Gear ratio help

[SKEETER1978]

Hello Im a newbie here so ill give a little info.
My name is Mike and i recently got my kids a old used kart with a 5hp briggs, I repainted it replaced some eng seals, carb seals, tires and brakes and got that that thing running good. (They love it).. so now i want to have fun too. So I got a used Haase corsa full size frame and a 1 1/4 axle and i am going to put a 160cc Suzuki atv motor with 5sp trans in it. This motor runs a 520 chain with a 11 tooth eng sprocket and i have the 39 tooth axle sprocket but i think 39t wont work, and im not sure if i can get a sprocket for the eng side in a diff tooth count or chain size? What would be the best rear sprocket size to run with this, I was thinking a 29-33.... there is not alot of info on the Suzuki eng out there i think it runs 6000-7000 rpms and im guessing 14-16hp (I will be running 11in slick tires)(I found that a Suzuki 125 makes 11.7hp at 7000rpm)
Any help will be appreciated
Mike

 

[Joe-405]

I would try that gearing if I were you. I bet it’s not as far off as you think.

 

[SKEETER1978]

The atv the motor came out of had a top speed of 35-38mph with 22in rear tires so i would think using the same sprockets with a 11in tire whould make it slower?

 

[itsid]

it WILL make it slower;
but that's likely what you want anyways

(since it means it provides MORE TORQUE)
and although the weight doesn't fiffer that much, the overall acceleration would if you try to dial in towards the same top speed right from the get go.

It's something that needs to be tuned likely over more than one iteration I'm afraid
(weight is a huuge factor, if you gain or loose weight within the next two years you might want to regear again for example)

As a starting point, the stock bike gear ratio is a very good starting point
(especially since kart wheels are smaller)

if it's too snappy that way and you cannot keep up shifting, then yes a smaller axle sprocket is what you want.
(if you can find one that is)..
See if you can use smaller chain (428 comes to mind)
means if you can find a sprocket for your engine's PTO in 428

since it's a smaller pitch the toothcount will increase say from 11T to 15T ...
just look around what's available

'sid

 

[SKEETER1978]

I have not found a 428 sprocket that will fit the motor for sure, but i did find a 14t 520 for it and i can get a rear 520 sprocket from 33t and up

 

[itsid]

Well Mike, allow me to guess..
you want to go 80mph??

'sid

 

[SKEETER1978]

No!!!!! I would think 40-50 would be good, This thing will probably never see a track. I have access to some nice size parking lots i can mess around at on sat/Sundays. and i live in a cul-de-sac and that where my kids race theirs for now. Was just thinking that if the atv only did 35ish with 22in wheels the cart would go maybe half that with 11in wheels.

 

[itsid]

must've missed the atv part...
my apologies

Yes, if the atv was slow (and they usually are dialed in towards torque not speed)
it doesn't make much sense to slow it down and up the torque much more indeed.

But you'll still have a hard time fixing that ratio with a 520 chain IMHO.

first: chances are you cannot fir a 15T sprocket to the engine, even IF the splines match,
4 additional teeth increase the sprocket diameter by about .4" since that's heavy chain,
you must take care to keep some space around the sprocket
(one link of clearance as a rule of thumb)
Otherwise even a slightly sticking link can rattle like crazy and worse slam and crack the case.
same clearance will be needed at the engine cutout, if it catches on the edge it might break,
and being heavy maybe even bones just a split second later

So yeah 15T.. IDK.. not seeing the engine, I'd say at least take a good measurement first.

worse: you cannot (should not that is) use an axle sprocket that's much smaller;
reason being: the smaller the sprocket the fewer teeth are in contact with the chain
and the quicker the teeth will wear down.
I'd say no less than 30 teeth for the axle tbh
(with ideal chain routing you might have maybe 16 or 17 in contact with the chain)
maybe that's already stretching it and there's a reason for you not finding sprockets with fewer than 33 Teeth

a smaller pitch would serve you much better to be honest.
it runs much smoother as well

But alright, say you take the 33T rear sprocket... a 12T engine sprocket would
bring your ratio down to 2.75:1 (from originally 3.55:1)
if a 13T engine sprocket fits it'd be 2.55:1, 2.36:1 for a 14T and finally 2.2:1 for the 15T;
but again: first make perfectly sure you can safely install the engine sprocket without running into clearance issues!

