Question on rear wheel size

[Touchngo]

I have a question on rear wheel size/weight and was hoping someone here could help me out. I am currently building a cooler racer (similar to a bar stool racer). It has a HF 6.5 HP engine with a larger emulsion tube, jet, and air cleaner. Plan to add an exhaust pipe as well. I am using a TAV 30 on it as well with a 12 tooth sprocket. Axle sprocket is 73 teeth. Solid 1" hardened steel rear live axle. #35 gold chain. I have a 10 tooth sprocket I can put on the TAV as well.

I expect the frame to weigh in at about 50 pounds. Add another 50 for the motor, and another 300 pounds worth of cooler, beverages, and rider for a total running weight of about 450-500 pounds (once the weight of the wheels/tires is also added in)

So, I was planning on using 6" wheels with 145/70-6 knobby tires for all four wheels. I know most bar-stool racer use go-kart slicks, but I'm building a more "off-road" one. That is plan "A" for the wheels / tires.

I also am interested in the following for the rear: 18 x 9.50-8 knobby tires, while keeping the fronts at 145/70-6. This is plan "B" Supposedly these tires weigh in at about 20 pounds each, not including the rim.

Having no experience with building a go kart before, I just don't know if the engine will be able to turn the larger wheels and generate enough torque to get the whole thing moving.

I am more interested in torque than top speed, and know the smaller wheels would offer more torque, but if the larger wheels would work, I would prefer those. As long as it could go about 20-25 MPH that's all I care about for top speed.

Any advice would be greatly appreciated. Thanks!

 

[The Noose]

Since you are using a torque converter, you should have no problem getting enough torque to use the 18 inch rear wheels.

 

[Poboy kartman]

Not necessarily , he may be pushing it with weight....

With the 145/70 6 (around. 13")....he may be fine...(probably is)... but with 18"....maybe not....

My suggestion is "run what ya brung"....(unless you don't have tires and rims yet).

Good news is....I think the 10 tooth sprocket will work with either tire!

(And....I suspect he may be overestimating the total weight as well! )

 

[itsid]

Exactly like Doug said..
no problems with the smaller wheels..
KartInfo by kartcalc.net:

[FONT="Verdana"]
[B][U]KART[/U][/B]
[INDENT][I]RW diameter[/I]: [B] 35.56 cm | 14 in[/B]
[I]Total weight[/I]: [B] 227 kg | 500.45 lbs[/B]
[/INDENT]
[B][U]ENGINE[/U][/B]
[INDENT][I]Original HP[/I]: [B] 6.5[/B]
[I]Asummed HP[/I]: [B] ~6.5[/B]
[I]Torque[/I]: [B] 12.86 Nm | 9.48 ft lbf[/B]
[I]RPM[/I]: [B] 3600[/B]
[/INDENT]
[B][U]TRANSMISSION[/U][/B]
[INDENT][I]Final ratio[/I]: [B] 6:1[/B]
[I]TC type[/I]: [B]  series 30 6" driven[/B]
[I]Lowest ratio[/I]: [B] 16.2:1[/B]
[I]Highest ratio[/I]: [B] 5.4:1[/B]
[/INDENT]
[B][U]PERFORMANCE[/U][/B]
[INDENT][I]Max Wheel Torque[/I]: [B] 208.33 Nm | 153.66 ft lbf[/B]
[I]Min Wheel Torque[/I]: [B] 69.44 Nm | 51.22 ft lbf[/B]
[I]Acceleration[/I]: [B] 2.93 m/s² | 9.61 ft/s²[/B]
[I]Top Speed[/I]: [B] 44.69 km/h | 27.77 mph[/B]
[/INDENT]
[/FONT]

(145/70 - 6 mathematically are 13.99"... so 14" where assumed)

18"ers will be causing premature wear on the belt though when 12T sprocket is used on the TC..
KartInfo by kartcalc.net:

