	67	3.72	29	51	103
18	68	3.78	29	51	101
18	69	3.83	29	50	100
18	70	3.89	28	49	98
18	71	3.94	28	49	97
18	72	4.00	27	48	96
18	73	4.06	27	47	94
18	74	4.11	27	47	93
18	75	4.17	26	46	92
18	76	4.22	26	45	91
18	77	4.28	26	45	89
18	78	4.33	25	44	88
18	79	4.39	25	44	87
18	80	4.44	25	43	86
18	81	4.50	24	43	85
18	82	4.56	24	42	84
18	83	4.61	24	41	83
18	84	4.67	23	41	82
18	85	4.72	23	41	81