But be aware.. 40-50mph is highly unlikely to be possible.
Again, IDK what engine you have, but if the ATV only managed to get up to 35,
you can reasonably expect maybe 30mph on the kart with proper chain ratio (single stage)

maybe that engine is rev limited (CDI limiter) and can be sped up a notch, maybe not,
maybe it doesn't even have the power to reach much higher speeds
(since at one point drag is going to eat all horsepower.. w/o knowing the engine's hp it's tough to make a call though)

So ...
personally I'd still say mount the original sprocket sizes for now and see how it goes;
just to judge the acceleration of the kart,
since it's a five speed..
try a take off in second, maybe third...
that'd give you an idea of the 'to be expected acceleration'
If you know the internal reduction stage you could even calculate a matching chain reduction,
to know for sure

'sid

 

[SKEETER1978]

Thank for the great info. I would prefer to use a 428 chain as the rear axle i bought has a 428 sprocket and hub on it already (i don't know how many teeth yet still being shipped.) and if i use the big 520 i would have to use a special hub for the 520 rear sprocket i have. I found some 428 pto sprockets that fit Suzuki motorcycles last night but i need to measure the spline opening to see if its the same. If i find a 428 for the eng what ratio should i start with?

The eng is cdi and there are some aftermarket boxes that give 1000 more rpm and some timing curve changes. But i think factory the motor will turn 6000-7000 rpm.
I added a pic of the motor
Mike

 

[itsid]

w/o the engine model number (exact type of engine that is)
it's hard to make an educated guess tbh..
without at least a good estimation about it's power and torque curve..
all you really can do is testing.
as I said before..
current ratio as your starting base since it's likely going to provide all the torque you need;
then trying to take off in second/third gear to get a feeling for what'll be possible when changing changing to a higher gear ratio.

personally I think 3.55:1 (as it is stock) is maybe a bit much indeed, 2.55-3.00:1 or something would give you a closer starting point.
BUT here's the thing... you'll need to buy a set of sprockets that you'll only use for a few minutes (the testing)
And frankly, I don't see the point in buying these.
So yeah.. stock,
then use the gear box to check what change in ratio allows you to still take off quickly and smoothly, and once that's found buy the sprockets for the gear ratio you'll actually end up using.

Want a guess that's not more than a rough direction...?
2.3:1 (13:30 in 520 chain; or 15:35 in 428 terms)
keep in mind that this is unlikely to be the perfect gear ratio for you
(in fact it could be way off)
but without engine information and such it's all I can do atm.
If I had to pick a gear ratio it'd be around 13:35 (2.7:1) maybe even lower (3:1)
since acceleration is much more fun than top speed on a kart IMHO.
but you know this isn't my kart and you wanted more speed, right

The Haase (being a racing kart) does not have enough room for compound gearing..
so unfortunately you're limited to a single chain stage and available diameters of the sprockets
luckily 428 is a rather common shifter kart chain,
so split sprockes (incl keyed hub) are widely available in insanely small sizes (less than 30T)
unfortunately all I know are metric bore (40 or 50mm axles)
but sourcing on your side of the pond might help finding one that fits your oddball 1.25" axle *shrugs*

'sid

 

[qtband]

Why don't you use the original sprockets and get bigger rear wheels?

 

[anderkart]

Skeeter, If you can't find a #428 counter sprocket to fit your engine, check out the #520 rear split sprockets at this site: https://www.qrckarts.com/collections/drive-components


If your old sprocket hub isn't made to fit their #520, 4 x 4" bolt-patern sprockets, they also have Hubless #520 split-sprockets made to fit 1-1/4" racekart axles.

 

[SKEETER1978]

Bigger wheels is a option but i kind of like the look with smaller.

Thanks for the link, that 4 bolt hub might work with my sprocket but i need to figure out the pattern. The hub-less gear looks nice but a little pricey not knowing if the ratio i chose will work. If that hub will bolt my 520 rear to my 1 1/4 axle im going to do that first as it will be the most cost effective way to start. I do have the 520 chain also so i just need get a master link.
Thanks Mike

 

[anderkart]

Here's a couple links you can use to calculate your top speeds in each gear:

Specifacations: http://www.off-road.com/atv/tech/suzuki-quadrunner-ltf160-29175.html
Calculator: https://www.rbracing-rsr.com/gearspeed.html

I already ran some numbers for you:

An 11-tooth counter sprocket with a 39-tooth axle sprocket, and 11" tall rear tires would give you an estimated top speed of only 18mph @7000rpm in 5th gear.

If you only swapped to a 25-tooth axle sprocket, your top speed would increase to around 28mph.

