pic: HiGrips after two events
 

Re: pic: HiGrips after two events
 

2 or our 4 are almost gone with 2 events; we were only running for about half of the first event. With only about 4 or 5 hours of good practice they wear a lot faster then we thought they did. They still do their job well though.

Re: pic: HiGrips after two events
 

Actually this sounds like they are perfect to me: ideally you would like to have easily replaceable wheels which would be as soft as possible while lasting you 1 regional.


some teams may even opt for even softer wheels which would have to be replaced during the regional, in exchange for higher traction!

Re: pic: HiGrips after two events
 

Considering we replace our blue (nitrile) roughtop once per event (we could probably do once per two events if defense is light) at a cost of over $5 per wheel, these wheels (and the vex equivalent) are darn good values.

Re: pic: HiGrips after two events
 

We are planning to swap out the higrips for custom wheels with blue nitrile. Just curious, why does it cost so much per wheel? We got our roughtop from Mcmaster at $1.60 a foot

Re: pic: HiGrips after two events
 

We run 2" Wide 3.7" (metal face) diameter wheels.

Once you account for some waste when cutting, and one or two treads scrapped per batch of 20-30, it's a tad over $5 a wheel for us.

We have a father that is very meticulous cutting them. We could do a slightly more efficient cut and save maybe 20%, but the results he gets are worth it to us.

Re: pic: HiGrips after two events
 

About par for the course. We put two new center wheels on Thursday at Palmetto; this is what they looked like after the Orlando finals. (No pictures in between, but reportedly most of the wear was eliminations themselves.)

Haven't had it as bad in the corners, but we will have spares in St. Louis just to cover ourselves.

Re: pic: HiGrips after two events
 

Ah ok. Ours are only 1 inch wide.

Re: pic: HiGrips after two events
 

Are your wheels wearing significantly? We also have 2" wide wheels, using the same McMaster nitrile, and we're soon to go into our third event with no tread changes. The wheels have little damage that I can see, and I can't really say that defense was light at either Inland or Sacramento.

Re: pic: HiGrips after two events
 

Out of curiosity is there a noticeable change in traction between a new and worn (to this degree) wheel?

I would suspect that there's actually fairly little change if you were to measure it. I wouldn't even be surprised if the CoF increased slightly.

Re: pic: HiGrips after two events
 

My driver said that when the wheels became worn during the finals at Orlando he had a much harder time pushing teams. All six teams in the finals at Orlando had 6CIM drive trains. Now I'm not sure if it was the wheels at that point or if the team he tried to push was down-shifting.

Re: pic: HiGrips after two events
 

I was in the pit of one of the teams attending their 3rd district event this weekend that were using the white tread hi-grips and after their first couple of matches they were wondering why they were now getting pushed around when they used to be the ones pushing others around. Their wheels looks almost identical to the one pictured. After they changed them they were back to pushing people around. So based on that I'd say that their coefficient of friction is way down when they look like that.

Re: pic: HiGrips after two events
 

Surface area does not have an effect the friction. I would think it would lose grip because the tread pattern provides some mechanical grip on the carpet.

Re: pic: HiGrips after two events
 

Plain and simple: this statement is false, especially when considering polymers intended for traction. Please don't portray a simplification that nearly every physics teacher uses as a fact.

Here is a link to one of the numerous posts I've made on the subject: http://www.chiefdelphi.com/forums/sh...4&postcount=23

It comes down to something called "mechanical keying" in the racecar world (where this sort of interaction is investigated in great detail). Basically as a wheel is loaded more and more the mechanical interlocking of the tire's tread into its driving surface eventually saturates and then the calculated coefficient of friction is reduced as the wheel is loaded more. This isn't a step change, but a gradual progression as wheel load is increased.

There have been teams who've tested 1in wide vs 2in wide wheels and found that 2in wide wheels provide a higher coefficient of friction. There have been teams (including one this year) that test larger diameter wheels as generating more friction, presumably due to a larger contact patch and thus lower contact pressure.

Re: pic: HiGrips after two events
 

Thank you. I did't know that. I was under the impression that a material had the same CoF regardless of the shape or tread pattern.