[FONT="Verdana"]
[B][U]KART[/U][/B]
[INDENT][I]RW diameter[/I]: [B] 45.72 cm | 18 in[/B]
[I]Total weight[/I]: [B] 227 kg | 500.45 lbs[/B]
[/INDENT]
[B][U]ENGINE[/U][/B]
[INDENT][I]Original HP[/I]: [B] 6.5[/B]
[I]Asummed HP[/I]: [B] ~6.5[/B]
[I]Torque[/I]: [B] 12.86 Nm | 9.48 ft lbf[/B]
[I]RPM[/I]: [B] 3600[/B]
[/INDENT]
[B][U]TRANSMISSION[/U][/B]
[INDENT][I]Final ratio[/I]: [B] 6:1[/B]
[I]TC type[/I]: [B]  series 30 6" driven[/B]
[I]Lowest ratio[/I]: [B] 16.2:1[/B]
[I]Highest ratio[/I]: [B] 5.4:1[/B]
[/INDENT]
[B][U]PERFORMANCE[/U][/B]
[INDENT][I]Max Wheel Torque[/I]: [B] 208.33 Nm | 153.66 ft lbf[/B]
[I]Min Wheel Torque[/I]: [B] 69.44 Nm | 51.22 ft lbf[/B]
[I]Acceleration[/I]: [B] 2.28 m/s² | 7.48 ft/s²[/B]
[I]Top Speed[/I]: [B] 57.45 km/h | 35.7 mph[/B]
[/INDENT]
[B][U]PROBLEMS[/U][/B]
[INDENT][B]You might burn your clutch/belt![/B]
[B]Gear ratio too high![/B]
[I]Suggested final ratio[/I]: [B] at least 6.5:1[/B]
[/INDENT]
[/FONT]

theoretically 11T will do the trick already (ratio 6.55:1)
but 7.2: 1 gives you even more torque (which is what you want to 'off road' or climb a curb or stick.. or mud... you get the idea)

......
KartInfo by kartcalc.net:

[FONT="Verdana"]
[B][U]KART[/U][/B]
[INDENT][I]RW diameter[/I]: [B] 18 in | 45.72 cm[/B]
[I]Total weight[/I]: [B] 500.45 lbs | 227 kg[/B]
[/INDENT]
[B][U]ENGINE[/U][/B]
[INDENT][I]Original HP[/I]: [B] 6.5[/B]
[I]Asummed HP[/I]: [B] ~6.5[/B]
[I]Torque[/I]: [B] 9.48 ft lbf | 12.86 Nm[/B]
[I]RPM[/I]: [B] 3600[/B]
[/INDENT]
[B][U]TRANSMISSION[/U][/B]
[INDENT][I]Final ratio[/I]: [B] 7.2:1[/B]
[I]TC type[/I]: [B]  series 30 6" driven[/B]
[I]Lowest ratio[/I]: [B] 19.44:1[/B]
[I]Highest ratio[/I]: [B] 6.48:1[/B]
[/INDENT]
[B][U]PERFORMANCE[/U][/B]
[INDENT][I]Max Wheel Torque[/I]: [B] 184.39 ft lbf | 250 Nm[/B]
[I]Min Wheel Torque[/I]: [B] 61.46 ft lbf | 83.33 Nm[/B]
[I]Acceleration[/I]: [B] 8.99 ft/s² | 2.74 m/s²[/B]
[I]Top Speed[/I]: [B] 29.75 mph | 47.88 km/h[/B]
[/INDENT]
[/FONT]

looking good to me.

'sid

 

[Poboy kartman]

One thing, I have those tires on my kart (145/70-6) knobbies, and it's a stretch to say they are 13"...(they are actually a little less). Now, as they age, (and are run overinflated)....(6 psi max recommended) ....they WILL grow...but even then, not to 14"....AFAIK. I don't know where the mix up is, but, it in fact, helps him out even more in the torque department!

 

[Touchngo]

Thanks for all the replies! I have not purchased the wheels and tires yet, but think I'm going to go with the larger ones, or maybe see what they have for 16" tires.