---------

If you installed a 14-tooth counter sprocket (with a 25-t axle sprocket, your top speed would increase to around 36mph @7000rpm.

14-tooth was the largest commonly available counter sprocket I could find for sale for your engine, but there's a few shops around that'd custom build larger sizes. Here's one: http://www.superiorsprockets.com/ They could custom build any larger size, in your choice of #428 or #520 pitch...

-----------

PS: when buying racekart axle sprockets, you need to measure your hubs bolt-circle patern like this pic:

You also need to confirm the center-hole sizes of your hub & sprocket match perfectly, so the hubs lip will perfectly center the sprocket to the hub. The 4 bolt holes in the sprocket will be slightly oversized, so they cant do a very good job of centering all on their own... An exception to this would be if you found a sprocket with an 1-1/4" center-hole, then the axle would center it.

 

[SKEETER1978]

Thanks for doing that research for me it helps a lot. I think im going to have to find a 428 , 35 or similar sprocket for the eng. (Itsid) is right i think anything below 30 teeth for the rear and the there wont be a lot of teeth to grab.

The axle i bought came with a 35 chain and sprocket (not sure how many teeth but there are a lot in the picture i have) so ill look for one of those first,
I wonder how much a custom sprocket is?
My frame and axle will be delivered to me next Friday so i have some time to look around.
Mike

 

[anderkart]

Nothing wrong with using a #428 or #520 pitch, 25-tooth axle sprocket. Shifter racekarts with way more power that your engine commonly use as low a 21 tooth axle sprockets...
Those 21-tooth Sprockets are avalible at this site, but they dont stock anything for 1-1/4" axles: https://sharkshifter.com/zc/index.p...96_103&zenid=2ab45e551fd6e29c61046c0efc6f931d

 

[SKEETER1978]

Thanks for the calculator also. So if its safe to use a 25t rear ill do that. 11/25 at 28 mph is a good start.
14/25 36 mph
so if i want more speed i can still go up a 14t in the front later.
Never could find any hp/t specs so hard to know how its going to accel.
Im guessing 15-16hp?

 

[Joe-405]

I think you might be off........... remember your particular vehicle has internal ratios also,

Lt 160 ratios are as follows

Primary ratio:

3.736 (71/19)

Gear ratios:

1st 3.166 (38/12)

Gear ratios:

2nd 2.142 (30/14)

Gear ratios:

3rd 1.588 (27/17)

Gear ratios:

4th 1.200 (24/20)

Gear ratios:

5th 0.950 (19/20)

Gear ratios:

reverse 2.833 (34/12)

Final reduction ratio:

3.545 (39/11)

 

[itsid]

I punched the five gear numbers in my own calculator (71/20 since 71/19*19/20 is 71/20)
used the 22" wheels 14hp (I read it's 10kW on some german website) and the ATVS dryweight together with the ATVs final chain ratio (39/11) to get a good guess about the engine's peak rpm.

6500 rpm: 33.79mph
6700 rpm: 34.83mph
7000 rpm: 36.39mph
7300 rpm: 37.95mph
7500 rpm: 38.99mph

so if indeed the top speed was 35-38mph I think 7000 plus minus 300 is indeed good enough of a guess

now changing the wheel size to 11" and the final ratio to 25/11
and got 28.39mph @7000 rpm and 29.2mph @7200

and with 25/14 36.13mph @7000 and 37.16mph @7200

and just for the record:
a final ratio of 21/15
would be needed for 46.09mph @7000 and 47.41mph @7200
(which would be the 40-50mph we talked about earlier )

Anyways, I don't like axle sprockets that size, I doubt they're hardened (as the engine sprocket is) I might be wrong..
but at the very least I'd prepare for additional wear and maintenace (and increased replacement cycles)

But now the good news:
the engine itself is very well capable of that on a kart (within reasonable weight);
frankly I guess there's even enough left to add another 10mph..
but IMHO that'd be best done by altering the primary reduction to something easier to work with chain-wise

'sid

 

[SKEETER1978]

Thanks again you guys have been a great help. I think my plan will be to order a 14t 520 eng sprocket and rebelgears.com can make a 520 rear anywhere between 18-76t for 50 bucks and ship in 1-2 days. so i will order a 25t and between the 11/25 or 14/25 i can play with those for a bit and if i decide if want it faster i will try to find a gears/chain made in a different size.

Now a different question i will need a fuel pump for this motor now that the tank will be below the carb what pump do you recommend?
The carb is a mikuni 24mm vm i think.
Mike