HPI Tires

[Bulldogger]

Okay switching the Rally stock tires to HPI Tarmac tires yields a 4 mph increase at top end. Maybe more, car was last run and tuned in 35-40* weather today was 50 and windy. Car was running rich though and I didn't bring any tools. Prior top speed on the Rally was 36 mph with Jetpro and 990 car, running 31-29-26-24. Next run will be 35-25-26-24.

 

[Phill]

Okay switching the Rally stock tires to HPI Tarmac tires yields a 4 mph increase at top end. Maybe more, car was last run and tuned in 35-40* weather today was 50 and windy. Car was running rich though and I didn't bring any tools. Prior top speed on the Rally was 36 mph with Jetpro and 990 car, running 31-29-26-24. Next run will be 35-25-26-24.

Keep an eye on your clutch.

Mine didn't like 35/25 when I tried it.

 

[Bulldogger]

Phil,

Which buggy were you running? Also you switched to belt drive was there any gain in top end vs metal gears? The belt drive you bought was the one that only came with the two pulleys the belt and idler correct? It uses our gear plate.

 

[chrisscott961]

I have the belt drive on my xb and it's alot faster on take off than top end but that's with 1to 1 ratio.

 

[Bulldogger]

I have the belt drive on my xb and it's alot faster on take off than top end but that's with 1to 1 ratio.

Do you have any options other then 1:1

 

[chrisscott961]

The newer belt drives have different ratios

 

[Bulldogger]

Can you adjust the one you have? are different pulley's available

 

[chrisscott961]

No unfortunately you have to buy the new set up

 

[Bulldogger]

It seems the belt drives have better take off and less top end for the 1:1 ratio, how many teeth or belt cogs did he use? The gears were 29 start 24 end, did he split it 27/27 ??

 

[Phill]

Phil,Which buggy were you running? Also you switched to belt drive was there any gain in top end vs metal gears? The belt drive you bought was the one that only came with the two pulleys the belt and idler correct? It uses our gear plate.

Mine is a Dune Runner

I find top end great as it seems to allow the motor to rev higher.

The belt drive from Stern RC in Germany is available with different ratios.

Check him out on ebay and you may be able to get the pulleys seperately.

Yep it uses stock plate.

 

[chrisscott961]

If you buy the new set up you are able to change pulley but I have 1st Gen and you can't interchange the pulley I also suggest to change the gear plate to aluminum.

 

[Bulldogger]

If you buy the new set up you are able to change pulley but I have 1st Gen and you can't interchange the pulley I also suggest to change the gear plate to aluminum.

I have the aluminum gear plate, as far as the belt drive goes, I need to know what size pulley he is using to determine what top speed will be. The ratio of 1:1 and 1: 0.8 really don't mean that much unless to know the outside diameter of the pulley and how that compares to say the 29 or 31 gear.

 

[Ice_2k]

The ratio of 1 is all you need to know. The 29-31-26-24 gears on the DuneRunner for instance come up to 0.987 ratio ((31/29) * (24/26)). So moving to a ratio of 1 means more torque but less top speed. So top speed when moving from 0.987 to 1 will decrease by 1.3% (e.g. 40mph becomes ~39.5mph)

 

[Bulldogger]

The ratio of 1 is all you need to know. The 29-31-26-24 gears on the DuneRunner for instance come up to 0.987 ratio ((31/29) * (24/26)). So moving to a ratio of 1 means more torque but less top speed. So top speed when moving from 0.987 to 1 will decrease by 1.3% (e.g. 40mph becomes ~39.5mph)

That's not totally correct, because it is only two pulleys the diameter / circumference or the pulleys play a part. I can use two pulleys the size of the 25T size gear or say two the size of the 35t gear. Most people with the belt drive seem to have better acceleration and less top end....This is why a two speed tranny would be a better way too bad someone doesn't start making them again that aren't problematic

 

[Ice_2k]

I don't see how the size of the pulleys matter if you're using equal size pulleys, you'll still be translating 1 engine rpm to 1 pinion rpm. The only thing I can think of is bigger pulleys -> higher rotational mass.

The better acceleration people are getting is most likely related to the decreased friction between gears and the lower rotational mass.

 

[Bulldogger]

I don't see how the size of the pulleys matter if you're using equal size pulleys, you'll still be translating 1 engine rpm to 1 pinion rpm. The only thing I can think of is bigger pulleys -> higher rotational mass.The better acceleration people are getting is most likely related to the decreased friction between gears and the lower rotational mass.

Think about it like tire size, stock tire on the rally ran 36mph and HPI tires which were only a little taller add 4 mph, because they are covering more distance per revolution. If the engine turns 17,000 rpm a larger pulley covers more distance per rotation then a smaller one. Without knowing the actual size he uses I can't determine if it will be better or worse

 

[Ice_2k]

I'm pretty sure that's not correct. In the case of a tire, the size matters because one rotation of a tire covers more distance for a larger radius (2 * PI * R to be precise) because the tire is the one actually translating rotation to distance. In the case of pulleys in a belt drive, all they need to is translate the engine's RPM in pinion RPM. All that matters is the difference in size between the two pulleys.

 

[Bulldogger]

I'm pretty sure that's not correct. In the case of a tire, the size matters because one rotation of a tire covers more distance for a larger radius (2 * PI * R to be precise) because the tire is the one actually translating rotation to distance. In the case of pulleys in a belt drive, all they need to is translate the engine's RPM in pinion RPM. All that matters is the difference in size between the two pulleys.

Being the pulleys are the same size, you don't think the size will matter then? so any two pulleys of the same size will work, and not effect performance?

 

[Ice_2k]

HPI Tires

They will affect performance in that bigger pulleys increase rotational mass and so eat some of the engine's power. But they won't offer different speeds at the same engine rpm.

 

[Bulldogger]

They will affect performance in that bigger pulleys increase rotational mass and so eat some of the engine's power. But they won't offer different speeds at the same engine rpm.

Well the rotational speed of a pulley is faster at its outside point then in at its center., I would think that the pulley size he uses will have an effect on overall top speed and performance based on speed with in a diameter. Two smaller pulleys I think would yield less top end then two larger ones both being 1:1 ratio