 

[Poboy kartman]

As said....if you run the 10 tooth, you should be fine with the 18's....but 16's would up the torque... (But to be honest....I think you'll have plenty! )

 

[itsid]

One thing, I have those tires on my kart (145/70-6) knobbies, and it's a stretch to say they are 13"...(they are actually a little less). Now, as they age, (and are run overinflated)....(6 psi max recommended) ....they WILL grow...but even then, not to 14"....AFAIK. I don't know where the mix up is, but, it in fact, helps him out even more in the torque department!

that's why I said mathematically...

145 (that's mm) * 70 (that's percent) is 101.5 (again mm);
twice that (since you have two sidewall heights per diameter )
is 203 mm and that converts to 7.992 (per definition an inch is 25.4mm)
8" roughly.. plus the six of the rim... 14...


Now a six inch rim is likely just a hair over 5" at the shoulder..
and that's what's causing most of the error...
but if we estimate, I'd rather overshoot the wheel diameter, since worst case, you end up with more torque and better acceleration (reducing stress at the belt and/or clutch)
So no harm, right

It'd be best to sit in the kart, measuring from the center of the axle straight down and multiply by two though...
THAT number will give the most accurate result of course
(and that might be even smaller than 13" in your case).

'sid

 

[chancer]

You are getting good advice so far.
I think you are overestimating the weight of the cooler. The HF 6.5 is not 50lbs either closer to 25. But unless YOU are a big ol boy 300lbs of rider and cooler is one heavy cooler.
Also do you have an Idea for frame deign yet length and width?

 

[Touchngo]

Yes, I am a big guy. 6'2" and 270ish Think I am going to go with some 16/650-8 Kenda K502 Terra Trac tires on 8x5.375 rims for the rear (or all the way around), unless it would be better to use smaller tires on the front? From the advice everyone has given, it seems like 16 might be a happy medium (and I like the look of the tires too).

---------- Post added at 12:34 AM ---------- Previous post was at 12:26 AM ----------

"main" frame and engine mount is already built. 52" long and about 18-19" wide. I made it just wide enough to hold my cooler. I am using 1" square tubing, 1/8" wall thickness. total length of tubing used is about 45 feet. putting several cross members in between the frame rails and made foot platforms

Still need to weld on the rear axle bearing supports, front axle and spindles, and figure out some way to set up the t-bar steering (I have some ideas) and controls (which is my greatest concern). I have almost all the parts I think, but I won't know that until I go to start hooking up controls.

 

[Poboy kartman]

Yes, I am a big guy. 6'2" and 270ish Think I am going to go with some 16/650-8 Kenda K502 Terra Trac tires on 8x5.375 rims for the rear (or all the way around), unless it would be better to use smaller tires on the front? From the advice everyone has given, it seems like 16 might be a happy medium (and I like the look of the tires too).

---------- Post added at 12:34 AM ---------- Previous post was at 12:26 AM ----------

"main" frame and engine mount is already built. 52" long and about 18-19" wide. I made it just wide enough to hold my cooler. I am using 1" square tubing, 1/8" wall thickness. total length of tubing used is about 45 feet. putting several cross members in between the frame rails and made foot platforms

Still need to weld on the rear axle bearing supports, front axle and spindles, and figure out some way to set up the t-bar steering (I have some ideas) and controls (which is my greatest concern). I have almost all the parts I think, but I won't know that until I go to start hooking up controls.

A bit off-topic, but I recently bought a Coleman cooler....(52 qt. IIRC)....anyway...exact replacement for the cooler I use as a combination dry storage/livewell/cooler/ seat....in my 10' jonboat....$20 on sale at Academy!

Sooooo....I used it to brine some pork shoulders for homemade ham....and wanted to drain the water.....SAY WHAT????? NO DRAIN PLUG!!!!! ARRRGH!!!! "BUYER BEWARE!"