Chozwoz

I was wondering if anybody has taken into account the fact that our 1/10 scale belt driven AWD cars in VTA, because of the two different tire sizes you are not getting equal travel distance per tire rotation. The rear tires are a little taller than the front tires. By how much? I haven't measured yet. But the key thing is, like a real AWD car (not 4WD), the gear ratios to every wheel have to match. I have had mechanics tell me it's very important to watch the wear of your tires, maintain equal pressure and rotate often. Even a difference a little as 3/8 less on a tire can put alot of strain on the drive train on asphalt because now that tire isn't spinning like the other three. So with that applied I was looking at my chassis and BOOM! The front wheels are being over driven by the back wheels. Even though the ratio is the same front to back, the larger diameter rear tire will travel further per rotation than the smaller front tire. Again by how much I don't know yet. What I'm thinking is change the gearing for the front spool so the front tires match the rear tires in travel distance per rotation or get as close as possible. Do you think this will result in a faster, more stable, more predictable car to drive? Or does carpet provide enough give that the front tires slip a little and it really doesn't matter?

glennhl

iTrader: (16)

I posted this same thing a few months ago in the VTA thread. By the way, with HPI tires the fronts and rears are the same diameter. This is mainly a problem with PF tires. The thing that came to my mind to fix it was that cool Reflex Racing (Cristian Tabush) Gizmo that has two spur gears with one driving the front wheels and one driving the rear wheels.

sosidge

I wouldn't worry about the comparison with full size 4wd cars - our cars are small, lightweight and always changing speed and direction - the extra scrub of having a different rotation speed on the front axle isn't a concern. Tyres are always slipping on the surface anyway, there is no such thing as 100% grip, even on sticky carpet tracks.

Broadly speaking you'd expect the smaller front tyre to heat up more, and for the car overall to tend towards oversteer because the rear end wants to take a longer (wider) line around corners.

It would be an interesting experiment to try and set up a car with a relatively over-driven front axle to compensate for the tyre diameter difference and see if it is "better". Unfortunately 1/10th tourers haven't had that option for a long time (Losi offered it on the XXX-S, only one I can think of).

bentouttashape

iTrader: (5)

The slight change in rollout due to the difference in the tire's diameter (usually <1mm) is typically going to be far less than the change in rollout by going up/down a tooth on either the center pulley/diff/spur/pinion gear. Additionally, these tires will swell over time and the tread will wear down; thus the difference in diameter between the tires is not going to remain a constant value. Consider the difference in the rollouts to be negligible.



I think there would be some value in driving the car a bit first.

belewis01

iTrader: (5)

Nicely done!

Chozwoz

Nice table! So I guess its not really an issue. I looked again at my tires side by side and somewhere I got it in my head they were def different sizes...they are almost the same so you could say it's negligible. Thanks alot for the all comments and knowledge from everybody! Thank You!

olivermoore

I think you're absolutely right to consider the difference in tire size and its impact on the performance of your AWD car. It's always important to pay close attention to the wear and tear of your tires, especially in competitive racing situations like VTA. Even a slight difference in tire diameter can cause a significant imbalance in the drive train and have an adverse effect on the car's handling.
In terms of changing the gearing for the front spool to match the rear tires' travel distance per rotation, I believe it could potentially result in a more stable and predictable car to drive. However, keep in mind that carpet does provide some give, which could allow the front tires to slip a little and compensate for the difference in tire diameter.

old_dude

iTrader: (1)

Some cars do offer a sprocket that has a tooth less for the diff/spool. That could correct the slight issue. With the old Losi XXX that sprocket came in the kit.

gigaplex

iTrader: (2)

Read a few posts back. A single tooth change on an internal gear makes a much larger rollout change than 1mm of tyre diameter delta.

old_dude

iTrader: (1)

I didn't notice that so thanks. Just responding with something I knew.
But the question is with the change in tire dia. The VTA legal tires are not belted. I don't have a new and old set to compare but the growth from running them is much more than 1mm in dia. The uneven growth F/R is the problem he is concerned about and that does happen too.

glennhl

iTrader: (16)

I've always fought a loose condition when running the PF tires on asphalt. I wonder how much is due to the rear tires being larger diameter and the rear trying to outrun the front.